World Fertilizer October Issue 2021

MAGAZINE | OCTOBER 2021

Sustainable fertilizer technology We accept the challenge! Do you?

• 75 years of experience in designing, licensing and developing fertilizer plants • Helping the world to feed itself and improving quality of life • Exceeding the highest safety standards and environmental regulations • Challenge us at www.stamicarbon.com

The innovation & license company of Maire Tecnimont.

CONTENTS 03 05 08

Comment World News A Spotlight On Sulfur

29

Meena Chauhan, Argus Media, UK, provides insights into the global sulfur and sulfuric acid markets, with a focus on Russia.

a

In the second part of a two part article, Brandon Forbes and D.J. Cipriano, AMETEK/Controls Southeast Inc., USA, explain how the challenges created by the storage of sulfur at a refinery on the US Gulf Coast were addressed.

34

T

he availability of sulfur supply and the market balance has been a key focus point over the past year, with the global COVID-19 pandemic taking its toll on output as fuel oil demand collapsed on the back of restrictions and lockdowns throughout 2020. Sulfur prices reached 2-year highs earlier in 2021 before easing once availability began to improve with the roll out of vaccination programmes and the lifting of restrictions in many regions. There is some uncertainty around the short-term view, as the processed phosphates market appears to have potential to firm up based on strong demand in South Asian markets. Beyond 2021, however, sulfur prices are expected to see further downward correction in sync with the view for downstream markets, including diammonium phosphate (DAP).

The capacity outlook for sulfur is robust for the mediumterm. Several projects in the Middle East are expected to ramp up in 2022 following delays as a result of COVID-19. KNPC’s Clean Fuels Project in Kuwait and the Barzan project in Qatar will have a combined capacity of over 3 million tpy. In the medium-term, projects in the Middle East are forecast to add 4.6 million tpy. Northeast Asia is the second largest driver after the Middle East for capacity growth. An additional 1.6 million tpy of sulfur supply is forecast by the end of 2022, but the recent Chinese government cuts for refiners’ export quotas for 2H21 have led to uncertainty around how new sulfur projects will be impacted.

ORY R ST

COVE

RAPID REPAIR AND RECOVERY

08

Valérie Lebrun and Harold van der Zande, Stamicarbon, the Netherlands, highlight how the company’s spare parts service can support effective plant maintenance.

The Key To Reliability Dr Pablo Cardín and Pedro Imízcoz, Schmidt + Clemens Group, Spain, describe new technologies, materials and services to improve the reliability of steam refomer tubes under demanding operational conditions.

19

34

38

44

The Advance department offers a broad range of fertilizer services, including comprehensive inspections during a planned turnaround, training of operators, plant consultancy activities and the supply of a wide range of fertilizer equipment. The last of these services includes not only the supply of measuring equipment for optimising production (such as N/C meters, leak detection systems and radar level measurement devices) but also replacements of existing high-pressure (HP) equipment in the urea synthesis section (such as urea reactors, HP carbamate condensers and HP strippers). The replacement equipment can either be offered in a one-to-one replacement design or offered in an upgraded design to achieve a longer lifetime, higher capacity, higher efficiency and/or lower emissions.

Spare parts services It is essential for plant owners to have the assurance that they are working with reliable equipment, as this helps prevent

unsafe conditions and unscheduled plant shutdowns. However, the corrosion potential of ammonium carbamate poses a severe threat not only to the integrity of urea process equipment but also to equipment and piping components.

Therefore, to support urea producers operating Stamicarbon-designed urea plants – with the main HP process cycle designed with proprietary Safurex® equipment – Safurex spare parts are supplied for all necessary components, including manual control and safety valves, mounting bolts and nuts, granulator nozzles, piping (Figure 1), fittings and other spare parts.

Spare parts services were established in 2016 to assist fertilizer producers with timely and effective plant maintenance. Instead of ordering their spare parts from many different manufacturers, urea producers operating plants based on Stamicarbon technology and Safurex equipment can request all of their required Safurex-based components directly from the company.

Optimising Ammonia Tank Management

A Bridge To Digital Transformation Paolo Gallieri, Max Panaro, Ezio Pasqualon and Giuseppe Tornatore, Maire Tecnimont Group, Italy, explain how a digital transformation platform can improve the performance of industrial plants.

Leave No Sulfur Unburned Bruno Ferraro, Breno Avancini, Eduardo Almeida, Victor Machida, Vitor Sturm and William Lima, Clark Solutions, Brazil, explain why complete burning and proper atomisation of sulfur during plant operation is essential for extending the life of equipment.

T

he Full Life Cycle philosophy of Stamicarbon, the innovation and licence company of Maire Tecnimont Group, aims to offer ongoing support to urea producers throughout the entire lifecycle of their plants, providing tailor-made technology solutions, products and services that cater to the specific needs of a plant at a particular phase of its lifecycle. As part of this philosophy, the company has established a dedicated services department (Advance) to support producers in achieving continuous fertilizer production, regardless of whether they use the company’s proprietary urea technology or other third-party technologies.

Jim Olson, The Equity Engineering Group, Inc., USA, considers how to develop and improve an ammonia tank mechanical integrity programme.

Blue Hydrogen For Blue Fertilizer Lorenzo Micucci, Siirtec Nigi SpA, Italy, considers the mechanics and environmental benefits of producing ‘blue hydrogen’ for fertilizer production.

24

Ready For Rapid Repair And Recovery Valérie Lebrun and Harold van der Zande, Stamicarbon, the Netherlands, highlight how the company’s spare parts service can support effective plant maintenance.

Meena Chauhan, Argus Media, UK, provides insights into the global sulfur and sulfuric acid markets, with a focus on Russia.

on sulfur

13

Sulfur Storage Tank Challenges: Part Two

49

A Mesh Of Material Technology And Chemistry Martyn Dean, Begg Cousland Envirotec, UK, examines the fibre bed filter technology and pH control needed to reduce harmful emissions from ammonium nitrate production.

54

Add LIBS And Innovate

WORLD FERTILIZER

Marius Sugentaitis, Lyncis, Lithuania, examines how the adoption of new sensor measurement technologies, such as laser-induced breakdown spectroscopy (LIBS), can lead to more efficient mineral processing.

OCTOBER 2021

59

MAGAZINE | OCTOBER 2021

Maintaining Material Flow Chris Schmelzer and Sid Dev, Martin Engineering, USA, discuss how air cannons ensure efficient material flow in fertilizer production, whilst minimising air consumption.

Sustainable fertilizer technology We accept the challenge! Do you?

WWW WORLDFERTILIZER COM

• 75 years of experience in designing, licensing and developing fertilizer plants • Helping the world to feed itself and improving quality of life • Exceeding the highest safety standards and environmental regulations • Challenge us at www.stamicarbon.com

ON THE COVER

Stamicarbon’s innovations in fertilizer technologies play a vital role in enabling the world to feed itself and improving quality of life. The Ultra-Low Energy plant concept with the lowest energy consumption, MicroMistTM and Jet Venturi scrubbing technologies for reducing emissions, digital solutions for optimising production efficiency, and Green Ammonia technologies for producing carbon-free ammonia facilitate future-proof fertilizer production with minimal environmental impact.

The innovation & license company of Maire Tecnimont.

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Copyright © Palladian Publications Ltd 2021. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner. All views expressed in this journal are those of the respective contributors and are not necessarily the opinions of the publisher, neither does the publisher endorse any of the claims made in the advertisements. Printed in the UK. CBP006075

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link and you’ll miss it, such is the pace at which new green ammonia projects are being announced (though I could equally be talking about energy suppliers here in the UK going out of business on the back of record natural gas prices). As I write, in the past week details of a project backed by Egypt’s sovereign wealth fund and Fertiglobe, an OCI-ADNOC joint venture, were announced, while Incitec Pivot Ltd. and Fortescue Future Industries have started a feasibility study into green ammonia production in Queensland, Australia. These are heady times for the fertilizer manufacturing industry; in the potash sector, a clutch of companies in Australia (Kalium Lakes, Australian Potash, Salt Lake Potash, Agrimin, BCI Minerals and Reward Minerals), Eritrea (Danakali) and Morocco (Emmerson) are seeking to ride the wave of record prices as they begin commercial production in the next decade. Kalium Lakes recently produced its first batch of sulfate of potash (SOP), although the race to be the first commercial SOP producer in Australia is still ongoing.

As is so often the case however, there are two sides to the story. The International Energy Agency (IEA) recently published an ‘Ammonia Technology Roadmap’ that outlined three different scenarios for ammonia production and emissions between now and 2050.

Some key conclusions were that “Nearly 60% of the cumulative emission reductions in the Sustainable Development Scenario [by 2050, direct CO2 emissions from ammonia production have fallen by over 70%] stem from technologies that are currently in the demonstration phase” and that, amongst other infrastructure deployments required, an average of ten 30 MW electrolysers need to be installed per month to achieve the Sustainable Development Scenario. While (rightly) lauding the efforts of governments and industry so far, the report’s authors say that greater ambition is required.1 While a report can be discussed and then quietly filed away, commodity prices can’t.

The high gas prices that have felled UK energy suppliers left, right and centre have also forced the likes of Yara, Borealis and CF Industries to curtail ammonia production at facilities across Europe, sending shivers down the supply chain. CF Industries’ Billingham Complex in the UK will continue operating until at least the end of January 2022, following agreements made with firms that purchase the CO2 that is a by-product of its ammonia production. However, CF Industries has said that it expects the UK government and industrial CO2 consumers to work together over the next 3 months to develop a longer-term strategy for the supply of CO2. With UK industry and government alike grappling with the repercussions of Brexit, COVID-19, the global supply chain crisis and the expectation that high gas prices will persist through the rest of 2021, meeting CF Industries’ expectations seems a tall order – further output cuts could become a thing of 2022.

So, to borrow a phrase that has been in plentiful supply of late, let’s cross fingers and hope this isn’t a winter of discontent for the European fertilizer industry.

Reference 1.

International Energy Agency, ‘Ammonia Technology Roadmap: Executive Summary’.

(October 2021).

OCTOBER 2021 | WORLD FERTILIZER | 3

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WORLD NEWS GERMANY South Harz Potash signs drilling contract for Ohmgebirge project

S

outh Harz Potash (SHP) has signed the drilling contract for the first confirmatory hole at its Ohmgebirge Mining Licence area with deep drilling specialist company H. Anger’s Söhne Bohr- und Brunnenbaugesellschaft (Angers), conditional on permit approval.

SHP plans to drill two holes, OHM-02 and OHM-01, within the Ohmgebirge Mining Licence area in the South Harz region of Germany. OHM-02 is planned in 4Q21 to a depth of 665 m which is expected to fully penetrate the known potash horizon in the area.

The aim of the drilling is to collect potash core samples from depth to assist in verifying historical drilling in the licence area by the former East German state in the 1980s. The confirmation drillholes will allow the company to upgrade its current inferred resources to indicated within the mining licence area, thus allowing the release of a Technical and Economic Assessment (Scoping Study)

in 1Q22.

To further progress and complete the drilling programme, SHP applied to the regulatory authority, TLUBN, in August for permission to a drill second hole, OHM-01, which is currently being processed. For reasons of shorter hole depth and other logistic considerations however, it was decided to drill OHM-02 first.

At Ohmgebirge, the company plans to drill two holes to verify results from the historic drillholes that were used to calculate and declare an inferred resource of 325 million t grading 13.1% K2O. It is intended that the two confirmatory holes will lead to a revised mineral resource estimation with the inferred resource upgraded to the Indicated category.

SHP received landowner and tenant permission for the second of two confirmatory drill holes at the Ohmgebirge project in July 2021.

EGYPT Fertiglobe, Scatec and Egypt’s sovereign fund to develop green ammonia project

O

CI N.V. has announced that Fertiglobe, the partnership between OCI and Abu Dhabi National Oil Co. (ADNOC), has entered into an agreement with Scatec ASA and TSFE to jointly develop a 50 – 100 MW electrolyser facility to produce green hydrogen as feedstock for green ammonia production.

The facility will be located near Fertiglobe’s subsidiary EBIC in Ain Sokhna in Egypt and is a first step towards developing a green hydrogen hub in Ain Sokhna.

Under the agreement, Scatec will build, operate and majority own the facility, and EBIC will use the green hydrogen as a supplementary feedstock for the production of up to 90 000 tpy of green ammonia under a long term off-take agreement. The final investment decision is expected in 2022, and start-up is targeted for 2024.

The parties will seek support from the Egyptian government for required regulatory approvals and sourcing of competitive renewable power from the grid, with the intention to build out new solar and wind capacity to power Egypt’s green hydrogen ambitions in the years to come. The project will be realised in close cooperation with hydrogen technology providers and multilateral development institutions for financing.

Required engineering and development, including

structuring of commercial agreements for the new facility, will start imminently.

Incremental demand for low carbon ammonia from new applications is currently estimated in the range of 8 million t by 2025, growing to more than 25 million t by 2030 compared to a current global merchant ammonia market of approximately 20 million t.

OCI N.V., ADNOC and Fertiglobe have also announced their intention to proceed with an IPO of Fertiglobe and to list its shares for trading on the Abu Dhabi Securities Exchange (ADX), with listing expected on 27 October.

OCI and ADNOC intend to collectively offer 13.8% of Fertiglobe’s issued share capital in the offering, which could be worth up to US$827 million. OCI is expected to indirectly continue to own a majority of Fertiglobe’s share capital post-IPO, while ADNOC is expected to indirectly own at least 36.2% of Fertiglobe’s share capital post-IPO. The price range for the offering has been set at AED2.45 – AED2.65 per share, implying an equity value of US$5.5 – US$6 billion.

The offering will be the first listing of a free zone company onshore in the UAE, and is open to all citizens and residents of the UAE as well as local and international institutional investors in a number of countries.

OCTOBER 2021 | WORLD FERTILIZER | 5

WORLD NEWS DIARY DATES CRU Sulphur + Sulphuric Acid 2021 01 – 04 November 2021 Online events.crugroup.com/sulphur/ home

15th Annual GPCA Forum 07 – 09 December 2021 Dubai, UAE gpcaforum.com

Turbomachinery & Pump Symposia 2021 14 – 16 December 2021 Houston, Texas, US tps.tamu.edu

72nd Laurance Reid Gas Conditioning Conference 21 – 24 February 2022 Norman, Oklahoma, US

AUSTRALIA Incitec Pivot and Fortescue Future Industries to

carry out green ammonia study

I

ncitec Pivot Ltd. (IPL) is to partner with Fortescue Future Industries (FFI) on a feasibility study into the industrial-scale production of green ammonia at IPL’s existing Gibson Island fertilizer manufacturing facility in Murarrie, Queensland, Australia.

The study will assess whether industrial-scale manufacturing of green ammonia at Gibson Island is technically and commercially feasible on an existing brownfield site. It will investigate building a new water electrolysis facility on the site to produce approximately 50 000 tpy of renewable hydrogen, which would then be converted into green ammonia for Australian and export markets. Currently, the facility uses

natural gas as a feedstock.

The project, if successful, will safeguard several hundred manufacturing jobs in Queensland, in addition to creating a new domestic and export market for green, renewable ammonia.

The resulting green ammonia could also provide a low-carbon fuel supply to the Port of Brisbane and Brisbane airport.

Preliminary results from the feasibility study are expected to be available at the end of 2021.

Incitec Pivot is Australia’s largest supplier of fertilizers, producing approximately 2 million tpy.

FFI is aiming to generate 15 million tpy of green hydrogen by 2030, rising to 50 million t in the decade thereafter.

pacs.ou.edu/lrgcc/

CRU Phosphates 2022 07 – 09 March 2022 Tampa, Florida, US events.crugroup.com/phosphates/ home

ANNA 2022 02 – 07 October 2022 Houston, Texas, US annawebsite.squarespace. com/2022-conferenceannouncement To stay informed about the status of industry events and any potential postponements or cancellations of events due to COVID-19, visit World Fertilizer’s events page: www.worldfertilizer.com/events

AUSTRALIA Trigg Mining publishes scoping study for

Lake Throssell SOP project

T

rigg Mining has completed a scoping study on its Lake Throssell sulfate of potash (SOP) project in Western Australia and has now started a pre-feasibility study as well as continuing environmental baseline surveys, with the aim of giving project referral to Australia’s Environmental Protection Agency in 2022.

The study has indicated the project is capable of achieving a nameplate production target of 245 000 tpy of SOP over an initial Life-of-Mine of 21 years.

Following the positive outcomes of the groundwater model, a review of the drill logs and reinterpretation of the resource block model has led to the reclassification of the highly permeable mineralised domains within the basal aquifer to Indicated status for a total drainable indicated mineral resource estimate of 4.2 million t of SOP at

6 | WORLD FERTILIZER | OCTOBER 2021

4770 mg/L potassium (K) (or 10.6 kg/m3 K 2SO4).

The total drainable mineral resource for the Lake Throssell project now stands at 14.4 million t at 4665 mg/L potassium (or 10.4 kg/m3 K2SO 4).

The initial capital cost of the project is estimated at AUS$378 million, including a AUS$70 million contingency with an accuracy of ±25 – 35%. According to the study, Lake Throssell will generate an average EBITDA of AUS$97 million per annum at a US$550/t SOP price.

The Lake Throssell project, located in the Eastern Goldfields of Western Australia, is approximately 1080 km² of granted and pending tenements and will comprise the harvesting of brine water from subterranean aquifers, evaporation ponds, processing plant and supporting infrastructure to produce SOP.

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a on sulfur

8

Meena Chauhan, Argus Media, UK, provides insights into the global sulfur and sulfuric acid markets, with a focus on Russia.

T

he availability of sulfur supply and the market balance has been a key focus point over the past year, with the global COVID-19 pandemic taking its toll on output as fuel oil demand collapsed on the back of restrictions and lockdowns throughout 2020. Sulfur prices reached 2-year highs earlier in 2021 before easing once availability began to improve with the roll out of vaccination programmes and the lifting of restrictions in many regions. There is some uncertainty around the short-term view, as the processed phosphates market appears to have potential to firm up based on strong demand in South Asian markets. Beyond 2021, however, sulfur prices are expected to see further downward correction in sync with the view for downstream markets, including diammonium phosphate (DAP).

The capacity outlook for sulfur is robust for the medium-term. Several projects in the Middle East are expected to ramp up in 2022 following delays as a result of COVID-19.

KNPC’s Clean Fuels Project in Kuwait and the Barzan project in Qatar will have a combined capacity of over 3 million tpy. In the medium-term, projects in the Middle East are forecast to add 4.6 million tpy. Northeast Asia is the second largest driver after the Middle East for capacity growth. An additional 1.6 million tpy of sulfur supply is forecast by the end of 2022, but the recent Chinese government cuts for refiners’ export quotas for 2H21 have led to uncertainty around how new sulfur projects will be impacted.

9

Outside of expected growth areas there are also trends leading to reduced sulfur supply in the refining sector, as smaller and older refineries are closed or converted to import terminals. This has happened across several regions, including Australia, Europe and South Africa. Meanwhile, in North America, there has been a steady decline in supply from Canada as gas-based recovery has declined since the mid-2000s. The preference for lighter, sweeter crudes in the US refining sector in recent years has also contributed to the decline in North American sulfur production. These trends are expected to continue, supporting the view for a tighter regional market.

The drive for battery materials to meet demand for the growing electric vehicle (EV) market is a significant market consideration for sulfur and sulfuric acid. In the US, there are several projects for lithium and copper that have the potential to shift trade patterns significantly as sulfur demand from these projects would be over 1 million tpy. The projects are concentrated in Nevada and Arizona, with most planning to install sulfur burners. Sourcing supply to meet this demand is likely to be challenging, especially if all the projects materialise.

Increased volumes of molten sulfur could be railed from Canada or even bulk product shipped from Vancouver, but logistical constraints and costs may limit options for the projects.

Russia spotlight: sulfur Russia produced approximately 7 million t of sulfur in 2019 and output is dominated by Gazprom. Production from the country is expected to remain stable at 7 million tpy in the long-term.

Gazprom’s sulfur output largely comes from gas processing, with two fields located to the east of the Volga river. The majority of the company’s sulfur production comes from the Astrakhan region, near the Caspian Sea and the Kazakh border.

Sulfur is produced from an onshore gas and condensate field that was discovered in 1976. The field is very sour with high hydrogen sulfide content, and was developed at the end of 1986 as the first train of the Astrakhan gas complex was commissioned.

Gazprom also produces a significant volume of sulfur from its Orenburg operations, located approximately 500 km

southeast of Samara and near to the Kazakh border. The oil, gas and condensate field was discovered in 1966, also with a high hydrogen sulfide content. Commercial gas production began in 1974.

Russia’s refining sector has undergone a major expansion and modernisation programme since 2011, adding almost 800 000 bpd of crude distillation capacity between 2012 – 2017, along with a range of other modernisations to enable production of fuels compliant with West European standards. As a result, sulfur production from oil refining increased to just over 1 million tpy in 2019 from less than 0.3 million tpy in the early 2000s. Argus currently expects refinery-based sulfur production to increase slightly to 1.3 million tpy from 2023, but there is scope for further growth in the sector if additional modernisations take place.

Sulfuric acid Global sulfuric acid demand is forecast to grow by more than 15 million tpy in 2021, after a steep drop in 2020 because of the global pandemic. Total consumption is excepted to rise by 42.8 million t between 2020 and 2025. The leading sector driving demand over the period is phosphoric acid, with growth estimated at close to 19 million t, equivalent to a 15% increase. Most of this is expected in Africa, accounting for more than half of the total increase. Morocco is the leading driver with sulfur-based capacity also being brought online to meet demand. The global metals and industrial markets combined are expected to reflect steeper consumption growth than fertilizers. Together these markets will add over 22 million tpy of demand by 2025. Northeast Asia accounts for around half of the growth. Demand in Southeast Asia will also increase, with Indonesian demand for nickel becoming the dominant end use for acid in the country. Nickel sector growth is being driven by demand for battery materials, with other projects expected to emerge in Latin America in the medium-term.

Sulfuric acid prices have seen unprecedented growth through 2021, with major benchmarks reflecting a significant premium on the elemental sulfur market. This has led to sulfuric acid becoming costly for some phosphoric acid producers, with elemental sulfur providing better margins on

Figure 1. Argus forecasts for global sulfur capacity changes, year on year, and China sulfur capacity outlook.

10 | WORLD FERTILIZER | OCTOBER 2021

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end products. Average Northwest European sulfuric acid prices increased by over 400% between January and August 2021, according to assessments in the ‘Argus Sulphuric Acid’ report.

The outlook for the short-term remains firm, based on market fundamentals, with the tight balance for smelter-based acid expected to continue into the start of 2022. Western European sulfuric acid supply has been tight through 2021, with increased demand in the domestic and offshore markets. Sulfur-based capacity in the region is forecast to drop by approximately 300 000 tpy between 2020 and 2022 following the permanent closure of Inovyn’s UK acid plant earlier in 2021. Total acid production in the region is expected to dip to 12.8 million t in 2021, down by 0.1 million t on 2020 followed by a stable long-term outlook of 12.7 million tpy from 2022.

Russia spotlight: sulfuric acid Russian sulfuric acid capacity has totalled over 10 million tpy since the early 2000s to support the domestic processed phosphates, fertilizer and industrial markets. PhosAgro has the largest burner capacity in the country. EuroChem and Uralchem also have significant phosphoric acid capacity, with captive sulfuric acid production from sulfur burners. Smelter and other sources of supply comprise 26% of the country’s total capacity at just over 4 million tpy. The vast majority of this is linked to copper production, with small volumes linked to zinc and lead production.

Norilsk Nickel shut down its smelting facilities at its Kola division at the end of 1Q21 in an effort to reduce sulfur dioxide emissions. This was expected to lead to a small loss of acid supply. Beyond this recent change in capacity the long-term outlook for supply from smelters is currently stable.

On the demand front, Russian sulfuric acid consumption was estimated at 12.8 million t in 2019, expected to grow by 2.7 million tpy by 2025 and be stable at approximately 15.6 million tpy in the long-term. Argus estimates 90% of acid demand is for the production of fertilizers, primarily phosphoric acid. In line with sulfur-based acid capacity, PhosAgro is the largest processed phosphates producer and is driving developments in the country as part of its Strategy 2025 initiative. The fertilizer sector is the leading driver for demand growth in the outlook. PhosAgro has unveiled plans to spend US$223 million on its Balakovo site to 2025. The funds

will be used to modernise the facility. PhosAgro is already expected to launch a phosphoric acid expansion programme at the site during 2022.

Copper-based sulfuric acid demand in Russia is also expected to rise with the development of the Udokan Copper (previously Baikal Mining Co.) project located in the eastern part of the country. Phase 1 start-up is expected in 2H22.

Construction at the mining and metallurgical plant has been ongoing through 2021, with work underway on the concentrator and leaching site. In June 2021, VEB.RF, Gazprombank, Sberbank and Udokan Copper signed a co-operating agreement to fund the second stage of the development. Investment in the project will amount to US$4 billion, according to preliminary estimates. An official announcement is still pending on whether sulfuric acid demand will be met by captive capacity from a sulfur burner or procured directly on the merchant market. An investment in a sulfur burner is a likely scenario because of the location of the project, but this remains to be seen. Approximately 1% of Russian demand is for uranium leaching operations

by ARMZ with mines in Dalur, Khiagda and Priagunsky. The remaining consumption sector is the industrial market, at over 1 million tpy.

Conclusion The after effects of COVID-19 on global sulfur and sulfuric acid markets continue to influence regional supply and demand balances. Broader macro-economic and geopolitical drivers remain at play and are shaping the direction of both markets.

All eyes are on the potential rise of new sulfur capacity in the Middle East over the next year while Chinese copper smelter additions will be a key indicator for the acid market balance in the outlook. In Russia, the rise of new phosphoric acid-based and potential metals-based sulfur demand will impact the availability of sulfur for the export market.

Bibliography 1.

2.

3.

4.

5.

6.

Argus Sulphur Weekly, various.

Argus Sulphuric Acid Weekly, various.

Argus Sulphur Outlook, August 2021.

Argus Phosphates Outlook, July 2021.

Argus Sulphur Analytics, June 2021.

Argus Sulphuric Acid Analytics, August 2021.

Figure 2. Argus forecasts for global sulfuric acid demand changes, year on year, and Russia and Central Asian sulfuric acid demand growth.

12 | WORLD FERTILIZER | OCTOBER 2021

The key to

RELIABILITY A

s hydrogen demand increases, steam methane reformers (SMRs) are becoming larger and operating in more severe conditions, increasing the inherent risk of unexpected failures that have a severe impact on process and plant economics. It is hence necessary to implement inspections and operation strategies to minimise plant upsets.

Dr Pablo Cardín and Pedro Imízcoz, Schmidt + Clemens Group, Spain, describe new technologies, materials and services to improve the reliability of steam refomer tubes under demanding operational conditions.

New materials for reformer components Increasing reformer reliability starts with proper material selection. Identifying typical damage mechanisms and selecting the most resistant materials is the first step to improving reliability.

The primary failure mechanism of catalyst tubes and outlet components is creep damage. However, materials must also have high temperature stability and good corrosion resistance.1, 2 13

Centrifugally cast materials offer the best performance for SMR applications. Creep resistance relies on the precipitation of carbides, formed during material solidification. Additional carbide precipitation takes place during reformer tube operation, generating small secondary carbides and significantly increasing creep resistance.1, 3 Nowadays, reformer tubes consist of ‘micro alloys’ (HP-niobium [Nb] micro alloy [MA] or Centralloy® G4852 Micro), where additions of strong carbide-forming elements (titanium [Ti], zirconium [Zr] and others) create an added strengthening effect by forming additional secondary carbides.

Schmidt + Clemens Group (S+C) has developed a range of creep-resistant alloys called ‘Micro R materials’ or the Centralloy G4852 Micro R, which has some small, controlled additions of strong carbide-forming elements and balances several key element contents, producing a very fine, nano-sized and uniformly dispersed precipitation (Nb, Ti) (carbon [C], nitrogen [N]) in the matrix, improving creep resistance.1

Higher creep resistance adds additional flexibility for the operator to target different operational scenarios, depending on actual market demands. Table 1 summarises some of these possible scenarios.

It should be noted that API RP 530 only considers a continuous operation at design conditions, while it is well known that plant cycles such as shutdowns and start-ups have a significant impact on material life.3 A new alloy enables minimum sound wall (MSW) reductions, increased resistance to thermal shock and tube weight reduction, while keeping design time. If outer diameter (OD) is maintained, higher catalyst volume is available.3 Retaining original design dimensions (OD/inner diameter [ID]) allows substantial increases in lifetime.

Operating temperatures can be increased, keeping the original design time and providing more hydrogen.

Lowering temperatures will increase the lifetime of tubes.

Outlet components operate at lower temperatures than reformer tubes (< 1000˚C) and more factors contribute to damage incidence. The malfunction or deterioration of support systems, Table 1. API RP 530 calculations. Effect of alloy over tube minimum sound wall restricted thermal expansions and (MSW) thermal cycling add extra unbalanced Centralloy P (bar g) T (˚C) ID (mm) OD (mm) MSW (mm) Design time (hr) stresses to these parts. Consequently, a strong material ductility after ageing G4852 Micro 39.3 900 128 150 10.2 100 000 is needed.2, 4, 5 G4852 Micro R 39.3 900 130.2 150 9.1 100 000 The most typical alloy is G4852 Micro R 39.3 900 128 150 10.2 267 000 20Cr32NiNb (Centralloy G4859). The G4852 Micro R 39.3 918.5 128 150 10.2 100 000 company developed an improved 20Cr32NiNb alloy called Centralloy G4859 Micro. Small additions of Table 2. ASME B31.3 calculations. Effect of alloy material over part wall thickness strong carbide-forming elements, such as Ti, increase creep resistance in Centralloy P (bar g) T (˚C) ID (mm) OD (mm) ts (mm) Design time (hr) comparison to Centralloy G4859. Ti G4859 38 880 200 253 26.5 100 000 carbides form, disrupting continuous G4859 Micro 38 880 200 250.1 25 100 000 interdendritic carbide precipitation G4859 Micro 38 880 200 253 26.5 190 000 and further enhancing creep resistance.

G4859 Micro 38 887.9 200 253 26.5 100 000 The improved creep resistance of G4859 Micro allows wall thickness reduction, weight reduction and increased resistance to thermal shock.

Keeping the original part dimensions and operating conditions can substantially increase lifetime if G4859 Micro is selected. Some exemplary calculations are shown in Table 2.

Ductility after ageing has been related to the precipitation of G-phase (Ni16Nb6Si7) and η’-phase (Nb3Ni2Si).6, 7, 8 Some of these studies also suggest that such intermetallic phases might lead to lower creep resistances.6 Other studies indicate that elements such as Ti are inhibiting or delaying these transformations by forming more thermodynamically stable primary carbides.9 As seen in Figure 1, test results indicate that Figure 1. Ductility after ageing comparison between Centralloy G4859 and G4859 Micro.

14 | WORLD FERTILIZER | OCTOBER 2021

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micro additions of these strong carbide formers (such as Ti) help to improve ductility over G4859.

Remaining life assessment and material performance evaluation of SMR components In order to maintain the reliable operation of SMR units, it is necessary to identify the main failure mechanisms that would lead to unexpected shutdowns. Moreover, periodical material status assessment is required to predict any maintenance/material replacement operations well in advance.

Several companies offer inspection services.

S+C always recommends performing destructive examinations to corroborate non-destructive inspection findings. The company offers the following services: Remaining life assessment (RLA).

Material performance evaluations using finite element analysis (FEA).

RLA The company has provided these services for more than 40 years and has experience in analysing ex-service samples.

Microstructure material inspection and accelerated creep tests are probably the most important information considered for RLA. Microstructures provide a graphic view of material status, creep damage evolution, corrosion and temperature exposure on carbide structures.

Figure 2 represents different stages of the material deterioration of HP-Nb MA during operation, from the as cast sample (a), to the overheated material (c), while (b) shows a typical aged/creep damaged structure.

Accelerated creep tests provide a direct quantification of creep incidence on materials. The company uses two different methodologies, based on accelerated creep tests: the Larson-Miller method and Omega (Ω) method. Both methods are included in the API 579-1/ASME FFS-1 Fitness for Service Code remaining life assessment section for components operating in the creep range.10, 11 Both methods are equivalent; Ω results are more comparable with Larson-Miller parameter (LMP) average values than the LMP minimum, which is the design basis for reformer tubes. A lack of sufficient creep strain information limits the Ω method’s potential and accuracy.10

Material performance evaluations using FEA Figure 2. Microstructure of HP-Nb MA material: a) as cast, b) aged/creep damage, c) overheated.

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The accuracy of these analyses depends on the quality of the material behaviour model, boundary conditions, geometrical models and correct meshing. Typical creep models

considered on these programmes might lack accuracy for dynamic modelling where relaxation behaviour is required.5 Two different case studies are presented, showing the potential of FEA for gathering information about material behaviour during operation and its limitations.

The first case represents the effect of material selection on a standard outer header system. A static structural simulation evaluated stress and strain distribution and a 1-year creep regime for materials G4859 and G4859 Micro.

Results indicate that ASME B31.3 is a conservative design model (Figure 3). Material G4859 will have a time to rupture of 133 000 hr on the T-piece/arm tube zone, while alloy G4859 Micro will have a time to rupture of 255 000 hr.

Lack of maintenance or inadequate alignment adds additional stresses on the part, reducing lifetime significantly. In this case, deviations on the tube arm supports produced a localised overstressing, leading to lower part life (48 203 hr for G4859 and 97 854 hr for G4859 Micro). The second case represents an Figure 3. Lifetime estimation: T-piece/arm tube zone on a standard outlet header system (effect of material selection). unexpected creep failure after 5 years in operation.

ID profilometry tool The stress/strain simulation for 5 years of the S+C jointly developed an ID profiling device with Methanex, outlet manifold system under creep regime confirmed named ‘S+C Sauron’ (Figure 5), intended to provide higher the location of the most damaged areas (Figure 4).

SOME THINK THAT CUSTOMER SUPPORT ONLY WORKS ANALOGOUSLY. WE THINK DIFFERENT. beumer.com

The typical replacement criterion for steam reformer tubes is high diametric expansion (3 – 5% diametric expansion). OD measurements have much higher levels of uncertainty than ID readings.

Nevertheless, normal ID tolerance (+0/-0.8 mm) also results in substantial uncertainty in determining creep damage.

Having a baseline with the original dimensions of tubes adds a much more accurate estimation of damage evolution. As of today, more than 7600 new reformer tubes have been inspected with this Figure 4. Creep strain ANSYS simulation of an outlet header system failing device.

The S+C Sauron generates a laser ring after 5 years in service. projection on the inner surface of the tube that is converted into tube ID information, as shown in Figure 6.

Conclusion

Figure 5. S+C Sauron: ID profilometry inspection tool.

It is possible to improve steam reformer reliability; higher creep resistant materials, such as Centralloy G4852 Micro R and Centralloy G4859 Micro, can significantly increase reformer tube life under creep regime over previous materials, minimising failure risks and increasing operational flexibility in SMRs. Periodical inspections and RLA give a deeper view of damage mechanisms that are present. Process simulation techniques allow for the evaluating of material performance and detecting possible deviations on associated equipment.

The company offers ID Baseline of reformer catalyst tubes. Results obtained are compatible with commercially available techniques for furnace inspection, allowing for higher precision in remaining life management.

References 1.

2.

3.

4.

5.

6.

7.

Figure 6. S+C Sauron: typical ID profile readings. quality products and extra value to its clients. The main reasons for performing ID profiling are: Ensuring product quality.

Detection of notches, over-machining or over-grinding during machining.

Providing an ID baseline that could be used for further inspections.

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8.

9.

10.

11.

JAKOBI, D., KARDUCK, P., and VON RICHTHOFEN, A., ‘Superior Spun Cast Material for Steam Reformer furnaces: Alloy Centralloy® 4852 Micro’, paper presented at 55th Annual Safety in Ammonia Plants and Related Facilities Symposium 2010, San Francisco, California, US (2010).

GOMMANS, R., JAKOBI, D., and JIMÉNEZ, J.L., ‘State-of-the-Art of Materials and Inspection Strategies for Reformer Tubes and Outlet Components’, paper presented at 46th Annual Safety in Ammonia Plants and Related Facilities Symposium, Montreal, Canada (2001).

JAKOBI, D., and HUBER, J., ‘Centricast Materials for High Temperature Service’, paper presented at Nitrogen + Syngas 2011, Düsseldorf, Germany (2011).

BARNETT, D., and PRICE, J., ‘Reformer Outlet System Reliability, Design and Repair’, paper presented at Nitrogen and Syngas 2013, Berlin, Germany (2013).

CARDÍN, P., IMÍZCOZ, P., and JAKOBI, D., ‘New Alloy Materials for Reformer Outlet Systems’, paper presented at 63rd Annual Safety in Ammonia Plants and Related Facilities Symposium, Toronto, Canada (2018).

HOFFMAN, J.J., ‘High Temperature Aging Characteristics of 20Cr32Ni1Nb Castings’, paper presented at NACE Corrosion 2000, Orlando, Florida, US (2000).

ALMEIDA, L.H., et al., ‘Microstructural characterization of modified 25Cr-35Ni centrifugally cast steel furnace tubes’, Material Characterization, Vol. 49, No. 3 (2003), pp. 219 – 229.

IBAÑEZ, R.A.P., DE ALMEIDA SOARES, G.D., et al., ‘Effects of Si Content on the Microstructure of HP-Mod Austenitic Steels’, Materials Characterization, Vol. 30, No. 4 (1993), pp. 243 – 249.

CABALLERO, F.G., IMÍZCOZ, P., et al., ‘Use of titanium and zirconium in centrifugally cast heat resistant steel’, Materials Science and Technology, Vol. 23, No. 5 (2007), pp. 528 – 534.

CARDÍN, P., IMÍZCOZ, P., and JAKOBI, D., ‘Damage Mechanisms and Lifetime Estimation in Steam Reformer Tubes’, paper presented at 65th Annual Safety in Ammonia Plants and Related Facilities Symposium 2021 (online conference).

Fitness-For-Service, Code API 579-1 /ASME FFS-1, 2016.

for blue fertilizer Lorenzo Micucci, Siirtec Nigi SpA, Italy, considers the mechanics and environmental benefits of producing ‘blue hydrogen’ for fertilizer production.

L

arge volumes of hydrogen are used as feedstock in the petrochemical and chemical industries to produce ammonia as feedstock for the fertilizer industry, refined petroleum products and other chemicals.

Today, depending upon the source, hydrogen is currently labelled as: Grey, if it is extracted from fossil fuels (e.g. coal, naphtha, LPG and natural gas).

Blue, if it is produced from fossil fuels in combination with carbon capture, utilisation and storage (CCUS).

Turquoise, when it is co-produced along with carbon black by natural gas pyrolysis.

Green, if it comes from renewables (e.g. solar photovoltaic, hydropower and wind) and electrolysers.

The different colours of hydrogen entail different production costs. Blue hydrogen can be less expensive than green hydrogen without emitting carbon, as the production of grey hydrogen does. The most widespread and at the same time least expensive process used for extracting hydrogen from fossil fuels is methane steam reforming (MSR), which involves the reaction of natural gas and steam over a nickel-based catalyst, resulting in the breaking of the hydrocarbons contained in natural gas into carbon monoxide and hydrogen.

Since almost 50% of hydrogen consumed worldwide is produced via MSR, this article will outline the MSR process for the production of both grey and blue hydrogen with a focus on ammonia production for nitrogen fertilizer facilities, most notably for urea plants.

19

Grey hydrogen production through MSR A steam reformer consists of a convection section – where process streams are heated against the hot flue gas originated in a radiant section – and a radiant section, where heat is supplied (mainly by radiation) to the chemical system by burning fuel gas, as shown in Figure 1.

The radiant section of the reformer is where the reforming reactions take place, i.e. where methane is converted into hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2). It consists of a number of catalytic reaction tubes made of a high chromium (Cr) and nickel (Ni) alloy, arranged in rows in fire boxes fitted with a number of burners. Approximately 50% of the heat released by the burners is transferred to the process. Most of the remaining heat is recovered by pre-heating the reactants and air and superheating high-pressure (HP) steam in the convection section. The exhausted flue gas – containing a sizeable quantity of CO2 – is withdrawn by the convective section with a blower and discharged to the atmosphere through a stack.

In a fertilizer complex producing urea, a secondary reformer follows the methane steam reformer. The heat content of the process gas exiting the secondary reformer is recovered by raising HP steam, part of which is used as reactant for the steam reforming reactions. The remaining part is routed to the steam balance section of the fertilizer complex.

Ni-catalysts for MSR are vulnerable to sulfur. Therefore, before natural gas is admitted into the tubes, the sulfur species in the feedstock has to be scavenged by means of adsorption onto zinc-oxide absorption beds operated at 350 – 400˚C. In a traditional steam reformer, radiation is the main heat transfer mechanism along with a small contribution from convection. The thermal efficiency of a reformer can thus be improved (and the CO2 emissions reduced as well) by increasing the share of the convection mechanism in the overall heat transfer process.

This is what the convection reformers do. In this reformer arrangement, the firebox is a horizontal combustion chamber topped by a vertical bundle of catalytic tubes, and the reforming

Figure 1. MSR process flow diagram.

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reactor looks like a vertical bayonet heat exchanger wherein the catalyst is accommodated in the annulus of the bayonet. The hot flue gas generated by the single burner of the firebox flows upwards along the outer bayonet tube’s external wall, supplying convective heat to the reforming reaction. The reactants flow downwards in the annulus filled with catalyst. The reaction products are extracted by flowing upwards in the inner tube of the bayonet. In this arrangement, the share of the convective heat transfer mechanism is comparatively higher than that of a conventional methane steam reformer; as much as 80% of the fired duty is utilised in the process, against the 50% in a conventional steam reformer. This translates into an approximately 20% reduction of the CO2 footprint due to the MSR operation.

The process gas exiting the secondary reformer contains nitrogen (N2), H2, unreacted methane (CH4), CO and CO2. CO is removed from the synthesis gas in the shift reactor and CO2 is removed in the HP carbon capture (HPCC) system and used as the co-feedstock for urea synthesis. The HPCC is typically based on mature, well-proven absorption technologies. An aqueous solution of methyldiethanolamine (MDEA) is most frequently used for this purpose. The almost pure CO2 stripped at low pressure from the MDEA regenerator of the HPCC is thus delivered, after compression, to the urea unit of the fertilizer plant.

In doing so, a urea plant seemingly achieves some sort of carbon capture and utilisation (CCU). However, the use of urea as fertilizer is a source of greenhouse gases (GHGs), as urea is hydrolysed shortly after application in fields and contributes to the emission of nitrous oxide (N2O), due to microbial conversion in the soil. According to Fertilizers Europe, the total GHG emissions due to urea amount to 11.2 kg CO2 eq/kg-N, of which approximately 2 kg CO2 eq/kg-N is attributable to the urea plant.1

Blue hydrogen from natural gas for ammonia production The environmental impact of grey hydrogen production can be reduced and the hydrogen turned into blue hydrogen by capturing CO2 from the flue gas for sequestration or utilisation.

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The removal of this acid gas can be achieved by passing the flue gases from the convective section of the reformer through a low-pressure removal carbon capture system (post-combustion system), as shown in Figure 2.

In this process set-up, the flue gases are quenched in a water direct cooler, cooled to approximately 45˚C and sent to the post-combustion system at a pressure near the atmospheric pressure. This low-pressure system looks like the HPCC system.

However, the traditional solvents already used in petroleum and petrochemical industries (in particular alkanolamines) are vulnerable to the oxygen (O2), nitrogen oxides (NOX) and sulfur oxides (SOX) contained in flue gases. Therefore, chemical additives must be added to the solvent solutions to make them resistant to the degradation induced by these species.

Alternatively, hindered amines or diamines can be used.

Moreover, due to the low partial pressure of CO2 and the low density of the gas flowing through the absorption column, the process calls for larger equipment and higher solvent circulation rates compared to the HPCC process. This results in comparatively more expensive plants. According to the International Energy Agency (IEA), the post-combustion enables more than 90% carbon removal from flue gases with a cost of approximately US$80/t CO2.2 Following compression and dehydration where appropriate, the low-pressure captured CO2 can be used onsite to produce saleable chemicals. Alternatively, it can be used as feedstock for the production of synthetic fuels and building materials or it can be permanently stored in geological formations (e.g. depleted oil and gas reservoirs, aquifers or saline formations).

In North America most of the captured CO2 is sold to oil companies for enhanced oil recovery (EOR) for recovering an extra 10 – 20% of the reservoir’s original oil in place. The low-pressure CCUS costs thus translate into US$5 – US$25 per barrel of oil equivalent, depending upon the reservoir’s location, the quality of crude oil, the associated gas to oil ratio and other site variables. It goes without saying that the economic viability of using CO2 for EOR is pegged to the price of crude oil.

Therefore, with oil prices at around US$70 per barrel at the time

of writing, lifting extra oil volumes with CO2 might prove to be profitable.

It is worth noting that the price of natural gas, accounting for 45 – 75% of the overall production cost, is the largest cost factor for both grey and blue hydrogen. Therefore, the economics of MSR coupled with a CCUS process (hence, the price of the blue hydrogen) vary from region to region.3 In the Middle East, Russia and the US, where natural gas is priced low, the cost of blue hydrogen production is approximately US$1.40/kg H2.

In other countries, the blue hydrogen price may be greater than US$2.40/kg H2, the IEA reports.3 In any case, this cost is significantly lower than green hydrogen – about US$6/kg H2.

Takeaways Today, natural gas is the primary source of hydrogen production, and MSR is the least expensive process used for chemical synthesis in the fertilizer industry. However, approximately 9 – 10 kg of CO2 is generated per kilogramme of produced grey hydrogen; traditional steam methane reformers (SMRs) are thus sizeable contributors to anthropogenic GHG emissions and ultimately are contributors to today’s climate change.

In a urea plant, 70 – 90% of this CO2 is converted in the fertilizer and up to 2 kg CO2/kg-N is emitted when grey hydrogen is being produced. The carbon footprint due to the operation of an SMR can be reduced by 15 – 18% by adding a post-combustion CCUS system to the low-pressure flue gas exiting the MSR’s convective section. In doing so, blue hydrogen is produced for ‘blue fertilizer’ production.

References 1.

2.

3.

Figure 2. Post-combustion CO2 capture for blue hydrogen production.

22 | WORLD FERTILIZER | OCTOBER 2021

Fertilizers Europe, ‘Carbon Footprint Reference Values – Energy efficiency and greenhouse gas emissions in European mineral fertilizer production and use’, file:///Users/admin/Downloads/ carbon_footprint_web_V4.pdf International Energy Agency, ‘Energy Technology Perspectives 2020, Special report on carbon capture, utilization and storage’ (September 2020), https://www.iea.org/reports/ccus-in-cleanenergy-transitions International Energy Agency, ‘The Future of Hydrogen’ (June 2019), https://www.iea.org/reports/the-future-of-hydrogen

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Bruno Ferraro, Breno Avancini, Eduardo Almeida, Victor Machida, Vitor Sturm and William Lima, Clark Solutions, Brazil, explain why complete burning and proper atomisation of sulfur during plant operation is essential for extending the life of equipment.

24

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common problem for many sulfur-burning sulfuric acid plants is sulfur-rich hot gas backflow during shutdown, which can damage equipment upstream from the furnace, such as the drying tower and its internals.

Some instances of this phenomenon may result in the solidification of carried sulfur vapours on the drying tower’s mist eliminator system and even on tower packing and distributors, requiring replacement or maintenance to ensure that the tower’s performance is not compromised after plant start-up.

The phenomenon occurs when two factors combine: the return of hot gas during shutdowns and the presence of sulfur vapours in the furnace.

Both of these factors will be briefly discussed to clarify the potential causes of the problem.

Sulfur burning Sulfur (S) is burned to form sulfur dioxide (SO2), which is further converted to sulfur trioxide (SO3) in manufacturing sulfuric acid. The combustion of sulfur can be divided into two stages: the liquid molten sulfur is first vaporised, and then combined with oxygen (O2) to form SO2.

A generic sulfur oxidation equation SO2) shows that the theoretical (S + O2 amount of oxygen for burning is equimolar. In practice, the air providing oxygen for combustion in sulfuric acid plants is supplied in excess, in order to avoid problems that may result from unburnt sulfur condensation and solidification in the coldest stream surfaces of the plant.

25

Figure 1. Pure elemental sulfur viscosity.

Figure 2. Gas phase sulfur allotropes.

The upper limit of practicable concentrations of SO2 after the burner is therefore less than the equimolar concentration.

While theoretically it is possible to reach concentrations of SO2 around 20 vol%, usually the gases from sulfur combustion furnaces associated with sulfuric acid plants contain 10 – 12 vol% of SO2, corresponding to an O2/SO2 ratio close to 1:1, as usually applied in double absorption processes. The remaining oxygen in the gaseous stream is key to the conversion of SO2 to SO3.

Most liquid sulfur is sprayed between 140 – 150˚C, where its viscosity is low enough that it can be atomised by spray nozzles (Figure 1). As a result of atomisation, finer droplets increase the overall surface area, which helps sulfur vaporise more rapidly. Sulfur burners should provide thorough mixing of air and sulfur to accelerate the oxidation process.

Sulfur chemistry is unusual due to its tendency to catenation, which is the bonding of atoms of the same element in a chain in series. Sulfur forms a range of open and closed SN species in the gas phase, of which disulfur (S2) and octasulfur (S8) are dominant (Figure 2).

According to Ullmann’s Encyclopedia of Industrial Chemistry, molecules of S2 in the vapour phase are the main oxidised species. Liquid sulfur evaporates primarily as S8 molecules, which begin to decompose into S2 at 600˚C and above. In practice, a portion of the oxidised sulfur is the heat source required to vaporise it. This initial phase is required for maximum mass transfer rates.

Thorough mixing of the air and sulfur, good atomisation and proper temperatures are key to preventing sublimated sulfur carryover. Good atomisation also allows droplets to be easily evaporated, avoiding accumulation of sulfur pools at the furnace’s bottom. Sulfur inject nozzles should be monitored for nominal plant capacity. Atomisation at turndown conditions may be unsatisfactory, through either low nozzle pressure differential or the risk of plugging at lower rates; when significantly altering capacity, nozzles typically need to be changed.

Backflow in shutdowns Figure 3. Gas duct in drying tower outlet after condensation of sulfur vapours.

Figure 4. Drying tower mist eliminator after condensation of sulfur vapours.

26 | WORLD FERTILIZER | OCTOBER 2021

Gas backflow during plant shutdowns is a familiar observed phenomenon. At times, hot fumes can be seen when opening a drying tower’s upper manholes shortly after a plant shutdown. When associated with the presence of sulfur vapours, furnace gas backflow leads to the appearance of sulfur inside the drying tower, which may require an intervention or maintenance on the internals.

Unburnt sulfur carryover arising from inadequate process conditions, poor air mixing turbulence and/or inadequate nozzle atomisation may cause the formation of liquid sulfur pools in the furnace’s bottom. During shutdowns, delays in interruption of furnace sulfur injection or inlet sulfur leakage may form or increase these liquid sulfur pools.

Any remaining oxygen inside the furnace is consumed by sublimating sulfur pools due to the residual heat from the hot ceramic lining. Once O2 is rarified the residual subliming sulfur mixes with the remainder of the hot gases, which can be dragged upstream depending on flow resistance. This hot gas spreads over the plant and can backflow; its temperature and occasional sulfur vapour may damage equipment such as blowers and drying tower mist eliminators.

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Figures 3 and 4 show photos taken by William Lima from Clark Solutions’ troubleshooting team during a backflow with the condensation of sulfur vapours.

Gas backflow is a complex phenomenon and it can create problems for plant equipment even without the presence of sulfur vapours, since temperatures in the order of 400 – 600˚C can be reached in the reverse flow gas, damaging instrumentation, valves, polymeric co-knit mist eliminators and other equipment.

To exemplify and understand the hot gas return phenomenon, a simplified plant model can enable the

Figure 5. Simplified plant model diagram.

prediction of the transient gas flow during shutdowns.

A diagram of a simulated mathematical model is shown in Figure 5.

The developed model allows the dynamic simulation of the gases in the plant, as well as the analysis of gas flow in the piping between the drying tower and the blower.

The simulation shows the behaviour of a typical double-absorption sulfuric acid plant with approximately 900 tpd capacity. Clark Solutions investigate gas dynamics for a steady-state operation case in which the blower ceases to operate at time 0 under an emergency condition, imposing a linear discharge pressure decrease to the system in a 5-second interval. Once the blower is stopped, the pressure in the plant is rapidly lowered, allowing the depressurising gas to flow through the plant outlets with less resistance. In this simulated case, it is possible to verify that for approximately 7 seconds (hatched area) the gases from the plant equipment return to the drying tower as the mass flow inside the ducting between the drying tower and furnace becomes negative. The dynamical response of pressures within the plant during depressurisation and its duration are governed by the resistances imposed on the outlet gas flow.

Figure 6 shows the verification of the plant pressure response, which registers the blower pressure behaviour in the furnace and drying tower. In this simulation, it is possible to see that 3 seconds after the blower is turned off the pressure gradient inside the equipment is inverted, which generates backwards flow. The system depressurisation time is a decisive factor in the intensity of the reverse side gas flow. Higher gradients of depressurisation increase the duration of reverse flow. Due to the plant gas volume inertia, steep drops in the system pressure contribute to the occurrence of the reverse flow. Real plant data collected indicates that drying tower differential pressure manometers had registered up to 30 seconds of negative values during failure shutdowns, indicating intense prolonged backflow.

Conclusion

Figure 6. Gas dynamics simulation result for blower shutdown.

With the results obtained through the plant model simulation, it is possible to verify the existence of a backwards flow of the plant gas volume to the drying tower during plant shutdown, which is intensified by the depressurisation ramp of the blower (Figure 7). This provides quantitative data to develop procedures to attenuate gas return and its potential damaging effects. Furthermore, even though the model does not capture all the plant physics (such as heat transfer phenomena), it is possible to verify the presence of reverse gas flow.

It is well known that when the reverse flow contains condensing sulfur vapours its damage potential is intensified.

Consequently, complete burning and proper atomisation of sulfur during operation is essential for extending the life of plant equipment, avoiding the formation of sulfur pools inside the furnace and preventing its spread as vapour to other sensitive equipment. In scheduled shutdowns after sulfur inlet interruption, it is desirable to maintain air flow up until there is no unburnt sulfur in the system.

Bibliography 1.

Figure 7. Pressure dynamics on simulated blower shutdown.

28 | WORLD FERTILIZER | OCTOBER 2021

2.

MÜLLER, H., ‘Sulfur dioxide’, Ullmann's Encyclopedia of Industrial Chemistry (2000).

Freeport Sulphur Co., Freeport Sulphur Handbook (1958).

SULFUR STORAGE TANK CHALLENGES: PART TWO In the second part of a two part article, Brandon Forbes and D.J. Cipriano, AMETEK/Controls Southeast Inc., USA, explain how the challenges created by the storage of sulfur at a refinery on the US Gulf Coast were addressed.

I

n the first part of this article, published in the May/June 2021 issue of World Fertilizer, the challenges arising from the storage of sulfur were outlined. The concluding part of this article will explore how a team at a working facility on the US Gulf Coast successfully met these very challenges.

Prior to 2006, sulfur tanks at a company’s refineries on the US Gulf Coast were heated primarily with internal steam coils.

The tanks were fully insulated, but no additional methods were employed to maintain the wall or roof temperature. These tanks did not typically last longer than 10 years before full replacement was required due to extensive corrosion.

Corrosion would occur in several locations, with the roof and upper shell being the most common. Corrosion of the roof and upper sidewall would occur both from the inside and from the outside. Corrosion from the inside was likely due to iron sulfide formation; corrosion from the outside was likely due to ambient water contact.

Additionally, the internal steam coil would occasionally fail and release steam into the tank. The increased moisture content would accelerate the formation of iron sulfide and compound the problems.

Repairs were typically required on a yearly basis to patch or replace corroded sections.

Implementing repairs required that the tank be taken out of service and cleaned so that maintenance personnel could enter the tank.

This process was both costly and disruptive to plant operations.

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A better way In 2006, a sulfur tank at one of the Gulf Coast refineries was identified as being beyond its usable service life; the tank was only 7 years old. The company started looking for an

Figure 1. The tank completed in 2007.

alternate tank heating method to apply to the replacement tank. This heating system needed to increase tank safety and reduce tank corrosion to extend the service life. Preventing the formation of iron sulfides was considered to be of primary importance, as this would reduce the amount of flammable material in the tank as well as reduce the corrosion rate. The company established two key improvements that they wanted to see in a tank heating system: The heating system should be configured in such a way that steam leaks would not introduce additional moisture into the interior of the tank.

The heating system should provide heat to the shell and roof.

At the time, Controls Southeast Inc. (CSI) had extensive experience heating tanks and vessels using ControTrace panels. These were typically applications where the objective was process temperature maintenance. CSI also had extensive experience heating sulfur vapour and tail gas lines where the objective was to maintain a uniform pipe wall temperature. Experience with sulfur tanks specifically, where the objective is both process and wall temperature maintenance, was limited to only two prior applications in 2003 and 2005 (and one concurrent 2006 application). These were working well but were young enough that a detailed review of the tank condition had not yet been performed.

Thus, the use of ControTrace on sulfur tanks was a relatively new technology.

The company recognised that the ControTrace external heating system met and exceeded their criteria. Specifically, the heating system not only provided heat to the tank shell and roof but did so in a way that ensured a uniform surface temperature throughout. The company therefore chose this technology for their new sulfur tank at the Gulf Coast facility.

New sulfur tank

Figure 2. Tank chime overview (bottom corner).

Figure 3. Corrosion and scale under tank chime.

30 | WORLD FERTILIZER | OCTOBER 2021

In 2007, the company commissioned a new sulfur tank at the Gulf Coast facility. The tank is 40 ft dia. by 48 ft tall and fabricated from A36 carbon steel. Sulfur in the tank typically contains approximately 100 ppm hydrogen sulfide (H2S). The tank utilises the ControTrace heating system, designed to maintain the sulfur at or above 275˚F (135˚C) and the tank wall/roof surface at or above 255˚F (124˚C). The system is comprised of external, bolt-on heating panels applied to both the shell and the roof. Heating elements were also provided for various nozzles, including the roof vents.

The panels are attached with a combination of circumferential cables on the shell and studs on the roof. Overall, the installation went smoothly. A few improvements to the installation hardware were identified, including increasing the cable length; decreasing the stud length; providing extra attachment hardware near large nozzles where tank wall distortion is likely; and improving the instructional clarity of the documentation. CSI’s current offering considers these and other design improvements.

In 2016, the company performed the first major inspection of this sulfur tank. The tank had operated continuously from 2007 to 2016 without any notable problems. The inspection revealed corrosion of the

tank floor, but no significant corrosion of the heated tank wall, roof or nozzles. Highlights of the inspection by tank region were as follows:

calculated to be occurring at a rate of 0.0034 in./yr. At this rate, the tank wall’s thickness is projected to drop below the design thickness in the year 2082.

Tank – external

Tank floor

Insulation deterioration was noted at several locations. One quadrant of the roof had particularly poor insulation; regular water intrusion was likely occurring in this area. At the base of the tank, significant corrosion was observed on the under-side of the chime (joint between the shell and the tank bottom). Additionally, sulfur was observed seeping out from under the tank at two locations around the tank perimeter. Some cracking and chipping of the concrete tank foundation was observed, particularly in the area closest to the tank base.

Ultrasonic wall thickness measurements were taken at 209 different locations on the tank floor. Measurements at 32 of those locations showed that the floor’s thickness was at or below the design thickness. All 32 of these locations were within 1 in. of the chime. A single through-hole was found – also at the tank perimeter. The corrosion of the tank bottom occurred primarily on the bottom-side of the plates (from the ground-up); the top surface of the plates was observed to be relatively corrosion-free.

Epoxy coating Tank roof and vent nozzles Ultrasonic wall thickness measurements were taken at 24 different locations on the tank roof and four locations on each vent nozzle. A light coating of rust was noted on both the internal and external surfaces, but there was no scale/pitting. The ultrasonic testing (UT) measurements showed that no wall thinning had occurred. The vents were all clear, with no significant sulfur build-up.

The tank utilises an internal epoxy coating applied only to the tank floor and bottom 10 ft of the shell. The epoxy coating was mostly intact but had failed around weld seams and a few other locations. No additional corrosion was observed in the areas where the coating had failed, leading to the conclusion that the coating was likely to not be providing much benefit.

Corrosion mechanism Tank shell Ultrasonic wall thickness measurements were taken at 156 different locations on the tank shell. Again, a light coating of rust was observed on both the internal and external surfaces.

Wall thinning of the shell was observed only on the bottom 1 in. near the chime. Wall thinning in this region was

As can be deduced from the above observations, the only significant concern revealed by the inspection was the corrosion of the tank floor occurring from the outside-in. The mechanism for this corrosion was thought to be water and sulfur making their way under the tank from the outside.

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The concrete pad on which the tank sits has a significantly larger diameter than the tank and does not slope away from it. Rainwater that falls on the pad sits up against the chime and seeps under the tank. The water by itself is likely to cause some corrosion of the tank floor. However, if sulfur were to mix with the water, the corrosion rate would accelerate.

The hot tank bottom would likely drive off some portion of the water, leaving a more concentrated water/sulfur mixture.

This mixture is likely to form sulfuric acid and/or iron sulfide.

In either case, accelerated corrosion would be expected.

Sulfur is observed to condense around the tank vents and occasionally spill as a result of maintenance activities. Thus, some quantity of sulfur is typically observed on the concrete pad. There is high confidence that the corrosion mechanism described above is accurate.

Heating system performance

Figure 4. Typical interior shell/roof surface with light coating of rust.

The ControTrace heating system provides heat to the tank shell, roof and vent nozzles. Of these surfaces, the only area that experienced corrosion was the bottom 1 in. of the tank shell. This result shows that the heating system was effective at keeping the tank surfaces hot and preventing the corrosion mechanisms that had been experienced with previous sulfur tanks.

The corrosion on the bottom 1 in. of the shell is likely the result of three factors: The diameter of the tank bottom is approximately 12 in. larger than the tank shell. The floor plates thus extend out beyond the tank shell and insulation, forming a thermal ‘fin’ that draws heat away from the bottom corner of the tank.

Water intrusion under the tank creates a significant heat load that also draws heat away from the bottom corner of the tank.

The tank insulation does not extend all the way down to the floor of the tank. A small section of the tank shell is left exposed, further lowering the shell temperature at the bottom corner of the tank.

Tank repairs

Figure 5. Tank shell measured thickness compared to nominal and minimum thickness; note single point of wall thinning at 0.08 ft elevation.

To address the tank floor corrosion, the company replaced the old 3 8 in. floor with a new ½ in. floor. The new floor is expected to provide a service life of approximately 10 years, at which time it will likely need to be replaced again. Other minor findings were addressed, including replacing the insulation, applying a new internal epoxy coating and sealing the cracks observed in the concrete pad. It is expected that sloping the pad away from the tank and changing the design of the bottom corner of the tank would significantly reduce the rate of floor corrosion. However, it was decided that the cost of such changes could not be justified on an existing tank.

Comparison tank

Figure 6. Typical tank floor surface with bottom-up corrosion near perimeter; boxes mark UT measurement locations.

32 | WORLD FERTILIZER | OCTOBER 2021

A separate (second) sulfur tank was also commissioned in 2007, this one located at a separate Gulf Coast facility owned by the same company. Similar to the first tank discussed above, the company wanted to use an external heating system that would remove the internal coils and maintain the temperature of the shell and roof. To reduce costs, the company chose to use panel coils (or plate coils) to heat the second tank.

Panel coils are constructed from two plates that are stitched together to form a panel. Steam is applied to the space between the plates, and the assembly is attached to the exterior surface of the tank. Panel coils are practically limited to a rectangular profile; thus, they must be placed on

the tank with considerable space between them to accommodate the tank roof’s geometry and to avoid nozzles.

These gaps between the panels are large enough that the resulting tank surface temperature is non-uniform.

In 2017, the second sulfur tank was inspected in the same manner as the first. The detailed report was not made available for review, but the following repairs were necessary due to extensive corrosion: The complete tank roof was replaced; roof corrosion was most prominent around the nozzles.

Two patches were required on the shell due to wall thinning.

Two patches were required on the floor due to wall thinning.

An annular ring was installed on the floor to address wall thinning at the perimeter.

concrete pad; this will help prevent sulfur from seeping under the floor. Minimising the diameter of the concrete foundation is one method of achieving this.

Bibliography 1.

2.

3.

Molten Sulfur Tank External/Internal Visual and Ultrasonic Inspection Report for the company, Gulf Coast facility (August 2016).

CLARK, P.D., HORNBAKER, D.R., and WILLINGHAM, T.C., ‘Preventing Corrosion in Sulfur Storage Tanks’, paper presented at Brimstone Sulfur Symposium 2008, Vail, Colorado, US, and British Sulphur 2008, Montreal, Canada.

AFPM, ‘Process Safety Bulletin – Flammability Hazards of Hydrogen Sulfide Accumulation in Sulfur Tanks’ (June 2018).

Both ControTrace and panel coils effectively maintain the liquid sulfur’s temperature. However, only the former maintains a uniform wall temperature distribution.

Contrasting the first and second tank highlights the benefit of keeping the tank surface above the freezing point of sulfur at all locations.

Lessons learned The company’s tank experience leads to several key takeaways that can be applied to other sulfur tank applications: Maintaining the tank shell, roof and vent nozzles above the freezing point of sulfur should be a high priority.

Without adequate heat, plugging of the nozzles can result in hazardous H2S build-up in the vapour space, and sulfur on the wall/roof surface can result in the formation of pyrophoric iron sulfides and rapid tank corrosion.

The ControTrace tank heating system maintains a uniform temperature for the tank shell, roof and vent nozzles.

This approach can reliably prevent costly corrosion and the hazardous situations mentioned in this article.

The tank heating system also effectively maintains the temperature of the liquid sulfur. While it was not discussed in detail in this report, this sulfur tank included internal steam coils as a back-up heating system, but they were never used.

The bottom corner of the tank is susceptible to corrosion due to a combination of heat loss and water/sulfur intrusion under the tank. Adopting some minor design changes to this area should reduce the corrosion rate significantly: Slope the concrete foundation away from the tank; this will help prevent water/sulfur from seeping under the floor.

Design the tank chime area so that it does not protrude beyond the tank insulation; this will help maintain the temperature of the bottom corner.

Extend the tank shell insulation all the way down to the foundation; this will help maintain the temperature of the bottom corner. Foamglass or other waterproof insulation should be used where the insulation meets the ground.

Configure the tank vents and other equipment to minimise the amount of sulfur that drips on the

Figure 7. The second sulfur tank panel coil arrangement.

Figure 8. Summary of recommended changes to tank design to reduce floor corrosion.

OCTOBER 2021 | WORLD FERTILIZER | 33

R E COV

Y R STO

RAPID REPAIR AND RECOVERY Valérie Lebrun and Harold van der Zande, Stamicarbon, the Netherlands, highlight how the company’s spare parts service can support effective plant maintenance.

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T

he Full Life Cycle philosophy of Stamicarbon, the innovation and licence company of Maire Tecnimont Group, aims to offer ongoing support to urea producers throughout the entire lifecycle of their plants, providing tailor-made technology solutions, products and services that cater to the specific needs of a plant at a particular phase of its lifecycle. As part of this philosophy, the company has established a dedicated services department (Advance) to support producers in achieving continuous fertilizer production, regardless of whether they use the company’s proprietary urea technology or other third-party technologies.

The Advance department offers a broad range of fertilizer services, including comprehensive inspections during a planned turnaround, training of operators, plant consultancy activities and the supply of a wide range of fertilizer equipment. The last of these services includes not only the supply of measuring equipment for optimising production (such as N/C meters, leak detection systems and radar level measurement devices) but also replacements of existing high-pressure (HP) equipment in the urea synthesis section (such as urea reactors, HP carbamate condensers and HP strippers). The replacement equipment can either be offered in a one-to-one replacement design or offered in an upgraded design to achieve a longer lifetime, higher capacity, higher efficiency and/or lower emissions.

Spare parts services It is essential for plant owners to have the assurance that they are working with reliable equipment, as this helps prevent

unsafe conditions and unscheduled plant shutdowns. However, the corrosion potential of ammonium carbamate poses a severe threat not only to the integrity of urea process equipment but also to equipment and piping components.

Therefore, to support urea producers operating Stamicarbon-designed urea plants – with the main HP process cycle designed with proprietary Safurex® equipment – Safurex spare parts are supplied for all necessary components, including manual control and safety valves, mounting bolts and nuts, granulator nozzles, piping (Figure 1), fittings and other spare parts.

Spare parts services were established in 2016 to assist fertilizer producers with timely and effective plant maintenance. Instead of ordering their spare parts from many different manufacturers, urea producers operating plants based on Stamicarbon technology and Safurex equipment can request all of their required Safurex-based components directly from the company.

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Corrosion-resistant materials for urea plants Active corrosion of stainless steels caused by ammonium carbamate is a significant daily challenge faced by urea plant operators. Corrosion can disrupt the seamless operations of the plant, requiring a quick repair or replacement of equipment, piping or parts. It could therefore lead to unforeseen costs, as most parts must be repaired or replaced during the plant shutdown.

Stamicarbon has used the Safurex family of duplex stainless steels, developed in close cooperation with Sandvik, as the standard material for all HP equipment and piping in urea plants designed by Stamicarbon since 2003. In addition, based on the strong corrosion resistance of this material, a broad range of spare

Figure 1. Safurex piping.

parts products for plant maintenance has been developed. These spare parts support urea producers operating plants designed and built based on Stamicarbon technology, with Safurex steels used for the critical HP components. Furthermore, to prepare for the regular intervals during which maintenance is carried out on the installations, customers can send their orders for different components using Safurex to Stamicarbon. By supplying complete maintenance packages the company assists urea producers, fulfilling its promise to provide Full Life Cycle support.

Such spare part packages can be supplied as part of the replacement equipment supplies, but also in preparation for turnarounds or for maintaining off-the-shelf availability of critical components. During the well-planned maintenance intervals, producers can change existing parts that require replacement due to excessive wear or other reasons.

Stamicarbon offers spare parts made of Safurex to replace components in the HP process cycle where generally higher corrosion rates are observed. Other proprietary equipment or components can also be supplied. In addition, to support repairs of HP equipment, Safurex stock materials such as plates, bars and pipes can be made available, including the necessary welding materials. An extensive range of suppliers that can manufacture these spares or even supply separate components is available.

What are spares?

Spare parts are defined according to customer perception as being a one-to-one replacement of Safurex material, product type or stock replenishment.

Typically, such parts are replaced during service intervals or turnarounds. The identification of the components is based on the original specifications of the plant with clear serial part numbers, which enables a swift identification and replacement process. Spare parts are tailor-made to match the individual requirements of each plant to achieve a 100% fit of a spare part and prevent risks and complications due to corrosion in the plant. In addition, smaller components that do not require customisation according to individual technical specifications – such as nuts and bolts – can be ordered from available stock.

Examples of spare parts include: Intermediate products (flanges, hub and seal ring for flange connectors, fittings, piping, gasket and valves).

Components (bolts, J-bolts and nuts).

Welding consumables.

Raw materials (piping, plates and bars).

Other proprietary equipment or components.

Valves

Figure 2. Automated control valve with Safurex components.

36 | WORLD FERTILIZER | OCTOBER 2021

Valves offered in the spare parts business include manually operated control valves, on/off valves, metering valves, sample valves, hub and seal ring for flange connectors, etc. These components can be part of the primary HP synthesis circuit and a secondary measuring circuit, such as in the N/C meter. Next to complete valves, other components can be supplied for automated control (Figure 2) and on/off valves, such as seats, gland bodies and sealing rings. These will include

material specifications from the original equipment manufacturer (OEM) and other certificates.

Angle globe valves are the standard valves offered by Stamicarbon. These valves are characterised by good control of liquid services, enabling high flow rates with low pressure loss and good shutoff capabilities. Other valve types, such as butterfly valves or straight globe valves, can also be supplied to maintain compatibility with the connecting pipelines, enabling installation of the valve without modifications.

Components Spare parts components include granulator nozzles (Figure 3), installation tools, fasteners (bolts and nuts) and manway gaskets.

Dedicated granulator nozzles for Stamicarbon’s fluid bed granulators are part of overhaul programmes for proprietary fluid bed granulators. Fasteners are generally replaced when a maintenance hole is opened during an inspection. Generally, it is advised not to reuse such fasteners but to replace them. Next to standard fasteners, design-specific fasteners (such as J-bolts) can also be offered. Serrated gaskets in Safurex, in combination with a polytetrafluoroethylene (PTFE) envelope, are also part of the supply programme.

Fitting components – such as flanges, hub and seal ring for flange connectors, fittings, piping, gaskets and olets, weldolets, sockolets, elbolets and thredolets used in piping designs – are also offered.

Lower investment and operational costs.

Limited need for maintenance and repairs.

Higher process safety.

Decreased sensitivity to upset conditions.

Access to expert know-how.

Stamicarbon can provide advice on spare parts stock, and the delivery of spare parts at the right time is arranged based on information about the planned maintenance schedules. As a result, detailed overviews of the necessary components to be replaced during regular maintenance intervals can be proactively provided to urea producers. In case of particular circumstances in the plant (e.g. excessive wear of parts, need for improved performance of redesigned parts or other questions), process, engineering, corrosion and metallurgy expertise is available at short notice. As the technology licensor, Stamicarbon holds extensive detailed engineering specifications for all plants designed by the company as a means of identifying the right components for replacement.

At the same time, striving for continuous improvement, design and material upgrades are also being implemented on the spares portfolio for greater reliability of components, lower corrosion rates and longer service intervals. Furthermore, in the future, the ordering process will be streamlined to ensure a better user experience.

Safurex stock material Aside from intermediate products and components, raw materials, such as HP piping, bar material and plates required by producers to make the necessary repairs during turnarounds, are also supplied. In addition, some of these stock materials can be used by local machine shops partnering with Stamicarbon to make overnight repairs or to manufacture replacement components in cases when there are long lead times to order such components. The stock materials are provided with all mechanical and corrosion certificates.

To enable the welding of bars and plates while maintaining high corrosion resistance, Safurex welding consumables are essential. These welding consumables are also supplied when customers require their teams to be trained and qualified in welding with Safurex. Furthermore, stock for emergency repairs is available on demand.

Figure 3. Granulator nozzle.

Equipment components Other spare parts products include replacement components for measuring equipment, such as N/C meters (Figure 4), radar level measurement devices, etc. However, replacement components – such as ferrules used in strippers, sleeves for condensers and reactor trays – often need specialist (re-)design and are not strictly regarded as spare parts. In addition, pressure-sensitive valves – requiring careful checking by engineering specialists, as they have to meet stringent safety requirements – are not considered spare parts but are also available from the Advance team.

Advantages of Safurex spare parts for urea plants Safurex spare parts allow plant operators to achieve the following benefits:

Figure 4. N/C meter.

OCTOBER 2021 | WORLD FERTILIZER | 37

38

OPTIMISING AMMONIA TANK

MANAGEMENT Jim Olson, The Equity Engineering Group, Inc., USA, considers how to develop and improve an ammonia tank mechanical integrity programme.

T

he global demand for fertilizer continues to grow, and the speed at which farmers can plant their crops during the planting season creates a high demand for safe and reliable asset performance in anhydrous ammonia manufacturing facilities and terminals. Storage tanks are a vital element in this supply chain to build inventory and deliver ammonia as needed during the planting season. Taking a tank offline for inspections or repairs can have a significant business impact on the tank owner, create logistical challenges for farmers and possibly cause damage to the tank itself. Executing a

robust mechanical integrity (MI) programme that ensures ongoing safe and reliable operation is a must for every owner. This article will discuss MI activities utilised throughout the lifecycle of a typical ammonia storage tank, and briefly discuss case studies performed to support MI programme improvements and address potential risks. Ammonia storage tanks designed and constructed to API 620 – Design and Construction of Large, Welded, Low-pressure Storage Tanks (API 620) and API 625 – Tank Systems for Refrigerated Liquefied Gas Storage (API 625) will be the primary focus.

39

Background Along with the code requirements in API 620 and API 625, best practices (information, guidance and industry knowledge) regarding the design, fabrication, commissioning and operation (running and maintenance) of ammonia storage tanks are readily available from many industry sources and internal company practices. The SEVESO III Directive, OSHA 1910.119 Process Safety Management of Highly Hazardous Chemicals (PSM), and other similar regulations define expectations for asset management programmes, specifically MI programmes. Key elements for the MI programme include master asset lists; written procedures; training; inspection, testing and preventive maintenance (ITPM) activities; deficiency management; and quality assurance. Finally, API 653 – Tank Inspection, Repair, Alteration, and Reconstruction (API 653) provides minimum requirements for maintaining the integrity of tanks while in service. API 653 was developed and is maintained to support petrochemical refiners; however, the application of this code to ammonia tanks has become best practice. To help focus discussions and activities for the MI programme, the lifecycle management (LCM) model shown in Figure 1 provides a framework to break down the major elements of an asset’s lifecycle.

Initial design, design code compliance and commission At the start of the LCM of an asset, the design team should understand the business goals and objectives to ensure the design

and subsequent activities for the asset are in alignment. This alignment will establish boundaries for decision-making related to risk, reliability and financial budgets that influence the MI programme. As business goals and objectives change over time, the ammonia tank MI programme will need to keep up with any new goals and objectives.

While the first three phases – initial design, design code compliance (or fabrication) and commission – of the ammonia storage tank’s lifecycle are relatively short in time compared to the total lifecycle, decisions made during these phases will have the biggest impact on the performance of the asset. It is therefore important to have all stakeholders involved. Material selection, double wall versus single wall, vapour recovery systems, foundations and leak containment are examples of these key design decisions. The design team should also address known modes of failure for ammonia tanks; mitigation of known damage mechanisms, such as external corrosion and ammonia stress corrosion cracking (SCC); and features to support ongoing in-service inspection activities after the tank is placed in service.

API 653 identifies several design features that may enable extended inspection frequencies if included in the tank design.

The design team can use API 581 – Risk-Based Inspection Methodology (RBI) to compare the upfront costs of design improvements with the long-term risk reduction and inspection savings they generate.

Once the design specifications are established, a robust inspection and testing plan (ITP) should be developed to verify that the materials and fabrication meet design requirements and that any deficiencies are identified and resolved. The ITP is an excellent tool for the PSM and MI elements of quality assurance and deficiency management during these early LCM phases.

In a case study regarding the fabrication of an ammonia tank, the ITP identified material hardness testing on the tank shell welds after welding. The results came back above acceptable limits, presenting a higher risk of SCC if left unmitigated. In this case, a change in the material properties from the expected parameters was identified during the fabrication process, allowing for a corrective action to reduce the risk of this damage mechanism.

Written procedures for commissioning, operations, in-service inspections and maintenance work should also be developed in these first LCM phases. The written procedures provide a basis for training of personnel and help to establish repeatable performance of MI-related activities while the tank is in service.

In service

Figure 1. LCM model.

40 | WORLD FERTILIZER | OCTOBER 2021

Few teams get to experience the first three LCM phases and are working with assets in the middle of the in-service phase, which includes ongoing operations, in-service inspections and preventive

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maintenance activities. Teams often face legacy inspection cycles and procedures that may drive unnecessary tank outages and costs – and, in some cases, increase damage risks to the asset.

Several tools and methodologies are available to challenge legacy practices and provide improvements to the ammonia storage tank MI programme. The results of these tools and methodologies help to define what damage should be anticipated, along with the necessary corresponding actions required for the tank to remain in service.

contours prior to inspection and the determination of critical areas to concentrate inspection activities. These proactive FFS analyses can help target the inspection activities towards the most critical components of the tank and provide the pass/fail criteria for the eventual inspection(s) of these same areas.

Predictive repair plans can work hand-in-hand with FFS. If predetermined limits are exceeded, having repair procedures, materials and repair organisation requirements on hand can limit downtime due to added work scope and delays.

RBI

Integrity operating windows

Methods for evaluating the probability of failure (POF) and consequence of failure (COF) of complex tank designs have been developed and successfully utilised for assisting owner companies with the RBI analysis for inspection timing and risk assessment that fits with the owner company’s risk profile. The results have helped quantify the risk; provided justification to proceed with necessary inspections where required; and have provided the analysis and recommended timing to extend these inspections where the tank condition and risks allow. These evaluations may be used for MI programme improvements and in discussions with regulatory authorities to adjust locally imposed time-based inspections.

The identification and establishment of integrity operating windows (IOWs) can be used to improve safe and reliable operations. API 584 – Integrity Operating Windows can guide users in defining parameters and associated limits that can predict/prevent damage leading to failure for the ammonia storage tank. An IOW programme is a key element of an effective running and maintenance programme, and is most effective when connected with additional PSM elements for training, procedures and management of change (MOC) programmes.

Repair/rerate/replace Proactive fitness-for-service The proactive use of API 579-1/ASME FFW-1 – Fitness-For-Service (FFS) may be used to help optimise the ammonia storage tank inspection programme. A proactive tank FFS may provide a brittle fracture screening, a proactive development of permissible crack-like flaw sizes prior to inspection, the proactive development of permissible corrosion under insulation (CUI)

When inspections reveal unanticipated damage, an assessment to identify the extent of the damage needs to be performed. In many cases a repair or replacement decision is straightforward, and for these scenarios an ITP should be developed for the work, as previously described in this article. Additionally, the inspection strategy and IOW programme should be evergreened to capture this unidentified mode of failure.

In a case where the damage does not clearly warrant a repair or replacement, FFS is recommended to determine what remediation work may be required, along with an updated inspection strategy to monitor the damage.

Many case studies involving Level 3 FFS finite element analysis have been performed to support repair versus continued service conditions. Examples of these FFS analyses include localised thinning, shell distortion – due to settlement, wind loading (Figure 2), or operating conditions – critical flaw sizing and crack growth calculations for determining remaining asset life.

Conclusion

Figure 2. Level 3 Tank FFS assessment of a settled tank.

42 | WORLD FERTILIZER | OCTOBER 2021

MI programme activities for ammonia storage tanks are established to help ensure safe and reliable operations, which becomes ever more important as business objectives, supply chain constraints and demand from the agriculture industry continues to grow. Several tools and methodologies presented in this article have been successfully utilised by owner companies to improve their MI programmes and justify the costs and investments required for taking a tank out of service for inspections and repairs. Efforts to continuously improve and optimise the MI programme should be evergreened to ensure ongoing alignment with the business’s needs through the lifecycle of the asset (Figure 1).

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Paolo Gallieri, Max Panaro, Ezio Pasqualon and Giuseppe Tornatore, Maire Tecnimont Group, Italy, explain how a digital transformation platform can improve the performance of industrial plants.

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A bridge to

DIGITAL transformation M

aire Tecnimont has leveraged its experience as an engineering, procurement and construction (EPC) contractor to create a digital transformation platform, NextPlant, that can guide plant owners in the chemical, petrochemical, fertilizer, oil and gas and green chemistry industries on their digitalisation journey. When digital transformation is value-driven, it can deliver significant savings for plant owners and make industrial complexes increasingly sustainable from the perspective of health, safety and environmental protection.

The EPC sector is a significant employer and is the cornerstone of the economy in countries around the world. However, particularly in the context of the energy transition, it lags behind in implementing digital transformation when compared to financial services, logistics, media, retail and many other industries. In a challenging market scenario, the company’s goal is to provide clients with digital transformation that combines the DNA of an EPC contractor with advanced IT and a business-driven approach.

The company believes that the EPC contractor is the natural bridge between all the parties involved in the digital transformation process. A contractor is well-positioned to interpret and execute a client’s need to reduce CAPEX investments and OPEX costs, thus minimising the total cost of ownership (TCO) and shortening the return on investment (ROI).

The NextPlant digitalisation platform leverages enabling technologies such as artificial intelligence (AI) and machine learning techniques, allowing plant owners to optimise the actions to be performed during plant operation and maintenance, with the aim of reducing OPEX and increasing the plant’s productivity, reliability and maintainability.

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Besides managing the ‘conventional business’, the company is also actively working to provide solutions for the energy transition and green chemistry to meet clients’ expectations with regards to decarbonisation. A holistic approach is taken to plant digitalisation, starting from internal design processes.

Plant design optimisation Maire Tecnimont’s digital suite for the entire design lifecycle (i.e. from engineering up to the commissioning phase) starts with internal processes, and is made up of solutions that aim to improve the efficiency and transparency of all EPC phases (and even before, in the case of FEED execution). This reduces both CAPEX and the risk that project time overruns affect the expected ROI. The digitalisation of internal processes leverages: Robotisation of routine working processes.

Servicification of tasks to improve time and cost control of activities.

Use of analytics and AI to support cost-driven decisions.

Use of a design collaboration solution based on 3D modelling.

Development of 4D (i.e. 3D model linked to time schedule for constructability analysis) and 5D (i.e. 3D model linked to costs and quantities of materials).

Use of a remote collaboration solution to reduce response time for tasks closure.

Digitalisation of construction working processes to reduce the overall construction site supervision and simultaneously enhance safety during the erection phase as well as quality control on executed works.

Plant productivity and carbon footprint reduction Process optimisation engine Process data is captured during the plant’s operation to feed a digital replica of plant processes. The process optimisation engine, leveraging not only thermodynamics but also machine learning models, simulates the process and optimises its operations as precisely as possible, integrating production programmes and economics. The optimisation is also driven by the reduction of utilities’ consumption and by energy saving, thereby reducing the carbon footprints of new plants.

Prescriptive and predictive maintenance suite Key features of prescriptive maintenance are maintenance planning, spare parts management, workload tracking, work orders management and planning improvements. The improvement of the traditional maintenance suite is obtained by the merging of the database typically used to plan maintenance activities with a 3D model of the plant. Moreover, as a natural evolution driven by a predictive approach, process, machine and environmental parameters are monitored and analysed through statistical and machine learning algorithms to identify abnormal operating conditions and predict failures in advance. An optimal and more sophisticated approach to maintenance – unlocked by a predictive approach – cuts OPEX by reducing the cost of unplanned maintenance activities and avoiding the loss of production due to unexpected shutdowns; it may also increase plant safety by reducing the risk of unexpected asset failures and associated hazards for human beings and the environment.

Figure 1. 5G technology for future-proof industrial plants.

Virtual reality digital training and operator training simulators

Figure 2. Kima fertilizer complex in Egypt.

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Through a combination of virtual reality (VR) and the equivalent of flight simulators (e.g. operator training simulators [OTS]), operators are trained in a fully immersive 3D environment ahead of plant start-up and operations.

This approach allows plant owners to maximise production effectiveness and efficiency, starting from the first months of plant operation. The integration of the VR platform with the OTS model creates an advanced training environment, introducing more realistic interaction between the

control room and field operators. This approach to training creates new job opportunities (allowing the upskilling/reskilling of the current workforce and leveraging the native digital skills of younger generations). In addition, it may facilitate and speed up the transfer of competences when expert crew members retire, and it may create the best virtual simulation scenario to test any potentially dangerous plant upset status in a safe situation, without creating any real risk for human beings and the environment.

Connected field operations Health, safety, security and environment platform All operators are provided with smart devices that monitor potential health, safety, security and environment (HSSE) risks.

By connecting smart devices to a central control room (via Wi-Fi, beacons etc.) it is possible to prevent dangerous conditions while maintaining an operator’s regulatory privacy.

With this approach, the workers are geo-localised and their healthy parameters may be remotely controlled in order to limit any potential risk of injuries or access by personnel without the proper training and authorisation to hazardous or restricted areas, thus reducing the risk of fatalities.

Digital field force Field operators are supported by mobile applications during daily operations in a fully connected plant: every piece of equipment is uniquely tagged, all plant data is saved on a central repository and experts are connected to the field force to provide technical support remotely. Thus, on a single app/device operators can access a range of functionalities to improve the productivity of their day-to-day activities. In this way, the maintenance and operation activities of the field team are facilitated because any information needed is available at their fingertips (through access to a tag-based structured database). Remote assistance can be easily accessed, thereby limiting the circulation of experts across various countries while still providing support in real-time. This approach fosters the continuous learning of workers and minimises the risk of injuries due to incorrect operations, which in turn protects human beings, the environment and assets. The backbone needed to unlock any digital field service is plant connectivity, characterised by ample bandwidth and extremely low latency time. Overcoming resistance to innovation is therefore paramount, as this can allow the application of a new communication paradigm (such as 5G technology) in the industrial environment though new telecommunications technology and facilitate the adoption of edge computing concepts (e.g. the elaboration of data at its source).

Plant connectivity is inseparable from cybersecurity by design, protecting an industrial complex from any type of cyber risk deriving from the application of IoT devices that might theoretically be the entry gates for unauthorised access.

Conclusion Maire Tecnimont Group is capable of engineering and building a fully digitally-enabled plant. The company’s digital platform involves technological partners (as links with the overall supply chain) that are orchestrated by the company, thereby providing a single reference point for the plant owner.

Preparation Technology

for Solid Fertilizers Mineral fertilizer | Organic bio-fertilizer | Soil improver

Highlights of the EIRICH Technology Mixing, granulating, coating and reacting in a single machine or optional in combination with a disk pelletizer Use of secondary raw materials in the form of filter cakes, sludges and nutrient salt solutions Environmentally friendly granulating process, no escaping fine dust or aerosol Custom-tailored plant solutions Maschinenfabrik Gustav Eirich GmbH & Co KG

www.eirich.de

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Martyn Dean, Begg Cousland Envirotec, UK, examines the fibre bed filter technology and pH control needed to reduce harmful emissions from ammonium nitrate production.

P

rocess gases from the production of high-density ammonium nitrate (HDAN) and ammonium nitrate-based fertilizers (as well as explosives grade low-density ammonium nitrate [LDAN]) are contaminated to differing degrees by soluble or insoluble solids and ammonia, which means the installation of gas scrubbing or gas filtering equipment is required to prevent harmful emissions to the atmosphere.

Fibre bed technology has been used for decades, and with Brownian Diffusion type designs prilled ammonium nitrate and ammonia emissions can be minimised. A key requirement for using fibre bed candle filters is that there are

no insoluble elements in the exit air, which would block the filters.

Fibre bed candle filters using polytetrafluorethylene (PTFE) media can sometimes also be used to treat the vapour from ammonium nitrate neutralisers, capturing ammonium nitrate particles and ammonia (NH3).

In a recent case a client had a two-stage system installed that needed to be upgraded. They had new environmental limits to follow that entailed the reduction of NH 3 vapour to below 50 mg/Nm3 and were experiencing loss of performance in the removal of ammonium nitrate particles using glass fibre filters. The revamp solution is covered later in this article.

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The technology of fibre bed mist eliminators The development of hydrophobic fibre bed technology

by I.C.I. in the UK began in the late 1950s for Brownian Diffusion ‘candle filters’ using glass fibres and was patented by the company in 1960.1 In 1963, a commercially effective production agreement and licence was established with Begg Cousland & Co. Ltd., and some of the original methodology is still used, albeit with more modern equipment.

A multiplicity of fibres are compressed in bulk, layered in mat-form or wound in rope-form to make cylinders of different diameters and of varying lengths, supported by a structure of metal or synthetic material.

When installed, according to process and equipment needs, the gas can pass from outside the cylinder to the inside and then upwards to the filter’s top exit (Figure 1), or from inside to outside and then generally upwards to the vessel exit (Figure 2).

Figure 1. Hanging type mist eliminator.

Figure 2. Standing type mist eliminator.

High efficiency – by Brownian Diffusion In simple terms, a Brownian Diffusion type mist eliminator requires a uniform fibre bed of at least 25 mm thickness and a maximum gas velocity of 0.25 m/sec. Below that velocity the gas molecules can move in random directions and thereby cause the mist particles to move equally randomly. The non-uniform arrangement of the glass fibres is such that the mist particles will be captured on a fibre, drop-wise and film-wise, or between fibres and so prevented from flowing onwards with the gas stream. There is a correlation between the diameter of the fibre and the size of liquid particle it can collect, and the technology is capable of capturing sub-micron mists and aerosols to leave an optically invisible stack exit.

The density of the fibre bed of such Brownian Diffusion mist eliminators is typically more than 192 kg/m3, with a fibre diameter of less than 12 μm. The resistance of these filters depends on the amount of surface area used and is usually designed for a clean pressure loss of between 100 – 300 mm H2O.

High capacity – by impaction

Figure 3. Ammonium nitrate prilling process schematic.

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The further development of hydrophobic fibre bed filters was in order to serve applications where there was less need to remove sub-micron mist particles (which are generated by chemical or thermal reactions) than to remove principally larger particles at higher velocities. It meant less equipment cost as well.

High velocity in a mist eliminator can mean up to 2.5 m/sec. for capturing droplets larger than 3 μm, and there are coarser fibres ranging from 15 – 25 μm in diameter that can be used from 0.3 – 0.6 m/sec. for medium-sized particles (1 – 3 μm and above). All of these will be ‘standing type’ (Figure 2) to avoid the risk of re-entrainment of collected liquid from the exit surface of the mist eliminator, since the gas velocity is

slowing down as it exits to the remaining volume of the vessel.

The density of impaction filters is not more than 192 kg/m3, and efficiency is reliant on maintaining sufficient velocity to prevent the particles avoiding fibres; otherwise they will collide with the fibres and drain away by gravity.

The use of PTFE fibre beds on neutraliser and evaporator emissions As shown in Figure 3, there are neutraliser and evaporator stages in advance of the prilling tower in an ammonium nitrate plant. NH3 and nitric acid are fed to the neutraliser first, which can be operating under pressure, under vacuum or at atmospheric pressure, depending on the process technology. This is a highly exothermic reaction, which produces ammonium nitrate (NH4NO3) and steam.

While the NH4NO3 solution is then fed to the evaporator stage, there is some NH4NO3 entrained by the steam flow. The contaminant load (AN) can be up to 15 000 mg/Nm3 (4 kg/t) and the particle size usually 3 – 5 μm.

When the steam is treated separately before release to the atmosphere, there can be impaction type mist eliminators installed made of PTFE fibre with 304L stainless steel structures to capture the liquid droplets. The PTFE fibre is capable of operating at temperatures above 100˚C, which is important. Initially these fibre beds were made using long, bulk PTFE fibres, which were compressed into rectangular panels. Uniformity was difficult since the fibre is very smooth and slippery. Begg Cousland use a specially developed PTFE fibre mat (type T80.35) that provides better efficiency and life. It also allows filters to be made cylindrically as well as in rectangular panel form.

and then into the throat. The throat can be static or can be adjusted for varying gas volume flows and efficiencies.

Here the gas mixes intensively with the scrubbing liquor to capture particles in the gas flow, typically efficient between 95 – 99%. The dirty effluent water is discharged into a tank, from which it may be re-circulated. Since they are continuously wetted, venturis are not prone to plugging. They are, however, high-energy consumers due to the relatively high pressure loss involved.

Where a random packing – such as saddles, rings or other shapes and geometries – is used, the vertical gas flow is contacted by the counter-current scrubbing solution within the height of the packed bed, which is supported on a plate or grid. Efficiency here is mainly a function of liquid volume, even liquid distribution, packing height/residence time and packing drip points.

The risk of blockage by insoluble solids and the pressure loss of the packing are the usual concerns. If a structured packing is used, the same issues apply.

Some types of mesh are also suitable for use as scrubber packings in vertical columns and in horizontal vessels that are sometimes referred to as ‘cross-flow’ type.

The layers of mesh, made of knitted wire or pyramidically formed plastic monofilament, have a large void space and can drain by gravity easily within reason, provided the gas velocity and liquid load does not cause flooding. These mesh pads are effective solids removers in a vertical orientation within a horizontal vessel, so long as there is an effective, continuous wash spray. The residence time can also be sufficient for absorption of NH3 within multiple stages. The mesh pads are easier to remove for washing or other maintenance than random packings.

The Bluefil® mesh panels were constructed to allow the company to add and remove finer or coarser layers to increase solids removal efficiency or reduce the effects of

The technology of packed bed wet scrubbing There are various conventional methods of wet scrubbing process gases; each technology and design is dependent on factors such as residence time, nature of contaminants, presence of soluble or insoluble solids, energy requirements and scrubbing solution availability, to name only a few.

A simple form of vertical column gas scrubber is the wet cyclone, which has no internals other than counter-current spray nozzles and perhaps guide vanes, which means it is virtually free of the risk of blockage.

The efficiency is a function of spray volume, sprayed droplet size and solubility of contaminants.

A venturi scrubber is used to collect fine and coarse particulate and Figure 4. Bluefil MX905 mesh. is especially effective in Table 1. Typical Bluefil combinations’ removal efficiencies, face velocities and pressure loss handling particles Efficiency Efficiency Efficiency Style Velocity range Pressure loss range Efficiency that are sticky or > 10 >5 >3 >2 (m/sec.) (mm H2O) wet. Dirty gas MX 99-10 2 – 3.5 7.5 – 20 99% 70 – 85% is forced down into an inlet MX 99-5 2 – 3.5 15 – 50 100% 99% 70 – 90% section, where MX 99-3 2.5 – 4 40 – 150 100% 100% 99% 80 – 85% the scrubbing MX 99-2 2.5 – 5 60 – 250 100% 100% 100% 99% liquor is injected OCTOBER 2021 | WORLD FERTILIZER | 51

filters required to remove the fine NH4NO3 particle.

The key project data were: Air flow: 41 700 Nm3/hr at 100˚C. NH4NO3 load: 1700 mg/Nm3.

NH3 load: 3400 mg/Nm3.

Figure 5. Four-stage cross-flow scrubber.

Figure 6. Panels used in first-stage cross-flow scrubber. blockage (Figure 4). Typical combinations for the mesh are given in Table 1.

As the Bluefil is mechanically robust the layers can be easily cleaned with a high-pressure washer and re-used.

Revamp project A client had a previous limit of 300 mg/Nm3 for NH3 vapour that needed to be reduced to 50 mg/Nm3, and was experiencing NH4NO3 particle bypass that was causing a visible stack.

The existing system consisted of a four-stage cross-flow scrubber with standard metal knitted wire mesh panels (Figure 5). The first three stages are irrigated with nitric acid for NH3 removal and the final stage is a droplet catcher prior to the second stage fibre bed

52 | WORLD FERTILIZER | OCTOBER 2021

It was decided to replace, in the first stage, the metal knitted wire mesh panels with ethylene tetrafluroethylene (ETFE) pyramidal structure mesh to not only improve the material chemical resistance but provide a higher active surface area for improved mass transfer. The uniform structured mesh promotes redistribution of liquid to cover the whole wire surface without the problem of dry unwetted areas required for gas/liquid interaction. Begg Cousland also looked at the required amount of nitric acid required to react with the inlet NH3 loading and adjusted the operating Ph to 2. The first three stages were panels made from layers of Bluefil MX-094H and the last panel MX-040/MX-094H combination for a cumulative removal of 99.5% > 2 μm for particulate/droplets (Figure 6). Each of the first three stages produced a minimum 1.4 number of transfer units (NTUs), giving at least 4.2 NTUs of mass transfer.

For the second stage the Becofil T80.35 style PTFE fibre was selected for the mist eliminators with 304L stainless steel standing type structures. The existing set of 28 glass fibre mist eliminators of 610 mm dia. x 3650 mm long would have given a gas velocity below the optimum range for this type of impaction fibre size, and it was decided to make the mist eliminators shorter to improve their efficiency. Finally, a set of 28 mist eliminators of 600 mm dia. x 2000 mm long were used inside the existing vessel.

The guaranteed efficiencies were less than 50 mg/Nm3 of NH3 and less than 10 mg/Nm3 of NH4NO3. The amount of NH4NO3 particle was measured at 1 mg/Nm3.

Conclusions For the reduction of NH3 vapour two key factors are required: firstly, the selection of a high active surface material (such as a structured pyramidal mesh for increased mass transfer) and, secondly, reliable pH control to ensure the correct addition of nitric acid to complete the fast irreversible chemical reaction.

Teflon PTFE fibre bed filters are the correct material to use for lengthy mechanical lifecycles and resistance to occasional break though of NH3 vapour, compared to standard design glass fibre beds that experience alkali corrosion.

Reference 1.

PLANT, W., and FAIRS, G.L., ‘Fibre filters for the removal of fine mists’, US Patent 3,107,896. (29 March 1960).

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Marius Sugentaitis, Lyncis, Lithuania, examines how the adoption of new sensor measurement technologies, such as laser-induced breakdown spectroscopy (LIBS), can lead to more efficient mineral processing.

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INNOVATE A

t the end of February 2021, a NASA rover landed on the surface of Mars, starting the next stage in the exploration of the ‘Red Planet’. The mission will gather information on the planet’s geology and possibly determine whether life ever existed on Mars.

The rover is equipped with the latest sensing technologies to gather information on rock properties in Mars.

An understanding of rock and raw ore properties is crucial to the fertilizer mining and processing industry as well. This article will examine fertilizer manufacturing to see if the industry is keeping pace with the latest sensor technologies and whether this technology can bring benefits to the industry.

Traditionally, raw materials used in the fertilizer industry are analysed in laboratories. Typical tasks involved in the assaying include collecting samples from stockpiles or conveyor belts and delivering them to the laboratory’s facilities. Various degrees of sample preparation are usually involved before the analysis can be carried out, such as sample drying, crushing, milling and pressing or chemical treatment. Next, the prepared sample is placed in a laboratory device for analysis. The entire process is often a time-consuming job that takes at least several hours to complete. Such a process is used for product certification and general quality control purposes. But is there room for improvement?

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Carlos Perucca, a potash and phosphate process design professional from CPPC Ltd. in Canada, has said that potash producers have been going through a long period of low prices and increasing costs and regulations. He believes that there is ample room to look for process optimisation alternatives that might result in reduced operating costs, increased efficiencies and lower regulatory requirements.

A potential area of improvement, according to him, would

be highly automated operations with tight online measurement systems.

Raw ore often has a significant variation in chemical and mineralogical composition. Variations in mineralogy and the presence of impurities not only influence processing efficiency but also increase production costs and decrease the final product quality. Online measurement technologies are used for process optimisation, and help mining and mineral processing companies control the production process without delaying waiting for laboratory results. In this way the production process can adapt to raw material changes in real-time and act accordingly. Such real-time process control improves mineral recovery and can extend the mine’s lifetime. Operation costs can be reduced by minimising consumption of reagent, water and energy.

At the mine site, such systems are most commonly used for grade sorting and stockpile formation. The raw material flow is automatically diverted to different stages of the beneficiation process or stockpiles based on the incoming ore grade.

Another application is impurities Figure 1. This artist’s concept depicts the Curiosity Rover as it uses its rejection, when waste rock is removed Chemistry and Camera (ChemCam) instrument to investigate the composition from the feed at the earliest mining stage of a rock surface. prior to further processing. As a result, mill throughput can be increased with the same processing infrastructure.

In the processing plant, online measurement systems are used for feed-forward control by monitoring incoming production quality or tailings.

The dosage of reagents, water and additive can be adjusted based on real-time data to ensure the highest mineral recovery.

Tailings are monitored, making sure the production is set to minimise the loss of Figure 2. Laser measurement system focused on a moving conveyor with valuable minerals. potash product.

One of the most common online measurement systems used in the potash industry is the K40 online analyser.

Potassium ore contains small quantities of the radioactive isotope K40. The concentration of potassium oxide (K2O) and/or potassium chloride (KCl) in an ore is measured by detecting variations in K40 radiation. Such measuring technology has been used for several decades in the potash industry and continues to be the dominant presence in the online analysis process. The vast majority of these analysers are installed at the front-end, working in tandem with conveyor scales to measure the quantity of KCl feeding the mill at any given time. Such information is used for accounting purposes and can be incorporated into the flotation process to control reagent dosages.

Figure 3. Manual sampling for laboratory analysis.

56 | WORLD FERTILIZER | OCTOBER 2021

For more complex process control tasks at further stages of the beneficiation process – especially at higher concentrations of KCl – more advanced online measurement technologies are required.

One such technology is laser-induced breakdown spectroscopy (LIBS). The technology has low detection limits and can provide composition measurements of all required elements simultaneously. By way of example, NASA’s rover is equipped with a LIBS measurement system for gathering essential data on the composition of rocks on Mars. The same measurement principle is used in the fertilizer processing industry. The LIBS measurement unit is installed above a conveyor belt and provides online chemical composition measurements of raw material flow. Some plants use such systems for online measurements of slurry and brine. The technology can provide accurate measurements of calcium (Ca), potassium, phosphorus, nitrogen, magnesium (Mg), aluminium, iron or any other element or compound of interest.

The principle of a LIBS online measurement system is as follows: a laser beam is focused on the surface of the material to be analysed at a frequency ranging from 1 to 100 times per second. The laser beam raises the local temperature of the material above 50 000˚C and thus generates plasma. The plasma quickly cools down, emitting a light that is detected through a lens system. Next, special software processes the obtained light spectral data and determines the concentration of all the elements in the material. Parameters such as moisture can be measured as well, based on relevant elements such as hydrogen. It is

important to note that the system does not emit any ionising radiation and can be safely used at any site.

Case study: US Lyncis, a Lithuanian-based company, supplied a US phosphate producer with LIBS online laser measurement technology to drive raw ore sorting applications. One of the producer’s plants was experiencing high dolomite content in their feed.

Installing real-time process control based on magnesium oxide content in the raw ore allowed them to remove the waste ore before the processing stage. The final product quality was improved and, more importantly, consumption of reagents and water was reduced; the technology promises cost-effective and more sustainable mining.

With improving sensors and advanced machine learning algorithms, such technologies can be pushed to much higher levels every day. The data streams allow the processing plants to make better control decisions more quickly and with greater confidence.

According to Perucca, mineral processing is still a conservative industry but there is a new generation of managers taking over. With the new crop of engineers and technicians in place, changes will come faster and faster.

Potash crystallisation and flotation circuits (to name just a few of the most critical processes) are at the core of a potash processing plant, and running a highly efficient circuit has a significant impact on any company’s bottomline.

Just recently LIBS online elemental measurement technology was implemented in the potash crystallisation process.

chemical composition of the concentrate cake based on laser online analyser data and manually adjust the process to maintain product quality.

However, one difficulty is that the technological process is characterised by certain fluctuations, and to maintain an economical mode of washing off the concentrate cake the operator must frequently change the water flow rate.

The automatic process control system has become a key solution for the company. Today, the operator sets the key parameters for the system – the required NaCl content – and the system continuously compares it with Figure 4. Lyncis online element analyser in operation at Belaruskali facility. the NaCl value measured by the LIBS online analyser and automatically Case study: Belarus adjusts the water supply for washing off the concentrate With the help of a laser online elemental analyser cake.

Belaruskali is able to measure the mass fraction of all the Conclusion main elements – KCl, sodium chloride (NaCl), Ca and Mg Improving measurement technologies and online – in the final product in real-time. Constant monitoring measurement capabilities allows fertilizer and other mineral prevents the overuse of the valuable components (e.g. processing companies to understand the nature of potassium) in the process and at the same time removes fluctuations in the chemical composition of raw materials in impurities such as Na, Ca and Mg. As a result, the final KCl real-time. Improved product quality, better utilisation of concentrate is obtained with values as close as possible to scarce resources and decreased energy consumption can be the specifications. achieved by implementing automated process control According to Vadim Naukovich, deputy chief engineer at solutions based on online sensor technologies. one of Belaruskali’s plants, the operator can control the

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MAINTAINING

material flow

Chris Schmelzer and Sid Dev, Martin Engineering, USA, discuss how air cannons ensure efficient material flow in fertilizer production, whilst minimising air consumption.

E

fficient material flow is a critical element of fertilizer production, and accumulation or blockages can significantly impact a plant’s operating efficiency and profitability.

Build-ups in process vessels and storage systems can choke material movement, causing bottlenecks that create expensive obstacles to equipment performance and often require manual cleanout or costly third-party interventions, such as vacuum trucks, carbon dioxide (CO2) blasting or air lancing. As a result, poor material flow raises maintenance expenses, diverting manpower from core activities and, in some cases, introducing safety risks for personnel.

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If these become severe enough, flow problems can bring production to a complete stop, which is particularly troublesome – and expensive – when it results in unplanned downtime. Although many plants still use manual techniques to remove build-up, the cost of labour and periodic shutdowns has led some producers to investigate more effective methods for dealing with this common production issue.

One technology that has proven itself over more than four decades of use is the air cannon, also known as an air blaster: a flow aid device that can be found in a wide range of industries. Early cannon designs were engineered to use very high pressures – some as much as 34 474 kPa (5000 psi) – which were expensive to operate and introduced safety issues. The controlled-pressure air blaster technology in widespread use today was patented by Martin Engineering in the 1970s, creating the global market for the devices. At present, applications vary widely, from clearing transfer chutes to emptying stagnant bulk material storage silos to purging boiler ash and even cleaning high-temperature gas ducts. As a result of new and

emerging technologies, air cannons can even be used in applications involving extreme temperatures and other hostile service environments that limit the use of other flow aid options.

Basic operation The two basic components of an air cannon are a fast-acting high-flow valve and a pressure tank. The device performs work when compressed air in the tank is suddenly released by the valve and directed through a nozzle strategically positioned in the vessel, duct, cyclone or another location. Often installed in a series and precisely sequenced for maximum effect, the network can be timed to best suit individual process conditions or material characteristics.

A ‘typical’ air cannon application might consist of a fast-acting valve on a 70 l (2.5 ft3) tank with free air compressed to 7 bar (100 psi) inside. The valve is designed to be held in a closed position by the pressure of the air supply until a signal triggers a solenoid, releasing the captive air. These fast-acting valves can release the tank volume in a fraction of a second, creating a high magnitude force at the exit nozzle that is installed through the wall of the vessel or duct.

The timed discharge breaks down material accumulations and releases blocked pathways, allowing solids and/or gases to resume a normal flow. In order to customise the air cannon installation to the service environment, specific air blast characteristics can be achieved by manipulating the operating pressure, tank volume, valve design and nozzle shape.

A new series of cannons designed for ambient temperature applications has also been developed to deliver a high-velocity discharge of stored air, while avoiding the costs of special alloys engineered to withstand high-temperature conditions. The new product family features a hybrid valve concept that provides more force, uses less air and simplifies maintenance in challenging applications with limited budgets.

Cost of ownership New, more efficient valve designs will deliver higher blast forces than previous designs, as will higher operating pressures. Larger tanks deliver longer blast durations because of the greater air volume being discharged.

Figure 1. Air cannon installation on a conveyor transfer chute However, peak force is generated only during the first to prevent clogging. few thousandths of a second following the valve opening, so in those applications requiring high-force output to move the material the duration of useful energy is extremely short.

In most facilities, an air cannon network will be connected to the plant air system, sharing the compressed air with other equipment and processes. If the plant has no air system in place, or if the requirements of the air cannons will cause the plant to exceed the existing system’s capacity, the cannons may be supplied by a dedicated compressor. Because blast forces are a direct function of supply pressure, effective performance depends on an adequate pressure and volume of compressed air.

Figure 2. Cannons installed in a series and sequenced for maximum effect.

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Compared to other sources of energy, compressed air is relatively expensive. There is increasing value in finding ways to maximise the benefit of air cannon systems while minimising compressed air consumption, which has led to the development of modular systems to suit specific operating conditions and layouts, while avoiding the additional costs that frequently accompany customised solutions.

The flexibility of these new systems is a key element.

The ability to alter blast characteristics, frequency and sequencing means operators can adapt to changing material conditions and weather to maintain optimum flow and system performance. The more powerful blast force from the new designs can extend firing intervals – helping to conserve compressed air – and pressures can be controlled to deliver maximum performance and efficiency.

One way to minimise compressed air use is to specify a cannon design that employs high-efficiency valve technology. With supply pressures being equal, more efficient valves mounted on smaller tanks can deliver higher discharge forces than less efficient valves on larger tanks. The savings are compounded when the more efficient valve with higher blast force reduces the frequency of the air cannon discharges, which delivers a saving on compressed air.

Systems that require a high volume of air usage can become expensive, but new air cannon designs use relatively little volume for the amount of work they perform. For example, 50 discharges from a 70 l cannon would consume approximately 28 m3 (1000 ft3) of compressed air, at a cost of approximately US$0.14 using current pricing. If the device were set to discharge three times per hour, 24 hr/d and 365 days per year, the annual compressed air cost would be approximately US$100.

Service While conventional cannon designs still require technicians to remove the tanks for servicing and access valves from inside the vessel or chute, the ability to change nozzles and valves without a system shutdown delivers a significant reduction in maintenance hours and downtime. By avoiding the need to remove the tanks or enter the vessel to perform a service, these modular systems and their quick-change components mean that maintenance time is now measured in minutes, rather than hours. Direct drop-in

Figure 3. New high-efficiency valves can be serviced without removing the tank, with no process shutdown.

Figure 4. Air cannon being installed during production by a trained technician.

replacements are available for ageing cannon designs, facilitating easy upgrades and minimal downtime to maximise system performance.

Even in just the last few years new valve technology has produced significant performance advancements in air cannon designs. The new family of positive-action valves from Martin Engineering produces approximately twice the blast force output of the previous valve generation, while using approximately half the compressed air volume. If the two designs were set to deliver the same discharge force, the new design would operate at about half the pressure,

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further reducing the compressed air consumption to approximately a quarter of that used by the old valve design. Specifying an air cannon network with the more advanced valve will cost a little more up front, but the savings more than pay back the difference over the lifetime of the system.

In addition, with innovative outward-facing valves and Y-pipe assemblies, air cannons can now be serviced without removing the tank, disturbing the vessel wall or scheduling downtime. Furthermore, with the recent introduction of a specialised process for installing cannons,

Figure 5. A technician installs a Y-pipe to allow quick nozzle change from outside the vessel.

they can be added to an existing process without shutting down the operation, even in high-temperature applications.

Nozzles As the evolution of cannon and valve technology nears its logical limits, researchers are beginning to focus more on nozzles as a way to improve system performance through better customising blast patterns and forces to suit the specific materials and process conditions of individual operations. The nozzle is the component that takes the stored energy in the form of compressed air and directs it to do work, so it has a considerable effect on the performance of any air cannon. The application dictates the type of performance needed, including the shape of the air blast, length of the plume, etc. A primary goal in every application is to use the stored energy as efficiently as possible.

The heat-resistant nozzle is a critical component of most systems, designed and manufactured to deliver the optimum force and blast pattern to suit the application.

These nozzles are currently available in a variety of shapes, sizes and materials of construction. In recent years, the most commonly used are cast alloy fan shapes and stainless steel pipes. While a pipe nozzle is reasonably light and easy to install, it has a limited area of influence on a flat vertical wall. In contrast, the fan nozzle typically has a wide area of influence and shorter range.

A new series of retractable air cannon nozzles has also been introduced for high-temperature applications, extending into the material stream only during the firing cycle to protect the nozzles from extreme temperatures and abrasion. These ‘smart’ nozzles allow the cannon and nozzle to be installed independently, so the nozzle can be accessed for inspection or service during production without stopping the process or removing the cannon.

The new design solves two common industry problems: effectively dislodging accumulations in hard-to-reach areas without shutdown or manual labour, while significantly extending nozzle life. Furthermore, the units can be serviced from outside the vessel without disturbing the refractory, reducing potential damage while minimising service time and risk of injury.

Case study

Figure 6. Refractable nozzles extend into the material stream only when firing.

62 | WORLD FERTILIZER | OCTOBER 2021

A fertilizer producer in the midwestern US transported petroleum coke through a square chute ending in a cylindrical spout. The internal transition caused material to enter the spout unbalanced, leading to bridging. Bridging happens when an arch of condensed material builds around the downspout, preventing cargo from flowing freely.

Martin Engineering was invited into the plant to assess the situation and offer solutions. The technicians installed two 35 l air cannons. Connected to the plant’s compressed air system, a powerful shot of pressurised air was fired in response to a positive signal from a solenoid valve. The valve design provides more force to loosen bridged material, using less air than larger cannons.

One cannon was fitted onto the existing clean-out port, pointing downwards into the cylindrical downspout.

The other was installed on the opposite side above the transition – the common bridging point – to sweep the

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schedule, based on the needs of the application. Since installation, operators have reported zero downtime due to clogging and no need to pull workers from other essential tasks to lance obstructions. A manager close to the project said that they were very pleased with the outcome, adding that the shutdowns were getting unsustainable so the solution had offered a fast return on their investment. Plant managers are planning to install cannons on other problem chutes/head boxes in the future.

Conclusion

Figure 7. One cannon was fitted onto the existing clean-out port, the other on the opposite side above the transition.

back wall of the chute and loosen any compacted material that could lead to clogging.

Installation of the cannons was performed during scheduled downtime and required minimal changes to the chute structure. The cannons are easily fired from a nearby solenoid box when needed or can be set on a firing

In the most basic terms, maintaining material flow and minimising air consumption improves system efficiency and reduces operating costs. On new installations, specifying an air cannon system with high-efficiency valves will deliver effective material movement while reducing compressed air requirements. Upgrading the valve and/or installing a piston return reservoir can significantly reduce the air demand of existing systems, even those with old-style cannons.

The benefits of specifying high-efficiency technology for air cannon networks include reduced energy costs, improved system performance and increased availability of compressed air for other processes within the plant.

All three contribute to a healthier bottom line, justifying the added up-front expense with a payback period that is far exceeded by the equipment’s expected lifespan.

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