Solutions to problems facing Natural Gas processing(dehydration) in Tanzania by valentine elvis

UNIVERSITY OF DAR-ES-SALAAM

COLLEGE OF ENGINEERING AND TECHNOLOGY DEPARTMENT OF CHEMICAL AND MINING ENGINEERING PRACTICAL TRAINING REPORT [PT3] 2011/ 2012. COMPANY: PAN AFRICAN ENERGY TANZANIA,(PAT).

PROJECT TITLE: MONO ETHYLENE GLYCOL TRAINS EFFICIENCY EVALUATION. DEGREE PROGRAMME: CHEMICAL AND PROCESSING ENGINEERING STUDENT NAME: ELVIS VALENTINE REGISTRATION NUMBER: 2008-04- 03459 INDUSTRIAL TRAINING OFFICER: ENG.JAMES MUGENYI TRAINING SUPERVISOR: BAKAR FRANCIS DURATION: 25TH JULY-30TH SEPT [10 WEEKS].

ACKNOWLEDGEMENT: I would like to thank Pan African Energy administration and the whole management for granting me the chance to conduct my practical training in the company, because for me it was a golden chance that I couldnâ&#x20AC;&#x2122;t dare to lose. My ten weeks at PAT have been the time to learn, with a lot of challenges that I am sure have helped me to expand my knowledge to a large extent. All these couldnâ&#x20AC;&#x2122;t happen without having cooperative and patient people who could even sacrifice their time to share with me, whatever information I needed. Below are the people whom wherever I talk about my success, I would have to remember them concerning their contributions and support which they gave me. First I would like to express my gratitude to all members in all departments of Pan African Energy Tanzania. I did appreciate your cooperation, thanks a lot. My special thanks should go to Eng. James Mughenyi and Mr. Onestus .E.Kajumulo , my Industrial training officers who have been very kind and cooperative; Actually They were my stabilizers in the plant, guiding me as well as correcting me wherever I go wrong. Truthfully these were the best thing I needed as a student. Pan African Energy Tanzania has got a lot of employees and every one used his/ her own position to support me. I just want to say thanks to everybody, may God bless you all. Finally I would like to thank my University Supervisor Eng. Bakar Francis from department of Chemical and Mining Engineering, University of Dar-es-salaam for his valuable suggestion and consultation on my training as well as my report.

ABSTRACT: The aim of this report is to give the explanation of the natural gas production processes at Pan African Energy Tanzania in brief as well as the explanation of the project part beginning from the influencing factor(aim) of carrying out the project ,theory till its conclusion. The report consists of two major parts these are: Processing part Project part The processing part consists of two major sub parts these are processing and distribution processes. The project part itâ&#x20AC;&#x2122;s all about the solution to mono ethylene glycol loss facing the company production processes especially in natural gas dehydration. Mono ethylene glycol reclamation unit efficiency fluctuation seems to be the major causes and this is due to operate the plant under overloaded situation, maintaining system operating conditions (i.e re-boiler temperature and glycol concentration to specific and designed conditions) even ensuring proper retention time for glycol separation(using designed tank) the glycol loss can be reduced to 90% which will rescue the company from high/overspending natural gas dehydration operational cost. The methodology used was the analysis of meg quality and properties, performance of each units operation in meg trains and vessels capacity based on data recorded during normal/designed against current overloaded situation. The result obtained for Meg concentration of the data analyzed were under specifications for normal operation, and out of specification (for about 30-34% rich meg concentration)for maximum operations even under the current overloaded situation. Unit operations efficiency ranging in 80-90% for normal operations 60-70% for maximum and below 60% for overloaded conditions. During normal, maximum even current situation vessels capacity were the same that means that they are overloaded.

Table of Contents ACKNOWLEDGEMENT: ...........................................................................................................i ABSTRACT: ..............................................................................................................................ii INTRODUCTION: ..................................................................................................................... 1 HISTORICAL BACK GROUND: ............................................................................................... 3 MISSION OF THE COMPANY: ................................................................................................ 3 VISSION OF THE COMPANY : ................................................................................................ 4 POLICY OF THE COMPANY: .................................................................................................. 5 COMPANY ORGANIZATION STRUCTURE. ...................................................................... 5 NATURAL GAS PROCESSING: ............................................................................................... 7 Background: ............................................................................................................................ 7 History: ................................................................................................................................... 7 Natural gas raw materials: ....................................................................................................... 8 Natural gas composition: ..................................................................................................... 9 The manufacturing process: ................................................................................................... 10 Extraction:......................................................................................................................... 10 Process description: ............................................................................................................... 11 NATURAL GAS TRANSPORTATION: .................................................................................. 13 Natural gas pipeline ............................................................................................................... 13 NATURAL GAS DISTRIBUTION: .......................................................................................... 14 Natural gas safety in distribution: .......................................................................................... 14 THE FUTURE OF NATURAL GAS: ....................................................................................... 15 OTHER PROCESSES ACCOMPANY THE PRODUCTION: .................................................. 16 Plant Meg reclamation and circulation system: ...................................................................... 16 Plant Condensate processing: ................................................................................................ 17 Condensate transportation:................................................................................................. 18 Plant Produced water handling systems: ................................................................................ 19 PLANT UTILITIES: ................................................................................................................. 20 Water plant: .......................................................................................................................... 20 Instrument Air Plant: ............................................................................................................. 20 Electricity production: ........................................................................................................... 21 Safety Systems: ..................................................................................................................... 21 iii

PROJECT ................................................................................................................................. 22 INTRODUCTION .................................................................................................................... 23 STATEMENT OF THE PROBLEM: ...................................................................................... 25 OBJECTIVE: ............................................................................................................................ 26 SIGNIFICANCE OF THE STUDY. ......................................................................................... 26 LITERATURE REVIEW: ......................................................................................................... 27 Process description: ............................................................................................................... 27 Meg trains efficiency: ............................................................................................................ 29 Mono ethylene glycol chemistry: ........................................................................................... 34 i)antifreeze chemistry ........................................................................................................ 35 ii)hydrate inhibition chemistry: .......................................................................................... 38 METHODOLOGY:................................................................................................................... 40 Equipment used ................................................................................................................. 40 Experimental part: ................................................................................................................. 40 RESULTS, CALCULATION AND DISCUSION: .................................................................... 42 Experimental results: ............................................................................................................. 42 Vessels capacity evaluation: .................................................................................................. 54 Problems facing the system caused by plant overloading: ...................................................... 58 Current efforts made to solve the current system problems:.................................................... 63 OVERVIEW: ............................................................................................................................ 65 CONCLUSSION AND RECOMMENDATION:....................................................................... 66 Recommendation: ................................................................................................................. 66 Conclusion: ........................................................................................................................... 67 REFERENCES: ........................................................................................................................ 68 LIST OF ABBREVIATIONS: ................................................................................................... 69

List of figures: Figure 1;Company organisation structure .................................................................................... 6 Figure 2:General Process overview............................................................................................ 11 Figure 3:Gas Transportation System .......................................................................................... 13 Figure 4:Meg regeneration Unit ................................................................................................. 16 Figure 5:Condensate Processing overview ................................................................................. 17 Figure 6:produced water handling Overview ............................................................................. 19 Figure 7:Plant Utilities overview ............................................................................................... 20 Figure 8:Dew point Control Train overview .............................................................................. 24 Figure 9:Meg regeneration Unit ................................................................................................. 28 Figure 10:Graph of meg freezing point vs concentration ............................................................ 36 Figure 11:graph showing temperature in meg lab test carried ..................................................... 44 Figure 12:Graph showing lean glycol water ratio vs time ........................................................... 45 Figure 13:laboratory rich glycol vs time .................................................................................... 47 Figure 14:monthly average properties of lean glycol train 2 ....................................................... 48 Figure 15:monthly average properties of lean glycol .................................................................. 49

List of Tables: Table 1;natural gas composition ................................................................................................ 10 Table 2:plant specifications according to design ........................................................................ 32 Table 3:Ethylene glycol concentration vs temperature ............................................................... 35 Table 4:Boiling point vs concentration ...................................................................................... 37 Table 5:Meg boiling point Vs concentration .............................................................................. 38 Table 6:lean glycol properties in train1. ..................................................................................... 43 Table 7: monthly properties of rich glycol in train 1 .................................................................. 46 Table 8:monthly average properties of rich glycol ..................................................................... 50 Table 9:monthly average properties of rich glycol 2................................................................... 51 Table 10:monthly data on dew point control trains ..................................................................... 51 Table 11:monthly average data on dpc 2 .................................................................................... 52 Table 12abbreviations ............................................................................................................... 70

INTRODUCTION: Pan African Energy Tanzania is the company whose principal activities is to carry out the production, distribution and sales of the natural gas in Tanzania. It operates gas wells, processing plant in Songosongo island within kilwa district in Lindi region and the whole downstream gas distribution network to consumers here in Dar es Salaam. The company also owns and manages Compressed Natural Gas stations (CNG) for gas storage and transportation to the non-pipelined areas. Also company work with Lootah BC Gas as a sub-contract in downstream networking operation and maintenance for efficiently supply of natural gas to consumers. The company distribute natural gas to residential houses, industries and power plants for electricity generation. PAT daily activities are well organized and this is actually what contributes much to the great achievement. The company has got a lot of departments and each department has got its own function or contribution to the plantâ&#x20AC;&#x2122;s development. Below are the departments found in this company and their functions. The logistic department this is one of the very important department since it coordinate transportations, maintain company facilities, order and supply equipments and goods for plant production process. Health and safety is department which ensures safely working condition of workers and their environment during normal operation of gas processing and distribution. Human resources is a department which manage human resources and ensuring good working and social interaction among workers. Finance department this is actually concerned with financing all companies needs to assist all activities in the whole production, processing and distribution of natural gas. Operation department this is one of the department found in any processing industry, the main function of this is to give support to the production process by providing utilities and carry out maintenance to the productive equipment whenever necessary or according to the schedule. To ensure all these the department is divided into several sub sections these are: Utilities section: This section comprises with Instrument and utility air system, meg regeneration units, portable water and sea water system. This section is for preparation of plant usefulness/utilities for natural gas processing. 1

Wellheads section: Wellhead section is comprised of three onshore onshore wells ss10 and ss4 are commingled to manifold and one of offshore(ss5) currently is tubing. All of these wells flow are metered and input.

wells and three offshore wells.Two 4â&#x20AC;? pipeline that supply to the inlet not in use due to corrosion in its gathered in inlet manifold for plant

Gas Processing Plant: Processing plant consist of inlet manifold and pig launching, high pressure and temperature separation (inlet separator),dehydration units ,sales gas metering skid, produced water handling unit condensate storage and flare systems.

HISTORICAL BACK GROUND: Pan African Energy Tanzania (PAT) is a subsidiary of Orca Exploration Group, Inc. (the Group), an international public company engaged in the exploration and production and marketing of natural gas. The Group is listed on the Toronto Venture Exchange (TSXV) and previously operates as East Coast Energy Corporation, originally a subsidiary of Pan Ocean Energy Corporation that was in 2004 distributed to shareholders and listed separately before changing its name to Orca Exploration Group Inc. in 2006.

MISSION OF THE COMPANY: Pan African Energy Tanzania (PAT’s) Mission is to become a leading integrated energy company. In its quest to achieve this mission, the company will: Make a positive contribution to the people, Government and economy of Tanzania through provision of efficient, reliable, high quality and safe gas supply services. Provide a clean energy source with no significant environmental damage. Engage our stakeholders with respect, trust and understanding to progress solutions that benefit all parties in a timely manner. Support social developments to ensure that quality of living is improved. Manage our workforce in a manner which enhances individual performance, develops staff members, sets a culture of co-operation, motivation and trust, and delivers reliable results. Protect and enhance shareholder interests through delivery of financial performance leading to increased shareholder value or financial returns. Attract investment in further programmes by optimizing the balance between Tanzania’s needs and investor requirements within a competitive global market. Explore and develop further the country’s energy resources in a sustainable manner by identifying and progressing new energy opportunities.

VISSION OF THE COMPANY : The Company endeavors at all times to provide a working environment that will permit employees to achieve the highest level of individual and company performance. It seeks at all times to: Provide fair and equitable treatment of employees; Encourage and provide opportunities for self-development and advancement; Discourage, in any form, discrimination in employment because of race, color, religion, sex, nationality, national origin, tribe, age or disability, social origin, political opinion, gender, pregnancy, marital status even HIV/AIDS. Encourage and provide opportunity for staff communication and interaction in personnel issues.

POLICY OF THE COMPANY: The Company and specifically its Board of Directors and management team has a primary and continuous commitment to protect the environment, the health, safety and security of its Employees and of all personnel involved in or affected by its activities. This is achieved through the active implementation and continual monitoring of its HS&E Policy, which sets specific standards and targets, which are mandatory and applicable to all locations and activities. Full details are contained in the Company Safety and Environmental Management System (SEMS). Every Employee and contractor has a responsibility to familiarize themselves with the policies and procedures contained therein.

The board will regularly review HS& activities and ensure that targets for continuous improvement are maintained.

As part of their key accountabilities, the executive team will ensure that an appropriate HS&E organization is maintained with clear lines of responsibility. In particular, the management team will make available the necessary fund and resources for the effective management of HS&E activities are not compromised in any, shape or form in the pursuit of business objective.

COMPANY ORGANIZATION STRUCTURE. PAT comprises of different departments and section .The departments includes Drilling , Health, safety and the environment , Human resource, Finance and Operation. The different sections are function support to the Departments, these includes distribution manager, production superintendent, production engineer, upstream assert manager, financial controller.

General manager

HSE manager

Deputy general manager

Upstream manager

Production engineer

Us ssi operation

Head of production

Production superintendant

Ssi operation

Op main coordinator

Project manager

Distribution manager

Financial controller

Function support

Ds dar operations

Figure 1;Company organisation structure 6

Drilling manager

Finance department

Drilling operation

MAIN REPORT:

PART ONE NATURAL GAS PROCESSING: Background: Natural gas is a mixture of combustible gases formed underground by the decomposition of organic materials in plant and animal. It is usually found in areas where oil is present, although there are several large underground reservoirs of natural gas where there is little or no oil. Natural gas is widely used for electric power generation, as well as for a variety of industrial applications. History: Natural gas was known to early man in the form of seepages from rocks and springs. Sometimes, lightning or other sources of ignition would cause these gas seepages to burn, giving rise to stories of fire issuing from the ground. In about 900 B.C. natural gas was drawn from wells in China. The gas was burned, and the heat was used to evaporate seawater in order to produce salt. By the first century, the Chinese had developed more advanced techniques for tapping underground reservoirs of natural gas, which allowed them to drill wells as deep as 4,800 ft (1,460 m) in soft soil. They used metal drilling bits inserted through sections of hollowed-out bamboo pipes to reach the gas and bring it to the surface. The Romans also knew about natural gas, and Julius Caesar was supposed to have witnessed a "burning spring" near Grenoble, France. Religious temples in early Russia were built around places where burning natural gas seepages formed "eternal flames." In the United States, the first intentional use of natural gas occurred in 1821 when William Hart drilled a well to tap a shallow gas pocket along the bank of Canadaway Creek near Fredonia, New York. He piped the gas through hollowed logs to a nearby building where he burned it for illumination. In 1865, the Fredonia Gas, Light, and Waterworks Company became the first 7

natural gas company in the United States. The first long-distance gas pipeline ran 25 mi (40 km) from a gas field to Rochester, New York, in 1872. It too used hollowed logs for pipes. The development of the Bunsen burner by Robert Bunsen in 1885 led to an interest in using natural gas as a source of heating and cooking, in addition to its use for lighting. In 1891, a highpressure gas deposit was tapped in central Indiana, and a 120 mi (192 km) pipeline was built to bring the gas to Chicago, Illinois. Despite these early efforts, the lack of a good distribution system for natural gas limited its use to local areas where the gas was found. Most of the gas that came to the surface as part of oil drilling in more remote areas was simply vented to the atmosphere or burned off in giant flares that illuminated the oil fields day and night. By the 1910s, oil companies realized that this practice was costing them potential profits and they began an aggressive program to install gas pipelines to large metropolitan areas across the United States. It wasn't until after World War II that this pipeline program had reached enough cities and towns to make natural gas an attractive alternative to electricity and coal. By 2000, there were over 600 natural gas processing plants in the United States connected to more than 300,000 mi (480,000 km) of main transportation pipelines. Worldwide, there are also significant deposits of natural gas in the former Soviet Union, Canada, China, and the Arabian Gulf countries of the Middle East. Natural gas raw materials: Raw natural gas is composed of several gases. The main component is methane. Other components include ethane, propane, butane, and many other combustible hydrocarbons. Raw natural gas may also contain water vapor, hydrogen sulfide, carbon dioxide, nitrogen, and helium. During processing, many of these components may be removed. Some such as ethane, propane and butane are completely removed processed and transported by TPDC loading ships. Other components such as water vapor and carbon dioxide are removed to improve the quality of the natural gas so as to make it easier to move the gas over great distances through pipelines to Dar es salaam. The resulting processed natural gas contains mostly methane , although there is no such thing as a "typical" natural gas. Certain other components may be added to the processed gas to give it special qualities. A chemical known as mercaptan is added to give the gas a distinctive odor that warns people encase of a pipeline leak.

Natural gas composition: The natural gas used by consumers is composed almost entirely of methane. However, natural gas found at the wellhead, although still composed primarily of methane, is by no means as pure. Raw natural gas comes from three types of wells: oil wells, gas wells, and condensate wells. Natural gas that comes from oil wells is typically termed 'associated gas'. This gas can exist separate from oil in the formation (free gas), or dissolved in the crude oil (dissolved gas). Natural gas from gas and condensate wells, in which there is little or no crude oil, is termed 'none associated gas'. Gas wells typically produce raw natural gas by itself, while condensate wells produce free natural gas along with a semi-liquid hydrocarbon condensate. Whatever the source of the natural gas, once separated from crude oil (if present) it commonly exists in mixtures with other hydrocarbons; principally ethane, propane, butane, and pentanes. In addition, raw natural gas contains water vapor, nitrogen, and other compounds.

Gas Composition C1

i-C4

n-C4

i-C5

n-C5

neo-

C6+

CO2

H2O

ppm

C5 Mole

Mole

97.21

0.990

0.289

0.064

0.080

0.028

0.024

0.000

0.132

0.734

97.20

0.991

0.289

0.064

0.081

0.028

0.025

0.000

0.136

0.734

0.441 4.000 3

0.440 4.000 7

97.21

0.991

0.289

0.064

0.081

0.028

0.023

0.000

0.134

0.734

97.20

0.991

0.289

0.064

0.081

0.027

0.024

0.000

0.137

0.734

97.20

0.991

0.289

0.064

0.081

0.028

0.024

0.000

0.136

0.734

97.20

0.990

0.288

0.064

0.080

0.029

0.024

0.000

0.134

0.734

97.20

0.990

0.289

0.064

0.081

0.028

0.024

0.000

0.137

0.733

0.441 4.000 4

0.441 4.000 1

0.442 4.000 3

0.443 4.000 6

0.442 4.000 8

Table 1;natural gas composition

The manufacturing process: The methods used to extract, process, transport, store, and distribute natural gas depend on the location and composition of the raw gas and the location and application of the gas by the end users. Here is a typical sequence of operations used to produce natural gas for Tanzania power plants, industries and domestic demand. Extraction: The Songo songo underground natural gas reservoirs are under enough internal pressure that the gas can flow up the well and reach Earth's surface without additional help. Through wells tubings the gas flows upward to the surface. When the raw natural gas reaches the surface, it is carefully controlled by wellhead Christmas tree valves and is finally piped to a gas processing plant. About five wells current feed into the Songo songo processing plant.

Process description: Gas processing: P-141 P-18

wellhead

Plant bypass

test separator

P-142

P-124

P-4

P-132 P-140 P-125 P-10

P-17

P-24

P-143 P-24 P-130

XV V-4

P-25

Cold separator

G/G h.e

P-12

P-11

P-24

P-128

P-26

P-50

P-88 P-87

inlet separator

P-31

P-30 P-28

J.t P-32 valve

flare SDV

P-33

P-39

Glycol gen P-90

P-131

SDV

P-93 P-89

P-99

P-65 P-54

C.P.I

P-55

P-53

P-52

Skimmer

P-83

P-51 LV

Cond pre heater

P-119

P-120

P-103

P-94

P-40 Sales gas

LV LV

P-123

P-96

P-108

P-41

P-118

P-115flare

P-122

WATER STORAGE TANK

P-58

P-60

P-61

P-63

FILTER

Water disposal to sea

P-45

P-116

Fuel gas

Pump

VENT

P-104

Cond heater & flash tank

P-107

P-121 P-106

P-105

To jetty for export

C.D.D header P-110

Gas boot

P-109 LV

P-78

P-71

P-67

P-95 P-111

OIL STORAGE TANK

P-68

Pump

SLOP OIL TANK

P-69

P-112

pump P-72

CONDENSATE CONDENSATE TANKS TANKS

P-77

P-76

pump

P-113

pump

Figure 2:General Process overview With the assistance of Christmas trees in well heads the well fluids from the two offshore wells SS-7 and SS-9 and three onshore Wells SS-3,SS-10 and SS-4 injected with mixture of corrosion inhibitor and water clarifier are transported in two individual 6” and two individual 4” buried flow lines respectively to the gas plant inlet skid where they tie into their individual inlet flow control valves. The flow lines then run to the gas plant inlet metering and manifold skid where each well’s production is measured in a meter run. The inlet manifold consists of a 10” HP production header and a 10” test header for gas stream mixing which is done purposely to allow set up of production “well sets “so that for a given production level, the best reservoir utilization, well flow composition can be selected from the available wells. The gas from test header flows into the test separator. With valves assistance 11

P-114

provided, the inlet manifold permits any or all producing wells to be diverted to test separator. Test separator is a three-phase separator complete with a boot. Accounting type gas (senior orifice type fittings) and liquid metering (turbine flow meter) is provided in the outlet piping from the vessel to allow for periodic well testing. The gas stream flows from the test separator to the inlet separator (V-110) gas outlet line. The hydrocarbon liquid stream is metered and dumped under level control to the condensate flash tank. Produced water separated in the boot is metered and dumped under level control to the produced water handling system. The gas from HP production header flows into a three phase Inlet Separator for separation. Inlet separator is a three-phase (gas, condensate and water) separator complete with a boot. The vessel is sized to handle any liquid slugs from the well flow lines. A high-level dump system is provided such that in the event of a large slug the liquids are automatically dumped to the closed drain drum. Hydrocarbon liquids are separated from the gas and water behind a weir in the main vessel and are dumped under level control to the condensate flash tank. Produced water is separated in the boot and is normally dumped under level control to the produced water handling system. The gas from test and production separators is commingled and then the stream is split to enter two dew point control trains. The gas first enters the tube side of the gas-gas exchanger where it is pre-cooled by counter-current heat exchange with the outgoing dry sales gas. Lean glycol solution is sprayed onto the inlet tube sheet of each exchanger to absorb water and prevent the formation of hydrates. The gas from heat exchangers is further cooled by pressure drop across the Joule Thomson valves, upstream of cold separators. During this cooling process, hydrocarbon liquids are condensed. Cold separators are three phase Separators where gas, condensate and rich glycol are separated. The separated condensate flows under level control to the condensate stabilization unit and rich glycol flows under level control to the Glycol Regeneration units for re-concentration prior to re-injection at the gas-gas exchangers. The separated dry gas from the cold separator flows through the shell side of the gas- gas exchanger and leaves the plant as sales gas. The treated gas streams from both the dew point control trains are commingled. A portion of this gas is sent to the fuel gas system for make-up requirements and the remaining dry gas flows to the marine pipeline and onto the mainland. This fuel gas is metered, heated across Fuel Gas Heater and let down across a Pressure control valve to about 350 kPag and 30Â°C before entering the Low pressure fuel gas scrubber. The sales gas is metered in a metering unit (ultrasonic sales gas meter) and odorized prior to its entering the 12â&#x20AC;? marine pipeline for gas transportation to Dar es salaam.

NATURAL GAS TRANSPORTATION:

Figure 3:Gas Transportation System Natural gas pipeline Fundamentally, the best and efficient method of gas transport worldwide is through pipeline network. Mercaptan is injected into the processed natural gas to give it a distinctive warning odor, and then gas is piped in 12â&#x20AC;?marine pipeline to Somanga funga(25kms) where is then connected to another 16â&#x20AC;?onland pipeline from Somanga funga to Dar es salaam(about 225kms).The gas leaves processing plant with pressure about 87bars transported through pipeline by pressure difference mechanism. After reaching Dar es salaam the gas is then distributed to consumers through pressure reduction stations for monitoring and pressure controlling.

NATURAL GAS DISTRIBUTION: Through these pipelines that bring the gas into Dar es salaam city where it is to be used. The pressure is reduced to below 68-78bars, and the gas is distributed in underground pipelines that run throughout Dar es salaam industrial customers and power plants. Before the gas is piped to customers it must pass through two city gates(ubungo and gongolamboto pressure reduction stations) where the pressure is further reduced to about 6-7bars for industrial customers. In big Power plants no need for pressure reduction. For customers in which the distribution pipeline doesnâ&#x20AC;&#x2122;t reach to their area (like movenpick hotel,mickocheni residential houses and some of industries)the compression station in ubungo compress the gas filling to trailers for transportation to those customers.

Natural gas safety in distribution: Natural gas burns readily in air and can explode violently if a large quantity is suddenly ignited. Because natural gas is odorless, foul-smelling mercaptan is added to the gas so that even a small leak will be immediately noticeable. To protect high-pressure underground gas pipelines, a bright yellow plastic tape is buried in the ground a few feet above the pipeline to warn people who might be digging in the area. Warning signs are also placed at ground level along the entire length of the pipeline as an additional precaution.

THE FUTURE OF NATURAL GAS: Because natural gas is clean burning, it is being considered as an alternative fuel for motor vehicles. About 30 car Compressed natural gas (CNG) cars and trucks are already on the road here in Dar es salaam. Many Companies using industrial processes that require high temperatures are also turning to natural gas instead of other fuels in order to reduce the air pollution emitted by their plants and overcoming energy costs even being ensured of continuous energy supply in the power crisis situation. This includes companies involved in manufacturing steel, glass, ceramics, cement, paper, chemicals, aluminum, and processed foods here in Dar es salaam.

OTHER PROCESSES ACCOMPANY THE PRODUCTION: Plant Meg reclamation and circulation system: COLD SEPARATOR RICH GLYCOL

P-48

R.CONDENSER

P-15

pckg P-17

BURNER

P-44

P-51

P-59

RE BOILER

P-11

P-43

P-57

FUEL GAS

P-50 P-58

P-21

P-46

P-40

P-19

P-65 P-66

FILTER

P-34

SURGE DRUM

FLUSH VESSEL

P-22

P-62

LEAN GLYCOL

CLOSED DRAIN DRUM PUMP

G/G EXCHANGER

Figure 4:Meg regeneration Unit The rich glycol from the cold separators enters the reflux coils above the packing in the still columns of the ethylene glycol Re-boilers, where self refluxing occurs. The rich glycol is then passed through integral lean / rich glycol coils in the surge tank section of the Ethylene Glycol Re-boilers. After being preheated by the lean Ethylene Glycol in the accumulator, the rich glycol stream flows to the Glycol Flash tanks where any free gases that exist are flashed off and sent to flare. Any liquid Hydrocarbon that have been carried over to the flash tank is also removed utilizing the Hydrocarbon skimmer connection. Glycol from flash tank flows under level control to the top of the packed section in the glycol still column through Particulate filters and carbon filters. In the glycol still column, water is stripped out of the rich MEG as it flows downward through the packed section consisting of PALL rings, counter-current to the steam that is generated in the Ethylene Glycol Re-boilers. The steam is discharged to the Low Pressure flare header at the top of the still column. Once the desired concentration (temperature) is achieved in the Ethylene Glycol Re-boilers, lean MEG flows by gravity to the 16

Glycol surge tank (integral with the glycol re-concentrator) where it is cooled by heat exchange with the rich MEG flowing through the integral lean/rich glycol coils. From the surge tank, the glycol flows to the suction of the glycol pumps, where it is pressurized for reinjection in the gas/gas exchangers. The lean glycol concentration leaving the EG regeneration skids is maintained at approximately 80% as glycol concentrations outside of these ranges may lead to crystallization at low temperatures, high plant pressure drops, and ultimately freezing â&#x20AC;&#x201C; off of the Gas/Gas Heat exchangers. Plant Condensate processing:

VENT TO ATM

V-5

LP FUEL GAS BLANKETING

CONDENSATE STORAGE TANK SLOP OIL TANK P 701 & 703 WATER-PWS

EXPORT TANKERS

P 710

BURNERS

P 700

Figure 5:Condensate Processing overview The hydrocarbon liquids recovered from the dew point control unit cold separators and test / inlet separator are mixed and preheated in the Condensate pre-heater. The preheated condensate is let down in a pressure control valve to about 350 kPag prior to introduction into the Condensate Flash tank. Final stabilization occurs in flash tank, by ensuring that the condensate remains at a boiling temperature of 71Â°C. The temperature is maintained by an 17

Electric Element. The stabilized condensate from the flash tank flows under level control and is passed through the shell side of condensate pre heater where it is cooled. From Condensate preheater, the condensate flows to the Gas Boot, for further degassing and finally to storage for further export. Condensate from gas boot is transferred to the Condensate Storage Tanks by condensate transfer pumps. Export Pump, transfers the condensate from the condensate storage tank to the Jetty through a condensate pipeline (6â&#x20AC;?). The export condensate flow is measured in a turbine flow meter. Excess Condensate produced is routed to a liquid burner for disposal through Condensate Pump. The vapors from condensate flash tank exit under pressure control to the Low Pressure Fuel gas Scrubber. The scrubbed gas from gas scrubber then enters Low Pressure Fuel gas filters for removal of any particles and liquid components. Outlet dry gas from the filter is used as plant fuel gas. The vapors from gas boot are vented to atmosphere under pressure control. Condensate transportation: As soon as the amount of condensate in the condensate storage tank is found sufficient, then it is the right time for empting the tank to allow continuous gas production. The RVP test is conducted so as to determine the type of the shipâ&#x20AC;&#x2122;s storage tank to come. After the ship is at the jet, the condensate transfer pipe is connected to the ship and the condensate export pump is turned on. There-after, the ship leaves with the condensate to Dar es Salaam.

Plant Produced water handling systems: From separatorsE-2

P.W.skimmer

Water out From CPI

Sludge out

P-10

P-18

P-12 P-9

P-17

E-4 P-13

E-3 P-14

P-2

P-4 P-11

Temporary oil Storage tank

Carbon filter

E-5 P-1

Water storage tank

P-16

P-9

E-7 P-1

P-5

P-15

E-6

pumps

To slop oil tank

E-8

Drain

Figure 6:produced water handling Overview Produced Water from the test/production separator is sent to the produced water skimmer (designed for 3 phase separation), where the dissolved gases are separated and sent to the flare and oil is skimmed and separated from the produced water. The separated oil is coalesced, collected and dumped under level control to the slop oil tank. The treated water flows to the Corrugated Plate Interceptor (CPI)for further de-oiling purposes. Feeds to the CPI include effluent water from the produced water skimmer and contaminated rainwater from the open drain system. Treated water from corrugated plate interceptor is sent to a carbon filter for final clean up prior to disposal to the ocean. The recovered oil from the CPI unit is sent to the slop oil tank. Slop oil tank accumulates slop oil from the produced water skimmer, oil from the CPI, and liquids from the closed drain drum. Hydrocarbon liquids collected in the tank is pumped to the condensate storage tank for export and water separated in the tank is pumped to the produced water skimmer for treatment by Slop oil and water pumps.

Treated Water outlet

C.P.I

PLANT UTILITIES:

Figure 7:Plant Utilities overview Water plant: Sea water sucked by bevel pumps from the ocean at Electro-Chlorination Unit (ECU) is pumped into the sea water storage tank. The stored sea water is used for mainly two purposes, first in water type fire extinguisher systems and secondly in portable water treatment plant. The treated portable water is used for domestic purposes at the plant, camp and village.

Instrument Air Plant: Compressed instrument air plays major roles in valves opening and closing mechanisms. This is done purposely to avoid the use of electricity which could act as a source of sparks and hence resulting into explosion. This compressed is processed by two compressors installed at the Instrument Air Plant by trapping and compressing atmospheric air to the required pressure.

Electricity production: Despite the fact that electricity is not basically recommended for valves operation in gas industries, but it still plays imperative role in gas production process. It is used to drive motors, pumps, engines, Programmable Logic Control, office computers and lighting purpose (at the plant, camp and village). Electricity is generated by using three Gas Engine Generators which uses gas to generate electricity. The gas is tapped from the Sales Gas Metering Skid. To ensure constant presence of electricity even in case of plant shut down, then there is emergency tapping of gas for generators from the export line. Safety Systems: Safety running of the plant is both mandatory and crucial aspect that is highly observed in SSI Gas Plant. To ensure this, a number of safety systems have been installed in entire plant. These systems include: Low and High Pressure flare (LPF & HPF). Fire extinguishers (FM -200, Foam and Water). Detectors (smoke, flame and gas). Blow Down Systems. Shut down systems (Level 1&2).

PART TWO.

PROJECT

PROJECT TITLE: MONO ETHYLENE GLYCOL TRAINS EFFICIENCY EVALUATION.

INTRODUCTION A common method to remove water from natural gas is glycol dehydration. In this process, mono ethylene glycol (MEG) is used to remove the presence of water in the gas stream. Water vapor can cause hydrate formation at low temperatures and high pressures or corrosion when it is in contact with hydrogen sulfide (H2S) or carbon dioxide (CO2), components regularly present in the gas stream. Meg regeneration units are typically represented by a reflux condenser, surge drum(heat exchanger), a flash tank, filters, packingâ&#x20AC;&#x2122;s and a re-boiler. As shown in Figure 1.below The glycol, usually MEG, enters at the gas/gas heat exchangers of the dew point control trains and absorbs water as it progresses toward the cold separators at the bottom of the trains.

GAS INLET

TO SALES GAS MEG INJECTION MEG INJECTION

MEG INJECTION MEG INJECTION

COLD SEPARATOR J-T VALVE

TO CONDENSATE STABILISER LV

TO MEG REGENERATION LV

Figure 8:Dew point Control Train overview In cold separator three phase separation of gas ,hydrocarbon condensate and a mixture of water and glycol is performed. With the help of level transmitters and level valves the cold separator can easily be drained to respective condensate and meg lines. Finally, the glycol flows to the Meg units where it is regenerated by boiling off the water and returned to the dew point control units and closed loop continues.

STATEMENT OF THE PROBLEM: Natural gas downstream from the separators still contain water vapor to some degree . Water vapor is the common undesirable impurity usually found in untreated natural gas. The main reason of removing water vapor is due to the fact that vapor becomes liquid under low temperature and high pressure conditions which can result in problems in the quality of natural gas and pipeline problems during natural gas transportation. Carefully low temperature separation is done to prevent pipeline plugging due to hydrate formation, lowering of gas heat value and pipeline corrosion due to carbon dioxide and hydrogen sulphide formation. In the scientific facts, one of the challenges pertains to the dehydration of the natural gas is to ensure continuous supplying of mono ethylene glycol under precise qualities for effectively separation of natural gas, water and hydrocarbons due to currently plant overloaded situation. As it is well known that mono ethylene glycol produced from meg trains is used for water absorption in natural gas stream, dry the gas to a required specification ready to be transported through pipelines to Dar es salaam to our customers.

In mono ethylene glycol closed loop system we have come across different operating problems resulting to day to day decreasing train performance even efficiency. As we know mono ethylene glycol loss (meg loss)seems to be the mostly common problem in these trains and this is due to meg carry over in condensate lines, pumps leakages, meg exported in sales gas line and inefficiently /manually meg and condensate separation done by unskilled workers. Overcoming these losses we need to have a good separation with a required specific residence time, regular servicing of rubber in pumps, educating people about methods used for meg laboratory properties determinations, meg utilization and chemistry behind about meg dehydration even hydrate inhibition.

OBJECTIVE: The general objective of this study is to evaluate the meg trains efficiency from the designing and normal plant operations, maximum plant operation to the current overloaded situation. SPECIFIC OBJECTIVES: To perform the mono ethylene laboratory analysis that will lead to the realization of the trains status/efficiency when compared to designed and normal train and plant general performance. i.e. identification of meg quality loss and other chemical properties To perform simple mathematics on vessels capacity to see if the meg trains can with stand the new plant performance situation. To perform trains analysis that will help to know the results of current Meg utilization and circulation rate against normal operating conditions. To evaluate Meg units current efficiency and compare it with the designed efficiency. To tackle the problem of Meg loss which results to more utilization of mono ethylene glycol due to the fact that it is carried in condensate line. This will lead to installation of settling tanks for condensate/meg mixture that will increase residence time corresponding to plant overloaded situation while waiting for dehydration plant expansion.

SIGNIFICANCE OF THE STUDY. The achievement of this project will be very important since it will help in the trains performance and meg utilization. This will be achieved during evaluating Meg properties, vessel capacities and performance of different components in trains. It will also give the train status by identifying all meg losses and operation problems and it will lead to engineering mathematical calculation on efficiency of trains for monitoring of trains current performance. The efficiency evaluation will lead to solve the problem of Meg loss by taking into account all the causes of the problems and their solutions.

LITERATURE REVIEW: Process description: Glycol injection is provided by the injection pumps with the minimum to maximum flow rates of each pump ranging 0.19 – 0.69 m3/hr according to design. The rich glycol is separated from the condensate in the Cold Separators, about 35-120 minutes retention time dependant on the EG circulation rate, this is provided for the glycol to ensure proper separation of the glycol and condensate. The glycol exits the Cold Separators, under level control and flows to the reflux coils above the packing in the still columns of the EG Re boilers where self refluxing occurs. The rich glycol is then passed through integral lean/rich glycol coils in the surge tank section of the M.E.G Re-boilers. After being preheated by the lean M.E.G. in the accumulator the rich glycol stream flows to the Glycol Flash Tanks which are operating at a lower pressure of 448 kPa (65 PSIG). In the flash tank, any free gases that exist are flashed off and sent to flare. Any liquid hydrocarbons that have been carried over into the flash tank can also be removed. Under level controls valves, glycol exits the bottom of the flash tanks and flows to the glycol filters. Particulate filters (10 micron), and carbon filters filtering dust particles and hydrocarbons contained in rich glycol ready to be boiled. Upon exiting the filters, the rich glycol proceeds to the top of the packed section in the glycol still column. In the glycol still column, water is stripped out of the rich MEG as it flows downward through the 10’-0” packed section consisting of 25mm Pall rings counter current to the steam that is generated in the MEG Re boilers. The steam is discharged to the low-pressure flare header at the top of the still column. Once the desired concentration (temperature) is achieved in the MEG Re boilers. Lean MEG flows by gravity to the glycol surge tank (integral with the glycol re concentrator). Here it is cooled by heat exchange with the rich MEG flowing through the integral lean/rich glycol coils. From the surge tank the glycol flows to the suction of the glycol pumps where it is pressurized for reinjection in the Gas/Gas Exchangers.

COLD SEPARATOR RICH GLYCOL

P-48

R.CONDENSER

P-15

pckg P-17

BURNER

P-44

P-51

P-59

RE BOILER

P-11

P-43

P-57 P-50

FUEL GAS

P-58

P-21

P-46 P-40

P-19

P-65 P-66

FILTER

P-34

SURGE DRUM

FLUSH VESSEL

P-22

P-62

LEAN GLYCOL

CLOSED DRAIN DRUM PUMP

G/G EXCHANGER

Figure 9:Meg regeneration Unit

Meg trains efficiency: To facilitate a practical Meg trains efficiency assessment there must be a need for a practicable scheme to relate the plant gas flow rate, gas dehydration practices, meg chemistry and meg units performance in daily operations and on how they depend one another to facilitate natural gas quality determination. Under this section we will deal with chemistry behind of glycol, systems/units capacity and trains data analysis on monitoring plant operating conditions. Meg circulation(closed loop) under designed conditions required to operate with normal/ little system glycol loss to the exported gas and normal train operations. When plant flow rate increased beyond to its maximum holding capacity stream turbulence increases resulting to insufficient phase separation due to decreasing cold separator residence time. This leads to little glycol loss in gas export line but much and more in condensate line. The condensate line is manually tapped to manually separate condensate and mono ethylene glycol in order to overcome glycol loss in condensate line. To avoid this loss meg chemistry and vessel capacity even plant operating data must be taken into considerations. Perfectly, the trains performance depends much on cold separator capacity, glycol circulation rate, quality of lean and rich meg required, heat load of re boiler and glycol flash separator capability. Due to meg carried in condensate line it comes a time that meg is lost in highly amount that the surge tank needs to be topped up to overcome circulation problems which can lead to insufficient gas dehydration. Some amount of meg remains in the system while other leaks out through pumps and manually separation practices. Hence during efficiency evaluation, the followings will be well thought-out: 1. Effective make a follow up on the actual amount of Meg topped up in the system by analyse the data recorded from normal to overloaded situation. 2. Working out the actual amount of meg loss leaking out from the network mostly caused by meg carried in condensate line. 29

3. Checking vessels operating capacity when compared to designed conditions. 4. Perform efficiency evaluation on data recorded compared to required (recommended) specifications. Procedures followed to accomplish the mentioned tasks: 1. Comparing amount topped up to the system and that recovered. 2. Evaluating efficiency of the system by considering data obtained when compared to required specifications.(meg concentrations, re boiler temperature) 3. Evaluating vessel capacity by comparing their working ability with the designed specifications. Mathematical expressions governing vessels capacity, and meg circulation rate, heat load of re boiler, required settling volume in flush tank, mount of water to be removed in natural gas. 1) From Petroleum Production Engineering (a computer-assisted approach) by Boyun guo, William C. Lyons and Ali Ghalambor. coldseparator .gas.capacity  separator. Area  gas.velocity Qg  A  V Qg  A  k

(l  g ) g

k  0.45  0.5

Nomenclature: Qg=cold separator gas capacity A=Area of Cold separator and V=Volume of cold separator 3) From Petroleum Production Engineering (a computer-assisted approach) by Boyun guo, William C. Lyons and Ali Ghalambor. glycol .circulatio n.rate  G.W .R  gas.water .content  cold .separator.capacity

Nomenclature: 30

G.W.R=Glycol Water Ratio. 4) From Petroleum Production Engineering (a computer-assisted approach) by Boyun guo, William C. Lyons and Ali Ghalambor.

heat .load .. for ..reboiler . perhour  2000  glycol .circulatio n.rate overall.size.of .re  boiler  heat .load .of .re  boiler . perhour required .settling .volume.in. flush. tan k 

Qg  residence.time (tr )in. min 60

Pumps.BHP  2  10000000  Qg  pump. pressure electical .kwh  1.833  10000000  Qg  pump. pressure

Nomenclature: Qg=cold separator gas capacity. 5)From handbook of natural gas transmission and processing by Saeid Mokhatab

amount.of .water .to.be.removed 

Qg  ( water .content .of .gas.in  water .content .gas.out ) 24

Nomenclature: Qg=cold separator gas capacity. 6) Design/Normal plant capacity according to design The whole plant was designed to operate under the following specification

Table 2:plant specifications according to design 1)The whole plant according to design

maximum

current situation

Train 1: 989,000 (35.0)

1271571.429(45)

1554142.857(55)

Train 2: 989,000 (35.0)

1271571.429(45)

1554142.857(55)

Total: 1,978,000 (70.0)

2543142.857(90)

3108285.714(55)

11,000/8900

Gas Flow Rate, Sm3/d (MMSCF/D)

Hydrocarbon Flow Rate, m3/d (BPD): 5.6 (35.0) Free Water Flow Rate, m3/d (BPD): 11.1 (70.0) Operating Pressure, kPag : 11,000/8900 Maximum Inlet Temperature ยบC : 37.8 (100.0) Normal Inlet Temperature ยบC : 21.5 (70.7) Minimum Inlet Temperature ยบC : 18.9 (66.0) Specific Gravity, Gas: 0.58

0.575394

Design Pressure, kPag : 12500

110

1.6

Design Temperature, ยบC : Maximum: 65.6 Minimum: -28.9 (-20.0) Corrosion Allowance in vessels(mm)

HEX Fouling Factor 0.001/0.002

0.001/0.002

gas pressure drop in kpa HEX Tube-Side: 34

HEX Tube-Side:

HEX Tube-Side: 34

34 HEX Tube-Side: 69

HEX Tube-Side:

HEX Tube-Side: 69

69 Gas Composition: Sweet

Sweet

Inlet Separator Slug Capacity, m3 : 4.0 (141.2) 2)Meg system: Meg circulation rate

Sweet

0.19-0.69m3/hr. Output Meg concentration 80/20 v/v (meg to water ratio). Glycol Concentration, % by Wt. 80

Glycol Circulation Rate, m3/hr : 0.19 – 0.69

0.19-0.69

0.19-0.69(need to be improved to cope with current situation)

Mono ethylene glycol chemistry: Mono Ethylene glycol (ethan-1,2-diol) is an organic compound used as an antifreeze and hydrate inhibitor in natural gas industry. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid which is toxic, and ingestion can result in death. Meg components: Mono ethylene glycol is produced from ethylene (ethene), via the intermediate ethylene oxide. Ethylene oxide reacts with water to produce ethylene glycol according to the chemical equation: C2H4O + H2O → HO–CH2CH2–OH This reaction can be catalyzed by either acids or bases, or can occur at neutral pH under elevated temperatures. The highest yields of ethylene glycol occur at acidic or neutral pH with a large excess of water.

i)antifreeze chemistry Due to its low freezing point and tendency to form glasses, ethylene glycol resists freezing. A mixture of 60% ethylene glycol and 40% water does not freeze until temperatures below −45 °C (−49°F).The antifreeze capabilities of ethylene glycol have made it an important component of natural gas dehydration process where it enhance efficient low temperature three phase separation by prohibiting water freezing. Ethylene glycol disrupts hydrogen bonding when dissolved in water. Pure ethylene glycol freezes at about −12°C (10.4°F), but when mixed with water molecules, neither can readily form a solid crystal structure, and therefore the freezing point of the mixture is depressed significantly. The minimum freezing point is observed when the ethylene glycol percent in water is about 70%, as shown below. This is the reason pure ethylene glycol is not used as an antifreeze because water is a necessary component as well. Table 3:Ethylene glycol concentration vs temperature Ethylene glycol freezing point vs. concentration in water Weight Percent EG (%)

Freezing Point (deg F)

Freezing Point (deg C)

-4

-7

-15

-10

-23

-30

-34

-55

-48

-60

-51

-50

-45

-20

-29

100

-10

-12

Graph of Freezing temperature vs Meg concentration

Figure 10:Graph of meg freezing point vs concentration The boiling point for aqueous ethylene glycol increases with increasing ethylene glycol percentage. Thus, the use of ethylene glycol not only depresses the freezing point, but also elevates the boiling point such that the operating range for the heat transfer fluid is broadened on both ends of the temperature scale.

Table 4:Boiling point vs concentration Ethylene glycol boiling point vs. concentration in water Weight Percent EG (%)

Boiling Point (deg F)

Boiling Point (deg C)

212

100

215

102

215

102

220

104

220

104

225

107

230

110

240

116

255

124

285

140

100

387

197

Here the graph for boiling point vs weight % meg.

Table 5:Meg boiling point Vs concentration

ii)hydrate inhibition chemistry: Because of its high boiling point and affinity for water, ethylene glycol is a useful desiccant. Ethylene glycol is widely used to inhibit the formation of natural gas clathrates (hydrates) in long multiphase pipelines that convey natural gas from remote gas fields to an onshore processing facility. Ethylene glycol can be recovered from the natural gas and reused as an inhibitor after purification treatment that removes water and inorganic salts. Natural gas is dehydrated by ethylene glycol. In this application, Mono ethylene glycol (as mist form) sprayed to dew point control unit heat exchangers and meets a mixture of water vapor and hydrocarbon gases. This mixture flows down to the cold separator through a J.T valve for gas throttling. Dry gas exits from the top of the cold separator while condensate and meg are drained at their respective lines. The glycol and water are separated, and the mono glycol recycled. Instead of removing water, ethylene glycol can also be used to depress the temperature at which hydrates are formed. The purity of glycol used for hydrate suppression (mono-ethylene glycol) is around 80%. 38

To maintain efficiently performance of the system under specifications, avoiding abnormal meg loss and proper gas dehydration the system must be examined for its currently operating conditions against the designed ones.

METHODOLOGY: This will involve data taking in meg and dew point control trains even principles from different literatures. Quality of mono ethylene glycol and dew point can can be monitored and examined by operators daily data taking exercise. This is done for every hour in control room and after eight hours by operators in field area. The obtained data from field and results from laboratory experiments for a period of months from January to August (data in considerations)shows us how glycol properties fluctuates according to plant different operation situations.(I took data for august, the time I was in plant and perform lab experiment).On other hand vessel capacities and operation conditions evaluation was done considering data obtained from operating manuals and literatures. Equipment used i.

Data sheets and pen for data taking.

ii. Sampling bottles for laboratory Meg concentration determination, ph meter, hydrometer and thermometer. iii. Manuals and literature books. Experimental part: To ensure that glycol meet the specific set up concentration required for water dehydration (80/20v/v lean glycol and 60/40v/v rich glycol) laboratory Meg test was performed. Mono ethylene glycol concentration plays a great role in natural gas dehydration specifically in dew point depression and helps much glycol reclamation practice. Test Sampling points: Lean MEG soon after pumps. Rich MEG soon after carbon filters. Test Procedures: 40

I Pour sample (rich/lean) into a measuring cylinder then immerse probe to get a required temperature in degree ( F) and meg ph. Then I insert Hydrometer in a measuring cylinder to obtain MEG specific gravity. By using the specific gravity, temperature obtained and the Microsoft Excel Program (prepared for this purpose) I predict the value of lean/rich concentration. By enter the temperature measured into temperature side of the program. I was varying the rich/lean concentration ( by try and error) until i got the same value of specific gravity as the one i have measured. Then in a program I took rich/lean concentration that gives the same value of specific gravity as the measured one.

RESULTS, CALCULATION AND DISCUSION: Experimental results: Meg train 1: Lean meg Temperature =100F Specific Gravity =1.082 Lean meg Ph =7.9 Concentration =74/26(2.85) Rich meg: Temperature = 100F Specific Gravity = 1.064 Rich Meg Ph = 7.4 Concentration = 57/43(1.326) Pump speed =41.1% Flow rate in D.P.C = 57362 Rich Meg level = 39.8(process value) = 40 (set value) Meg train 2: Lean meg Temperature =100F Specific Gravity =1.084 42

Lean Meg Ph =8 Concentration =78/22(3.55) Rich meg: Temperature = 100F Specific Gravity = 1.070 Rich Meg Ph = 6.7 Concentration = 63/37(1.703) Pump speed =41.1% Flow rate in D.P.C = 57362 Rich Meg level = 55.8(process value) Data for period of months for trainâ&#x20AC;&#x2122;s performance gas flow rates and mono ethylene glycol utilization. Monthly average properties of lean glycol in train 1 Month

JANUARY

TEMP deg f

specific gravity

Conc(80/20) 4max

Ph 6-7.5

situation comp to design

1.086

3.167

7.2 normal

95.61818182

1.087

3.35

7.344444444 normal

94.875

1.08675

3.167

8.6 normal

96.54545

1.086182

3.38

7.425 normal

97.2

1.086

3.35

7.55 normal

JUNE

99.77777778

1.082

3.167

JULY

99.71428571

1.083

3.167

7.686 overload

95.625

1.0845

3.167

7.2575 overload

FEBRUARY MARCH

APRIL MAY

AUGUST

7.2625 max to overload

Table 6:lean glycol properties in train1. 43

Graphical representation:

Temperature(F) vs time(Months) for meg lab sample tests 101 100 99 98

97 96 95 94 93 92 JANUARY

FEBRUARY

MARCH

APRIL

MAY

JUNE

JULY

AUGUST

Figure 11:graph showing temperature in meg lab test carried Calculations: Test done in laboratory to get meg properties must be done at 100F sometimes temperature fluctuation results into incorrect laboratory meg data obtained. Here is the laboratory temperature efficiency evaluation for the data obtained efficiency 

average.obtained .value  100 recomended .value 96.92  100 lab.sample.temp.effy  100

 96.92%

Purity of glycol determination can sometimes being affected by testing temperature fluctuation. Also,

Specific gravity of lean glycol recommended to be at 1.085 test in laboratory must be done to check if the glycol conform to a required set value.Below is the efficiency evaluation of glycol specific gravity test for average of the data taken during this period.

lab.s.g.efficiency 

1.085  100 1.085

 100% Graphical representation:

Figure 12:Graph showing lean glycol water ratio vs time

lean.glycol .concentrat ion.efficiency 

3.24 100 4

 81% p.h.efficiency 

7.45 100 7.5

 99.3%

In above calculations average lean glycol concentration from train 1 decreases by 19% ,while ph deviates by…..% from required specification. This is due to high meg circulation, low vessel

capacities even operating plant beyond its normal designed conditions which result to fluid turbulence.

Monthly average properties of Rich glycol in train 1 Month

JANUARY FEBRUARY

TEMP deg f

specific gravity 92.85714

Conc 80/20max

Ph 6-7.5

situation cmp to design

1.081143

2.125

6.54 normal

92.90909091 1.08145455

2.226

6.511111111 normal

93.625

1.08025

2.125

6.42 normal

94.36364

0.989833

2.15

6.225 normal

1.0796

2.125

6.233333333 normal

JUNE

98.66666667

1.074

1.86

6.25 max to overload

JULY

98.14285714

1.071

1.63

6.73 overload

94.875

1.07125

1.564

6.485 overload

MARCH

APRIL MAY

AUGUST

Table 7: monthly properties of rich glycol in train 1 Graphical representation:

Lab.Rich glycol s.g vs time(month) 1.1 1.08 1.06 1.04 1.02

Series1

1 0.98 0.96 0.94 JANUARY

FEBRUARY

MARCH

APRIL

MAY

JUNE

JULY

AUGUST

Figure 13:laboratory rich glycol vs time

average.of .obtained .value  100 recomended .value 95.05  100 lab.sample.temp.effy  100  95.05% 1.07  100 lab.s.g .efficiency  1.085  98..6% 1.98  100 rich.glycol .concentrat ion.efficiency  1.5  132%(deviate.by.32% from.required .specificat ion ) 6.42  100 p.h.efficiency  7.5  85.6% efficiency 

Concentration recommended for rich glycol in circulation loop required to be 60/40v/v(1.5) but these days the value rises up to(66.4/33.4v/v) 1.98 this means that the rich glycol concentration purity recommended decreases by 32%.According to glycol chemistry stated above this drop affects glycol properties resulting to poor performance of glycol units and inadequate natural gas dehydration.

Monthly average properties of lean glycol in train 2 Month

JANUARY

TEMP deg f

specific gravity

Conc(80/20) 4max

Ph 6-7.5

situation comp to design

95.42857

1.086857

3.35

6.84 normal

95.89

1.0858

3.35

7.7 normal

95.5

1.0835

3.35

8.966666667 normal

97.54545455

1.084364

3.3

7.625 normal

97.4

1.0848

3.35

7.625 normal

JUNE

97.22222222

1.085

3.35

6.9 max to overload

JULY

98.57142857

1.0843

3.35

7.8 overload

97.375

1.0815

2.85

7.31 overload

FEBRUARY MARCH

APRIL MAY

AUGUST

Figure 14:monthly average properties of lean glycol train 2 Graphical representation:

Figure 15:monthly average properties of lean glycol Calculations:

average.of .obtained .value  100 recomended .value 96.87  100 lab.sample.temp.effy  100  96.87% 1.085  100 lab.s.g .efficiency  1.085  100% 3.3  100 lean.glycol .concentrat ion.efficiency  4  82.5% 7.5  100 p.h.efficiency  7.5  100% efficiency 

Again train 2 calculations shows that average lean glycol concentration decreases by 17.5% ,while ph deviates byâ&#x20AC;Ś..% from required specification. Also this is due to high meg circulation, low vessel capacity even operating plant beyond its normal designed conditions which result to fluid turbulence.

Monthly average properties of Rich glycol in train 2 Month

TEMP deg f

specific gravity

JANUARY

Conc (60/40)1.5max

Ph 6-7.5

situation comp to design

1.082286

2.226

6.42 normal

93.38

1.0814

2.226

6.566666667 normal

93.625

1.0805

2.226

6.64 normal

94.63636

1.08

2.33

6.2 normal

94.8

1.0808

2.33

6.025 normal

JUNE

95.66666667

1.0822

2.125

JULY

99.28571429

1.071

1.8

6.6 overload

95.375

1.073

1.86

6.4175 overload

FEBRUARY MARCH

APRIL MAY

AUGUST

6.085714286 max to overload

Table 8:monthly average properties of rich glycol

Graphical representation:

Table 9:monthly average properties of rich glycol 2 average.of .obtained .value  100 recomended .value 95  100 lab.sample.temp.effy  100  95.% 1.08  100 lab.s.g .efficiency  1.085  99.5% 2.14  100 Rich .glycol .concentrat ion.efficiency  1.5  143.7% 6.4  100 p.h.efficiency  7.5  85.3% efficiency 

Again concentration recommended for rich glycol in circulation loop required to be 60/40v/v(1.5) but here the value rises up to(68/32v/v) 2.14 this means that the rich glycol concentration purity recommended decreases by 43.7%.According to glycol chemistry stated 51

above this drop affects glycol properties resulting to poor performance of glycol units and inadequate natural gas dehydration. Table 10:monthly data on dew point control trains Average monthly data on dew point control unit 2!! Meg total Injection Cond Month level(%) rate(lpm) level(%) rate JANUARY

S. tank level(%)

meg top ups(lts) normal

FEBRUAR Y

normal

MARCH

normal

APRIL

normal

MAY

normal

49.2

max to 2667 overload

49.8

17978.8 overload

3.32 53.73 51.1 Table 11:monthly average data on dpc 2

18906 overload

JUNE

3.07

JULY

55.05

3.085

AUGUST

46.42

60.01 56.3

Data in table above shows how glycol consumption (based on trains top ups) being affected by current overloaded situation. This is due to high meg loss caused by insufficient separation in cold separators facilities which in turn causes decreasing in required meg amount in circulation loop. According to vessel capacity and mono ethylene glycol chemistry the problem can be solved by plant facilities expansion. This will emphasize on dehydration systems to provide the required residence time for effectively separation according to design.

Vessels capacity evaluation: According to data obtained above the plant now is operated at overloaded conditions and this affect more in Meg trains performance. As u can see above the required concentration of lean meg (80/20v/v meg/water) is not attained now days due to overloading plant operations. Apart from Meg concentration fluctuation current plant overloading situation resulting to meg trains and the whole gas dehydration systems to operate inefficiently. Gas capacity of cold separator, glycol circulation rate, re boiler heat load and pumps functioning are the parameters/working conditions which are being affected much by now plant overloaded operations.

Effects of plant overloading to the system: Gas capacity of cold separator can be obtained from whole day capacity of the dew point control train divide by 24 hours of operation in cold separator. According to design 35mmfsd and 60 minutes were required values of train flow rate and residence time but for current situation the daily dpc flow rate increases to 55mmfsd while its residence time keep on decreasing due to increase of gas flow rate. Daily flow/production when divided to 24 hours we get the cold separator gas capacity per hour. Since it designed to have a residence time of 60 minutes, that is according to designed capacity of cold separator. By calculations As per design: a)cold separator: Coldseparator .gascapacit y ď&#x20AC;˝

35mmscfd 24

Cold separator Gas capacity=1.45833mmscfhr (41208.33sm3/hr) Therefore cold separator gas capacity is 41208.33sm3. Overloaded situation: Coldseparator .gascapacit y ď&#x20AC;˝

55mmscfd 24 54

Required Cold separator Gas capacity =2.29167mmscfhr (64755.95238sm3/hr) Therefore we overcapacity the cold separator by= current.value  designed .value

 (64755.95238  41208.33) sm3  23547.62238sm3 %cold .separator..overcapacity 

overcapacity..value  100 designed ..value 23547.62238  100  41208.33  57.14

This overcapacity of cold separator by 57% of designed capacity resulting to an increase of 20mmscfd of daily production in one dpc train. For both two trains the increase is 40mmscfd.Therefore the whole plant capacity is increased by 57% beyond normal. b)Glycol re-concentrator: glycol circulation rate, heat load of re-boiler and overall size of a re-boiler depends much on cold separator gas capacity. When increasing cold separator capacity even glycol circulation rate and other parameter stated above will be affected. Let us see how the cold separator affect unit operations in glycol re-concentrator trains. 1) glycol .circulatio n.rate  G.W .R  gas.water .content  cold .separator.capacity original .gas.water .content 

original .glycol .circulatio n.rate designed .W .G.R  designed .cold , separatorcapacity

0.5(0.19  0.69)  10 6 sm3 under .1.hour.basis (80 / 20)  41208.33sm3  2.679 

By assuming that gas water content is constant(since no data were taken ) Due to plant overloading the now needed glycol circulation Qg new will be

Qg.new. perhour 

(G.W .R)  gas.water .content .  New.coldseparator .capacity

where.glycol .water .ratio (G.W .R)  80 / 20.and gas.water .content  2.679 Therefore (80 / 20)  2.679  64755.95238 Qg.new 

under .hour.basis

Qg.new  693924.8sm 3 Therefore Qg  Qg.new  Qg.original Qg  693924.8sm3  (0.5(0.19  0.69)  10 6 sm3 ) Qg  253924sm3

By how much the system circulation is overloaded?

Qg  100 original .Qg 253924 %overloaded   100 440000  57.71% %overloaded 

The overloaded percent above means that the current system vessels are being overloaded more than 50% of their normally design. Therefore we need to expand the dehydration sub-plant to twice as much by installing new two dew point control units and two meg trains. This will allow the plant to operate under normal operation conditions. 56

from heat .load .. for ..reboiler . perhour  2000  glycol .circulatio n.rate increase.heat .load .of .re  boiler . per .hour  2000  Qgbtu H  2000  253924btu H  507,848,000 Btu again 507848000 % reboiler .overloaded   100% 2000  440000 % reboiler .overloaded  57.71% sin ce, overall.size.of .re  boiler .. ..heat .load .of .re  boiler . perhour then also % reboiler .size.overloaded .will .be  57.71% required .settling .volume.in. flush. tan k (Vs ) 

Qg  residence.time (tr )

basis.of .one.hour

designed .(Vs )  Qg.designed  recomended .(tr ) Vs  440000 sm 3 per .hour  0.0833hrs Vs  36666.7 sm 3 . per .design new.Vs  100% Designed .Vs Qg  residence.time %overloading .of . flush. tan k   100 designed , Vs 253924  0.0833 %overloaded   100 36666.7 %overload  57.68% %overloading . flush. tan k 

Pumps.BHP  2  10000000  Qg  pump. pressure electical .kwh  1.833  10000000  Qg  pump. pressure Qg  ( water .content .of .gas.in  water .in.gas.out ) amount.of .water .to.be.removed  24

Since pumps.BHP, electrical consumption(in kwh), even amount of water to be removed both depends on circulation rate. This shows us that the incoming now gas stream 57

(105mmfscd)contains water 57.71 above compared to that carried with 70mmfscd(normal operation) that if we want to overcome problems in our whole system we need to expand the system above 60% of normal design. Problems facing the system caused by plant overloading: Cold separator and whole circulation performance: Due to low residence time compared to the design one, insufficient natural gas dehydration is obtained, this accompanied with three phase separation failure in which meg is carried in condensate line. The gas leaving cold separator seems to contain high amount of water compared to that allowed as a result of often hydrates formation in shell side of gas heat exchangers. Excess water content in lean glycol produced due to re-boiler temperature fluctuation, low lean glycol temperature compared to required, high inlet gas temperature, vessels capacity and under circulation of glycol (not match to this current plant overloaded situation) affects much cold separator performance which leads to insufficient whole natural gas dehydration process. Meg to condensate carryover: Insufficient gravity separation in cold separator due to low residence time results in meg to be carried out in condensate line. Here the condensate line is manually tapped to get the mixture allowing it to settle by gravity for some period of time then manually separation is done and meg obtained is topped up in the system. The whole separation and topping up of meg is manually without scientific considerations. This leads to insufficient separation which leads to condensate been injected in a glycol loop. Condensate in glycol system affects the re-boiler burner resulting to periodical burner failure and circulation pumps leakages. Even though when this happens the surge tank is topped up to overflow which will result into meg condensate density separation leading to condensate to be overflow out. Working under this basis (manually way) still creates some problems to glycol quality and whole system operation cost. b)Mono ethylene glycol quality:(concentration/temperature) The obtained data from field and results from laboratory experiments for a period of months from January to August shows us how glycol properties fluctuates according to plant different 58

operation situations. Its well seen from data collected above that both rich even lean glycol properties in now overloaded situation they donâ&#x20AC;&#x2122;t conform to specific/recommended ones. Compared to normal operations glycol purity in now abnormal plant situation is out of specification due to water content, inefficient phase separation and re boiler operating temperature fluctuation. c) Re-boiler temperature fluctuation frequently topping up new/recovered lean glycol in the system affects much on units operating condition especially temperature. From the data collected system re boiler temperature seems to drop frequently when system is charged with new glycol. Even though sometimes re boiler can drop due to other factors affecting operations but this seems to be common. Re-boiler temperature drop can result to lean glycol be out of specifications which can lead to hydrate formation in heat exchangers.(Nb:I have witness dpc depressurization in plant due to hydrate formation caused by re boiler temperature drop) On other side rising up of re boiler temperature above its required specification results to glycol degradation. This is well explained in glycol chemistry above as u have see above 124C lean glycol degrades.(Nb:I have witness re-boiler 125C operating temperature when I was in Control room) d) Burner failure and pumps leaks: Due to inefficiently condensate and meg separation caused by plant overloading, condensate is sometimes carried in the meg circulation system. This affect much re boiler performance since it present burner failures and pumps leakages which can result in increased operation cost due to maintenance. d)Vessels and equipment capacity: Plant overloading situation creates a big problem in vessel and equipment capacity since it forces the trains units to operate below the designed efficiency. By considering 57% plant overloading and normal designed trains efficiency(assuming perfectly 100%) ,the trains efficiency without consider pumps seems to drops more than 30%. 59

On another side circulation pumps are still able to cope with the overloaded situation because up to day they still operates below 50%.As we know that these are positive displacement plunger type still are able to operate. What we have to do is to ensure the meg injection is varying with natural gas flow rate. e) Meg loss: Overloading plant gas flow rate resulting to high meg utilization due to high quantity of gas to be dehydrated. Due to cold separator over capacity operation proceed, the retention time required for three phase separation is not attained. This affect much the separation resulting to meg being carried in condensate line. Apart from manually separation practice of the mixture from condensate line to be major cause of meg loss also re boiler temperature, and normal loss in sales gas caused by high flow rate also contributes to the loss. f) Overloaded situation operational costs: Man power: Apart from two field shift operators and one in control room to increase their concentration in the units. Also the company employs four casual workers for manually meg/condensate separation practice. This increases manpower operation costs. i.e montly.casual.wor ker s. payement  14000  4  30  1,680,000tsh

Assuming operator paid 1000000tsh per month and he increases concentration on units by two hours per day. His overtime payment can be calculated as follows operator .overtime. payement . per .hour 

1000000 30  24

 1400tsh

By considering operators one hour additional to concentrate with meg unit per day Two operators and casual workers costs can be calculated as follows 60

total .manpower. cos ts. per.month  3684200tsh

%increase.man. power . cos ts. per .month 

3684200  2000000  100 2000000

%increase.man. power . cos t  84.21% System maintenance: In current working situation (based on august data collected) Pumps maintenance costs increases due to several pumps services but there is no data recorded for this. Particulate filter change (average 10times per month)which cost about 660 USD (990000tsh),while during normal operation it was average once after a month. %cost .increase(system. impurities increases) compared to normal operation.

660  66  100 66  90% 

Activated filter carbon change not nown. Total maintenance cost

 pumps  filters  other .units . cos ts  990000tsh Mono ethylene glycol utilization: By considering meg charged to the system(surge tank top up) and meg recovered. Meg cost can be calculated as follows Considering data taken August(overloaded situation)

meg.top.up. cos t. per .month 

litres .topped .up. per .month  drum. cos t 200lts (1drum)

18906  825.33  1500 200  1170276667.4tsh.witout .transportation . cos ts 

When compared to normal cost by which averagely meg consumption was 10 drums per month

normal.meg. cos t.  10  825.33  1500 normal.meg. cos t  12379950tsh increase of meg consumption will be

new.meg.use  normal.meg.use  100 normal.meg.use 18906  2000 incr  2000  8.5 incr 

Meg utilization in overloaded situation seems to be almost nine times that in normal operations.

Total meg trains monthly operational cost (based on August)  total .manpower. cos t  total .ma int enance. cos t  total .meg.utilizatio n. cos t which.is.equal .to  1174950867tsh

The new installation of tanks is the proper solution to glycol loss and high operation costs to run meg trains. But it seems to be more temporally because the production even demand of natural gas keeps on increases. Apart from that we need proper separation in cold separators that will conform to new flow rate even being able to hold more for future high demand of this new clean and environmentally friend energy/power solution. 62

Current efforts made to solve the current system problems: With the use utility saving potentials (utility management opportunities) gravity settling tanks were recommended and tanks were installed. Here is the simple mathematics showing Normal/designed conditions Current system conditions Recommended improvement Calculated benefit and implementation cost and Simple payback or return on investment Current system condition Overloading plant situation resulted to high cost of meg trains operations which approximately cost about Tsh 1174950867 /= monthly.(based on August data) During normal operating conditions cost was 14,478,950tsh. Recommended improvement done: As per current situation the project is purposely intended to provide required residence time (more than 35 minutes) to reduce meg loss and therefore units operation costs. To save operation cost of about 1160471917tsh per month new tanks were installed to provide additional residence time. Payback period:

P. period 

cos t.of .implementa tion cos t.saved

p. period 

1958731500000 1160471917tsh

 16months Return of investment:

R.investment  (1 / p. period 100 R.investment  16  6.25

)  100%

Calculated benefit: After 16 months the implemented tanks installation will return their implementation costs, and they will continue to overcome the increase meg units operation costs caused by current overloaded situation(about 1160471917tsh) and allow normal meg units operation costs even if the plant will continue to operate beyond normal.

OVERVIEW: Based on the literature for mono ethylene glycol chemistry, vessels capacity, and the regeneration process for glycol presented in literature review above, the rest of project part was used for parameters, units ,system efficiency evaluation ,problems investigation even suggestion and discussion on system improvements to the Meg trains. Most of the improvements concerned on regeneration and dehydration process is especially on the process expansion by which currently is the use of new tanks to get the required additional residence time(about 35 minutes) for proper meg and condensate separation. This seems to be proper but temporally solution to the problem due to the fact that the natural gas production and demand keep on increasing day to day.

CONCLUSSION AND RECOMMENDATION: Recommendation: Based on the presented discussions the following conclusions are reached: As long as the natural gas demand and production increases due to new wells drilling going on, possibilities of joint venture with nearby small companies like Ndovu and Tanzania awareness on natural gas, dehydration sub plant expansion more than separation tanks installed is needed. As we have seen in above vessels capacity calculations gas capacity of cold separators even the whole glycol circulation (including meg trains).Vessels and the whole circulation closed loop are being overloaded for 57.1%.Therefore installation of Two dew point control trains(or one with capacity twice that present ) and two Meg trains for meg regeneration (or one with capacity twice that present) will be the solution to current plant problems caused by abnormal plant operation. (dehydration process design of new system I will do it as my final year project).

Conclusion: By implementing the natural gas plant expansion stated above the company will work under low operational costs, high quality and quantity of gas production which will fulfill the country every day increasing natural gas demand. Investing on plant expanding is a good opportunity for the company because it will increase company business opportunities through joint venture with small companies in processing and transportation of natural gas.

REFERENCES: 1. Boyun Guo and William C. Lyons, Petroleum Production Engineering “A Computer – Assisted Approach” 2. Havard Devold, Oil and Gas Production Handbook. 3. Virg Wallentine, The U.S. Natural Gas Transmission Pipeline System. 4. Ali Mesbab, The Effect of Major Parameter on Simulation of Gas Pipeline. 5. Saied Mokhatab, William A.poe and James G.Speight, Handbook of Natural Gas Transmission and Processing.

LIST OF ABBREVIATIONS:

In order to simplify the write-up part, some abbreviations ware used at appropriate places in this document. ABBREVIATION DESCRIPTION AIT API BDV BOPD BWPD CPI d/s EGE ESD F&G FFG H.C HEL HOT H.P HVAC ID JT K.O.D LEL LO MEG MMSCFD MOC NFPA Nos. P&ID PFD PCS ppm PSD PSV

Auto Ignition Temperature American Petroleum Institute Blowdown valve Barrels of Oil Per Day Barrels of Water Per Day Corrugated Plate Interceptor Downstream thylene Glycol Emergency Shutdown Fire and Gas Flame Front Generator Hydrocarbon Higher Explosive Limit Hand Operated Travelling High Pressure Heating Ventilation and Air Conditioning Inner Diameter Joule Thomson Knock Out Drum Lower Explosive Limit Locked Open Mono Ethylene Glycol Metric Million Standard Cubic Feet Material of Construction National Fire Prevention Associati Numbers Piping and Instrumentation Diagram Process Flow Diagram Process Control System Parts per million Process Shutdown Pressure Safety Valve 69

PVSV RVP SDV SSV SSSV S/S T/T UPS u/s USD

Pressure Vacuum Safety Valve Reid Vapour Pressure Shutdown Valve Surface Safety Valve Sub Surface Safety Valve Seam to Seam Tangent to Tangent Uninterrupted Power Supply Upstream Unit Shut Down Table 12abbreviations