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issue no 1 _april 2011

magazine for better air quality where science meets practice

Progress in Corona Discharge Adsorption Technology nanotechnology Low Pressure Fluctuation RTO

magazine for better air quality

issue no 1_april 2011

content issue no 1 _aPril 2011

4 act – react 6

new paths in adsorption technology

Dear readers,  


air is crucial for life, and its quality is crucial not only to our health, but also to the survival of all living creatures – flora and fauna alike.


Nowadays, the quality of the air we breathe is not only a private matter, but has also become a political concern. Both UK and EU legislation, for instance, recognize the “worst offenders” when it comes to air pollution, namely sulphur dioxide, oxides of nitrogen, carbon monoxide, particulate matter and heavy metals – notably mercury and lead.

meindl – a giant   footstep to clean air

thimbles for depositing nanorubbish


progress in corona discharge


low pressure fluctuation rto


fairs & conferences

imprint Publisher: CTP GmbH, Austria Editor: Angelika Hebesberger Authors: Oliver Canet, Fabrice David, Christoph Fasching, Thomas Lippitz, Susanne Lux, Christian Mülleder, Christian Roschitz, Muhammad Saleem, Matthäus Siebenhofer, Muhammad Suleman Tahir Head Office: Schmiedlstrasse 10, 8042 Graz, Austria Tel.: +43 316 41010; Fax: +43 316 4101 80 e-mail: Graphic & Production: Printed by: ?? Disclaimer: The views and opinions expressed in AIR are not necessarily those of CTP GmbH. The magazine and publishers are in no way responsible or legally liable for any statements, picture captions, reports or technical anomalies made by authors in their commissioned articles. All articles are protected by copyright and written permission must be sought from the publishers for reprinting or any form of duplication of their contents.

Air quality is influenced by a myriad of natural and anthropogenic factors. Many factories and industries operate 24-7, thus becoming a constant source of pollutant emissions. Furthermore, not only does the quantity of the pollutants being released need to be taken into account, but also the nature of their release and what happens to them once they are in the atmosphere. In order to provide information on this very interesting and extensive matter, our journal aims at covering a wide range of topics, including state-of-the-art research, cutting-edge information on emissions, best practice examples, and the like. Our ambitious target is to keep our readers informed while sharing our knowledge with them. We would like to thank all those who have contributed to this edition of the journal and would also welcome thoughts and ideas from our readers. Please feel free to contact us at to let us have your input or to keep us up-to-date regarding any news you think might be worth sharing with our reading public. Yours,

Angelika Hebesberger, Editor in Chief



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Act – React author: Christoph Fasching, Montanuniversität Leoben

awareness of issues such as environmental protection and sustainable development has increased considerably in recent years. the ultimate challenge is the search for alternative methods to avoid emissions and to comply with legal regulations, as well as the urgent need for innovation. the following article aims to provide an insight into one such alternative approach. Origins of modern environmental awareness In Europe, the Industrial Revolution gave rise to increased environmental pollution. The boom of factories run on wood and coal generated unprecedented levels of air pollution. The large volume of industrial waste and untreated human waste had a considerable impact on fauna and flora alike. Although early environmentalist movements grew steadily, it took time for public awareness of the global consequences of pollution to spread, and a general conscious effort to take steps to REACT to the issue was slow in coming. Reaction: Emission trading Emission trading, a market-based approach to control pollution, also known as ‘cap and trade’, aims at reducing emissions by means of economic incentives (as opposed to using legal regulations). The first emission trading initiative was taken by the United States. An apparent global pollution problem that ­required (re)action was the acid rain issue. ­Although the phenomenon of acid rain had already been identified in the 19th century, it was not until the second half of the 20th century that scientists began their studies on the matter. Thousands of tons of sulphur dioxide were released into the atmosphere and were only noticed due to the increased forest decline and attack on (limestone) buildings.

In the mid 1990s, the United States initiated a two-phase ‘acid rain’ programme aiming to reduce their overall SO2 emissions by 50% by the year 2000. In order to reach this goal, a ‘cap and trade’ system was launched. All industries emitting more than the permitted SO2 amount (=cap) were required to buy certificates. Every ton of SO2 produced exceeding this cap generated a tradable certificate. Operators began to install desulfurization units (e.g. scrubbers) to be able to generate and sell their certificates (trade). The sooner they acted, the more they were rewarded. Companies reacting later had to buy their certificates from their competitors. The greenhouse effect and the emission of greenhouse gases, however, are more of a recent problem. In addition to CO2, CH4 and N2O have a negative impact on the global climate. Over a period of 100 years, methane (CH4), for example, has a GWP (global warming potential) factor 25 times higher than that of CO2, whilst nitrous oxide (N2O) has a staggering ­factor of 298 over a 100-year period. As a result of the Kyoto Protocol, binding targets have been set for several industrialized countries in order to reduce their greenhouse gas emissions. To respect these regulations, the European Union established its own trading system (EU ETS), which is broken down into three phases. The second phase expires by the end of 2012 and the third by the end of 2020. From the beginning

of phase three (i.e. 01.01.2013), nitrous oxide will be included in the scheme. Anyone involved in the certificate trade can act now to avoid a ‘must-react’ approach later on. Thermal or catalytic laughing gas abatement combined with modern recuperators can almost completely destroy N2O at low operating costs. The perfect solution also includes NOx abatement and has practically no harmful emissions. Time to ACT: laughing gas – avoidable future costs The thesis, which the author of this ­article is currently working on is ­entitled ‘Thermal decomposition of nitrous ­oxide’. The author is examining the ­influence of various factors such as moisture, oxygen content, temperature and residence time on degradation. At a temperature of more than 900°C, ­nitrous oxide decomposes into its nitrogen and oxygen components in accordance with the reaction ­2N2O->2N2+O2. Besides the main reaction there are a number of side reactions that produce NOX. By optimizing the above ­mentioned factors, maximum N2O degradation with minimal NOx formation can be achieved. Three models were able to be created from the obtained measurement values. Model 1 is not useful, as it only covers a limited ­temperature range. Model 2 depicts a high N2O ­degradation range. The third model is a combination of both, covering almost the whole temperature range.

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A number of scientific articles have been published recently in the field of catalytic purification of nitrous oxide, while only a limited range of publications exists regarding thermal abatement. However, these two processes (catalytic and thermal abatement) need to be compared: The catalyst achieves high degradation at low temperatures (which means that less energy is needed), but this advantage is nearly negligible in the operation of a regenerative thermal plant. The

thermal way to reduce N2O is a simple heating-up process. The contents of the gas are basically not important. A catalyst, on the other hand, is susceptible to catalyst poison which deactivates its active centres; it could also be ­affected by high humidity. A comparison of precious metal catalysts shows that a rhodium catalyst is the best choice. Comparing the prices of precious metal catalysts (rhodium, for example, is sold at between 50 € and 200 € per gram) provides some good arguments in ­favour of thermal abatement.

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As mentioned above, the ‘laughing gas’ topic will become a matter of interest in 2013, especially for those having to REACT. The following simple calculation speaks for itself: An annual emission of 2,520 tons of N2O equals 781,200 tons of CO2-the permission to emit one ton of CO2 costs about 10 €. Companies that can avoid 95% of those emissions will be able to generate certificates with a value of more than seven million Euros.

(10 g N2O/Nm3 x 30,000 Nm3/h x 8400 h/a x 310 t CO2e/t N2O x 10 €/t CO2e x 95%)

ACT now to avoid future costs!  

Fig. 1: N2O degradation model

Conversion rate




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New Paths In Adsorption Technology author: Christian MĂźlleder, CTP Austria

regenerative thermal oxidation is still proving to be the most successful voc abatement method thanks to its versatility and robustness, but catalytic and adsorptive gas purification are both becoming increasingly important. this article describes innovative developments, which have resulted in cleaning performance being significantly improved and outlines factors that influence adsorption techniques. Improved cleaning performance, highest level of efficiency and reliability The ever-growing awareness of the need for the step-by-step reduction of existing emission limits to protect the quality of life of future generations has definite consequences in the field of air purification. According to the 31st edition of BImSchV, also known as the “Solvents Regulation�, old plants which exceed a certain

emission threshold must be equipped with an appropriate air pollution control system. However, four years after the respective period expired in 2007, not all plants have taken the necessary steps to implement change. In some instances, the energy recovered from the oxidation of pollutants could be used to almost completely cover the energy needs for the relevant air purification system.

New and refined techniques are required to be able to efficiently clean air flows (<200 mg/Nm3) with a very low concentration. In addition to using commercially available adsorbents such as activated carbon granules and zeolite pellets, developments have been made that allow for an optimization of the applied processes to specific applications.

Physical adsorption

Tab. 1: Adsorbents and their applications

Chemical adsorption




Activated carbon (AC)

Solvent recovery, Styrene adsorption, odour removal

Zeolite (hydrophilic)

Dehumidification, adsorption of ammonia, CH3SH, CH3-S-CH3, thermal processes


Thermal processes

Zeolite (hydrophobic)

Separation of n-paraffins and i-paraffins, alcohols, aromatics

Molecular sieves

O2 in air, solvent drying

Silica gel

Dehumidification, odour removal


Dehumidification, odour removal, HF

Activated alumina

Bleaching and deodorization of fats, wastewater treatment

Metal impregnated AC

Adsorption of CO, cyanides

Acid impregnated AC

Ammonia, triethylamine

Base impregnated AC


Catalytically activated AC, KMnO4

NO, H2S, amines, aldehydes

Ion exchange resins, polymers

Ammonia, trimethylamine, H2S, R-SH



Iron oxide

H2S, acetic acid

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Method Fixed bed (TSA, PSA, Ultra Fast TSA)


Particle size





Cascade, moving bed Rotor Fluidized bed Entrainment process

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Adsorption methods differ primarily in terms of the mobility of the adsorbent.

TSA – Thermal swing adsorption (desorption takes place due to an increase in the temperature) PSA – Pressure swing adsorption (desorption takes place by lowering the pressure) Tab. 2: Adsorption methods

From amongst the most economical adsorption processes that have emerged in the field of air purification, the RotorSorbTherm® is particularly suitable for continuous waste air streams. The fixed bed, however, is ideal for very low or short-time (< 8 h/day) emissions. These developments have resulted in a significant improvement in the cleaning performance, as well as in increased efficiency and reliability of the systems in question. Conventional adsorbents As well as economic aspects and performance, the material used (adsorbent), the method applied and the geometry all significantly influence the result of the adsorption technique in question.

Adsorbents Classical adsorbents and their applications, of which activated carbon and zeolite are the best known, are listed in Table 1. Adsorption methods The selected adsorption method determines which adsorbent is to be used and in which form. Geometry and dimensions The variety of standard shapes and dimensions of adsorbents is due to the fact that, besides the adsorption properties and a favourable surface-to-volume-ratio, factors such as mechanical strength, pressure drop, and manufacturing costs can be decisive.

Other important aspects that must be considered for the use of adsorbents: •D  ue to the high internal surface area of some adsorbents, unstable compounds can be catalytically polymerized or modified. • F or some combinations of adsorbents and adsorptive material, the possibility of spontaneous self-ignition has to be considered. •H  igh-boiling compounds can accumulate on the adsorbent, which increases the risk of fire. •A  dsorption properties become stronger or weaker depending on temperature and/or humidity. • F or multi-component systems, displacement effects are possible.



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Honeycomb plate

Monolith metallic

Tab. 3: Geometry

Innovative developments Fixed bed: Washcoat (coating of ceramic honeycombs with adsorbents) SecuSorb® (closed loop desorption at < 3 % O2 with integrated catalytic oxidation)

N2 porosimetry measurements have shown that the binder has no negative effect on adsorption in the micropores.

RotorSorbTherm®: Recirculation, peak removal for 2-bed RTO systems

In parallel, new honeycomb-shaped extrudates of activated charcoal mixed with silicates as a scaffold have been developed together with a sub-supplier. These adsorbents are characterized by their non-flammability, low specific weight and large surface area at a minimum pressure drop.

In order to create a balance between cost-effective production and high ­performance (high capacity and low pressure loss), a special coating technology – washcoat – has been developed, which allows ceramic honeycombs to be permanently coated with an adsorbent.

(The non-flammability could be demonstrated by setting fire to a sample soaked in acetone, which self-extinguishes ­automatically in the air flow ­after combustion of the acetone and only slightly loses its adsorption capacity. Thus, with regards to the fire ­behaviour, no signifi-

cant difference between the zeolite and the AC-silicate mixtures actually exists.) Both the new coating technology and the extrudates combine the benefits of a low pressure drop with high mass transfer area and the suitability for a continuous adsorption process. In addition, the risk of forming a “hot spot” is eliminated by the ceramic content and the uniform laminar flow, thereby preventing fire in the adsorber.   ■


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Meindl – a giant footstep to clean air author: Thomas Lippitz, CTP Austria

footwear manufacturer meindl boasts a longstanding tradition and the very best quality whilst being synonymous with cutting-edge technology in its sector. in 2009, meindl’s status reached new heights when the decision was taken to install a state-of-the-art air pollution control system to efficiently remove waste gases resulting from its production process. this article aims to give a brief overview of the company and of the system which was installed at its plant. MEINDL – A family business The beautiful town of Kirchanschöring is located in the vicinity of Lake Chiemsee and is home to “Lukas Meindl GmbH”. The current owners, brothers Lukas and Lars Meindl, are the 11th generation to run this family business. “Production of outdoor shoes & boots” is the short corporate description which can but briefly summarise the 300 years of Meindl’s history.

From the moment that you set foot in the factory you can instantly feel that the legacy of past generations and the responsibility that they left to their heirs is all around. The reputation that has been built up over centuries is great. Made in Germany The description of the more than 200 stages in the Meindl boot production process could fill books. However, there are some key factors that have shaped this business from the beginning, including:

• Continuous development and improvement (R&D) • Material & quality (leather combined with high-tech textiles) • Awards (e.g. by outdoor magazines) • Various categories of products (boots, shoes, textiles, clothing, ...) • Activities that do not involve production (e.g. sponsoring) • Interdisciplinary thinking (cross-country skiing, Nordic walking, ...) • State-of-the-art technologies (GORE TEX) • Competition (HANWAG, LOWA, ...) • Customer service (“Meindl Movements”)

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The Meindl brand stands for the highquality production of over 1,300 pairs of boots each day. More than 600 employees work to ensure that the trust built up amongst generations of their customers lives on. Customers can even send their worn boots to the in-house repair workshop where Meindl takes care of repairing or resoling. Although figures are regarded as confidential, turnover is estimated to be around 60 million Euros. Responsibility for the business and the products has been handed down from one generation to the next and it goes without saying that a major part of all future investments is dedicated to protecting the environment.

The main features of production have always been continuously improved, with the way in which the company deals with raw materials, packaging, recycling, energy management and the like being developed and optimised from year to year. In 2009, Meindl’s position as a socially responsible company reached new heights when the decision was taken to install a state-of-the-art air pollution control system to treat waste gases resulting from the production process. In July 2010, Meindl approved the delivery of a bespoke air pollution control system.

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The aims were: • respect all relevant emission limits in accordance with European and national legislation • pre-empt future changes, for example in the event of production expansion or updated emission regulations • minimise investment, operating costs and maintenance costs • minimise visual and audible impact of the system • do not interfere with production • ensure maximum efficiency • choose the system with the lowest risk for people, production and the environment • enable easy operation and maintenance



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After 4 months of manufacturing, the unit was delivered and installed on site in December 2010, and came into ­service in January 2011. A closer look at the technology involved Before the air pollution control system was installed, the production waste gas was extracted using fans that transferred it into a dust filter before emitting it over the roof into the atmosphere. An air/water heat exchanger was used at that time to recover some energy. 1. Adsorption All emission sources have since been channelled into one collecting ductwork that leads into a police filter (1) and is then connected to the adsorption unit (2). The police filter is equipped with differential pressure monitoring to make sure that the cartridges are replaced during downtime before the ­filter becomes blocked completely. The waste gas flow enters the adsorption unit that consists of two separate layers of zeolite and an inert ­material

with a very large inner surface and strong adsorption potential. The selection of the zeolite material has been optimised to suit the solvents that are used in the production. The waste gas contaminants are adsorbed within the zeolite and the ­purified air leaves the system through the stack. To compensate for the continuously increasing pressure drop of the police ­filter, the main fan (3) has been equipped with a frequency controller. This assures that the required waste gas volume from all emission sources is ­extracted without production being unexpectedly interrupted.

2. Desorption For desorption of the collected solvents, the system uses the time between production cycles. This means that the cleaning of the zeolite takes place over night or at the weekend. A separate desorption fan (4) creates a circulating gas flow that is heated up by means of an electric heater (5). This hot air flows through the adsorption unit and causes the collected solvents to evaporate from both zeolite beds. Enriched with the desorbed solvents, the high-calorific desorbed air is fed into the catalytic reactor (6), where the organic compounds are oxidised at the surface of a high-performance noble metal catalyst. The resulting combustion enthalpy heats up the gas until it leaves the catalyst bed. Due to the steadily increasing desorption activity, the catalytic oxidation process releases even more combustion heat. This effect means that the ­supporting electric heater can be switched off, ­allowing the process to run without the need for any additional heating energy.

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Within this cycle of the catalytic oxidising process, the incoming desorption air is preheated by the hot clean gas in a recuperative heat exchanger (7). The resulting raw gas temperature is high enough to start the oxidation reaction on the catalyst surface without extra heating.

sophisticated process control system (9, 10) ensure that the solvent concentration constantly stays at a safe level before the gas enters the catalytic oxidiser.

By definition, any kind of oxidation requires oxygen. To satisfy this oxygen demand, a small part of the clean gas flow is released into the atmosphere. An equal amount of fresh air is used to compensate for the flow reduction and to provide the required oxygen.

Future prospects The condition of the zeolite and the catalyst will be monitored and checked frequently, however, a long lifetime of the materials is expected.

Due to the high efficiency of the system, the desorption process could result in a solvent concentration higher than 25% of the LEL (Lower Explosion Limit). Redundant monitoring (8) as well as a

The status of the desorption and the expected residual time for this process can be monitored using various parameters.

The potential of production expansion (e.g. 2-shift operation) has been considered, and it would be possible for a second adsorption unit to be added later on. In that case, the desorption cycle of unit #1 would take place when unit #2 is in adsorption mode.   ■

Functional principle of CTP’s air pollution control system.



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Thimbles for Depositing Nanorubbish author: Christian Mülleder, CTP Austria

nowadays, nanotechnological materials are present in almost every product that we use in the course of our daily lives. the public, however, is barely aware of the potential associated dangers. as toxicological examinations of these products are in their early stages, this article aims to point out the toxicity and impact of nanotechnological products and highlights the most important questions for discussion in this context. The term “nano” origins from the Greek word for dwarf (nánnos). Nanoparticles cover a size range from 1 nm to 1 µm and are very interesting because of their special properties. Special properties of nanomaterials • Structure and quantum effects (electrical, optical and mechanical) • Self organisation • Nanomagnetism and spintronics • Outstanding strength, heat conductivity (CNTs)

Examples of nanomaterials and their application Nowadays, nanotechnological elements are present almost everywhere, for example in products such as detergents, tomato ketchup, soups, cosmetics, deodorants, tooth paste, suntan lotion, textiles and car tyres. These products are not required to be labelled accordingly – and customers are highly probably not even aware of the possible risks linked to these materials [1] .

The critical point In contrast to the field of genetics where early publications about the possibility of direct impact on the genetic code of human beings sparked a discussion on ethical concerns and the development of safety measures and regulations to prevent the uncontrolled release of ­genetically modified food, nanotechnology has become an important financial factor without generating a high level of critical public attention.

In 2010, the worldwide sales revenue for nanomaterials reached $ 10 billion, whilst nanotools generated $ 6 billion [2].

It could be pointed out that experts, especially members of Nanosafe (a ­European project concerned

Tab. 1: Nanoparticulates and their field of application


Field of application

Carbon nanotubes (CNTs), single-wall, double-wall or multi-wall; fullerenes; graphene

CNT/polymer composites, conductive nanotube films, fuel cell electrodes, field emission for flat panel displays, sporting goods

Inorganic nanowires, oxides of the elements Ti, Si, Ge and Al, nitrides and carbides as well as metallic nanowires and nanoglasses

Electronics, optoelectronics, sensors (chemical, biological, ...), energy sector, self-cleaning windows

Nanoparticles & films

Medical applications: drug delivery, diagnostics (protein and nucleic markers), fluorophores, labels, tumour-targeted drug delivery systems, implants

Polymer nanoparticles

Renewable energy, optoelectronics, magnetics, energy storage


Construction materials with improved properties in respect of durability and strength, paints, adhesives, coatings, redispersible latices, pressure-sensitive adhesives, corrosion inhibitors

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Fig 1: Zinc oxide (ZnO) nanowire; © Deli Wang / Department of Electrical and Computer Engineering, UC San Diego

with the safe production and use of ­nanomaterials) have been working on these problems for many years, but ­apparently there has been very little public focus on this matter until now. Given that toxicological examinations (which usually take decades before a final and comprehensive conclusion or understanding can be reached) of these new products are in their early stages, it is appropriate to consider methods and techniques to protect mankind from unintended contact with these substances via aspiration, skin contact or food.

Fig 2: Graphene – single layer graphite; © Jannik Meyer, University of Manchester

The most commonly employed protection measures for staff at nanoparticulate production sites are respiratory protection masks and HEPA filters. But as these measures collect but do not ­destroy these particulates, nobody knows how this sleeping danger will ­ultimately manifest itself. Furthermore, the cleaning efficiency for common ­agglomerate sizes between 80 and 200 nm is very poor for HEPA filters. Even thermal combustion can not automatically be considered as a sufficient way to destroy these particulates. Therefore, suitable tests would have to be carried out, since physical data such as vapour pressure and surface tension differ considerably from one analogue substance to the next on a macroscopic scale. However, this method does pres-

Open questions Environmental and medical effects • Enrichment in the food chain • Biodegradation • Cross-linked effects (combination with other environmental poisons) Treating nanowaste • How can special composites and films be collected and separated? • How can nanowaste be recycled or destroyed? Emission limits for nanoparticles • How can they be monitored? • How should waste gases, liquid and solid waste containing nanoparticles be treated?

ent a good opportunity for the avoidance of nanoparticulate waste disposal. Prospects In view of the fact that products such as carbon nanotubes are able to act as trans-membrane channels, it is not unlikely that environmental poisons which are already widespread will become more dangerous when the uptake into the cells is enhanced by nanoparticulates, even if many of those materials themselves are currently not reported to be toxic. Besides the direct toxicity of nanoparticulates, the enrichment of nanoparticulates in the food chain and the ­environment must be studied, as must the possibility of biodegradation.   ■

Links References [1] Park, M.V., Annema, W., Salvati, A., Lesniak, A., Elsaesser, A., Barnes, C., McKerr, G., Howard, C.V., Lynch, I., Dawson, K.A., Piersma, A.H., de Jong, W.H. In vitro developmental toxicity test detects inhibition of stem cell differentiation by silica nanoparticles. Toxicol Appl Pharmacol. 2009, 240, 108–116. [2] Report Code: NAN031D, Published: July 2010, Analyst: Andrew McWilliams



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Progress in Corona Discharge authors: Muhammad Suleman Tahir1, 2, Muhammad Saleem3, Susanne Lux, Matthäus Siebenhofer1 1 Department of Chemical Engineering and Environmental Technology, Graz University of Technology, Austria 2 NFC Institute of Engineering & Fertilizer Research, Faisalabad, Pakistan 3 Institute of Chem. Eng. & Technology, University of the Punjab, Pakistan

in the past, electrostatic precipitation (esp) used to be a powerful tool in industrial dedusting. due to improvements in fibre quality and cloth design, however, the dedusting process has changed, ­replacing esp with baghouse filters in many industrial applications. the limited operational accuracy of esp, ozone formation through corona discharge and stringent emission limits were the main reasons for esp’s decreasing role. the redesign of discharge electrodes, causing an increased corona current, may contribute to re-establishing esp in wet off-gas purification. Wet tube-type electrostatic precipitators are powerful pollution control tools for the precipitation of submicronic particulate matter with sticky properties. Experimental studies were conducted to determine the effect of the geometry of discharge electrodes on the performance of tube-type electrostatic precipitators. The objective was to intensify the precipitation field intensity EP, a factor which directly contributes to the rate of migration w(x) of particulate matter in electrostatic precipitators as shown in equation (1) below.

E ·E ·x                 (1) w(x)= d P 4·π·η

w(x) Ed EP x η

Particle rate of migration Discharge field intensity Precipitation field intensity Particle diameter Dynamic viscosity

For comparable operation voltage, brush-type discharge electrodes show a significantly higher corona current than wire-type discharge electrodes. As a result, improved collection ­efficiency of particulate matter is observed. ­According to state-of-the-art modelling of corona discharge in tube-type electrostatic precipitators, the specific corona current I for wire type electrodes and homogeneous discharge is well ­represented in equation (2) below.

U · 2 · K · (U–U0) I=                 (2) R2 · ln    R   rw

( )

I U U0 K R r w

Specific corona current Operation voltage Corona start-up voltage Ion mobility Tube radius Wire radius

Figure 1 below shows the comparison of current/voltage characteristics of a wire-type discharge electrode and a brush-type discharge electrode for r = 0.15 mm and R = 66 mm and an electrode length of L = 500 mm. The experimental current-voltage ­characteristic of the wire-type discharge electrode compares well with equation (2). Equation 2 does definitely not suffice to describe the experimental currentvoltage characteristic of brush-type discharge electrodes, and although ­literature has mentioned a different algorithm for elevated specific corona current, several equations fail.

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Fig. 1: Current/voltage characteristic of wire-type discharge electrodes and brush-type discharge electrodes in a tube-type electrostatic precipitator of L = 500 mm, R = 66 mm, r = 0.15 mm, brush diameter: 8 mm; T = 293 K, P = 1013 hPa

Based on the investigation of brushtype electrodes of different brush diameters and different wire diameters, an appropriate equation (3) was developed.


The comparison in Figure 1 demonstrates the significant impact of the shape of electrodes on the specific ­corona current. Specific corona current I is linked with precipitation field intensity EP according to equation (4).


U–U 2    U 0  0                 (3) I= 3 · K · U2 ·  R–r ( R–rb )2 · ln    b   rw



Equation (3) considers brush diameter rb as well as wire diameter rw and it compares well with current/voltage data obtained during experiments.

2 · I                 (4) EP= K

As demonstrated, brush-type electrodes significantly improve the current/ voltage characteristic of electrostatic ­precipitators. It follows that precipitation performance is ­improved as well. These results were achieved ­during a PhD research project at the Institute of Chemical Engineering and ­Environmental Technology of Graz ­University of Technology.   ■

Figure 2 shows the shape of corona discharge for the specified operation conditions.

Fig. 2: Image of corona generation with brush-type discharge electrodes in ambient conditions and with the application of a voltage of 20 kV.



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Low Pressure Fluctuation RTO author: Christian Roschitz, CTP Austria

pressure fluctuations at the raw gas inlet of regenerative thermal oxidation systems are a wellknown issue in voc removal technology. they can be best described as a type of fingerprint of a regenerative gas cleaning system operating as a voc oxidizer. the innovative low pressure fluctuation system, however, makes distinctive pressure peaks in rto operation disappear. this article describes the development and testing of an rto system, which does not interfere with the customer’s production line. Process air containing low-concentra­ tion organic substances (VOCs) is cleaned within an RTO by oxidation and further destruction of the organic compounds. This energy-efficient air cleaning technology is based on regenerative heat exchanger beds and a combustion chamber. Depending on the cleaning efficiency, systems with two or more beds are used. This article presents the development of and research into a 3-bed system usually consisting of two beds, which are in operation with another bed on stand-by (see Fig. 2 for an example of a 3-bed system). The results are similar

to those of 3-bed and 5-bed systems for applications where this technology is suitable. Generally, gas treatment systems are an end-of-pipe technology and should not affect production processes. The diverse range of industries where VOC removal is required includes very pressure-sensitive production processes as well as processes, in which pressure peaks do not play a role. In the pressure-sensitive film coating industry, for example, pressure peaks would influence the product quality and lead to production losses

and higher costs. Industries dependent on such production processes therefore used to be limited in their choice of adequate gas treatment systems available. This article describes an RTO technology with the lowest possible pressure peaks in the range of less than 10 Pa, which is thus suitable for pressure-sensitive ­production lines. Regenerative 3-bed systems are operated using special heat exchanger bed cycles. While two heat exchanger beds are in operation, the third is on stand-by (see Fig. 2, Cycle 1 and Cycle 3). For the continuous operation of the system raw gas and clean gas are alternately passed through the heat exchanger beds. This sequence is realised by switching the main poppet valves. In Cycle 1, the raw gas is led through bed A, the clean gas passes through bed C. During the procedure, which changes the heat exchanger bed from bed A to bed B, the raw gas is led through beds A and B first (Cycle 2). Instead of two beds, three beds are in operation at the same time. In the next step, the raw gas is led through bed B only (Cycle 3), while the clean gas continues to flow Fig. 1: The pilot plant

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 

Normal operation, raw gas inlet through one bed A – full pressure drop





 

Switching operation, raw gas inlet through two beds A/B – decrease in pressure drop



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 

Normal operation, raw gas inlet through one bed B – full pressure drop

Fig. 2: Origin of pressure peaks in 3-bed RTO systems, example of raw gas switching from bed A to bed B

through bed C. Obviously, the operation sequence passes through a certain period in which three heat exchanger beds are used, while during normal operation the gas stream flows through two beds only. It is precisely during this short period when all three heat exchanger beds are used that the pressure drop of the system suddenly decreases (see Fig. 2, Cycle 2). Presuming that there is a continuous flow rate, the inlet pressurecontrolled fan runs at a constant speed. The fast decrease in backpressure at an unchanged fan speed results in a sudden flow rate increase. The pressure at the plant inlet suddenly decreases and the pressure peak is generated (Fig. 3). Among further improvements, the main innovations of the design are:

•S  mooth operation and continuously controlled poppet valves (Fig. 4) • Installation of a special flap valve in an integrated RTO bypass (Fig. 5) The installation of special controlled poppet valve actuators effectively reduces pressure peaks. The main advantages are the smooth and continuous movement of the valves and the ability to actuate each valve independently. The weight-balanced flap valve is the sensitive element of the plant and ­contributes to an even ­smoother ­operation process. During normal ­operation the valve regulates the plant flow rate, allowing for a slight clean gas recirculation. Any change of flow rate originating from the customer process

Fig. 3: Typical pressure fluctuation of a standard RTO system

Fig. 4: Special poppet valve actuator for smooth operation and valve speed control

magazine for better air quality

issue no 1_april 2011

Controlled poppet valve



A Opening angle during operation

B Opening angle during bypass operation

Flap valve

Fig. 5: Flap valve positions

is detected and compensated by the innovative control concept. During the heat exchanger bed change, the flap valve provides the “missing” flow rate by increasing the clean gas recirculation. Thanks to its location and operation, the valve reduces the pressure peaks. Another benefit is the integrated automatic plant bypass, which is activated when the RTO comes to a sudden halt. Early in 2009, the low fluctuation ­concept became a reality when a 3-bed low pressure pilot plant (Fig. 6) was ­constructed. It was not necessary to build a complete system to carry out the tests; the pressure drop was simulated using throttle valves. After a short test period, it was clear that the ambitious aim of the low pressure fluctuation concept had been achieved.

Fig. 6: Basic plant design of the pilot plant

Pressure [Pa]


The pilot test results show that pressure stability within the range of 10 Pa can be reached. The plant was adjusted to have a positive flap valve angle at all times in order to avoid raw gas shortcuts towards the stack. With the controlled poppet valve and the integrated flap valve, pressure fluctuations of less than 10 Pa at the plant inlet can be achieved.   ■


Fig. 7: Resulting pressure at pilot plant inlet

magazine for better air quality

issue no 1_april 2011

Fairs & Conferences Date



Apr 04–08, 2011

Hannover Messe 2011 Showcase for Industrial Technology

Hannover, Germany

Apr 05–10, 2011

Okotech International Environmental Protection Trade Fair

Budapest, Hungary

Apr 13–15, 2011

Environmental International Forum SAVE the Planet – Waste & Water Management, Recycling

Sofia, Bulgaria

May 05–07, 2011

EPTEE (China Environmental Protection Expo) IFAT China (International Trade Fair for Water, Sewage, Refuse, Recycling and Natural Energy Sources)

Shanghai, China

May 18–20, 2011

Flowexpo The 14th International Trade Fair for Valve, Pipe Fitting, Fluid Machinery and Process Equipment

Guangzhou, China

May 24–26, 2011

Sustainabilitylive! Consisting of: BEX (Brownfield Expo), ET 2011 (Environmental Technology), NEMEX (The National Energy Management Exhibition) and SB (Sustainable Business)

Birmingham, UK

Jun 06–09, 2011

Entsorga – Enteco International Fair for Waste Management and Environmental Technologies

Köln, Germany

Jun 07–09, 2011

Petro t. ex Africa 2011 (Refining and Petrochemical Industry Exhibition) The Star Energex Exhibition 2011 (Alternative Energy Event) Pumps, Valves & Pipes

Midrand, South Africa

Jun 21–24, 2011

Air and Waste Management Association Annual Meeting AWMA, Pittsburgh, PA., USA

Orlando, FL., USA

Jul 24–29, 2011

10th International Conference on Mercury as a Global Pollutant

Halifax, NS., Canada

Aug 25–27, 2011

CIEPF 2011 China International Environmental Protection Fair

Dalian, China

Sep 27–30, 2011

EMAT (6th International Environmental Protection, Eco Technology and Municipal Equipment Fair)

Zagreb, Croatia

Sep 28–30, 2011

Control-Tech (14th Fair of Industrial Measuring Technology)

Kielce, Poland

Oct 5–7, 2011

CEM International Conference on Emissions Monitoring

Prague, Czech Republic

Oct 19–21, 2011

Chem-Med 2011

Milan, Italy

Oct 26–29, 2011

ECO Expo Asia Business Solutions to Climate Change

Hong Kong

Nov 09–12, 2011

Ecomondo Expo of Green Technologies and New Lifestyles

Rimini, Italy

Nov 15–17, 2011

Environmental Technologies & Renewable Energies: The Israel Trade Fairs and Convention Center Ltd., Tel Aviv, Israel

Tel Aviv, Israel

Nov 22–25, 2011

Enviro-Asia 2011 – 5th International Environmental Technologies Exhibition & Conference


Nov 23–26, 2011

Poleko Environmental Protection and Municipal Management

Posen, Poland

Dec 01–04, 2011

Pollutec Horizons 2011

Paris, France



magazine for better air quality

issue no 1_april 2011

VOC Regulations In France

When the late but growing awareness of environmental issues drives the reinforcement of the law… author: Oliver Canet, Fabrice David, CTP France

annual investments made by industrial companies in france regarding air pollution control increased from 200 million € in 1992 to more than 475 million € in 2009. these investments were all related to the purchase of air pollution control systems such as thermal oxidizers, scrubbers or filters. the target was to respect the international commitment taken by france through the protocol of gothenburg signed in 1999, to reduce the non-methanic voc emissions from 2300 kt in 1998 to 1050 kt in 2010. a more demanding regulation is in preparation to fix a much lower voc emission target for 2020! all concerned actors are being driven by the legal engine. In France, about 30 % of the total VOC emissions are emitted by the manufacturing industry and a constantly growing control is being reinforced by the Environmental Authorities according to the updating regulations. This environmental control concerns a special and typical French industrial ­regime known as ICPE (Classified Installations for the Protection of Environment) subject to Authorisation. A classified installation, as defined in detail by Book V of the French Environment Code, is any industrial or agricultural ­installation that is likely to present a risk or cause pollution or nuisance, affecting the health and safety of local residents or the environmental surrounding. This installation can require either a simple declaration to the Prefecture for less polluting or hazardous activities or an authorisation for higher levels of risk and pollution.

Out of the 500 000 ICPE in France, 60 000 are subject to Authorisation and have to abide by the decree of 2  February 1998 which regulates all emissions to the air, water and soil. This decree has continuously been updated to integrate new regulations and emission limits. The requirements of the ­European Directive 99/13/EC of 11 March 1999 on VOC emissions due to the use of solvents, imposing limit values for channelled and diffuse VOC emissions and specific obligations with regard to the most toxic solvents (reduction, ­replacement), were transposed into the French legislation by the decree of 29 May 2000 which then modified the initial 1998 decree. Since then, 2 other modifications were brought to this ­decree to strengthen the legal obligations on VOC emissions: the decree of 2 May 2002 and quite recently the decree of 1 June 2010.

The requirements of the now modified decree of 2 February 1998 can be summarised into the following 3 obligations: • Article “27.7.a” for the general case: if the massic flow of VOC exceeds 2 kg/h, then the legal emission limit is fixed at 110 mg/Nm3 in Total Organic Carbon •A  rticle “27.7.b” for VOC listed in Appendix III (ex : Formaldehyde, Phenol, Chlorinated Solvants, etc.): if the massic flow of VOC exceeds 0,1 kg/h, then the legal emission limit is fixed at 20 mg/Nm3 • Article “27.7.c” for dangerous VOC (Riskphrase or danger assigned compounds): if the massic flow of VOC exceeds 10 g/h, then the legal emission limit is fixed at 2 mg/Nm3 A particular requirement concerns the general case…when applying an oxidation technique to eliminate the VOC. This requirement is shown in the flowchart hereafter.   ■

magazine for better air quality

Special VOC requirement in France for air pollution control by oxidation

Emissions of Volatile Organic Compounds (VOC)

Massic flow > 2 kg/h

issue no 1_april 2011


Not concerned by the decree 2 February 1998


Thermal treatment


Emission limit value for canalised emissions: 110 mg/Nm3 (in total carbon) Emission limit value for diffused emissions: fixed by prefectoral decree

YES VOC: â&#x20AC;˘ Cleaning efficiency > 98 %: 50 mg/Nm3 (total carbon) â&#x20AC;˘C  leaning efficiency < 98 %: 20 mg/Nm3 (total carbon) NOx (equivalent to NO2): 100 mg/Nm3 CH4 : 50 mg/Nm3 CO: 100 mg/Nm3

Flow > 15 kg/h or > 10 kg/h if cleaning equipment is used

Continuous monitoring of non-methanic VOC emissions

If oxidation technique is used, then emission limits of NOx, CH4 and CO need to be verified once a year



issue no 1 _april 2011

magazine for better air quality where science meets practice

Progress in Corona Discharge Adsorption Technology nanotechnology Low Pressure Fluctuation RTO

issue no 1 _april 2011

magazine for better air quality where science meets practice

Progress in Corona Discharge Adsorption Technology nanotechnology Low Pressure Fluctuation RTO


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