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SCHWARZ PHARMA

APPENDIX 1 BASIS OF DESIGN AND PROCESS DUTY

The justification for the choice of abatement technique is discussed in a separate BAT report for the BPC and Nitration plants. However the following bullet points summarise the overall system:

BPC: . Small dedicated scrubbers for specific reactors/processes

. Combined inerted and air-dilute header systems, with pre- scrubbers (acid/base) for removal of HCI/NHB generated by process.

. Regenerative Flameless Thermal Oxidizer

. Post-oxidation 2 stage quench and scrubber system for HCI removal (Venturi quench, packed tower scrubber)

. Heat exchange for visible plume reduction

Note : there are options for either DCM recovery by adsorption/desorption or removal prior to the oxidation stage by scrubbing. These are explored in more detail in the BAT document.

Nitration:

. lnerted header

. Regenerative Flameless Thermal Oxidizer

. Post-oxidation quench

. Heat exchange for visible plume reduction

BPC Plant Non-Chlorinated Streams:

Operating Maximum Minimum Flowrate Nm3/h 5000 10000 3000 Pressure mbarg atmospheric 10 -10 Temperature “C IO-15 30 5 voc , mg/m3 1000 - 2000 8000 500

VOC Components Contaminants

Acetone IMS Methanol Toluene Ethyl Acetate

water: (saturation at up to 30%) Dichloromethane: traces HCI: cl Omg/m3 NH,: ~5 mg/m3 H2 cl 000 mg/m3

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MTBE Acetic Acid MEK IPA Hexanes Heptanes THF Butane lsobutylene

balance: air

BPC Plant Chlorinated Streams:

Operating Maximum Minimum Flowrate Nm3/h 50-100 400 5-10 Pressure mbarg 5-10 50 atmospheric Temperature “C o-1 0 50 -10 voc mg/m3 20-50000 200000 0

Note: maximum conditions not coincident. DCM load will range from 5 to 40 kg/h.

VOC Components

DCM Acetone IMS Ethyl Acetate Toluene Hexanes Heptanes

Contaminant

water: (saturation at 5’ - 10%) HCI: cl0 mg/m3 (ex scrubber) balance: air

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Nitration Plant

Operating Maximum Minimum Flowrate Nm3/h 5000 5000 1500 Pressure mbarg -15 atmospheric -30 Temperature “C 0 40 -5 voc mg/m3 1000-2000 8000 500

VOC Components

Toluene MIBK IMS Acetic Acid

Contaminant

water: (saturated at 10’ - 15’C) balance: air

EMISSION DATA FROM FLAMELESS REGENERATIVE OXIDATION OPTION

BPC Plant Combined chlorinated and Non-chlorinated

Flowrate Nm3/h

Temperature

voc DCM HCI

co NO,

Nitration Plant

“C

l- Operating 5000-I 0000

>50

Comment No additional combustion air required.

This will normally be higher depending on organic load. Use 50 as worst-case dispersion temperature.

Can be lowered by improved scrubber design if required

This low level can be guaranteed if the NH3 from the process is limited to ~5 mg/m3. Also assumes no NO, in the process.

Flowrate Nm3/h Operating Comment

5000 No additional combustion air required.

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Temperature “C 50-70 Use 50 as worst-case dispersion temperature.

voc mgC/Nm” co mg/Nm3 NO, mg/Nm3

<20 <50 <IO This low level can be

guaranteed if the NH3 from the process is limited to 41 mg/m3. Also assumes no NO, in the process.

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SC.H WARZ PHARMA

APPENDIX 2 BAT ASSESSMENT FOR ABATEMENT OF RESIDUAL VOC EMISSIONS

STAGE 1: DEFINITION OF BAT ASSESSMENT OBJECTIVE

To appraise candidate options for the prevention and minimisation of residual VOC releases from the pharmaceutical production facilities of the Schwarz Pharma site in Shannon. These residual VOC emissions are assumed to arise after the upgrade to primary vent condensers is carried out.

The options must be capable of meeting the requirements of the Solvents Emissions Directive.

STAGE 2: GENERATION OF OPTIONS TO MEET OBJECTIVE

The choice of technology for pharmaceutical process emission control is influenced by the following factors:

. Batch processing and the intermittent nature of the releases

. Variation in flow and concentration throughout batch cycles

. Usually there is a complex mixture of solvents used in the various production stages (reactor, washing, phase separation, drying etc). These VOC mixtures may be further complicated by the presence of water vapour, particulate and other waste gas compounds

Due to the multi-purpose nature of the site and the high degree of removal/destruction required, the technologies not taken forward for detailed consideration are:

. carbon adsorption,

. membrane technologies and

. absorption.

The principal disadvantage with using granulated carbon is that for multiple solvent streams the adsorption capacity of the bed can be affected. One solvent will adsorb at the expense of leaving another less selective solvent to pass through. A further disadvantage is that a significant amount of wastewater is produced following regeneration of the bed with steam. There are also safety concerns due to the highly reactive nature of the carbon that can produce high heats of combustion and the potential for bed fires, particularly during periods of start-up and shutdown.

Typical levels of VOC in exhaust gas for carbon adsorption plants are 20 to 80 mg/Nm3 (depending on organic). In terms

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of the carbon regeneration 4kg of steam (per kg of organic adsorbed) typically leaves sufficient VOC on the carbon to provide measurable levels of VOCs’ in the exhaust gas.

Due to the asymptotic nature of the relationship between steam used and residual VOC in the carbon, achieving VOC levels below the typical requires significantly more steam to the point that it is economically unviable.

Molecular sieves and similar membrane systems have similar advantages and disadvantages but water vapour and some solvent materials can also poison the adsorption media.

Absorption using selective solvents and polyethylene glycol can achieve a 98% reduction in releases but again there is a resulting liquid waste stream of glycol and solvent that needs to be desorbed, resulting in an aqueous /solvent mixture for disposal or effluent treatment. The glycol is also very expensive.

Section 3.2.2 discusses the basis of choice for techniques taken forward for detailed consideration.

In summary, the technologies recommended for consideration for the proposed process duties of the BPC and Nitration plants are therefore:

l Low temperature cooling/condensation with recovery of solvent and

l Regenerative thermal oxidation with heat recovery

The following features can be applied to both technologies, which makes them suitable potential candidates for the Schwarz Pharma application:

. Both of these two options are capable of achieving very low final emission concentrations so there is a degree of future proofing included in the technology choice.

. Both technologies are non-specific in their treatment. Cryogenic condensation requires control of the exchanger temperature but it is capable of recovering most VOCs.

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The elimination of the non-viable techniques in the previous section leaves the following two options for further detailed consideration:

. A recovery technique of cryogenic condensation followed by solvent recovery

n A destruction technique of regenerative thermal oxidation

The following features can be applied to both technologies, which makes them suitable candidate for the Schwarz application:

l Both of these two options are capable of achieving very low final emission concentrations so there is a degree of future proofing included in the technology choice.

l Both technologies are non-specific in their treatment. Cryogenic condensation requires control of the exchanger temperature but it is capable of recovering most VOCs.

The principal features of the two candidate technologies are discussed in the main text (Section 3) of this report.

Comparison of Lona-term releases

Both candidate options are capable of and would be designed to achieve the 20mgCINm3 emission standard for VOCs. There is no difference between the options in the effect of long-term releases.

The thermal oxidation route includes a post scrubber for the acid gases. The water from the scrubber will contain a small amount of alkali and approximately 12 kg/hr of salt formed by the neutralisation of hydrogen chloride by caustic soda.

Salt has an inhibitory effect upon biological systems at high concentrations however the mass of salt discharged to downstream effluent treatment is small in comparison with the total site discharge and its effect is minimal.

Comparison of Short-term releases

Both candidate options are capable of and would be designed to achieve the 20mgC/Nm3 emission standard for VOCs. There is no difference between the options in the effect of short-term releases.

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P F-t A ‘R M A

Comparison of Global Warminq Potential

The thermal oxidation option results in a release of approximately:

. 15,000 tonnes/year of carbon dioxide which is used as the basis for comparison of global warming potential (i.e. a GWP value of 1)

. the release of oxides of nitrogen is only O.OGkg/hr so this is insignificant in terms of global warming potential.

Comparison of Photochemical Ozone Creation Potential

In this case, the most significant substances are solvents. For both options, the final emission limit value will be ~20 mgC/Nm3 so there is no significant difference between the options.

Generation of Waste

For cryogenic condensation the recovered solvent mix is a potentially useful product. However, pharmaceutical process recipes are developed with virgin or high purity solvents.

There are a number of potential azeotropes in the Schwarz mixture of solvents as discussed previously. This further complicates recovery into useful products. In addition, the recovery process requires expensive distillation and storage plant.

There is therefore limited scope for re-use of the recovered solvent and it thus becomes a waste stream for disposal off site. Off-site recovery may be possible but in terms of the site, it can be considered as a waste stream.

The thermal oxidation option does not have any additional waste streams.

Other Considerations

The potential for plume visibility needs to be addressed in a separate assessment. In the case of the thermal oxidation route the potential for plume visibility is reduced by allowing for the addition of excess heat to the exit stream.

There is no significant difference between the options in terms of odour generation

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STAGE 4: SUMMARY OF ASSESSMENT

The two candidate options of cryogenic condensation and regenerative oxidation have very similar environmental releases in that they are both capable of, and would be designed for, achieving the requirements of the Solvent Emissions Directive (a VOC emission concentration of ~20 mgC/Nm3).

There is no difference between the Environmental Quotient of either option for the long and short-term releases of VOCs.

There are some minor differences between the options in terms of the secondary impacts such as:

n Global warming potential n Ozone creation potential n Releases to water n Plume visibility

However, the main difference relates to the volume of solvent that would be recovered by the cryogenic condensation process. For the Schwarz Pharma application, this solvent is a complex mixture with potential azeotropes. There is limited scope for solvent reuse in pharmaceutical processes and the potential for contamination (loss of entire batch and risk to patient health) outweighs potential benefits.

In addition to the above points, there is a novelty factor associated with cryogenic condensation. Although the theory is sound, there are very few cryogenic units operating on multi-solvent streams at this sort of scale. There is therefore an associated technical, environmental and financial risk in this particular application. There is an apparent large variation in quoted capital costs for such systems due to the lack of background information and historical installations.

The capital cost of the thermal oxidation option is significantly lower than that of the cryogenic condensation unit. The flameless oxidiser is currently deemed to be the Best Available Technique for the treatment of residual VOC emissions from the BPC plant. In summary this is because:

. There is no difference in the final release concentration achievable with either option

. Both options will achieve a very high degree of VOC removal in line with the requirements of the Solvents Emissions Directive.

. The recovery of a mixed stream of condensed solvents causes additional practical problems for the site which cannot easily be addressed (location of additional storage, increased fugitive emissions)

n Technical risk due to novelty of cryogenic condensation at this scale of flowrate

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n Technical risk due to novelty of cryogenic condensation for this complex mixture of solvents

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APPENDIX 3 VOC ABATEMENT TECHNOLOGIES

Appendix 3.1 Emission Control Overview

Abatement of VOC emissions to atmosphere can be divided into four main sections:

1. High Temperature (Thermal) Oxidation 2. Catalytic Oxidation 3. Adsorption; 4. Absorption; 5. Condensation.

Each of the generic technologies are divided into separate sub-sections covering the various specific types of process equipment.

Each method has specific chemical contaminant and VOC concentration ranges to which it is most suited and certain characteristics that can render it unsuitable for use. The efficiency of a specific process can be significantly affected by the inlet concentration of organic.

The remainder of this section will review each of the nine sub-sections.

Appendix 3.2 Thermal Oxidation Overview

Thermal Oxidation is a common method used for the destruction of gas-phase and liquid-phase organics. Relatively low operating temperatures and short residence times are used for VOC destruction (700 to 800% and 0.5 to 1 second). These conditions should be compared with the more rigorous requirements for liquid disposal, i.e. 2 seconds residence and 1 ,l OO’C plus temperature; allied with secondary combustion chambers and rapid quenching for dioxin/furan control. While these conditions may not be required for VOC control they indicate a trend towards turbulent combustion, longer residence times, higher temperatures and the control of dioxins/furans.

Section 3.3.2 of the main report discusses Regenerative thermal Oxidation in some detail. In particular, it focuses on then flameless configuration.

Appendix 3.3 Catalytic Conversion

Appendix 3.3.1 Process Description

Catalytic incineration is a low temperature oxidation process that uses one of two types of catalyst to convert organics into carbon dioxide and

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e

water. The catalysts are based on either precious metals or transition metals, supported on a ceramic matrix. The matrix can be in the form of an extruded cylinder, or in a fabricated shape such as a honeycomb.

VOC containing air enters a pre-heat chamber and is raised to the operating temperature of the catalyst: 250 “C for the transition metal catalyst and approximately 350 “C for the precious metal catalyst. The preheat is supplied by either hot gas entering from a small burner or a preheat heat exchanger in a thermal oil circuit.

The heated air then flows through the catalyst bed, typically 12” deep, and is oxidised. The air passes through a heat exchanger for heat recovery prior to being exhausted to a local stack. The heat exchanger can be connected so that it provides the pre-heat for the incoming air. Typically at 70% heat recovery and 20% LEL VOC concentration the system is self sustaining.

The method operates at low temperatures and is fabricated from low cost materials. Only oxidation of the organics takes place, and NO, production does not occur. Typical destruction efficiencies are in the region of 95% to over 99% for the common organic solvents. Volumetric flowrates for the units typically vary from 2,000 m3/hr to 40,000 m3/hr.

Appendix 3.3.2 Operating Cost, Data and Process Status

External Fuel Operating cost Process Status Small pre-heat burner (or heat exchanger) Catalyst Catalytic converters to heat the unit to operating temperature replacement cost is are widely available and maintain that temperature. Should the main operating insufficient VOC be present for the system

and well proven in cost. Catalyst VOC destruction.

to be self supporting. replacement periods can be eight to ten years depending on process conditions but two years is more typical.

Appendix 3.3.3 Process Problems

The main problems associated with catalytic converters are described below:

l Particulates in the exhaust gases can lead to blockages in the catalyst bed

l Breakdown products and trace components can poison the catalyst sites

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l High levels of halogenated organics can poison the bed

Appendix 3.4 Overview of Adsorption

Adsorption is the retention of substances from the gas phase on solid surfaces. One or more components from a gas are retained on solid adsorbent. The reverse process is called desorption.

Purely physical adsorption is reversible, i.e. the molecules stored on the surface of the solid can be desorbed again unchanged. This corresponds exactly to the requirements of solvent recovery.

The mosf important industrial adsorbents include activated carbon, silica gel and molecular sieves. Due to its hydrophobic character, activated carbon is particularly suitable and is commonly used for the recovery of solvents. Furthermore, it is distinguished by a very large surface area relative to mass and hence also by a high retention capacity for the substances concerned.

Activated alumina and silica gels tend to be primarily used for drying gases, particularly under pressure. Molecular sieves are characterised by a smaller pore size than carbon and have a higher desorption temperature, 100 ‘C to 140 OC for carbon, 200°C to 300 OC for molecular sieves.

Activated alumina, silica gel and molecular sieves (essentially dehydrated zeolites) can be used for solvent recovery but their relatively high price and lower efficiency tends to exclude their use in the majority of applications for VOC control. Additionally they all have a high affinity for water vapour and preferentially adsorb water before any other pollutants. Subsequently any gas streams to be treated by these adsorbents must be fully dehydrated. Their strong affinity for water also excludes the direct use of steam as the heat source for desorbing the organics. This results in additional capital cost for gas heaters or vacuum units for the desorption step. Their high desorption temperatures also tend to preclude the use of steam as a gas heating medium and forces the use of costly heat transfer systems.

The equilibrium in the solvent/air/activated carbon system is determined by the characteristics of the adsorption isotherms. It is true to say that with increasing concentration of an adsorptive in the gas phase, the loading of the adsorbent at a certain temperature also increases. At the same concentration, the equilibrium loading decreases with increasing temperature.

At constant temperature, the maximum obtainable equilibrium loadings depend on the vapour pressure and the molecular weight of the substance to be adsorbed. The adsorption rate must also be controlled

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for certain organic compounds, i.e. ketones and for highly concentrated streams of benzene, where the energy release during adsorption can raise the bed temperature to its ignition point. Fires in early acetone recovery units were caused by this heat release.

In practice, the equilibrium loading is reduced to the so-called working loading of the carbon. This ranges from 5-20% of the theoretical maximum weight. The loading is affected by the factors tabulated below.

Factors Affectinq AdsorDtion Description

Moisture Water vapour is preferentially adsorbed by carbon.

Residual Solvent Loading (Heel)

Fouling

Thermal Shock

While carbon exhibits hydrophobic characteristics to liquid water, water vapour is often adsorbed in preference to organics. This “loads” the carbon and reduces the

overall organic loading. The residual heel on the bed reduces the removal efficiency. Fine particulates and poisons, such as sulphur compounds can enter the bed and become attached to the carbon. This reduces its adsorption capacity, and subsequently shortens its effective life. Thermal cycling of the bed causes thermal cracking of the carbon pellets, producing dust which blinds the carbon.

a Appendix 3.4.1 Process Description

Depending upon the volume of gas to be treated two options are available, both operating on the same principle;

l Single use and reusable canisters

. in-situ units with adsorbent regeneration and solvent reclaim

Appendix 3.4.1 .l Single use canisters

Single use canisters tend to dominate the low volume gas cleaning market. Once a canister has adsorbed its full complement of VOC it is removed from site. The adsorbent is either sent to land-fill or

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regenerated. Canister based systems can achieve lower VOC outlet concentrations than in-situ units as “fresh adsorbenf’ contains no residual organics, or other contaminants. The potential problems of poisoning, water contamination and particulate blockage can be experienced.

Different canisters are available depending on the duty they are required to perform. For relatively low flow rates with high VOC concentrations deep bed units are available, with canister sizes ranging from about 0.5m diameter by 0.75m high to about 1.5m diameter by 2m high and flow rates from about 200m3/hr to 6000m3/hr. Typical applications for these would be on vents from tanks during filling and drum filling operations etc..

For high flow rates with low VOC concentrations, typically building extraction systems, larger area units are available. The size of these is typically about 2.5m by 2.5m by 2.5m and can handle flow rates of around 10000 to 30000m3/hr. For higher flowrates modules can be linked together.

Reusable canisters can be installed, these are steam cleaned to remove the organic waste and placed back into the process.

The manufacturers of the carbon canisters estimate that some 3 tonnes of carbon per day will be required. This is felt, by the manufacturers to be an impractical option and a small in-situ adsorption process plant would be required.

Appendix 3.4.1.2 In-situ units

Fixed beds are used almost exclusively by adsorption process plant manufacturers and it is this type of unit that will be described in more detail.

Before continuing it is worth mentioning that the trend in the early 1960’s towards fluidised bed systems has now ceased. The drawbacks associated with this type of operation have now become known. Typical problems included shortened carbon life due to particle attrition, high running costs, difficulties in optimising control of fluidising velocities and slightly lower removal efficiencies.

In most cases, the production plants upstream of the adsorber operate continuously. Consequently, parallel operation of two or more fixed beds is commonplace. One bed is loaded with the adsorptive (the VOC) while the other, or others, are being regenerated. Rotating beds are also available, which have a single cylindrical bed which rotates continuously through three chambers, namely adsorption, regeneration and drying/cooling. The rotating bed gives perhaps the most ‘continuous’ mode of operation.

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Fixed-bed processes are further sub-divided by the type of desorption procedure:

the steam regeneration process inert gas regeneration vacuum regeneration

The selection of the ideal regeneration process emerges from the plant conditions, the legislative requirements and the physical properties of the solvents.

For solvents which are insoluble or sparingly soluble in water desorption by steam has proved extremely successful and the use of carbon as the adsorber medium has almost become the industry standard. This is due to the fact that steam is the most widely used industrial heat carrier and carbon a durable, economic adsorbant. For the continuous operation of the unit, the regeneration time of an absorber unit must be less than the total loading time of the other vessels.

The operation of a fixed bed adsorber follows a specific sequence that is described below:

\ - adsorption of the solvent vapours from the gas stream

onto the carbon; desorption of the solvents with steam; drying of the carbon with hot air; cooling of the carbon.

The solvent-bearing gas is passed through the on-line adsorber and a purified waste gas leaves the unit.

Once the carbon bed is saturated it is taken out of the process air stream and the next adsorber is put on-line. The switch-over is carried out automatically either by a continuous gas monitor which detects breakthrough or a timer.

Desorption is more commonly carried out with dry superheated steam which passes counter-currently through the bed. The steam is condensed in the adsorber and taken up by the activated carbon. The steam supplies the energy and acts as the transport medium for the solvents that are desorbed.

The solvent/steam mixture leaving the adsorber is condensed and passed to a phase separator vessel. Due to the solubility of some solvents in water steam distillation may be required to separate the solvent from the water. In some cases the partial solubility of some organics will require steam stripping of the aqueous phase prior to discharge of the aqueous phase.

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The duration of the steaming step depends on a residual loading (heel) which is economically achievable. After desorption it is necessary to dry and cool the hot and moist bed. Drying is carried out with hot air that is followed by cooling with ambient air.

Appendix 3.4.2 Operating Cost, Data and Process Status

Operating conditions Operating costs Process Status 4kg of steam typically leaves sufficient The main cost of VOC on the carbon to provide measurable

This process is operation is the widely available and

levels of VOCs’ in the exhaust gas. steam required for well known. Typical level of VOC in exhaust gas - 20 to desorption. 80 mg/m3 (depending on organic). 4kg steam per kg of Due to the asymptotic nature of the organic recovered. relationship between steam used and The typical life of residual VOC in the carbon. Achieving VOC the carbon bed is levels below the typical requires five to eight years. significantly more steam to the point that it is economically unviable.

Appendix 3.4.3 Process Problems

The main problems associated with carbon adsorption are listed below:

l The presence of fine particulate carbon in the exhaust stream may give rise to emission problems

l A larg‘e amount of steam may have to be used to ensure low VOC levels in the exhaust stream during the desorption cycle

l There is a significant fire risk associated with ketones, aldehydes and high concentrations of benzene

l It is possible that the carbon may be contaminated by particulates, entrained liquids, high boiling point organics and sulphur compounds

l Lower molecular weight organics tend to be displaced by the higher molecular weight organics in mixed organic systems

l There is a risk of contaminating water during steam stripping

l Polymerisation may occur on the adsorbent

Appendix 3.5 Overview of Absorption Systems

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Absorption is the physical transfer of a solute (the organic) from one phase (air) into solution in another liquid phase (water/oil). It differs from adsorption as molecules of the solute are dissolved into the second phase and may often be chemically changed.

The pollutants are absorbed to the point at which the vapour pressure of the pollutant in the liquid produces a concentration of pollutant just above the liquid surface that matches the concentration of pollutant in the gas phase. This is known as the equilibrium mixture and in practice the concentration in the liquid phase is always slightly lower than this.

The main method for achieving this physical transfer is the gas/liquid contactor. With the solute transferring from the gas phase to the liquid, the contactor is described as a scrubber. For transfer from the liquid phase to the gas phase, desorption, the contactor is referred to as a stripper.

Contactors are defined by mechanical type and scrubbing media, although the medium and duty of the contactor effectively fix the mechanical design. Subsequently the contactors are grouped by scrubbing media and only important mechanical design details mentioned.

Appendix 3.5.1 Aqueous Scrubbers

These use water to remove the pollutants from the air stream. They tend to be limited to the removal of dust and water soluble compounds.

Appendix 3.52 Chemkal Scrubbers

These operate in the same manner as a water scrubber, but as the pollutants enter the liquid phase they are chemically converted into another compound. This prevents the pollutant from exerting its true vapour pressure and allows more pollutant to be absorbed into each unit volume of solution.

This chemical conversion and the slight solubility of all organics in water, allows relatively insoluble compounds to be absorbed at levels far beyond their normal level. For organics, the chemical systems are normally aimed at converting the organic into water soluble alcohols, or to directly oxidise it to carbon dioxide and water. Typical chemical systems for oxidation are hydrogen peroxide solutions (plus a soluble catalyst), hypochlorite solutions, or a mixture of ozone (generated in- situ) and UV light (shining into scrubber sump).

The main disadvantage of this type of system is that they are not suited to a large throughput of organic. The chemical destruction of the organics takes a significant period of time. This leads to large volume sumps to provide sufficient residence time and large volumes of media

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to hold the organic in solution. The end result is that the systems are more suited to dilute 500mg/m3 or less organic concentrations or odour control problems.

Appendix 3.5.3 Biological Scrubbers

These are a derivative of a chemical scrubbing system. The primary difference is that the chemical scrubbing medium is replaced by a biological system which “feeds” on the dissolved organics. The biological systems can be retained on open matrices (large pore plastic sponges), or may be freely suspended in the scrubbing medium. Additional feeds of salts, nutrients and pH control chemicals would be required.

An example of a typical fixed matrix biological scrubber is a Peat Bed Scrubber (see figure 6). The process air is drawn into the top of a closed unit and then down through a bank of mist sprays. This cools and humidifies the air to conditions that the biomass will find acceptable. If the inlet air is too hot additional cooling may be required. The gas passes through the wet peat (often synthetic) where the gas to

water transfer of the organic takes place.

Due to the low efficiency of the transfer, the gas flowrate through the bed is low and the beds are very large in comparison with a typical chemical scrubber. The biological species in the bed use the organics as a food source. The clean air exits the bottom of the bed and is exhausted locally. The water flowing down the bed falls into a sump and is re-circulated back to the top of the bed. Nutrients are added to the re-circulated water and excess scrubbing medium is bled off.

The main disadvantage of this type of system is that they are not suited to a large throughput of “food”. The organics are assimilated into the biomass cellular structure and the process, being natural, takes a significant period of time. This leads to large volume sumps to provide sufficient residence time and large volumes of media to hold the organic in solution. The end result is that the biological systems are more suited to dilute 500mg/m3 or less organic concentrations or odour control problems.

Appendix 3.5.3.1 Process Status

Water scrubbers used to remove water soluble organics only are widely available in many designs. However, units specifically designed for the removal of non-soluble VOCs are rare. Only one UV/Ozone unit is known to exist in the UK and it is at a pilot plant stage. Chemical and biological scrubbers for low level VOCs exist but their effectiveness and operability at high VOC levels are relatively unknown.

Appendix 3.5.3.2 Process Problems

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. Not effective for high level non water soluble organics.

l Low mass transfer rates for no water soluble material require large packed beds.

l Certain organics such as phenols and halogenated compounds adversely affect biological systems.

l Aqueous phase destruction of organics requires significant amounts of energy and/or additional chemicals.

l Organics that are water soluble tend to produce large volumes of contaminated waste water.

Appendix 3.5.4 Glycol and Oil Scrubbers

Appendix 3.5.4.1 Process Description

Changing the liquid scrubbing medium from water to an organic is a very effective method of VOC control. Removal efficiencies in the region of 99.7%+ are not uncommon. Oil scrubbers are still subject to equilibrium constraints but the solubility’s of organics are higher. This higher solubility allows a higher concentration in the liquid phase and hence a lower volume of oil is required.

After absorption the oil is usually passed directly to a steam stripper, where live steam is used to desorb the organic from the oil. The steam organic mix is then condensed and the water/organic mixture gravity separated.

The efficiency of the stripping operation, the volatility of the oil, the solubility of the organic in water all effect the design and operation of oil scrubbers. If the stripping efficiency is low, the off-gas concentration of VOC will be high.

High volatility oils, such as the commonly used kerosene fractions, will replace the original VOC contamination with the organics contained in the oil.

Glycol scrubbers operate in a similar manner to oil scrubbers, but by using a low volatility glycol the contamination of the air leaving the scrubber is reduced to acceptable levels. Typically concentrations of 1 to 2 mg/m3 of glycols in the stripped air stream are obtained.

If the VOC is partially soluble in water the condensate will require treatment prior to discharge. In the cases where the organic is totally

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soluble in water, the organic will require distillation to separate organic carried over from the steam stripping column.

One alternative to this stripping operation is to absorb the organic in a low volatility oil and then send the oil to a boiler. This is only effective for facilities with large oil fired boilers and small VOC streams.


Available as a custom designed plant with process guarantees.


There are several potential problems associated with this technology which are described below:

l any solid particulates will tend to block the packing in the absorber column;

l the exhaust gas from the column may not be within legal limits, if high volatility oils are used;

* contamination of the solvents with the stripping organic will reduce the value of the solvent recovered;

l secondary water treatment would be required to remove water soluble solvents and the small proportion of partially soluble organics.

0 glycol systems use an alkaline stabiliser and acid ingress into the scrubber must be prevented.

Appendix 3.5.5 Emulsion Scrubber


Emulsion scrubbing overcomes the problems encountered in aqueous and oil media scrubbing by the use of an oil dispersed in water.

The organic is absorbed from the gas phase into the water phase in the same manner as in aqueous scrubbing. The organic is then absorbed into the oil dispersed in the water. This allows the water to absorb more organic and even the slightly water soluble organics are absorbed. The oil/water organic distribution mechanism differs from the water/gas equilibrium in that the oil can hold higher concentrations of organic than those present in the aqueous phase. This allows a volume of emulsion to hold far more organic than a water or oil based system.

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The emulsion also prevents recontamination of the air stream by the oil as the oil has no free gas/oil surface.

The oil is separated from the emulsion and stripped of the organic. The efficiency of the stripping can be lowered to prevent contamination of the organic by the oil. The oil can then be re-emulsified and returned to the scrubber without any efficiency decrease as the level of organic in the oil is not the controlling factor.

The absorber illustrated operates in the following manner. VOC laden air is drawn through the primary filter to remove any particulate. It is mixed with the emulsion in a swirl chamber where the gas/liquid transfer occurs. The emulsion is then disentrained in an impingement filter and droplet collection zone. The air passes through a final filter to remove any droplets prior to entering the fan from which the air is ejected to atmosphere.

Quoted efficiencies of 95 to 99.5% are given and typical duties include VOC control from paint spraying. The units come in 5 sizes - 3,000; 4,000; 6,000; 8,000; and 10,000 m3/hr throughput, and require a distillation unit if the vegetable oil used is to be separated from the organic for re-use.


Only one manufacturer of emulsion scrubbers has been identified. Nine units have been constructed, four are in manufacture. The longest operating life of installed plant has been 18 months as of February 1992. Visual inspection of the equipment showed significant short falls in the engineered quality and indications from the manufacturer are that the process requires individual blending of oil mixes for each application.


Short oil life; due to its high biodegradability the oil becomes rancid;

Reclaim of the oil requires a secondary unit;

Oil blends are required for differing VOC types;

Dust and particulate require removal prior to entering the unit to prevent the emulsion becoming contaminated with solids.

Appendix 3.6 Overview of Condensation

Ambient condensation is the most commonly used technique for removing high concentration VOC streams. The process is carried out

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by removing the heat of condensation to cool the organics to below their dew point.

Cryogenic systems, which use more energy, have the advantage that they can handle much more dilute streams. There are various configurations available for each of the systems, each of which will be discussed in more detail in the following sections.

Appendix 3.6.1 Ambient Indirect Contact

Appendix 3.6.1 .I Process Description

Ambient Indirect Contact is the most commonly used method of organic recovery. VOC laden gas, typically well above the upper flammable limit, often with steam as the primary constituent, and occasionally an inert gas, is passed over a bank of heat exchangers operating at between -2X to 30 “C. The organics, and water, condense out and are collected. The exhaust gas is then vented.


The vapour pressure of most solvents at ambient conditions ensures that their exit concentrations are well above regulatory guidance discharge concentrations.

If cold brine is used ice formation on the heat exchanger tubes can prevent the system operating at temperatures near to zero. Additionally a significant proportion, up to 90%+, of the energy removed during cooling of the gas stream is used to remove the latent and sensible heat content of the water vapour.

Appendix 3.6.2 Ambient Direct Contact


The cheapest option available for the removal of VOC laden air is to use a spray condenser which injects cooling water directly into the vapour stream. The organics and water condense and are collected. The exhaust gas is then vented to atmosphere.

Appendix 3.6.2.2 Process Limitation

As discussed in the previous section the main problem with this type of system is that the exhaust gas is still well above the concentration .guidance limit for VOCs.

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As the gas is cooled by direct liquid contact it will be necessary to further treat the liquid stream. If the solvent is insoluble in water then this will be achieved by gravity separation. However, if the solvent is soluble then this contaminated stream will need to be treated. If it is economic to recover the stream then a fractionation system will be needed.

Appendix 3.6.3 Cryogenic Indirect Contact


A typical cryogenic indirect unit is described below. Alternative types of this design are available but all are based on the same basic technique and have similar drawbacks.

The VOC laden gas enters the first heat exchanger where an air blast cooler is used to remove the bulk of the heat from the gas stream. The gas then enters a second heat exchanger that is cooled to approximately -20%. It then enters a cryogenic heat exchanger where it is cooled to approximately -40%. As the gas cools, the VOC saturates the gas and condenses onto the heat exchange surface. The gas then flows back into the second heat exchanger and cools the incoming gas prior to being recycled or vented.

Liquid nitrogen is used to cool the cryogenic heat exchanger and the gas evaporated from this is fed into the inert gas stream. The liquids that condense in the heat exchangers are collected and pumped out to storage.


Cryogenic indirect systems are typically used if water vapour is not present in the VOC laden gas and the gas is to be recycled back to the process or further treated. Typically, the source of the cryogenic gas feed is an inert gas supply system.

If water is present cycling the heat exchangers to above 4 “C so that ice can be melted from the heat exchange surfaces is possible. The thawing cycle requires multiple exchangers to be used in parallel and as the ice melts it tends to drop into the base of the exchanger. This can block the drain lines and tends to increase the period required to clear the exchanger of solvent laden ice/water. Heating the shell of the exchanger prevents this but adds significantly to the unit cost of the exchanger. Additionally the heat exchange surfaces have to be significantly enlarged to allow for the decrease in heat transfer caused by the layers of ice that form.


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This system is primarily used in printing and coating where the drying ovens, for organ& only, are inerted and gas and solvent recycling are economically practical. Any water ingress into this system would block it and particulate would foul the heat exchange surfaces.

Water laden gas streams can be treated but at increased capital cost and significant operational increase. The off-gas concentration from these units will also be significantly above the VOC control limits.

Appendix 3.6.4 Cryogenic Direct Contact


There are three main types of direct contact cryogenic units:

liquid gas/coolant spray systems; cleaned metal surface; liquid bed.

Liquid spray systems use a quench tower approach to VOC removal by spraying the cryogenic medium into the gas stream. They achieve rapid removal of organics, but require the cryogenic liquid to be pumped. Ice formation within the units also occurs and thawing cycles are often required.

Scraping or abrading the heat transfer surface to remove ice build-up is a common method of removing the requirement for thawing cycles. Designs similar to scraped wall condenser designs are commonly used for this application and allowances are made for the removal of ice and solids.

Throughputs are low for this type of unit due to the restricted heat transfer area.

An alternative method of surface cleaning is to place chilled metal objects (i.e. bars) at cryogenic temperatures into a rotating barrel through which the gas passes. As ice forms, it is removed by the abrasion between surfaces and allowed to drop out of the barrel. The metal objects are periodically chilled by gas at cryogenic temperatures. This design requires significant mechanical detail in the equipment seals and chilling systems.

Another more novel approach employs a column packed with steel spheres which are circulated by removing them from the bottom of the column and returning them to the top via a bucket elevator. The spheres are cryogenically cooled at the top of the column by either direct or indirect contact with liquid nitrogen. The VOC laden gas stream is introduced at the base of the column where most of the vapour

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condenses, the remainder desublimates out towards the colder top of the column. As the spheres convey to the warmer condensation zone of the system the ice melts and drips down, together with the accumulated condensate, through the perforated base. After the spheres leave the base of the column they are dried before being returned to the top.

The final system is the direct contact fluid bed system, and a description of a commercially available unit follows;

VOC laden gas is initially cooled to a pre-set temperature. This cooling is done as an economy measure and may be omitted. The vapour stream then passes into the bottom of the chiller where it flows up through liquid organic and is cooled typically to -40%. The system then vents via the economizer heat exchanger. In the chiller, the organics are condensed and separated, any water is converted to ice and low melting point organics solidify. The chilled organics leave via the overflow and are collected in a water/organic separator. Solids are flushed out of the bottom of the chiller periodically into the same separator (or an alternate unit if the solvent is to be kept water free). In the separators the solvent is returned to store and the water sent for final treatment.

The solvent in the chiller is kept at -40% by a refrigeration unit and therefore does not require liquid gases for its operation.

Appendix 3.6.4.2 Process Application

This system overcomes the problems of ice and liquid gas use for processes with small gas flows (less that 1,000 m3/hr).


Water laden gas streams can be treated but at increased capital cost and significant operational cost increase. Theoretically the off-gas concentration from these units will meet tight emission limits as removal efficiencies can be optimised by lowering the outlet temperature.

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APPENDIX 4 P&IDS for VENT HEADER and ABATEMENT SYSTEMS

BPC Plant

E3432-53-2102-A-i Proposed Special Scrubber Systems E3432-53-2103-Al HSI & HS2 (Halar) Vent Headers E3432-53-2104-Al SSl & SS2 (Stainless) Vent Headers

Nitration Plant

E3432 -53-2101 -Al Scrubber System of Nitration Plant (Under Revision)

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schwarz - environmental protection agency · concentrations however the mass of salt discharged to...

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