Control of air pollution has been identified popularly as the reduction of sulphur dioxide, Nitrogen Oxide and particulate matter. Regulating agencies and industries have well defined limits for emissions and control of these pollutants. However, air pollutants such as volatile organic compounds, organic and inorganic odorous compounds have so far not been regulated by Pollution Boards in India. Attention to the control of these pollutants has been meagre or non-existent by the industry.
Volatile Organic Compounds (VOCS):
Volatile organic matter, particulate matter and nitrogen oxides react in presence of ultra violet light to produce a haze of chemicals and result in an increase of the ground level concentration of ozone. Exposure to ozone is hazardous to mankind and it can cause chest pain, cough, bronchitis, emphysema and asthma. The environmental protection agency (EPA) in the USA imposes an air quality standard of 0.08 ppm of ozone measured over 8 hours.
ADVERTISEMENTS:
Europe, USA and Japan are introducing regulations and controls to limit all pollutants including VOCs and Ozone. Odours caused mostly by volatile organic compounds such as amines, sulphides and others are also being regulated. For the gasoline industry, European community is limiting VOC emissions to 35 grams TOC (total organic carbon) per m3 of gasoline loaded. In the USA, this limit is 10 g/m3 of VOCs. In the absence of limits for VOCs, it is estimated that 2,31,000 tons of gasoline will be emitted by the gasoline distribution industry alone in USA.
Similarly 12,000 tpa of organic compounds will be emitted by the US. Petrochemical industry in the absence of VOC control. Besides the petroleum and petrochemical industries, volatile organic carbon emissions are to be regulated and controlled in plastics, rubber chemicals, electronics and printing industries.
In addition to an increase in the overall pollution loads, volatile organic compounds can cause acute discomfort and nuisance due to odours. Industries such as distilleries, paper and pulp, asphalt, paints, printing/film industry, food processing and waste-water treatment plants emit odours.
Compounds containing amines, sulphides, aldehydes, mercaptans, ketones and hydrogen sulphide gas cause odours which can be beyond the threshold limits for the surrounding population. Fragrance and flavours of flower and sweet industries may have pleasant odours but they can be a source of discomfort and air pollution for the neighbourhood if they are constantly exposed.
In European countries, several flowers and fruit processing plants have installed odour removal units. The odour threshold limits for concentration of H2S and some organic compounds in air are given in Table 10.1.
This is only a short list and several other examples can be given for compounds which originate from chemical and food processing industries and cause strong odours. Unfortunately, no legislation or regulation exists in most countries.
Odour removal plants have been put up by a few industries in Europe, USA and Japan only in response to objections by the surrounding population.
Technology for Removal of VOCs and Odour:
Both VOCs and odours can be controlled by technologies which are well known and can be selected on the basis of suitability and cost. It is, however, essential to characterise the emission by the flow rate of contaminated air, the concentration and nature of VOCs and odour causing compounds.
ADVERTISEMENTS:
Some of the technologies for their control are listed below:
1. Biological oxidation.
2. Absorption with chemical reaction.
3. Absorption and desorption.
ADVERTISEMENTS:
4. Thermal oxidation-regenerative or recuperative.
5. Catalytic oxidation-regenerative or recuperative.
Here biological oxidation and regenerative catalytic oxidation will be discussed.
Biological Oxidation or Biofiltration:
Biological oxidation or biofiltration has been successfully applied in Europe for the control of odours and volatile organic carbon emissions. In this process, the air containing VOCs is passed through a chamber which is humidified by water (Fig. 10.1). It is led to the top of a biofilter which consists of a bed of active material. The biological oxidation is carried out by active organisms which are present on the surface of compost material. Compost or biofilm is supported on a packing material such as rings or saddles made of plastic.
The down flow fixed film reactor can achieve 95-99 per cent removal of VOCs and odorous compounds. Flows of 15,000 m3/hr. and 3,000-5,000 mg/m3 of VOC load can be handled at room temperature.
The biological bed requires small amounts of chemical nutrients and has to be kept wet by sprinkling water over it. A typical bed or biofilter has a life of 3 to 5 years.
There are currently more than 500 biofilters operating in USA and Europe for VOC removal. They have the advantage of low operating costs. Products of oxidation are water, carbon dioxide and a small quantity of liquid effluent which contains no hazardous material. Control of moisture in the bed by an automatic control system avoids dry out of bed which can kill the bioactive organisms.
Biofiltration is an attractive technology for economically removing biodegradable organic compounds from air. Relative biodegradability of various VOCs is given in Table 10.2.
Flow sheet of Monsanto’s Dynazyme process including a biofilter is shown in Fig. 10.1. It consists of a bed of proprietary support material durafil for the compost, and moisture control system. Residence time depends on the type of VOCs and is usually in the range of 15-90 seconds. Moisture content in the bed is kept in the range 40-60 per cent and the bed temperature is 20-35°C. pH of the liquid drain is controlled by addition of nutrients.
Biofilters are widely used for removal of odorous compounds from air. In Europe, particularly Holland, they are also used to remove fragrance from exhaust air. Applications are found in food industries such as coffee, sweets and chocolates and in flavour and fragrance industries.
The filter for fragrance removal consists of a polymer or active carbon support on which a film of special bio-seed material with enzyme is grown. The bed has a life of 4-5 years and can be reactivated by fresh inoculation of active material.
Odours can also be removed by chemical reaction of Mercaptans and H2S with alkaline sodium hypochlorite solution. ICI, UK markets a specially designed odourgard process in which a small quantity of catalyst is used to enhance the rate of removal of H2S by scrubbing the solution of hypochlorite. There are 30 odourgard installations working in various food processing, chemical and sewage treatment plants.
1. Typical example of a simple Biofilter plant-St. Louis, Lemay Plant, 3500 cfm, inlet 10-200 ppm H2S/mercaptan, outlet-less than 1 ppm.
2. Typical example of an odourgard plant – Bridlington POTW, 24,000 m3/hr, inlet 70 ppm organic sulphides, outlet 0.3 ppm.
Biological oxidation cannot be applied to VOCs which are not easily bio-degradable and when concentrations of VOCs are high. Absorption and desorption can be applied in special cases depending on the nature of the VOC, suitability of the absorbent material and reclaim value of the VOC material. The most widely applicable method of VOC removal is oxidation which essentially destroys the VOCs whose cost of recovery is prohibitively high.
Two alternatives for oxidation are:
Heat is added to gas stream to incinerate or burn VOCs present. The gases have to be heated to a temperature of about 800°C for 0.5 to 1 second.
Oxidation of VOCs is carried out in the presence of a catalyst. The activation energy is lower than that for thermal oxidation and the reaction takes place at 200°-500°C with residence times of 0.2 to 1 second.
Several variations of the above processes such as recuperative or regenerative thermal or catalytic oxidation processes have been practiced for removal of VOCs. Regenerative catalytic oxidation has the advantage of recovering the sensible heat of gases leaving the catalyst bed for preheating of inlet gas. They can attain high destruction efficiency of 99 per cent for VOCs and high thermal efficiency of 90-95 per cent. The fuel required to achieve the destruction of VOCs is minimum for regenerative catalytic oxidation.
The catalysts used for oxidation of VOCs are Platinum group metals or base metal oxide catalysts. The Platinum group metals are expensive but are compact and offer lower pressure drops. Base metal oxide catalysts (Fe, Cr, Mn) in pellet form are less expensive and can be designed for a wide range of flow rates and pressure drops.
Ease of oxidation varies from methane which is most difficult to oxidise to oxygenates which are easily oxidised as per Table 10.3.
Regenerative Catalytic Oxidation of VOCs:
Regenerative catalytic oxidation consists of a bed of base metal oxide catalyst pellets with a layer of ceramic media below and a second ceramic layer above the bed. The ceramic beds act as heat sink and trap the sensible heat available in the gases after the combustion of VOCs and fuel if used. This heat is transferred to cold inlet gases containing VOCs to preheat them to the reaction temperature prior to the oxidation of VOCs in the catalyst bed.
A typical design of Regenerative Catalytic Oxidation system is shown in Fig. 10.2. This is the Dynacycle system offered by Monsanto Enviro-Chem Systems, USA, in which there are two chambers each consisting of a catalyst bed and two ceramic layers. In a typical cycle, air with VOCs enters the bottom ceramic layer which has been heated in a previous cycle. When it reaches the catalyst layer, both the air and catalyst are at the reaction temperature required for oxidation.
The temperature of the catalyst bed and that of exit gases increase and the gas temperature falls as the gases flow through the second ceramic layer which has been cooled by loss of sensible heat in the previous cycle. The exit gas temperature reduces and the temperature of the second ceramic layer increases as a result of heat transfer. After a specified interval of time, the entire flow is reversed by opening and closing of valves and the same cycle repeats with the air entering the second ceramic layer in the reverse direction.
The concept and plant design of this unsteady state catalysis were first developed by Prof. Yuri Matros at the Institute of catalysis in Novosibirsk. This was commercialised by Monsanto in collaboration with Prof. Matros in USA and has now been applied extensively for the regenerative catalytic oxidation of VOCs. The flow diagram in Fig. 10.2 shows two chambers but the basic principle employed is the same and with two chambers the flow reversal is achieved smoothly without any significant discontinuity. Typical interval for reversal of flow is 5 to 10 minutes.
There are several operating installations of regenerative catalytic oxidiser based on the design developed originally by Prof. Matros. These units are known as Dynacycle owing to the cyclic nature and periodic reversal of flow directions. Capacities range from 800 to 80,000 m3/hr, and VOCs such as C4 – C8 alcohol, aldehyde, toluene, styrene, MEK, mineral oil, etc. are removed effectively. The regenerative catalytic oxidiser handles a flow rate turn down of 10:1 and changing VOC concentrations of 1 ppm to 5000 ppm efficiently.
Care must be taken to avoid use of catalytic oxidisers for air streams containing phosphorus, heavy metals and silica which may act as poison for catalysts. The VOC concentration should be lower than that which will generate a continuous flame. VOCs should be at a concentration level that will provide heat for raising air to the catalyst activation temperature. If the concentration is too low, small amounts of fuel may be needed for achieving the reaction temperature of 200° – 500°C. Dynacycle units have been successfully used in aluminium rolling mills, electronics and magnetic tape manufacturing units, plastics and plasticiser industries, spray painting/drying shops and phenol/acetone plants.
Thus, the technology for controlling emission of hazardous VOCs and odour causing compounds is now developed and available to industries in India. There is a need to introduce proper legislation, regulations and awareness amongst the industries to apply the most appropriate technology to tackle the problems of VOC and odour.
The implementation of the available proven technologies will improve the environment and benefit the population and industries.
Advanced Scrubber Technology Solutions for Pollution Control:
In the wake of stringent pollution control regulations, scrubbers have come a long way in effectively reducing gaseous industrial emissions. Different models of wet gas scrubbers which use circulating liquid to absorb acid vapours, are available for cleaning the flue gas. It gives an insight on different types of wet gas scrubbers and their mechanism of action together with the factors that impact the performance of the scrubbers.
Throughout the world, more and more stringent air pollution regulations require industrial and utility operations to install pollution control equipment with better efficiencies. In many cases, scrubber technology can, and should, be used.
In the past, scrubbers have been used to perform three basic operations:
1. To quench the flue gas down to its adiabatic saturation temperature.
2. To absorb acid gas emissions.
3. To remove particulate material.
In many cases, the scrubber is required to handle not just one, but two, or even three of these functions in one unit. While scrubber technology has been around for many years, changes have been made to the auxiliary equipment surrounding the unit, so that the scrubber is more effective and more reliable. In addition, costs associated with various reagents and disposal of the scrubber effluent, requires that the plant operator investigates all possible options to ensure that the scrubber unit selected meets the overall air emission requirements, while being economical to operate, and be reliable in its performance.
Finally, the plant operator must ensure that solving one environmental issue does not lead to other problems.
There are many types and models of wet gas scrubbers in the marketplace. Basically, all have a section where liquid, (typically water), is contacted with the incoming flue gas. All scrubbers have a method for removing the water droplets from the gas before it leaves the scrubber. How the liquid is introduced, and how droplets are removed vary from one model to another. When water is mixed with a hot gas that is not saturated, adiabatic saturation occurs, and the gas is ‘quenched’. Depending upon particle size and pressure drop, a percentage of the particulate matter in the flue gas will collide with the water droplets.
Finally, acid gases are absorbed in the scrubbing liquid, where it can be reacted with a chemical reagent (Fig. 10.3).
Requirements for Acid Gas Removal:
One of the most common reasons for use of a wet scrubber is for acid gas removal. Depending upon the upstream process, different acid gases can be present in the flue gas as vapours. Typical acid gases include SO2, HCl and HF, though there could be many other gases.
The amount of the acid vapour that can be removed from the flue gas is a function of:
1. Process parameters of the mass transfer device.
2. Kinetics of the reagent.
3. Characteristics of the effluent.
Wet gas scrubbers use circulating liquid to contact the flue gas and absorb the acid vapours into the liquid stream. The amount of circulating liquid is a key process parameter for wet scrubbers. Generally referred to in terms of L/G (liquid to gas ratio; gpm/1000 acfm), the amount of circulating liquid must be enough to fully quench the gas and absorb the appropriate amount of acid vapours from the gas stream.
There are a number of different designs of wet gas scrubbers that are used for acid gas absorption. The type of device may limit which reagent can be used. This will affect the total L/G ratio, which will have a direct impact on operating power. Some examples of the various types of units include packed towers, spray towers and froth scrubbers.
1. Packed Tower:
Packed tower is an efficient mass transfer device requiring relatively low L/G ratios. However, both the reagent and the resultant salts formed must be soluble, as otherwise, the packed tower is susceptible to pluggage. In addition, packed columns are not effective at removal of particulates from the gas stream since gas side pressure drop is typically very low.
2. Spray Towers:
Spray towers generally have the highest L/G ratios for a particular application, but can use liquids with either suspended or dissolved solids. Again, spray towers can only operate at low-pressure drop. They are therefore not very effective at removal of particulate from the gas stream.
3. Venturi Scrubbers:
Venturi scribbers are effective for particulate removal, but are not that good as a mass transfer device.
4. Reverse Jet Froth Scrubbing Technology:
Reverse jet froth scrubbing technology of MECS Dyna wave can handle a liquid with both dissolved and suspended solids. In addition, L/G ratios are modest, and the gas side pressure drop can be varied. This allows this unit to handle both acid gas emissions and particulate with the same device.
Simple kinetics of chemical reactions can affect the amount of acid gas vapours that will be absorbed in a scrubbing device. Once the acid gas vapour is absorbed into the liquid, acid is formed, decreasing the pH of the circulating liquid. Lower pH tends to inhibit further acid vapour absorption. To overcome this, reagents are added to the circulating liquid to react with the acid in solution, maintaining an acceptable pH range for further vapour absorption. Figure 10.4 indicates the effects of reagent and L/G selection on SO2 removal efficiency. There are numerous reagents that can be used, including caustic, limestone and magnesium oxide.
Typical Reactions when Absorbing SO2:
Using Caustic as the reagent, it is soluble and the salt products formed are also soluble.
The absorption of SO2 with caustic is the easiest method of removing SO2 from the flue gas. The acid-base reaction is fast and the equipment required is minimal. However, the caustic reagent is the most costly and the resulting by-product, soluble sodium sulphite/bisulphite can be a potential disposal problem. The sulphite/bisulphite composition depends upon operating pH. Higher pH shifts the salt formation to sulphites.
In the case of limestone as the reagent, which is insoluble, the salts formed are also insoluble.
Limestone is probably the most commonly used reagent for reaction with SO2. In addition, the salt formed is insoluble which means that it can be filtered from the liquid and then disposed off in solid form. This system does have higher capital cost. Reagent preparation, and vacuum filtration equipment add significantly to the overall project costs. However, for very large flue gas flows, these costs are quickly offset by the lower operating costs. Limestone is also considerably less reactive than most other reagents.
A third possible reagent is magnesium oxide. The reagent slurry used is magnesium hydroxide, which is insoluble. However, the reaction product is soluble. Overall reactions are –
MgO has the disadvantage of requiring expensive equipment for reagent preparation. It also has the disadvantage of forming a soluble salt, which may cause disposal concerns. As for reactivity, MgO is more reactive than limestone, but less so than caustic. Cost of the reagent makes it less expensive than caustic, but more than limestone.
Some other reagents used for reaction with the absorbed SO2 are lime, zinc oxide, soda ash, and ammonia. Usually, unique site conditions dictate the use of these reagents.
Typical Reactions when Absorbing HCl:
Another very common acid gas vapour requiring emission controls is HCI.
Typical Reactions when Absorbing HF:
The third acid gas vapour that is encountered frequently is hydrogen fluoride.
Reagents Use-Economics:
In listing of some typical reactions, there are numerous options, when selecting a reagent. As is usually the case, the economics of the situation dictates which reagent is most attractive for a particular application.
In general, for small gas flow rates where minimal amount of reagent is required, caustic is usually favoured. For large gas flow rates where large amounts of reagent is needed, then limestone is usually favoured.
Caustic is considerably more expensive than limestone. While prices vary for different geographical regions. When significant amounts are going to be used, operating costs favour using limestone. However, limestone has the burden of requiring more expensive material handling equipment upstream of the scrubber. For small applications, the savings in capital cost of not needing this, additional equipment when using caustic, easily offsets the higher operating costs.
Cost for handling the effluent will also be different depending upon which reagent is selected. For each application, the end-user should work closely with his equipment supplier to determine which type of system provides the overall best total cost.
The reaction products formed can also impact the overall design of the scrubber system, impacting both the capital and operating costs. As is obvious from the data listed above, one of the key differences is whether the salts formed are insoluble or soluble. Insoluble salts mean that the circulated liquid in the scrubber will be slurry with suspended solids. This can be a disadvantage for some of the scrubbers available for use.
Packed Columns:
Packed columns do not handle suspended solid slurries, and can become plugged very easily. Spray tower can handle limited slurries, provided that the concentration of solids do not become too high. However, because spray towers use numerous spray headers, and hundreds of spray nozzles, they can become prone to erosion if salt concentration becomes high.
Venturi Scrubbers:
Venturi scrubbers can handle medium amounts of dissolved and suspended solids. They have only limited piping which is essential for slurry piping. However, they do have the drawback of medium pressure drop through the nozzle which limits the total percentage of solids.
Reverse Jet Froth Scrubbers:
Reverse jet froth scrubbers with only very few, low pressure nozzles and minimal vessel internals can handle high solids concentrations and minimise the total effluent stream.
Insoluble salt products can minimise disposal costs and water consumption. The insoluble salt products can usually be filtered with vacuum filtration equipment. Much, if not all, of the recovered water can be sent back to the scrubber. The resulting dried, solid products can be disposed off in a landfill.
Soluble salts are easier to handle in the scrubber, since they are in solution, and thus do not tend to either erode, or plug, certain type of scrubber units. However, disposal means that a liquid effluent stream with the dissolved salts must be discharged. In some cases, local sewer systems, or deep well injections can handle this liquid. However, if neither of these options is available, then disposal costs become much higher.
Fundamental Principles for Particulate Removal:
Another basic operation that scrubbers are called on to deal with is the removal of particulate from the flue gas. Removal of particulates requires energy, in the form of gas side pressure drop.
Two fundamental principles govern the amount of particulate that can be removed:
1. Particle size distribution of the catalyst fines (PSD).
2. Gas side pressure drop utilised by the scrubber.
In order to predict a particulate efficiency for a given application, the particle size distribution of the particulates is required. At a given pressure drop, the removal of particulate at each size range varies. The smaller the particulates, the less is removed. Particulates less than 1 micron in size are especially difficult to remove. Therefore, high removal efficiencies of small PSDs require high pressure drops. Assuming a particle size distribution as given in Table 10.4, a curve (Fig. 10.5) can be created that relates the expected particle removal efficiency with gas side pressure drop.
As can be clearly seen from the examples above, for effective particulate removal, the scrubber must be capable of sufficient gas side pressure drop.
Venturi Scrubbers:
Venturi scrubbers are very effective in this respect, and if only particulate removal is required, they are very often the type of scrubber chosen.
Packed Columns and Spray Towers:
Packed columns and spray towers are very low pressure drop, devices. As such, they are not used as a primary means for particulate removal.
Reverse Jet Froth Scrubbers:
Reverse jet froth scrubbers can be designed for either low or high, gas side pressure drop. For applications requiring particulate removal and acid gas absorption, they are the ideal choice for a single scrubber that can handle both issues.
Distinction of SO3 Removal Mechanism:
Opacity from a flue gas source is often regulated, and requirements can vary. Opacity is caused by the diffraction of light waves by small particles of solid or mist. Particles having a diameter between 0.3 and 0.6 microns cause the greatest diffraction of light, since their size is closest to the wavelength of visible light. SO3 hydrolyses to form sulphuric acid mist, H2SO4 as it is cooled in the presence of water vapour. The mist formed is a very fine submicron liquid droplet (∼0.4 microns) and is thus a major contributor to opacity.
For a liquid droplet, the removal mechanism is not an absorption phenomenon, but rather by mechanical means similar to that required for solid particulate matter. This mechanism remains the same for any wet scrubber and makes SO3 much more difficult to remove than SO2. In wet gas scrubbers, particulate matter (solid or liquid) requires energy to be imparted on the gas stream to capture the particulates by means of inertial impaction. This energy is usually measured in the form of gas side pressure drop.
The smaller the size of the particulate, the more energy (higher pressure drop) must be imparted to capture the particulate. Figure 10.6 reflects approximate removal efficiencies of a scrubbing device using inertial impaction for removal of SO3 (H2SO4 mist) at different gas side pressure drops.
Both venturi scrubbers, and froth scrubbers such as the MECS Dyna Wave, can be designed for the proper gas side pressure drop. Packed columns and spray towers are low pressure drop units, and as such cannot remove significant amounts of SO3. It should be mentioned that SO3 and particulates can also be removed by wet electrostatic precipitators (WESPs). These devices are very efficient in removing submicron particulates but can be capital intensive. However, if the acid gas scrubber is a packed column or spray tower, then a device such as a WESP is almost always required if SO3 is a concern.
Achieving Effluent Requirement Norms:
Depending upon the acid gas being removed and the reagent used, either a soluble or insoluble salt is formed. The soluble salts must be discharged from the scrubber to prevent build up. When discharged, they can be sent to either the plant waste-water system, to an evaporation pond, or to deep well injection. Many waste-water treatment facilities are now restricting the amount of salts that they can handle because of limitations set on their discharge.
Thus, discharge of soluble salts may require the additional cost of either an evaporation pond, or a deep well injection system. Both can add considerably to the cost of the basic scrubber system. For units handling insoluble salts, it is very common to install a vacuum filtration system. Here, the water is removed, and the salts can be disposed off as a solid waste. Usually, most of the water removed can be recycled back to the scrubber.
In either case, if the primary acid gas is SO2, it is very common to oxidise the salts generated. In the case of sodium salts, the sodium sulphite and bisulphites formed have a very high chemical oxygen demand (COD). Discharge of these salts to a waste-water treatment system can very quickly overload the capacity of that system to inject enough oxygen into the liquid. In this case, it is common to oxidise the sulphites in the scrubber sump to the sulphate form.
When limestone is used as the reagent, calcium sulphite is formed in the scrubber. This is an insoluble salt, but due to its structure, is very difficult to filter. Again, the salt can be oxidised to the sulphate form. This salt is also insoluble, but is easily filtered. In both cases, the oxidation of the sulphites to sulphate is required. To handle this, air can be injected into the scrubber sump liquid to oxidise the sulphite to sulphate. This is referred to as in situ oxidation. Likewise, the scrubber effluent can be sent to a separate vessel where air is injected, referred to as ex situ oxidation.
Three main process parameters are required to achieve adequate oxidation:
1. Air/liquid ratio.
2. Residence time.
3. Air dispersion.
All three of these process parameters are required to enhance the oxygen dissolution rate limiting step. The molar ratio of O2:SO2 stoichiometrically is 0.5:1.0. However, forced oxidation systems should run at much higher ratios, a minimum of 1.5:1.0. The amount of time that the liquid spends in the scrubber (based on effluent rate) is known as residence time.
The residence time should be long enough to ensure that the oxidation reaction can take place. This duration of several hours is significant. This has a direct effect on vessel sump sizing. Finally, air dispersion throughout the entire liquid volume is enhanced by small bubble size and mechanical agitation.
Thus scrubbers have been available for many years, and have been used for numerous applications. There are different types of scrubbers available in the market. Today’s environmental requirements are much more stringent than in the past, not only for emissions from the scrubber system, but also for the resulting liquid effluent discharge from the scrubber.
For each application, the scrubber is called on to perform different functions. It is imperative that the end user analyses initial capital cost not only for the scrubber system itself, but also for all the auxiliary equipment required with the scrubber. These capital costs must be balanced against the operating cost of the unit, and the impact the scrubber will have on the operating cost of other downstream equipment, in particular, the waste-water treatment system.
There is now a wealth of experience with the use of scrubber technology. It is particularly important that the end-user works in close collaboration with the technology provider to take advantage of this knowledge, to determine the overall best solution. Looking merely at the initial capital cost of the lowest cost provider may end up being a costly answer.