THE CATALYTIC COMBUSTION A METHOD OF INDUSTRIAL GASES PURIFICATION. Class 18

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1 THE CATALYTIC COMBUSTION A METHOD OF INDUSTRIAL GASES PURIFICATION Class 18 THE ATMOSPHERE POLLUTION: THEIR TYPES AND THE UTILIZATION METHODS. Air pollution is the introduction into the air of: solids, liquids or gases in quantities which can influence in the negative way the human health, climate, fauna and flora, soil, water or cause other damages to the environment. Such definition is given in the : Environmental protection and management Act,effective 1980 January 31 (Dz.U.Nr 3, poz.6). The pollution can be transported by wind what cause its spreading far from the emission sources and environment contamination in unusual places. Therefore, the air protection against pollution is crucial for the prevention of environment degradation. In the late1960s people began to realize that the natural resources cannot be used limitlessly, and also waste cannot be introduced to the environment in the unlimited amounts, especially in case of air pollutants. The measures were taken to limit the pollution emission. These are e.g.: the elimination of technological processes generating a lots of waste, introduction of new technologies which minimize the pollution emission. If it is not possible to reduce the emission at the stage of production, the waste gas must be purified. The types of atmosphere pollution The air is colorless and scentless mixture of gases which surrounds the Earth. Except for the invariable components the atmosphere consist of steam, which rate depends among other things on temperature and of other components which enter the atmosphere as a result of a natural or humans activity. These are e.g. dust, bacteria, plants spores and gases: carbon monoxide, sulfur oxides, hydrogen sulfide, nitrogen oxides, hydrocarbons and other. The air pollutants can be divided according to the physical state: -dust - aerosols - gases Dust consists of the particles with the diameter of more than 100 μm. The dust composition may vary with respect to the emission source. In cities, there is a lot of soot. These are the carbon particles with a very large surface area and extraordinary adsorptive properties. Therefore, on the soot surface many pollutants hazardous for human are adsorbed, i.e: hydrocarbons, heavy metals salts, nitrogen and sulfur oxides. The dust consists also of mineral particles like: aluminum and silica oxides, cement dust. The industrial dust consists of oxides and other compounds of heavy metals. The atmospheric aerosols are systems of the minute solid and liquid particles suspended in the air. The particle size varies from 0,01 μm to 100 μm [1]. The example of atmospheric aerosol is a fog. The fog occurs naturally in the nature and have nothing in common with air pollution. However, various pollutants, e.g sulfur dioxide or nitrogen oxides can accumulate in fog microdroplets. The other air pollutants are fumes, which are a product of all combustion types. They consist of solid and liquid particles. The liquid particles are in majority hydrocarbons, i.e. 2

2 petrol, oils, tar, while solid ones consist mainly of soot. The tobacco or household chimney smoke is an example of such aerosol. The gaseous pollutants consist of hazardous inorganic and organic compounds, e.g. nitrogen oxides, sulfur oxides, carbon oxide, carbon dioxide (in excess), ozone, hydrocarbons and their derivatives. The sources of gaseous pollutants emission into the atmosphere The air pollution originates from various sources: natural, i.e. biogenic or human-related i.e. anthropogenic. Natural sources: - Volcanoes eruptions - Woods and steppes fires - Decay of biomass - Lightning discharge - Sandstorms The main anthropogenic sources: - Electricity and heat production (Heat and power plants, municipal or household boiler rooms) - Industrial plants - Vehicles - Farms The air pollution in form of dust is the effect mainly of the industrial processes. Also its sources comprise all activities where the friction occurs, e.g.: wearing away of brake linings and tires. The most significant emission source is however the power and fuel industry, including in particular the electric power and heating industry. They produce almost only fly -ashes. The next source is metallurgy of iron and steel. In this case over half of waste is dust. The dust emission into the atmosphere is caused also by a chemical industry, in particular by inorganic one mainly fertilizer factories and by organic one- mainly: plastics factories (major product flue-ashes). Also the building (cement) industry is an unquestionable source of dust. The main source of NO x emission is fuel combustion in the industry, heat and power plants, households and the vehicles engines. When the fuel is combusted the nitrogen oxides may be produced as a result of: - the atmospheric nitrogen oxidation, however their amount depends on the incineration temperature; less nitrogen oxides is to be produced at low temperatures, below 1300 o C - the oxidation of nitrogen compounds occurring in fuel; however nor the type of the nitrogen organic compounds, neither the flame temperature influences the production of nitrogen oxides The considerable part of nitrogen oxides originates from biomass combustion. This however to the great extent is an effect of natural processes (woods fires). The nitrogen oxides are also produced during lightning discharges, volcanic activity and oxidation of ammonia produced during protein decomposition. The primary sources of sulfur dioxide emission are power plants, central heating boilers, 3

3 foundries and chemical industrial plants. The sulfur dioxide is produced during the combustion fuels containing sulfur. The sulfur is remover from the liquid and gaseous fuels prior to burning the fuel, the purification methods are established and have been used for many years. Then, these fuels do not emit SO 2 during combustion. The highest SO 2 emission occurs in case of the coal combustion since its desulfurization is not effective enough. The emission of hydrocarbons and their derivatives vapors can originate from the natural and industrial sources. The various biochemical processes that occur in the environment emit many organic compounds, e.g. during decay, the methane is produced. The all sorts of technological processes are the industrial sources of the organic compounds. These compounds are produced in form of vapors or in particular - solvents. The aim of gas purification in this case is not only contaminants removal but also the solvents recovery. In recent years, the waste gases produced during municipal or industrial waste combustion and by motor transport have become a serious problem. Next to chloroorganic compounds (dioxins), the polycyclic aromatic hydrocarbons (PAH) are the components of waste gases. The air pollution prevention methods At present the reduction of gaseous pollutants emission is carried out by two methods: - The atmospheric emission of gaseous pollutants is reduced at the stage of the technological process planning (including fuel combustion) the appropriate selection of materials, the initial purification of materials, air-tight sealing and automation of industrial processes. - The waste gases purification - in case when the total reduction of pollutants emission is not possible during technological process or fuel combustion. THE PROCESSES DESIGNED TO WASTE GAS PURIFICATION The waste gases purification from gaseous contaminants is carried out with help of almost all mass exchange processes; these are so called physical change: - Absorption - Adsorption - Condensation - Filtration (membrane methods) and the chemical changes (the chemical reaction are occurring ): - The direct combustion - Catalytic methods: o Catalytic oxidation o Catalytic reduction and also biological processes (with microorganisms used) ABSORPTION The absorption is the diffusive transport of molecules from one phase (gaseous) through phase boundary into the volume of second phase (liquid) caused by the difference in concentrations between these phases. The absorption occurs when the liquid (absorbent) takes in the gaseous pollutants. 4

4 In order to transfer a specific pollutants mass from gas to liquid the molecules have to pass through an area which adjoins to the phase boundary and also through the phases boundary, i.e. through the interfacial surface. The molecules transfer to the phase boundary either in gaseous phase or in an aqueous phase is called diffusion. The absorption rate increases together with the increase of both the interfacial surface and the diffusion rate. The growth of interfacial surface can be achieved by dispersing one phase in another, e.g.: a dispersion of gaseous phase in liquid with help of the sparger or by mixing. The enhancement of diffusion is realized by contacting the phases for the long enough time and by increasing the flow turbulent in both phases, e.g.: by a rapid mixing. The absorption takes place when the pollutants concentrations reach several percent and in case of diluted gas when the pollutants dissolve easily in absorbent. The absorbents are: water, the oxidizing and reducing acids, bases and salts solutions. The absorption rate increases when liquid and the pollutant present in gas react with each other. During the absorption with chemical reaction the component of the gas stream reacts with the compound present in liquid yielding the product possessing different properties from the original substance. Such product should be harmless to the environment and should not require to be utilized again. In case of waste gas purification, the absorption enhanced by the chemical reaction is one of the basic method of acid pollutants removal, e.g. SO 2, NO x, CO 2, hydrocarbons and others. Absorbers In order to contact gas with water during absorption the liquid is broken up into droplets or thin layers and the gas into tiny bubbles. These processes take place in the process apparatus absorbers. In the absorbers used in waste gas purification the gas-liquid contact area should be maximal while the resistance of gas flow should be minimal. The most often used are the spray chambers and towers where the gas flows up counter-currently to the liquid. In the spray column the liquid is sprayed in the gas stream and collected together with contaminants at the tower bottom. In the bubble column the gas stream is broken up into the dispersion of bubbles in the liquid. In the packed column the liquid absorbent runs as a thin layer over a solid packing. Absorption methods in purification waste gases from hydrocarbons However in the adsorptive methods the removed substances can be recovered the gases require to be completely dedusted and also preleiminary dehumidified. These methods are expensive, they require an usage of multistage systems. The cheaper methods allowing for effective organic compound removal are based on the phenomenon of absorption. There are known methods of organic solvents vapors removal from the air which are based on the absorption in the high-boiling organic solvent, adsorption and subsequent catalytic burning. The scheme of the volatile organic compounds (VOC) absorption system is shown in Fig. 1. The blue lines indicate the contaminated air flow (VOC), while the black lines indicate the flow of medium, in this case an organic solvent. The system consists of absorber and regenerator. In the absorber the contaminated air flow up and counter-currently to the organic solvent (absorbent) that is coming from the top of the column. The purified air exits the column at the top while the solvent exit at the bottom and is sent to the regenerating column. In the regenerator due to heat-up VOC desorbs and leaves the column at the top of column while the purified absorbent is sent to the absorber after having been cooled down in the heat exchanger. A part of the solvent is warmed up in the heater by the overheated steam and is returned to the regenerator. 5

5 Fig 1. Scheme of VOC contaminated fume gases absorptive purification system. VOC volatile organic compounds ADSORPTION In the adsorption process the molecules (or particles, the part of molecule a radical, an atom) of one substance are bound to the surface of the other one. The adsorption increases these molecules concentration on the phase boundary. Adsorptive the substance that is being bound on the phase boundary Adsorbent the substance that adsorbs on its surface Adsorption is an exothermal process. The opposite process desorption is an endothermic one. The first stage of the gas adsorption is its movement towards the adsorbent external surface. Like in the case of absorption. In the next stage gas diffuses through adsorbent s pores into the internal surface and binds to this surface. Fig. 2. The internal adsorbent surface is large, several thousands m 2 /kg. Fig.2. A cross section of the adsorbent grain. The internal canals are shown. D- pollutants molecules diffusion from the gaseous phase into the external surface and vice versa, D w molecules diffusion in the adsorbent s pores into its internal surface The adsorption process stages a) The molecules diffusion from the gaseous phase interior into the external surface b) The molecules diffusion in the adsorbent s pores into its internal surface 6

6 c) The molecules physical adsorption on the adsorbent surface The adsorption rate is limited by the slowest stage diffusion. This process rate can be improved by the increase of gas stream turbulence and the adsorbent surface enlargement, i.e. grains fragmentation from several mm to <200µm. When the adsorbed substance mass is close to the equilibrium amount, the next stage of the adsorption applied in gas purification is the removal of this substance from the adsorbent surface. This process, contradictory to the adsorption is called desorption or the adsorbent regeneration. A desorption is the endothermic process and requires the energy supply, e.g. bed warming up. Desorption can be also carried out by passing an inert gas through the adsorbent bed at higher temperature or by lowering the pressure. Adsorbents One of the oldest and the best known adsorbent is coal recognized as activated carbon or charcoal. A specific surface area reaches 1000 m 2 /g. The activated carbon used in gas purification should be granular and have sufficient mechanical strength. The silica adsorbents is the largest oxide sorbent class, like silica gel, aluminosilicate. The most polar oxide sorbents e.g. aluminum oxide are rarely used in waste gas adsorptive purification. The aluminosilicate adsorbents of zeolite forms, are molecular sieves with structure characterized by empty spaces which form canals and cavities of precisely defined shapes and dimensions. Hence only the molecules of shapes and dimensions fitting the canals size of the given zeolite bed are adsorbed. Adsorbers The adsorption and adsorbent regeneration can be carried out periodically in the same apparatus or in the continuous manner. In case of adsorbers with the stationary layer the cycles of adsorption and regeneration are carried out in the same apparatus. At the first stage the contaminated gas is passed through the adsorbent bed until the conditions corresponding to breakthrough are reached. Then the contaminated gas inflow is stopped and bed regeneration cycle starts. In case of adsorbents with moving layer the adsorption is carried out continuously. The apparatus is still working when the layer is regenerated. The adsorbent stream is passing down the adsorptive column concurrently to the purifying air and is directed into the desorptive column. Here the adsorbent is warming up and the contaminants are desorbed. The regenerated adsorbent is sent to the top of the adsorptive column. Active carbon in purification waste gases from hydrocarbons In many industrial processes the volatile solvents are used. During the process they evaporate into the air. The removal the vapors from the air prevents the atmosphere pollution and simultaneously enables the recovery of solvents which can be reused. To do that the phenomena of adsorption and desorption are applied. The activated carbon is the most often used as an adsorbent. Systems for the solvents adsorption consists usually of battery of adsorbers with activated carbon, that are working simultaneously. Fig. 3. The mixture of air and solvents vapors after initial dedusting is sent to the adsorber. The gases temperature is kept possibly low. It should not exceed o C. After the bed is being saturated with solvent, air access is cut off and the regeneration cycle starts. The desorption is carried out with help of the steam stream. The steam while adsorbing on the carbon surface displaces those adsorbed substances (VOCvolatile organic compounds), whose partial pressures are lower than the equilibrium one. The steam passing out of the adsorber is directed to condenser, where they are condensed. 7

7 Fig.3. Absorber with stationary layer. VOC = volatile organic compounds The further method of the condensate treatment depends on its composition. If it contains the water-soluble compounds, they are extracted by fractional distillation in another system. If the desorbed solvents do not mix with water, the organic layer is separated in separator. The bed of activated carbon after desorption is dried out and cooled down prior to the next cycle. In the adsorbers with moving layer the adsorption is carried out continuously. The apparatus is not turned off when the layer is regenerated. After adsorption stage the stream of carbon saturated with hydrocarbons is directed into the regenerator. There desorption occurs under the influence of high temperature and steam flow. The regenerated carbon is sent back to the adsorber. Although the methods with adsorbent regeneration are the most beneficial from the economical point of view, in practice the adsorbents are usually used once, particularly when a e.g. solvent is cheep. The saturated adsorbent is either a waste or can be combusted in case when carbon is a sorbent. Aluminosilicate in purification waste gases from hydrocarbons If aluminosilicate is an adsorbent then, on contrary to activated carbon, desorption may be carried out by means of: an adsorbent heating, the flow of inert gas through the saturated adsorbent layer, the decrease in pressure or by the combination of mentioned methods. The heating of adsorbent layer up to the adsorbed substance s boiling point is the most common method of regeneration. When adsorbed compound is desorbed either by air or nitrogen or other inert gas, the impurities retains in that gas. This method of regeneration can be used when the impurities are to be combusted. It happens that during the regeneration process the desorption does not occur completely or organic compounds decompose. Then a tar or coke can form on the adsorbent surface what make its reuse impossible. Then, adsorbent is burned off in the oxidation furnace and the residue organic compounds are burned off from the surface and pores of adsorbent. CONDENSATION Condensation is a waste gases purification method used in case of the substances with high boiling points realized by means of cooling down, by water or air in heat exchangers, to be 8

8 condensed and this way, separated. In case of the volatile solvents condensation this method is applied when the precise purification is not required (up to several ppm). The limitation of this method is fact that the gas needs to be cooled out at the final stage. Moreover this method is not applicable in case of gases emitted into the atmosphere. In gaseous contaminants condensation two cooling methods are used: direct and with wall. In the direct method the solvent s vapors are in contact with the cooling liquid stream, e.g. water. This method produces new waste contaminated water. The applications of this process are limited. In a method with wall, the process is commonly carried out in a pipe exchanger, where gas contaminants flowing inside of the pipes are condensed by the cold pipe wall, still cooled by a cooling agent flowing between the exchanger pipes. High thermal conductivity of the wall material is needed to achieve the best efficiency of this process. MEMBRANE PROCESSES The membrane processes are applied in the separation of contaminants which molecules and particles size are at the molecular and ionic level. With respect to the membrane properties, they are used to separate the particles of size ranging from 500 to 0,5 µm and also to separate components differing insignificantly in size, e.g. gases, ions or low molecular weight compounds. When the ion exchanging membranes are used the different ions can be separated. The separated components undergo any chemical, thermal, biological transformations during the process. Hence, the recovered components can be reused. Membrane is a thin layer which serves as a barrier allowing for a selective mass transport. Separation is possible due to a difference in the rate of transport through the membrane. Simplifying this definition - membrane is a boundary which enables the controlled transport of one or many components from the mixtures of solids, liquids or gases. During a membrane process the feeding stream (feed) is divided into the concentrate stream (retentate) and the filtrate stream (permeate), and either permeate or concentrate or both streams can be a product. Fig. 4. The principle of streams sepatation in membrane process [2] Transport of the molecules through the membrane occurs due to the sufficient propelling force. Such force is a difference of: 1. Pressures 2. Concentrations 3. Temperatures 9

9 4. Electric potential The separation of particles occurs due to the difference in rate of compounds transport through the membrane. The membrane methods used in waste gas purification are applied for: - SO 2, NO x, CO 2 and industrial gases dust removal - fumes extraction from industrial gases - biogas purification - volatile organic compounds removal from the waste gases COMBUSTION Combustion is the most common method of waste gases purification from the flammable substances hazardous for the environment like hydrocarbons, carbon oxide, organic solvents, etc. Hydrocarbons oxidation in purification waste gases from hydrocarbons The organic compounds can be removed from the fume gas by oxidation to carbon dioxide and water according to the reaction: C n H 2n+2 + (3n+1)/2 O 2 nco 2 + (n+1)h 2 ) (1) for methane: CH 4 + O 2 CO 2 + 2H 2 O (2) The hydrocarbons oxidation methods: direct flame (temp ~1500 K) thermal ( K) catalytic ( K) biological ( K, best 310 K) Direct flame incineration The incineration of gasous pollutants may be carried out directly in the flame, however in case of the low concentrations this method is inefficient. In practice the concentration of pollutants in flue gas is low, hence the method of direct incineration is rarely applied. Application: The combustible waste gas burning: at refineries, at oilfields as safety flames prevents hydrocarbon gases comcentration. Thermal incineration When the VOC concentrations is too low to maintain the flame or/and the catalytic method are not applicable (the mixture of gases comprises of the components that can cause rapid catalyst deactivation) the thermal incineration is applied. This method requires an additional gaseous or liquid fuel. A scheme of thermal incineration apparatus is presented in Fig

10 The contaminated air preheated by fumes in the exchanger is introduced to the oxidizing chamber. In the chamber the contaminants undergo the oxidation to CO 2 and water. Fig. 5. Schematic diagram of thermal oxidation system. 1- burner oxidation chamber with the burner fed with fuel 2- shell and tube heat exchanger 3- contaminated gas inlet 4- purified gas otlet 5- gaseous or liquid fuel 6- additional air CATALYTIC METHODS The catalyst is defined as a substance which accelerates the rate of reaching the equilibrium state by reaction, it is not consumed by the reaction and its symbol does not occur in stoichiometric equation of the reaction. The catalyst activity (A k ) is determined as a difference between the reaction rate running with catalyst v k and without catalyst v h : A k = v k - v h (3) The reaction rate without catalyst is extremely low in comparison to the catalytic reaction rate. Hence, the catalyst activity is directly a reaction rate v k. If the reaction accelerated by catalyst in one direction only yields the product of a high purity while the consumption of raw materials is low, the catalyst is considered as selective. The catalyst selectivity S i is defined as the ratio of the amount moles of one from possible products (p i ) to the total amount moles of products (Σp i ) : cat X P1 + P2 + P P (4) n 55 S 1 n pi = (5) n pi Selectivity of most industrial catalytic processes reaches only 70-90% while in case of enzymes it is 100%. A distinct majority of catalytic processes used for waste gases purification is carried out in the presence of solid catalysts, so-called contacts. The one of the most significant problem of heterogeneous catalysis is catalyst poisoning. It happens when catalyst loses partially or completely its activity due to the action of small quantities of substances called contact poisons. 11

11 The catalyst poisons are: hydrogen sulfide, organic and inorganic sulfides, arsenic compounds, hydrogen phosphide, ammonia. Except for the poisoning the catalyst activity can decrease as a result of the reduction of active surface due to recrystalization or sintering and due to the catalyst surface mechanical coating by contaminants e.g. dust or solid substances produced during catalysis e.g. tar or coal. The catalyst regeneration is realized by means of burning off. Catalytic oxidation of hydrocarbons The catalytic oxidation is a more economical method due to the lower energy consumption. The appropriately active catalyst enables the oxidation at o C. The platinum metals i.e. platinum, palladium, and rhodium are the most often used as catalysts in complete combustion of hydrocarbons due to their high activity and in particular due to their stability at high temperatures and poison resistance. Because the catalytically active noble metals are expensive the metals deposited as thin layer on inorganic carriers, are used in the industry. The fine grained ceramic carriers or monolith, honeycomb carriers based on aluminum oxide or aluminosilicates can be used. The exothermic complete oxidation of the organic contaminants proceeds in diffusion region. This reaction exhibits both high space velocity and conversion. Therefore the carriers must have well developer surface. The catalytic oxidation can be proceeded in the apparatus presented in fig. 6. The contaminated gas is preheated in the exchanger by gases from catalyst, and next it is warmed up to the required temperature in the heater. If there is not enough oxygen to burn all contaminants in the raw gases stream the additional air is supplied to the heater. Next when mixed with additional air, the gases are sent on catalyst bed. While passing through the catalyst layer the contaminants diffuse to the catalyst surface and are adsorbed at the active sites. There the oxidation occurs. The oxidation products (CO 2 and H 2 O) diffuse to the flowing gas and exit the apparatus as a purified gases. Fig. 6. schematic diagram of catalytic oxidation system 1 heater (heating by combustion of the gaseous or liquid fuel) 2 reactor with catalyst 3 heat exchanger 4 - raw gases inlet 5 additional air outlet 6 purified gas outlet 12

12 Catalytic reduction Catalytic reduction using carbon monoxide CO, hydrogen, and hydrocarbons is method for removing NO x from waste gases. Noble metals such as rhodium, palladium and platinum can be used as catalyst. The noble metals are usually supported on oxides such as Al 2 O 3, zeolites Selective catalytic reduction (SCR) of nitric oxide by ammonia over V2O5/TiO2 based catalysts is the most technically advanced post-combustion technology capable of reducing NO x emission to extremely low levels mandated in many areas of the world. 4NO + 4NH 3 + O 2 4N 2 + 6H 2 O (6) 2NO 2 + 4NH 3 + O 2 3N 2 + 6H 2 O (7) BIOLOGICAL METHODS Many substances which contaminate the waste gases can be effectively removed during bidegradation by microorganisms (aerobic bacteria). The bacteria oxidize volatile organic compounds (VOC) to carbon dioxide and water or mineralize the heteroatoms present in VOC. The energy generated in this process is consumed by bacteria. [CH 2 O] + O 2 CO 2 + H 2 O + H (8) The anaerobic bacteria convert VOC into a biogas (up to 75% methane). Reaction (11) 2[CH 2 O] + H 2 O CO 2 + CH 4 + H (9) [CH 2 O] simplified formula of organic compounds The contaminants concentration in the air stream should not exceed 100 ppm. The most important advantage of the biological methods of gas purification is a fact that this process can be carried out at the ambient temperature and atmospheric pressure. The biological gas purification is based on two main processes: - impurities absorption in water - biological decomposition of the contaminants absorbed In practice, the gases are purified by the biological methods in the following systems: - biofilters (biological filters) - biowashers (biological washers), bioscrubers The biofilter basic element is a filtrating bed, on which toxic substances are sorbed and next gradually decomposed by microorganisms. The air intended for purification is pumped in and flows along the bed from the bottom to the top or opposite (Fig 3). Compost, peat or other material of organic origin can be used as a filtrating bed. However the structure of this material must be homogeneous, the pores volume constant and this material must be sufficiently humid. 13

13 Fig.7. Biofilter operating scheme. In the biological washers the hazardous substances absorption from the air is separated from their biological decomposition. Biowasher consist of absorber and biodegradation unit (Fig. 8). In the absorber the oxygen and impurities go to the water while purified gas (air) exits the device. Fig.8. Biowasher (bioscruber) operating scheme. The water regeneration takes place in the separate aeration chamber (biodegradation unit) filled with microorganisms. The fact that biological methods generate low cost makes them popular. In case of low contaminants concentration their advantage increases even more. With help of microorganisms the waste gases are purified from: SO 2, hydrocarbons and other organic compounds. Biological methods in purification waste gases from hydrocarbons The biological degradation of volatile organic compound emitted into the atmosphere is an option to many physical and physicochemical methods of air purification. In nature, there are many microorganism which are able to assimilate the organic matter. The effect of that is for instance, the environment clean-up and renovation. Some bacteria strains are able to adapt to decompose the organic matter that does not occur in the nature 14

14 The biological gas purification conditions and limitation are as follows: The contaminants removed from the flue gases must be prone to biological decomposition The contaminants must be soluble, even weak, in water which is microorganisms environment The gas purification temperature must be within the limits of biological activity of microorganisms (0-55 o C, optimal o C) The gases cannot contain the substances toxic to microorganisms, e.g. heavy metals compounds or acid vapors. 15