Cleaner production in the ammonia–soda industry an ecological and economic study(1)

Cleaner production in the ammonia–soda industry:an ecologicaland economic studyT.Kasikowski *,R.Buczkowski,E.LemanowskaFaculty of Chemistry,Nicolas Copernicus University,ul.Gagarina 7,87-100Torun´,Poland Received 3June 2003;revised 4August 2004;accepted 4August 2004AbstractFive methods to reduce the negative influence of soda ash factories on the natural environment are presented:1.obtaining calcium–magnesium phosphates by treating the suspension from raw brine purification with orthophosphoric acid (H 3PO 4),2.production of precipitated chalk from soda processing waste,3.production of gypsum and semi-brine,4.desulphurisation of fume gases from the factory power plant,5.utilization of distiller waste.The tests,accomplished on a laboratory scale,showed the high efficiency of these methods.Economic analysis has proved that only four out of the five presented processes can have a positive financial effect on soda ash factories,as well as being well justified economically.The value of two of the innovations presented is confirmed by their implementation in factories.q 2004Elsevier Ltd.All rights reserved.Keywords:Solvay process;Ammonia–soda industry innovations;Waste utilization;Clean technologies;Cleaner production1.IntroductionIn 1989,Poland rejected the ‘centrally planned’econ-omic system (The European Economic Community)and switched to the ‘free market’system.Since then,radical changes in the industrial factories policy have been observed.This process has also been clearly visible in the soda ash factories.To compete in the European market 1Polish soda ash plants had to ensure the low prices of their products on one hand and high quality on the other (Groat,2001).Frequently,the only possible way to reduce production costs is pro-ecological activity(Kruszyn´ski et al.,1999).This leads to a decrease in charges paid by factories for polluting the natural environ-ment.Moreover,the Polish soda ash industry seeks to reduce production costs by means of ecological invest-ments 2(Go´rski,1998;Environmental protection law,1995).In this paper,five technological concepts which may help to lower the negative influence of soda ash factories on the natural environment are presented.A short profile of these innovations as well as the ecological and economic 3effects of their implementation are also demonstrated.However,the authors emphasise that the experiments presented below are in their preliminary (laboratory)stages.0301-4797/$-see front matter q 2004Elsevier Ltd.All rights reserved.doi:10.1016/j.jenvman.2004.08.001Journal of Environmental Management 73(2004)339–356/locate/jenvman*Corresponding author.Tel.:C 48566114331;fax:C 48566542477.E-mail addresses:kasik@chem.uni.torun.pl (T.Kasikowski),tomek kasikowski@ (T.Kasikowski).1The world market is almost exclusively occupied by American natural soda ash because its sale price is two times lower than that of the synthetic one.The high cost of shipping soda from the USA to Europe means that the real price of both natural and synthetic soda ash in Europe is similar.Thus,Polish soda ash plants only send their product to the European market.2Especially after spring 2004,when Poland joins the European Union,environmental policies in industrial factories will have to be realized very restrictively.3The examples of clean,not waste generating methods of soda ash production are the following processes:DUAL,New Asahi or Dry Lime.Unfortunately,there is little demand for ammonium chloride,a by-product of these methods,which limits the employment of these processes in several plants all over the world.A brief description of the ammonia–soda process (the classic Solvay method)is introduced below.1.1.Ammonia–soda processThe first step in the ammonia–soda process is brine preparation.Sodium chloride solutions are usually obtained by solution mining of salt deposits,which gives a raw,nearly saturated brine containing a low concentration of impurities such as magnesium and calcium salts.The brine has to be purified to prevent the scaling of processing equipment and contamination of the product.To purify it,the brine is treated with lime milk to precipitate magnesium and with soda ash to precipitate calcium.The brine,separated from precipitated impurities (con-sidered as waste),is then divided.One part is used for the production of evaporated salt,4the other is directed to the soda process.The waste products,which result from the salt evaporation process,are known as sludge.Sludge is saturated brine containing other substances (50g dm K 3Na 2SO 4and 0.1g dm K 3FeCl 2),and therefore cannot be used as brine in both the salt-obtaining and the soda ash processes.The brine needed for the soda process is sent to the ammonia absorbers.In the absorption tower the strong brine is saturated with ammonia gas.The ammoniated brine is pumped into the carbonator tower,in which rising CO 2(compressed lime kiln gas and bicarbonate calciner gas)meets falling ammoniacal brine.A bicarbonate sediment,a solution of unprocessed NaCl and NH 4Cl is obtained from the carbonation process.The slurry of NaHCO 3which forms,is fed into vacuum filters or centrifuges which separate the crystals from the filter liquid.The filter cake (crude bicarbonate)is calcined to carbon dioxide and sodium carbonate,called soda ash 2NaHCO 3ÿÿÿÿ/ðCALCINATION ÞNa 2CO 3C CO 2[C H 2O [An important part of the Solvay process is the recovery ofammonia from the filter liquid.The filter liquid (a solution of NaCl and NH 4Cl)is fed to sections of the distiller where it is treated with lime milk obtained during the process of burning the limestone.Here,the ammonium chloride reacts with the lime milk and the evolved ammonia is vented back into the absorber.The final solution,known as distiller waste (DW),contains calcium chloride,unreacted sodium chloride and a small excess of lime.The distiller waste is the main waste material that is formed during the Solvay process.This waste liquid is pumped to the settling basins where the suspended solids which were present in the lime are deposited.The clear overflow is deposited in the sea,which poses no appreciable problem,or flows into rivers.The average composition of distiller waste is shown in Table 1.In Fig.1the flow diagram for the production of ammonia–soda by the Solvay process ispresented (Koneczny,1978;Hou,1942;Roskill Information Services Ltd,1985;Kostick ).2.Experimental part2.1.Calcium–magnesium phosphatesThe ‘lime and soda’method is used to purify raw brine from calcium and magnesium ions.The precipitation of magnesium ions in the form of Mg(OH)2proceeds under the influence of lime milkMgCl 2C Ca ðOH Þ2/Mg ðOH Þ2/C CaCl2Table 1Components of distiller waste ElementConcentration (kg/m 3)Water 956CaCl 2112NaCl 56Ca(OH)27CaCO 310CaSO 41SiO 23NH 30.1–0.014The evaporated salt installations are situated near two Polish soda ash factories.T.Kasikowski et al./Journal of Environmental Management 73(2004)339–356340The calcium ions present in brine as well as those introduced in the lime milk are precipitated with a sodium carbonate (soda)solutionCaCl 2C Na 2CO 3/CaCO 3/C 2NaClThe suspension formed during this process creates a problematic waste product (Mg(OH)2/CaCO 3),which was carried away into sediment ponds (until 1997).The new solution described is based on the waste converting into highly assimilable mineral additives for animal feed.For this reason,the suspension is filtered to obtain the filtration cake,of 30%humidity,which reacts with orthophosphoric acid (Fig.2)CaCO 3C H 3PO 4C H 2O /CaHPO 4$2H 2O C CO 2[Mg ðOH Þ2C H 3PO 4C 5H 2O /MgHPO 4$7H 2OThis process results in the formation of calcium and magnesium hydrophosphates,5which are high quality foodsupplements,rich in calcium,magnesium,phosphorus,and micronutrients (Foss and Buczkowski,1997).Micronutri-ents contained in calcium–magnesium phosphates come from raw brine.They are precipitated from raw brine in the form of insoluble salts,together with calcium and magnesium compounds.The content of microelements and magnesium means the obtained phosphates are of high quality and have a relatively good selling price on themarket (Buczkowski and Kasikowski,2002;Kruszyn´ski et al.,1998).In the first step of the investigation the analysis of raw and purified brine compounds was performed.The concen-tration of sodium chloride was determined based on the analysis of all other ions contained in the brines.The concentration of chlorides was determined by the argento-metric Mohr method.Calcium and magnesium ions were analysed by potentiometric titration (0.05M EDTA),using Titrino 736GP (Metrohm)equipped with the computer program TiNet 2.20,fluorides were determined by the standard addition method,using an ion-selective electrode.Microelements (Cu,Mn,Cd,As,Pb,Zn,Ni and Co)were determined by the XRF method (spectrometer RMA Inc.:Spectroscan V)in solid material obtained by the evaporation of brines (Application Bulletin;PN-93/C-84300/13;Jenkins et al.,1995).Phosphorus was determined (in products)by the gravimetric method in the form of quinoline phosphate–molybdene (yellow sediment).The total phosphorus content was determined as well as fractions soluble in 1M HCl and soluble in water.Contents of calcium and magnesium in products were determined after dilution of product samples,by titration with EDTA.6Fluorides and sodium were determined using ion-selective electrodes,by the standard addition method.The results are presented in Table 2.The XRD analysis of products was performed using a HZG4/A-Z diffractometer,Cu K a (l Z 1.5405nm),20mA,40kV,slits:0.79;0.6;0.44.The identification of compounds was executed with the help of diffractometric standards tables (Powder Diffraction File,1976;PCPDFWIN and X’Pert ).The results of the XRD analysis showed that the basic product’s compounds are dicalcium phosphates:CaHPO 4,CaHPO 4$2H 2O and dimagnesium phosphate:MgHPO 4$7H 2O.The technology described for the co-production of animal feed additives was employed in Janikowo Soda Ash Plant in 1998.This technology allows full utilization of the waste product from the raw brine purification process,and a partial recovery of purified brine (mother liquid).The comparison of the material balance for the classic and the modified Solvay process is presented in Table 3.Fig.2.Flow diagram of suspension from raw brine purifying utilization.5As a result of the reaction of the filtration cake with orthophosphoric acid,a number of salts:Ca(H 2PO 4)2,CaHPO 4,Ca 3(PO 4)2,Mg(H 2PO 4)2,MgHPO 4,Mg 3(PO 4)2can be obtained.Their biological values are different and are determined not only by the nominal content of phosphorus but also by the factors affecting their assimilation;such as the Ca/P ratio,hydration degree,solubility,pH of the solution,purity,and crumble.The research has shown that the best feed properties belong to monohydrophosphates:CaHPO 4and MgHPO 4and their hydrates.6However,before titration phosphorus was removed from samples by percolating solution through anion exchanger.T.Kasikowski et al./Journal of Environmental Management 73(2004)339–356341The following materials were included in tabular form:material,amount of raw materials in the traditional soda ash process (Solvay method),amount of raw materials in modified technology (Solvay process equipped with the above described pro-ecological process).In the two last columns (in Table 3)the amounts of products or waste generated has been shown.In a typical synthetic soda ash factory (which produces 500thousand tones of soda ash yearly and the same amount of salt—an example from Poland)the demand for NaCl (in the form of brine)is about 1293thousand tones per year.In the classic Solvay process unreacted NaCl (together with CaCl 2—in the form of distiller liquid)is considered to be a waste product (marked in Table 3as ‘others’).In the case of the application of the pro-ecological process introduced above,about 30thousand tones of NaCl per year is recovered from the process.The suspension created during the brine purification process (about 5thousand tones yearly)reacts with 6thousand tones of H 3PO 4which,in effect,results in the production of 11thousand tones of calcium–magnesium phosphates.2.2.Cosmetic chalkThe precipitation of chalk is based on the reaction between calcium ions contained in distiller waste and carbonate ions from a soda solutionCa 2C ðDW ÞC CO K 23ðSODA ASH SOLUTION Þ/CaCO 3YFor the preparation of the soda solution,a defective soda ash assortment is used (a product which fails to meet the standards for light or dense soda ash).The precipitated chalk obtained in this way is sold and used in the cosmetic and pharmaceutical industries (which require chalk of a very high quality,especially,with a low concentration of NaCl,and ferric or ferrous ions).The overflow of distiller waste isused in the process (Trypuc´and Buczkowski,1993).The obtained CaCO 3sediment is centrifuged and washed in order to remove chloride ions from the suspension.The well established conditions of the precipitation allow clean (with no undesirable ions)semi-brine to be obtained above the precipitated chalk.The semi-brine is turned back to soda ash or evaporated salt production (after saturation).The quantityTable 2Compounds of brines,suspension,technical o -phosphoric acid and product Type of determ.Results Raw brine Purified brine Suspension H 3PO 4(67%mass.)Product Density 1196g/dm 31190g/dm 3–1522g/dm 3–Humidity ––33.3%––Na 122.2g/dm 3120.8g/dm 3 4.35%– 3.2%Cl 188.6g/dm 3184.9g/dm 3 6.71%–4.8%Ca 0.44g/dm 30.00g/dm 317.91% 1.01g/dm 313.4%Mg 0.26g/dm 30.00g/dm 3 4.53%0.00g/dm 3 3.4%F 0.04g/dm 30.04g/dm 30.00% 2.58g/dm 30.12%P –––317.8g/dm 314.7%Cu 0.032ppm 0.000ppm 7.7ppm 0.8ppm 6.3ppm Mn 0.127ppm 0.000ppm 27.5ppm 1.5ppm 21.6ppm Cd 0.001ppm 0.000ppm 0.2ppm 1.2ppm 1.1ppm As 0.003ppm 0.000ppm 0.5ppm 2.2ppm 0.7ppm Pb 0.002ppm 0.000ppm 0.4ppm 0.9ppm 0.9ppm Zn 0.052ppm 0.000ppm 11.6ppm 9.2ppm 15.2ppm Ni 0.006ppm 0.000ppm 1.3ppm 1.3ppm 1.9ppm Co0.006ppm0.000ppm1.3ppm1.0ppm1.6ppmTable 3The material balance of calcium–magnesium phosphates process a (solid substances)IngredientRaw material (Gg/year)Product or waste (Gg/year)Standard technologyModified technology Standard technology Modified technology NaCl (in raw brine)12931293––Suspension (from brine purif.)––5–H 3PO 4–6––Calcium–magnesium phosphate–––11Water and others 5415541967036707Total6708671867086718aExample of Janikowo Soda Factory ‘JANIKOSODA’S.A.,ul Przemysłowa 30,88-160Janikowo,Poland.T.Kasikowski et al./Journal of Environmental Management 73(2004)339–356342of precipitated chalk produced is rather low (4000Mg/year 7)and depends on the demand (Janikowo,2000).Fig.3shows the flow diagram of precipitated chalk production.Basic mass balance for the precipitated chalk production is presented in Table 4.2.3.Sludge utilizationThe distillation waste from the soda ash process and sludge from solid salt production,which are dangerous to the natural environment,can be used to obtain gypsum of standard value.The main aim of the process described below is to receive calcium sulphate in the form of gypsum,by means of calcium ions contained in the distiller waste liquid and sulphate ions contained in sludge.The advantage of this process is the production of not only a gypsum sediment but also a sodium chloride solution in the form of Semi-brine (Buczkowski,2000)Fig.4.Basic mass balance for the sludge utilization is presented in Table 5.CaCl 2C Na 2SO 4C 2H 2O /CaSO 4$H 2O Y C 2NaCl The aim of the investigation was to optimise calcium sulphate precipitation parameters.Firstly,a factor experiment was performed.The gradient of gypsum properties (dependent variables)in the function of indepen-dent variables (parameters)was determined,based on theexperiment’s results (Zien´ko,1991).Then,three optimis-ation procedures using the simplex method were performed.In this stage only three out of five independent variables were selected (Spendley et al.,1962).In the first step of optimisation,five independent factors were taken into consideration:–the order of waste (sludge and distiller waste)flowing to the reactor,–the time of the second reactant dosage to the reactor,–the pH of the post-reaction mixture,–the precipitation temperature,–the excess of first/second waste.To accomplish the factor experiment in the form:2n ,considering the five above mentioned independent vari-ables,it was necessary to perform 25Z 32processes of gypsum precipitation (Parczewski,2001).All of the experiments took place in a glass,thermostatic reactor.The glass mixer was placed centrally in the reactor,5mm above the bottom of the reactor.A mercury thermometer was also placed in the reactor.Each of the 32experiments was performed as follows:the proper volume of the first waste liquid was placed in the reactor and the temperature of it was controlled.The second waste liquid was placed in the thermostatic dropper connected to the reactor.When the temperature of both waste liquids was appropriate,the process of adding waste from the dropper to the reactor was started.After that,the reactor insert was mixed further for 300s.Then,the sample of the suspension from the reactor was observed under 250!enlargement (using an opticalTable 4Basic mass balance for cosmetic chalk production a IngredientRaw material (Gg/year)Product or waste (Gg/year)Standard technologyModified technology Standard technology Modified technology NaCl(in raw brine)12931286––NaCl(in semi-brine)–7–7Distiller waste (dry mass)––900893Soda ash 1519500500CaCO 3–––4Water and others 5400540853085316Total6708672067086720aExample of Janikowo Soda Factory‘JANIKOSODA’.Fig.4.Sludge utilizationscheme.7Mg stands ed below Gg stands 109g.T.Kasikowski et al./Journal of Environmental Management 73(2004)339–356343microscope).The length and width of at least100crystals were noted(Kasikowski et al.,2004).Based on the geometrical parameters it was possible to determine the crystal size distribution(CSD).In practice,crystal graining is evaluated based on the values of four primary distribution factorsm k Z ðNnðLÞ$L k d Lðk Z0;1;2;3Þwhere m0is the number of crystals in1m3of suspension;m1, total length of crystals contained in1m3of suspension;m2, total surface area;and m3is the total volume of crystals in 1m3of suspension(Nyvlt,1982).After precipitation,the suspension was poured through a glass crucible:G3.Then,100cm3of the mother liquid was poured through a gypsum cake collected in the crucible.The time offiltration was noted(Machej,1973).Then,the humidity was removed from the gypsum cake with a vacuum:D P Z200mmHg(2.58!104N/m2),which worked in300s.After this,the rest of the humidity was determined in the gypsum(1058C).Thermogravimetric (Fig.5)and XRD analysis of the gypsum sample were carried out.Following that,the gypsum sample was dissolved in20cm3of HNO3(1:10).In the solution chlorides(Mohr method)were determined.The thermogravimetric and XRD analysis results agree with each other:the dihydrated calcium sulphate is the basic product compound.This is confirmed by the temperature of decomposition and the volume of mass loss.Statistical analysis of the relationships between indepen-dent variables and gypsum parameters was performed (Statistica5.0computer software).It was stated that the order in which waste liquids were introduced to the reactor is most important and has a significant influence on every measured parameter of gypsum.The dosage time and precipitation temperature are not significant.The pH value of the post-reaction mixture only influences two gypsum properties:thefiltration time and the average surface area of crystals.The simplex optimisation showed that independent of the place where the simplex optimisation procedure was started, only one out of three independent variables is significant: the pH of post-reaction mixture.When the pH value is higher a gypsum sediment of a better properties(low humidity)is created(Kasikowski et al.,in review).To validate the linear model(based on the32previous experiments)it was put into use.The results of the model were compared with results obtained in thesimplex Table5The material balance of the sludge utilization processIngredient Raw material(Gg/year)Product or waste(Gg/year)StandardtechnologyModifiedtechnologyStandardtechnologyModifiedtechnologyNaCl(in raw brine)12931255––NaCl(in semi-brine)–38–38Distiller waste(dry mass)––900893Sludge––44–Gypsum–––7Water andothers5415551157645866Total67086804167086804T.Kasikowski et al./Journal of Environmental Management73(2004)339–356344optimisation stage.It was then possible to calculate the validation variation:s v2s2v Z P qi Z1ðy i K~y iÞ2q K1where q is a number of test-reaction(simplex optimisation): q Z55.The significance of the model(s y2)was also calculateds2y Z P ni Z1ðy i K yÞ2n K1where n is a number of reactions performed in the factor-experiment:32.Finally,it was possible to calculate the validation coefficient:Q2Q2Z1K s2v s2yThe calculated value of the validation coefficient was large: Q2Z0.838,which confirms a high prediction power of the designed model,however,cross-validation(CV)was also performed.In this case,the variation of CV(s cv2)was calculateds2cv Z P ni Z1ðy i K~y iÞ2n K1and the CV coefficientQ2cv Z1K s2cv s yThe calculated CV coefficients(Q cv2)were as follows:–for thefiltration time:0.844–for the chloride ion content in gypsum samples:0.625–for humidity:0.863,and–for the average surface area of crystals:0.409.In summation,the results of the optimisations ascer-tained that to obtain large gypsum crystals with a low content of chloride ions and humidity it is necessary to use distiller waste of a high pH(11)and that distiller waste should be introduced to the sludge placed in the reactor.The rest of the independent variables(time of dosage,tempera-ture and the excess of any waste liquid)are not significant.The significance of the order of the waste dosage arises from the oversaturation of CaSO4in the post-reaction solution(Kaufmann,1960).When the sludge is added to the distiller waste,the saturation of the created CaSO4is exceeded40times.However,in the opposite situation it is only14times.Additionally,keeping in mind the very wide meta-stable zone of CaSO4solutions and increasing of its solubility together with the increasing of NaCl concen-tration,it could be said,that when distiller waste is added to the sludge much better nucleation and crystal extension conditions are set up.2.4.Neutralization of combustion gasesThe technology of fume gas utilization presented is a variation of the wet-lime method.It is based on the absorption of fume gases generated during the coal combustion process in the overflow of distiller waste (Sorensen,1988).The excess of lime milk,which is added in the process of ammonia regeneration fromfilter liquid (in the Solvay process),results in the strong alkalinity of the distiller waste.Also,the high pH value(11)favours the absorption of acid combustion gases.During the absorption process the following chemical reactions take place (Eqs.(1a)–(1f))CO2C CaðOHÞ2/CaCO3Y C H2O(1a) SO2C CaCO3/CaSO3Y C CO2(1b) SO2C CaðOHÞ2/CaSO3Y C H2O(1c) CaSO3C1=2O2C2H2O/CaSO4$2H2O Y(1d) SO3C CaCO3C2H2O/CaSO4$2H2O Y C CO2(1e) SO3C CaðOHÞ2C H2O/CaSO4$2H2O Y(1f) The research of fume gases absorption in the distiller waste was performed in the laboratory of the Technical University in Czestochowa,Poland.Fumes created during the combus-tion of coal samples were absorbed in theflushing with the distiller waste sample placed inside(the equipment used was similar to that described by Dagaonkar et al.(2001)). Firstly,a coal sample(3.000g)was placed in a thermo-regulated furnace equipped with a quartz tube.The burning of the coal sample(temperature used:1123K)created combustion gases which bubbled8through the distiller waste sample(400cm3)placed in theflushing.After absorption gases were directed to the analysers(continuous emissions monitoring(CEM)):Multor610(analyse of:SO2, NO x and CO)and Modular System S710(analyse of CO2 and O2):Fig.6(Buczkowski,2003).Twelve tests of combustion gas absorption in the distiller waste were performed.Four airflow rates(as mentioned) and three temperatures of distiller waste(293,313and 333K)were applied.In each of the tests three samples of coal were burned(3!3.000g).The concentration of gases after absorption and the pH of distiller waste were measured simultaneously.After absorption,the suspension created was separated from the mother liquid,rinsed and dried. Samples of the solid phase obtained in a such way were analysed(XRD,Fig.7;thermogravimetric,Fig.8;and pore measurement,Table6)(Toth et al.,1999;Os´cik,1979). Also,images of the solid phase samples were made 8Fourflow rates of the air above burned coal samples were used:0.1,0.3, 0.6and1.0m3/h.T.Kasikowski et al./Journal of Environmental Management73(2004)339–356345(scanning electron microscope:Fig.9).The results of pore measurement (BET,N 2:77K)were presented in Table 6.A very simple,linear model of the absorption process was considered.The validation was performed by the cross-validation method (Kasikowski et al.,in review ).The results are presented in Table 7.The XRD analysis of precipitates has shown that the main component is CaCO 3in the form of ponents initially expected (gypsum,CaSO 4and CaSO 4$1/2H 2O)were not detected.9Unexpected alu-minium signals (Fig.7)were recorded,because the solid phase samples were very small (0.05–0.1g)and the metal which the goniometer is made of was visible.In the qualitative and quantitative analysis of the solid phase components the thermogravimetric method was also used (Ghardashkhani and Cooper,1990;Cortabitarte et al.,1992).The results of TG analysis confirm the previously mentioned XRD results:the main component of the analysed solid phase is calcium carbonate (Fig.8).Use of the obtained solid phase as an adsorbent-insert in the fluidised combustion technology (FCB)10was suggested (Johnson,1995;Nowak,1996).The large content of CaCO 3(at least 80%)and its great surface area (S BET ,2.7–7.3m 2/g)(Clausen and Fabricius,2000)results in its higher quality when compared with ground limestone.The small quantity of calcium and sodium chlorides which come from the incomplete removal of the mother liquid is not a problem inthis case.It was shown that (in small quantities)these compounds support the process of desulphurization in the fluidised combustion bed technology (Szymanek,2002;Bis,2002;Lyngfelt and Leckner,1999).The typical CFB unit consists of a furnace and cyclones (where dense dust is separated from light ash).Then,the dense dust is transported back to the furnace.Only a small percentage of the bed content is coal (Li,2001).The advantages of CFB boilers are (Sablik,2002;Wieckowska,1995):–their relatively low combustion temperature (1073–1173K),which limits NO x formation,–chemisorption of 90–95%SO x created,–the possibility of burning a wide range of materials,–the relatively small cubature of CFB boilers.The properties of solid sorbents used in CFB technology such as their granulation,surface area,porosity,distribution of pore diameter and also the specific reactivity determine the demand for sorbents,its utilization coefficient,and most importantly,the desulphurization efficiency.GroundFig.6.Graph of SO 2and NO x concentration in gases after absorption.Each peak is a consequence of one (3.000g)coal sample burning.The value of pH,marked on the graph,represents pH of distiller waste after each step ofabsorption.9There is only one,very low peak of CaSO 3on the Fig.7.10The process of fluidization is based on creating suspension of small particles of coal (up to 8!10K 3m)in the up-flow stream of air.The proper size of the coal particles as well as an adjusted air flow rate causes the burning coal particles to create the fluidal phase which exhibits properties similar to those of liquids.A greater surface area coal–air contact increases the intensity of burning,so the temperature inside the fluidized combustion bed (1073–1173K)is lower,than in a standard coal combustion bed (1473–1873K).T.Kasikowski et al./Journal of Environmental Management 73(2004)339–356346。