Study of oxidative desulphurization process of coal with different metamorphism degrees

第40卷第2期燃料化学学报Vol 40 No. 2012年2月Journal of Fuel Chemistry and TechnologyFeb.2012文章编号:0253-2409(2012)02012909Study of oxidative desulphurizationprocess of coal with different metamorphism degreesS PYSHYEV. V GUNKA Y PRYSIAZHNYI K SHEVCHUK. A PATTEK-JANCZYK(1. Institute of Chemistry and Chemical Technology, Lviv Polytecnic National University, St. Bandery 12, 79013 Laiv, Ukraine2. State Higher Vocational School in Tarnow, Mickiewicz 8, 33-100 Tarnow Poland)Abstract: The oxidative desulphurization process of coal with different metamorphism degrees treated by an air-steam mixture hasbeen studied. It has been shown that the pyrite present in black coal and anthracite is oxidized with the sulphur dioxide formationand the process chemical mechanism does not depend on the quality of organic matter. The medium-metamorphized coal, capable ofturning into a plastic state and cake in the range of investigated temperatures( 350-450 C), is desulphurized with the greatestdifficulty. The chemical mechanism dealing with the transformations of pyritic sulphur present in brown coal differs from similarprocesses taking place in black coal and anthracite, because Fes, is converted with hydrogen sulphide formation at desulphurizationKey words: oxidative desulphurization; organic matrix; pyrite; metamorphism degree; sulphurCLC number: TQ533 Document code AThe use of coal at heat power plants( HPPs)is stage in the two-staged coal burning at HPPs, andcomplicated because of the sulphur high present in the desulphurized coal can be seen as comprising thecoal. The burning of such a fuel leads to the so, second stage of burnemission into the atmospherePrevious studies(6-91 conducted on some coalNowadays SO2 emissions accompanied by smoke samples showed the effect of temperature and waterfumes decrease due to their sorption by potassium steam on the chemical mechanism of the coalompounds with the following gypsum obtaining. desulphurization process:However if we do not take into consideration theIt was observed that process intensification takesbenefits from the environmental protection, thanall place at 425 C and higher temperatures due to thethese desulphurization methods willmposition of pyrite to pyrrhotite and sulphur witheven if by-products( gypsum, dry ash, ammonium their following oxidationsulphate etc. )find an application"1-It was assumed that the addition of water steamMost of the other existing desulphurization to the air enhances the process due to the fact that themethods are either economically unprofitable or under steam may form complexes with pyrite, therebydevelopment. Thus, we may say that the efficient and increasing its reactivity. Water adsorption changes theprofitable industrial technology relating to so2 highest occupied molecular orbital HOMOemissions reduction for the combustion of high- characteristics of the surface, for instance, H2O to Fesulphur coal is absentions by electron donation. The resulting LUMO statesWe develop the technological basis of coal attributed to the orbitals in S2 dimers occurring in bulkpreventive desulphurization by using the oxidative can promote the surface reactionsmethod The essence of this process lies in theUsing data from 6-9, the scheme of the processselective oxidation of pyritic sulphur, which chemism was suggested( Figure 1)constitutes the main part of sulphur in the highOn the other hand. the authors( 3, 11, 12) showedlphur coall2-, by an air-steam mixture at 350- that coal organic matter(C)and its transformation450 C. The desulphurization products of black coal products(CO) may participate in reactions of pyriteand anthracite are solid fuel with a relatively low oxidation, Fes Fe-s) formation and itssulphur content, resin formed by partial transformationdecomposition of coal organic matter, andFeS,+C+H20- H2S+ Fes+ codesulphurization gases with a high content of so2FeS2+C→CS2+Fe(2)The latter may be used for the production of liquefied2FeS(Fe- S)+C- CS,+ 2Fe(3)concentrated So, by using known methods 101FeS2+CO→Fes+COSThe proposed process can be seen as the firstIt is well known that for coal treatment by waterReceived date: 2011-06-07: Recelved in revised form: 2011-09-21Corresponding author: Serhiy Pysh'yev( 1972-),male, Ph. D, associate professor, main凵中国煤化工mandhydrocarbon fuels, E-mail: gaja@ polyet. Viv. ua.CNMHG本文的英文电子版由Elsevier出版社在ScienceDirect上出版(hp://www.sciencedirect.com/science/joumal18725813)。130燃料化学学报第40卷steam or an air-steam mixture, the hydrogen may be on COM reactivity. Therefore, the followingformed due to the gasification reactions of the coal questions emerge:organic matrix COM ). Therefore, the pyriteAre black high-metamorphized and brown coalstransformation may be expressed by the following desulphurized in the same manner as the samplesequationsIn previous experiments?FeS2+H2→Fes+H2S(5)Is pyrite chemism the same for all types ofFes(Fe1S)+H2→Fe+H2S(6) black and brown coalPyrite hydration in accordance with EquationsThus, the aim of this work was to establish the5)and(6) is also possible due to atomic hydrogen. effect of COM on the oxidative desulphurizationAtomic hydrogen is formed by the compounds that are process and the dependence of the reaction rate andcapable of generating it during heating 3Jdirection of pyrite conversion on COM characteristicsThese experiments would allow a comparison of thFe, ( Sondesulphurization process of different types of coal andwill improve or refute the possibility of its application350℃for any type of coalith watercam1 ExperimentalsDAFoThe following samples of Ukrainian coal were425℃selectednvestigation: brown coal(B)from400℃Morozivskyy deposit of Dnieper brown-coal basinFecandle(C)from Buzanska mine of Lviv-VolynFe (SO4hcoal basin; gas coal (G)from Chervonograd mine ofFeSOFe, o.Lviv- Volyn coal basin; fat coal F1) fromSamsonovska concentrating mill of Donetsk coalFigure 1 Scheme of process chemismbasin; fat coal ( F2)from Lisova mine of Lviv-VolynIn earlier works, desulphurization of low (61 and coal basin; lean coal(L)from Shidna mine ofmedium-metamorphized coals with a relatively highDonetsk coal basin; and anthracite (A)fromreactivity of the organic matrix was investigated. It isRovenska concentrating mill of Donetsk coal basin. Aknown that COM reactivity depends on the degree offraction of 0. 10. 25 mm was used for researchthe coal metamorphism. High-metamorphized coalbecause it is the optimal size for coal burning atfor example, lean coal and anthracite )has an inertHPPsorganic matrix. Brown coal has a higher reactivity ofA model mixture of pyrite mixed with inertthe organic matrix than low- and medium-material in such a way that the content of pyriticnetamorphized coals and high analytical moisturesulphur in the mixture was comparable with that in the(usually more than 10% mass ) The possibility ofriginal coal) was prepared(1)-(6)reactions proceeding depends, first of allThe analytical data pertaining to the initial coaland model mixture are presented in Table 1Table 1 Characteristics of the initial samples and model mixtureMoisture Ash, Volatiles Sulphur content for dry mass, mass%Relative content of sulphurCoal typecontentyielddifferent types /9( symbol)Mpyritic, organic, sulphate, sy/s s,/s, sso, /s,mass%w/%sSBrown(B)13.9·9.4263.784.2849.0748.362.57Candle(C)Gas(G)12116.8040.917.95Fat(Fl)2.3310.1434.323.681.3163.8635.600.541.4235.566.9l.1764.5616.7918.65Lean (L)1.0043.1016.534.4885.0412.0Anthracite(A) 3.50 6.22 2.001.411.2149.4742.468.0Pyrite( mixture of中国煤化工Fes2 and Sio,) 1.543.863.720.130.26CNMHGfor moist ash-free sample(w.):: unidentified form of sulphur#2 Serhiy Pysh'yev et al Study of oxidative desulphurization process of coal with different metamorphism degrees 131Table 1 depicts that all samples are high-sulphurTo study the oxidative desulphurization processcoals with pyritic sulphur of 5%-90%. The laboratory plants are used. Their flowcharts arehigh content of sulphate sulphur in some presented in Figure 2. The detailed scheme andcoals can be explained by the fact that there was an description of these plants are describedaccess for air in some placeselsewhere[ 141water condensatedesulphurizationgasesaneous andblock of air-steam mixture(ASM)_ASM e reactionblockpreparation and heatingdesulphurizationFigure 2 Flowchart of the laboratory plant for coal oxidative desulphurizationThe desulphurization process was performed in a sample, massfluidized-bed reactor under isothermal conditions. TheThe gaseous products of the desulphurizationreactor was heated by an electric furnace. The process were analyzed by a chromatographic methodtemperature was controlled using a thermocouple using chromatograph LHM (N 479)with a thermallocated inside the reactor. The flow rate of the conductivity detector and two columns of Polisorb-1reaction mixture was controlled by a flowmeter.separation of carbon dioxide, ethylene, ethaneThe linear rate of the steam-air mixture ( m/s) hydrogen sulphide, propane propylene, and sulphurand the coal grain size were chosen to ensure the dioxide)and zeolite Cax separation of nitrogenpyrite oxidation in the kinetic area. The rates were oxygen, methane, and carbon monoxide ) Heliumabove 0. 013-0 025 m/s for the low- and high- was used as a gas carrier. The hydrogen content inmetamorphized black and brown coals; whereas they the gases was determined using the chromatographwere above 0. 030+0.052 m/s for the medium- Zvet( gas carrier - nitrogen; adsorbent- Nax, heatmetamorphized black coals. The higher values of the conduction detector)oxidant linear rates, necessary for the F-type coal, areThe 57Fe Mossbauer measurements wereexplained by the ability of the coal to turn into plastic performed in the transmission geometry. The recordedstate and cakespectra were numerically analyzed by means of aOn the basis of obtained results, the sulphur least-squares procedure under the assumption of theconversion and removal were calculated. Pyritic Lorentzian shape of the absorption lines. After thesulphur conversion was calculated by the following numerical deconvolution of the spectra,theformula(%)without taking into consideration its Mossbauer parameters of each subspectrum weredetermined. The isomer shift values versus a-Fe△s=5·100-5xcvalues were quoted. The parameters including isomershifts proportional to the electron density at the Fewhere S%o is the content of pyritic sulphur in thenuclei, quadrupole splittings related to the electricfield gradients, and Zemass % so is the content of pyritic sulphur in the the intemal magnetic fields at the iron nuclei weredesulphurizated coal while calculating for the used to identify the different iron compounds formedanalytical sample,mass%, and c is the yield of the during the desulphurization process. The spectral areadesulphurizated coal, mass%of each subspectrum was applied to evaluate theThe removal of pyritic sulphur( %)is calculatedrelative content of the iron-containing phase byby the following formula:assuming that the recoil-free fractions f for all the△S2 Results and discussionwhere sdo is the content of pyritic sulphur in theTo determine the effect of COM and its qualityinitial coal while calculating for the dry sample, on the processmass% and s, is the content of pyritic sulphur in the investigations of pyrdesulphurizated coal while calculating for the dry types of coals weremyH中国煤化工ifferentCNMHG燃料化学学第40卷132steam and temperature on the desulphurization of clear dependence between metamorphism degree anddifferent coals was compared. The coal rank increases the removal of pyritic sulphur. Obviously, the qualityin the order of B→C→G→F-L→A( Table1). The of COM( except for the medium-metamorphizedobtained results also allow determining whether thecoal) does not practically affect the desulphurizationeffect of temperature and water steam on the processchemism, which was established in previous worksis similar for different types of coals. The proces100time and oxidant flowwere constant. Thented in Table 2 and80esults areFigures 3 and 4Table 2 Characteristics of pyrite and coalDesulphurized Content of pyriticConversion20samples of pyrite sulphur for Coal yield, of pyritic10and differentmass50types of coal mass%, spC0.2382.271975.33Figure 3 Effect ofoxidative desulphurization of different types of coal83.1172.611.0771.24The presence of organic matrix in the reactionzone exerts a different influence on the process 8proceedings. It increases the conversion of pyriticsulphur by 10%-20% for the black coal with thelowest and highest metamorphism degree(C and L),5by approximately 9% for the G-type coal, and byonly 1. 5% for the F2-type coal. The reason ofpyrite-less conversion for G- and F2-coal types is theformation of non-volatile components of thermal0102030405060decomposition(the coal turns into a plastic state andSteam content in oxidant x_/%cake), resulting in the complication of oxidant accessFigure 4 Effect of oxidant composition on theof coalto the pyrite particlesoxidative desulphurization of differentThe data depicted in Figure 3 show the similaritySolid products of high-metamorphized coalof the temperature effect for different types of coalsdesulphurization(L-type)with the low reactivity ofThe removal of pyritic sulphur essentially increasesthe COM were analyzed using Mossbauerwith the increase of temperature to 425 C, and thegreatest increase is in the range of 400-425 Cspectroscopy(Table 3, Figure 8). The results showthat at 425-450 C, pyrite decomposes to pyrrhotiteAt high temperatures(425 C and, especiallyand sulphur followed by their oxidation. The increase450C), the least removal is observed during theof water-steam amount in the oxidant decreases thedesulphurization of medium-metamorphized F-type amount of non-converted pyrite and increases thecoal( Figure 3). The reason is the difficulty justamount of oxidation end-products iron oxides ).Thementioned for oxygen access during the processgreatest effect of water steam is observed at relativelywhich occurs due to the ability of the F-type coal to low temperatures(350-400 C),because at highturm into a plastic state and cake.temperatures( above 425 C),pyrrhotite is formedWith the increase of the water-steam content inindependently despite the presence or absence of waterthe oxidant, the sulphur removal shows the maximasteam. Pyrrhotite interacts with the oxidant( air withFigure 4)a reaction rate higher than that of water with the pynteMoreover, these maxima shift to the oxidant中国煤化工ueLcontaining a greater water-steam content with thetythe dataincreasing of the total and pyritic sulphur content in obtained duringCNMHGw. 16) andthe initial coal. It should be noted that there is noTable 3 Mossbauer spectroscopy data for black coal of L-typesContent ofFesFeSO4·mH2OFe species3O4a-Fe2O3IS QSISAISHHsteammms mm/smm/s mmsmmsms kGmmsmm/mm/s0.30(1)0.60(1)79.1(3)1.26(1)2.7(1)15.5±140.30(1)0.60(1)71.4(4)1.25(1)2.70(1)10.8(5)1.24(1)3.14(2)4.1(4)0.38(1)1.14(1)75(3)500.30(1)0.62(1)50.4(3)1.32(1)2.88(1)15.7(9)0.27(3)490(3)4.3(8)0.37(1)0.20(1)515.2(6)12.5±120.56(3)446(3)5.5(6)0.39(2)0.22(3)501(2)3.4(8)coal was desulphurized at 400 C0.3(1)0.63(2)54.3(0)1.32(4)2.66(8)7.0(3)0.30(1)492(1)6.7(7)0.38(1)0.19(1)517.2(3)12.3(9)0.57(2)457(2)7.8(5)0.41(2)0.18(4)503(2)3.5(8)5500.30(1)0.62(2)406(3)1.28(1)2.7(1)8.3(4)0.3(1)491(1)11.2(8)0.37(1)0.20(1)514.7(3)26.8±1.20.56fx447(3)6.1(7)coal was desulphurized at 425 C0.31(1)0.62(1)32.61.31(1)2.70(2)74(4)0.39fx1.16(3)5.9(5)0.37(1)0.17(1)516.0(2)29.6±1.80.6619297tos0.38(1)0.20493(2)19.4±2.6H300.30(1)0.60(1)22.7(6)0.39fx1.10(2)7.7(6)0.32(1)491(2)6.0±2.30.37(1)0.19(1)5182(3)32.5±2.70.6619278.4(4)0.56fx458(3)5.4(7)0.40(2)0.18(2)505(1)10.3*4.1coal was desulphurized at 450 cae0.31(1)0.61(1)27.8(3)039fx1.09(2)3.8(3)0.32(1)488(1)7.8±2.00.37(1)0.20(1)518.0(2)31.2±1.20.66217-3029.6(3)0.57(2)454(1)7.5(5)0.38(1)0.16(2)502(1)6.7±2.70.31(1)0.60(1)18.6(3)0.39fx1.02(2)5.2(3)0.37(1)0.20(1)516.5(7)52.8(8)0.662342945.5(5)0.34(1)0.14(2)494(1)11.8±1.1sample of studied coal contains additionaly 5. 5%-8.5% of component with parameters IS = 1. 08(2)-1. 10(2)mm/s and Qs 2 65(2)-2. 76(2)mm/s that remains unchanged in all experimentsand may be ascribed to mineral illite Fe:: isomer shift and line width were constrained in all fits IS isomer shift versus room temperature a-Fe: Qs quadrupolA: relative contribution to the total spectrum中国煤化工CNMHG燃料化学学报第40卷medium-metamorphized71coals. It means that process chemism for black coals with differentchemism and the mechanism of conversion of pyrite metamorphism degrees at the temperatures nearcontained in black coal do not practically depend on 425 C. These activation energies of all three types ofcoalificationcoals(C, G, and L)decrease with an increase intemperature, indicating the changes in the process一350℃chemism( pyrite decomposes to pyrrhotite and sulphur425℃followed by their oxidation ). The decrease inactivation energy( Table 4)cannot be explained by0⑩00400othe change of the process area( kinetic for diffusion)because the oxidant linear rate and grain sizes ensurethat the pyrite oxidation reaction occurs in the kineticarea within the investigated range of temperatures asmentioned earlierOne can observe from Figure 4 that the removalof pyritic sulphur exceeds 75% for any type of coal. It0 5 10 15 20 25 30 35 40 45 50 55 6065 80 should be noted that the oxidant composition effectwas investigated under similar conditions for all typesFigure 5 Effect of process time on the oxidativeof coal. Therefore, the process time and oxidantdesulphurization of C- type black coal at different temperatures amount, for example, were non-optimum during thedesulphurization of the L-type coal. This means that●-350℃—400℃the method of sulphur removal is effective for all types80425℃of high-sulphuric black coal·-450℃The desulphurization of brown coal displays otherregularities as well. The increase in temperature hasthe least effect on the process the most flatdependence between the removal of pyritic sulphur andtemperature as shown in Figure 3), and sufficientlhigh concentrations of hydrogen sulphide occur in thegases(4.6%7. 1%, Table 5). At desulphurizationof black coal of different types and anthracite0510152025303540455055Time ,/minpractically the amount of all removed sulphur turnedFigure 6 Effect of process time on the oxidativeinto dioxide( Table 6). All these facts indicate thedesulphurization of G-type black coal at different temperatures changes in the desulphurization process chemism usingl00brown coal (compared with black coal)350℃—400℃The investigations of chemism and the mechanism425℃of brown coal desulphurization were not the aim of the450℃present work. Therefore, it may only be assumed that60the formation of hydrogen sulphide takes place due to50the high reactivity of COM. This is described inEquations(1),(4), and(5). The further formationof hydrogen sulphide during the process may be alsocaused by the moisture adsorbed in the brown coal andis described in the following equations\312]0102030405060708090100II01202Fes(Fe S)+3H20-Fe, 0,+ 2H2S+H2 (7)3FeS(Fe- S)+4H2O-Fe, O+3H2S+ H2 (8)Figure 7 Effect of process time on the oxidativeFes(fe-s)+H,o+ Feo +H,sdesulphurization of L-type black coal atHydrogen sulphide may be formed due to COsdifferent temperatureshydrolysis formed in accordance with Equation 4The analysis of literature data shows that theThe calculations of the effective activation majority of theenergies of pyrite oxidation(Table 4. The initial data intensively only中国煤化工 nan processfor calculations of effective activation energies are temperatures(35dCNMHGgiven in Figures 5-7)confirm the uniformity of the is not a pure carbon and hydrogen; therefore, the$ 2 Serhiy Pysh yev et al: Study of oxidative desulphurization process of coal with different metamorphism degrees 135proceeding of the reactions between the hydrocarbon Figure 1)and COM at the temperatures belowpart of the coal and its sulphuric compounds is possible 200 Cl15). The possible participation of pyrite in theat lower temperatures. For instance, hydrogen reactions with coal organic fragments was alsosulphide can be produced as a result of the reaction predicted(is]between the sulphur formed during pyrite dissociationTable 4 Calculation results of the effective activation energies within different temperature rangesTime, at which pyritic sulphurReaction rate constant, ki,sActivation energy, E, k/ molnversion Is x%,τ/sRln(k/k,)·10t.E350c40042540354e42540-63/T673698623K)(673K)(698K)(723K)(6023K)(673K)(698K)(723K)-673K-698K-723K23221260.012920.151520.208330.23810171.14922.3G14161861260.021190.161290.208330.23810141.139.922.310801741560.027780.121950.172410.19231102.853.918.3C42962462160.011640.128210.203250.23148166.871.8G2640462100.018940.151520.203250.23810144.645.826.5cGLcGLcGL480580.010020.104170.170070.19380162.876.421.9l0140.059170.204080.238102.925.812182460.049260.204080.2439221.429.83300.062110.151520.18182138.930.580%0.148150.1960846.911526780.069440.1179988.76425340.124610.1498130.8Average value for C-type coal169.0104.729.2Average value for G-type coal142.8102.341.8Average value for L-type coal132.889.725.4Average value for all black coal148.232.1Table 5 Average characteristics of desulphurizationgases composition for different types of black coal and anthraciteContent in desulphurization gases v /%sO2HecocON22.2-4.90.3~1.30.2-1.20.93.45.8-13.60.9~7.878.2-80.10.9-0.92samples obtained during desulphurization of low- and medium-metamorphized coals contain below 0. 1% of hydrogen sulphicand 0. 1% of hydrogen. Oxidant contains 30%-70%( volume ratio of water steamTable 7 depicts the comparative composition of Table 7 show the main role of COM in the reactionsdesulphurization gases obtained using dry and wet related to hydrogen sulphide formation, because H, Ssamples of the brown coal with the highest reactivity and H, are not formed using anthracite. duringof its organic mass and anthracite( the most inert desulphurization of both dry and wet brown coal,theCOM)amount of all removed sulphur converts into H,S.ItThe analysis of gases composition shows that should be noted that hydrogen sulphide is formed evenwater steam still plays an insignificant part in the at 350 c during desulphurization of the brown coalreactions related to pyrite conversion. At its high This fact allows the assertion of the directcontent in the oxidant 30- 70%), traces of participation of pyrite in the reactions with COMhydrogen sulphide and hydrogen see Table 5because it cannot中国煤化工 pyrrhotiteappear in the desulphurization gases. The results of and sulphur at suchCNMHG燃料化学学报第40卷Velocity / s)Velocity /(mms)Velocity /(mms)(e)10-1010-10Velocity /(mms)Velocity /(mms)Velocity /(mm-s)(B)10-10Velocity A(mm. s)Velocity /(mm-s)Velocity A(mm.s)Figure8 Mossbauer spectra of initial and desulphurized L-type black coal( the symbols A-I see in Table 3)Table 6 Average characteristic of desulphurization gases composition for coal BContent in desulphurization gases v/9H2SH3.2-7.40.8-1.91.0-192.6-5.818.1-28.71.6~3.656.6~71.40.6-0.80.6-1.5Table 7 Characteristics of gases obtaining at desulphurization of wet and dry samples of coalContent in desulphurization gases v/%H,SCHAON2H2analytical sample of brown coal(w_=13. 96%, mass ratio)0.55sample of dry brown coal(w=0. 44%, mass ratio)0.980.64analytical sample of anthracite(w=3.55%, mass ratio)0.352.9814.9278.67sample of wet anthracite(w,=14.54%, mass ratio)0.80.60traces3.5514.43traces3 Conclusionsoxidation except for the medium-metamorphized coalWhen black coal is used, the presence of theAt high temperatures(425 C and, especiallyorganic matter in the reaction zone affects the pyrite 450 C), the least removal of pyritic sulphur isoxidation with the increasing pyritic sulphur observed duringconversion of 1. 5-20. 0%. The quality of this metamorphized中国煤化工 d by theorganic matter does not practically influence the pyrite difficulty for oxyCNMHGprocess of2 M Serhiy Pysh yev et al: Study of oxidative desulphurization process of coal with different metamorphism degreesdesulphurization in which F-type coal is used because 425 C), pyrrhotite is obtained independently in spiteit is capable to turn into plastic state and cakeof the presence or absence of water steam. ThisFor all types of black coal at 425 C and higher highly reactive component reacts with the oxidanttemperatures, process intensification takes place ( air). Its reaction rate is higher than that of waterowing to the decomposition of pyrite to pyrrhotite and with the pyrite complexsulphur followed by their oxidation. This is confirmedBy means of the supposed method, any type ofby the results of desulphurized coal with different black coal may be desulphurized, and at least 75%etamorphism-degree investigations using Mossbauer 95% of pyritic sulphur may be removedspectroscopy as well as by the changes in the effectiveUsing brown coal, its organic mass participatesactivation energy from 132. 8 to 169.0 k/ mol at the in the reactions related to pyrite conversion withtemperatures from 350-400 C to 25.. 2 kJ/mol hydrogen sulphide formation in the end. The chemismat425~450℃of brown coal desulphurization needs additionalWater steam may play an insignificant role in the investigationconversion of pyritic sulphur of black coal. It may ACassume that the water steam forms pyrite complexesacknowledgmentwith increasing pyrite reactivity. Water steam displaysThe authors are very grateful to Professor J.the greatest effect at low temperatures (350- Stanek from M. 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