煤气化过程痕量元素迁移实验研究

第32卷第35期中国电机工程学报VoL.32 No.35 Dec.15, 20122012年12月15日Proceedings of the CSEE92012 Chin.Soc.for Elec.Eng. 21文章编号: 0258-8013 (2012) 35-0021-10中图分类号: TQ 534文献标志码: A学科分类号: 470-.20煤气化过程痕量元素迁移实验研究蔡铭'，许世森'，郜时旺'，吴龙”，刘练波'，D. Dugwell2, R. Kandiyoti2(1. 中国华能集团清洁能源技术研究院有限公司，北京市海淀区100098;2.英国帝国理工大学化学工程系，伦敦SW7 2AZ)Experimental Study ofTrace Elements Release From Coal Gasification ProcessCAI Ming , XU Shisen', GAO Shiwang', WU Long, LIU Lianbo', D. DUGWELL2, R. KANDIYOTI(1. Huaneng Clean Energy Research Institute, Haidian District, Bcijing100098, China;2. Department of Chemical Engineering, Imperial College London, SW7 2AZ, London, UKABSTRACT: The release of toxic trace elements from coal模拟结果进行对比分析。结果表明，中试试验与热力学模拟gasification is a matter of environmental concern. A laboratory结果比较吻合，中试试验条件下痕量元素反应达到了平衡状scale wire-mesh reactor (WMR) was used to simulate trace态;WMR试验中Pb、V、Ba、Mn及Co的排放规律与热element releases from coal particles in an entrained flov力学模拟结果比较-致，而As和Se的试验结果与热力学gasifier. Char samples were produced from WMR under模拟结果相差较大，可能是WMR试验中反应时间较短，受various gasification and pyrolysis conditions, within the动力学因素影响较大的原因。operating window of the gasifier. The samples of char as well关键词:煤气化;痕量元素;迁移;金属丝网反应器:气流床as raw coal were analyzed by inductively coupled plasma-massspectrometry (ICP-MS) for the contents of an array of mostly0 INTRODUCTIONtoxic trace elements: As, Se, Pb, V, Co, Ba, Cr and Mn. Coaland slag samples from a pilot scale, entrained flow gasifierCoals contain most of the elements in thewere also analyzed for comparison with the WMR data. Thereperiodic table, although many are present at very lowis good agreement between the thermodynamic predictions andconcentrations. Trace elements have been defined as .the pilot scale data, showing that equilibrium with respect tothose with concentrations below 1 000 mg/kgtrace element partitioning is reached in the pilot scale gasifer.(0.1 wt%). Some of them are released duringAgreement with the WMR data is less consistent. There iscombustion or gasification, such as Hg, As, Se and Pb.agreement for the elements Pb, V, Ba, Mn and possibly Co. It isinconsistent for As and Se, which may be due to a kineticOthers are bound to, or react with, clays or silicate orlimitation, resulting from the short duration of the WMR test.other mineral forms, which tend to remain in theKEY WORDS: coal gasification; trace elements; release;bottom ash or slag. Until recently, the major work onwire-mesh reactor; entrained flowthe partitioning of trace elements is focused on摘要:煤气化过程痕量元素排放引起的环境问题是成为关注p.f. -coal combustion. With the increasing large scale的热点之一。 为了研究和掌握气流床气化炉中的痕量元素排utilization of gasification technology and more放规律，利用高温高压金属丝网(wire-mesh reactor, WMR)stringent emissions regulations, trace elements反应器模拟气流床气化不同的气化和热解条件,对煤样及反emissions from coal gasification needs to be应器产生的煤焦样中的As、Se、Pb、V、Co、Ba、 CT、Mn.investigated in more detail.痕量元素进行电感耦合等离子体-质谱(inductively coupledTrace elements occurrence in coals， theirplasma mass spectrometry, ICP-MS)分析。 WMR实验结果与气化炉中试装置试验煤、灰、渣样品中数据及热力学模型emission in gases as well as their partitioning in flyash and s中国煤化工combustion have基金项目:国家重点基础研究发展计划项目(973计划)been studirCNMHGReed et al used a(2010CB736202);中国华能集团公司科技项目(HNKJ09-H14)。TH.The National Bsic Research Program (973 Program)pilot scale gaslier to stuay une aisuribution of several(2010CB736202); China Huancng Group R&D Project (HNKJ09-H14).trace elements under conditions of coal gasification22中国电机工程学报第32卷[3-4]. Researchers [5-7] studied the transformation ofpressure, in CO2, the operating temperature is limitedtrace elements during coal gasification process byto 1 500 C, due to reaction of the mesh. Molybdenumthermodynamic equilibrium calculation approach.mesh was selected for this study, as it's inert underSome laboratory scale experimental studies have alsothese reaction conditions and has no influence on thebeen conducted. For example, George et al [8] used atrace elements' reaction and partitioning. Fig. 1 shows“hot rod” reactor and Miller [1,9] used a 'suspensiona schematic diagram of the reactor.firing reactor' to study the trace elements partitioningunder different conditions, but they studied traceelement partitioning at lower temperatures andpressures compared with the conditions in pilot o3commercial scale entrained flow gasifiers.41The objective of this study is to investigate thetrace elements partitioning between char and gasduring coal gasification, using a bench scalehigh-pressure wire-mesh reactor to produce charsamples under different pyrolysis and gasification7g981710conditions. The concentrations of trace elements (As,1- -Gas exit; 2- Quart bll; 3- Electrode clamps; 4 -Mesh support plate;Se, Pb, V, Co, Ba, Cr and Mn) in these char sampless_ Curent supply; 6- -Sinter disc; 7- Support plate stands, hollow toallow water flow;8- Copper seal; 9- Gas iniet; 10- -Base plate;as well as in the parent coal were determined. For11- -Throw over sealing ring; 12- -Flow smoohing cell; 13- -Spring,comparison, samples (bottom ash/slag) collected fromhollow to allow water flow; 14- -Wound corrugated tube; 15- Pressureexperiments in the pilot scale entrained-flow gasifierbell; 16- -mesh; 17--Line to pressure gauge.were also analyzed. The results for trace elements ,图1高压金 属丝网反应器结构示意图partitioning between the residual char and gas phaseFig. 1 High pressure wire-mesh reactorare compared for the two scales of operation.Detailed descriptions of the equipment have beenpresentedelsewhere [10-13]. Experiments ar1 EXPERIMENTALnormally undertaken with around 5~7 mg of coal1.1 Coal Samplesample (with particle size 125~150 um). The amountShenmu low volatile bituminous coal was usedof char formed depends upon the coal type andfor both the bench and pilot- scale experiments. It wasexperimental conditions. In this study, experimentssupplied by CERI. The proximate and ultimatewere carried out at a heating rate of 1 000 C/s andanalyses are given in Tab. 1.holding time of 1 s. Several runs had to be conducted表1神木煤工业分析和元素分析under the each set of experimental conditions toTab.1 Proximate and ultimate analyses of Shenmu COalgenerate sufficient char (> 10mg) for trace elementsProximate analyis/%Utimate analyis%analysis. After each test, the mesh and char wasMa Vaf_ Am_ CarHan! Nar Sauf Oas?*carefully weighed and the char sample was then4.936.1 11.279.04.8.9.014.3removed and combined with the other test char●by dfference.samples, in preparation for analysis. Sufficient sample1.2 The High Pressure WMRwas collected in this way to enable determination ofThe high pressure WMR is used to simulate theAs, Se, Pb, V, Co, Ba, and Mn. Hg is determined ingasification conditions and produce char samples forour laboratp i「tgtn=er. This requires a中国煤化工、the trace elements analysis. Operation has beenmuch grTYHCNMH&) and itwas notachieved at temperatures up to 2 000 C, and pressurespractical t∪accuuluiaic uIC aiuunt required fromin excess of 3 MPa, under inert conditions. Under highmultiple tests in the WMR.第35期蔡铭等:煤气化过程痕量元素迁移实验研究231.3 CERI pilot-scale entrained-flow gasifierashing breaks down the entire sample, completelyA novel two-stage, dry feed, pulverized coal,releasing all trace elements into solution. However,pilot-scale gasifier (36 t(coa1)/d) has been developedsome of the more volatile element (e.g. As, Se} wouldby Clean Energy Research Institute (CERI). Ae lost during digestion. The 'softer’ microwaveschematic diagram of the gasifier is shown in Fig. 2. digestion method was adapted in this study for theDuring opcration, coal, steam and oxygen are injecteddetermination of As and Se. The‘microwave digestioninto the first stage, where gasification reactions occurmethod was specially developed for volatile elementsat a temperature in the range 1 500~1 700 C andunder wet digestion conditions and was proved bypressure of approximately 3.0 MPa. Melted ash (slag)Standard reference materials (1 632b Coal; 1 633bflows down to the bottom of the gasifier, where it isFly Ash issued by NIST); Different heating programsquenched. The product gas and entrained fly ash flowwere used for ash/slag and coal samples and these areto the second stage, where coal and steam are injected.shown in Tab. 2.The endothermic reactions occurring in the second表2煤、灰、渣微波消解流程stage reduce the gasifier outlet temperature to aroundTab. 2 Microwave digestion programs for coal, ash and900 C. An important feature of the CERI gasifier isslag samplesthat it incorporates a fly ash recycle system, toSample Step No.Microwave Digestion Programsmaximize the carbon conversion. When the gasifierHeatupto130Cfor20mincoaloperation reached the desired conditions and full load,Hold at 130C for 15 minHcatupto70Cfor5minslag samples were collected for trace elementsHoldat70Cfor5minanalysis.Heatupto100cfor5min↑Product gas andash/slagfly. ashHold at 100C for 5 minHeatup to 130C for 5 min .Hold at 130 c for 20 min1.5 Inductively Coupled Plasma-Mass Spectrometry. 1000~1 200 C(ICP-MS) AnalysisIn the study, the ICP-MS analysis was conductedcoal,steam-→-Pon a PQ2+ STE instrument. The detection limit of this.1500~-1 700 CICP-MS is down to 0.001~0.1 ugL. Two importantcoal, oxygen,steamfactors are introduced for ICP analyses.Taking into account of the instrumentalsensitivity and sample preparation, the limit of↓Slagdetection (LOD) is defined as:图2 CERI 两段式气流床气化炉结构示意图Fig. 2 Schematic diagram of CERI two-stage entrained1o=3- STDRCan-SCcopp]Dpflow gasifer20ppb1.4 Sample Preparation: Digestion Methodswhere STDRC.。 is the standard deviation of the rawThe quantification of trace elements in solidcounts of the procedure blank, Rc20ppb is the mean ofsamples by Inductively Coupled Plasma-Massthe raw counts of the 20 ug/L calibration standard, RcBspectrometry (ICP-MS) requires that the sample mustis the mean of the raw counts of the calibration orbe dissolved in an acidic solution. In this study, twoICP-MS中国煤化工; concentration ofseparate digestion methods were used:“wet ashing”the calibrntion and Dr is theYHCNMHGand“microwave" digestion. The wet-ashing methoddilution facwr. me accurauc measurement of the tracehas been described in detail elsewhere [14]. Wetelements contents in a solid sample is therefore24中国电机工程学报第32卷dependant on these two parameters.gaseous species. These assessments are then comparedThe standard deviation (SrD) is calculated, towith what is observed in the analyses of data from thereflect the extent how the test results spread OIWMR and CERI pilot plant.disperse, as follows:2.2 Trace elements analysis of Shenmu coalTab.3 presents concentrations of trace elementsSm =六2(x-wof interest in Shenmu coal. These elements are: As,where x; is the concentration of trace elements in theSe, Pb, V, Ba, Co, Cr and Mn. Five repeat analysessample, μ is the average of x: Five parallel digestionswere conducted; the standard deviations are also givenand analyses are done for each sample in this study,in the table. The sample contained significant amountsand the standard deviation represents the repeatabilityof Mn and Ba, whereas the concentrations of the otherfrom the analysis by the repeated digestions.elements are below 10 mgkg. Se and As were foundat the 1.5 and 0.3 mg/kg levels, respectively. It should2 RESULTS AND DISCUSSIONbe borme in mind that the very low concentrations of2.1 Thermodynamic Equilibrium Modelingsome of the trace elements in the coal sample causeA preliminary insight into trace elementssignificant uncertainties in their measurement. This ispartitioning during gasification under entrained flowbecause the values give rise to concentrations in theconditions can be gained by the application osample solutions that are close to the detection limit ofthermodynamic equilibrium modeling. Althoughthe ICP-MS (LOD) and the errors are magnified whenthermodynamic equilibrium may not actually bethe measured concentrations are multiplied by theattained because of kinetic constraints, predictions ofsample dilution factor (DF)[1,8].this type are quick and can serve as a guide to what表3神木煤中痕量元素含量might happen under the conditions that are studiedTab. 3 Trace elements Concentrations in Shenmu Coalexperimentally. The program used for this purposeTrace element Concentration in coal/(mgkg) Standard deviation/(+(mg/kg))was MTDATA, This model uses the Gibbs free energyAs.50.1minimization method to calculate the concentrationsSe.30.0.6and phases for a pre-defined system.3.60.6The thermodynamic equilibrium modeling wasdeveloped on basis of Charpenteau's work [15]. ToCo3.3.0simplify the calculations, some unlikely events wereMn8.1excluded from the overall scheme prior to the2.2).3_equilibrium calculations. For instance, the predicted2.3 Total Volatile Yields of Shenmu Coal duringlevels of formation of many compounds between tracethe Wire Mesh Experimentsand minor elements may exceed the level of actualTab. 4 lists the operating conditions for the WMRformation. Due to the low probability of theseas well as the total volatile and char yields under theseelements coming into contact， during the shortconditions. Methods for determining the total volatileresidence times available in the reactor, such speciesyields under pyrolysis and gasification conditions inhave been excluded from the study. Trace-element vs.the WMR have been described elsewhere [16]. Thistrace-element interactions are even less likely todata and the trace elements concentrations have beenoccur, as are compounds containing multiple atoms ofused to calculate the trace elements partitioningthe same element. These categories have also beenbetween中国煤化工calculated usingexcluded from the calculations. The results have beenthe follow.TYHCNMHGused to assess the temperatures at which solid speciesABTrace Element Partition in char(%-=-000zx100%for individual elements or compounds tend towards100%第35期蔡铭等:煤气化过程痕量元素迁移实验研究25where A is the trace element concentration in the chargasifier. The tests at both scales were set up with thesample (mg/kg), B is the char yield (%， db)same coal, maximum temperature and total pressure,determined by the wire-mesh experiment and C is thebut there were unavoidable differences in the particletrace elements concentration in the coal sampleresidencetime, gaseousenvironment and(mg/kg). .time/temperature history of the particles. The WMRThe trace element partitioning to the product gashas a relatively straightforward contacting system andhas been calculated by:a defined residence time at known conditions. TheTrace Element Partition in product gas(%)=tests in this reactor were done in either pure N2 or100 - Trace Element Partition in char(%)pure CO2, i.e. the inorganic material was not exposedA previous study [17] has shown that the weightto the transient oxidizing conditions, as must haveloss of the slag sample obtained from the pilot-scaleoccurred in the entrained flow reactor. The situation isgasifier was less than 1%, when it was burmed in puremuch more complex in the pilot scale gasifier as itoxygen at 900 °C for 10 minutes. Therefore, in thiscontains two stages, each with their individual coalstudy, it is reasonable to assume that the pilot-scaleinputs, gaseous environment and temperatures. Thegasifier had achieved near total conversion. The traceslag sample used for the analysis represents thelements partitioning in the slag and product gasinorganic residue from the fuel added to the firstgenerated from the pilot-scale gasifier was thereforestage. Its residence time is not known. In addition, 0is added to the gasifter, so the fuel will have beencalculated by:exposed to transient oxidizing conditions. TheseABTrace Element Partition in slag(%) =二x 100% .differences will conceivably cause differencesbetween the measured trace elements partitioning inTrace Element Partition in fuel gas(%) =the two types of system. It is more likely that1- Trace Element Partition in slag(%)equilibrium will have been achieved (or at leastwhere A is the trace element concentration in the slagapproached)in the pilot scale plant than in the WMRsample (mg/kg) obtained from the pilot scale gasifier,(with its short residence time). In the followingB is the ash content of the coal sample (%, db) and Csections the results for individual elements areis the trace element concentration in the coal samplecompared to assess similarities and differences in(mg/kg).behavior.表4神木煤WMR实验中挥发性和煤焦量Arsenic and Selenium. These elements wereTab.4 Total volatile & char yields of Shenmu coal fromdetermined in solutions prepared by the microwaveWMR experimentsdigestion procedure. They are the more volatileExperi-ConditionsTotal Volatile Char yield/elements in the suite studied. The partitioning Oment No. Temperaure/C PressureMPa Sweep gas Yield/%, db) (% db)arsenic and selenium in the wire-mesh reactor underWMR 110002.0Nitrogen36.9several operating conditions is shown in Fig. 3 andWMR2.15002.42.857.2Fig. 4, respectively. For comparison, the distributionsWMR320003.44.455WMR 41 0001.59.5of these two elements in the slag and product gas fromWMR 5_2.0CC39.160.9the CERI gasifier are also presented in the Fig. 5. TheSample particle size: 125- _l50um, beating rate: 100 C/s, holdingtest conditions for WMR 1, 2, 3 and 5 are shown ontime 1s.Tab.4. The results show a completely different2.4 Comparison of Trace Elements Partitioningpartitionin HV口中国煤化工“MR test samplesin the WMR and the CERI Pilot Scale Gasifierand the piYHCNMHGThere are clearly substantial differences in theDuring uc opcrauon U1 une pilot-scale gasifier,modes of operation of the WMR and the pilot scale most of arsenic and selenium was released with the26中国电机工程学报第32卷100condensed arsenic species could be formed.Thermodynamic equilibrium modeling [1] predictedselenium to be gaseous, as either SeO or SeO2 during0combustion of a Polish coal. However, it wassuggested that the equilibrium model might not have20叶included some selenium compounds that could beWMR1 WMR2 WMR3 WMR5 CER1retained in the ash or slag. Reed [4] also calculated theProduct gas;■Char/slag.thermodynamic- equilibriumconcentrationso图3 WMR 实验和中试试验中痕量元素As的分布selenium under gasification conditions and indicatedFig.3 Arsenic partitioning in the WMR and pilotthat gaseous H2Se would be the predominant species.scale gasiferSo, the WMR results for both As and Se appear to beat variance with the thermodynamic predictions and80|with data obtained under combustion and gasificationconditions (at lower temperature, but longer residence50ftime) and with the CERI pilot plant data. The datafrom the pilot scale gasifier is consistent with the20 tpredictions made using the thermodynamic data andWMR1 WMR2 WMR3 WMR5 CERthe results suggest these species will be voltilized.J Product gas; ■Char/slag.The experimental techniques were fully checked in图4 WMR 实验和中试试验中痕量元素Se的分布this work and the results are acceptable. Therefore, itFig. 4 Selenium partitioning in the WMR andseems that the short residence time in the WMR (1pilot scale gasifersecond) was insufficient for the species of these00elements to be volatilized and released. Instead, the30resident time in the gasifier (2~5 s) was much longer,for the transformation of these trace elements from50-solid compounds to gaseous species such as As4O40}[19] and SeO2 [20].20All of the following elements were determinedWMR4 .WMR5CER1using the wet ashing procedure for preparing the0 Product gas;■ Char/slag.solution for ICP-MS analysis.图5 WMR 实验和中试试验中痕量元素Pb的分布Lead. Fig. 5 shows the lead partitioning in twoFig.5 Lead partitioning in the WMR and pilot scaledifferent wire-mesh experimental conditions, togethergasifierwith partitioning data from the pilot scale gasifier. Itfuel gas. However, the analysis from the WMRcan be seen that in the WMR, over 80% of the leadsamples suggests no arsenic and selenium specieswas released during the test in CO2 at 1 000C. Thewere vaporized under the range of experimentalresult is in agreement with the partitioning measuredconditions tested (and these included temperatures infor the pilot scale slag sample. A previousthe range 1 000~2 000^C). Other work in thisthermodynamic equilibrium study [4] indicated thatlaboratory under combustion conditions has suggestedunder the conditions of coal gasification, condensedpartial as release at 800~900 C and a reaction time ofPbS woul中国煤化工叩to temperatureat least several seconds [18]. Reed [4] calculated theof 500~60YHCNMH Gus species (PbClthermodynamic equilibrium compositions of arsenicand PbCl2) would be more important. The effect ofunder gasification conditions and concluded that no temperature on the lead partitioning during the coal第35期，蔡铭等:煤气化过程痕量元素迁移实验研究2gasifcation was also observed by Reed et al [1]gasification at pressure of 3MPa, solid Cr3C2 is theThey found that reducing the temperature in the hotpredominant species above 1400C. It is also ingas filter of a pilot scale gasifier could substantiallyagreement with the analytical results from the samplesreduce lead emission in the fuel gas. Data on Fig. 5derived from the WMR experiments, conducted underalso indicates that increasing the gasification pressure,gasification conditions (in CO2). However, underfrom 1.0 to 2.0MPa, in the WMR, at 1 000 C, maypyrolysis conditions (in nitrogen) in the WMR, ascause a small increase in the amount of lead retainedshown in Fig. 7, approximately 30% of chromium wasin the char.released into the sweep gas at 1 000 C, 2 MPa andVanadium. Thermodynamicmodeling wa2000C, 3MPa. It is not possible to explain thesecarried out in this study to calculate the equilibriumdata in terms of the thermodynamic stability of the Crcompositionsvanadium compounds undercompounds.gasification conditions. It suggests that only solid10(vanadium compounds could exist, with no significant8(formation of gas phase species. Reedili made similarpredictions in his thermodynamic study. The measured4(vanadium partitioning under different conditions inthe WMR and the pilot scale gasifier are ilustrated inFig.6. It is shown that except for the experimentWMR1 WMR3 WMR4 WMR5 CERIconducted at 1000C and 1 MPa in CO2, completeJ Product gas;Char/slag.vanadium retention in the char was measured for the图7 WMR 实验和中试试验中痕量元素Cr的分布WMR and in the slag from the pilot scale gasifier. TheFig. 7 Chromium partitioning in the WMR andreason for the vanadium distribution in the gas phasepilot scale gasifierat low temperature and pressure is still unclear andCobalt.Thethermodynamicequilibriumwould need further investigation.prediction indicates that during coal gasification, solid00CoFe2O4 is the major species until the temperature30goes up to 1 500~1 600 C. After that, gaseous elementcobalt and Co(OH)2 begin to be the dominant species.50However, Reed [4] predicted that the main cobaltspecies in the gaseous phase is CoCl2. This might bedue to the different coal samples used for thecalculation. The thermodynamic modeling results areWMR1 WMR2 WMR3 WMR3 WMRS CER10 Product gas;■Char/slag.partially validated by the analysis carried out in this图6 WMR实验和中试试验中痕量元素V的分布study, as shown in Fig. 8. The analysis of the pilotFig. 6 Vanadium partitioning in the WMR andscale gasifier slag shows that, around 30% of cobaltwas released into the fuel gas. The cobalt contents inChromium. Fig. 7 shows chromium partitioningthe char samples obtained from the WMR also show aunder different conditions in the WMR and thecomparatively low concentration, showing that thepilot-scale gasifier. From the pilot scale gasifier tracemajority was released to the gas phase. The differenceelements slag analysis, it is found that all thein the amounts between the WMR and pilot gasifierchromium was retained in the gasifier bottom slag,may be中国煤化工Tions between thewhich is in agreement with the thermodynamicreactors.TCHc N M H Endicated that themodeling work carried out simultaneously in thissweeping gas usea aunng une w MK experiments maystudy. The modeling results suggest that during coalplay an important role in determining the cobalt28中国电机工程学报第32卷ditributions in the char and released gas, since cobaltmajor manganese species up to 1 700 C: Above thispartitions in the char samples obtained from thetemperature, it comes unstable and gaseous HMngasification experiments (in CO2) are about 10% higher becomes favoured.than those from the pyrolysis experiments (in N2).003080o叶|6010} |400叶820。WMR1 WMR3 WMR4 WMR5 CERIWMR1 WMR2WMR3WMR3WMR5 CERI口Productgas;■ Char/slag.口Product gas;■Char/slag.图9 WMR实验和中试试验中痕量元素Ba的分布图8 WMR实验和中试试验中痕量元素Co的分布Fig. 9 Barium partitioning in the WMR andFig. 8 Cobalt partitioning in the WMR and pilot scalepilot scale gasifiergasiferBarium. The thermodynamic modeling forbarium showed that under coal gasificationconditions, below 900 C, the main species is solid0BaCO3, and between 900 C and 1 300 C, condensedBaS may be preferred. Above 1 300 C, BaClOHdominates the solid phase and gaseous species, suchoas Ba(OH)2 and BaCl2, begin to appear. AnalysisWMR1 WMR2 WMR4 WMR5 CERIconducted in this study show that in the pilot-scalegasifier, most of the barium was released with the fuel图10 WMR 实验和中试试验中痕量元素Mn的分布gas, as illustrated in Fig. 8. Similar results wereFig. 10 Manganese partitioning in the WMR and pilotobtained in the samples from the WMR (WMR 3),scale gasifierwhen the operating temperature reached 2 000 C, the2.5 Overview of Resultspressure was 3MPa and nitrogen was used as theThe data set is compared in Tab. 5. The columnsweeping gas. However, at lower temperatures andfor thermodynamic prediction gives an indication ofpressures, more barium was retained in the char (up tothe temperature at which the gas phase species30% actual).predominate in theequilibrium mixture ofManganese. The manganese analysis from thecompounds. There is generally good agreementWMR experiments (Fig. 9) shows that at low between this indication and the partitioning measuredtemperatures (1 000°C)，all the manganese wasfor the CERI pilot scale gasifier. This suggests that theretained in the char under both pyrolysis andresidence time in the pilot gasifier was sufficient forgasificationconditions; however, when theequilibrium conditions. Data for 1 000 and 2000 Ctemperaturc rcached 1 500 C, around 50% manganeseare presented for the WMR in N2. The agreementwas released into the product gas. This result is in abetween the prediction and WMR data at eitheragreement with the analysis of the pilot scale gasifier temperature is not as good as seen with the CERIslag, where the operating temperature was 1 700 C:，gasifier di中国煤化工tdoesseemtobe40%~ 50% manganesewasvaporized.Thebetter atCNMHGfor some of thethermodynamic modeling predicted that under theelements. The residence time at mesh temperature isconditions of coal gasification, solid Fe2MnO4 is theonly 1 s in the WMR and it seems that this may not be第35期蔡铭等:煤气化过程痕量元素迁移实验研究29sufficient for thermodynamic equilibrium to bewith the CERI and thermodynamic data.reached for all of the species. The individual element表5 WMR 实验和中试试验痕量元素数据对比表kinetics will be different and so a variable extent ofTab. 5 Comparison of Trace elements Dataapproach towards equilibrium may account for theCERI gasifer traceWMR trace elementdiferences between the measured data from the WMRTrace Thermodynamic_ element partitionpartitiontests and the other data. If this is correct, then it wouldelementpredictionTempe- To ToTo gas% To slag/%rature/C Gas/*% Char/%appear that the rates of equilibration between the solidGaseous dominant10000 10and gas phases for As and Se species is slow,As9(> 900°C)2000) 100compared with the 1s time at temperature, as no gas1 0000 100Se Gaseouominant91phases species are indicated. This is in contrast with00000the thermodynamic prediction and the CERI results.921000'3515(> 600 C)There is good agreement for Pb with a WMR1000temperature of 1 000 C and the thermodynamicV Solid dominant 0200prediction (which indicates that the gas phase species58will dominate above 600°C) and CERI result. Ther Solid dominant 074agreement is also good for all sets of data for V andCo323614no gas phase species are expected or measured. The口1500C)782Cr data obtained in the WMR using N2 indicates that3a8(> 1300C)98approximately one third of the element has partitionedto the gas phase, whereas none is expected from theMn(> 1700C)15005317thermodynamics and none is indicated in the CERI* % Gas calculated as 100 -% soliddata. A slow rate of equilibration cannot explain thisresult, as the element is expected to remain in the3 CONCLUSIONSsolid phase. When CO2 was used as the sweep gas inThe high-pressure WMR has been used tothe WMR, all of the Cr was found in the solid char,simulate the main operating conditions of an entrainedwhich is in contrast to the result in N2. We cannotflow gasifier. The partitioning of selected traceexplain this observation at present. The Co dataelements between the solid residue and gas phase (100suggests a high proportion of element partitioned tominus % remaining in char) have been compared withthe gas phase in the WMR. This is in agreement withthe partitioning obtained by thermodynamic modelingthe thermodynamic prediction, except that suggestsand in samples of slag taken from a pilot scale gasifiergaseous compoundsdominant above 1 500 "C,(CERI two stage gasifier). Shenmu bituminous coalwhereas the WMR data suggests a substantial gaseouswas used in both experimental studies. In the study,partition above 1 000 C. The CERI data shows ahe parent coal and char/slag samples were treatedlower proportion of partitioning to the gas phase. Theusing the wet-ashing and microwave digestiondata for Ba in the WMR suggests an increase in themethods and their trace elements contents werepartitioning to the gas phase when the temperaturedetermined by ICP-MS.was raised from 1000 to 2000°C. The value atIn qualitative terms, there is agreement between2000 °C is very similar to the value measured for thethe results obtained by thermodynamic analysis and inCERI gasifier and this is consistent with thethe slag samples from the CERI gasifier. This suggeststhermodynamic prediction. The WMR data for Mnthat equilibrinm is achieved in the gasifier andshows that at 1 000 C, there is no partitioning to thethermodyIYH中国煤化工ed to pedict thegas phase, whereas at 1 500 C, approximately balf ofpartitionin.cnMH Greement betweenthe Mn is partitioned. The latter result is consistentthese data and the WMR derived data is not soExtended Summary正文参见pp.21-30Experimental Study of Trace Element Release FromCoal Gasification ProcessCAI Ming' , XU Shisen', GAO Shiwang', WU Long', LIU Lianbo', D. DUGWELL, R. KANDIYOTI2(1. Huaneng Clean Energy Research Institute, 2. Imperial College London)KEY WORDS: coal gasification; trace elements; release; wire-mesh reactor; entrained flowThe release of toxic trace elements from coalmicrowave digestion methods and their trace elementgasification is a matter of environmental concern. Untilcontents are determined by ICP-MS.schematicrecently, the major work on the partitioning of tracediagram of the gasifier is shown in Fig. 2.elements has focused on p.f-coal combustion. With the↑Product gas andincreasingly wide large-scale utilization of gasificationfly ashtechnology and stringent emissions regulations, traceelements emissions from coal gasification need to beinvestigated in more details.In order to investigate the trace element partitioning.1000~-1 200Cduring coal gasification, a laboratory-scale wire-meshreactor (WMR) is used to simulate the release of traceelements from coal particles in an entrained flowcoal, steamgasifier. Char samples are produced from WMR under.1500~1700Cvarious gasification and pyrolysis conditions, within thecoal, oxygen,operating window of the gasifier. The samples of char assteamwell as raw coal are analyzed by ICP-MS for thecontents of an array of mostly toxic trace elements: As,Se, Pb, V, Co, Ba, Cr and Mn. Fig. 1 shows a schematic↓Slagdiagram of the reactor.Flg.2 Schematic diagram of CERI two-stage entrained flowgasifierIn qualitative terms, results obtained bythermodynamic analysis and are fairly accorded withthose obtained from the slag samples of the CERIgasifier. This suggests that equilibrium is achieved in thegasifier, and thermodynamic modeling can be used topredictthe partitioning in the gasifier. While these dataare not consistent with the WMR derived data. There is! 981710 Ian agreement between Pb, V, Ba, Mn and possibly Co.Fig.1 High pressre wire-mesh reactorHowever, the data for As, Se and Cr is not in agreement.To serve as a guide to what might happen under theIt is suggested that in the WMR there is a kineticconditions that are studied experimentally, a preliminarylimitation due to the short residence time at temperature.insight into trace element partitioning during gasificationFor some elements (As, Se), this limitation will influencender entrained flow conditions is gained by ththe ability of the WMR (with a 1s hold time) to simulateapplication of thermodynamic equilibrium modeling.the behavior in a gasifier, although a longer hold timeThe program used for this purpose is MTDATA,should overcome this deficiency. The result for Cr in theThe high-pressure WMR is used to simulate thWMR cannot be explained at present.main operating conditions of an entrained flow gasifier..There is a good agreement between theThe partitioning of selected trace elements between thethermodynamic predictions and the pilot scale data,solid residue and gas phase (100 minus % remaining inshowing that an equilibrium with respect to tracechar) is compared with the partitioning obtained byelement partitioning is reached in the pilot scale gasifier.thermodynamic modeling and in samples of slag takenAgreemen中国煤化工; consistent. Therefrom a pilot scale gasifier (CERI two stage gasifier).is an agreeYH.Pb,V,Ba,MnandShenmu bituminous coal is used in both experimentalpossibly (C N M H Gistent with the datastudies. In the study, the parent coal and char/slagfor Se, which may be due to the kinetic limitation,samples are treated by using the wet-ashing andresulting from the short duration of the WMR test.34