煤炭氣化氣流床氣化爐的數學(xué)模擬

第24卷第4期煤炭轉化2001年10月COAL CONVERSIONOct.2001煤炭氣化氣流床氣化爐的數學(xué)模擬步學(xué)朋)彭萬(wàn)旺1)徐振剛2)摘要簡(jiǎn)要介紹了煤炭氣流床氣化的原理,總結了到目前為止煤炭氣化氣流床氣化爐數學(xué)模擬情況,包括簡(jiǎn)單平衡模型和動(dòng)力茡模型(一維或多維),給岀了這些數學(xué)模型模擬的主要內容(對氣化過(guò)程流體力學(xué)、熱力學(xué)、化學(xué)反應和質(zhì)量、能量及動(dòng)量平衡考慮情況)和模型的主要結論,以及典型氣流床氣化爐的模擬煤氣組成和煤炭轉化率數值與實(shí)驗值或實(shí)際操作值旳比較情況,結果顯示主要組分模擬誤差較小關(guān)鍵詞煤炭氣化,氣流床氣化,數學(xué)模擬中圖分類(lèi)號TQ529造,而我國第一座IGCC示范電廠(chǎng)也已立項,其氣化0引言島也將采用氣流床氣化工藝.因此應重視對氣流床氣化工藝的研究及開(kāi)發(fā)工作煤炭氣化是煤潔凈利用的關(guān)鍵技術(shù)之一,它以對氣化爐氣化過(guò)程數學(xué)模擬的研究不僅有利于提高碳轉化率、冷煤氣效率,降低氣化過(guò)程旳氧耗及深入了解氣化過(guò)程規律,而且可以用于指導氣化爐煤耗為目標,并向加壓及液態(tài)排渣、大型化等方向發(fā)設計及生產(chǎn)過(guò)程優(yōu)化控制.對氣流床氣化爐的數學(xué)展,從而達到改善環(huán)境及降低產(chǎn)品成本的目的.加壓模擬主要始于20世紀70年代,國內外對此進(jìn)行了氣流床氣化技術(shù)是國內外優(yōu)先發(fā)展方向之,氣流床大量研究,取得了許多成果氣化技術(shù)有如下特點(diǎn):①能夠氣化任何變質(zhì)程度的煤及煤的加氫殘渣、石油焦等;②氣化強度很高,碳1氣流床氣化原理轉化率高;③產(chǎn)品煤氣中不含焦油和酚類(lèi)物質(zhì),環(huán)境友好;①其缺點(diǎn)是氧耗高、需設置磨粉、顯熱回收1.1氣流床氣化過(guò)程描述及除塵等較龐大的輔助裝置.已工業(yè)化或正在示范從氣流床氣化工藝分析看,煤粉(或水煤漿)與的加壓氣流床氣化技術(shù)包括濕法加料的 Texaco,氣化劑(O2/HO)經(jīng)噴嘴噴入氣化爐的燃燒區,由于Detec和干法加料的 Shell,, Prenflo及GSP等,并氣化爐該處溫度高達1500C~2000C,因此煤粉在世界范圍內得到廣泛應用受熱升溫速度很快(>104C/s),可認為煤粉中的我國20世紀⑦0年代先后進(jìn)行過(guò)熔渣爐氣化及殘余水分快速(瞬間)蒸發(fā),同時(shí)由于熱分解反應速K-T氣化研究,也建立過(guò)工業(yè)化裝置,后因耐火材度大大高于煤粉的燃燒及氣化反應速度,所以細小料等問(wèn)題而停止.20世紀80年代后在魯南化肥廠(chǎng)、的煤粉顆粒開(kāi)始發(fā)生快速熱分解,即脫揮發(fā)分,生成上海焦化有限公司、渭河化肥廠(chǎng)、淮南化肥廠(chǎng)等引進(jìn)半焦和氣體產(chǎn)物.在富含氧氣及高溫條件下,揮發(fā)分了 Texaco氣化爐用于生產(chǎn)合成氨及甲醇,通過(guò)多中的活性可燃成分如CO,H2,CH1及焦油與O2發(fā)年的實(shí)踐積累了豐富的經(jīng)驗,已達到了長(cháng)周期、高負生氣相燃燒下應生成CO和HO,并放出大量熱荷、安全和穩定運行的要求,且在噴嘴、耐火磚及水量中國煤化工應的進(jìn)行.由于氣相燃煤漿泵等設備國產(chǎn)化方面取得了突破性進(jìn)展目前,燒CNMHG認為在氧氣存在的情況利用干法加料的 Shell氣化工藝正用于某化肥廠(chǎng)改下,上述氣相燃燒反應達到完全,亦即在氧氣存在國家“九五”科技攻關(guān)計劃項目(97-A26-02-02-05)1)高級工程師;2)研究員,煤炭科學(xué)研究總院北京煤化學(xué)研究所,100013北京收稿日期:2001-01-16;修回日期:2001-05-20煤炭轉化2001年時(shí),氣相中不含CO,H2,CH4及焦油.煤中的揮發(fā)分反應平衡時(shí)的煤氣組成及平衡溫度.項友謙用能析岀后,發(fā)生半焦燃燒及氣化反應,與水蒸氣及CO2量最小原理,建立了加壓氣化平衡模型,并用4種方反應,如此時(shí)仍有氧氣存在,則在氣相中仍發(fā)生CO法對微分方程求解模擬結果顯示平衡模型對氣流和H燃燒反應.氣化爐中的氧氣反應完后,半焦與床的模擬效果要好于固定床. Watkinson提出平水蒸氣、CO2和H2等繼續發(fā)生氣化反應,同時(shí)氣相衡模型,通過(guò)質(zhì)量和能量平衡及反應平衡方程式關(guān)中還有水煤氣變換反應和甲烷裂解反應等對氣流聯(lián),可以得到產(chǎn)品煤氣組成、產(chǎn)率和最佳適宜溫度床氣化,一般將變換反應和甲烷化反應視為平衡反并對9種氣化爐型的工業(yè)化和半工業(yè)化氣化數據進(jìn)行了比較.對產(chǎn)品煤氣中的CO和H2含量誤差在士從如上分析可以認為在對氣流床模擬時(shí),考慮%之內,H2S和COS濃度可以準確的預測,但氣化爐中氣固相的組成分別為氣相:O,H1O,CO,CO2預測值的準確性要差一些.結果還表明該模型CO,H2, CH,, N2(E NH3 ), H,S(+COS), Tar對氣流床氣化爐模擬效果最好,流化床次之,而固定相:C,H,O,N,S,Ash, Moisture.另外考慮氣固相由于一些不確定因素如揮發(fā)分含量組成等的存溫度?,T∷數學(xué)模擬的目的就是求出氣化爐內每在,模擬誤差較大 Ruprecht等建立了平衡模型質(zhì)點(diǎn)處的上述參數的值并用于評價(jià)試驗數據分析.平衡模型可用于對出囗組成及溫度進(jìn)行簡(jiǎn)單預測,由于其假定的條件較理1.2氣化反應動(dòng)力學(xué)想,如假定所有反應都達到平衡,在實(shí)際過(guò)程是不可煤粉熱解反應速度很快,主要根據經(jīng)驗式對熱能的,因此其用途受到一定限制,對過(guò)程控制及氣化解速度和產(chǎn)物進(jìn)行估算,大致有wen等給出的爐設計參考價(jià)值較少幾種表達形式.氣固非均相反應,由于氣化爐內反應2.2考慮氣化過(guò)程動(dòng)力學(xué)的模型溫度很高,最高溫度可達2000C以上,所以半焦與為了更準確的用數學(xué)模型對氣化及燃燒過(guò)程進(jìn)O2,H2O,CO2的反應速度由氣膜擴散及灰層擴散控行模擬,需考慮氣化過(guò)程三傳一反及動(dòng)力學(xué)行為.許制,而半焦與H的反應較慢,它由化學(xué)反應控制.多研究者對此進(jìn)行了研究,建立了一維、二維及多維從非均相反應動(dòng)力學(xué)模型看,分為未反應核收縮模模型,Fild等對1967年以前的工作進(jìn)行了歸納,模型及灰層剝離模型,文獻[5認為灰層在反應過(guò)程中型屬活塞流 Ubhayakar等忽略了表面反應,但考剝離,因此反應受氣膜擴散和化學(xué)反應動(dòng)力學(xué)控制慮了軸向混合、揮發(fā)分的氣相反應及熱解反應而文獻[1,6認為,由于氣流床氣化爐中煤粉顆粒所 Smith等先后建立了一維及二維煤粉氣流床燃占體積很小(<1%),且停留時(shí)間只有2s~3s,因燒及氣化模型,模型中考慮了煤粉顆粒大小分布對此煤粉顆粒碰撞幾率較小,在煤粉顆粒表面因反應反應速度的影響.Wen等給出一維模型來(lái)描述形成的灰層可認為仍保留而不剝離,所以反應速度 naco氣化爐中的混合情況,每一微元被處理成氣可由未反應核收縮模型得到反應速度其它學(xué)者也相是完全混合固相以活塞流通過(guò)整個(gè)反應器,固相研究了氣化反應動(dòng)力學(xué)問(wèn)題,基本一致的觀(guān)點(diǎn)是要粒子的速度用 Stokes方程近似描述模擬了中試裝同時(shí)考慮化學(xué)反應控制及擴散控制.使用比較多的置使用煤及加氫殘渣氣化情況操作參數的變化對如對加氬氣化過(guò)程模擬時(shí),采用了 Johnosn的加煤氣組成的影響等. Govind等對上述模型進(jìn)行了氫熱解動(dòng)力學(xué)模型;wen等提出的未反應核收縮修正,加入了動(dòng)量平衡.考查了煤氣組成與進(jìn)料速模型也使用較多, Smith等也采用了獨特的動(dòng)力度、氧/煤比及汽/煤比的關(guān)系. Sprouse等模擬學(xué)表達式.加氫氣化反應,前者使用了經(jīng)驗關(guān)聯(lián)式,但不適合次2氣流床氣化數學(xué)模型綜述煙r中國煤化工,但因其復雜性導致其應CNMHG了4種煤沿氣化爐的軸向冋氣柜組成分巾,訂論了氧碳比及蒸汽量等2.1平衡模型對模擬結果的影響. Vamyuka建立了一維穩態(tài)模型,發(fā)現氣固相最大溫度位于氧氣耗盡處,考察了關(guān)平衡模型認為氣化過(guò)程所有化學(xué)反應達到平鍵參數對操作的影響.我國科技部“九五”期間也安衡,通過(guò)對氣化過(guò)程質(zhì)量及能量平衡方程求解得到排了對流化床、干法及濕法加料氣流床氣化爐進(jìn)行第4期步學(xué)朋等煤炭氣化氣流床氣化爐的數學(xué)模擬數學(xué)模擬的攻關(guān)課題,取得了豐碩成果.現將最近的仼何模型模擬的目的是能反映氣化爐內物料研究成果及文獻[6,12]對以前的煤粉氣流床氣化及動(dòng)及化學(xué)反應情況,并獲得出口處煤氣組成及溫度、燃燒模擬情況的總結一并列于表1中碳轉化率、氣化效率等參數.氣流床氣化爐數學(xué)模擬與實(shí)際(或實(shí)驗)結果的對比情況見(jiàn)表2,可見(jiàn)對幾3模擬煤氣組成與實(shí)際(或實(shí)驗)結果種不同爐型煤氣中的主要組分,模擬誤差小,說(shuō)明模對比擬基本上是成功的.表1氣流床氣化數學(xué)模擬匯總Table 1 Reviews of models for coal entrained-bed gasifiersAuther(s) ReferencesMain Contents/ DescriptieMajor ResultsMehta1976 Phenomenological model combination of plug-flow Describes the outlet conditions for aand perfectly-stirred calculations, gas phase chemi- three-stage entrained flow gasifieral equilibrium, overall char gasification with Arrh1979quilibrium chemistry; one-step devolatilization and around the particles of Rock well iOne-dimensional hydrogasification; free-stream ehydrogasification modelFHP gasifier, compared well with outmeasurements for coalFinson et al1978 Steady, one-dimensional model. with gaseous ki- Predictions compared with laboratornetics: kinetics from data for coal pyrolysis het- gasification measurements of axial tem-erogeneous oxidation: considered the char struc- perature and gas compositionUbhayakar1977 One-dimensional steady-state; two-step de- Applied to gasification combustion andStickler & Cannonbined diffusion & surface reac- hydropyrolysis with good agreementBlake et al1977-1979 Three-dimensional, transient, mixed finite-ele- Study the effect of particle sizement, finite-difference scheme with separate Eule- conservation of mass, momenturm andparticle equations; two equation gaseous tur- energy, studied the loctbulence: separate turbulent kinetics energy for par- vectorsticlesBarnhart et alCombination of plug-flow and perfectly-stirred ele- Predicts carbon burnout product gasments; gas phase in equilibrium with two-equation composition, temperature; reportediment&. theory for cyclone gasifier er.kinetics for pyrolysis, char oxidation and CO oxi- fair to good comparison between exper1979-1981 One-dimensional steady-state, two-step de- Good agreement with one-dimensionaltion rates, one-dimensional zonal radiation, equi- gasifier measurementslibrium gas phase reactionsSmith. Fleche*,12 1979-1981 Two-dimensional, axisymmetric, with recircula- Gas-phase components reported andion, k-E turbulence model, Lagrangian partdevolatilization, diffusicerogeneous rates, four-flux radiation with scatterCl1978fier into three zones: one-step de- Predicted temperature and gas compogas phase combustion completely or sition data for Texaco gasifierequilibrium gas phase reactions, consider diffusion pared with pilot plant gasified coal andand kinetic rates for char reactionH-coal residue, with good agreement.1980 One-dimensional steady-state model, Johnsons Modeling bench-scale hydrogasifier ofhydropyrolysis model, continuity equations for Citys Service R& D Coboth phases, mixture momentum balance and ther中國煤化工Govind and shan1984efined the Wen & Chuang mo-composition and carbon conmomentum balanceTHCN MH Gpends on three essential pameters: the fuel rate, the oxygen tofuel ratio and the steam-fuel ratio: theoptimum steam-fuel ratio is betweension: the steam-fuel ratio significantlyaffects the gas product composition.煤炭轉化續表1Auther(s)eferences Yeain Contents/DescriptionMajor ResultsGong Suning et al1987 Image the gasifier being composed of several paral- Axial gas/solid temperature and conlel reactors of which each has respective homoge- version profiles were got, the initial reneous particle size and also its own material and action rate very fast, and then slowheat balances; one-dimensional equations similar to down significantly the wall tempera-Smith's: the finite element method was used to cal- ture has influence on reaction. andculate the wall temperature distribution and heat should be taken as an important param5 1988 Refined the Smith two-dimensional model, gave Modeling the radial and axial gas phaseof full/ partheterogection rates and heatloss on prediction results; the effect ofO/C and steam on gas compoRuprecht et al1988 Considered only theaction, the gas composi- The agreement between prediction andtion include CO, H2. COz, no CHa: equilibrium gas measured data is very good, the dis-phase reactions, carbon conversion controlled by crepancy normally amounts to 1% orO/C: mass and energy balance.less: it has been used for the evaluationka et al1995 One-dimensional steady-state, plug-flow, assh didhe boundary between combustionhe reacting particle surfadistinctbined diffusion and chemical reaction kinetics. usedepend on the gasTGa data, equilibrium gas phase reactions, the sure: peak temperature of gas and solidmomentum balance neglectednear the boundary coal conversion isnot sensitive to the pyrolysis rate, bisensitive to pressure: the effect of opNi & willia17 1995 A multivariable model was set up on the basis of e- The oxygen to coal ratio is the mostquilibrium, mass balance and energy balance, the important control variable for theShell gasifieral model the gas composieffhasIngture of inlet flow, steam to coal ratiohas influence on the efficiency.Liu g s et al1999 One-dimensional steady-state, plug-flow. the gas The predicted carbon conversion agreeturbulence is neglected, kinetic data from Ptga with those measured in the gasifier of 8ests: considered the pore structure and reactivity coals; the better prediction results canof char: the heat balance between the wall, gas, be got by considered char structure;modeled the CSIRO atmospheBu XuepengOne-dimensional steady-state, divided gasifier into The 48 t/d and 2 600 t/d Prenflo gaPeng Wanwangthree zones: the devolatilization composition by fiers were modeled, axial gas-solidXu Zhengangcalculated, gas phase combustion completely, oth- temperature and composition were goter gas reactions equilibrium: considered diffusion main gas composition agree with reaand kinetic rates for gas-char reactionsdata; the effect of oxygen to coal ratiogastrication results wasYu Zunhong2000 Based on cold model experiment, divided gasifier Based on Texaco gasifier realistic opernto three zones, the reactions different in each ation data, predicted the feature tem-ong Xin et alne the mixed time and reaction time are consid- perature and gas composition at threeered as main variables, chemical reactions equilibri- different load, they are agreement withLi zhenDivided gasifier into lots of zones along axial diPredicted axial gas-solid temperaturetion, in order to consider thrV凵中國煤化工sition of Texaco gasifier;Wang Tianjiao et altructure and size; gas phasetion kinetics: retention timeCNMHGn, coal kinds on operationGao Juzhong* 2000 Equilibrium model, only thermodynamics was con- Predicted the gas composition and gasiwang ningboidered took the relation between carbon conver- fication indexes of two coals gasified inZhang yaruion and O/C ratio, reaction extent as boundary Shell gasifiers in pilot plant and demonstration plant respectivelyFrom reference 12,** See95"item reports第4期步學(xué)朋等煤炭氣化氣流床氣化爐的數學(xué)模擬表2模擬結果與實(shí)際結果的對比Table 2 Comparison of computational results from the models with experimental/ operation resultsAuthor(s)/Gas composition/%I)CO CO2 CH. H,S+COS N2+Ar H20 Carbon conversion/%37.3047.8614,450.050.26atkinsonxperiment24.3047.1013.200.090.4012.7Model7047.2013,300,332.210.3013,0WatkinsonExperiment30.6061.501.600.001.30ShellModel30.3061,501.400.085.38WatkinsonExperiment34.6055.407.000.001.951.01K-T34,9055.406.700.001.931.03Qizhi NiL17.8065.401.700.000.940.001.9029.7165,651.360.01Yu Zunhong7.4745.8416.0.1038.3144,8415.010.110.822)Li Zheng29.8041.0511.100.8Texcao30.5540.8010.270.13Gao JuzhongOperationShell63,790.800.0357.981.19Bu XuepengPrenfloModel25.9360.212.660.020.7710.41Note: 1) Percent of volume: 2) Include NH3; 3) Others 0. 21礎上,建立二維及多維動(dòng)態(tài)模型,并充分考慮顆粒大4結束語(yǔ)小分布、氣化爐內氣固相流體力學(xué)行為等.另外為適應氣化爐使用中國煤種的操作,需要研究適宜中國囯外對氣流床氣化爐的數學(xué)模擬研究起步較煤粉的髙溫髙壓快速熱解反應動(dòng)力學(xué)以確定其熱解早,經(jīng)過(guò)最近幾年的努力,我國對氣流床氣化爐的數速度及熱解煤氣組成,研究適宜煤種的氣化反應動(dòng)學(xué)模擬也取得了初步成功,但正如專(zhuān)家們指岀的那力學(xué),為數學(xué)模擬提供基礎數據.最后對建立的數學(xué)樣,目前離真正應用還有一定距離.根據在模型建立模型還要到生產(chǎn)實(shí)際中進(jìn)行檢驗,對某些參數進(jìn)行及求解過(guò)程的經(jīng)驗,筆者認為下一步應繼續進(jìn)行氣修正,以求能較準確反應氣化爐內氣化行為并用于流床氣化爐的數學(xué)模擬工作.在目前一維穩態(tài)的基指導氣化爐設計及生產(chǎn)操作[] Wen C Y, Chuang T Z. 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In: Prospects for Coal Sciencein the 21st Century. Taiyuan: Shanxi Science & Technology Press,1999.579-582MATHEMATICAL MODELING OF COAL ENTRAINEDBED GASIFIERSBu Xuepeng Peng Wanwang and Xu Zhengang( Beijing Research Institute of Coal Chemistry, China Coal Research Institute, 100013 BeijingABSTRACt The coal entrained-bed gasification principle was briefly introduced in this paper. Based on relative documents, the mathematical modeling of coal entrained-bed gasifiers werereviewed. These include simple equilibrium models and kinetic models (one-dimensional or two/three-dimensional). The main contents-about hydromechanics, thermodynamics, chemical reac-ion kinetics, and mass balance, energy balance, momentum balance, of the models were givenout. The major results of models were also given. Finally, the comparison of computational results from the models with experimental or operational results were given It can be seen that theerrors of the main gas composition are very loKEY WORDS coal gasification, entrained-bed gasification, mathematical modeling(上接第6頁(yè))DEVELOPMENT OF COAL STRUCTURECheng Jun Zhou Anning and Li Jianwei( Department of Material Engineering, Xi'an University ofience and Technology, 710054, Xi'an)aBSTRaCt The coal aggregative structure is discussed, including the origin, structure andswelling behavior of several macerals. Coal chemicalH中國煤化工 I structure modeland synthesized models are analyzed and discussedCN MH Gructure research israised. At last. the utilization of coal structure research in new material field is summarizedwhich reveals the importance of coal structure research in ftKEY WORDS coal structure, physical structure, comprehensive structure, computer aidemolecular design