烟煤焦在H_2O和CO_2气氛下的结构演变与气化反应性关联（英文）
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摘要
本研究以烟煤在1000℃热解所制得的焦样为研究对象,考察了其在H_2O、CO_2及两者混合气氛下的结构演变,以及气化反应性的影响。为了探究焦样在气化过程中的结构演变,利用氮吸附、SEM和拉曼光谱等表征手段分析不同碳转化率下的焦样结构。结果表明,H_2O气氛对焦样结构的演变明显不同于CO_2气氛,揭示了焦样在两种气氛下的反应路径不同。因结构演变的不同,随碳转化率的增加,焦样在两种气氛下表现出不同的气化反应性能。在CO_2气氛下,焦样的气化反应速率随碳转化率的增加而逐渐降低,与H_2O气氛存在下变化趋势相反。在H_2O和CO_2共气化条件下,煤焦在H_2O和CO_2混合气氛下的反应速率高于单气氛下的反应速率的计算值,表现出一定的协同作用。这是因为焦样与H_2O反应能够产生较大的比表面积,为焦样与CO_2反应提供更多的反应场所,促进了焦样与CO_2的反应。
This work aims to investigate the structural evolution of the char during gasification under a single or mixed atmosphere of H_2O and/or CO_2 with the synchronized investigation of the effect of the varying char structure on the gasification reactivity. The experimental char was prepared from a bituminous coal at 1000 ℃. The changes of the char structure along with the progress of the carbon conversion during gasification were characterized using N_2 adsorption,SEM,and Raman spectroscopy. The results revealed that H_2O showed a more dramatically change on the char structure than CO_2 and two reactants had different reaction pathways. The different pathways of reactants affected the evolution manners of the char structure and different gasification reactivity of char was related to structural evolution. The specific reaction rate between the char and CO_2 decreased monotonously with increasing carbon conversion. However,the opposite trends are observed when H_2O exist,either H_2O alone or the mixtures of H_2O and CO_2. The char gasification reactivity was under the common effect of physical and chemical structure. In terms of the mixture of H_2O and CO_2,the significant specific surface area caused by H_2O provided more active sites for CO_2. The interactions between H_2O and CO_2 promoted reaction between C and CO_2( C + CO_2→ CO) in mixtures of H_2O and CO_2,leading to higher amount of CO and higher specific reaction rate than calculated.
This work aims to investigate the structural evolution of the char during gasification under a single or mixed atmosphere of H_2O and/or CO_2 with the synchronized investigation of the effect of the varying char structure on the gasification reactivity. The experimental char was prepared from a bituminous coal at 1000 ℃. The changes of the char structure along with the progress of the carbon conversion during gasification were characterized using N_2 adsorption,SEM,and Raman spectroscopy. The results revealed that H_2O showed a more dramatically change on the char structure than CO_2 and two reactants had different reaction pathways. The different pathways of reactants affected the evolution manners of the char structure and different gasification reactivity of char was related to structural evolution. The specific reaction rate between the char and CO_2 decreased monotonously with increasing carbon conversion. However,the opposite trends are observed when H_2O exist,either H_2O alone or the mixtures of H_2O and CO_2. The char gasification reactivity was under the common effect of physical and chemical structure. In terms of the mixture of H_2O and CO_2,the significant specific surface area caused by H_2O provided more active sites for CO_2. The interactions between H_2O and CO_2 promoted reaction between C and CO_2( C + CO_2→ CO) in mixtures of H_2O and CO_2,leading to higher amount of CO and higher specific reaction rate than calculated.
引文
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[18]UMEMOTE S,KAJITANI S,HARA S.Modeling of coal char gasification in coexistence of CO2and H2O considering sharing of active sites[J].Fuel,2013,103(1):14-21.
[19]FUSHIMI C,GOTO M,TSUTSUMI A,HAYASHI J I,CHIBA T.Steam gasification characteristics of coal with rapid heating[J].J Anal Appl Pyrolysis,2003,70(2):185-197.
[20]ZHANG R,WANG Q H,LUO Z Y,FANG M X,CEN K F.Competition and inhibition effects during coal char gasification in the mixture of H2O and CO2[J].Energy Fuels,2013,27(9):5107-5115.
[21]TAY H L,KAJITANI S,ZHANG S,LI C Z.Effects of gasifying agent on the evolution of char structure during the gasification of Victorian brow n coal[J].Fuel,2013,103:22-28.
[22]WANG M J,ROBERTS D G,KOCHANEK M A,HARRIS D J,CHANG L P,LI C Z.Raman spectroscopic investigations into links betw een intrinsic reactivity and char chemical structure[J].Energy Fuels,2014,28(1):285-290.
[23]ROBERTS D G,HARRISA D J.Char gasification in mixtures of CO2and H2O:Competition and inhibition[J].Fuel,2007,86(17/18):2672-2678.
[24]LI X J,HAYASHI J I,LI C Z.FT-Raman spectroscopic study of the evolution of char structure during the pyrolysis of a Victorian brown coal[J].Fuel,2006,85(12/13):1700-1707.
[25]SEKINE Y,ISHIKAWA K,KIKUCHI E,MATSUKATA M,AKIMOTO A.Reactivity and structural change of coal char during steam gasification[J].Fuel,2006,85(2):122-126.
[26]WANG M J,TIAN J L,ROBERTS D G,CHANG L P,XIE K C.Interactions between corncob and lignite during temperature-programmed co-pyrolysis[J].Fuel,2015,142(15):102-108.
[27]LIU X H,ZHENG Y,LIU Z H,DING H R,HUANG X H,ZHENG C G.Study on the evolution of the char structure during hydrogasification process using Raman spectroscopy[J].Fuel,2015,157(1):97-106.
[28]LIVNEH T,BAR-ZIV E,SENNECA Q,SALATINO P.Evolution of reactivity of highly porous chars from Raman microscopy[J].Combust Sci Technol,2000,153(1):65-82.
[29]ESPINAL J F,MONDRAGON F,TRUONG T N.Thermodynamic evaluation of steam gasification mechanisms of carbonaceous materials[J].Carbon,2009,47(13):3010-3018.
[30]JING X L,WANG Z Q,ZHANG Q,YU Z L,LI C Y,HUANG J J,FANG Y T.Evaluation of CO2gasification reactivity of different coal rank chars by physicochemical properties[J].Energy Fuels,2013,27(12):7287-7293.
[31]MALEKSHAHIAN M,HILL J M.Effect of pyrolysis and CO2gasification pressure on the surface area and pore size distribution of petroleum coke[J].Energy Fuels,2011,25(11):5250-5256.
[32]DING L,ZHANG Y Q,WANG Z Q,HUANG J J,FANG Y T.Interaction and its induced inhibiting or synergistic effects during cogasification of coal char and biomass char[J].Bioresour Technol,2014,173:11-20.
[33]WU X J,ZHANG Z X,PIAO G L,HE X,CHEN Y S,KOBAYASHI N,MORI S,ITAYA Y.Behavior of mineral matters in chinese coal ash melting during char-CO2/H2O gasification reaction[J].Energy Fuels,2009,23(5):2420-2428.
[34]KLOSE W,WOLKI M.On the intrinsic reaction rate of biomass char gasification with carbon dioxide and steam[J].Fuel,2005,84(7/8):885-892.
[2]LI C Z.Some recent advances in the understanding of the pyrolysis and gasification behaviour of Victorian brown coal[J].Fuel,2007,86(12/13):1664-1683.
[3]ZHANG L,LI T T,QUYN D,DONG L,QIU P H,LI C Z.Structural transformation of nascent char during the fast pyrolysis of mallee wood and low-rank coals[J].Fuel Process Technol,2015,138:390-396.
[4]LU L M,KONG C H,SAHAJWALLA V,HARRIS D.Char structural ordering during pyrolysis and combustion and its influence on char reactivity[J].Fuel,2002,81(9):1215-1225.
[5]MARQUES M,SUAREZ-RUIZ I,FLORES D,GUEDES A,RODRIGUES S.Correlation between optical,chemical and micro-structural parameters of high-rank coals and graphite[J].Int J Coal Geol,2009,77(3/4):377-382.
[6]FENG B,BHATIA S K.Variation of the pore structure of coal chars during gasification[J].Carbon,2003,41(3):507-523.
[7]WU H W,YIP K V,TIAN F J,XIE Z L,LI C Z.Evolution of char structure during the steam gasification of biochars produced from the pyrolysis of various mallee biomass components[J].Ind Eng Chem Res,2009,48(23):10431-10438.
[8]IRFAN M F,USMAN M R,KUSAKABE K.Coal gasification in CO2atmosphere and its kinetics since 1948:A brief review[J].Energy,2011,36(1):12-40.
[9]MITSUOKA K,HAYASHI S,AMANO H,KAYAHARA K,SASAOAKA E,UDDIN M A.Gasification of woody biomass char with CO2:The catalytic effects of K and Ca species on char gasification reactivity[J].Fuel Process Technol,2011,92(1):26-31.
[10]FUSHIMI C,WADA T,TSUTSUMI A.Inhibition of steam gasification of biomass char by hydrogen and tar[J].Biomass Bioenergy,2011,35(1):179-185.
[11]BAI Y H,WANG Y L,ZHU S H,YAN L J,LI F,XIE K C.Synergistic effect between CO2and H2O on reactivity during coal chars gasification[J].Fuel,2014,126(15):1-7.
[12]GUIZANI C,ESCUDERO-SANZ F J,SALVADOR S.The gasification reactivity of high-heating-rate chars in single and mixed atmospheres of H2O and CO2[J].Fuel,2013,108:812-823.
[13]EVERSON,R C,NEOMAGUS H W J P,KASAINI H,NJAPHA D.Reaction kinetics of pulverized coal-chars derived from inertinite-rich coal discards:Gasification w ith carbon dioxide and steam[J].Fuel,2006,85(7/8):1076-1082.
[14]HUANG Z M,ZHANG J S,ZHAO Y,ZHANG H,YUE G X,SUDA T,NARUKAWA M.Kinetic studies of char gasification by steam and CO2in the presence of H2and CO[J].Fuel Process Technol,2010,91(8):843-847.
[15]BUTTERMAN H C,CASTALDI M J.Influence of CO2injection on biomass gasification[J].Ind Eng Chem Res,2007,46(26):8875-8886.
[16]ROBERTS D G,HARRIS D J.Char gasification in mixtures of CO2and H2O:Competition and inhibition[J].Fuel,2007,86(17/18):2672-2678.
[17]CHEN C,ZHANG S,XU K,LUO G Q,YAO H.Experimental and modeling study of char gasification with mixtures of CO2and H2O[J].Energy Fuels,2016,30(3):1628-1635.
[18]UMEMOTE S,KAJITANI S,HARA S.Modeling of coal char gasification in coexistence of CO2and H2O considering sharing of active sites[J].Fuel,2013,103(1):14-21.
[19]FUSHIMI C,GOTO M,TSUTSUMI A,HAYASHI J I,CHIBA T.Steam gasification characteristics of coal with rapid heating[J].J Anal Appl Pyrolysis,2003,70(2):185-197.
[20]ZHANG R,WANG Q H,LUO Z Y,FANG M X,CEN K F.Competition and inhibition effects during coal char gasification in the mixture of H2O and CO2[J].Energy Fuels,2013,27(9):5107-5115.
[21]TAY H L,KAJITANI S,ZHANG S,LI C Z.Effects of gasifying agent on the evolution of char structure during the gasification of Victorian brow n coal[J].Fuel,2013,103:22-28.
[22]WANG M J,ROBERTS D G,KOCHANEK M A,HARRIS D J,CHANG L P,LI C Z.Raman spectroscopic investigations into links betw een intrinsic reactivity and char chemical structure[J].Energy Fuels,2014,28(1):285-290.
[23]ROBERTS D G,HARRISA D J.Char gasification in mixtures of CO2and H2O:Competition and inhibition[J].Fuel,2007,86(17/18):2672-2678.
[24]LI X J,HAYASHI J I,LI C Z.FT-Raman spectroscopic study of the evolution of char structure during the pyrolysis of a Victorian brown coal[J].Fuel,2006,85(12/13):1700-1707.
[25]SEKINE Y,ISHIKAWA K,KIKUCHI E,MATSUKATA M,AKIMOTO A.Reactivity and structural change of coal char during steam gasification[J].Fuel,2006,85(2):122-126.
[26]WANG M J,TIAN J L,ROBERTS D G,CHANG L P,XIE K C.Interactions between corncob and lignite during temperature-programmed co-pyrolysis[J].Fuel,2015,142(15):102-108.
[27]LIU X H,ZHENG Y,LIU Z H,DING H R,HUANG X H,ZHENG C G.Study on the evolution of the char structure during hydrogasification process using Raman spectroscopy[J].Fuel,2015,157(1):97-106.
[28]LIVNEH T,BAR-ZIV E,SENNECA Q,SALATINO P.Evolution of reactivity of highly porous chars from Raman microscopy[J].Combust Sci Technol,2000,153(1):65-82.
[29]ESPINAL J F,MONDRAGON F,TRUONG T N.Thermodynamic evaluation of steam gasification mechanisms of carbonaceous materials[J].Carbon,2009,47(13):3010-3018.
[30]JING X L,WANG Z Q,ZHANG Q,YU Z L,LI C Y,HUANG J J,FANG Y T.Evaluation of CO2gasification reactivity of different coal rank chars by physicochemical properties[J].Energy Fuels,2013,27(12):7287-7293.
[31]MALEKSHAHIAN M,HILL J M.Effect of pyrolysis and CO2gasification pressure on the surface area and pore size distribution of petroleum coke[J].Energy Fuels,2011,25(11):5250-5256.
[32]DING L,ZHANG Y Q,WANG Z Q,HUANG J J,FANG Y T.Interaction and its induced inhibiting or synergistic effects during cogasification of coal char and biomass char[J].Bioresour Technol,2014,173:11-20.
[33]WU X J,ZHANG Z X,PIAO G L,HE X,CHEN Y S,KOBAYASHI N,MORI S,ITAYA Y.Behavior of mineral matters in chinese coal ash melting during char-CO2/H2O gasification reaction[J].Energy Fuels,2009,23(5):2420-2428.
[34]KLOSE W,WOLKI M.On the intrinsic reaction rate of biomass char gasification with carbon dioxide and steam[J].Fuel,2005,84(7/8):885-892.