胜利褐煤热解过程中结构演变及气体生成机理分析
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摘要
褐煤的热解反应是褐煤利用的重要研究方向之一。为了分析褐煤热解过程中结构演变及气体生成机理,首先将胜利褐煤(SL)在固定床上进行热解制焦,利用800℃时SL热解气体生成速率曲线选取半焦终温,同时用气相色谱在线检测其所生成的热解气;其次结合煤焦傅里叶变换红外光谱(FT-IR)的表征进行分析,将半焦的FT-IR分峰拟合计算;最后将计算参数结合热解气生成规律,提出了热解升温过程中各反应阶段生成气体机理和气体生成过程中煤体结构的演变规律。结果表明,SL具有羟基、脂肪烃、芳环、羰基、醚键等丰富的官能团,热解温度低于350℃,胜利褐煤中主要官能团未发生明显变化; 350～450℃,脂肪族侧链含氧官能团分解,热解温度450℃比350℃时煤焦中C=O相对含量(C1)降低78%; 560～800℃,热解反应主要以芳香烷基侧链含氧官能团裂解为主,热解温度800℃时煤焦中C—O相对含量(C2)比560℃时降低27%;热解温度710～800℃时,煤热解以缩聚反应为主,热解温度800℃煤焦中芳香稠和度(D2)比710℃时升高65%。对4种热解气生成过程进行研究分析,CO2主要来源于中低温区煤中不同结构的羧基官能团分解;高温区生成CO,来源于煤中酚类、醚类、含氧杂环等结构的分解; CH4主要由芳环侧链的甲基、亚甲基或连接芳环结构亚甲基的分解;高温区产生的约60%H2主要来自于煤中芳香结构的缩聚反应。
Pyrolysis reaction of lignite is one of the important research directions in lignite utilization. Firstly,Shengli Lignite( SL) was pyrolyzed on a fixed bed for coking in order to analyze the structure evolution and gas formation mechanism of lignite during pyrolysis.The final temperature of semi-coke was determined by using the curve of SL pyrolysis gas generation rate at 800 ℃. The pyrolytic gases was detected on-line by gas chromatography. Secondly,the characterization of Fourier transform infrared spectroscopy( FT-IR) of coal char is analyzed.And the FT-IR peak of semi-coke is fitted and calculated.Finally,combining the calculation parameters with the law of pyrolysis gas generation,the mechanisms of gas generation in each reaction stage during pyrolysis heating and the evolution law of coal structure in the process of gas generation were proposed.The results show that SL has abundant functional groups such as hydroxyl,aliphatic hydrocarbon,aromatic ring,carbonyl and ether bond. And the main functional groups in lignite have not changed,when the pyrolysis is below 350 ℃.Aliphatic oxygen-containing functional groups are decomposed between 350 and 450 ℃.The C=O relative content( C1) at the pyrolysis final temperature of 450 ℃ is 78% lower than that of 350 ℃.When the pyrolysis temperature is between 560 and 800 ℃,the pyrolysis reaction is mainly based on the decomposition of oxygen-containing functional groups of aromatic alkyl side chains.And the C—O relative content( C2) at the pyrolysis final temperature of 800 ℃ is 27% lower than that of 450 ℃.At 710-800 ℃ range,the main pyrolysis reaction is polycondensation.The aromatic condensation( D2) of chars at a final pyrolysis temperature of 800 ℃ is 65% higher than that at 710 ℃.Four kinds of pyrolysis gas generation processes were studied and analyzed that CO2 is mainly derived from the decomposition of carboxyl functional groups of different structures in the middle and low temperature zone.CO is generated in the high temperature,which is derived from the decomposition of the structures of phenol,ether and oxygen containing heterocyclic rings in coal. The decomposition of CH4 is mainly from the aromatic ring or methylene connecting the aromatic rings.The approximate 60% H2 mainly comes from the polycondensation reaction of aromatic structures in coal at a high-temperature zone.
Pyrolysis reaction of lignite is one of the important research directions in lignite utilization. Firstly,Shengli Lignite( SL) was pyrolyzed on a fixed bed for coking in order to analyze the structure evolution and gas formation mechanism of lignite during pyrolysis.The final temperature of semi-coke was determined by using the curve of SL pyrolysis gas generation rate at 800 ℃. The pyrolytic gases was detected on-line by gas chromatography. Secondly,the characterization of Fourier transform infrared spectroscopy( FT-IR) of coal char is analyzed.And the FT-IR peak of semi-coke is fitted and calculated.Finally,combining the calculation parameters with the law of pyrolysis gas generation,the mechanisms of gas generation in each reaction stage during pyrolysis heating and the evolution law of coal structure in the process of gas generation were proposed.The results show that SL has abundant functional groups such as hydroxyl,aliphatic hydrocarbon,aromatic ring,carbonyl and ether bond. And the main functional groups in lignite have not changed,when the pyrolysis is below 350 ℃.Aliphatic oxygen-containing functional groups are decomposed between 350 and 450 ℃.The C=O relative content( C1) at the pyrolysis final temperature of 450 ℃ is 78% lower than that of 350 ℃.When the pyrolysis temperature is between 560 and 800 ℃,the pyrolysis reaction is mainly based on the decomposition of oxygen-containing functional groups of aromatic alkyl side chains.And the C—O relative content( C2) at the pyrolysis final temperature of 800 ℃ is 27% lower than that of 450 ℃.At 710-800 ℃ range,the main pyrolysis reaction is polycondensation.The aromatic condensation( D2) of chars at a final pyrolysis temperature of 800 ℃ is 65% higher than that at 710 ℃.Four kinds of pyrolysis gas generation processes were studied and analyzed that CO2 is mainly derived from the decomposition of carboxyl functional groups of different structures in the middle and low temperature zone.CO is generated in the high temperature,which is derived from the decomposition of the structures of phenol,ether and oxygen containing heterocyclic rings in coal. The decomposition of CH4 is mainly from the aromatic ring or methylene connecting the aromatic rings.The approximate 60% H2 mainly comes from the polycondensation reaction of aromatic structures in coal at a high-temperature zone.
引文
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[22] MENG F R,YU J L,TAHMASEBI A,et al.Characteristics of chars from low-temperature pyrolysis of lignite[J]. Energy&Fuels,2013,28(1):275-284.
[23] MENG F R,YU J L,TAHMASEBI A,et al.Characteristics of chars from low-temperature pyrolysis of lignite[J]. Energy&Fuels,2013,28(1):275-284.
[24] LIU J X,JIANG X M,SHEN J,et al.Pyrolysis of superfine pulverized coal.Part 1.Mechanisms of methane formation[J].Energy Conversion and Management,2014,87:1027-1038.
[25] LIU J X,JIANG X M,SHEN J,et al.Pyrolysis of superfine pulverized coal.Part 2.Mechanisms of carbon monoxide formation[J].Energy Conversion and Management,2014,87:1039-1049.
[26] IBARRA V J,MOLINER R,BONET A J. FT-IR investigation on char formation during the early stages of coal pyrolysis[J].Fuel,1993,73(6):918-924.
[27] MRZIKOVJ,SINDLER S,VEVERKA L,et al.Evolution of organic oxygen bonds during pyrolysis of coal[J]. Fuel,1986,65:342-345.
[28] HEEK K V,HODEK W.Structure and pyrolysis behaviour of different coals and relevant model substances[J]. Fuel,1994,73:886-896.
[29] HODEK W,KIRSCHSTEIN J,HEEK K V. Reactions of oxygen containing structures in coal pyrolysis[J]. Fuel,1991,70:424-428.
[2] LIU P,ZHANG D X,WANG L L,et al.The structure and pyrolysis product distribution of lignite from different sedimentary environment[J].Applied Energy,2016,163:254-262.
[3]刘源,贺新福,杨伏生,等.热解温度及气氛变化对神府煤热解产物分布的影响[J].煤炭学报,2015,40(2):497-502.LIU Yuan,HE Xinfu,YANG Fusheng,et al.Impacts of pyrolysis temperature and atmosphere on product distribution of Shenfu coal pyrolysis[J].Journal of China Coal Society,2015,40(2):497-502.
[4] ZHENG M,LI X X,LIU J,et al.Pyrolysis of Liulin coal simulated by GPU-based reax FF MD with cheminformatics analysis[J].Energy&Fuels,2014,28(1):522-534.
[5] LIU P,WANG L L,ZHOU Y,et al.Effect of hydrothermal treatment on the structure and pyrolysis product distribution of Xiaolongtan lignite[J].Fuel,2016,164:110-118.
[6]宋昱,朱炎铭,李伍.东胜长焰煤热解含氧官能团结构演化13CNMR和FT-IR分析[J].燃料化学学报,2015,43(5):519-528.SONG Yu,ZHU Yanming,LI Wu.Structure evolution of oxygen functional groups in Dongsheng long flame coal by13C-NMR and FT-IR[J].Journal Fuel Chemistry Technology,2015,43(5):519-528.
[7] WIJAYA N,ZHANG L.A critical review of coal demineralization and its implication on understanding the speciation of organically bound metals and submicrometer mineral grains in coal[J]. Energy&Fuels,2011,25(1):1-16.
[8] LI G Y,DING J X,ZHANG H,et al.Reax FF simulations of hydrothermal treatment of lignite and its impact on chemical structures[J].Fuel,2015,154:243-251.
[9]刘钦甫,徐占杰,崔晓南,等.不同煤化程度煤的热解及氮的释放行为[J].煤炭学报,2015,40(2):450-455.LIU Qinfu,XU Zhanjie,CUI Xiaonan,et al. Release behavior of nitrogen in different rank coals during pyrolysis[J]. Journal of China Coal Society,2015,40(2):450-455.
[10] YE C P,HUANG H J,LI X H,et al.The oxygen evolution during pyrolysis of HunlunBuir lignite under different heating modes[J].Fuel,2017,207:85-92.
[11]邹晓鹏,盛羽静,陆海峰,等.粒径对不同煤阶煤焦气化反应活性的影响研究[J].燃料化学学报,2017,45(4):408-417.ZOU Xiaopeng,SHENG Yujing,LU Haifeng,et al.Effect of particle size on gasification of char with different coal ranks[J].Journal Fuel Chemistry Technology,2017,45(4):408-417.
[12] JAYARAMAN K,GOKALP I.Thermogravimetric and evolved gas analyses of high ash Indian and Turkish coal pyrolysis and gasification[J]. Journal of Thermal Analysis and Calorimetry,2015,121(2):919-927.
[13]周晨亮,刘全生,李阳,等.固有矿物质对胜利褐煤热解气态产物生成及其动力学特性影响的实验研究[J].中国机电工程学报,2013,33(35):21-27.ZHOU Chenliang,LIU Quansheng,LI Yang,et al. Effect of inherent minerals on the production of pyrolysis gases and the corresponding kinetics for Shengli lignite[J].Proceedings of the CSEE,2013,33(35):21-27.
[14] QIN Z H,CHEN H,YAN Y J,et al.FTIR quantitative analysis upon solubility of carbon disulfide/N-methyl-2-pyrrolidinone mixed solvent to coal petrographic constituents[J].Fuel Processing Technology,2015,133:14-19.
[15] ZHAO Y,QIU P H,CHEN G,et al.Selective enrichment of chemical structure during first grinding of Zhundong coal and its effect on pyrolysis reactivity[J].Fuel,2017,189:46-56.
[16] MALUBAZO N,WAGNER N J,BUNT J R D,et al.Structural analysis of chars generated from South African inertinite coals in a pipe-reactor combustion unit[J]. Fuel Processing Technology,2011,92(4):743-749.
[17] IBARRA J V,MUOZ E,MOLINER R.FTIR study of the evolution of coal structure during the coalification process[J]. Organic Geochemistry,1996,24(6/7):725-735.
[18] MIURA K,MAE K,LI W,et al.Estimation of hydrogen bond distribution in coal through the analysis of OH stretching bands in diffuse reflectance infrared spectrum measured by in-situ technique[J].Energy&Fuels,2001,15:599-610.
[19] DONG P W,CHEN G,ZENG X,et al.Evolution of inherent oxygen in solid fuels during pyrolysis[J]. Energy&Fuels,2015,29(4):2268-2276.
[20]迟铭书,王擎,李松阳,等.酸洗对桦甸油页岩矿物质以及有机结构的影响[J].燃料化学学报,2017,45(12):1424-1433.CHI Mingshu,WANG Qing,LI Songyang,et al. Influence of demineralization on minerals and organic structure in Huadian oil shale[J].Journal of Fuel Chemistry Technology,2017,45(12):1424-1433.
[21]李娜,刘全生,甄明,等.不同变质程度煤燃烧反应性及FTIR分析其热解过程结构变化[J].光谱学与光谱分析,2016,36(9):2760-2765.LI Na,LIU Quansheng,ZHEN Ming,et al.Coal combution reactivity of different metamorphic degree and strucrure changes of FTIR analysis in pyrolysis process[J].Spectroscopy and Spectral Analysis,2016,36(9):2760-2765.
[22] MENG F R,YU J L,TAHMASEBI A,et al.Characteristics of chars from low-temperature pyrolysis of lignite[J]. Energy&Fuels,2013,28(1):275-284.
[23] MENG F R,YU J L,TAHMASEBI A,et al.Characteristics of chars from low-temperature pyrolysis of lignite[J]. Energy&Fuels,2013,28(1):275-284.
[24] LIU J X,JIANG X M,SHEN J,et al.Pyrolysis of superfine pulverized coal.Part 1.Mechanisms of methane formation[J].Energy Conversion and Management,2014,87:1027-1038.
[25] LIU J X,JIANG X M,SHEN J,et al.Pyrolysis of superfine pulverized coal.Part 2.Mechanisms of carbon monoxide formation[J].Energy Conversion and Management,2014,87:1039-1049.
[26] IBARRA V J,MOLINER R,BONET A J. FT-IR investigation on char formation during the early stages of coal pyrolysis[J].Fuel,1993,73(6):918-924.
[27] MRZIKOVJ,SINDLER S,VEVERKA L,et al.Evolution of organic oxygen bonds during pyrolysis of coal[J]. Fuel,1986,65:342-345.
[28] HEEK K V,HODEK W.Structure and pyrolysis behaviour of different coals and relevant model substances[J]. Fuel,1994,73:886-896.
[29] HODEK W,KIRSCHSTEIN J,HEEK K V. Reactions of oxygen containing structures in coal pyrolysis[J]. Fuel,1991,70:424-428.