准东煤加压气化过程中Na迁移规律的热力学研究
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摘要
准东煤中高含量的碱金属会在燃烧过程中引发严重的结渣与沾污问题,但准东煤气化过程中,在加压条件下碱金属的迁移转化规律仍不明确。为探究准东煤中NaCl在加压条件下的迁移转化机制,根据系统吉布斯自由能最小原则的热力学计算方法,采用HSC Chemistry的化学热力学平衡计算模块,对纯NaCl和准东煤中NaCl在加压过程中Na基化合物的物质的量进行计算。研究结果表明,压力显著影响纯NaCl的气化温度,在常压下,开始气化温度和气化完成温度分别为800℃和1 400℃;压力升至4 MPa时,气化开始温度和气化完成温度分别升至1 500℃和2 200℃。准东煤中Si、Al、H和O参与反应时,在0. 1 MPa条件下,300℃开始,NaCl逐渐与煤灰中的SiO_2、Al_2O_3和H_2O反应生成大量的NaAlSi_3O_8、NaAlSiO_4和Na_2SiO_3等Na基化合物。在1 500℃时,生成的气相NaCl仅占Na物质的量的25%左右。系统反应压力越高,生成低熔点且具有助熔作用的NaAlSi_3O_8、NaAlSiO_4、Na_2SiO_3就越多,导致炉内产生结渣的风险越高。
The high content of alkali metals in Zhundong coal induces serious slagging and fouling problems during combustion,however,the migration and transformation rules of alkali metals under pressurized condition in Zhundong coal gasification are still ambiguous.In order to obtain the migration and transformation mechanism of Na Cl in Zhundong coal under pressurized condition,according to the thermodynamic calculation method of Gibbs free energy minimum principle of the system,the thermodynamic equilibrium calculation module of HSC Chemistry was adopted to calculate the molar mass of sodium-based compounds in the pressurized gasification process of pure Na Cl and Zhundong coal.The results show that pressure impacts the gasification temperature of pure Na Cl significantly.At ordinary pressure,the start and finish temperatures of gasification are 800 ℃ and 1 400 ℃ respectively.When the reaction pressure up to 4 MPa,the start and finish temperatures of gasification increase to 1 500 ℃ and 2 200 ℃ respectively.When the Si,Al,H,O of Zhundong coal participate in the reaction under the condition of 0.1 MPa,300 ℃,the Na Cl will react with SiO_2,Al_2O_3 and H_2O in the coal ash to form a large number of sodium-based compounds,such as NaAlSi_3O_8,NaAlSiO_4,etc.In 1 500 ℃,the generated gaseous Na Cl accounts for only about 25% of the molar mass of Na.The higher the reaction pressure of the system is,the more NaAlSi_3O_8,NaAlSiO_4 and Na_2SiO_3 with low melting point and fluxing action will be generated,and the higher risk of slagging in the furnace will be.
The high content of alkali metals in Zhundong coal induces serious slagging and fouling problems during combustion,however,the migration and transformation rules of alkali metals under pressurized condition in Zhundong coal gasification are still ambiguous.In order to obtain the migration and transformation mechanism of Na Cl in Zhundong coal under pressurized condition,according to the thermodynamic calculation method of Gibbs free energy minimum principle of the system,the thermodynamic equilibrium calculation module of HSC Chemistry was adopted to calculate the molar mass of sodium-based compounds in the pressurized gasification process of pure Na Cl and Zhundong coal.The results show that pressure impacts the gasification temperature of pure Na Cl significantly.At ordinary pressure,the start and finish temperatures of gasification are 800 ℃ and 1 400 ℃ respectively.When the reaction pressure up to 4 MPa,the start and finish temperatures of gasification increase to 1 500 ℃ and 2 200 ℃ respectively.When the Si,Al,H,O of Zhundong coal participate in the reaction under the condition of 0.1 MPa,300 ℃,the Na Cl will react with SiO_2,Al_2O_3 and H_2O in the coal ash to form a large number of sodium-based compounds,such as NaAlSi_3O_8,NaAlSiO_4,etc.In 1 500 ℃,the generated gaseous Na Cl accounts for only about 25% of the molar mass of Na.The higher the reaction pressure of the system is,the more NaAlSi_3O_8,NaAlSiO_4 and Na_2SiO_3 with low melting point and fluxing action will be generated,and the higher risk of slagging in the furnace will be.
引文
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[2]YUAN Y,LI S,YAO Q.Dynamic behavior of sodium release from pulverized coal combustion by phase-selective laser-induced breakdown spectroscopy[J].Proceedings of the Combustion Institute,2015,35(2):2339-2346.
[3]XU J,YU D,FAN B,et al.Characterization of ash particles from co-combustion with a Zhundong coal for understanding ash deposition behavior[J].Energy&Fuels,2013,28(1):678-684.
[4]ZHOU H,ZHOU B,LI L,et al.Experimental measurement of the effective thermal conductivity of ash deposit for high sodium coal(Zhundong coal)in a 300 k W test furnace[J].Energy&Fuels,2013,27(11):7008-7022.
[5]WANG X,XU Z,WEI B,et al.The ash deposition mechanism in boilers burning Zhundong coal with high contents of sodium and calcium:a study from ash evaporating to condensing[J].Applied Thermal Engineering,2015,80:150-159.
[6]WEI B,TAN H,WANG Y,et al.Investigation of characteristics and formation mechanisms of deposits on different positions in fullscale boiler burning high alkali coal[J].Applied Thermal Engineering,2017,119:449-458.
[7]WEI B,WANG X,TAN H,et al.Effect of silicon-aluminum additives on ash fusion and ash mineral conversion of Xinjiang high-sodium coal[J].Fuel,2016,181:1224-1229.
[8]WU X,ZHANG X,YAN K,et al.Ash deposition and slagging behavior of Chinese Xinjiang high-alkali coal in 3 MWth pilotscale combustion test[J].Fuel,2016,181(1):1191-1202.
[9]张军,汉春利,刘坤磊,等.煤中碱金属及其在燃烧中的行为[J].热能动力工程,1999,2(2):83-85.ZHANG Jun,HAN Chunli,LIU Kunlei,et al.Various forms of alkali metal in coal and its behavior during coal combustion[J].Journal of Engineering for Thermal Energy&Power,1999,2(2):83-85.
[10]周永刚,范建勇,李培,等.高碱金属准东煤灰熔融过程的矿物质衍变[J].浙江大学学报(工学版),2015,49(8):1559-1564.ZHOU Yonggang,FAN Jianyong,LI Pei,et al.Mineral transmutation of high alkai Zhundong coal in ash melting process[J].Journal of Zhejiang University(Engineering Science),2015,49(8):1559-1564.
[11]王智化,李谦,刘敬,等.准东煤中碱金属的赋存形态及其在热解过程中的迁移规律[J].中国电机工程学报,2014,34(S1):130-135.WANG Zhihua,LI Qian,LIU Jing,et al.Occurrence of alkali metals in Zhundong Coal and its migration during pyrolysis process[J].Proceedings of the CSEE,2014,34(S1):130-135.
[12]王学斌,魏博,张利孟,等.温度和SiO2添加物对准东煤中碱金属的赋存形态及迁徙特性的影响[J].热力发电,2014,43(8):84-88.WANG Xuebin,WEI Bo,ZHANG Limeng,et al.Effect of temperature and silicon additives on occurrence and transformation characteristics of alkali metal in Zhundong coal[J].Thermal Power Generation,2014,43(8):84-88.
[13]魏博,谭厚章,王学斌,等.准东煤灰沉积与无机元素迁徙特性研究[J].工程热物理学报,2016,37(8):1783-1788.WEI Bo,TAN Houzhang,WANG Xuebin,et al.Ash deposition and inorganic element transformation during Zhundong coal combustion[J].Journal of Engineering Thermophysics,2016,37(8):1783-1788.
[14]俞海淼,曹欣玉,周俊虎,等.高碱灰渣烧结熔融过程中的物相变化[J].煤炭学报,2007,32(12):1316-1319.YU Haimiao,CAO Xinyu,ZHOU Junhu,et al.Phase transformation of high alkaline ash residue on the process of sintering and fusion[J].Journal of China Coal Society,2007,32(12):1316-1319.
[15]金涌,胡永琪,胡山鹰,等.煤炭热力学高效和化学高价值利用新工艺[J].化工学报,2014,65(2):381-389.JIN Yong,HU Yongqi,HU Shanying,et al.New technology for thermo-chemical comprehensive utilization of coal[J].CIESCJournal,2014,65(2):381-389.
[16]杨红深,谷小虎.压力对煤气化反应的影响[J].洁净煤技术,2012,18(2):65-68.YANG Hongshen,GU Xiaohu.Influence of pressure on coal gasification[J].Clean Coal Technology,2012,18(2):65-68.
[17]胡日查,刘春龙,毕勤成,等.γ射线法测量亚临界汽-水两相流截面含气率的实验研究[J].热能动力工程,2015,30(6):842-847.HU Richa,LIU Chunlong,BI Qincheng,et al.Experimental study of theγ-ray method for measuring the gas content in a cross section with a subcritical steam-water two-phase flow[J].Journal of Engineering for Thermal Energy&Power,2015,30(6):842-847.
[18]王艳坤.HSC Chemistry软件在高校化学科研中的应用[J].河南教育学院学报(自然科学版),2013,22(2):28-30.WANG Yankun.Application of HSC chemistry software in university chemical scientific research[J].Journal of Henan institute of Education(Natural Science Edition),2013,22(2):28-30.
[19]卫小芳,刘铁峰,黄戒介,等l.澳大利亚高盐煤中钠在热解过程中的形态变迁[J].燃料化学学报,2010,38(2):144-148.WEI Xiaofang,LIU Tiefeng,HUANG Jiejie,et al.Transformation of Na in an Australian high-sodium coal during pyrolysis[J].Journal of Fuel Chemistry and Technology,2010,38(2):144-148.
[20]宋国良,齐晓宾,宋维健,等.新疆准东高碱煤流态化气化过程中碱金属的迁移特性[J].过程工程学报,2015,15(4):542-546.SONG Guoliang,QI Xiaobin,SONG Weijian,et al.Migration characteristics of alkali metals in Zhundong high-alkali coal from Xinjiang during fluidized gasification process[J].The Chinese Journal Process Engineering,2015,15(4):542-546.