新疆高碱煤四喷嘴气化炉结渣特性研究
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摘要
针对新疆高碱煤为气化原料造成气化炉堵渣的问题,以四喷嘴气化炉实际运行过程中产生的渣块为研究对象,采用扫描电子显微镜结合X射线电子能谱(SEM-EDX)、X射线荧光光谱(XRF)和灰熔点测试仪等分析了灰渣物化及矿物学特性。对新疆北山煤和牧场煤以及2种煤的混煤进行气化试验,考察了煤中矿物质高温演变行为规律。结果表明,新疆煤中矿物质具有不均一性,在高温热转化过程中,矿物质相互作用发生一系列复杂的物理化学反应,导致形成的矿物质灰渣具有多样性。采用新疆煤为气化原料时,大量灰渣在气化炉渣口处积累,形成了层状灰渣,主要由Na、Ca、Mg和Fe的硅酸盐或硅铝酸盐共熔物和Na-Al-Si-O构成。新疆煤气化后不同形态灰渣中Na含量差别较大,Na含量差异导致矿物质灰渣的黏温特性及固化温度不同。通过热力学模拟发现,Na-Si-O体系中其初始液相形成温度仅为800℃左右,随着Na_2O含量升高,其初始液相形成温度基本保持不变;混入一定量Al_2Si_2O_7后,其液相初始形成温度迅速升高至1 050℃左右。矿物质高温下发生熔融形成组分复杂的共熔物,随温度降低液态灰渣中具有高熔点的矿物质体系将结晶形成晶核,晶核迅速生长形成结晶颗粒而析出。在高温热转化过程,煤中活性Na可与石英黏土类矿物质发生反应生成低熔点的NaAlSiO_4;而Ca、Mg和Fe等与酸性矿物质反应生成具有高熔点的硅铝酸盐矿物质,在降温过程中首先从熔渣中析出,导致堵渣的发生。通过选取或调配煤种的熔渣黏温特性和灰熔融温度与气化运行参数一致可预防煤灰结渣发生。
Aiming at the problem of slag plugging in gasifier caused by Xinjiang high alkali coal as gasification raw material,the slag produced in the actual operation of four-nozzle gasifier was taken as the research object and the physical and chemical characteristics of ash and slag were analyzed by means of scanning electron microscopy,X-ray electron spectroscopy( SEM-EDX),X-ray fluorescence spectroscopy( XRF) and ash melting point tester.In addition,the ash transformation behaviors of Beishan( BS) coal,Muchang( MC) coal and their mixture were examined in a high temperature furnace.The results show that the distribution of minerals in Xinjiang coal are heterogeneous.During the process of thermal transformation at high temperature,a series of complex physical and chemical reactions occur among minerals,which result in the diversity of mineral ash.When Xinjiang coal is used as gasification material,a large amount of ash accumulates at the slag mouth of the gasifier and form layered slagwhich is composed of silicate or alumina silicate eutectic of Na,Ca,Mg and Fe and Na-Al-Si-O.The contents of Na in the different forms of slags after coal gasification are quite different,which leads to different viscoustemperature characteristics and curing temperature of mineral slag.The thermodynamic simulation shows that the initial liquid phase forming temperature of Na-Si-O system is ca.800 ℃,and it varies slightly with the increase of Na_2O.Nevertheless,the liquid phase forming temperature rapidly increases to 1 050 ℃ when a certain amount of Al_2Si_2O_7 is mixed. The minerals melt to form complex eutectics at high temperatures with the decrease of temperature,the minerals in liquid ash with high molten point would form crystal nucleus,and then the crystal nucleus grows rapidly and precipitates out into crystalline particles.In the process of thermal transformation at high temperature,the active Na can react with quartz and clay minerals to form Na Al SiO_4 with low melting point.However,Ca,Mg and Fe react with acid minerals to form silica-aluminate minerals substances with high melting point,which are firstly precipitated from slag during the cooling process,resulting in slag blocking.The coal ash slagging propensity could be prevented by selecting or blending the coals with viscosity and melting temperature approaching to the gasification operation parameter.
Aiming at the problem of slag plugging in gasifier caused by Xinjiang high alkali coal as gasification raw material,the slag produced in the actual operation of four-nozzle gasifier was taken as the research object and the physical and chemical characteristics of ash and slag were analyzed by means of scanning electron microscopy,X-ray electron spectroscopy( SEM-EDX),X-ray fluorescence spectroscopy( XRF) and ash melting point tester.In addition,the ash transformation behaviors of Beishan( BS) coal,Muchang( MC) coal and their mixture were examined in a high temperature furnace.The results show that the distribution of minerals in Xinjiang coal are heterogeneous.During the process of thermal transformation at high temperature,a series of complex physical and chemical reactions occur among minerals,which result in the diversity of mineral ash.When Xinjiang coal is used as gasification material,a large amount of ash accumulates at the slag mouth of the gasifier and form layered slagwhich is composed of silicate or alumina silicate eutectic of Na,Ca,Mg and Fe and Na-Al-Si-O.The contents of Na in the different forms of slags after coal gasification are quite different,which leads to different viscoustemperature characteristics and curing temperature of mineral slag.The thermodynamic simulation shows that the initial liquid phase forming temperature of Na-Si-O system is ca.800 ℃,and it varies slightly with the increase of Na_2O.Nevertheless,the liquid phase forming temperature rapidly increases to 1 050 ℃ when a certain amount of Al_2Si_2O_7 is mixed. The minerals melt to form complex eutectics at high temperatures with the decrease of temperature,the minerals in liquid ash with high molten point would form crystal nucleus,and then the crystal nucleus grows rapidly and precipitates out into crystalline particles.In the process of thermal transformation at high temperature,the active Na can react with quartz and clay minerals to form Na Al SiO_4 with low melting point.However,Ca,Mg and Fe react with acid minerals to form silica-aluminate minerals substances with high melting point,which are firstly precipitated from slag during the cooling process,resulting in slag blocking.The coal ash slagging propensity could be prevented by selecting or blending the coals with viscosity and melting temperature approaching to the gasification operation parameter.
引文
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[17] BRYANT G W,BROWNING G J,EMANUEL H,et al.The Fusibility of blended coal ash[J]. Energy&Fuels,2000,14:316-325.
[2]林雄超,杨远平,徐荣声,等.新疆高碱煤分选组分中碱性矿物赋存及差异演化研究[J].燃料化学学报,2017,45(2):157-164.LIN Xiongchao,YANG Yuanping,XU Rongsheng,et al.Occurrence and transformation behavior of AAEMs in the flotation fraction of a typical Xinjiang coal[J].Journal of Fuel Chemistry and Technology,2017,45(2):157-164.
[3] YANG Y P,LIN X C,CHEN X J,et al.The formation of deposits and their evolutionary characteristics during pressurized gasification of Zhundong coal char[J].Fuel,2018,224:469-480.
[4]宋国良,齐晓宾,宋维建,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):541-547.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 of Process Engineering,2015,15(4):541-547.
[5]陈衡,王云刚,马海东,等.循环流化床锅炉燃用准东煤结渣、沾污分析[J].热能动力工程,2015,33(3):431-435.CHEN Heng,WANG Yungang,MA Haidong,et al. Analysis and study of the slagging and contamination of a CFB boiler burning Zhundong-originated coal[J]. Journal of Engineering for Thermal Energy and Power,2015,33(3):431-435.
[6]崔育奎,张翔,乌晓江.配煤对新疆准东高碱煤沾污结渣特性的影响[J].动力工程学报,2015,35(5):361-365.CUI Yukui,ZHANG Xiang,WU Xiaojiang.The effect of coal blending ratio on slagging/fouling characteristics of Zhundong Xinjiang high-alkali coal[J].Journal of Chinese Society of Power Engineering,2015,35(5):361-365.
[7] ZENG X,YU D,LIU F,et al. Scavenging of refractory elements(Ca,Mg,Fe)by kaolin during low rank coal combustion[J].Fuel,2018,223:198-210.
[8]徐荣声,王永刚,林雄超,等.配煤和助熔剂降低煤灰熔融温度的矿物学特性研究[J].燃料化学学报,2015,43(11):1303-1310.XU Rongsheng,WANG Yonggang,LIN Xiongchao,et al.Mineralogical properties of lowering coal ash melting temperature using blending coal and fluxing agent[J].Journal of Fuel Chemistry and Technology,2015,43(11):1303-1310.
[9] WANG D,LIANG Q,GONG X,et al.Influence of coal blending on ash fusion property and viscosity[J].Fuel,2017,189:15-22.
[10] XUAN W,WHITTY K J,GUAN Q,et al.Influence of isothermal temperature and cooling rates on crystallization characteristics of a synthetic coal slag[J].Fuel,2014,137:193-199.
[11] LIU X,YU G,XU J,et al.Viscosity fluctuation behaviors of coal ash slags with high content of calcium and low content of silicon[J].Fuel Processing Technology,2017,158:115-122.
[12] XUAN W,WHITTY K J,GUAN Q,et al.Influence of SiO2/Al2O3on crystallization characteristics of synthetic coal slags[J]. Fuel,2015,144:103-110.
[13] DAI X,BAI J,HUANG Q,et al.Viscosity temperature properties from molecular dynamics simulation:The role of calcium oxide,sodium oxide and ferrous oxide[J].Fuel,2019,237:163-169.
[14] SAIMIR A L,HAJRI H,ROLANDA D,et al.Correlation between ash fusion temperatures and chemical composition in Albanian coal ashes[J].Fuel,2002,81:2257-2261.
[15] SHEN Z J,HUA X,LIANG Q F,et al. Reaction,crystallization and element migration in coal slag melt during isothermal molten process[J].Fuel,2017,191:221-229.
[16] CHENG X L,WANG Y G,LIN X C,et al.Effects of SiO2-Al2O3-CaO/Fe O low-temperature eutectics on slagging characteristics of coal ash[J].Energy&Fuels,2017,31:6748-6757.
[17] BRYANT G W,BROWNING G J,EMANUEL H,et al.The Fusibility of blended coal ash[J]. Energy&Fuels,2000,14:316-325.