新疆高碱煤四喷嘴气化炉结渣特性研究

Study on the slagging characteristics of Xinjiang high-alkali coal in four-nozzle gasifier

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Na2O含量升高,其初始液相形成温度基本保持不变;混入一定量Al2Si2O7后,其液相初始形成温度迅速升高至1050℃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NaAlSiO4;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 viscous-temperature 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 Na2O.Nevertheless,the liquid phase forming temperature rapidly increases to 1 050 ℃ when a certain amount of Al2Si2O7 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 NaAlSiO4 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.