Experimental Investigation Of Coal Ash Melting Characteristics Under Entrained Flow Gasification Condition

Coal gasification is one of the important technology that utilizes coal in anefficient and clean way, and syngas cooler is the key equipment in the entrained bedcoal gasification process to ensure reliability and efficiency. Coal ash meltingcharacteristics affect the design and operation reliability of syngas coolers directly,until now there are many fouling and slagging problems occouring in syngas coolersdue to lack of understanding of the coal ash melting characteristics, and few studieshave been made to investigate the coal ash melting characteristics in entrainmentcoal gasification atmosphere. The paper aimed on the coal ash meltingcharacteristics in entrainment coal gasification atmosphere by using a DTF facilitywith SEM-EDX and XRD instruments, and made a comparation of coal ash meltingcharacteristics forming in these conditions: entrained bed condition, fixed bedcondition with heating under constant temperatue and fixed bed condition withheating and cooling under constant temperatue.The DTF experimental results of ash melting characteristics showed that theslag formed in the entrained bed condition had much crystal component in500~900℃, which was dominat by its characteristics of rapid heating and cooling.Anorthite was the main crystal component in the ash, the more CaO and Fe2O3inthe coal ash, the more Ca and Fe rich compounds would emerge in the slag likeanorthite and hedenbergite; and the slag of Shenhua N contained more hedenbergitebecause of more Fe2O3in the coal ash. There was a lot of porous structure in500-900℃on the slag surface because the interaction between the frameworkconstructed by crystal component and eutectic mixture. SEM-EDX analysis showedthat the higher the Na, K content in the ash was, the more likely the ash fouled onthe heat transfer surface, and the higher the S, Fe content in the ash was, the morelikely the FeS formed in slag surface, FeS emerged an eutectic mixture that meltedin800~1000℃, which led to foul and slag.The comparation of ash melting characteristics in three conditions showed thatin the fixed bed condition with heating under constant temperatue, simple oxide andsulfate minerals reacted to form complex compounds, which could emerge aeutectic mixture and melt, the ash was not the same as that formed in the entrainedbed condition on morphology and composition In the fixed bed condition withheating and cooling under constant temperatue, the crystallization occoured in a fullmolten mixture, wich is similar to the slag formation in entrained bed condition, theslag was similar on morphology and composition, the slag formed in this conditionhad a higher precipitation temperature, which made it easier to crystallize in the same temperature, so as to predict the ash melting characteristics, but it wasdifferent with that formed in the syngas cooler.The fixed bed condition with heating under constant temperatue was suitable toinvestigate the coal ash fusion formation and fusion temperature; the fixed bedcondition with heating and cooling under constant temperatue was suitable topredict the component contained in the slag and crystallization characteristics; theentrained bed condition was similar to the actual slagging and fouling condition insyngas coolers, it was suitable to verify the the experimental results got in the fixedbed condition with heating and cooling under constant temperatue, and predict themorphology and composition of slag that formed in the actual syngas coolers.