Effect Of Sulfate Compounds On Contamination And Slagging In High-alkali Coal Combustion

According to the present situation of energy structure and fossil energy development in our country,the energy structure dominated by coal-electricity in China will not change in the long term.Therefore,the optimization of coal-electricity industry is of great significance in the long term.Because of its advantages of low cost of development,easy combustion,stable combustion and low pollution,Zhundong coal is an ideal coal chemical and coal raw material.However,Zhundong coal has a serious pollution of fouling and slagging in the combustion process,which seriously affecting the safe and economical operation of the boiler.In this paper,according to the results of XRF analysis and previous studies by Zhundong coal and fouling-slagging,we concluded that the fouling and slagging of Zhundong high-alkali coal was likely related to the content of sulfate compounds.Therefore,based on the selection of Shuicheng bituminous coal with low content of alkali-metal sulphate as experimental coal,the prepared Shuicheng bituminous coal ash and samples added different amount of sulfate were examined by scanning electron microscopy(SEM),ash melting point,ash column liquid phase shrinkage experiment.At the same time,X-ray diffraction(XRD)and Factsage were used to further simulate and analyze the influence law.It can be concluded that sulfate compounds(including Na2SO4,K2SO4,CaSO4,MgSO4)will reduce the ash melting point,increase the liquid phase ratio of coal ash after high temperature reaction,exacerbate the ash fusion within a certain range.The reason is that the sulfate compound will promote the interaction between SiO2 and some oxides to form a low-temperature eutectic.For CaSO4 and MgSO4,their reaction mechanism with Na2SO4,K2SO4 has some differences.The addition of Na2SO4 and K2SO4 to the coal ash will generate a small amount of complex sulfates(Na3Fe(SO4)3,K3Fe(SO4)3)during the reaction.These small amounts of complex sulfates have a great effect on the fusibility.When the amount of MgSO4,CaSO4 exceeds a certain range,the sample will weaken the fusibility of coal ash for reflecting its own high melting point characteristics partially.Alkali metal complex sulfate is even stronger than the alkali metal sulfate on the fusibility of coal ash.In addition,the alkali comlex sulfate and sulfate systems not only exacerbates the fouling and slagging problems during coal combustion,but also greatly aggravates the corrosion of sulfates during high temperature corrosion.