Review on characteristics and utilization of entrained-flow coal gasification residue

In accordance with the rapid development of China’s coal to chemical industry,the production of coal gasification residues has accordingly increased dramatically.However,the beneficial utilization of coal gasification slag,either researches or practical applications,is unreasonably limited.It is thus becoming a hot area in the coal to chemical industry to develop the coal gasification residue associated reduction,harmless and reutilization technology.In the present article,the status and progress with respect to entrained-flow coal gasification slag physiochemical properties(mineralogical properties,chemical composition and physical properties),beneficial utilizations as building materials,sewage treatment adsorbents and boiler fuels were presented.The current technical barriers and practical limitations for the utilization of coal gasification slag were discussed,based on which the future development needs for the utilization technology of coal gasification slag is proposed.According to the analysis,the mineral composition of coal gasification slag is mainly amorphous (residual carbon and vitreous),with a small amount of quartz,cristobalite,mullite,feldspar and other mineral crystals.Its chemical composition is mainly SiO2,CaO,Fe2O3 and Al2O3,this is similar to the chemical composition of ash after coal combustion,the Cao mass fraction of liquid slag discharge furnace is generally more than 10% due to the addition of cosolvent.The low mass fraction of SiO2,Fe2O3 and Al2O3(the total amount of these three substances in part of gasification slag is less than 60%)，high mass fraction of residual carbon and total water (the residual carbon of wet exhaust fine slag is as high as 30% and total water is 60%),and unstable composition of gasification slag are the main factors restricting its resource utilization.There are some problems in the utilization of gasifier slag,such as narrow field,low added value,poor product quality,small dosage,lack of relevant standards and technical specifications.Building materials and mixed combustion of circulating fluidized bed boilers are the main utilization ways at present，sintered ceramsite and its use as adsorbent to treat waste gas and wastewater are one of the ways of comprehensive utilization with high added value.The research on resource utilization of gasifier slag should be based on the suitable dehydration technology,efficient separation of residual carbon and ash,and graded utilization of residual carbon and vitreous.It is necessary to seek a comprehensive utilization scheme which combines high added value with large-scale consumption and is suitable for the market.