Effect Of Oxy-fuel Combustion Conditions And Special Atmospheres On Release Rules Of Alkali And Alkaline Earth Metals

Coal is main fossil fuel in our country. Greenhouse gases (GHG) such as CO2 emitted into the atmosphere from burning fossil fuels. Oxy-fuel combustion can reduce the emission of CO2 by producing a stream of concentrated CO2 ready for sequestration. The release of alkali and alkaline earth metals (AAEM) in coal may cause problems, such as corrosion of heater tubes and fouling, to combustion furnace during coal combustion. Compare to traditional combustion, differences of atmosphere exist in oxy-fuel combustion. The change of atmosphere conditions leads to the variation of combustion characteristic, which affect migration rules of AAEM. The aim of this paper is to investigate the release rules of AAEM during oxy-fuel combustion.In the study, the oxy-fuel combustion experiments were conducted in a drop-tube reactor for YZ coal, YM coal, XM coal, JC coal. For comparison purpose, tests were also carried out in a fixed-bed reactor. The ion chromatography was used to determine the concentration of AAEM. The effects of combustion conditions and atmospheres on the release rules of AAEM during oxy-fuel combustion were investigated systematically.The research results show that the release rates of AAEM increased with rising of temperature during oxy-fuel combustion. The reaction rate of coal and release rates of AAEM enhanced with increasing oxygen concentration. The existence of SO2 in the atmosphere can decrease the release of alkali metal due to sulfation of AAEM. On the contrary steam can enhance the reactivity of coal and promote the release of alkali metal. The release rates of AAEM are higher in SO2+H2O than in H2O. The change of release rates of alkaline earth metals is unobvious in the presence of SO2 and H2O.The release rates of AAEM in the drop-tube reactor is lower than that of fixed-bed reactor with the same temperature and oxygen concentration due to the react time is short. With extending residence time, the release rates of Na and K are increased. Combined the results of tests with different coal particle size, it seems that the release of AAEM is under the control of diffusion of AAEM in coal.Among YZ coal, YM coal, XM coal and JC coal, the release rates of AAEM of XM coal are the highest whereas those of JC coal are lowest. The release rates of AAEM are associated with coal rank, lower coal rank has higher release rates of AAEM.