Comparison of char structural characteristics and reactivity during conventional air and Oxy-fuel combustion
The capture and sequestration of CO2 generated from large-scale stationary power plants is considered to be one of the leading technologies that could potentially have a significant impact on reducing greenhouse emissions.Among these emerging technologies,the oxy-fuel combustion is a near-zero emission technology that can be adapted to both new and existing pulverized coal-fired power stations.The goal of this work is to make a comparative study on char structural characteristics (including char yield,swelling ratio,BET surface area,pore distribution,morphology) and reactivity during conventional air and oxy-fuel combustion.Specific experimental designs include two series.One is carried out in pure N2 and CO2 (pyrolysis experiments),and another is prepared in N2+5％O2 and CO2+5％O2.Coal samples included raw coal,low density fraction coal and medium density fraction coal in all experiments.The present study is a further effort to extend our knowledge about physical and chemical structural characteristics and reactivity of char in the presence of high concentration CO2.Combustion and pyrolysis of a density fractionated China coal at drop tube furnace yielded the following conclusions.Compared to oxy-chars obtained under pure CO2 atmosphere,the swelling ratios of char obtained in pure N2 atmosphere are higher.When adding 5％ O2,experimental results are completely different with those of the pyrolysis experiment.In comparison with the oxy-chars obtained under CO2 + 5％O2 atmosphere,the swelling ratios of the char obtained in N2 + 5％O2 atmosphere are lower.In the pyrolysis experiment,the BET surfaces Area of the oxy-chars are about ten to twenty times as much as chars.When adding 5％ O2,the BET surfaces Area of the oxy-chars are about two to four times as much as chars.During pyrolysis experiment,the total pore volumes of the oxy-chars obtained under pure CO2 are larger in comparison with chars obtained in pure N2.The pore distributions of the oxy-chars are mainly mesopore and the chars have macropore mostly.The micropore and mesopore volume of oxy-chars are about ten times as much as chars separately and the macropore volume of oxy-chars are about two times as much as chars.When adding 5％ O2,the total pore volumes of the oxy-chars obtained under CO2 + 5％O2 are also larger in comparison with chars obtained in N2 + 5％O2.In the pyrolysis experiment,the reactivity indexes of oxy-chars obtained under pure CO2 are lower in comparison with chars obtained in pure N2.When adding 5％ O2,no significant differences can be observed,which may be due to the ordering of carbon microcrystalline structure.In pure CO2 atmosphere,the oxy-chars have a highly order polycrystalline structure,but chars obtained at pure N2 atmosphere have a highly disordered carbonaceous structure.
Oxy-fuel combustion Char swelling ratios pore distributions reactivity
T.Hashimoto K.Sakamoto M.Fujita
Power Systems,Mitsubishi Heavy Industries,Ltd.Nagasaki,Japan Power Systems,Mitsubishi Heavy Industries,Ltd.Yokohama,Japan
国际会议
The 7th International Symposium on Coal Combustion(第七届国际煤燃烧学术会议)
哈尔滨
英文
655-661
2011-07-19（万方平台首次上网日期，不代表论文的发表时间）