Experimental Study On Influence Of Coal Ash And Its Mineral Matter On Coal Pvrolvsis

More and more attention is paid to coal staged conversion technology based on solid heat carrier pyrolysis in order to utilize the high value components from coal efficiently and produce power,heat,chemicals and liquid fuels.Hot coal ash is usually used as the solid heat carrier during coal pyrolysis in the technology,so that it is urgent to carry out mechanism research on influence of coal ash and its mineral matter on coal pyrolysis.The influence of Fe2O3,Fe3O4,CaSO4,CaO,quartz,metakaolin and Huainan bituminous coal ash on Huainan bituminous coal pyrolysis was studied in a fixed bed pyrolysis reactor at different temperatures.The experiment results were combined to analyze the mechanism of effects of coal ash and mineral matter in coal ash on coal pyrolysis.The catalytic promotion effect of Fe2O3 on aromatization and polycondensation reactions of intermediates in coal pyrolysis process leads to the increase of char yield at low temperatures,while its inhibition effect on cracking reactions of intermediates in coal pyrolysis process leads to the decrease of tar yield in the whole temperature range.As the temperature increases,the catalytic promotion effect of Fe2O3 on secondary formation reactions of CH4 becomes more and more obvious,and to some extent this leads to the decrease of char yield and CO and H2 production,and the increase of CH4 production and pyrolysis water yield.Fe2O3 may react with carbon in char and the reducing gases in the coal pyrolysates,such as H2,CO and CH4,to yield water and CO2,and these reactions finally lead to the decrease of char yield and H2 and CO and CH4 production,and the increase of pyrolysis water yield and CO2 production.These reactions occur more easily at high temperatures than at low temperatures.The effect of Fe3O4 on Huainan bituminous coal pyrolysis is mainly at high temperatures,such as 800?.At 800?,Fe3O4 may react with carbon in char and H2,CO and CH4 in pyrolysis gas,resulting in a decrease in char yield and in H2,CO and CH4 production.Unlike Fe2O3,the addition of Fe3O4 has few effects on tar yield.The influence of CaSO4 on coal pyrolysis is mainly reflected at 800?,CaSO4 may react with carbon in char and H2,CO and CH4 in pyrolysis gas,resulting in a decrease in char yield and in H2,CO and CH4 production.CaSO4 has no effect on tar yield.The effect of CaO on coal pyrolysis occurs in the whole temperature range used in the experiment.CaO might decrease char and tar yield,while increase gas yield.This is due to the fact that CaO can promote the decomposition of the macromolecule structure in char and catalyze the secondary cracking reactions of tar.CaO may absorb CO2 in pyrolysis gas,resulting in a decrease in CO2 production.But CaO can increase H2,CO,CH4 and C2-C3 production to some degree.This is due to the catalysis of CaO on the secondary cracking reactions of tar,the decomposition of oxygen-containing functional groups,and the cleavage of alkyl side chains.Quartz has no effect on coal pyrolysis because it's inactive.Metakaolin may result in a slight decrease in tar yield and a slight increase in gas yield.This might be because metakaolin can catalyze the cleavage of alkyl side chains of aromatic rings in tar,resulting in more light hydrocarbons C1-C3.Huainan bituminous coal ash has effects on Huainan bituminous coal pyrolysis mainly due to Fe2O3 and CaSO4 contained in Huainan bituminous coal ash,while SiO2 contained in Huainan bituminous coal ash has no effects on coal pyrolysis.