Experiments On The Effects Of Mineral Components On Coal During Fludized Bed Pyrolysis Process

Coal is the most important primary energy in China.The efficient and clean utilization of coal is a necessary measure to ensure the sustainable development of our country.When coal ash is used as solid heat carrier for coal conversion polygeneration technology,the circulating ash gets into the pyrolysis furnace and is fully mixed with the coal to provide heat for pyrolysis.In the process of coal combustion,many chemical reactions will occur at high temperatures,making the mineral components in the coal ash very different from that of raw coal.The influence of these mineral components in the coal ash on coal pyrolysis process is still not clear.So in this paper,the experiments about typical mineral components of ash?Fe₂O₃,CaSO₄ and CaO?influence on coal pyrolysis behaviors are carried out,to provide reference for the design and operation of coal conversion polygeneration process.The experiments were carried out in a small fluidized bed reactor.Zhungeer bituminous coal is selected as experimental materials,A systematical study on the effects of three kinds of mineral components in coal ash,Fe₂O₃,CaSO₄ and CaO,on coal pyrolysis products yields and pyrolysis gas components was carried out.The temperature ranges from 500 ? to 800 ?.The added mass fraction is 5%,10%and 20%.The experiment results combine with XRD technology to analysis.The results show that at the temperature between 500 ? and 600 ?,Fe₂O₃ will catalyze the aromatization and polycondensation of the colloid and inhibit the cracking reaction of the colloid,thus increasing the char yield and reducing the volatiles?including gas and tar?yield.Fe₂O₃ will also promote the recombination of oxyradical,so the formation of CO is suppressed.At the temperature between 700 ?and 800 ?,the semi coke reacts with Fe₂O₃,therefore increasing CO and CO₂ yield obviously.Also,semi coke gasification reaction will occur and Fe₂O₃ will catalyze the formation of CH₄.As a result,the effects of Fe₂O₃ on pyrolysis gas components vary.In addition,Fe₂O₃ will increase the water yield at the temperature range from 500 ?to 800 ?,because Fe₂O₃ will promote the oxygen free radicals of coal recombine,promoting generation of hydroxyl.With the increase of temperature,the reactions of Fe₂O₃ with H₂ and CH₄ also generate water.At the temperature between 500 ? and 600?,CaSO₄ has no obvious effect on the process of coal pyrolysis.At the temperature between 700 ? and 800 ?,the influence of CaSO₄ on pyrolysis process is mainly reflected on the reaction of CaSO₄ with some reducing substances,including semi coke,H₂,CH₄ and CO.So CO₂ and H₂O yields increase,and the yields of semi coke and H₂,CH₄ decrease.Due to the increase of CO₂,the gasification reaction of the semi coke is aggravated,thus the yield of CO slightly increasing.In addition,CaSO₄ has no obvious effect on tar yield at the temperature range from 500 ? to 800 ?,because CaSO₄ does not react with components in tar and has no catalytic effect on tar cracking.At the temperature between 500 ? and 600 ?,the effect of CaO on coal pyrolysis is mainly reflected on the reaction with CO₂,thus increasing the char yield.The total gas yield and CO₂ yield decrease significantly.At the temperature between 700 ? and 800 ?,CaO will catalyze the cracking of some macromolecular substances in char and tar,the char and tar yield decreased,thus increasing the total gas yield and a variety of gas components yield.In addition,CaO has almost no effect on the yield of pyrolysis water,because Ca?OH?₂ was not found in char,so CaO does not react with H₂O at the temperature between 500 ? and 800 ?.