Experimental Research On The Influence Of Atmosphere On Pyrolysis Characteristic During Coal Pyrolysis In Fluidized Bed Reactor

Coal has a high proportion in China's energy consumption,but the dependence of oil and natural gas of China on abroad is at a high level which is relatively up to 60%and 30%.The consumption structure of China's energy determines that coal will be the main energy source that support the development of economy and society of China.Due to the highlighted atmosphere pollution problems in recent years,clean and high-efficient utilization of coal has now become an important issue.The main ways of utilizing coal include combustion,gasification,liquefaction and staged conversion.One of the typical staged conversion process is the circulated fluidized bed pyrolysis and combustion poly-generating system developed by Zhejiang University.The pyrolysis process of this system uses ash from combustion furnace as a heating source of pyrolysis furnace and part of the circulated pyrolysis gas as a fluidizing gas.Pyrolysis is the very first step of coal conversion and has a significant effect on its utilization afterwards.Therefore,this paper used Chinese typical lignite-Xiaolongtan lignite and typical bituminous coal-Yulin coal to study the influence of H₂,CH₄,CO₂ and CO?main components of pyrolysis gas?on the pyrolysis product yield and its characteristic in a small fluidized bed reactor.The pyrolysis of two kinds of coal in CO₂ contained atmosphere indicated that,raising CO₂ concentration in pyrolysis atmosphere could decrease char yield and this effect became more obvious under higher temperature?700? and 800??.CO₂ has different effect on CH₄ yield of two coals:it can increase CH₄ yield of Yulin coal pyrolysis gas but decrease CH₄ yield of Xiaolongtan coal pyrolysis gas.CO₂ could stimulate the decomposition of heavy fraction in tar and increase the relative concentration of phenol.With the increase of CO₂ concentration,the combustion characteristic temperatures of lignite char decreased while these temperatures of bituminous coal increased when the CO₂ concentration is hider?40%?.The pyrolysis of two colas in CH₄ contained atmosphere indicated that,char yield decreased with the increase of CH₄ concentration when the pyrolysis temperature is lower than 600 ? while it increased under a higher temperature.Tar yield also increased obviously under higher temperature.CH₄ could increase the yield of H₂ and CH₄ while it has little effect on CO and CO₂.The combustion characteristic temperature of char obtained under higher temperature in CH₄ atmosphere increased due to fixed carbon generated by the cleavage reaction of CH₄ which could block pore structures of char.The pyrolysis of two coals in CO atmosphere indicated that,CO could increase the yield of char and tar over 600 ? while it could decrease water yield.CH₄ and C2-C3 yield increased when the CO concentration is raised under lower temperatures due to tis effect on the cracking of methyl functional groups which could provide more free radicals for the formation of CH₄ and C2-C3.CO could resist the precipitation of phenolic hydroxyl while it can improve the cracking of alkyl structure so that there will be more free radicals including methyl and methylene.The pyrolysis of two coals in H₂ atmosphere indicated that,H₂ could improve the pyrolysis of coal and decrease char yield.Tar yield and water yield increased when the H₂ concentration was raised,which became more obvious under higher temperature.CH₄ yield increased when the H₂ concentration is raised in the atmosphere under different temperature due to tis role of stabilizing methyl fractions into CH₄.H₂ could improve the combustion characteristics of char and improve the precipitation of phenolic hydroxyl.The pyrolysis of Yulin bituminous cola in pyrolysis gas showed that,pyrolysis gas could improve the conversion of coal and liquid product yield including tar and water.This is because H₂ and CH₄ in pyrolysis gas could improve the precipitation of volatile compounds in coal.The char obtained from pyrolysis gas atmosphere has better combustion characteristic which could also explain the increase of liquid product yield.The concentration of heavy fraction in tar decreased while other light fractions increased when the coal is pyrolyzed in pyrolysis gas atmosphere,which could increase tar yield and improve its quality.