The Study On Conversion Character During Pyrolysis Of Chinese Western Coals

Coal pyrolysis is an initial process of all major coal conversion, likegasification, liquefaction combustion and carbonization, therefore, research onpyrolysis is very important for coal conversion process. This paper mainlyinvestigated the evolution characteristics of pyrolysis products of three kinds ofChinese western coals in China with weak reductive property, such as,Shendong coal, Ningxia Lingwu coal and Xinjiang hami coal, and Pingshuo coalwith strong reductive property, from 200～600℃temperature, under the reactorwith characteristic of fluidized bed and fixed bed and the fixed bed reactor. Themain conclusions are as fllowing:1. It was obtainted that the distribution regulation of gasescontaining-carbon, containing-hydrogen and containing-oxygen at differenttemperature, by studying on the release, composition and properties of gaseousproduct from four Chinese western coals pyrolysis. Similar trend exist in the gases produced with temperature change for allcoals. HE begin to release about 450℃, then, yield of Ha rapidly increase.Because the different formation mechanism between CO and CO₂, their releasecurves is different. In the range of experiment temperation, yield of CO increasewith the elevation of pyrolysis temperature, and there exist higher peaktemperature than CO₂. Different from CO, CO₂ begin to release at about 200℃,and its yield reach maximum about 500℃, and decrease slowly about 600℃.The peak temperature of CH₄ is higher than C₂-C₄, their yields from Pingshuoand Xinjiang coals pyrolysis reach maximum at 550℃, those of Ningxia andShendong coals increase still at 600℃.The yields of HE and hydrocarbon from Pingshuo coal pyrolysis are allhigher than those of other three kinds of coals during rapid heating and slowheating pyrolysis experiments. It was closely relate to higher H content, higherH/C atom ratio and higher volatilation in Pingshuo coal. Because of the highercoal rank, Xinjiang coal showed higher stabilization than other coals. TG andDTG results showed Xinjiang coal has the lowest loss-weight rate and Pingshuocoal has the hightest loss-weight rate.2. The results from three kinds of different pyrolysis showed the yields ofH₂ and hydrocarbon Pingshuo and Shendong coals released were higher thanone of Ningxia and Shendong coals, and the yields of CO Ningxia andShendong coals produced were higher than Pingshuo and Xinjiang coals, at thesame pyrolytic end temperature. 3. The change curves of the yields of H₂, CO, CO₂ and CH4 with holdingtime was similar. The evolution of gaseous products duringtemperature-programmed pyrolysis manily occurred in heating period, and fastheating rate pyrolysis mainly focused in 20min of holding time. About 60min ofholding time, little of gaseous product were detected by GC.4. The results of TG and DTG showed the most loss weight, the most lossweight rate increased with the increasing of heating rate, and the initialtemperature, the highest temperature corresponding the most loss weight and theending temperature all moved towards higher temperature.5. The element analyses of chars showed, the H/C, O/C atom ratio and thecontent of H, O of in chars were lower much than in raw coals. Most of themwere released as tar and gas product. Except for Pingshuo coal, the content of Celement in char increased slowly within 400℃, and enhanced swiftly within400-600℃. The content of C and O in Pingshuo char didn't change regularlywith temperature. This indicated that the especial property of Pingshuo coalamong four coals was related to the especial structure of Pingshuo, for examplehigher content of H element, volatile, vitrnite, exinite and mineral matter.6. By calculation, it be gained that coals conversion under fast heating ratewas higher than under one of temperature-programmed experiments in thefixed-bed reactor. Meanwhile, the conversion of Pingshuo coal was the highest,and Xinjiang coal was the lowest in two kinds of pyrolysis type.