The Pyrolysis Process Optimization And Reaction Process Research On Low-rank Coal

Coal pyrolysis is the basic unit of coal grading refining, the content of heavy component in tar is higher in traditional pyrolysis process, and so it could block the separation unit and increase the consumption of hydrogen in the process of tar refining. In this paper, the aim of the research is to improve the yield and quality of tar from low-rank coal pyrolysis. The effect of thermal experience on the lowrank coal pyrolysis was investigated in a fixed bed and a rotary bed reactor. On the basis of the heat carrier technology, the heat carrier which is used for cracking volatile can be used to improve the quality of tar. In the pyrolysis process, the yield and quality of tar can be improved by introducing an external hydrogen source. The specific research contents and results are as follows:1) The effect of pyrolysis temperature, pyrolysis time, and thermal experience on product distribution and composition of SD coal was investigated in the fixed bed reactor. When the pyrolysis temperature was 600°C, the coal in the reactor after 10 min to reach 600°C and the tar yield was 5.11%, when the pyrolysis time was 30 min, the tar yield was 5.93%, it showed that a large part of tar produced during the heating process. With the increasing of heating rate, the conversion rate of coal and the yield of tar increased, but the quality of tar became worse, the percentage of n-hexane soluble in tar or coal both reduced.2) Due to coal has different thermal experience and volatile secondary reaction degree in different reactors, this paper studied the effect of fixed bed and rotary bed on the product distribution and composition from SD coal pyrolysis. The heating rate of SD coal in rotary bed faster than that in fixed bed reactor, when the temperature is 500 and 600°C, the tar yield from rotary bed than that from fixed bed increased by 1.12 and 1.31 percentage point, respectively and the volatile secondary reaction was mainly condensation polymerization reaction, the heavy component of tar(n-hexane insoluble) than that from fixed bed pyrolysis increased by 15.17 and 24.80 percentage point, respectively. When the pyrolysis temperature was 700 and 800°C, the tar yield from rotary bed than that from fixed bed reduced by 2.09 and 2.60 percentage point, respectively and the volatile secondary reaction was mainly thermal decomposition reaction, the gas yield from rotary bed than that from fixed bed pyrolysis increased by 6.24 and 10.00 percentage point, respectively.3)In the process of solid heat carrier pyrolysis, the quartz sand only has the function of heat storage and transfer, so the tar yield is the highest, which is 8.44%, but the tar quality was the worst. The tar yield of olivine and SD char heat carrier pyrolysis was respectively 7.30 and 7.01%, and the tar yield of SD coal alone pyrolysis was 7.24%, those pyrolysis tar yield differ not quite, but the hexane soluble of tar from olivine and SD char heat carrier pyrolysis than that from SD coal alone pyrolysis increased by 27.16 and 20.69 percentage point, respectively. Olivine contains Fe2O3, which has the cracking effect on pyrolysis volatile,and the content of Fe, Ca, and K on the olivine surface was higher than that on SD char surface.4)The effect of atmosphere on the product distribution and composition on HL coal pyrolysis was investigated in fixed bed reactor. Compared with coal pyrolysis in nitrogen atmosphere, HL coal pyrolysis in hydrogen or syngas atmosphere increased the coal conversion and reduced the char yield, the yield and quality of tar both increased, the pyrolysis gas had higher methane content. Hydrogen and syngas atmosphere has the function of hydrogen donating in the coal pyrolysis process.