Study On De-volatilization Behavior Of Low-rank Coal In Low-temperature Pyrolysis

Xilinhaote lignite(XL)and Hongliulin lignite(HL)were used as raw material.The basic properties of coal's low temperature pyrolysis were investigated in N2 atmosphere on a fixed bed.The results showed that the tar yield of coal goes up with the temperature rise and fall off when the temperature reaches one point.The largest tar yield of XL is 8.41%with a temperature of 500?,and that of HL is 10.95%with a temperature of 600?.As the pyrolysis temperature goes up,the char yield decreases and the gas yield increases.A rise in pressure inhibits the escape of volatiles in coal,which decreases the yield of tar and increase the yield of gas and char.With the increase of pyrolysis temperature,the hindering effect of pressure to volatilization becomes weak.The effect of small molecular compounds extracted by thermal dissolution on pyrolysis performance of HL was discussed with the autoclave and fixed bed.The results showed that as the temperature of thermal dissolution rise from 260? to 340?,the volatiles yield of thermal dissolution residue decreased from 21.38%to10.49%,which is lower than the volatiles yield of raw coal(28.02%),the liquid yield of that decreased from 12.01%to 3.72%and the gas yield of that decreased a little.The liquid yield of the coal treated in 340?thermal dissolution was lower than that of raw coal close to 5%,and the char yield of thermal dissolution was higher than that of raw coal close to 6%,which demonstrates that the treatment of coal in 340? thermal dissolution removes some of small molecular compounds in coal which can provide free radicals to coal during the pyrolysis and promote the pyrolysis of coal.The thermal conversion behavior of asphaltene(AS)and preasphaltene(PA)were sthdied with HL,graphite powder(C),AS and PA by thermogravimetric analyzer.The results showed that entrainment is a main factor in the effect of HL on the thermal conversion behavior of AS.The volatiles in HL and some little molecular organics in AS entrain each other during pyrolysis.Besides entrainment,the effect of HL on the thermal conversion behavior of PA also has another aspect-some PA was separated out by the chemical reaction with the volatiles from the coal.Above all,the separate of asphaltene in the process of coal pyrolysis is complex.Some bituminic with small molecular can escape by evaporation,some bituminic with high boiling point can escape by entrainment with pyrolysis gas,and some bituminic can escape by chemical reaction with other volatiles of coal during the pyrolysis.