Effect of coal pyrolysis coupled with its product tar cracking behavior on tar quality

Heshituoluogai coal was pyrolyzed in a fixed bed reactor at 600 ℃ and its pyrolysis tar was cracked in the second fixed bed reactor. The effect of tar cracking temperature and Ni-based catalysts with varying carriers on the performance of tar pyrolysis was investigated at N2 atmosphere. The results show that when the temperature in the second stage increases from 400 ℃ to 600 ℃,tar yield decreases from 13. 3% to 12. 5%,yield of Hydrogen increases from 83. 5 mL/ g to 111. 8 mL/ g. There is no significant changes on yield of heavy tar as the cracking temperature is less than 500 ℃,but decreases obviously comparing with that in the first fixed bed reactor,it is suggested that low temperature cracking can improve tar quality. The degree of cracking increases when the cracking temperature is above 550 ℃,and the corresponding yield of heavy tar increases compared with the first fixed bed. Adding Ni-based catalysts at 550 ℃ with different carriers of USY,HZSM-5(38) and HZSM-5(50) into the second tube,tar yields all decrease but the fraction of light tar increase compared with the value of non-catalyst. The highest fraction of light tar reaches 71． 9% when Ni-USY is the catalyst,28. 2% higher than that of non-catalyst.