Behavior of trace elements during pyrolysis of coal in a simulated drop-tube reactor

摘要

Release behavior and chemical form distribution of As, Pb, Cr, Cd and Mn in Datong coal during pyrolysis was studied in a simulated drop-tube reactor at a heating rate of about 1000℃/s, including effects of temperature (300-1000℃), atmosphere (N_2 and H_2), and holding time (0.3-10min). Results show that the bleeding ratios of As, Pb, Cr, Cd and Mn increase with increasing pyrolysis temperature and holding time. Reductive environment results in higher emission of the elements. Among the five trace elements, As, Pb and Cd show similar behavior with volatilities higher than that of Cr and Mn at 1000℃. The five trace elements in the coal and coal-derived chars are separated into five fractions through an extraction procedure. Ion exchangeable form of the elements is not found in the coal and the chars, and the elements remained in the residue fraction is the most dominant occurrence form in the coal and the chars for As, Pb, Cd and Cr. All the forms for all the elements undergo transformation in the pyrolysis resulting in reduced content in the chars.