The effect of coal volatility on mercury removal from bituminous coal during mild pyrolysis

Two high volatile and one low volatile bituminous coals (Lower Freeport #6A , Pittsburgh #8 and Lower Kittanning, respectively) used primarily for elec tricity production were tested to determine the percentage of mercury conte nt removed during mild pyrolysis. Size-segregated samples of the well-chara cterized coals were tested in a tube furnace with a nitrogen blanket at dif ferent residence times for different processing temperatures through the ra nge 275-600 degrees C. The resulting char was analyzed for mercury and comp ared to the original parent coal concentration to determine the percentage of removal. Experiments have shown that as much as 80% of the original merc ury is removed from these coals at these conditions. The percentage mercury removal was found to be a function of residence time and temperature. The high volatile bituminous coals show a near-constant mercury removal rate as the temperature increases until the temperature reaches a level where merc ury removal is inhibited and the rate decreases with increasing temperature . For the low volatile coal, the rate of mercury does not show a change in mechanism as temperature increases and follows the Arrhenius form throughou t the temperature range studied. The results were modeled as a homogeneous reaction with distinct maximum percent mercury available for conversion( X- max) for a specified temperature. Data analysis indicates the following: at 500 degrees C, mild pyrolysis of the Lower Kittanning low volatile sample resulted in 75% maximum mercury removal and the corresponding reaction rate coefficient is 1.56 min(-1); mild pyrolysis of Lower Freeport #6A coal sam ple at 500 degrees C resulted in 74% maximum mercury removal and the corres ponding reaction rate coefficient is 0.42 min(-1); the Pittsburgh #8 coal s ample had a maximum mercury removal amount of 80% at a furnace temperature of 400 degrees C and a reaction rate coefficient of 0.44 min(-1). (C) 2000 Elsevier Science B.V. All rights reserved.