Mercury Removal Characteristics during Thermal Upgrading of Fractionated Alberta Subbituminous Coal

Abstract

In response to mercury emission control from coal combustion flue gases, coal cleaning and thermal upgrading are being considered as precombustion mercury emission control options. In our previous study, dry coal cleaning using an air dense medium fluidized bed (ADMFB) was shown to reject a substantial fraction of mercury in original coal while retaining acceptable combustible recovery. In this study, mercury removal characteristics by thermal upgrading were studied using Alberta subbituminous coals fractionated by a air dense medium fluidized bed (ADMFB). It was found that the bottom 28% of the run-of-mine coal cleaned by ADMFB separator contained over 57% ash-forming mineral matters and 46% mercury. Mercury removal from this fraction of coal increased rapidly at temperatures over 206–329 °C. During thermal upgrading, the mass of coal decreased and the calorific values increased with increasing upgrading temperature. The observed weight loss and increase in the calorific value of upgraded coal at temperatures between 106 and 329 °C were attributed mainly to the evaporation of moisture which does not contribute to calorific value, with a small amount to the loss of combustible volatiles.