Lower emission plant using processed low-rank coals

Abstract

Low-rank coals can be processed into non-fouling coal, ultra-low ash coal, and coals containing catalysts. Systematic studies of the action of acid to reduce ash in a number of low-rank coals have shown total ash reduction varied from 96% to 30%; the extent of ash reduction was limited by the nature of minerals, which may be removed using various acids, including HF, to produce ultra-low ash coal. A commercial process must operate at elevated temperatures, but this must not produce toxic wastewater; data are provided to show that wastewater may be treated and water recycled without polluting the environment. The addition of effective catalysts results in enhanced reactivity of the coal to oxygen and steam; experimental data show high yield of H 2 from char and steam, and accompanying post-gasification chemistry. Development of catalytic steam gasification requires an understanding of aqua-chemistry and the thermal transformations of inorganics as the coal is heated. The scientific basis exists for processing low-rank coals, but commercial application requires: (i) high production rates, (ii) treating wastewater produced from coal treatment plant, (iii) catalysts that increase the yield of H 2 from steam gasification, and (iv) plant that achieves high power and thermal efficiencies. Modelling studies for super-critical plant, and for direct coal-fuelled turbine in combined cycle, illustrate the potential for lower-emission technology; catalytic steam gasification offers the cleanest option for future coal-fuelled plant.