(195a) Oxycombustion Of Coal-Needs, Opportunities, And Challenges

Oxy-coal combustion with CO2 recycle is one of the few processes that might allow carbon sequestration systems to be applied to existing coal combustion units currently using air. This paper reviews the current state of this technology and identifies technical barriers to its implementation and important research issues to be solved. These issues arise from heat transfer differences due to the high CO2 concentrations in the combusion chamber, and from effects of variations in partial pressure of oxygen in the coal transporting fluid on flame stability and location. It is noteworthy that oxy-coal combustion introduces several additional degrees of freedom that can be adjusted for optimum performance. These include partial pressures of O2 in both primary and secondary air streams, the amount of CO2 to be recycled, the location from which the recycled CO2 is to be drawn, and the extent of pollution control required prior to CO2 disposal. For example, it has been suggested that upon compression of the exhaust CO2 rich stream, the NO is oxidized to NO2 and nitric acid, the SO2 is converted to sufuric acid, and these and trace metals, such as mercury are removed without additional clean-up processes being required. Research is urgently required to determine whether this chemistry does in fact ocurr for actual oxy-coal combustion flue gases.