Production of low-ash, low-sulfur coal-water fuel (CWF) will yield large quantities of high-ash but still low-sulfur “residual” CWF analogous to the residual fuel oil produced by petroleum refining. Relatively low in cost compared to the premium, low-ash CWF product, “resid” CWF will thus be available for in-plant industrial generation of conventional steam power or process heat. Due to its low sulfur content, however, a higher-value use of such a compliance fuel can be the indirect firing of gas turbines for the more efficient combination of power generation plus subsequent bottoming-cycle use or process heat applications (cogeneration).
To limit NOx emissions, staged combustion will be required. Such operation can be accomplished starting with substoichiometric CWF reaction in “conventional” slurry burners followed by final combustion completed in the bottom region of a deep, intensely-mixed, fludized-bed heat exchanger. By virtue of the highly enhanced heat-transfer characteristics of the strongly-stirred bed of non-reactive particles, the normal limitation of rates of non-pressurized fire-side heat transfer is elevated. The fuel ash particles, milled fine by passage through the bed of refractory heat-transfer particles, are collected in a conventional baghouse. The conceptual design of such a combustion-driven, fluid-bed heat exchanger system fired by high-ash, residual coal-water fuel is outlined and its advantages over a conventional fluid-bed, solid-coal combustor for indirect firing of gas turbines are enumerated.
Heat transfer mechanism between fluid bed and fluid bed wall. Concerning heat transfer of internal heat exchanger in fluid bed 3.
