Compact Heater Concept for Closed Power Cycles

The largest component of the closed-cycle gas turbine system is the heater. Many industrial and all non-stationary applications of the CCGT will require a compact combustor and heat-transfer system. This paper describes a heater concept consisting essentially of a deep, pressurized, fluidized-bed heat exchanger into which the products of partial fuel-air combustion are discharged from multiple pre-burners at the lower periphery of the bed. The combustion system can employ any clean fluid fuel, including a deeply de-ashed coal-water slurry. Tangential injection of the fuel-rich products from the pre-burners and complete combustion with the fluidizing air generate additional gas plus a strong tangential velocity component at the boundary of the final combustion zone, a region of intense mixing. Natural convection due to heat released in this annular zone adds an upward component at the wall. These velocity components, superposed upon the upward velocity of the fluidizing air, produce a helical upward flow at the periphery of the bed, with a net downward axial flow at its core. The additional scrubbing action of this combustion-driven flow enhances the rate of heat transfer to the heat-exchanger surfaces beyond the level (already high) characteristic of conventional fluidized beds. The properties of the ceramic bed particles and the auxiliary flow equipment are discussed briefly.