A COAL-FIRED HEAT-EXCHANGER FOR AN EXTERNALLY FIRED GAS-TURBINE

Significant improvements in efficiency for electricity generation from coal can be achieved by cycles that employ a high temperature, highly recuperative gas turbine topping cycle. The principal difficulty of e mploying a gas turbine in a coal-fired power generation system is the possible erosion and corrosion of the high-temperature rotating gas tu rbine components caused by the coal's inorganic and organically bound constituents (ash, sulfur, and alkali metals). One route to overcome t his problem is the development of an externally fired gas turbine syst em employing a coal fired heat exchanger. The solution discussed in th is paper is the design of a Radiatively Enhanced, Aerodynamically Clea ned Heat-Exchanger (REACH-Exchanger). The REACH-Exchanger is fired by radiative and convective heat transfer from a moderately clean fuel st ream and radiative heat transfer from the same of a much larger unclea ned fuel stream, which supplies most of the heat. The approach is to u tilize the best ceramic technology available for high-temperature part s of the REACH-Exchanger and to shield the high-temperature surfaces f rom interaction with coal minerals by employing clean combustion gases that sweep the tube surface exposed to the coal flame. This paper pre sents a combined experimental/computational study to assess the viabil ity, of the REACH-Exchanger concept. Experimental results indicated th at the REACH-Exchanger can be effectively fired using radiation from t he coal flame. Both computation and experiments indicate that the cera mic heat exchanger can be aerodynamically protected by a tertiary stre am with an acceptably low pow rate.