A Coal-Fired Heat Exchanger for an Externally Fired Gas Turbine

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Abstract
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 employing a gas turbine in a coal-fired power generation system is the possible erosion and corrosion of the high-temperature rotating gas turbine components caused by the coal’s inorganic and organically bound constituents (ash, sulfur, and alkali metals). One route to overcome this problem is the development of an externally fired gas turbine system employing a coal fired heat exchanger. The solution discussed in this paper is the design of a Radiatively Enhanced, Aerodynamically Cleaned Heat-Exchanger (REACH-Exchanger). The REACH-Exchanger is fired by radiative and convective heat transfer from a moderately clean fuel stream and radiative heat transfer from the flame of a much larger uncleaned fuel stream, which supplies most of the heat. The approach is to utilize the best ceramic technology available for high-temperature parts of the REACH-Exchanger and to shield the high-temperature surfaces from interaction with coal minerals by employing clean combustion gases that sweep the tube surface exposed to the coal flame. This paper presents a combined experimental/computational study to assess the viability of the REACH-Exchanger concept. Experimental results indicated that the REACH-Exchanger can be effectively fired using radiation from the coal flame. Both computation and experiments indicate that the ceramic heat exchanger can be aerodynamically protected by a tertiary stream with an acceptably low flow rate.