Ceramic Heat Exchangers-The Key to High Efficiency in Very Small Gas Turbines

Abstract

The requirements for the emerging new class of very small gas turbines (ie.25–75kw) to meet the needs of generator sets and hybrid electric vehicles are more demanding, in terms of both capital and power generation costs, than those associated with existing small simple cycle gas turbines. To be successful the reliability, maintenance, and economics of these very small gas turbines must offer advantages over existing prime-movers. With the plateauing of compressor and turbine aerodynamic efficiencies, and turbine inlet temperature increase paced by materials technologies, the use of an exhaust heat recovery exchanger is mandatory to meet performance goals. The first generation of these very small gas turbines, currently in the pre-production phase, are operating with very attractive efficiencies of around 30 percent based on the utilization of existing types of metallic recuperators. Performance advancement and evolution of these engines will be realized as ceramic component technologies mature, and to cost-effectively achieve an efficiency of 35 percent, and to ultimately exploit the full performance potential of over 40 percent efficiency, high temperature ceramic heat exchangers will be needed. In this paper the focus is on the use of the fixed-boundary type of recuperative heat exchanger because of its simplicity, high reliability, and with no moving parts the assurance of maintenance free operation over the life of the engine.