Ceramic Recuperator and Turbine: The Key to Achieving a 40 Percent Efficient Microturbine

Abstract

Based on the use of state-of-the-art component technologies and the use of existing metallic materials, achieving an electrical efficiency anywhere near 40 percent in low pressure ratio recuperated microturbines is proving elusive. Current microturbines, rated at say 100 kW, operate with efficiencies approaching 30 percent. Advancing this to an upper level of about 35 percent is projected based on the ability to operate at turbine inlet temperatures greater than 1100C, and the utilization of a higher cost superalloy recuperator. This paper puts into perspective the challenge of trying to achieve 40 percent efficiency for small recuperated turbogenerator designs with radial flow components; the major constraints being associated with stress limitations in both the turbine and recuperator. Various publications (issued by both industry and the Government) often mention an efficiency goal of 40 percent for small gas turbines of this configuration, however, it needs to be recognized that the means to achieve this are beyond current high temperature metallic component capabilities. To achieve this “goal” necessitates increasing the operating temperature of the turbine and recuperator above 1100C and 800C respectively. Such advancements are projected to be technically and cost-effectively achievable by utilizing ceramic components, which with a dedicated development program, could perhaps become a reality in less than a decade to meet both future distributed power generation needs and defense applications, and be in concert with ever-demanding conservation goals and reduced emissions.