Performance analysis of a solar-powered/fuel-assisted Rankine cycle with a novel 30 hp turbine

Abstract

The subject of this analysis is a novel hybrid steam Rankine cycle, which was designed to drive a conventional open-compressor chiller, but is equally applicable to power generation. Steam is to be generated by the use of solar energy collected at about 100°C, and is then to be superheated to about 600°C in a fossil-fuel fired superheater. The steam is to drive a novel counter-rotating turbine, and most of its exhaust heat is regenerated. A comprehensive computer program developed to analyze the operation and performance of the basic power cycle is described. Each component was defined by a separate subroutine which computes its realistic off-design performance from basic principles. Detailed predicted performance maps of the turbine and the basic power cycle were obtained as a function of turbine speed, inlet pressure, inlet temperature, condensing temperature, steam mass flow rate, and the superheater's fuel consumption rate. Some of the major conclusions are: (1) the turbine's efficiency is quite constant, varying in the range of 68.5–76.5 per cent (75 per cent at design) for all conditions, (2) the efficiency of the basic power cycle is 18.3 per cent at design, more than double as compared to organic fluid cycles operating at similar solar input temperatures, at the expense of adding only 20 per cent non-solar energy. This, combined with the fact that actual organic Rankine cycles operate typically at temperatures above 140°C, predicts that this system would be economically superior by using less than half of the collector area and by also using less expensive collectors.