Proposal and Characteristics Evaluation of a CO₂-Recovering Hybrid Power Generation System Utilizing Solar Thermal Energy

Abstract

A CO₂-recovering hybrid power generation system utilizing solar thermal energy was proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO₂ is recovered based on the method of oxygen combustion. Hence solar thermal utilization efficiency becomes considerably high compared with that of conventional solar thermal power plants in which superheated steam near 400°C has to be produced for using as the working fluid of steam turbines, and the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used in a exergetically excellent way in the system, that is, can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO₂ can be recovered by using oxygen combustion method, so that high CO₂ capturing ratio near 100% as well as no thermal NO_x emission characteristics can be attained. It has been shown through simulation study that the proposed system has net power generation efficiency of 63.4%, being higher than 45.7% compared with that of the conventional power plant with 43.5% efficiency, when the amount of utilized solar energy is neglected and when the temperature of the saturated steam is 220°C.