Energy and exergy evaluations of solar-aided double reheat coal-fired power generation system

Abstract

In this paper, solar heat with mid- and high-temperature collected by molten salt parabolic trough solar field was integrated into the boiler sub-system of the double reheat coal-fired power generation system. Three typical integration modes were, respectively, evaluated by energy and exergy perspectives in terms of solar-generated electricity and solar energy conversion efficiency. Integration modes I–III utilized solar heat to preheat the inlet superheated steam, inlet reheated steam and inlet double reheated steam, respectively. Based on the case study through energy evaluation, it indicated that integrating solar energy with lower temperature led to higher solar-generated electricity, higher solar-to-solar heat efficiency, and higher solar-to-electricity efficiency. Integration mode I was unreasonably regarded superior to the other two, because the energy evaluation method ignored the quality of solar energy and mistakenly regarded the efficiency of solar heat to solar-generated electricity as the cycle efficiency. As an update, exergy evaluation takes both energy quantity and energy quality into consideration by regarding the efficiency of solar heat exergy to solar-generated electricity as the cycle exergy efficiency. It indicated that integration mode II was more recommended, with the highest solar-to-solar heat exergy efficiency and solar-to-electricity efficiency being 34.0% and 24.7%, respectively. The corresponding aperture area and solar-generated electricity are 5.7 × 105 m2 and 136.1 MW, respectively.