Exergy destruction analysis of solar tower aided coal-fired power generation system using exergy and advanced exergetic methods

Abstract

The solar tower aided coal-fired power generation system (STCG) is based on a solar tower field and a conventional coal-fired power plant. Solar thermal energy is used to generate high-temperature and pressure steam to work in the coal-fired power plant. Indirect solar power generation and coal energy conservation goals can be achieved under this arrangement. The paper conducts a conventional and an advanced exergetic analysis of a 1000 MWe STCG. Exergy distribution of the system, exergy efficiency of each component and exergy destruction construction have been analyzed. Conventional exergetic analysis method has been used for exergy flow and loss distribution of STCG, whereas the advanced exergetic analysis method has been applied to exergy destruction of components, including endogenous and exogenous exergy destruction. These two methods complement each other and reveal the causes of exergy destruction in STCG. Results indicate that boiler and solar tower field systems are the components with the lowest exergy efficiency (53.5% and 26.0%, respectively). Total exergy losses of these two components account for more than 85% of all exergy losses of STCG. Exergy destruction of components is caused mainly by thermal performance of these components. Based on the degree of system and component association, the component ratio of endogenous and exogenous exergy destruction is different. Exogenous exergy destruction is directly proportional to the association degree. Connection complexity between a solar tower field and a coal-fired power plant system is the simplest, and 99.9% of solar tower exergy destruction is produced by the solar tower field itself. The results of this paper indicate that the boiler and solar tower field should be analyzed in detail when designing STCG systems. Before optimizing the system integration, thermal performance of components should be improved. Doing so, more energy from solar and coal can be converted to electricity, guiding the design and optimization of real demonstrators.