Thermodynamic Analysis and Case Study of a New Lignite-Fired Power Plant Using Solar Energy as Drying Heat Source

Abstract

Lignite usually has a high moisture content and low calorific value, and should be predried before combustion to enhance power generation efficiency. Steam extracted from steam turbine and boiler exhaust gas are often applied in lignite predrying systems. However, the bleeding gas from the steam turbine reduces its output, and the exhaust gas originating from the boiler has insufficient drying capacity. In the present work, a new lignite power plant integrated with a solar drying system is proposed. A solar energy collection and storage tank system were employed to solve the problem of low heat density and instability of solar energy. Thermodynamic analysis results show that the area of reflectors declines at a decreasing rate with an increase in the direct normal irradiation (DNI). The power generation efficiencies of a solar drying lignite power plant (SDPP) and steam extraction drying power plant (SEDPP) can be increased by 0.68% and 0.33% for every 0.1 kg/kg rise in the drying degree. When the drying degree is 0.3 and DNI is 0.5 kW/m2, the economic analysis indicates that the simple payback periods for a conventional lignite power plant, SDPP, and SEDPP are 2.38, 3.20, and 2.53 years, respectively. In addition, the solar-to-electricity efficiency declines at a decreasing rate with increasing drying degree. The power generation efficiency of SDPP with dryer exhaust recovery is increased by 0.83% for each 0.1 kg/kg increase in the drying degree.