Thermodynamic analysis of temperature boosting of hot primary air in an ultra-supercritical lignite-fired power plant: Scheme comparison and performance enhancement

Lignite-fired boilers usually encounter the insufficient drying capacity of the pulverizer due to the inherent drawback of high moisture content in fuel. In this study, four schemes of heat sources for temperature boosting of hot primary air are proposed for an ultra-supercritical large-scale single reheat lignite-fired power plant according to heat sources such as inlet flue gas of air preheater (Scheme 1), the third stage extraction steam (Scheme 2), outlet steam of low-temperature reheater (Scheme 3), and inlet flue gas of economizer (Scheme 4). The thermodynamic system models are built by using EBSILON Professional software. The thermodynamic performance of the four schemes is analyzed and compared from the perspectives of the first and second laws of thermodynamics. First law analysis indicates that the power generation standard coal consumption of Scheme 3 is reduced by 0.87, 0.42, and 0.04 g·kW⁻¹·h⁻¹ compared with Schemes 1, 2, and 4, respectively. Second law analysis indicates that the exergy loss of Schemes 2–4 is 3.7, 7.6, and 7.5 MW lower than that of Scheme 1. The present study may provide guidance for the energy efficiency improvement of lignite-fired power plants.