Simulation study on lignite-fired power system integrated with flue gas drying and waste heat recovery - Performances under variable power loads coupled with off-design parameters

Lignite is a kind of low rank coal with high moisture content and low net heating value, which is mainly used for electric power generation. However, the thermal efficiency of power plants firing lignite directly is very low. Pre-drying is a proactive option, dehydrating raw lignite to raise its heating value, to improve the power plant thermal efficiency. A pre-dried lignite-fired power system integrated with boiler flue gas drying and waste heat recovery was proposed in this paper. The plant thermal efficiency could be improved by 1.51% at benchmark condition due to pre-drying and waste heat recovery. The main system performances under variable power loads were simulated and analyzed. Simulation results show that the improvement of plant thermal efficiency reduced to 1.36% at 50% full load. Moreover, the influences of drying system off-design parameters were simulated coupled with power loads. The variation tendencies of main system parameters were obtained. The influence of pre-drying degree (including moisture content of pre-dried lignite and raw lignite) on the plant thermal efficiency diminishes gradually with the decreasing power load. The dryer thermal efficiency and dryer exhaust temperature are also main factors and the influences on system parameters have been quantitatively analyzed.