Investigation on the off-design performances of flue gas pre-dried lignite-fired power system integrated with waste heat recovery at variable external working conditions

This paper describes a simulation investigation on the FPLPS (flue gas pre-dried lignite-fired power system) integrated with WHR (waste heat recovery). The plant thermal efficiency of a 600 MW power unit based on FPLPS is found to be improved by 1.70% compared with the CLPS (conventional lignite-fired power system) unit and the water saving is 81 t h−1. The WHR system is composed of air pre-heater and condensate pre-heater. The contributions of condensate pre-heating to the improvement in plant thermal efficiency and water saving are 0.19% and 34 t h−1, respectively. Moreover, the impacts of power load, ambient air temperature, and raw lignite moisture content on the off-design performances of FPLPS are studied. Simulation results suggest that the improvement in plant thermal efficiency remains around 1.70% with the decreasing power load. Lower ambient conditions lead to an increase in plant thermal efficiency and water saving with the safety operation of the boiler air heater due to the existence of air pre-heater in WHR system. In addition, the plant thermal efficiency of FPLPS increases slightly with the raw lignite moisture content, indicating that FPLPS is more suitable for firing lignite with high moisture content.