Simulation on the flue gas pre-dried lignite-fired power plants firing high moisture lignite

The integration of flue gas fan mill dryer with an open pulverizing system significantly improves the plant thermal efficiency of the Flue Gas Pre-dried Lignite-fired Power Systems (FPLPS). The aim of this article is to simulate the flue gas drying process applied for high moisture lignite and to find an optimal operation mode for various lignite compositions. A previously validated GSE simulation model of the FPLPS is used in the present work. Two types of lignite from China and Greece have been investigated as the feeding coal. The plant thermal efficiency of a 600 MW supercritical unit increases by 1.46 % at design case when the moisture content of lignite is being reduced from 39.50 % to 12 %. The improvement value reduces from 1.46 % to 1.19 % in water-cooled units and 1.39 % to 1.13 % in air-cooled units when the moisture content of Chinese raw lignite decreases from 39.50 % to 29.95 %. When Greek lignite is supplied, with moisture content varying from 53.20 % to 60 %, and lower heating value from 5.44 MJ·kg^-1 to 6.31 MJ·kg^-1, the plant thermal efficiency drops by a maximum value of 0.53 %, without considering the limited drying capacity of the pulverizing system. Moreover, two operational modes are compared in order to address the issues of fuel type variation, including the adjustment of the drying degree to maintain the boiler load, as well as the reduction of the boiler steam output. Case studies are presented to highlight the importance of the match between lignite pre-drying system and the boiler thermal system. Both the energy-saving potential and the flexibility to fuel type variations are concluded as the benefits of lignite flue gas pre-drying.