Thermodynamic analysis of pre-drying methods for pre-dried lignite-fired power plant

Lignite is considered to be a competitive energy raw material with very high security of supply viewed from a global angle. However, the utilization of raw lignite faces many thorny issues, such as a low plant thermal efficiency, a high investment in construction of the lignite-fired power plant, etc. Lignite pre-drying seems to be an attractive way to tackle these issues. We have performed a thermodynamic analysis of two pre-drying methods (both boiler flue gas drying and steam drying). Results show that both pre-drying methods can improve the plant thermal efficiency. Nevertheless, the boiler flue gas drying improves the plant thermal efficiency only in the case when the temperature of the dryer exhaust is low enough and the dryer thermal efficiency is high enough. The steam pre-drying has a higher potential in plant thermal efficiency improvement. The flow rate of steam extraction for the steam dryer is much lower than the flow rate of flue gas extraction for flue gas dryer, so we consider that the steam pre-drying is more appropriate for the revamp of the conventional lignite-fired power plant. In addition, we have calculated and analyzed main factors.