Using pre-drying technology to improve the exergetic efficiency of bioenergy utilization process with combustion: A case study of a power plant

Biomass fuel sometimes contains a very large proportion of water, which could reach as high as 60%. The high moisture content of biomass reduces the exergetic efficiency of the combustion process. Therefore, pre-drying technology using low-grade energy as a heat source was applied in this study to improve the exergetic efficiency of the biomass utilization process with combustion. A reference case of a 12 MW biomass power plant was analyzed to quantitatively determine the energy saving potential of pre-drying technology. Results showed that pre-drying could decrease the exergy destruction in the combustion process significantly. If the exergetic efficiency of the heat exchange process in the boiler is equal to that of the conventional biomass power plant, then the exergetic efficiency of such power plant could be increased by 1.95 and 3.16 percentage points when steam extraction and fluegas are used as pre-drying heat sources. In addition, economic analyses of the proposed systems were performed, and the economic limits for the cost of the dryer, under which the integration of the dryer could be economically applicable, were determined.