An improved configuration of low-temperature pre-drying using waste heat integrated in an air-cooled lignite fired power plant

An improved low-temperature lignite pre-drying configuration using waste heat integrated in an air-cooled lignite fired power plant was proposed and examined in this study. In the proposed configuration, a portion of the steam exhaust from the low-pressure turbines condenses and then releases the latent heat in tubes embedded in a fluidized bed lignite dryer to heat the raw lignite while the warmed air from the air-cooled condensers is utilized as the fluidizing and drying medium, passing through the fluidized dryer. Through employing the proposed drying system, a part of the rejected heat of the air-cooled condensers could be recovered efficiently and beneficially utilized to dry and upgrade the raw lignite, thus leading to an improvement in the overall energy efficiency of the power plant. The results of a detailed thermodynamic analysis showed that, for a typical 600 MW air-cooled lignite fired power plant using the proposed configuration, the net power plant efficiency could be improved by 1.3 percent points with additional net power output of 19.7 MWe as compared to the reference plant without lignite pre-drying. The levelised cost of electricity (LCOE) is reduced from $47.3/MWh in the reference power plant to $45.1/MWh in the proposed power plant.