Thermal Simulation and Economic Study of Predried Lignite Production Retrofit of a Greek Power Plant for Enhanced Flexibility

Abstract

The use of predried lignite as a factor to enhance flexibility of existing power plants is considered as a practically feasible step to ensure power supply and grid stability. In this work, the retrofit of a Greek lignite-firing power plant for the production of predried lignite through integration of drying systems has been investigated from a technical point of view through thermal cycle calculations and an economic one. The impact on efficiency and power output of the power plant and the predried lignite production cost are derived, respectively. The predried lignite is considered to be used in the plant or as an end product independently. The operation of the plant is simulated at 60%, 80%, and 100% load with drying systems integration. Three different technologies were integrated: a fluidized-bed dryer with internal waste heat utilization (WTA dryer), a tube dryer, and a drum dryer. The economic assessment is focused on the production cost of predried lignite as an end product. The drying plant’s operating hours and the electricity price are considered as highly influencing production cost factors and a parametric analysis was performed. Additionally, a parametric study, with respect to CO2 allowances, was performed for the utilization cost of raw and predried lignite. Results showed that among the three drying configurations, the WTA dryer has the least impact in terms of both power output loss and efficiency decrease on the thermal cycle of the unit for all three loads, with a net efficiency decrease in the range between 0.7% and 1.1%. Furthermore, the use of the WTA technology is also more favorable from an economic point of view, resulting in a predried lignite production cost only 8%–9.3% higher than the raw lignite production cost. The CO2 allowances cost as a parameter unveiled that the usage cost of predried and raw lignite has a break-even point, with respect to load operation, which varies in the area of 26.58–29.0 €/tCO2.