Performance analysis of an efficient waste heat utilization system in an ultra-supercritical coal-fired power plant

Abstract

With the rise of new energy sources in the power industry, improving the efficiency of coal-fired power plants is essential. Currently, the leading main causes of irreversible energy loss are the energy level mismatches of boilers and turbines. An ultra-supercritical coal-fired power plant thermodynamic system was reconstructed based on the first and second laws of thermodynamics to improve the efficiency of power plants, and an efficient condensate water preheating air integrated bypass flue waste heating efficient utilization system is thus herein proposed. Consequently, high and medium steam turbine extraction flow is returned to the steam turbine to do work, and cold source loss is reduced by increasing the extraction steam flow of the low-pressure cylinder. At the same time, the inlet air temperature in the air preheater is significantly increased by preheating the hot air with condensate water, resulting in a reduced heat transfer temperature difference and significantly improved exergy efficiency. Compared with conventional low-temperature economizer and bypass flue waste heat utilization schemes, the results indicate that the heat transfer exergy efficiency increased significantly from 78.49% to 95.88% in the air preheater, and the heat consumption rate of the turbine generator set decreased by 108.06 kJ/(kW⋅h). The generation efficiency increases by 0.74%, while the standard coal consumption rate decreases by 3.92 g/(kW⋅h). In terms of economic investment, the dynamic payback period is 3.31 years and the net present value is $2.20 M/year. This paper provides an effective energy conservation and emission reduction plan for coal-fired power plants to contribute towards achieving national carbon peaking and carbon neutrality goals.