Conceptual design of a small-capacity supercritical CO2 coal-fired circulating fluidized bed boiler by an improved design calculation method

Abstract

Carbon peak and neutrality strategy leads to rapid increase of renewable energy. Small-capacity thermal power units with supercritical CO2 (S–CO2) cycle have great prospects in the vigorously developing regional renewable energy power grids for high efficiency and superior flexibility of peak shaving. However, there is no effective and efficient design and design method for this new-type boiler with S–CO2 instead of steam cycle. In this paper, a 100 MW small-capacity S–CO2 circulating fluidized bed (CFB) coal-fired boiler is conceptually designed by an improved boiler design calculation method based on the process simulation coupling detailed combustion and working fluid cycle. The results show that the strategy of both increasing hot air temperature and introducing flue gas cooler for recovery residual heat of flue gas is preferred in the small-capacity CFB S–CO2 boiler. Under the optimized bed temperature 910 °C and primary air ratio 0.7, the power generation efficiency of the 100 MW S–CO2 unit can be improved to ∼47%, 8–9% higher than that of the same-capacity steam units. For boiler configuration, the conventional rectangular furnace is still applicable to the small-capacity S–CO2 boiler, but more high-temperature heating surfaces required to be arranged in the furnace to meet ∼72% of heat absorption.