Effect of ammonia co-firing on heat transfer, safety, and economy of coal-fired boilers

Abstract

Ammonia (NH3) co-firing provides a promising route to reducing CO2 emissions of coal-fired boilers. The thermodynamic calculation model of a 600 MW supercritical coal-fired boiler was established to investigate the effects of NH3 co-firing on the heat transfer, safety, and economy of the boiler. Co-firing 50 % of NH3 (on the lower heat value basis) reduced the emissivity and temperature of the flame, and decreased the heat load of the furnace by 6.2 %-7.1 %. Nevertheless, the heat absorption of both the main steam and reheat steam can still be satisfied by adjusting the ratio of flue gas in two vertical flues without modifications of the heating surfaces. With the NH3 ratio rising from 0 % to 50 %, the temperature of flue gas at the furnace outlet grew by only 7.0 °C. Besides, the tube wall temperatures of the platen superheater and the high temperature superheater increased by < 3.0 °C, ensuring the safety of the heating surfaces. At boiler rated load, low temperature corrosion of air pre-heaters was hardly aggravated by co-firing NH3 of 50 %, but it became more severe at lower boiler loads. Compared with single coal combustion, the temperature of exhaust flue gas rose by 6.2–13.9 °C when NH3 ratio was 50 %, and the boiler efficiency decreased by 0.7 %-1.2 %. The high price of NH3 greatly increased the running cost of the boiler, but a higher CO2 tax can highlight the economic benefits of NH3 co-firing.