Evaluating the Effect of Ammonia Co-Firing on the Performance of a Pulverized Coal-Fired Utility Boiler

Abstract

Ammonia (NH3), as a derivative of hydrogen and energy carrier, is regarded as a low-carbon fuel provided that it is produced from a renewable source or a carbon abated process of fossil fuel. Co-firing ammonia with coal is a promising option for pulverized coal-fired power plants to reduce CO2 emission. Applying the co-firing in an existing pulverized coal-fired boiler can achieve satisfying combustion performance in the furnace but may affect the boiler performance. In the present work, a thermal calculation method was employed to evaluate the impact of ammonia co-firing on the boiler performance of an existing 600 MW supercritical utility boiler, covering the co-firing ratio range up to 40% (on heat basis). The calculations indicated that, as compared to sole coal combustion, co-firing ammonia changed the volume and composition and consequently the temperature and heat transfer characteristics of the flue gas. These resulted in increased variations in the heat transfer performance of the boiler with increasing of the co-firing ratio. The evaluations revealed that co-firing up to 20% ammonia in the existing boiler is feasible with the boiler performance not being considerably affected. However, the distribution of the heat transferred from the flue gas to boiler heat exchangers is significantly deteriorated at higher ratios (30% and 40%), resulting in over-temperature of the superheated steam, under-temperature of the reheated steam and considerable reduction in boiler thermal efficiency. It implies retrofits on the heat exchangers required for accommodating higher ratio co-firing in the existing boiler. The comparison study showed that co-firing 20% ammonia provides a superior boiler performance over co-firing 20% biomass producing gases and blast furnace gas.