Thermofluid process simulation of wet biomass and ammonia co-firing in an industrial watertube boiler

Co-firing of ammonia with low-carbon biomass fuels can promote cleaner energy by employing a carbon-free alternative in tandem with traditional fuels. However, doing this in a boiler specifically designed for solid fuel with high moisture content could pose challenges. In the present work, an integrated thermofluid network model of a whole boiler firing sugarcane bagasse is developed and applied to investigate the effect of co-firing ammonia on the thermal performance. The results show that the primary impacts are an increase in the adiabatic flame temperature and a reduction in total flue gas flow rates. This is due to the higher HHV of ammonia compared to biomass, along with lower excess air ratios. At a blending ratio of 0.5 kg NH₃/kg biomass, there is a 58% reduction in CO₂ mass flow rate in the flue gas. The impact on furnace exit gas temperature, spray water flow rates and intermediate header temperatures are small, and the economizer does not run the risk of acid corrosion. It also shows that ammonia co-firing could potentially be used to stabilize boiler efficiency and reduce the sensitivity of the temperature control system when a batch of high moisture fuel is introduced. Therefore, for this boiler the co-firing of ammonia with wet biomass has a beneficial effect on both boiler operation and environmental impact.