Numerical analysis of flow and combustion of Coal-Ammonia blend in coal-fired furnace

Abstract

Co-firing ammonia (NH3) in coal-fired power plants presents an attractive method to expedite the global decarbonization process. Nevertheless, the challenge lies in reconciling the need for higher temperatures within the furnace with the imperative of maintaining low nitrogen oxides (NOx) emissions, which limits the widespread use of NH3 as a fuel. In this article, the flow and combustion of coal-NH3 blends in a 3x700 MW tangentially-fired utility coal boiler furnace are investigated using Computational Fluid Dynamics (CFD). The impact of NH3 blending ratios is examined through numerically simulated combustion involving five co-firing ratios (CRs) of NH3, including 0%, 10%, 20%, 30%, and 50%. Various combustion properties are assessed, including the furnace's temperature profile, flow distribution, species emissions, pollutant formation, and heat generation. To validate the approach, single coal and coal blend simulations performed depicted reasonable agreement in predicting furnace flame temperatures. The predicted flue gas temperature exhibited a decrease with an increase in NH3 CR, leading to a reduction in the furnace’s heat generation. Regarding flow characteristics, there was a notable increase in velocity as the concentration of NH3 was raised. The elevated NH3 content correlated with an observed rise in oxygen (O2) residue in the rear pass, coupled with a decrease in both carbon dioxide (CO2) and carbon monoxide (CO) concentrations. Pollutant formation, assessed in terms of nitrogen oxide (NO) emissions, revealed an increase in concentration with the rise in NH3 CR. Indeed, these findings suggest a promising strategy for adopting NH3 as a viable alternative to coal, representing an effective carbon-neutral fuel for the future.