Numerical study on the effects of co-firing ratio and stoichiometric ratio on biomass/ammonia co-firing

Co-firing of biomass and NH3 can generate positive effect on the energy and environment. However, there is limited research in this area. In this work, Ansys Fluent, a computational fluid dynamics software, was utilized to simulate the two-dimensional combustion process of mixed wood (MW) particles with NH3 in a 15 KW furnace under various operating conditions. Various models such as turbulence, species transport, particle phase, radiation, and pollutant were reasonably considered, and the reliability of these selected models was also evaluated by comparing with the experimental results obtained from the 15 KW furnace. The four combustion cases with different NH3 ratios (NRs) of 0%, 40%, 50%, and 60% were investigated (partial MW replaced by NH3 with equivalent calorific value). Moreover, the effects of stoichiometric ratios (SRs) of 0.8, 0.9, 1.1, and 1.3 on the combustion behavior was also explored at a fixed NR of 60%. The velocity, flame shape, furnace temperature, and emissions of pollutants (CO2 and NO) were described and analyzed. The findings show that the temperature at the center of outlet can reach 1209.0 K when the SR and NR are 0.9 and 60%, respectively, which exhibits the highest value among all operating conditions. The average value of CO2 concentration is 3.7% at the outlet under the condition of SR = 1.3 and NR = 60%, which presents the lowest level among all cases, while the average value of NO concentration presents a lowest value of 111 ppm under the condition of SR = 0.8 and NR = 60% at the outlet. In summary, these numerical simulation results can provide important support for further studies of the co-firing of biomass/NH3.