Modeling the co-combustion of bi-fuel blends in a drop tube furnace: A numerical approach

The present study focuses on the numerical modeling of the co-combustion of reject coal (RC) and sal leaves (SL) in a drop tube furnace (DTF) under different conditions, including air-fuel and oxy-fuel environments. The numerical results highlight the significant influence of replacing the N2 atmosphere with CO2 on the temperature profiles of individual fuels and their blends. For instance, when exposed to a 21%O2/79%CO2 atmosphere, Blend SL3 and Blend SL5 experience a decrease in temperature from 1372 K to 1559 K to 1327 K and 1395 K, respectively. Conversely, increasing the O2 concentration to 35% leads to a temperature rise. Furthermore, the combustion analysis reveals that the addition of 10% SL to RC in a 21%O2/79%N2 environment enhances the devolatilization rate from 1.41 × 10−12 kg/s to 1.77 × 10−12 kg/s. Additionally, the char combustion process for all blends is completed closer to the DTF inlet at 0.28 m, compared to 0.32 m for RC alone. These findings indicate that blending SL with RC promotes a favorable combustion process. Moreover, increasing the O2 concentration to 35% in oxy-fuel conditions enhances the temperature profiles. The numerical analysis demonstrates good agreement with experimental data within a range of ±5%–11%. This suggests that the developed model can be effectively utilized for optimizing and designing biomass co-firing systems in industrial applications, considering both air-fuel and oxy-fuel conditions.