Numerical Modelling of Oxyfuel Coal, Torrefied Biomass, and Biomass Combustion to Access Its Effects on Axial Velocity, Swirl Velocity, Temperature, and Oxygen Mole Fraction in a Cylindrical Combustor

The current research work investigated and compared the combustion dynamics of three different solid fuels, i.e. lignite coal, torrefied biomass, and raw biomass fuel under oxy-fuel conditions using a 100 kWth vertical pilot furnace. The research employs a Computational Fluid Dynamics (CFD) approach, integrating an Eulerian–Lagrangian framework to capture the interactions between gas-phase flow and solid fuel particles. The combustion behavior of above three different solid fuels was numerically solved using three widely recognized turbulence models, Standard k-ε, RNG k-ε, and realizable k-ε turbulence models. These simulations were rigorously validated against experimental data published by Toporov etal. (2008) to ensure accuracy and reliability. To account for the variability in fuel particle sizes, a Rosin–Rammler distribution was applied, which effectively characterized the particle diameter range from 0.90 µm to 123 µm, provides a realistic representation of the fuel’s physical properties. For radiative heat transfer, the Discrete Ordinates Model (DOM) was utilized in combination with the Weighted-Sum-of-Gray-Gases Model (WSGGM). This coupled methodology allowed for accurate modeling of radiation effects, which play a critical role in combustion processes. Additionally, the Finite Rate Eddy Dissipation Model (FR-EDM) was applied to simulate species transport and combustion kinetics. This comprehensive approach enabled a thorough combustion process analysis, integrating turbulence, radiation, and chemical kinetics to achieve a high-fidelity simulation. The comparative analysis of axial velocity, tangential velocity, temperature gradients, and oxygen mole fraction revealed that the realizable k-ε turbulence model closely aligned with experimental results. Axial velocity contours revealed peak near-burner velocities of 7.70 m/s for coal, 7.57 m/s for torrefied biomass, and 7.54 m/s for raw biomass, with the latter maintaining higher downstream velocities as a consequence of its relatively lower density. Temperature distributions confirmed biomass attaining the highest flame peak of 1720 K close to the burner region, whereas coal and torrefied biomass peaked at 1500 K and 1637 K, respectively. Oxygen mole fraction analysis demonstrated more complete utilization in coal combustion, with residual oxygen as low as 1.6%, compared to 9.7% for biomass along the axial position. Further results demonstrate that raw biomass ignites rapidly due to its high volatile content, while lignite coal sustains a longer and more stable combustion phase due to its higher fixed carbon proportion. Torrefied biomass exhibits moderate ignition properties, making it a viable alternative between the other two fuels. By bridging the gap between experimental combustion studies and numerical modeling, this work provides a valuable insight for optimizing oxy-fuel combustion for three different solid fuels. The findings support the transition toward cleaner and more efficient energy production, particularly in low-emission power plants utilizing biomass-based fuels.