Work

Influence of the devolatilisation kinetics on the numerical simulation of pulverised fuel swirl flames under oxyfuel conditions

Year: 2025

Type: article

Abstract: Numerous studies can be found concerning the development of various models to describe devolatilisation within the solid fuel conversion process. Despite the availability of detailed devolatilisation models, such as chemical percolation devolatilisation (CPD), simplified ones, such as the single first-order reaction (SFOR) and the competing two-step model (C2SM), are typically used in numerical simulations because of their low computational cost. In this study, walnut shells and Rhenish lignite are employed as pulverised fuels for an oxyfuel-fired reference case and their devolatilisation kinetics are determined experimentally using a fluidised bed reactor (FBR). To show the influence of devolatilisation kinetics on the flames, a simulation tool (Oxy-RANS 129) in Ansys Fluent is developed based on Reynolds-averaged Navier–Stokes (RANS) equations. The numerical tool is equipped with user-defined functions to take into account the modifications needed in an oxyfuel compared to air atmosphere regarding gas and particle radiation and particle kinetics. The parameter sets for devolatilisation kinetics are determined experimentally using a fluidised bed reactor and for comparison are also taken from existing numerical investigations in the literature. Significant differences can be observed, particularly in particle temperatures and the release of their volatile contents when using different parameter sets for devolatilisation kinetics. Particle temperatures obtained using the experimentally determined parameter sets in the simulations show improvements in the accuracy of the simulations up to 22 % compared to those obtained when using the available parameter sets in the literature. Further improvements in comparisons are observed by considering heat transfer limitations to particles in high-temperature zones. The numerical tool captures small heat transfer limitations leading to a reduction in reactivity of particles improving the agreement between numerical and experimental results on particle temperatures. • Development of a RANS simulation tool ( Oxy-RANS 129 ) for the combustion of pulverised solid fuels under oxyfuel conditions. • Adopted sub-models for particle devolatilisation, char burnout, and gas radiation for oxyfuel conditions. • Experimental determination of the kinetic parameters for devolatilisation using a fluidised bed reactor under similar heating rates as the combustion chamber simulated. • Validation of the simulation tool against experimental and LES results. • Assessment of the accuracy obtained in the numerical simulations when using the experimentally determined kinetic parameters compared to parameters taken from the literature.

Source: Fuel

DOI: 10.1016/j.fuel.2025.135177