CFD model for oxycombustion of biomass in laminar regime

  • Ryfa, Arkadiusz (Silesian University of Technology)
  • Klimanek, Adam (Silesian University of Technology)
  • Gładysz, Paweł (AGH University of Krakow)
  • Krysiński, Tomasz (Silesian University of Technology)
  • Sobek, Szymon (Silesian University of Technology)
  • Korus, Agnieszka (Silesian University of Technology)
  • Adamczyk, Wojciech (Silesian University of Technology)
  • Szlęk, Andrzej (Silesian University of Technology)

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The paper describes a CFD model of laminar oxycombustion of biomass particles in a vertical reaction chamber. Since the model will later be used to simulate combustion in a large-scale industrial boiler, it needs to combine accuracy with reasonable computational cost. The considered biomass was pulverized black pellets. The 2D axisymmetric model was developed in Ansys/Fluent. Combustion was modelled with species transport (finite rate) with seven volumetric reactions for the gaseous phase and three surface reactions for solid particle combustion. The binary mass diffusion coefficients in the gaseous phase were calculated using the Chapman-Enskog formula. Biomass particles were treated as a discrete phase and tracked using a Lagrangian approach with two-way coupling with the flow. Particle devolatilization is modelled using the chemical percolation devolatilization (CPD) model. The combustion kinetics of biomass particles is modelled using the kinetic-diffusion approach with diffusion rate parameters obtained experimentally. Analyses were carried out for different oxidizer temperatures and oxidizer composition, as well as for two carrier gases: N2 and CO2. The biggest challenge was posed by the laminar regime since it led to slow convergence and thus caused long computing times. It also required careful selection of a simple set of chemical reactions and their kinetics. The results were validated against measurement data for flue gas composition and biomass burnout rate. Good quality results were obtained for combustion in both the oxygen-nitrogen mixtures and the oxycombustion mixtures.