Rieth M., Rabacal M., Kempf A., Kronenburg A., Stein O., 2018, Carrier-Phase DNS of Biomass Particle Ignition and Volatile Burning in a Turbulent Mixing Layer, Chemical Engineering Transactions, 65, 37-42.
Direct numerical simulations (DNS) of a three-dimensional turbulent mixing layer are performed to study the volatile ignition and combustion behavior of biomass under conditions relevant for industrial applications. The DNS is designed such that it resolves the flame and all turbulent scales, but reverts to a point-particle description to avoid the resolution of individual particle boundary layers. The biomass particles are seeded in an air stream and mix with hot products from a second stream. The particles are heated up as they mix with the hot gases in the developing turbulent mixing layer. This is followed by devolatilization and volatile combustion. The volatile gas composition is modeled based on the composition and properties of the biomass particles. The gas phase is described by a reduced mechanism with 59 species and 462 reactions derived from the CRECK primary reference fuel and biomass mechanisms. The simulations are performed with the in- house LES/DNS code PsiPhi, coupled to Cantera to evaluate gas phase kinetics. The data is analyzed in terms of instantaneous contour plots of relevant quantities as well as spatially averaged statistics. The results are compared to a case of coal burning in the identical mixing layer setup such that differences and similarities between the ignition and burning behavior of biomass and coal can be analyzed. Both cases feature only small amounts of char conversion, hence the focus lies on volatile combustion. While zero-dimensional reactor calculations predict an earlier ignition of the volatiles from biomass for some conditions and biomass particles heat up faster, it is found that biomass ignites later than coal in the mixing layer. This is associated with the higher stoichiometric mixture fraction and lower heat release of the volatile-air mixture from biomass.
