Biomassan palamisen mallinnus numeerisella virtauslaskennalla käyttäen optimoituja reaktiivisuusparametreja

In this work, optimized apparent reactivity parameters are used for combustion modeling of two biomass fuels. The main goal is to examine how the existing solid fuel models in the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent function for pulverized biomass, as they have been originally developed for coal simulations. The models assume that the particles are spherical and isothermal, and the devolatilization and char combustion stages happen consecutively. A CFD model of the Drop-Tube Reactor (DTR) test device, which was used for the reactivity studies of the fuels, is constructed. The functioning of the optimized reactivity parameters is verified by the model. The results show that the apparent reactivity parameters can describe the biomass mass loss in low oxygen levels, regardless of the model assumptions. However, in an oxygen level of 21 vol-% the assumption of consecutive combustion stages does not hold. The simulations demonstrate how CFD modeling can provide useful information required for accurate biomass reactivity parameters. The verified reactivity parameters are further tested in a CFD model of 50 kW pulverized fuel test reactor. The model is validated by comparing lignite combustion results with previously conducted measurements. After this, a biomass simulation is conducted using the optimized reactivity parameters. The biomass simulation captures multiple realistic phenomena, such as lower burnout efficiency compared to lignite. The results further indicate that the spherical and isothermal assumptions can describe the biomass mass loss in combustion modeling, if the apparent reactivity parameters are carefully optimized based on experimental and CFD simulation data