During the initial stage of biomass combustion and gasification, biomass particles exchange mass and heat at the surface with surrounding environment; receiving heat from hot gas flow while releasing gas. Recent studies discovered that both interphase transport phenomena and chemical reactions are affected by the interaction between neighbour particles. However, no existing model in macro-scale simulation describes this effect.
This project is elucidating this effect by detailed numerical investigation and developing simple models that are easy to be implemented in macro-scale simulation. Only few previous studies have investigated the particle interactions including heat transfer and chemical reactions. The major part of this project is carried out with a high-resolution numerical platform of closely located reactive particles (distance: less than 10 times particle diameters) on fluid dynamic simulation. To make the problem simple, the parameter range will be limited to Re_p<100.
The study is carried out with resolved particle direct numerical simulation (RP-DNS) in OpenFOAM platform. This project is supported by Swedish Research Council in the same project title during 2016-2019. Project has three phases between 2017-2021.
In the first phase (SNIC 2017/1-248 and SNIC 2018/3-315), the effect of chemical reactions on particle-gas interaction was investigated with single particle in gas flow. The effect of chemical reactions is imposed in the form of Stefan flow (outgoing mass flow of gas at the particle surface). Specifically, the effect of Stefan flow on the boundary layer was investigated as a comparison with non-reacting flow conditions. With physical interpretation of boundary layer, we developed and expanded the modified correlation for heat, mass, and momentum transport (i.e. Nusselt number, Sherwood number, and drag coefficient) that account for the effect of Stefan flow. The results were published in two journal papers and two conference contributions.
In the second phase, the numerical platform will be improved to account for more realistic situations in biomass gasification. More specifically, the model will include temperature driven gas-solid reactions (pyrolysis, char gasification and combustion), intra-particle heat and mass transfer, and array of several particles in the computational domain. The previous studies are resolving either boundary layer or interior of single particle, and this project is going to be the first attempt to resolve both at the same time. It is expected to gain insight about how the particles interaction with respect to flow field surrounding them affects the progress of chemical reactions. This phase is expected to progress in 2019.
The last phase will introduce reduced kinetic scheme of gas phase reactions including the formation of soot. At this stage, further information about the chemical interaction of closely located particles, including the interaction via chemical reactions in gas phase, will be elaborated. This phase ie expected to progress in 2020-2021.