Abstract
A drag force model for spheroids, referred as the spheroid model, was implemented in OpenFOAM, in order to better predict the thermochemical conversion of pulverized biomass. Our previous work has found that the spheroid model predicts more dispersed results in terms of particle velocities and local concentrations comparing to other conventional particle models under non-reactive conditions. This work takes the spheroid model one step further, by validating against experiments performed under reactive conditions with a newly implemented heat transfer model for spheroids as well as updated devolatilization kinetic parameters. In addition, simulations were conducted in a configuration similar to a pilot-scale entrained flow gasifier for more realistic scenarios. Particle mass and axial velocity development were compared accordingly using four different modelling approaches with increasing complexity. When compared with models of spheroidal shape assumptions, the sphere and simplified non-sphere model predict 61% and 43% longer residence times, respectively. The combination of the spheroid shape assumption with the heat transfer model for spheroids tends to promote drying and devolatilization. On the other hand, the traditional spherical approach leads to longer particle residence times. These opposing effects are believed to be a major contributing factor to the fact that no significant differences among modelling approaches were found in terms of syngas production at the outlet. Furthermore, particle orientation information was reported in both experiments and simulations under reactive conditions. Its dependency on gas velocity gradient under reactive conditions is similar to what was reported under non-reactive conditions.
Highlights
The transport sector is a major emitter of harmful pollutants and accounted for approximate 25% of the global CO2 emissions in 2016 according to International Energy Agency [1]
Most results are presented along reactor radial direction, r/D, at different heights, z/D, of the reactor. r is the radial position of the reactor, z is the axial position of the reactor and D is the diameter of the inner tube where biomass particles are injected
A new spheroid model for particle hydrodynamics, a heat transfer model for spheroids and a new set of parameters for devolatilization kinetics have been implemented in OpenFOAM
Summary
The transport sector is a major emitter of harmful pollutants and accounted for approximate 25% of the global CO2 emissions in 2016 according to International Energy Agency [1]. As part of optimizing the underlying thermal conversion of the solid biomass, it becomes necessary to understand the details of the physical and chemical processes involved, both through experimental investigation as well as modelling and simulation. This involves comprehensive studies of gas-particle flows under reacting, and sometime highly turbulent, conditions. It is common practice for simplicity to assume that pulverized biomass particles are spherical [8,9,10] This approach could potentially lead to simulation results significantly deviating from reality as particle shape is known to affect particle behaviors in terms of hydrodynamics and thermochemical conversion. Studies of biomass in a condition that is similar to entrained flow gasification are scarce
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