  Determination of the explosion severity parameters of biomass is crucial for
the safety management and dust explosion risk assessment of biomass-processing
industries. These are commonly determined following experimental tests in the
20L sphere according to the international standards. Recently, CFD simulations
have emerged as a reliable alternative to predict the explosion behavior with
good accuracy and reduced labor and capital. In this work, numerical
simulations of biomass dust explosions are conducted with the open-source CFD
code OpenFOAM. The multi-phase (gas-solid) flow is treated in an
Eulerian-Lagrangian framework, using a two-way coupling regime and considering
the reactions of biomass conversion (moisture evaporation, devolatilization,
and char oxidation), the combustion of volatile gases, and convective and
radiative heat transfer. The model is validated with pressure-time and
concentration-dependent experimental measurements of two biomass samples.
Results suggest that the characteristics of the cold-flow (\i.e. turbulence
levels, actual dust concentration, spatial distribution of the dust cloud, and
turbophoresis effect) govern the course of the explosion process, and depend
strongly on particle size, dust concentration, and ignition delay time effects.
These findings may be relevant in the design of better dust explosion testing
devices and to the reexamination of the guidelines for the operation of the
experiment. Finally, a thorough discussion on the explosion pressures, degree
of biomass conversion, flame temperature, flame propagation patterns, and the
dust agglomeration effect is presented.
