Biomass drying in a pulsed fluidized bed without inert bed particles

- Fluidization of biomass without bed material is achieved with pulsed gas flow.
- Reducing opening time in a pulsation cycle benefits fluidization of wet particles.
- The addition of fines improves heat and mass transfer.
- Two-phase model can reasonably predict fluidized bed drying.
- Mass transfer rate at different frequencies is reflected by effective diffusivity.

Batch drying was performed in the pulsed fluidized bed with various species of biomass particles as an indicator of gas-solid contact efficiency and mass transfer rate under different operating conditions including pulsation duty cycle and particle size distribution. The fluidization of cohesive biomass particles benefited from the shorter opening time of pulsed gas flow and increased peak pressure drop. The presence of fines enhanced gas-solid contact of large and irregular biomass particles, as well as the mass transfer efficiency. A drying model based on two-phase theory was proposed, from which effective diffusivity was calculated for various gas flow rates, temperature and pulsation frequency. Intricate relationship was discovered between pulsation frequency and effective diffusivity, as mass transfer was deeply connected with the hydrodynamics. Effective diffusivity was also found to be proportional to gas flow rate and drying temperature. Operating near the natural frequency of the system also favored drying and mass transfer.