(691b) Biomass Torrefaction in a Pulsed Fluidized Bed

Torrefaction at 200-300°C in an inert or oxygen-deficient environment is a promising pre-treatment for improving the properties of biomass for energy utilization. Torrefied biomass has a higher heating value, increased hydrophobicity and better grindability.

Common reactor technologies adopted for biomass torrefaction are fixed bed, moving bed, rotary drum and auger type reactor. However, none of these technologies really stands out, because of associated problems of solid mixing, controllability, inefficient heating etc. Nevertheless, aforementioned technologies treat biomass at a small heating rate, which requires a large volume to achieve a commercial capacity. Fluidized bed on the other hand has enhanced heat and mass transfer, excellent uniform heating and mixing. A few applications of fluidized bed for biomass torrefaction have been studied. However, unconventional nature of biomass particles such as wide particle size distribution, low density and irregular shape is problematic and even causes defluidization. To improve the fluidization quality, inert materials are added to the bed. Extra efforts on separation make fluidization with bed materials unfavourable.

Another technique to assist biomass fluidization is gas pulsation. Biomass drying in a bench scale pulsed fluidized bed reactor has been performed and studied in our group. Based on the knowledge gained from the previous work, a novel pulsed fluidized bed (PFB) reactor for biomass torrefaction, with continuous feed and discharge, has been designed and commissioned in the presented study. The PFB unit has successfully demonstrated for sawdust torrefaction. Furthermore, effects of gas pulsation frequency, torrefaction temperature, biomass feed rate and oxygen concentration in carrier gas on torrefied product properties are being investigated. The latest results on suitable operating conditions for biomass torrefaction in PFB unit will be presented. This new torrefaction technology will promote the utilization of local biomass resources for displacing non-renewable fossil fuels.