Schatz Energy Research Center

Gasification: Torrefaction of Wood Samples

Wood chips before and after torrefaction.
Unprocessed wood chips (front) and the same feedstock after torrefaction. Photo credit Kellie Brown, HSU Photographer.

Although SERC’s three-year biomass gasification project is winding down, we are continuing to research biomass and its role as a renewable fuel. Our latest endeavour is torrefaction.

Torrefaction is a mild form of pyrolysis in which biomass is heated in an inert environment to a temperature between 200 and 300 °C. During the process, water and volatiles are removed and the hemicelluloses break down, yielding a dry, blackened solid product with a lower moisture content and higher energy content on a mass basis than the initial biomass.

In addition to improvements in the fuels properties, torrefaction also makes the biomass more friable, making it easier to grind or densify into pellets or briquettes. These characteristics increase the opportunities for torrefied biomass to be co-fired with coal or used as fuel pellets, fireplace logs, and barbeque briquettes for residential use.

Using a laboratory electric furnace equipped with a nitrogen purge system, SERC conducted torrefaction experiments using wood chips. The torrefied wood was tested for moisture content and heat of combustion using an adiabatic oxygen bomb calorimeter. We found that the energy density increased by as much as 25%. Best of all, the torrefied wood is hydrophobic and picks up much less moisture from the air than does raw wood.

We are currently working with Renewable Fuels Technologies (RFT) of San Bruno, CA. RFT is developing a mobile bio-coal processor unit for on-site conversion of waste wood biomass into torrefied wood. Our scope of work includes heat of combustion testing of wood samples produced from their bio-coal processor unit.

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