Stand-Alone Torrefaction Update

As we reported previously, SERC is collaborating with Renewable Fuel Technologies (RFT) to assess performance of RFT’s biomass torrefier. The torrefier converts wood waste from logging or forest thinning, roasting it to make a renewable energy product that can replace coal in power plants. The testing is funded by a grant from the California Energy Commission. The goal of the assessment is to determine whether waste heat from the torrefier can be used to make the device self-powered for off-grid use at timber harvest sites. Such use could make recovery of waste material at these sites more cost-effective.

This past fall, SERC engineers made multiple trips to RFT’s abrication and testing facility in Hayward, CA. We first procured about three tons of tanoak wood chips in Humboldt County and delivered them to RFT. Tanoak is of special interest because it is abundant in northwest California but considered of low value as a timber species.

TorrSolids-adj

An array of torrefied wood chips shows the effects of varying temperature and processing time. The raw biomass is shown in the column on the right.

We next performed a series of test runs with RFT engineers, in which we varied the moisture content of the feedstock, operating temperature, and residence time of the material in the roaster. We collected operating data such as temperatures, material flow rates, and electric power use during each run. In addition, we collected samples of the raw wood chips used for each run as well as the solid, liquid, and gas outputs from the process for later laboratory analysis. All of these data allowed us to perform a rigorous energy and mass balance for the process, key to determining the feasibility of stand-alone operation.

Our tentative conclusion is that such operation may be feasible, though the design may need further modification to reduce heat loss to the surroundings. We are now working to prepare our final report to the Energy Commission.