Bioenergy expert: torrefaction may be biggest biomass market

By Anna Austin | December 22, 2010

University of Minnesota Professor Doug Tiffany has been researching biofuels and biomass electricity for the last 15 years, and believes that blending torrefied biomass with coal represents the biggest potential market for biomass in the U.S.

A production economist in U of M’s extension service, Tiffany has immersed himself in renewable energy process economics, particularly those of running ethanol plants, producing biodiesel and wind energy, and using biomass to generate power.

Throughout his studies, one technology has continued to find its way into the economic equation—torrefaction. “I had an opportunity to look at torrefaction for some subcontract work that we did at the U of M to determine whether a torrefaction plant set up right next to an existing ethanol plant would be a good fit in terms of a business model,” Tiffany explained. “What happens in torrefaction is that a certain amount of volatile gases are driven off as the biomass is roasted, and those gases can be combusted to make steam. We determined that there would be sufficient steam from a good-sized torrefaction unit to supply about 69 percent of the thermal energy an ethanol plant would need.”

 That fact turned out to be an important issue in respect to the project economics of torrefaction, particularly if there is a community or other business nearby that can use the volatile gases that are driven off.

Tiffany said that during the torrefaction process, about 30 percent of the feedstock’s mass is driven off, and 10 percent of the Btus. However, the Btus become much more concentrated. “They are 130 percent more per unit of mass at the end, so we drive off the parts that don’t burn,” he said.

It’s also much more compatible with coal and could serve as a cleaner cofiring agent. “That’s what I think is very attractive about torrefied biomass; it allows for a gradual greening up of the electricity produced by blending it in over time.”

Coal is typically ground into a dust before it’s blown into burners, Tiffany pointed out. “The great thing about torrefaction, opposed to biomass or pellets, is that it takes more energy to grind pellets or chunks of wood. Torrefied material is very brittle and shatters nicely, so it will be very compatible with the whole logistic system of coal. That includes compatibility with transportation systems such as railroads, and possessing ideal properties that allow it to be piled near a power plant and get snowed on.”

But can people make money accepting biomass and torrefying it to produce biocoal, and what can the power industry pay in order to reduce the amount of greenhouse gasses emitted from their existing plants?

Tiffany will detail answers to both questions during his torrefaction presentation, Torrefied Biomass: Costs of Production and Value to Power Utilities, at the Pacific West Biomass Conference & Trade Show in Seattle, Jan 10-12.

 To learn more about the conference, visit pacificwest.biomassconference.com