Technology Research Area:

Cofiring Torrefied Biomass

What is torrefied biomass, what is cofiring, and what do they have to do with TVA's mission?

Renewable energy sources such as biomass — the name energy experts use for any organic material used as an energy source — have the potential to reduce overall greenhouse gas emissions and could help reduce global warming.

One way to use biomass in power generation is to burn it with coal at a standard fossil fuel plant. This is called cofiring biomass. By cofiring biomass, TVA's fossil-fueled power plants could reduce carbon and other harmful emissions.

Torrefaction of biomass greatly increases the energy content of biomass. Torrefaction consists of heating biomass at 200 to 340 degrees Celsius. The process changes the physical and chemical characteristics of the biomass, making it more combustible and increasing its energy per unit of mass by 30 percent. That makes it more attractive as a fuel for burning with coal.

What is TVA doing about it?

TVA currently cofires a very small amount of biomass at its Colbert Fossil Plant as a pilot project. The biomass comes from a local furniture manufacturer. TVA is also researching sources of biomass such as wood, plants and agriculture residues, along with new technologies for preparing the biomass for use.

Different torrefied biomass fuels will be test burned at TVA's Colbert Fossil Plant. Two hundred tons of each fuel will undergo a 24-hour test burn at a 10-percent cofire rate (the biomass will make up 10 percent of the total fuel burned).

Researchers will assess the positive environmental benefits of cofiring torrefied biomass while evaluating other possible adverse affects on existing emission-reduction equipment. If results of the first demonstration are positive, additional 48-hour test burns will be conducted.

What are the possibilities for cofiring torrefied biomass?

TVA is committed to increasing power generation from renewable energy sources such as biomass, and torrefaction could increase the energy available from biomass.

Biomass could reduce pollutants emitted in power production. Burning biomass is generally carbon neutral; net carbon emissions would be zero, and that would help control global warming.

Biomass is less expensive than other renewable energy sources; increased use of biomass as fuel could benefit the local agricultural economy; and the more biomass is used as fuel, the less certain kinds of biomass, such as wood waste, will have to go to landfill.

Because decomposition in landfills produces carbon dioxide and methane, biomass cofiring could reduce these sources greenhouse gases as well.

For use of torrefied biomass to be successful, production would have to be reliable, costs will have to be controlled and the process must not cause unforeseen damage to the environment. There may be additional costs in modifying existing plants to allow cofiring of biomass and competition with other industries for biomass resources might drive up the cost of the fuel.