Nebraska Public Power District evaluating biomass

By Anna Austin | March 29, 2011

The Nebraska Public Power District is taking a close look at the possibility of cofiring woody biomass with coal at its 229-megawatt Sheldon Station power plant near Hallam, Neb., using dead or dying trees that pose forest fire risks.

The state forest service approached the NPPD with the idea of utilizing the dead standing trees for electricity production because Nebraska is facing various disease and insect issues that are wreaking havoc on native tree species, according to NPPD Generation Strategies Manager John Swanson.

The NPPD has a goal of generating 10 percent of its power from renewable resources by 2020, Swanson said, and is on the road to that goal primarily via the wind power in its portfolio. Although it produces no biomass power yet, this won’t be the first time the NPPD has studied its potential.

“We already tested pelletized corn stover about a year ago,” Swanson said. For that work, the NPPD partnered with the Energy & Environmental Research Center in Grand Forks, N.D., a research institution that the NPPD has worked with on several other occasions, including work surrounding carbon capture and sequestration. “We found out that the EERC has and maintains a very large database of biomass materials that they’ve tested for other clients,” Swanson said.

Samples of different infected tree species have been sent to the EERC for a month-long testing period. “The EERC will model the impact on our boilers,” Swanson said. “It doesn’t sound like much, but it is a pretty specific environment when it comes to temperature, air and fuel ratios going through the boiler. When you introduce a foreign material, you have to know the impacts.”

Impacts could involve ash and boiler fouling and slagging, as a result of cofiring with 5, 10, 15 and even up to 25 percent biomass blending rates. Swanson noted that previous tests with corn stover showed that up to 10 percent blending rates would have no or little impact. “We’re not sure how the wood will work with the coal, or if one species will perform better than another,” Swanson said.

The NPPD expects results back from the EERC by the end of April. If the impacts are minimal, there are a couple of potential avenues the NPPD may take, one being a test burn at its Sheldon Station plant. “More than likely, what we’ll do right away is start evaluating material gathering and processing, because along with determining boiler impact will be determining the cost of the fuel,” Swanson said. “The trees will die, but unfortunately not right at the power plant.”

Harvesting, gathering, storing and transporting the material will cost money. Swanson said there is, however, the possibility of a grant option through the USDA Forest Service or other federal branches that have funds available for forest health/restoration work. “If there’s a good possibility of that happening, then that would definitely make this thing more attractive,” he said. “Logistics and transportation typically hinder this type of material—pricewise—from being used.”