UNIVERSITY PARK, Pa. — Blending biomass into the coal stream that feeds electricity-generation plants offers the opportunity to reduce harmful emissions and create a market for renewable fuel, according to a biomass-energy expert in Penn State’s College of Agricultural Sciences.
And Pennsylvania power-plant operators have a big incentive for co-firing coal with biomass they buy from farmers, noted Daniel Ciolkosz, senior extension associate in agricultural and biological engineering.
State mandate. “The state’s Alternative Fuels Portfolio Standard is a state mandate that requires, among other things, that 18 percent of Pennsylvania’s electricity be generated from renewable or alternative energy sources by 2021,” he said.
“Biomass co-firing is one of the most promising ways to meet that standard.”
Pennsylvania farmers and foresters interested in growing biomass such as switchgrass and small-diameter trees as energy crops soon are likely to have eager buyers for their products, Ciolkosz suggested.
Tests under way
“Several experiments have shown the feasibility of co-firing biomass with coal, including tests at the Shawville power plant in Clearfield County and the Seward power plant in Westmoreland County,” he said.
The most common type of facilities for co-firing are large, coal-fired power plants, Ciolkosz said. “However, other coal-burning facilities, such as cement kilns, industrial boilers and coal-fired heating plants, are good candidates for co-firing as well.”
One of the reasons biomass is well suited for co-firing with coal is that both biomass and coal are solid fuels, Ciolkosz pointed out. Therefore, equipment designed to burn coal can burn biomass as well.
However, several differences between biomass and coal — such as biomass’s typically higher moisture content and its propensity to clog equipment when burned — have scientists scrambling for solutions to allow co-firing.
“The chemical composition of coal is different from that of biomass,” he said. “Most notably, biomass has a higher hydrogen and oxygen content, and less carbon than coal.
“As a result, biomass tends to generate less energy than coal — about two-thirds as much.”
Biomass also tends to be less dense than coal, he added. And pulverized coal is nearly seven times denser than baled straw.
“This means that fuel-feed systems will need to handle and deliver much higher volumes of fuel if co-firing is used.”
Ciolkosz said one of the possible methods for reducing these problems is to convert the biomass to charcoal, which has a consistency similar to that of coal, or to densify biomass fuel into hard pellets or briquettes that may be more compatible with a combustor’s fuel-handling system.
Farmers and foresters should be aware that co-firing may create a massive market for biomass.
Currently, Pennsylvania uses approximately 57 million tons of coal per year. If 5 percent of the fuel were replaced with biomass, it would amount to 4.4 million tons of biomass per year.
“That would nearly triple the current rate of biomass use for energy,” Ciolkosz said.
“Consider a 1,000-megawatt power plant, which is a typical large plant by today’s standards. Co-firing at a 5 percent rate would require approximately 245,000 tons of biomass per year, which would require about 50,000 acres of high-yield production.”
Ciolkosz suggests that farmers and landowners consider securing long-term supply contracts from power producers, which could reduce the risk associated with growing biomass crops — especially perennial crops such as grasses or short-rotation woody crops, which require several years before they are ready for harvest.
“When we consider the buyer’s perspective, the main benefit of co-firing is that it reduces pollution from the power plant,” he said. “Biomass is virtually free of sulfur and mercury, which leads to reductions in emissions that are proportional to the amount of biomass being used.”
Because biomass is also essentially carbon neutral, Ciolkosz expects power plant operators will soon want to burn it for energy.
“When you consider the growing levels of concern and regulation surrounding the release of carbon dioxide from fossil fuels, even a 5 percent reduction in emissions can make the difference between meeting or missing an emissions target set by the government.”
Get the details
— Single copies of the Renewable and Alternative Energy Fact Sheet: Co-firing Biomass with Coal, is available free to Pennsylvania residents through county Penn State Cooperative Extension offices, or by contacting the College of Agricultural Sciences Publications Distribution Center at 814-865-6713 or by e-mail at AgPubsDist@psu.edu.
— For cost information on out-of-state or bulk orders, contact the Publications Distribution Center.
— The publication also is available online at http://pubs.cas.psu.edu/FreePubs/PDFs/ub044.pdf.
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