Blending biomass with the coal that feeds electricity-generation plants may create a market for renewable fuels while reducing harmful emissions. That’s according to a biomass-energy expert in Penn State's College of Agricultural Sciences.
"The state's Alternative Fuels Portfolio Standard is a state mandate that requires, among other things, that 18% of Pennsylvania's electricity be generated from renewable or alternative energy sources by 2021,” notes Daniel Ciolkosz, senior Extension associate in agricultural and biological engineering. “Biomass co-firing is one of the most promising ways to meet that standard."
That gives Pennsylvania power-plant operators a big incentive for co-firing coal with biomass such as switchgrass and small-diameter trees, Ciolkosz adds.
And it may give Pennsylvania farmers and foresters a massive market for biomass. The state currently uses about 57 million tons of coal per year. If 5% 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," he estimates. "Consider a 1,000-megawatt power plant, which is a typical large plant by today's standards. Co-firing at a 5% rate would require approximately 245,000 tons of biomass per year, which would require about 50,000 acres of high-yield production."
Farmers and landowners should consider securing long-term supply contracts from power producers to reduce risks, Ciolkosz suggests. Biomass crops, especially perennial crops such as grasses or short-rotation woody crops, aren’t ready to harvest the first year.
Experiments have shown that co-firing biomass with coal is feasible, including tests at the Shawville power plant in Clearfield County and the Seward power plant in Westmoreland County, he says. "The most common type of facilities for co-firing are large, coal-fired power plants. 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 reason biomass is well-suited for co-firing with coal is that both are solid fuels; equipment designed to burn coal can burn biomass as well. However, several differences between the two – 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. 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. 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.
"One of the possible methods for reducing these problems is to convert 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," he adds.
Single print copies of the Renewable and Alternative Energy Fact Sheet: Co-Firing Biomass with Coal, are free to Pennsylvania residents by contacting county Penn State Cooperative Extension offices, or the College of Agricultural Sciences Publications Distribution Center at 814-865-6713 or by email at AgPubsDist@psu.edu. For cost information on out-of-state or bulk orders, contact the Publications Distribution Center.