Biomass Substitutes for Coal

Several US coal-fired power plants are learning to co-fire biomass with the coal. The long-term goal is to substitute biomass for coal altogether. One Ohio project intends to retrofit a coal plant to run on 100% biomass.

The biggest problem with the plan is that it is not designed to capture waste heat. In other words, for every "tree's worth of energy" the plant recovers in electricity, 3 or 4 trees are being wasted, producing heat that is not recovered or used. That is a pathetic waste of resources, regardless of how economic it may seem in the short term -- considering government incentives, mandates, and carbon rules. Combined heat and power (CHP) provides both electricity and useful heat. Designers must learn to integrate the more efficient approach into their plans.

Converting a coal-fired power plant into one that uses biomass is precisely what First Energy plans to do. Last April the utility announced plans to repower its coal-fired R.E. Burger Plant Units 4 and 5 using biomass. Ultimately, the plan is for the 312 MW plant to be powered by up to 100 percent biomass. However, the plant also is being designed with co-firing up to 20 percent coal.

...When complete, the Burger plant will be among the largest biomass power plants in the U.S. Since a project of this size hasn’t been done in the United States, challenges do exist, said Durbin. While the company already has in place equipment and systems to monitor particulates and nitrogen oxide emissions, it will need to solve a number of problems before getting the project off the ground. One problem is storage.

“Coal can get wet, get snowed on,” said Durbin. By contrast, biomass needs to stay dry. Durbin said the company plans to source biomass much in the same way it sources coal: from the best supplier. That may involve using wood chips and/or waste wood and processing it in a manner similar to the way coal is processed, or it may involve sourcing pellets. It’s also possible the company would use organic material such as switchgrass. “We are still working through the logistics,” said Durbin.

...For now, First Energy Generation plans to use the biomass to produce electricity alone and not harvest waste heat for cogeneration or combined heat and power (CHP). And that’s a problem, according to Dan Richter, professor of soils and forest ecology at Duke University.

“If we burn wood for electricity only, about three to four logs need to be burned to recover the energy contained in one. If heat and electricity are recovered with advanced wood combustion (AWC) technology, we can capture three to four times the energy that is recovered when burning wood solely for electricity,” he said.

Richter said AWC technology is widely deployed in Europe with plants achieving up to 90 percent efficiencies from burning biomass. Interestingly, four of the five plants that First Energy Generation engineers visited in Europe are combined heat and power (CHP) plants, even though the Ohio plant will generate electricity only.

Richter and a consortium of experts in the forestry and energy industry believe that burning wood solely for electricity wastes sizeable amounts of thermal energy.

“When we do calculations on how much wood is available in the nation and we look at potential supplies for energy we find that there’s just not enough of it to waste,” he said. “But if we can use it efficiently — capturing 70, 80, 90 percent [of the embodied energy in wood] — then wood does become a pretty interesting source of renewable energy that the country isn’t really aware of yet.” _Bioenergy

There is nothing wrong with co-firing coal and biomass. Using gasification technologies -- such as integrated gasification combined cycle (IGCC) -- you can utilise even dirty coal, without producing significant pollution in the exhaust.

The biggest hangups to using new technology, are government rules, regulations, mandates, and incentives -- most of which lead away from economic efficiencies altogether.