Unlike fossil fuels, wood chips are a renewable source of energy.
With the recent completion of upgrades to its steam plant, the Department of Energy's Oak Ridge National Laboratory may be setting the pace for large physical plants that can use a renewable source of feedstock for energy.
ORNL updated a fossil fuel-fired steam plant that had been supplying ORNL's steam since the 1950s by adding a biomass-fired boiler system, representing a shift toward using renewable forms of energy for operation. The renovation, which replaced four fossil fuel-fired boilers with a biomass-burning system, was performed through an energy savings performance contract with Johnson Controls.
"It was all about sustainability," said Mark Downing, agricultural economist and senior scientist at ORNL who is helping provide potential options for procuring the renewable resource. "It was about what ORNL can do to change how it thinks about producing steam."
The fossil fuel-fired plant has been providing adequate amounts of steam used in research, energy, cooling and heating for the last 60 years. But the fossil plant's days have been numbered with the growing emphasis on renewable energy. Given the variation in wood, natural gas and oil prices, this project has increased the plant's energy options -- the additional fuel source allowing for more flexibility in terms of producing steam in the most economical manner.
"If I remove fossil fuels from the ground and I burn them, they're gone," Downing said. "At some point, I will run out of coal and natural gas."
An alternative solution to fossil fuels is biomass, or more specifically the gasification of wood products, which provides a cleaner, renewable energy source from which ORNL can produce steam.
Replacing fossil fuels with biomass promised to bolster ORNL's Sustainable Campus Initiative, but Downing and colleagues were faced with the question of how to supply nearly 70,000 tons of wood chips needed to power the plant per year. The answer was simple.
"Hardwood chips are plentiful enough that by using a 100-mile radius around ORNL, I would be able to procure enough hardwood chips to operate the steam plant sustainably," Downing said. "This is not about diminishing the landscape or about clear cutting. This is just considering the use of available wood sources within a 100-mile radius."
The steam plant does not require high-quality woods for gasification to steam. In fact, the majority of hardwood chips could come from logging resources otherwise left behind to decay on forest floors, or from sawmills and other manufacturing operations.
Wood chips may also be bought from other areas that have experienced major storms.
ORNL's new biomass plant can open a new spot market that can make use of these resources that had previously been left to decay or hauled to landfills.
One downside to this renewable source of energy involves economics: coal and natural gas currently cost less than biomass.
"Renewable energy sources allow you to reduce emissions and address sustainability issues by using the wood resource and planting more trees for supply in five to 15 years," Downing said. "This is as opposed to burning coal and waiting 500,000 years for fossil fuels to be replaced. Unfortunately, renewables are not necessarily less expensive."
Downing proposes that an investment in active forest management would ensure that wood supplies are available for future generations to come.
"I may be harvesting trees in one location, but if I don't replant them, the system falls apart," Downing said. "That way, in my lifetime or my children's lifetime, over generations, there will be more trees to harvest. How I deal with that and how I manage that is what matters."
ORNL considered shifting to a renewable source of energy because a decreased dependence on fossil fuels for steam allows ORNL to realize an estimated cost savings of about $4 million per year based on the federal requirements for renewable energy production in federal facilities. This plant also promises to decrease greenhouse gas emissions by 20,000 tons per year, which is equivalent to the amount of carbon dioxide emissions released after burning nearly two million gallons of gasoline. In addition the plant replaced four fossil fuel boilers that had reached the end of their useful life.
ORNL is not yet ready to do away with fossil fuels entirely, but the biomass-fired plant will reduce ORNL's fossil fuel usage by up to 70 percent.
The system can produce up to 60,000 pounds of steam per hour, which will satisfy ORNL's steam needs during the summer months. During the winter, ORNL requires 120,000 to 140,000 pounds of steam per hour, an enormous amount of steam that will be produced by burning both biomass and natural gas.
Ultimately, ORNL can obtain a significant portion of its steam from wood chips, providing energy from the materials once considered simply a waste.
August 01, 2012