BioCycle December 2008, Vol. 49, No. 12, p. 46
In January, Middlebury College in Vermont plans to begin full operation of its new $11 million biomass plant, replacing half of its annual consumption of more than 2 million gallons of fuel oil with regionally grown wood chips. Expected to consume 20,000 to 22,000 tons/year of biomass, the new plant will cut the college’s greenhouse gas emissions by almost 12,500 metric tons annually, according to Nan Jenks-Jay, dean of environmental affairs.
Commissioning of the new plant is scheduled to begin December 1, with full operation slated in January, according to Tom Corbin, Middlebury’s director of business services. The school added an addition to its existing boiler plant, “So we could tie into the cogeneration facility there, and to our steam-distribution center,” says Corbin.
According to Jenks-Jay, the college’s long-range goal is to obtain wood chips harvested in an environmentally friendly manner from local sources. “Our hope is that the college’s entry into biomass will greatly stimulate the growth of the local, sustainable wood chip market and bioenergy economy in Addison County, and Vermont,” she said. College officials also anticipate that the plant will provide demonstration and learning opportunities regarding the design, construction and operation of biomass heat and power technologies for other colleges, municipalities, state government, hospitals, dairy and food processors, and other small to medium sized enterprises.
To ensure a steady supply of wood biomass, “We started talking to local mills to find out what volumes they could provide and when,” says Corbin, both during the high-demand heating season and during the warmer months. The school has signed a three-year contract with Cousineau Wood Products, a broker based in Henniker, New Hampshire. “We felt a three-year contract would allow us to work the kinks out, get a better sense of how the market works and decide whether we should procure material on our own, or stay with a broker,” he continues. “We’re a big user, but compared to a wood-fired power plant, we’re tiny.”
The school’s contract with the supplier is structured to help keep a handle on prices as the heating fuel market fluctuates. “As the price per ton of chips goes up, their fee and commission will go down,” Corbin explains. “At $35 a ton, they will get $3 a ton [fee and commission]. If the price is $50 a ton, they will get $1.25 a ton.” The market rate is a function of the seasonal demand, and the price of oil, he notes.
The college’s gasification system is made by Bristol, Vermont-based ChipTech, a B Series model with a rated capacity of 29 million BTUs. Its Johnson Fire Tube boiler produces 250 pounds of saturated steam pressure. The approximately 7,000-square foot plant also has a West Salem Machinery disc screener and shredder, which “Allow us to accept a broader spectrum of [wood] fuel,” says Mike Moser, assistant director of utilities. “Oversized twigs and branches that would typically wreak havoc in these chute systems are rejected by the screener and fall into the shredder.”
To control particulate emissions, Middlebury’s new gasification system is equipped with a Flex-Kleen Bag House filter system. As part of its quest for local, renewable fuel sources, the college has also developed a nine-acre test plot on the outskirts of campus to explore the feasibility of fast-growing willow shrubs as biomass. It holds 30 different varieties, which will reach maturity at three years. If the willows appear to be a viable source for chips at the end of the test period, the college will contract locally to plant 400 acres per year for three years. This would allow a 400-acre annual harvest, helping the college through the peak winter months when the local supply of wood chips is least abundant. At that rate, the locally grown willows would supply a quarter of the college’s heating fuel supply, officials said.