Biomass Gasification

Biomass Gasification

Photo of Biomass Plant

Middlebury College celebrated the official launch of its biomass gasification plant with a reception, tours, and a lecture by author, activist, and Middlebury Scholar in Residence Bill McKibben on February 19, 2009, at McCullough Student Center.

What is biomass gasification?

Biomass is fuel derived from plants such as trees, grass, soybeans, and corn. Middlebury uses locally sourced wood chips, which are superheated in a low oxygen chamber where they smolder (not burn) and emit wood gas. Oxygen is introduced on the backside of the boiler causing the gas to ignite, producing heat (at temperatures of over 1100° F) to make steam that is distributed throughout campus for heating, cooling, hot water, and cooking.

What happens to the waste?

Exhaust from the gasification process circulates through a cyclone separator and then through a series of filters. This filtration system is rated to remove 99.5 percent of particulates, so most of what comes from the smokestack is water vapor.

Other energy-efficiency measures include using the exhaust from gasification to preheat the water entering the boiler, and the excess pressure from the steam to cogenerate approximately 3–5 million kilowatt-hours of electricity per year, which is distributed throughout campus. And local farms use the ash produced in gasification as a soil amendment.

Highlights:

  • More than 1,000,000 gallons #6 fuel oil saved each year
  • 99.5 percent efficiency of exhaust system removing particulates
  • Zero net carbon emissions, based on net growth of forests in our region

What are the benefits of Middlebury College using biomass?

A 40-percent reduction in net emissions of carbon eliminates one million gallons of #6 fuel oil and instead supports a local, renewable resource. The biomass plant also serves as a place to educate students and the public about energy use and research into new fuel sources. And purchasing local wood chips stimulates the local and state economy and creates less dependence on foreign oil.

Highlights:

  • Biomass gasification has been successful, but not without issues. Small fires in the plant led to modifications, and we developed our own patents to increase the safety and efficiency of the process.
  • The plant has a 25-year life expectancy, and we are continuously assessing new technologies to be well-informed about our options beyond that.

Is biomass gasification carbon neutral?

Burning biomass releases carbon into the atmosphere, but this carbon can be sequestered by growing forests. Although current carbon accounting rules count biomass as a neutral source, these accounting rules are under increased scientific scrutiny. Two sections of a senior seminar in environmental studies (ENVS 401) in 2010 studied this. In order for biomass to be carbon neutral, the land where the biomass is coming from must continue to grow biomass to capture carbon. Using data from the U.S. Forest Service, the class determined that the 20,000 tons of wood chips Middlebury burns represent less than one percent of the net growth of the forests in the region where we obtain the chips.

What percent of the College’s carbon footprint does the biomass plant reduce?

Middlebury projects that its carbon emissions will be reduced by about 12,500 tons, which represent an estimated 40 percent of the College’s 2006 carbon emissions.

Where do the wood chips come from and are they sustainably harvested?

Middlebury sources wood chips within a 75-mile radius from Vermont and New York, two heavily forested states where recent forest growth has exceeded forest harvests. If this remains the case, these forests can help provide a regional sustainable system of biomass that is carbon neutral over a period of time. Middlebury is working to develop a system to provide us with more information about our suppliers’ practices and help us understand the extent to which ecologically sustainable forestry practices are being used.

We tried something different—and learned from the willow project.

In 2006, Middlebury partnered with SUNY College of Environmental Science and Forestry to test the feasibility of growing willow trees as a fuel source for the biomass plant. The trees were planted on 10 acres adjacent to Middlebury’s Organic Farm over a three-year period. In 2011, the willows were cut and chipped and tested in the biomass plant. After various analyses, Middlebury concluded that willows are not a feasible fuel source.

How many wood chips does Middlebury’s biomass plant use?

The biomass gasification plant uses about 25,000 tons of wood chips annually, which is two or three truckloads of chips delivered daily during peak heating. A Biomass Fuel Assessment was prepared by Vermont Family Forests to determine the availability of such a supply in the local area prior to its implementation.

Is biomass now the only fuel source used for heating and cooling the campus?

Middlebury uses natural gas in addition to wood chips to provide adequate heating and cooling to the campus. #6 fuel oil is also used as a back-up.

How much did the biomass project cost and what is the payback?

The project cost was $12 million, which includes the construction costs for an 8,000-square-foot addition to the existing service building, alterations to other spaces within the existing building, the biomass gasification system, boiler, and control systems, plus design and permitting costs.

At $1.50 a gallon for #6 fuel oil and $37 a ton for wood chips, the internal rate of return is 8.75 percent and the payback period is approximately 12 years. The switch to biomass from oil saves Middlebury around $1,000,000 per year, with the expected savings increasing by 3 percent per year. The project will also pump $1,000,000 annually into the local economy through the purchase of wood chips. The expected life of the plant is 25 to 30 years. We are continuously assessing new technologies with an eye toward greater efficiency for the plant and to be well-informed about our options when the plant is retired.