Potential for a Biomass CHP Plant at Middlebury College
In 2002, Middlebury College in Vermont created a Carbon Reduction Initiative. A working group of administrators, faculty, staff, and students is developing a plan to significantly cut fossil-fuel consumption and create a "carbon neutral" campus.
The group has identified the college's annual consumption of about 1.7 million gallons of heavy fuel oil as the major contributor to campus carbon emissions.
BERC carried out a preliminary study of the technical aspects of using biomass to replace fuel oil - and possibly also to generate electricity - at the college's central heating and power plant. The study was funded by a grant to BERC from the U.S. Department of Energy. All cost estimates in this study are preliminary.
Potential Impacts
The study found that Middlebury College could wholly achieve its carbon-reduction goal by simply replacing its oil-fired oilers with wood-chip boilers for heat only.
But by producing electric power and by-product steam from biomass in a new CHP (combined heat and power) plant, the college could also replace the electric power it currently purchases from nuclear, fossil fuel, and hydro sources.
For estimated cost and other benefits from three scenarios, see "Estimated Cost Benefits" and "Summary."
College Needs
The college currently heats nearly all its campus with an oil-fired system of four steam boilers, at a central heating and power plant, feeding steam via buried pipes through five loops to college buildings. Construction of new college buildings is increasing peak steam demand to the extent that within three years, the college might not have sufficient backup capacity if a boiler should fail.
The college is thus in a position of needing to meet its looming heat and energy needs by careful planning, equipment upgrades, and equipment replacement.
Siting Considerations
A new biomass facility would need to meet the following criteria, among others:
- Adequate space for expansion;
- Out of the way of present campus buildings;
- Access for trucks from the south, rather than through town;
- Potential rail access;
- Nearby space for storage and chipping of wood;
- Compatibility with future campus facilities plan;
- Minimal practical distance for connection to current steam system;
- Aesthetic considerations.
Technologies Considered
All scenarios presented by the report are based on the dual fuel wood boiler, which can be fired directly with wood chips, or with biogas produced by a gasifier using wood chips as fuel. With either fuel source, this boiler is a fully commercialized, proven technology. It would be the backbone of the more advanced technology scenarios considered by the study.
The advanced system would likely employ fluidized bed, engine-fueling gasifiers, which are not yet a fully commercial technology, though they have been run successfully using wood chips as fuel. Engine-fueling gasifier technology produces a biogas similar to natural gas.
The phased approach considered by the study works from the first installation of a proven dual-fuel boiler. In later stages of system development, a gasifier can be added - first to produce biogas for boiler fuel, then to generate both steam and electricity sufficient to meet all the college's needs.
Estimated Cost Benefits
Estimates of potential cost benefits include:
- $440,000 in annual fuel cost savings from the single wood-chip boiler producing heat, with $3.5 million in estimated capital cost.
- $400,000 in annual fuel cost savings, plus $180,000 in annual electricity revenue plus $40,000 in Renewable Energy Certificates (RECs) for electricity, from installing the wood-chip boiler and also coupling it to an existing steam turbine, to produce a small amount of electricity. This scenario has an estimated $3.6 million in capital cost.
- $420,000 in annual fuel cost savings, plus $2 million in annual electricity revenue and $560,000 in annual RECs for electricity, from an integrated biomass gasification and power plant that would completely replace the oil-fired central heating and power plant, through a phased build-in. This project has an estimated $4.7 million in capital cost for Phase 1, and $12.8 million in estimated cost for Phases 2-3.
Summary
The scenarios start with a relatively simple, heat-only biomass boiler approach, and build on this to add advanced biomass gasification for clean power production, and to supply all the college's heating needs.
By producing heat and electric power from biomass, the college can:
- Achieve its carbon reduction goal;
- Replace the electric power it now produces from nuclear, fossil fuel, and hydro sources;
- Demonstrate a way for institutions and communities to reduce their dependency on electricity produced with high carbon-emissions fossil fuels, while replacing cost-fluctuating heavy fuel oil with woodchip biomass, whose costs tend to be both lower and more stable;
- Make a significant, long-lasting impact on rural development and forest-based industry in Vermont; and
- Demonstrate this public benefit, as well, to many areas of the U.S.