Project Profile: Colby College Cogen Plant

Firm name: Rist-Frost-Shumway Engineering P.C. 

Project building name and location: Colby College Cogen Plant, Waterville, Maine

Type of building and type of project: Cogen Plant, New Construction

Project completion date and project duration: 2012

Engineering challenges and solutions:

Colby College owns and operates a Central Heating/‌Cogeneration Plant, which provides thermal and partial electrical service to approximately 30 campus buildings totaling approximately 1,250,000 square feet. The Plant contains three high-pressure (300 psig) water-tube steam boilers, each 800 boiler-horsepower capacity. The Plant also contains a steam back-pressure turbine, 600 kilo-watt (kW) capacity.

Previous to this project, plant energy source has been No. 6 fuel oil, only. This project will include expansion of the Plant to install new biomass (woodchip) equipment and appurtenances, including fuel storage, materials handling and processing, gasification, combustion/steam production, and pollution control. Biomass system capacity will be 800 BHP. With this project, the primary energy source for the Plant will become biomass, and use of fuel oil will be reduced to peak-shaving and biomass back-up, only. (Biomass will produce approximately 90% of the annual energy needs of the buildings served.) All biomass fuel will be low-grade forest waste and debris from within a 50-mile radius of the Colby campus, all from sustainable forest operations.

The entire project design was produced as Building Information Model (BIM), using the Revit software platform. Custom Revit content was developed for all major equipment incorporated into the design. Total project cost will be approximately $11 million. Project construction cost will be approximately $9 million. The project is USGBC LEED® Registered.

Challenge #1

Assist Colby in achieving their goal to achieve carbon neutrality by 2015, and at the same time, enable Colby to achieve significant institutional operating cost savings.

Solution: The biomass fuel will offset approximately 1,050,000 gallons of current No. 6 fuel oil consumption. Considering forest regrowth, the biomass energy source change will reduce Colby’s carbon dioxide emissions by approximately 13,700 tons per year. Including added plant staffing to support the biomass process, Colby’s operating costs are expected to be reduced by over $1,000,000 per year (2010 $). Depending on escalation for both No. 6 oil and biomass fuels, the project is expected to pay for itself within six to ten years. In addition to operating cost savings for Colby, the project will also have long-term regional economic benefits, by strengthening the market for biomass fuel.

Challenge #2

Ensure that the project nurtures environmental awareness and is an example of Colby’s passion for environmental stewardship.

Solution: Colby’s initial vision for this project was for the biomass building expansion to occur behind the existing plant, to essentially “hide” the expansion and maintain the Plant’s very low profile on campus. As an alternative, RFS suggested placement of the expansion in front of the existing plant, to make the expanded Plant very visible from the main campus vehicular loop road, and also from a primary campus pedestrian way. Colby embraced this idea. The prominent siting of the building and the incorporation of large expanses of glass curtain wall for interpretive viewing of the biomass process add visual interest to the campus, and exemplify Colby’s respect for the environment and sustainable living. The building interior layout and equipment layouts have been designed to accommodate anticipated frequent tour activities for both the campus community and groups external to Colby. Pollution control measures includes a dual-cell electrostatic precipitator (EsP), which enabled air permit licensing at 0.03 lb. PM/MMBtu (compared to the final EPA NHSHAP standard of 0.07 lb. PM/MMBtu).

Challenge #3

Provide a high degree of reliability for the biomass process, and enable Colby to continue use of their existing 600kW steam back-pressure turbine for partial campus electric power generation.

The project design includes two parallel and independent biomass systems, including materials handling and processing, gasification, combustion/steam production, and pollution control. Capacity for each gasifier and boiler will be 400 BHP. While the parallel-steam biomass system approach added construction cost compared to a single-stream biomass system approach, it provided a significant benefit of system redundancy and anticipated biomass system uptime, and also enables much better combustion turn-down during the non-heating season. Regarding the existing steam back-pressure turbine, the design operating pressure for the new boilers is 300 psig, to enable steam delivery to the existing Plant steam header, upstream of the turbine.


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