New construction: Colby College, Central Heating/Cogeneration Plant Biomass Expansion; Rist-Frost-Shumway Engineering P.C.

Source: Rist-Frost-Shumway Engineering P.C.

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Project name: Colby College, Central Heating/Cogeneration Plant Biomass Expansion

Location: Waterville, Maine

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

Project type, building type: New construction, school (college, university)

Project duration: 3.5 years

Project completion date: Jan. 31, 2012

Project budget for mechanical, electrical, plumbing, fire protection engineering only: $5.54 million

Engineering challenges

The main challenge was assisting Colby in achieving its goal to achieve carbon neutrality by 2015, and at the same time enabling Colby to achieve significant institutional operating cost savings. The firm also had to ensure that the project nurtures environmental awareness and is an example of Colby's passion for environmental stewardship. Other challenges included providing a high degree of reliability for the biomass process and enabling Colby to continue use of its existing 600 kW steam back-pressure turbine for partial campus electric power generation. 

Solutions

The biomass fuel will offset approximately 1,050,000 gal 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 (in 2010 dollars). Depending on escalation for both No. 6 oil and biomass fuels, the project is expected to pay for itself within 6 to 10 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. 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 National Emission Standards for Hazardous Air Pollutants Compliance Monitoring (NESHAPS) standard of 0.07 lb. PM/MMBtu). 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 turndown during the nonheating 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.