Efficiency Improvements Grace State’s Heat Plant

by Bob Nuner

The new Montpelier District Heat Plant at twilight. Photo by Erin McIntyre.

The new Montpelier District Heat Plant at twilight. Photo by Erin McIntyre.

On a sunny March afternoon, Joe Aja, building project manager for Vermont’s Department of Building and General Services, gave The Bridge a tour of the steam plant renovation behind the Department of Motor Vehicles. Aja manages state construction projects in a district that runs from Brattleboro to Derby and has worked in Montpelier for the past two and a half years.

The state’s plant reflects the nation’s changing energy approach. It first came online in 1946, fueled by coal dropped from railroad hopper cars into a basement bin and hand-shoveled into boilers mounted on the basement floor. Those boilers eventually converted to #2 fuel oil, then #6 “bunker” (a heavy oil used in ships) and, in the 1980s, one of three boilers was converted to wood chips. The renovated plant’s new chip furnaces can be retrofitted with oil nozzles quite quickly, adding flexibility.

The state has burned wood chips in the Montpelier and Waterbury office complexes for some time. More recent Vermont heating conversions have also occurred at Middlebury College, Norwich University and National Life. (Burlington’s McNeill plant burns biomass to generate electricity but doesn’t distribute its “waste” heat.)

The renovation in Montpelier surrounds the original plant on its west, north and east sides, abutting the Washington County Railroad on the south where it crosses the Winooski. Much activity was invisible to casual view during construction, even with the new floor-to-ceiling south glass wall, because inside the original plant some floors were knocked out and others re-cast. The floor where railcars entered was knocked out to create an interior wood chip bin, and the basement floor was drilled to incorporate ground anchors (to prevent hydraulic lift during flooding) with a new floor cast atop it. The new boilers sit above historic 500-year flood elevation. They’re fed by a computer-controlled system that cleans, screens and transports chips that arrive via trailer trucks backing in from State Street.

Aja anticipates little waste, because the system incorporates cleaning magnets, vibrating conveyors, screens and an auxiliary chipper to reduce chips too large for the augers. All plant equipment, including district heat circulators, can take power from an on-site generator in the event of power failure.

There are two new 600-horsepower boilers. On Thursday, March 6 at 9 a.m., one started supplying steam for the state office complex. An older 450-hp oil-fired boiler was retained for “swing” months when heat demand may be insufficient to warrant using the wood furnaces. The state will soon disconnect a rented 350-hp unit, which heated the complex this winter, providing sufficient heat down to 10 degrees below zero (so the retained “backup” oil-burning boiler is 100-hp bigger than the boiler that heated state offices this winter).

Wood chips enter the enclosed two-story chip storage bin after screening and cleaning. Automated floor-mounted augers then pull the chips into the fuel feeding system. Photo by Bob Nuner.

Wood chips enter the enclosed two-story chip storage bin after screening and cleaning. Automated floor-mounted augers then pull the chips into the fuel feeding system. Photo by Bob Nuner.

Aja noted about the new chip-fired units, “With these two online 100 percent, the emissions are less than what we had before we started, because of the electrostatic precipitators.” Electrostatic precipitators, along with cyclonic flue gas cleaning equipment, capture ash from flue gases before they hit the plant’s smokestack. The ash is valued for “sweetening” soils.

Asked about wood-chip volume to feed the plant, Aja said it’s too soon to say, noting that until the city’s system is connected, the state won’t have a firm handle on demand. If district heat requirements are sufficiently great, the wood-fired boilers can run during shoulder months that bracket the State’s sales contract with the city, which extends from October 1 to April 30. If demand is less, the oil furnace will provide heat at the ends of the season.

Unlike the steam-heated state office complex, Montpelier’s district heat system circulates hot water. Heat transfer occurs in the new “city room” built on the expanded plant’s southeast corner. In a small room packed with shiny insulated piping, heat enters the district’s hot water system. The State will bill the city on a British thermal unit (Btu) basis, measuring temperature differences between the plant’s steam and the returning condensate after it’s passed through the heat exchanger. Three parallel pumps, each sufficient by itself, will circulate hot water throughout town. To promote minimal wear, all three pumps will operate together.

Aside from the sunlight flooding through the southern wall, noteworthy features include an exterior handicapped-accessible ramp designed for educational access; a planned metal screen on the eastern wall designed to support ivy climbing from a planter (avoiding brick damage); and, west, of a long, midwall computer-controlled combustion air intake, a large, colorful iron medallion from one of the 1946 boilers adorns the brick wall beside the north entrance.

At the end of the visit, a departing worker was overheard noting the variety of trades working the jobsite from IT technicians, electricians, welders, plumbers and mechanics, to landscaping and siding installers— the place was busy. However, Aja estimated the on-site project headcount to have fallen to around 30. He anticipates completion of the project in June.

Share this:
Share this page via Email Share this page via Stumble Upon Share this page via Digg this Share this page via Facebook Share this page via Twitter