Montpelier’s pipe dream

Vermont’s capitol city is readying to fire up its modernized and expanded district heating system, which includes two new biomass boilers and a new hot water distribution loop. 

By Anna Simet, Biomass Magazine

It’s been a long road for those who have spent the past several years working to see Montpelier’s biomass district heating system through to success, but the light is shining bright at the end of the tunnel. After a couple of decades of research, feasibility studies, discussion and planning, the system will enter full operations this fall.

The plant, located at the site of the state’s existing boiler facility, includes two new 600-horsepower, hybrid watertube/firetube, dual-fueled boilers rated at 20.1 MMBtu per hour. As backup, the newest existing oil boiler has been modified to operate on No. 2 fuel oil, rather than No. 6 fuel oil. Connected to the plant is an existing steam distribution system that has heated 17 state building complexes since the 1940s but was not modified due to its good condition, and a new hot water distribution loop that will deliver heat to city buildings, including fire and police stations. The new loop has been designed to allow potential connections for additional commercial and residential structures, with an expectation that the system will eventually heat 1.8 million square feet of the community.

Contractors began tearing up concrete for the distribution system in late April. According to William Fraser, city manager, the distribution line is complete and functioning, with just minor items such as final paving to be completed this spring. The heat plant is expected to be completed by March or April. “We will be testing the two systems together in late spring, with a full, integrated system startup in October,” Fraser says.

Early models of the facility proposed the plant as a cogeneration facility that would generate a small amount of electricity for government buildings, but plans were modified to focus on heat generation. The possibility of expanding only the distribution system was also initially explored, but it was found that using the existing plant as-is wasn’t feasible. “It was concluded that unless the state’s plant capacity was expanded, a shared system would not work,” Fraser says. “That led to the application for a U.S. DOE grant for both plant expansion and distribution system.”

In the midst of a major feasibility study performed by Veolia Energy, the project was granted $8 million in Recovery Act funds through the DOE’s Community Renewable Energy Deployment program, an event that nearly sealed the deal. The state and city made a deal to share remaining costs, which have totaled about $20 million. The final price tag for the plant ended up exceeding the initial estimate by about $6 million, for several reasons including redesigns during the development process and component part costs, according to Fraser, but the city’s distribution system ended up very close to the initial estimate of $5 million.

Besides cost sharing, according to the deal, the state and the city have each taken on specific, separate roles. The state’s included the sole responsibility of planning, designing, and constructing the heating plant, and it will operate and maintain the boilers, boiler auxiliary equipment, fuel conveyance and storage, ash collection and disposal systems, thermal conversion units and building structures that house all components. The city had the role of designing and constructing the city distribution system, and will own and manage the piping system, steam-to-hot water energy conversion equipment and all other components involved in the connection of city buildings.

System narrative
As described in engineering plans, whole green chips will be delivered to the site by live bottom trailers, unloaded onto a hydraulically operated walking floor, and discharged onto a vibrating conveyor belt at a rate of 20 to 25 tons per hour. The conveyor, which is fitted with a screen section to prevent oversized material from entering storage, sends oversized material through another size reduction before being pneumatically returned to the fuel receiving system.

After metal is removed from the oversized component of the fuel with a permanent magnet, screened chips are moved by a series of covered screw conveyors and an enclosed bucket elevator into two fuel storage bins, which can hold 366 tons of capacity. Stored chips in the fuel bins are extracted by reclaim screws and discharged onto vibrating conveyors that transfer fuel onto a series of screw conveyors in the basement of the facility, which feed a bucket elevator. The bucket elevator raises chips up to the boiler room operating level, and a screw conveyor moves fuels to a reversing conveyor that will service surge bins—which are set into a process line to change an inconsistent flow of material into a controlled or consistent flow—for either biomass unit. Distribution screws at the bottom of the surge bins feed into a rotary valve that seals and meters the fuel flow into 12-inch stainless steel stoker screws on each of the under-fed combustion units. The plant will consume around 12,000 tons of wood chips annually.

Benefits and challenges
The city government specifically will see long-term savings in heating costs, as will the connected customers since wood prices have historically grown at much lower rates than oil, Fraser points out. Using wood chips will replace about 300,000 gallons of oil per year. Fraser adds that the community will have improved air quality since 16 individual chimneys have been functionally replaced with one state-of- the-art chimney at the heat plant, and in a flood prone city, downtown basements will be safer, due to the fact that many private oil furnaces and underground fuel oil storage tanks will be removed.

The fact that this project was the first of its kind in the region was a challenge, Fraser points out, but there were some other hurdles as well, one being a back-and-forth vote by the city council. “[Council objections] had to do with specific provisions within our agreements with the state and some financial concerns,” Fraser says. “Once those concerns were addressed, the council supported the project.”

Community support for the project was consistent, as it voted on the project three times with about a 60 to 40 percent approval each time. “Generally, people in Montpelier are supportive of renewable energy efforts,” Fraser says. “Most criticism of the project has been concern that it is a lot of money and effort for a small amount of users. However, the projected long-term energy savings for the city government and its taxpayers resulted in basic support.”

Realizing that tearing up roads in a busy downtown would wreak havoc on traffic, the city took a few measures to make information more readily available to citizens, including an information hotline. “This was a big disruption, particularly because of the length of time to complete the project (April through November),” Fraser says. “We have a small, picturesque downtown, and local businesses reported big drops in sales during the construction period. The city tried to manage the project through a weekly recorded message, weekly updates on our website, press releases, attending merchant meetings and direct email messaging. In retrospect, I think we could have done even more to keep people fully informed.”

On advice to other cities contemplating or interested in doing something similar that Montpelier has, Fraser says, “Make sure you know your financials. Make sure you have fully investigated the system’s benefits, as well as how it stacks up against other heating alternatives.”

Understanding the customer base and what it takes to make the project work is also important, according to Fraser. “If you are working with partners—like we did with the state—be sure to have those relationships and agreements in place before going too far too fast,” he adds. “Our DOE grant was from ARRA money, which meant that there was a lot of pressure to get the job done fast. Therefore, we tried to manage a lot of these issues at once, which resulted in some moving targets and misunderstandings—hence the reservations by the city council.”

Finally, retaining a firm that has been through it before to serve as a guide is a must. “We worked with Ever-Green Energy from St. Paul, and their advice, business planning and experience was essential.”

Author: Anna Simet; Managing Editor, Biomass Magazine, asimet@bbiinternational.com