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Wood-Burning Boiler Balances Sustainability and Maintenance
Institutional and commercial facilities have undertaken a range of efforts over the last two decades to minimize the impact of their operations on the environment. From water conservation and recycling, to reflective roofing and solar energy, updated technology and processes have enabled organizations to curtail waste, minimize costs and benefit the environment.
The role of maintenance and engineering managers in these organizations is trying to ensure new and upgraded systems deliver intended sustainability and bottom-line benefits while still operating their departments efficiently and cost-effectively. Achieving these twin goals is often challenging.
Spotlight on the boiler
For Katie Norton, facilities manager with the city of Battle Creek, Michigan, the challenge involves a wood-burning boiler. The boiler serves Battle Creek’s city hall with 76,625 square feet and the police headquarters with 48,649 square feet, and it has been in operation for 13 years. Two natural gas boilers were installed at the same time.
Installation of the biomass boiler was one effort by the city to achieve its sustainability goals.
“The previous system was steam heat, and they used a lot of energy to heat water to reach boiling point,” Norton says. “The current system required less chemical treatment because it is a closed-loop system and did not waste as much energy having to boil large amounts of water.
“The city’s climate protection policy goal at the time was to establish 15 percent renewable energy in city facilities by 2015. (The manufacturer) predicted that the biomass boiler would take 90 percent of the heat load, and thus more than 40 percent of the energy consumed by the buildings would come from a renewable energy source, thus meeting the city’s climate protection policy goal of 15 percent renewable energy source and reducing carbon dioxide emissions.”
One unique aspect of the boiler’s operation is the system that feeds wood chips to the system.
“There is a wood bunker that houses the wood chip fuel and has an augur and conveyor belt system,” she says. “This system automatically distributes and delivers the appropriate amount of chips down into the boiler that is housed in the sub-basement of city hall. The biomass boiler was intended to cover 80-90 percent of the heating load for both buildings. During the coldest weather, the natural gas boilers kick in to provide second-stage heating and serve as backup to the biomass.”
During the boiler’s early performance, it delivered the intended benefits.
“The benefit of the system is that we are not using as much natural gas, which is better for the environment, and wood chips are far less expensive than natural gas consumption,” Norton says, adding, “According to the annual (manufacturer) energy savings report and my experience, I think the system was accurate in its energy efficiency predictions for the first 10 years.”
The wood-fired boiler’s operational challenges increased after its early performance life.
“There was never a great solution for getting the ash removed from the system,” Norton says. “The boiler is housed within the sub-basement, two flights of stairs down and in the center of the building. The guys have to empty the ash at least once a week and put them in garbage bags and carry them all the way out to the Dumpsters on the opposite side of the parking lot.
Another challenge is finding a fuel source.
“The system is very finicky about the type of wood we use,” Norton says.”It has to have low moisture content, hard wood, free of debris, and be deliverable on a semi-truck with moving bed. It’s been harder and harder to find anyone local that can deliver us this type of wood chips and in a timely fashion. The only qualified company we could find to work on the boiler is a refractory company out of the Detroit area, and it has been difficult to get them scheduled because they are so busy.”
Norton says the weather also can create additional maintenance issues.
“We cannot run the system if the outside air temperatures are consistently higher than 50 degrees because condensation builds up on the inside of the boiler,” Norton says. “It requires lots of maintenance and monitoring.”
The boiler’s challenges are not only unique. They are impacting the bottom line.
“They are down there monitoring and tweaking the system daily. What we are saving in energy costs is likely being consumed by labor costs. Making sure the grates are clear, the ash is emptied, removing stick jams for the augur system, routine chimney sweeping the inside, monitoring the oxygen level, adjusting the augur intake based on the wood we can get, and maintaining the wood supply. It takes both of my maintenance guys to clean the system, remove the ash and unload the wood from the semi.”
The system also has developed an air leak from the breakdown of the brick interior, and as a result, the facilities have been running on gas most of this season, Norton says.
“The wood boiler is reliant on a controlled feed of oxygen within the chamber,” she says. “If that feed is off, we have difficulty controlling the temperature within the chamber. After 13 years of running the boiler, there have been areas of wear within the seams, brick lining and gaskets causing a leak in the air-controlled chamber allowing uncontrolled oxygen to enter inside. It took some time to locate the leak. With an abundance of oxygen, the boiler was burning too hot and deformed the ash augur arm within the unit.”
Despite these challenges, Norton says the constraints of public financing make it unlikely the department will be able to replace the boiler anytime soon.
“We have no immediate plans at this time.” she says. “It is difficult for government entities to be proactive because of funding issues. The majority of taxpayer dollars immediately go back into the community to help the citizens, so government facilities have been forced to be very reactive. We are taking steps to be more proactive in the future, but it will be a complete culture shift that will take some time."
Dan Hounsell is senior editor for the facilities market. He has more than 25 years of experience covering engineering, maintenance, and grounds management issues in institutional and commercial facilities.