Gas From Wood

Looking for an environmentally friendly way to warm your buildings? A gasifier just might be the ticket to a cleaner—and cheaper—heating system.

The new heating system housed in the neat little building at Hartford Central School, in Hartford, N.Y., works a lot like the standard natural-gas boilers in millions of American homes. Except it’s different. Rather than using natural gas piped in from afar, the system makes its own gas—from wood. And it’s a lot cheaper than the heating oil the school consumed exclusively until this past winter.

Gas from wood? Let’s back up. A few years ago, voters in the Hartford School District, a rural area north of Albany, N.Y., voted for a nearly $16 million renovation and addition to their K–12 school. Part of the plan was to start using renewable plant or organic waste material, also known as biomass, for fuel and to cut consumption of fossil fuel. The district bosses asked their architects at CSArch Architecture/Construction Management of Albany to help figure out how.

“They didn’t have to twist our arm,” says Daniel Langer, a CSArch principal and the project’s manager. There are several methods for turning wood or various crops or organic waste into fuel, but not all of them are right for every situation. The point is to find a fuel source that’s relatively local and plentiful. The architects and district officials decided against burning cow manure or corn carcasses because they weren’t impressed with the technology’s ability to meet state emissions rules. “We eventually came across wood chips,” Langer says.

Up in those northerly forests, there is a lot of wood to chip from paper mills and tree farms. The system the school district chose relies on what is called wood gasification. (The basic technology of gasification dates to the 1800s, when the fuel source was primarily coal.) Wood chips arrive from a local supplier and are put into a bunker inside the 2,000-square-foot plant. They’re fed up an auger and into a “gasifier,” a large oven in which the wood is burned at 2,000 F. At that temperature, the wood gives off flammable gases, which are drawn out by induction fans and combusted beneath a huge and otherwise conventional boiler full of water. From there, the water goes off in a closed loop of metal radiator pipes to heat buildings and provide hot water.

The Hartford school’s wood gasifier burns quite cleanly—nearly all particulates are removed from the exhaust by a cyclonic fan. “You basically see nothing” coming out of the flue, Langer says, “and we passed all our [environmental] requirements with a one-page document.” All that remains of the wood is potash, which is distributed to local farms as fertilizer. And the clincher is the cost to the district, which typically paid $110,000 a year for heating oil and now plans to spend $40,000, at most, for wood chips (the gasifier consumes up to 36 tons of them per week in cold weather).

The school still uses some heating oil, however. State education rules require a fully redundant system alongside the gasifier. Also, the gasifier is too efficient—it works best at full throttle, so during “shoulder seasons” (late spring and early fall) Hartford Central turns it off and heats with oil.

Even when the gasifier isn’t operating, it’s always on view in its small building near the school’s driveway, with large windows so people can see the process in action. “We decided to make it an attraction,” says Tina Ceas, the architect at CSArch who designed the structure.

Architects are increasingly being asked by clients to help specify biomass fuel systems of various types. Nick Salmon, an architect at CTA Architects Engineers in Billings, Mont., has worked on nearly two dozen biomass boilers, many of them for schools. In Montana, the systems commonly burn wood removed from forests to reduce the threat of fire. And one, in Bismarck, N.D., uses “urban wood” collected during municipal tree trimming.

A major consideration for biomass burners is air quality—not all systems burn as cleanly as others, Salmon says. “Local air quality is always a concern, and determining what rules apply is important to what technology might work best.” Gasifiers are among the cleanest, while other biomass systems require costly devices to scrub particulates from the exhaust. “We’ve learned the hard way that there are a wide variety of fuels” used in biomass energy systems, Salmon says.

To educate future engineers and others interested in biomass boilers, Minneapolis-based HGA Architects and Engineers recently completed a research and demonstration facility at the University of Minnesota’s Morris campus that will burn corn stalks and leaves to heat 1.2 million square feet of school buildings. (The plant has not yet begun operating.) “They can source all the fuel this plant needs within a 10-mile radius” of campus, says HGA principal Doug Maust. An addition to the school’s existing power plant, the facility received a 2009 Honor Award from AIA Minnesota.

For a 19th century technology that’s gaining wider acceptance in a world increasingly focused on renewable energy, it’s tough to beat a calling card like that.