Traverse City Record-Eagle

Community

September 8, 2010

Wood energy involves many technologies

By BILL COOK Special to the Record-Eagle

Using wood for energy involves a variety of technologies. Not all wood is equally useful to a particular technology. And, different technologies produce variable mixes of energy. It's not all the same.

The way in which we use energy also varies. Energy is not a single commodity. We use energy to heat and cool spaces, produce electricity, and provide transportation fuel. Various energy sources, including wood, fit differently into each kind of use. Each combination has advantages and disadvantages.

We may most commonly think of wood energy as what we love to see in a fireplace or wood stove. Combustion has been used to produce space heat for millennia. Most of what we see is fairly inefficient, but high efficiency technologies exist. They've been deployed in parts of northern Europe for decades.

The most efficient use of wood, or any feedstock, is to utilize as much of the energy in a ton as possible. Capturing the energy and converting it to heat and electricity employs common engineering and can exceed efficiencies of 90 percent.

District energy produces heat in a central location and then distributes that heat through a system of underground hot water pipelines. The size of the heating plant depends upon the size of the demand. The same system can be used to supply cool water for air conditioning. Consumption may be large enough to warrant the addition of an electricity generation component.

District energy systems are becoming increasingly common across North America. There are several in the Upper Peninsula and northern Wisconsin.

A utility that produces both heat and electricity is called either a co-gen plant or a CHP (combined heat and power) plant. Plant sizes can vary from around 20 megawatts to several hundred megawatts. Wood chips are commonly used as feedstock, sometimes combined with other materials to improve combustion efficiencies. A large CHP plant in St. Paul, Minn., uses municipal solid waste. Other materials can serve as a feedstock depending what is available in the landscape.

Michigan has about seven electric utilities that use wood as a feedstock. Only one these has a heat distribution component. Finding a market for the heat can be difficult. Additional capital investment is needed to deliver heat to an industrial and/or residential network of consumers.

Pellets and briquettes are another increasingly common technology. The energy content of the woody material is concentrated, making transportation more economical. Combustion temperatures are higher and more consistent than that of firewood, so stoves need to be built accordingly. Pellet stoves tend to be more efficient and cleaner than wood stoves. The advantage of pellets comes with ease of use and consistency of burning. Also, pellets free-up time that might have otherwise been used to cut, split, and stack firewood.

Larger pellets, or briquettes, are used more for industrial applications, such as co-firing with coal. The Renewafuel facility near Gwinn is designed to supply briquettes to an electric utility in Marquette. Briquettes, like those made in Paradise, can also be used as a charcoal replacement for backyard grills.

Creating gasoline substitutes from wood, usually ethanol or biodiesel is the target product, on a commercial-sized basis, has not yet been done anywhere in the world. However, if this group of technologies can be brought on-line, then a portion of the transportation energy demand could be supplied by renewable resources.

In the United States, there are about a dozen commercial cellulosic ethanol plants in the making. Five of these plants plan to use wood. One of them is the Frontier plant to be located near Kincheloe, in the eastern Upper Peninsula.

As the United States moves further into a reduced fossil fuel economy, wood will need to part of the new energy fabric, especially in regions where using wood offers sustainable and competitive advantages. The northern Lake States is such a region.

Bill Cook, an MSU Extension forester, provides educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres.

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