Wood Energy and the Environment

Forest Products Laboratory retiree John Zerbe has told us about the many ways that wood is used as a form of energy, but how does its use affect the environment? The Forest Service has chosen climate change as one of its top areas of concern; therefore, this question is of great interest. Zerbe breaks the matter down for the reader.

This old stove is quaint, but not the best for the environment. Photo by Victor Grigas via Wikimedia Commons

This old stove is quaint, but not the best for the environment. Photo by Victor Grigas via Wikimedia Commons

Carbon Dioxide

The increasing accumulation of carbon dioxide and other greenhouse gases in the atmosphere is generally considered to be a threat to future stability of the earth’s climate.

There can be no doubt that our vast use of fossil fuels is the major contributor to increased atmospheric carbon. The renewability of wood and other biomass fuels makes them a desirable alternative to fossil fuels to prevent or retard increasing retention of carbon dioxide emissions. When new trees are grown to replace the wood that was the source of the fuel, carbon is constantly used and regenerated in the growth cycle. The carbon that is emitted to the atmosphere is absorbed by photosynthesis in new growth.

Sulfur

Sulfur emissions to the atmosphere are undesirable because they can precipitate and cause harmful acidic conditions in soil and water. Wood contains little sulfur, but some coal and some oil contain substantially more. Therefore, sulfur emissions from wood are more easily controlled than those from their fossil fuel counterparts.

Oxides of Nitrogen

Oxides of nitrogen emissions tend to be lower with wood fuel than with fossil fuels. On the other hand, forest fires are a major source of nitrous oxide (a greenhouse gas) in the atmosphere. Higher oxides of nitrogen emissions usually accompany combustion at higher temperatures. New technology stoves designed to be more efficient have higher oxides of nitrogen emissions than conventional stoves.

Particulates

Emission of particulates is the most common cause for concern in meeting environmental requirements with the burning of wood fuel. In the United States in some municipalities and under some atmospheric conditions, particularly air inversions, there are periods when wood burning in fireplaces and stoves is not permitted. Catalytic stoves can help in attaining lower emission rates. Inefficient stoves, such as outdoor wood boilers, which more and more places are banning, have been correlated to increases in asthma and other breathing difficulties.

Altogether, with increasingly sophisticated technology in wood stoves, fireplaces, and furnaces, wood is a more benign source of energy than fossil fuels as well as being renewable. FPL’s Mark Knaebe states that, “Burning wood efficiently can actually be better than letting it rot in the woods because a significant amount of methane is produced during decay.”

How Wood Is Used for Energy

Fireplacefire

Metapolisz Images through Wikimedia Commons

Doesn’t that fire look inviting? So what’s the scoop on firewood?

According to John Zerbe and FPL’s Mark Knaebe of the Forest Products Marketing Unit, cordwood is the most common kind of wood fuel we like to burn. The most common way of using cordwood for fuel is to burn pieces about 1–1 ½ feet long that are split from logs. We burn much of such wood in our fireplaces and wood stoves today, and, formerly, such firewood provided the main fuel source for home heating, domestic hot water, and food preparation. Wood is still used for heating some homes in industrial countries. Usually heat is not produced efficiently in fireplaces, but some fireplaces are sealed with glass doors and designed to use blowers to be more effective. Stoves and furnaces burn firewood more efficiently and are getting much cleaner.

However, for some applications, wood is converted to other forms of fuel that are more convenient, waste less energy, and are less prone to emit undesirable particulates and other pollutants to the air. Examples of other kinds of fuel are manufactured fireplace logs (firelogs), which are made from waste wood and wax to provide open-hearth warmth and ambience with clean fuel. More recently, however, the main alternative to cordword is wood pellets, the main advantage of which is their dryness and their ability to be automated.