raditional powerplants that make be closer to 35-40 %). Wood’s cost-saving benefits may get an even greater boost with renewable energy and climate change policy that avoids traditional fossil fuel energy sources. Regardless of the motivation, wood is a valuable fuel and feedstock. Current and future users will be motivated to fully combust and extract the maximum amount of energy (and value), while minimizing pollution.
Clean Air Standards
All industrial fuel users must comply with clean air standards and regulations regardless of the fuel type. Industrial combustion facilities are regulated by the United States Environmental Protection Agency and NC Division of Air Quality. These agencies manage air quality, through regulation, permits, and enforcement to ensure that new or existing facilities minimize air quality degradation. Regulations apply to all major combustion facilities, including specific emissions related to wood fuel combustion. It is important to note that emission standards are strictest for larger-scale facilities.
Figure 1 illustrates that a wood-fired power plant with modern emission control equipment emits 1⁄500 to 1⁄280 of the emissions of a wood stove, for the same amount of wood fuel input.
There are several air pollutants that any industrial facility must control regardless of fuel used. The most common regulated pollutants for oil, gas, coal and wood are nitrous oxides (NOx), carbon monoxide (CO, a product of incomplete combustion), sulfur dioxide (SO2), mercury (Hg), and particulate matter (very small, airborne particles). Greenhouse gases too have become a significant concern in recent years. In this section we will discuss several fuel sources in the context of each of these pollutants. The following table provides a comparison among various fuel emissions.
Natural gas is considered the cleanest industrial fuel because it can be burned to generate low levels of NOx, CO, SO2, and particulate matter, in comparison to other fossil fuels. Of late, natural gas has become very inexpensive and the go to choice for replacing coal buring electricity plants..
The use of oil as industrial fuel in the United States has declined because of very high cost; it is included here for comparison sake. Oil is available in different grades, and while the NOx and CO are usually low, sulfur levels in oil can be high, requiring methods to control SO2.
Wood as a supplement to coal shows promise. NOx emissions from wood are generally less than from coal, with studies reporting that mixing wood with coal reduced overall NOx from the facility. SO2 is much lower with wood than coal. Depending upon where the coal comes from, coal can contain 75 times more sulfur than wood on a per unit heat value basis. Therefore, while sulfur removal is a large part of the effort in coal-fired facilities, wood energy facilities generally require little effort is to meet SO2 emissions standards. There is technology and equipment available to effectively control the NOx, CO and SO2 from both coal and wood energy plants.
Wood combustion for energy results in negligible mercury emissions when compared to coal sources.
Coal and wood present additional air quality impacts compared to oil or natural gas. As solid fuels, coal and wood vary greatly in quality, energy value, moisture and ash. Variation in fuel quality makes handling the fuel, ash and emissions more difficult.
The control of fine particles is required for all solid fuel energy facilities as they are swept up in the combustion air stream and out the stack. While fine particles may not be toxic, per se, breathing extremely fine particulate matter has deleterious health impacts. Wood’s distinct advantage is that it contains about 90% less ash than coal.
Effective methods of control of particulate matter have been developed for both coal and wood combustion facilities that remove most particulate matter from the exhaust air. The particulate matter from either a coal plant or a wood plant is higher than a natural gas plant, but particulates from both types of facilities can be controlled