d 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 to minimize air quality impacts using best available control technology (BACT).
Particulates and Health Impacts From Wood Combustion
Particulate matter is the solid matter or very fine droplets that result from combustion or through secondary physical and chemical conversions in the atmospheric. Visible at larger sizes and invisible in its smallest form, particulates are the air pollutant of greatest concern when considering wood combustion. Particulate matter is a generic term and is defined without regard to chemical form in the Clean Air Act (Section 109). Small particulates range in size from 10 micrometers to 2.5 microns (PM10, PM2.5) and less in diameter. The smallest particles cause greatest human health concern, since small particles can lodge deep within the lungs when inhaled and remain airborne for longer periods and distances.
Many wood-fired boilers employ a “tall” stack of sufficient height to disperse emissions and reduce ground-level concentrations of particulate matter (and other pollutants) to mandated levels. Elaborate cyclonic and electrostatic precipitators (dry and wet) scrub the exhaust and collect particulates in the modern wood-fired operations. Therefore, most references to older wood burning systems may overstate wood combustion emissions relative to corresponding gas and oil systems of the same period. Specific wood-fired operations use the best available control technology (BACT) to ensure that they meet emission limits, prevent pollutant and associated deterioration of air quality.
Wood energy is the only traditional industrial fuel that does not substantially add to atmospheric carbon dioxide in the long term, if wood supply comes from sustainable sources and forest acreage is maintained. In the context of greenhouse gases, wood presents an advantage over all of the other fuel sources discussed in this article. While the combustion of wood and fossil fuels result in carbon dioxide and water vapor, over time the carbon stored in solid wood, roots, limbs and soil can offset the carbo