Furnaces, wood-burning

Whenever unvented combustion occurs iadoors or when venting systems attached to combustion units malfunction, a variety of combustion products win be released to the iadoor environment. Iadoor combustioa units include nonelectric stoves and ovens, furnaces, hot water heaters, space heaters, and wood-burning fireplaces or stoves. Products of combustion include CO, NO, NO2, fine particles, aldehydes, polynuclear aromatics, and other organic compounds. Especially dangerous sources are unvented gas and kerosene [8008-20-6] space heaters which discharge pollutants directly into the living space. The best way to prevent the accumulation of combustion products indoors is to make sure all units are properly vented and properly maintained. 

If a person has the choice of installing oil, gas, or electric systems to heat a house and believes that any one of the three would perform equally well, the system that is cheapest is the efficient choice. If, however, the individual compares heating with an oil furnace to heating with a wood-burning stove, monetary cost may not be the only consideration. 

In 1990, an estimated 82.2 million metric tons of wood were burned in US industrial furnaces.14 Assuming an average emission factor of 4.0 ng TEQ kg 1 wood from industrial wood-burning facilities in the US,3233 we estimate that 330 g TEQ are emitted each year from industrial furnaces. Using a slightly different emission factor, Rigo13 estimated total emissions from wood burning (both residential and industrial) at 420 g TEQ yr-1. 

TABLE 6.1 Comparison of Conventional Wood-Burning Furnace Characteristics ... 

An additional attempt for a further improvement of the emission behaviour is a detailed analysis of the combustion process by in-furnace measurements which is also carried out by [6]. In order to get experimental data of gas concentrations, temperatures and velocity fields within the reaction zones of different types of heating appliances the project Development of Newly Designed Wood Burning Systems with Low Emissions and High Efficiency f7I was carried out under the JOULE III program of the European Commission. 

The commercial production of PAHs is not a significant source of these compounds in the environment. The primary source of many PAHs in air is the incomplete combustion of wood and fuel (Perwak et al. 1982). PAHs are a ubiquitous product of combustion from common sources such as motor vehicles and other gas-burning engines, wood-burning stoves and furnaces, cigarette smoke, industrial smoke or soot, and charcoal-broiled foods (lARC 1983). Natural sources include volcanoes, forest fires, crude oil, and shale oil (HSDB 1994). 

In addition to wood burning stoves, a range of wood-fueled boilers are also now available tbat are as efficient as modern furnaces—converting over 90 percent of tbe fuel into heat. Compared to a conventional furnace, it does take effort to keep wood burners fed, and log stoves need to be refueled every day, but wood chip or corn or wood pellet stoves can be automated to control temperature settings and only need refilling every few days. 

More than 40 trace elements are routinely found in atmospheric particulate matter samples. These elements arise from dozens of different sources including combustion of coal, oil, wood burning, steel furnaces, boilers, smelters, dust, waste incineration, and break wear. Depending on their sources, these elements can be found in either the fine or the... 

The basic fundamentals of wood waste combustion entail three consecutive stages the evaporation of moisture, the distillation and burning of volatile matter, and the combustion of the fixed carbon. In the furnace combustion chamber, radiation and convective heat input evaporates the wood s moisture and distills the volatile matter. The evaporation of moisture to steam takes approximately 1100 Btu/lb of moisture. Once moisture has been evaporated, heat is absorbed by the fuel particles thus driving off volatile matter. The volatile matter burns in a secondary combustion reaction within the furnace chamber, but external to the actual wood fiber. Finally, the fixed carbon of the wood burns in the primary combustion reaction in conjunction with combustion air. 

Another furnace that does not require fuel preparation is the stoker boiler, which was used by New York State Electric Gas Corporation (NYSEG) in its TDE tests. At NYSEG, the stoker boiler, which has a 1649°C (3000°E) flame temperature (as does the cyclone boiler), has routinely blended low quaUty coal, and more recently, wood chips with its standard coal to reduce fuel costs and improve combustion efficiency. In the tire-chip tests, NYSEG burned approximately 1100 t of tire chips (smaller than 5x5 cm) mixed with coal and monitored the emissions. The company determined that the emissions were similar to those from burning coal alone. In a second test-bum of 1900 t of TDE, magnetic separation equipment removed metal from the resulting ash, so that it could be recycled as a winter traction agent for roadways. 

Continuous production ol charcoal is typically performed in multiple hearth furnaces, as illustrated in the Herreshoff patent shown in Figure 2. Raw material is carried by a screw conveyor to the uppermost of a series of hearths, /kir is supplied counter-currently and burns some of the wood to supply process heat. As the layers of wood carbonize, they are transported to the lower (hotter) hearths by rakes. The hot charcoal product is discharged onto a conveyor belt and cooled with a water spray. 

Rogers experimental work [2] deals with the combustion of a fuel bed in a batch reactor (pot furnace). Rogers primary objective was to study the effect of the primary air rates (underfire air) on the burning and ignition rates of wood fuel. 

Simmons W.W. and Ragland W.K., Burning Rate of Millimeter Sized Wood Particles in a Furnace , Combust. Sci. and Tech. 46, 1-15(1986). 

---