Dioxins/furans from waste combustion

Polyvinyl chloride (PVC) is a common plastic that can produce dioxins and furans when burned. PVC is often present in municipal waste in large amounts, and is believed to contribute to the dioxins and furans from incinerators. Many sources of combustion produce dioxins and furans. Incinerators, both municipal and industrial, are significant sources dioxins and furans have been found in incinerator ash and in gases and tiny particles escaping through smokestacks. Power plants, smelters, steel mills, oil and wood stoves, and furnaces all emit dioxins and furans. 

Two different technologies seem to be the most promising alternatives to reduce gaseous PAH emissions catalytic PAH destruction [6, 7] and PAH adsorption on carbonaceous materials [8, 9]. Historically, carbonaceous materials have been used for the removal of vapor phase organic compounds from about 100 ppmv to 10,000 ppmv concentrations in industrial waste gas streams [10]. Recently, it has been shown that dioxins, furans and PAH, at ppbv or lower coneentrations, can be effectively removed from waste incinerator combustion gases by using carbon injection or carbon bed technology [11]. 

The composition of the exhaust depends on the type and composition of the fuel and on combustion conditions. The main components are O2 (0-15%), CO2 (3-12%), H2O (6-18%) and N2. Typical ranges of air pollutants from the combustion of natural gas, oil and coal are shown in Table I. In addition to NOx, commonly encountered pollutants include carbon monoxide (CO), hydrocarbons or Volatile Organic Compounds (VOCs), sulfur oxides (SOx) and particulates. Municipal Solid Waste (MSW) incinerator or waste-to-energy plant exhausts may also contain acid gases (e.g., HCl, HF), dioxins, furans and trace amounts of toxic metals such as mercury, cadmium and lead. 

Experimental and theoretical studies are presented from a laboratory-scale thermal destruction facility on the destructive behavior of surrogate plastic and nonplastic solid wastes. The nonplastic waste was cellulosic while the plastic waste contained compounds such as polyethylene, polyvinyl chloride, polystyrene, polypropylene, nylon, rubber, and polyurethane or any of their desired mixtures. A series of combustion tests was performed with samples containing varying composition of plastic and nonplastic. Experimental results are presented on combustion parameters (CO, excess air, residence time) and toxic emissions (dioxin, furan, metals). 

Dioxins and furans Formation mechanisms from solid waste combustion... 

Hansen, E., D.W. Pershing, A.F. Sarofim, M.P. Heap, and W.D. Owens. 1995, An Evaluation of Dioxin and Furan Emissions From a Cement Kiln Co-Firing Waste, Waste Combustion in Boilos and Industrial Furnaces, Air Waste Management Association. 

Several countries have introduced stringent emission limits (0.1 ng-TE/Nm ) for chlorinated dioxins and furans emitted from combustion sources, in particular solid waste incinerators, because of concerns over their adverse health effects. Technologies for reducing their formation and emission in incineration processes have been studied extensively and can be applied in modern incineration plants. Activated carbon injection and fabric filtration are currently practiced in many installations. However, to minimize capital cost, a more fundamental approach is needed to control and limit formation of these pollutants in incineration processes, e.g., involving the postcombustion zone, the combustion chamber, and waste feeding. ... 

However, despite all the progress being made, the uncontrolled production unavoidably leads to environmental problems such as climate change or emission of toxic products. For example, dioxins and furans are unintentionally formed and released from various sources like open burning of waste, thermal processes in the metallurgical industry, residential combustion sources, motor vehicles, particularly those burning leaded gasoline, fossil fuel-fired utility and industrial boilers, waste oil refineries etc... 

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