Overview: Hazardous Waste Combustion

What is Hazardous Waste? Definition of Hazardous Waste –Hazardous wastes are distinguished from other wastes by: their listing in waste statutes and regulations; or exhibiting hazardous properties. –US defines a waste as hazardous if it is ignitable, corrosive, reactive or toxic. –Mixtures of hazardous wastes with other wastes may also be considered hazardous. Composition of hazardous waste mixtures is often uncertain. Hazardous wastes are heterogeneous mixtures of organic substances, minerals, metals and water. Hazardous waste incineration is preformed to reduce volume and hazard in waste and to destroy hazardous waste formed during incineration.

Hazardous Waste Incinerator Processes Incineration processes include: material transfer/handling/storage, pretreatment, incineration/energy recovery, flue gas cleaning, solid residue management and wastewater treatment.

Types of Incinerators Variety of furnace types – –Rotary kilns – most commonly used –Grate incinerators with co-firing of wastes –Fluidized bed incinerators –Static incinerators Generally designed for full oxidative combustion with temp ranging from C to reduce air pollution

Rotary Kiln Incinerator

What are Sources of Dioxin Emissions from Incinerators? Solid residues: bottom ash, boiler ash, fly ash, slag, filter cake from wastewater treatment, gypsum, and air polishing residues Wastewater Air emissions are largest source of dioxins/furans released form incinerators. –Air emissions depend on the composition of waste, firing conditions, and the design and operating conditions of the flue gas treatment systems. –In fully oxidative incineration, flue gas emissions consist of: water vapor, N, CO2, and O2. Other pollutants include: acid gases (HCl, SO2,NOx), PM, VOCs, and volatile metals (eg, Hg). –DF emissions from incinerators using best available techniques range from –0.05 ng/ I-TEQ/ Nm3; (see Stubenvoll, Böhmer et al. 2002).

What are alternatives to incineration? Destruction of wastes by other methods – Gas phase chemical reduction –Base catalyzed decomposition –Sodium reduction –Supercritical water oxidation Landfills

How are air emissions reduced? Best Environmental Practices –Waste minimization Practices –Incinerator Operation Methods –Best Available Incineration Techniques Rotary kilns – can accept liquids, pastes and solid wastes; well designed for hazardous waste Water cooled kilns – can operate at higher temperatures and accept wastes with higher energy values Waste heat recovery boilers have the possibility of dioxin/furan reformation Improved waste consistency and combustion -shredding of drums and other packaged wastes. Feed equalization system (ex. screw conveyors that crush waste) - help ensure continuous controlled feed to kiln and maintenance of uniform combustion conditions.

How are air emissions reduced? Best Available Incineration Techniques Rotary kilns – can accept liquids, pastes and solid wastes; well designed for hazardous waste Water cooled kilns – can operate at higher temperatures and accept wastes with higher energy values Waste heat recovery boilers have the possibility of dioxin/furan reformation Waste consistency and combustion can be improved by the shredding of drums and other packaged wastes. A feed equalization system (ex. screw conveyors that crush waste) help to ensure continuous controlled feed to kiln and maintenance of uniform combustion conditions.

What Control Measures are Used? Activated carbon injection or carbon bed systems to control dioxin and furans PM - Many combustors use dry air pollution control systems (e.g., fabric filters, electrostatic precipitators) to limit the gas temperature at the inlet to the particulate matter control device to levels that help inhibit the formation reactions of dioxin and furans. For these control systems, dioxin and furans are formed on particles entrained in the control device by surface-catalyzed reactions where the PM provides the reaction surface. Should be operated at temp less than 200 C