ncineration is a widely applicable method of hazardous. waste treatment. It is relatively simple, inexpensive, and is firmly I established in the field of waste management. Yet recent scientific evidence has brought into question the safety of conventional thermal treatment operations (Eduljee, 1995). A major point of contentioii is the toxicological hazard of organic pollutants released by incinerators, including compounds of the polychlorinated dibenzo dioxin and furan classes (Harrison, 1996). The public has shown growing concern over the impacts of incineration facilities on human health and the enviroinment.These factors, combined with increasingly strict environmental regulations, have prompted interest in the development of alternative waste treatment methods.The limitations of conventional incineration relate to the properties of fuel combustion environments. Thermodynamic and stoichicimetric constraints on the temperature and oxygen concentration around a flame limit the rate of oxidation reactions. Incomplete combustion of persistent organic contaminants (e.g ., halogenated aromatic hydrocarbons, PCBs, etc.) is largely responsible for the formation of toxic by-products such as dioxins and furans (Harrad, 1996;Williams, 1995).Variability in the waste composition also contributes to the problem. Incinerators have a high thermal inertia and cannot respond rapidly to changes in feed composition. The cost-eff iciency of incineration processes is notably low when a small fraction of contaminant i s nonhomogeneously dispersed in a large matrix, such as in contaminated soil.A typical incineration system comprises two thermal treatment stages.The primary stag.e is usually a rotary kiln through which solids and sludge travel over several minutes. The temperature is adjusted to allow complete volatilization and/or combustion of the organic fraction of the waste. An ashy solid residue is collected at the exit while the gas stream proceeds to a high-temperature secondary chamber (afterburner). The purpose of the afterburner is to promote complete combustion by providing supplemental fuel and air. Heat transfer rates are crucial in the operation of this unit, where the residence time is of the order of seconds. Liquid organic waste may be introduced at this stage (Brunner, 1996). Thermal plasmas are a potential alternative to combustion heat sources. The characteristic properties of atmospheric-pressure plasmasintense power dissipation, molecular dissociation and ionization -createThe use of a thermal plasma afterburner in hazardous waste incineration could prevent the formation of toxic organochlorine pollutants. The present work demonstrated cost-optimal adaptive operation of a laboratory model system composed of an induction plasma jet with optical emission diagnostic tools. Input settings (plasma power and oxygen content) were continually adjusted in response to on-line spectroscopic analysis of the product gas. This adaptive strategy allowed cost-effective destruction of organic contaminants under a variable fee...

This paper reports on a simple analytical procedure used to demonstrate the technical feasibility of adaptive plasma-assisted incineration. APAI is a novel concept that addresses current difficulties in the treatment of hazardous organic waste. It features continual optimization of a plasma afterburner's operating conditions for cost-effective destruction of persistent contaminants under variable feed loads. Hence, on-line composition monitoring is a key element of the process. A diagnostic method was specifically developed for an experimental model system that required optical measurements from the jet of a 25–kW induction plasma torch. The method used photodiode array detection of visible emission from the Swan band system of C2 to track the destruction of organic compounds. This rapid, simple, and inexpensive procedure proved adequate for demonstration purposes.

This work assesses the techno‐economic potential of using an adaptive d.c. thermal plasma afterburner in hazardous waste incineration. Preliminary cost estimates were developed for soil incineration, soil desorption and liquid waste incineration. In general, the annual operating costs of plasma‐assisted processes (including depreciation of capital) exceed the costs of fuel combustion processes by 50%. However, a qualitative examination of environmental, legal and technical factors suggests that plasma treatment offers significant benefits in terms of effectiveness, safety and regulatory compliance.