temperatures are high enough to break all chemical bounds, leading to extremely high DREs. Any downstream emissions are usually the result of recombination reactions rather than incomplete destruction.

This process is most advantageous for concentrated liquid and solid wastes. Dilute gaseous wastes place high demands on the energy inputs.

A potential advantage for both molten salt and molten metal technology is their application to wastes containing quantities of toxic metals. However, both technologies require extensive downstream particle control.

Molten Glass

This technology has been championed by Penberthy Eletromelt International, Seattle, Washington. It is based on charging waste (combustible or noncombustible) continuously to a pool of molten glass in an electric furnace. This approach is primarily attractive for ash-forming wastes; these ashes are melted into the glass, and the resulting composites are stable (resistant to leaching).

Although gaseous wastes do not contribute ash, the temperatures in these furnaces are sufficiently high (>2300°F) to achieve high DRE and low PIC levels. The residence time for the molten glass phase is long (hours), but the residence time for the gas phase is much shorter.

Plasma Systems

A plasma incinerator burns waste in a pressurized stream of preheated oxygen. Because temperatures can reach 5000°F, applying this technology to dilute streams is prohibitive. Such a system consists of a refractory-lined, water-cooled preheater, where a fuel is burned to heat oxygen to about 1800°F. This preheater is followed by the combustion chamber, where the waste and oxygen are mixed and auto-ignition occurs. From here, the gases pass into a residence chamber, where the destruction is completed at maximum temperature, followed by a quench chamber, a scrubber to remove acid gases, and a stack.

At plasma temperatures, the degree of dissociation of molecules is high, consequently reactivity increases; reaction rates are much higher than at normal incinerator temperatures. The high combustion efficiencies that are achievable lead to a compact design. High heat recovery is also possible. Thus, these systems lend themselves to a portable design.

Corona Destruction

The EPA has been researching VOC and air toxic destruction since 1988 (Nunez et al. 1993). This work features a fixed-bed packed with high dielectric-constant pellets, such as barium titanate, that are energized by an AC voltage applied through stainless steel plates at each end of the bed. The destruction efficiencies for VOCs such as benzene, cyclohexane, ethanol, hexane, hexene, methane, methylene chloride, methyl ethyl ketone, styrene, and toluene is predicted from the ionization potential and bond type for these compounds. The EPA studies did not report PICs; DREs ranged from 15% (methane) to ~100% (toluene) for concentrations of 50-250 ppmv. One advantage of this process is that it operates at ambient temperatures and appears not to be sensitive to poisoning by S and Cl compounds, as catalytic systems are.

A cost comparison with carbon adsorption and catalytic and thermal incineration is favorable. However, the results presented were based on a bench-scale system only; scaleup is clearly required for further engineering evaluation.

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