effectively removing them from the environment. Volatile metals from electrodes or feed stock will need remediation. A great deal remains to be done in characterizing plasma arc products, but there is hope of environmental advantage.

The high temperatures of the plasma arc ensure that the reactions are very fast, and this allows for short residence times of materials being pyrolyzed. On this basis, the plasma arc processor might be made smaller than an incinerator with comparable throughput. The downside of the comparison with the incinerator is the required power source for the plasma arc machine. The Navy (Alig, 1995) has a demonstration program under way with the space and weight parameters shown in Table 4.1. Data for a large incinerator are included for comparison.

Table 4.1 Plasma Arc and Incinerators for 1,000 lb/h Thermal Destruction

 

NAVY DEMONSTRATION

COMMERCIAL SYSTEM

INCINERATOR

Weight

63 tons (1)

93 tons (1)

70 tons (2)

Volume

12,000 ft3(2)

22,000 ft3(1)

3,200 ft3(2)

Availability

2010 perhaps

Now

Now

1  From Navy briefings.

2  From vendor information. Another vendor offers 65 tons and 4,100 ft3.

Thus, to match the size economy of current incinerators, plasma arc methods must achieve significant further size reductions. Note that the Diesel generator alone weighs 25 tons and consumes 1,700 ft3 of space. Diesel is a mature technology, and significant reduction of volume and weight is unlikely. Both incinerators and plasma arc machines need auxiliary apparatus, e.g., shredders, automatic feed, and ash or slag handling gear.

Vitrification

Vitrification is closely related to plasma arc. Waste is heated to about 3,000ºF by electrical current or by contacting an electrical discharge with the material to be destroyed. Organic materials are destroyed by pyrolysis and the products burned in an afterburner. A key feature of this technology is that inorganics are melted so that a liquid pool is formed at the bottom of the treatment chamber. When this melt is cooled, a vitreous solid mass is formed and elements contained therein are nonleachable by ground water. This is valuable when the waste is hazardous (specifically, radioactive), but the advantage for shipboard waste destruction is not so clear.

Battelle Pacific Northwest Laboratories (Chapman, 1994; Surma, 1995) has extensive experience in research, development, and application of this technique to management of radioactive and other hazardous wastes. The technology has been successfully tested on medical wastes at a nominal throughput of 25 tons/day. Shipboard waste on the largest ships in the Navy amounts to about 10 tons/day. Commercial interests are planning a demonstration plant to treat municipal wastes, which are similar in composition to shipboard wastes. A Navy contract is being negotiated for a demonstration plant to handle Navy waste including hazardous materials. With suitable modifications, vitrification can probably be employed to destroy black water sludge.

This technology is viewed as sufficiently advanced that major research is not required. Normal engineering and testing work remains for shipboard waste destruction applications. Flux addition may be necessary to obtain a stable glass. Proponents of the method see no major hurdles in applying vitrification to shipboard solid wastes.



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