The chemical weapons program of the U.S. military has lead to the production of thousands of tons of hazardous chemical warfare munitions. At the present time many of these weapons are being decommissioned by disassembly and destruction. Incineration has been approved for destruction of the chemical warfare agents, but concerns about generation of harmful byproducts has lead to reexamination of the wisdom of incineration.
In addition to destruction of chemical warfare agents, associated wastes such as wood pallets, demilitarization protection ensemble (DPE) suits, contaminated activated carbon and miscellaneous wastes (cardboard, plastics, metals), collectively, “dunnage,” must be decontaminated. Under U.S. Army regulations, solid waste potentially contaminated with chemical warfare agents must undergo “5x” treatment. Treatment of waste materials to 5x has been determined to result in solids free of chemical warfare agents and which are safe for handling by the general public. 5x treatment requires solids to be heated to at least 1000° F. for at least 15 minutes.
Unfortunately, many of the chemical warfare agents contain chlorine atoms. In addition, the dunnage may be contaminated with chlorine atoms. For example, the DPE suits comprise chlorinated organic polymers. Other dunnage wastes may be contaminated with chlorinated organic compounds, for example pentachlorophenol which is used for insect resistance and polychlorinated bi-phenol (PCB) compounds, both of which are toxic. Heating of the dunnage and chemical warfare agents containing chlorinated hydrocarbons in the presence of oxygen at temperatures between 400-800° F. has been found to result in the production of harmful dioxins and furans.
Several attempts have been made in the prior art to eliminate the production of harmful furans and dioxins during cracking or destruction of hydrocarbons in the presence of chlorine by removing chlorine atoms before high temperature incineration. For example, Zevenhoven and Saeed, Two-Stage Combustion of High-PVC Solid Waste with HCl Recovery, Proceedings of R′2000 World Congress on Recovery, Recycling, Reintegration, Toronto, Canada, Jun. 5-9, 2000, pp. 1212-1217 (HTTP:www.rrr2000.com)—discloses a waste to energy process based on high-PVC solid wastes that includes a two-stage combustion of high-PVC solid waste with hydrochloric acid recovery. In a first step, the PVC fraction is heated between 200-400° C. (396-750° F.) in the presence of an inert gas (nitrogen) in an attempt to remove chlorine from residual solids. The chlorine is removed in the form of a high temperature HCL gas. In a second stage the solids are incinerated in an oxidizing environment. Zevenhoven and Saeed teach that the removal of the chlorine before incineration limits dioxin/furan formation and removal of the hot HCL gas from the incineration minimizes corrosion. While Zevenhoven and Saeed teach the use of pyrolysis to remove chlorine molecules from the residual solids, they teach this removal in the range of 200-400° C., which is an optimum temperature range for the formation of harmful furans and dioxins. Thus, heating in this temperature range actually increase the chances of dioxin formation. Subsequent incineration in the presence of oxygen further enhances the opportunity for the formation of dioxins and furans from any chlorine molecules that were not successfully removed in the first stage.
In a like manner Kneko et al., U.S. Pat. No. 6,178,899, teaches the desirability of limiting a supply of oxygen during pyrolysis of chlorine containing solids so as to minimize the risk of formation of dioxins and furans. After a pyrolysis step the waste is subject to cracking in the presence of oxygen in a temperature range of 1000-1200° C. Kneko is silent with respect to the temperature at which the pyrolysis is conducted. As with Zevenhoven and Saeed, if this pyrolysis is done at temperatures over 400° F., a risk of dioxin formation remains notwithstanding the absence of oxygen.
With the prior art recognized that heating chlorinating organics in the absence of oxygen can remove chlorine compounds while minimizing production of undesirable dioxins and furans, the teachings of the prior art still run the risk of dioxin and furan formation from oxygen released from the heated hydrocarbons combining with chlorine molecules at a temperature suitable for dioxin and furan formation to yield undesirable dioxins and furans. Another problem faced by prior art treatments for decontaminating chemical warfare munitions is validating treatment of the solids under the 5x conditions, i.e., heating to at least 1000° F. for at least 15 minutes. Their problem results because solid wastes entering the unit can potentially pass through the unit at a rate faster than that predicted, causing an unacceptably short exposure times.