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APPLICATION OF ALTERNATIVE TECHNOLOGIES TO THE DESTRUCTION OF THE U.S. CHEMICAL WEAPONS 194 STOCKPILE analysis and the need to establish the absence of even very small amounts of residual agent and other toxic organic materials may still require that the waste salts be heated to the 5X criterion. Equipment for drying and heating waste salts would be required. Even so, the presence of fluoride and small amounts of heavy metals will generally result in this waste stream being classified as hazardous. Gas Waste Streams Because of their relatively large volumes, gas waste streams from common industrial oxidation processes are generally not stored before release. Instead, reliance is generally placed, as in the baseline technology, on chemical analysis of the leaving gas stream and on process control to verify that it meets all health-related requirements. However, the high toxicity of chemical warfare agents calls for special care in avoiding small transient emissions (puffs). Even with the careful design and operation of destruction processes, off-design conditions can occur. The current baseline system uses an afterburner to guard against agent puffs that might emerge from the primary combustion system. An additional precaution that could be used by the baseline system is the capture of gas emissions resulting from off-design operation until chemical analyses have been completed and needed corrective measures taken. There are three major options for managing such potential off-design agent emissions in chemical demilitarization: ⢠capture of transient puffs by activated-carbon adsorption; ⢠gas storage for time sufficient to allow chemical analysis and certification before release (gas of unsatisfactory purity would be recycled to an afterburner); and ⢠drastic reduction of waste gas stream volume by using oxygen and capturing CO2 with lime to form CaCO3 (a small amount of nitrogen from air leakage into the system and from the nitrogen in energetics and in VX will require treatment and discharge to the atmosphere). Any remaining waste gas stream could be stored and tested or purified by activated-carbon adsorption. Activated-carbon adsorption. Activated-carbon (charcoal) adsorption can remove extremely low concentrations of organic compounds. Activated carbon is the adsorbent used in gas masks. Because the organic compounds are stored on the charcoal, a series of charcoal beds is used and performance is monitored by analysis of the gas between beds. When the first bed is saturated, unadsorbed organic materials break through and are captured on the next bed. The saturated activated carbon must be removed and discarded
APPLICATION OF ALTERNATIVE TECHNOLOGIES TO THE DESTRUCTION OF THE U.S. CHEMICAL WEAPONS 195 STOCKPILE or detoxified (probably in the facilities used for metal detoxification), and discarded. This approach is best used for removing very small mounts of organic compounds, as for protection from transient puffs. Carbon adsorption beds are part of current Army designs to treat potentially contaminated ventilation air. In May 1992, the NRC sponsored a workshop that led to a recommendation that the Army consider using activated-carbon adsorption for chemical disposal facilities located in populated areas (NRC, 1993). Its use in treating waste gas from agent destruction is currently under study by the Army as is the use of the gas storage facilities discussed below. Gas storage and certification. For large-scale combustion operations, storage of waste gas before analysis and release generally requires a storage volume too large for gas holders to be economically viable. However, the smaller scale of chemical stockpile disposal facilities makes the gas holder a potentially practical option for ensuring that the waste gas meets environmental and health-related standards. A system of four gas holders could be used to store the gaseous effluents of any disposal process, including the current baseline technology. As one gas holder is filled, a second could be analyzed, a third could be emptied, and a fourth could be linked in as a spare at any juncture. Required gas holder volume varies over a wide range depending on cycle time and gas flow rate. The example presented in Chapter 5 estimates needed gas holder volume at 92,000 cubic feet for 8 hours storage, using air for internal firing, for oxidation of 100 pounds of GB per hour. The diameter of such a gas holder would be about 35 feet. Industrial atmospheric pressure gas holders that have been used for many years have storage volumes of several million cubic feet. Use of oxygen instead of air for oxidation would reduce needed storage volume to one-seventh the volume required for air. Capture of CO2 as solid carbonate could further reduce waste gas volume to that of air leakage and unused oxygen. Flue gas from fuel combustion (for internal firing) would increase gas volume. Either a gas storage system or a system of charcoal scrubbers can be designed to capture and hold pulses of agent that might be released by an accident or malfunction during disassembly of a munition or destruction of agent. Either approach can also handle lower amounts of contamination that might result from off-design operation. Facilities for storage, chemical analysis, and certification of the quality of the waste gas stream can convert all technologies for treating agent and weapon parts to a closed-loop system so that gases are not released to the environment until chemical analysis has demonstrated their satisfactory composition.
