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PROCESSES AT MEDIUM AND HIGH TEMPERATURES 169 operation of the MBE and the slurried alkali treater, and other operational features. Sodium phosphite formed in the MBE is probably not stable and is possibly accompanied by phosphine formation. It would have to be oxidized further. Similarly, the sulfide formed from destruction of mustard gas would require further oxidation for stability. Propellants and explosives would present special problems because of their reactivity. Related test work would be needed. In addition, heat and material balance information would be helpful. HIGH-TEMPERATURE, LOW-PRESSURE OXIDATION Catalytic Fluidized-Bed Oxidation Technology description. Catalytic fluidized-bed oxidation uses a fluidized, granular solid as a heat transfer medium; for chemical agent destruction, the solids of choice would be aluminum oxide (alumina) or calcium oxide. The material is kept in suspension by the gas flow, which is primarily air. A wide range of gas velocities has been used. A velocity of 1.5 m/s will produce a dense-phase bubbling fluid bed (e.g., as in test work at Picatinny Arsenal; Liota and Santos, 1978); much higher velocities, of 10 m/s or higher, lead to highly loaded dilute phase beds (e.g., as in the Circulating Bed Combustor of Ogden Environmental Services). High gas velocity can also be used in a spouted bed, depending on the configuration and method of gas injection. The beds act as well-mixed reactors with high thermal inertia. Fuel can be liquid, solid, and gaseous. Temperatures are kept relatively low, at roughly 800 to 1000°C (1470 to 1830°F), reducing potential emissions of NOx, dioxins, and CO. The exhaust from the reaction chamber is passed through a hot cyclone and the solids are circulated back to the reaction chamber. The gas would be treated further as necessary, possibly by a catalytic afterburner and a packed bed scrubber for removal of acid gases. For the destruction of explosives, the formation of NOx could be minimized by operating the bed in a staged mode into which is fed 63 percent of the air theoretically needed to oxidize an aqueous slurry of 15 to 25 percent TNT. An additional 59 percent of the air theoretically needed is fed in a secondary stage in the zone immediately below the disengaging section from the fluidized solids. With the addition in the TNT slurry of nickel equivalent by weight to 6 percent of the total fluidized solid, emissions of NOx have been kept to about 60 ppm, unburned hydrocarbons to about 10 ppm, and CO to 4 ppm. The addition of nickel to the fluid bed solids would add a possible carcinogenic hazard; extra care would be needed to handle solids and to capture dust from the bed.
PROCESSES AT MEDIUM AND HIGH TEMPERATURES 170 Development status. A catalytic fluidized bed incinerator was operated at Picatinny Arsenal for about 1 year. The unit was 2.44 m (8 ft) in diameter and 9.14 m (30 ft) high with a charge of 10,000 kg of alumina. Runs were made at 165 kg/h of 25 percent TNT slurry. Liota and Santos (1978) provided a very favorable evaluation of the technology. However, the technology was not adopted by the Army. Related technology has been demonstrated for the Environmental Protection Agency (e.g., the circulating bed combustor). Fluidized-bed applications are widely used in the petroleum industry, and fluidized-bed combustion is used in the utility industry and for waste disposal. Application to chemical weapons destruction. Slurries of organic materials of up to 25 percent in water have been successfully destroyed in a commercial size unit. To achieve high levels of destruction with a fluidized bed, an afterburner will be needed to complete the destructive process. Fluidized-bed equipment can be used to treat both hydrolysis products and energetics. Solids up to approximately 1 inch diameter can be handled offering the potential for dealing with shredded dunnage and metal parts. By-products and waste streams. A fluidized-bed oxidizer operating with a bed of alumina would yield products similar to those of baseline incineration. When the bed is lime or dolomite, a large fraction of the acidic components (HCl, HF, and SO2) axe be removed. This variation has not been tested by the Army. Advantages and disadvantages. Fluidized-bed oxidizers have many similarities to conventional rotary kiln incinerators. They have the following major advantages: ⢠Operating temperature is low enough to avoid formation of some undesirable products, such as NOx or dioxins. ⢠High thermal inertia of the bed avoids the flame-out and bypass of agent. ⢠Mixing also avoids a major combustion puff. ⢠High water content and small particle size in a slurry mitigate the concern for an explosion when feeding propellants or explosives. ⢠With a preheated bed, the unit allows rapid startup and shutdown of the feed stream. There are several disadvantages of fluidized-bed oxidation: ⢠Nickel on the fluidized-bed particles will lead to a disposal problem. The nickel will have to be recovered before solids disposal.
