K
Additional Data and Material Balances for Wet Air Oxidation, Supercritical Water Oxidation, and the Synthetica Detoxifier

WET AIR OXIDATION

An approximate material balance has been calculated with estimates for the size of equipment and the product streams.

The numbers are based on the following:

  • feed: 1,000 kg of GB;

  • oxygen: 25 percent excess over theoretical;

  • enriched air: O2/N2 = 1/1;

  • NaOH added to produce a 3 M solution after reaction (this large an excess of NaOH may not be needed.);

  • 20 percent of C-H in the feed is left as sodium acetate; and

  • the CO2 content of the gas is an estimate and is not based on equilibrium with liquid.

Feed:

GB:

1,000 kg (7.14 kg mol)

Water:

19,000 (1056 kg mol)

NaOH:

4,770 (119.2 kg mol)

O2:

50.7 kg mol

N2:

50.7 kg mol

Gas phase:

O2:

16.0 percent by volume (dry basis)

N2:

81.7 percent by volume

CO2:

2.3 percent by volume

CO:

500 ppm



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OCR for page 279
Alternative Technologies for the Destruction of Chemical Agents and Munitions K Additional Data and Material Balances for Wet Air Oxidation, Supercritical Water Oxidation, and the Synthetica Detoxifier WET AIR OXIDATION An approximate material balance has been calculated with estimates for the size of equipment and the product streams. The numbers are based on the following: feed: 1,000 kg of GB; oxygen: 25 percent excess over theoretical; enriched air: O2/N2 = 1/1; NaOH added to produce a 3 M solution after reaction (this large an excess of NaOH may not be needed.); 20 percent of C-H in the feed is left as sodium acetate; and the CO2 content of the gas is an estimate and is not based on equilibrium with liquid. Feed: • GB: 1,000 kg (7.14 kg mol) • Water: 19,000 (1056 kg mol) • NaOH: 4,770 (119.2 kg mol) • O2: 50.7 kg mol • N2: 50.7 kg mol Gas phase: • O2: 16.0 percent by volume (dry basis) • N2: 81.7 percent by volume • CO2: 2.3 percent by volume • CO: 500 ppm

OCR for page 279
Alternative Technologies for the Destruction of Chemical Agents and Munitions • Hydrocarbons: 500 ppm • Volume (dry basis): 62.1 kg tool   = 1.52 × 103 m3 @ P = 1 bar and T = 25°C • H2O in gas phase at reactor conditions kg mol Liquid phase: • H2O: 19,118 kg • NaF: 300 kg • Na3PO4: 1,171 kg • Na2CO3: 2,271 kg • CH3COONa: 234 kg • NaOH: 1.799 kg     24,893 kg Reactor volume (assuming feed = 1,000 kg GB/day, 0.5 V/h/V): 2.6 m3 (i.e., length = 7 m; diameter = 0.68 m) The calculations demonstrate that the volumes of material to be handled and the inorganic residue are many times greater than the volume of original agent to be destroyed. The calculations also demonstrate that it would be quite practical to operate as a closed system with material released from the process only after analysis. For example: basis: 1,000 kg GB/day; liquid holdup for 8 hours retention time = 8,300 kg (approximately 8 m3); and gas holdup for 8 hours retention, at 25°C and 60 bars (typical pressure): 8.4 m3 (dry basis). Holdup volumes of both liquid and gas for 8-hour retention times are modest. The compositions shown above will change under upset conditions. A low inlet temperature will quench the reaction, leading to little oxygen consumption and little organic destruction. A high inlet temperature will yield more complete oxidation to CO2 and H2O and possibly an undesirable temperature excursion.

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Alternative Technologies for the Destruction of Chemical Agents and Munitions Both conditions will lead to a shutdown. In the first case, the unreacted material is recycled to a feed tank. SUPERCRITICAL WATER OXIDATION Supercritical water oxidation has been applied experimentally a number of materials. (See Table K-1) Process Material Balance Estimated feed and product analyses and flow rates are shown below for destruction of 1,000 kg of GB. The case assumes a first-stage hydrolysis with NaOH followed by supercritical water oxidation of the hydrolysis product. Excess sodium hydroxide would be used in the hydrolysis reactor; this excess is then consumed in the oxidation reactor. The NaOH is limited, however, so that CO2 remains in the gas phase. (This is in contrast to the wet air oxidation case shown previously, where a large excess of NaOH was used for pH control and most of the CO2 ended up in solution as sodium carbonate.) Oxygen-enriched air (O2/N2 = 1:1) is assumed with 25 percent excess O2. The GB is 15 percent by weight of the feed solution. The over-all reaction assumed is Feed: GB: 1,000 kg   NaOH: 286 kg   H2O: 5.526 kg     6,812 kg

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Alternative Technologies for the Destruction of Chemical Agents and Munitions TABLE K-1 Chemicals Successfully Treated by Supercritical Water Oxidation and Typical Destruction Efficienciesa Organic Compound Bench Scale Pilot Scale Destruction Efficiencyb, % Acetic acid x     Acetylsalicylic acid (aspirin) x     Ammonia   x >99.71 Aroclors (PCBs) x x >99.995c Benzene x     Biphenyl x   99.97 Butanol x     Carbon tetrachloride   x >96.53c Carboxylic acids x     Carboxymethyl cellulose x     Cellulose x     Chlorinated dibenzo-p-dioxins x   >99.9999 Chlorobenzene   x   Chloroform   x > 98.83c 2-Chlorophenol   x > 99.997c o-Chlorotoluene x x >99.998c Cyanide   x   Cyclohexane x   99.97 DDT x   99.997 Decachlorobiphenyl x     Dextrose x   99.6 Dibenzofurans x     3, 5-Dibromo-N-cyclohexyl-N-methyltoluene-α, 2- diamine x     Dibutyl phosphate x     Dichloroacetic acid x     Dichloroanisole x     Dichlorobenzene x     4, 4'-Dichlorobiphenyl x   99.993 1, 2-Dichloroethylene x   99.99 Dichlorophenol x     Dimethyl sulfoxide   x   Dimethylformamide   x   4, 6-Dinitro-o-cresol x     2, 4-Dinitrotoluene x   99.9998

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Alternative Technologies for the Destruction of Chemical Agents and Munitions Organic Compound Bench Scale Pilot Scale Destruction Efficiencyb, % Dipyridamole x     Ethanol x     Ethyl acetate   x   Ethylene chlorohydrin x     Ethylene glycol x   >99.9998c Ethylenediamine tetraacetic acid x     Fluorescein x x >99.9992c Hexachlorobenzene x     Hexachlorocyclohexane x x >99.9993c Hexachlorocyclopentadiene x   99.99 Isooctane x     Isopropanol x x   Mercaptans x     Methanol x x   Methyl cellosolve x     Methylene chloride x x   Methyl ethyl ketone x   99.993 Nitrobenzene   x >99.998c 2-Nitrophenol x     4-Nitrophenol x     Nitrotoluene x     Octachlorostyrene x     Octadecanoic add magnesium salt x     Pentachlorobenzene x     Pentachlorobenzonitrile x     Pentachloropyridine x     Phenol x     Sodium hexanoate x     Sodium propionate x     Sucrose x     Tetrachlorobenzene x    

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Alternative Technologies for the Destruction of Chemical Agents and Munitions Organic Compound Bench Scale Pilot Scale Destruction Efficiencyb, % Tetrachloroethylene x x 99.99 Tetrapropylene H x     Toluene x     Tributyl phosphate x     Trichlorobenzenes x   99.99 1, 1, 1-Trichloroethane x x >99.99997c 1, 1, 2-Trichloroethane   x >99.981c Trichloroethylene x     Trichlorophenol x     Trifluoroacetic acid x     1, 3, 7-Trimethylxanthine x     Urea x     o-Xylene x   99.93 Complex Mixed Wastes/Products (Bench-Scale Tests) Adumbran Human waste Bacillus stearothermophilus (heat-resistant spores) Ion exchange resins (styrene-divinyl benzene) Bran cereal Malaria antigen Carbohydrates Olive oil Casein Paper Cellulosics Protein Coal Sewage sludge Coal waste Soybean plants Corn starch Sulfolobus acidocaldarius Diesel fuel Surfactants E. Coli Transformer oild Endotoxin (pyrogen) Yeast

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Alternative Technologies for the Destruction of Chemical Agents and Munitions Inorganic Compounds (Bench-Scale Tests)e Alumina Magnesium phosphate Ammonium chlorided Magnesium dulfate Ammonium sulfate Mercuric chloride Boric acid Potassium bicarbonated Bromides Potassium carbonated Calcium carbonated Potassium chlorided Calcium chlorided Potassium sulfated Calcium oxided Silica Calcium phosphated Sodium carbonated Calcium sulfated Sodium chlorided Fluorides Sodium hydroxided Heavy metal oxides Sodium nitrate Hydrochloric acidd Sodium nitrite Iron Sodium sulfated Iron oxided Sod Lithium sulfate Sulfur, elemental Magnesium oxide Titanium dioxide a Sources: Thomason et al. (1990), Thomason and Modell (1984), Modell (1985, 1989), and unpublished data from MODAR, Inc. b No entry for destruction efficiency indicates that a quantitative determination was not reported. c Compound undetectable in effluent; quoted efficiency is based on analytical detection limit. d Pilot-scale tests were also performed successfully. e Inorganic compounds were not destroyed but the process was operated successfully with those compounds present.

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Alternative Technologies for the Destruction of Chemical Agents and Munitions FIGURE K-1 Apparent first-order Arrhenius plot for oxidation of model compounds in supercritical water at 24.6 MPa. Source: Tester et al. (1991), Tester (1992).

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Alternative Technologies for the Destruction of Chemical Agents and Munitions Gas products: O2: 12 percent   N2: 59 percent   CO2: 29 percent   Volume = 2,400.5 m3 at 25°C, 1 atm. Liquid product: H2O: 81.4 percent by weight   NaF: 3.8 percent by weight   Na3PO4: 14.8 percent by weight   Mass = 1,106 kg   The product volumes are small enough to be easily retained long enough for analysis before discharge to the atmosphere. For example, for destruction of 1,000 kg GB/day and an 8-hour retention time of products: gas volume (eight hours) at P = 250 bars, 25°C: 3.2 m3; liquid (eight hours): 368 kg (about 0.368 m3); and upset conditions would lead to off-specification liquids, as well as possibly to off-specification gases. Provision for recycling would be required. A standard gas polishing unit, e.g., catalytic oxidation or carbon adsorption, would ensure gas quality before release. SYNTHETICA DETOXIFIER Heat and Material Balances Measured or design heat and material balances have not been disclosed. Estimates have been made, based in large part on operating conditions that have been presented: Temperatures in the moving bed evaporator (MBE): 1300°F (705°c) bottom 800°F (427°c) top Detoxification unit: T = 2400°F (1316°c) Adsorption beds: T = 350°F (177°c) Agent GB has been chosen for the calculated balances.

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Alternative Technologies for the Destruction of Chemical Agents and Munitions The reactions desired in the Moving Bed Evaporator (MBE) are steam reforming and acid gas neutralization. The precise alkaline agent has not been specified; NaOH is shown in the equation below for illustration only. Steam reforming: Neutralization: The overall reaction in the MBE is then the sum of these: The gas product shown is CO and H2. Excess H2O is required for the reaction, however, to reduce some stable hydrocarbons to very low concentrations, (e.g., methane, ethylene, benzoyl chloride). Additional steam will then lead to the water gas shift reaction to form CO2: Equilibrium for this reaction is favorable at the temperature of the MBE (800°F outlet). The equilibrium shifts at higher temperature, however, so that little CO2 should remain in the gas leaving the high-temperature detoxifier. Estimated heat and material balances are shown below (see Figure K-2). These values are based on estimates and assumptions that may not conform to ''Synthetica'' operating practice, but that practice has not been fully disclosed.

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Alternative Technologies for the Destruction of Chemical Agents and Munitions FIGURE K-2 Heat and material balances for the Synthetica System.

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Alternative Technologies for the Destruction of Chemical Agents and Munitions Basis: 1,000 kg GB destroyed. Gas composition to the MBE (assumed): CO: 16.7 percent H2: 33.3 percent H2O: 50 percent Solid balls fed to the top of the MBE: Alkali: 10 percent by weight of (assumed NaOH) Alumina: 90 percent by weight Temperature = 800°F (427°c) The unit could be operated as an enclosed system; the gas volumes to be held up would be substantial, however, because the unit operates at atmospheric pressure. The product gas going to catalytic oxidation is shown as 171.4 tool, at 177°C. Assuming an 8-hour hold-up (24-hour operation) and that the holdup gas would be cooled to 40°C, the hold-up volume requirement would be 1,600 m3. This would consist primarily of CO and H2; most of the water would have been condensed. The solid balls from the moving bed evaporator would mount to 4,830 kg over an 8-hour period (again assuming 24-hour operation). Electric power consumption in the detoxification reactor is large-estimated at 335 kW (24-hour operation). Some of the heat supplied is recovered in a series of heat exchangers. The heat requirement of the cold stream is much less than the heat content of the hot stream, however. Less than one-half of the hot stream enthalpy change is recovered; the rest is removed by addition of 100°C steam and by external cooling. The MBE requires heat; the reaction is endothermic, and the solid balls are heated in their passage through the unit. Sixty percent of the heat goes for heating the solids; 40 percent supplies the endothermic heat of reaction. The solids removed with the circulating balls consist of 1,356 kg of sodium fluoride and sodium phosphite together with a small amount of excess caustic. The sodium phosphite will require further oxidation to the phosphate for stability. The composition of the circulating gas is the product gas (CO/H2 ratio = 1/2) with 50 percent steam. The steam supply has been selected to be in 100 percent excess over the stoichiometric requirement. The product gas to the final catalytic oxidation unit has 50 percent steam as a

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Alternative Technologies for the Destruction of Chemical Agents and Munitions consequence. (If the circulating gas had been chosen to be primarily CO and H2 and steam had been limited to near stoichiometric, this product gas would have contained about 10 percent steam.) The excess steam will be useful, however, in mediating the temperature in the catalytic oxidation unit. This temperature must be kept low to avoid formation of NOx and to maintain catalytic activity. The oxidation temperature would be very high without the diluent steam. The flow rate of the circulating gas is calculated to be 50 m3/minute. A reasonable diameter for the moving bed evaporator would then be 1.9 m; the superficial gas velocity would be 0.3 m/second (i.e., 1 ft/second). The absorption beds would be expected to be about the same diameter, i.e., 1.9 m. No effort has been made to prepare a material and energy balance for propellant or explosive. It would be very different. Their decomposition would be highly exothermic, and the electric power requirement of the detoxification reactor would be greatly reduced. Little acid gas would be formed, and solid salt formation would be negligible.