Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
3 AEA SILVER 11 Technology Package INTRODUCTION AND OVERVIEW The technology provider team formed by AEA Technology, Inc., and CH2M HILL, Inc., has proposed a system based on the SILVER II chemical oxidation technology developed by AEA. (SILVER II is an elec- trochem~cal oxidation process that operates at relatively low temperatures t90°C; 194°F] and near atmospheric pressure.) A previous NRC committee evaluated the SILVER II technology for the destruction of chemical agents HD and VX stored in bulk (NRC, 1996a). This report evaluates SILVER II as part of a total system for destruction of the agents (HD, VX, and GB) and ener- getics in stored chemical munitions. The first stage of the total system uses the Army's existing baseline disassembly system. The output streams from the disassembly lines are either oxidized directly by SILVER II or are rendered ready for dis- posal. The technology provider proposes three sepa- rate SILVER II units: one for the destruction of chem~- cal agent, one for the destruction of energetics, and one for the destruction and/or decontamination of dunnage (also, small metal parts, decontamination solutions, and other mixed wastes). Large metal parts (i.e., munition bodies) are decontaminated using a combination of high-pressure jetting with recycled dilute nitric acid and thermal treatment in a heated decontamination chamber. Figure 3-1 shows an overview of AEA's package; Figure 3-2 shows a more detailed block flow diagram of the process. Table 3-1 summarizes how the AEA technology package accomplishes the six primary demilitarization operations listed in Chapter 1. \ Army \ disassembly system Silver 11 process Waste management Projectiles · Receipt Ton containers - a> · Disassembly · Segregation Bombs ~ Sprat Agent Energetics Metal parts Dunnage FIGURE 3-1 Overview of the AEA technology package. Source: AEA, 1997. 36 Destruction of: · agent · energetics · dunnage Decontamination of: · metal · DPE · carbon filters · Containment · Analysis · Treatment r Process chemical recycle _ Off-gas J Water/ nitric acid Inert solids disposal
/\ Q O ~ ~ T . . . . = CO ~ CO ~ E 03 s To Do, ce ~ X_ ~ m U) = .O > ~ ~ ID 03 ~ So LO ~ X - _ ~ [ t ~e, ,~.i~ ILImI~ U) ~ U) cO CO-A .m U)) ~ o I= ~ CO ~ Q Q CO ~ _ =~ ~ 03 0 C, ~D U) l CO t0 U~ ~ ~ E 1 1 1 1 | .o,, ~o ,,, g _ ~ N O 'U) == ~ 0 E m ° - E ~ ce ~ Q CO tD (D _ z oE 1-~ o u, .O u, ~ U) (D -O ~,= ~° E ° ~ =: ~ ,= ~ ce ~ ~QQ _ ~ cO cO E s~ y 3 1 LL ~ IL~ ~ ~ g E .m oJ .~ 0 - E cO-Q U)) ~ O CO ~ ~Q Q U) oS U, CD U, U, _ 37 ~/\ 3i ~ e-~= E t (~) ~ _1 CO Ce ~_ o r tDt cO ~ I (D _ ~ I ~ ~ ~ o 1 - ~ ~ Y ~ ~ 1, o 1 == U) (D I ~ CO .-~1 ~. C~ ~0 o V, S ~ O m Z~
38 ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS TABLE 3-1 Summary of the AEA/CH2M HILL Approach Major Demilitarization Operation Approach(es) Disassembly of munitions Modified version of Army's baseline disassembly method; processing of outputs from disassembly into pieces less than 1-inch in diameter; waterjet washout added; metal dissolution in nitric acid. Destruction using SILVER II electrochemical oxidation. Treatment of chemical agent Treatment of energetics Destruction using SILVER II electrochemical oxidation. Treatment of metal parts Heated in materials decontamination chamber to SX. Treatment of dunnage Destruction using SILVER II electrochemical oxidation. Disposal of waste Solids. Various solids from SILVER II process, caustic scrubber salts, and assorted dunnage (uncontaminated or SX) sent to permitted landfill; silver chloride sent off site for recovery of silver as silver nitrate; SX metal parts sent to a recycling facility. Liquids. Excess dilute nitric acid neutralized and released to local wastewater treatment facility; excess concentrated nitric acid sent off site for reuse. Gases. Off-gas from process treated in caustic scrubber, held and tested, and released to the atmosphere if the test results are acceptable. DESCRIPTION OF THE TECHNOLOGY PACKAGE SILVER 11 Process Chemist The SILVER II Process is based on the highly oxi- dizing nature of silver (II) (Ag(II)) ions in a nitric acid solution (Lehman) et al., 1996~. Ag(II) is one of the strongest oxidizing agents known; nitric acid also makes a significant contribution to the oxidizing pro- cess. In this process, a solution of silver nitrate in nitric acid is electrolyzed to produce the Ag(II) cation. The standard electrode potential of Ag(II) and other reac- tants involved in the process are given in Table 3-2. The standard half-cell reduction potentials are for all reactants and products having an activity of 1.0 M and all gases at 1.0 atmosphere and 25°C (77°F). For dilute concentrations (< 1.0 M), the activity can be approxi- mated by the molar concentration. Above 1.0 M, the activity will deviate progressively from the value of the concentration. Thus, the standard electrode potentials, E°, of the half-cell reactions for the desired electrolysis under standard conditions at 25°C (77°F) would be: Ag+ ~ Ag+2 + e~ E° = -1.98 V For an overall reaction: HNO3+2H++2e~ - HNO2+H2O E°= 0.94 V The overall reaction and standard potential for the electrolysis of the silver nitrate solution are therefore: 2Ag++HNO3+2H+ - 2 Ag+2 + HNO2 + H2O E°= -1.04 V The electrode potentials at other concentrations are given by the Nernst equation: E = E° + RT in(Q) where Q represents the standard expression for the Law of Mass Action, _ [Ag+2 ] [HNO2 ] [Ag+l][HNO3][H+]2 Also, T is the temperature in Kelvin, R is the universal gas constant, 3 is the Faraday constant (charge on one mole of electrons), and n is the number of electrons transferred in the reaction. The high concentration of nitric acid used in the SIL- VER II process prevents the electrolysis of water that would occur at a lower potential (-1.23 volts Ed]) than the electrolysis of silver nitrate in aqueous solution. For a simple 1.0 M silver nitrate solution, the follow- ing reactions would take place: 2H2O - O2+4H++4e~ E°=-1.23V HNO3 + 2 H+ + 2 e~ ~ HNO2 + H2O E° = 0.94 V 2 H2O + 2 HNO3 ~ O2+2HNO2+2H2O E°=-0.29v These standard electrode potentials are valid only at 25°C (298 K) and at unit activity of all reactants and products. However, the silver (II) process is normally
AEA SILVER II TECHNOLOGY PACKAGE TABLE 3-2 Standard Electrode Potentials of Reactions Related to the SILVER II Process. All Concentrations are 1.0 M Reaction E° (volts) Ag+2 ~ Ag+ + e O2 + 4H+ + 4e~ ~ 2H2O O2 + 4H+ (pH = 7) + 4e~ ~ 2H2O NO3~ + 4H+ + 3e~ - NO + 2H2O HNO3 + 2H+ + 2e~ ~ HNO~ + H^O Ag+ + e~ - Ag O2+2H2O+4e~~40H~ O2+2H2O+4e~~40H(pH=7) 2H+ + 2e~ ~ H2 2H2O+2e~ - H2+20H~(pH=7) 1.98 1.23 0.82 0.96 0.94 0.80 0.40 0.81 0.00 -0.42 carried out at about 90°C (194°F) and at 8.0 M HNO3. The potentials at this temperature and at these high concentrations of nitric acid are not well known. More- over, the reaction is aided by the formation of a brown complex, Ag(NO3~+, which lowers the required poten- tial for the oxidation of Ag+. The association constant for its formation is unknown. Although the electrochemistry for the conditions used is not known, there is no doubt that Ag(II) is formed and that it reacts only slowly with water to pro- duce intermediates, such as OH and other radicals. The Ag(II) formed in the electrolytic cells is then trans- ported into a reaction vessel. The generation of Ag(II) ions depends entirely on the electrical current to the cells, and it stops rapidly when the power is switched off. However, because Ag(II) is such a strong oxidiz- ing agent, it will corrode most metal systems that are not glass-lined or coated with a noble metal. Concen- trated nitric acid is also a strong oxidizing agent. In practice, an overvoltage must be applied for the reaction to proceed rapidly. The technology provider states that oxidation of the silver proceeds rapidly and 39 requires an overpotential of only 120 mV at 5 kA/m2. The technology provider intends to use 2.0 V. Ag(II) can oxidize all elements to their highest oxi- dation state if allowed to reach equilibrium. Thus, the following general theoretical reaction should occur: Organic + O2 ~ CO2 + inorganic salts/acids in water The NOX formed is converted to NO3-, but in prac- tice, am~nes (RNH2) are only converted to elemental nitrogen. Table 3-3 shows the reactions of Ag(II) with chem~- cal agents and energetic species and lists the number of electrons required. Table 3-4 shows the electrical energy requirements for the process in terms of energy per gram of material for a voltage of 2.0 V applied to the electrochemical cell. The technology provider claims that the total process will have 80 percent elec- trochemical efficiency (the fraction of current passing that produces useful oxidation to CO2~. The com- m~ttee's calculations in Table 3-4 agree with the tech- nology provider's claims. Sl LVER 11 Process Arrangement Figure 3-3 is a block flow diagram that shows a standard industrial electrochemical cell used in the SILVER II process. Ag(II) ions are generated by pass- ing an Ag(I) nitrate/nitric acid solution past a platinum anode. A sem~permeable membrane (to cations) sepa- rates the anode and cathode compartments of this cell, thus preventing buLk m~xing of the anolyte and catholyte solutions and allowing the transport of cations and water (but not anions) across the membrane. The cell is operated in the following configuration: packs of indi- vidual electrodes are connected in monopolar format (electrically in parallel), and the packs are then con- nected in bipolar format (electrically in series). The TABLE 3-3 Anode Reactions of Ag(II) with Chemical Agent and Energetic Materials Compound Reaction Number of Electrons GB H VX Comp B Tetryl TNT C4HloPFO2 + 10 H2O + 26Ag2+~4CO2 + H3PO4 + HF + 26H+ + 26Ag+ 26 C4H~SC12 + 12H2O + 28Ag2+ - 4CO2 + H2SO4 + 2C1- + 30H+ + 28 Ag+ 28 C~H26SNPO2 + 31H2O + 82Ag2+ ~ llCO2 + H3PO4 + H2SO4 + HNO3 +82H+ 82Ag+ 82 C4Hs 2N~ ~N'3 3Os 6 + 5.7H2O + lS.SAg+ ~ 4CO2 + l.lHNO3 + 1.65N2 + lS.SH+ + lS.SAg+ 15.5 C7HsN4N'O~ + 18H2O + 37 Ag2+ - 7CO2 + 4HNO3 + 0.5N2 + 37H+ +37Ag+ 37 C6H3N3O6 + lSH2O + 32Ag2+ - 6CO2 + 3HNO3 + 32 H+ + 32 Ag+ 32 -
40 ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS TABLE 3-4 Energy Required for the Destruction of Chemical Agents and Energetics Electrons Compound per Mole Molecular Mass Charge Required Energy (grams) (CouVmole) (kW-hr/mol) Moles Destroyed (per kW-hr) Mass Destroyed Grams Destroyed at (per kW-hr) 80% Efficiency GB 26 140.1 2,509,000 1.394 0.717 100.5 g 80.40 H 28 159.1 2,702,000 1.501 0.666 106.0 g 84.78 VX 82 267.4 7,913,000 4.396 0.227 60.8 g 48.66 Comp B 15.5 204.5 1,495,750 0.831 1.203 246.1 g 196.90 Tetryl 37 287.2 3,570,500 1.984 0.504 144.8 g 115.81 TNT 32 213.1 3,088,000 1.716 0.583 124.2 g 99.38 process liquids are fed to each cell in parallel via an external manifold, with each individual anode/cathode pair within the cell being fed in parallel by internal manifolds. The anolyte and catholyte solutions are cir- culated around separate closed loops between the cell and the anolyte and catholyte reaction vessels (see Fig- ure 3-3~. The organic-containing material is continu- ously metered into the anolyte tank to match the rate of destruction. According to the technology provider, Ag(II) ions generated at the anode of the electrochemical cell react with the water and nitric acid of the anolyte solution to form a range of other oxidizing radicals (OH, NOW. The Ag(II) ions and other oxidizing species then react with the organic material delivered into the anolyte vessel and are reduced to Ag(I) ions, nitrate ions, and water. The organic material itself is completely oxi- dized to carbon dioxide, oxides of nitrogen (NOx) and traces of carbon monoxide, protons (H+), and inorganic salts. No hydrogen is produced in the process. Off-gas from the reaction passes from the anolvte tank via a . ... .. . .. . . . caner tto condense nitric Accra vapors) to an NOX reformer. To balance the electrochemical reaction in the anolyte vessel, a cathode reaction reduces nitric acid to nitrous acid and water, while other reduction reactions generate NO2. The evolved gases pass from the catho- lyte tank to the NOx reformer. The overall process is operated at a temperature of 90°C ( 1 94°F) and at atmo- spheric pressure. During the electrochemical reaction, nitric acid is consumed in the catholyte circuit, and water is trans- ferred across the semipermeable membrane in the elec- trochemical cell from the anolyte to the catholyte. Some Ag(I) ions are also transferred across the cell membrane. In order to maintain steady-state operating conditions, proportions of the anolyte and catholyte circuits are bled to a nitric acid and silver recovery unit, which includes the previously mentioned NOx re- former. Here, a combination of evaporation and frac- tional distillation is used to recover the NOx as nitric acid and to generate streams for the return of (1) silver ions together with 16 M nitric acid to the anolyte cir- cuit and (2) 4 M nitric acid without any silver ions to the catholyte circuit. A dilute nitric acid stream is also produced, which is recycled within the plant and used to prepare organic materials before they are fed into the SILVER II process. After leaving the NOx reformer, all off-gas passes through a caustic scrubber to remove residual NOx. Treated gas from the scrubber is pumped into one of the two tanks of the hold-test-release system. The tanks have sufficient capacity to hold approximately 15 min- utes of generated off-gas at a nominal maximum pres- sure of 1 atm. When one tank is full, the second tank is switched on line, and the gas in the first tank is ana- lyzed. The gas entering each tank is continuously ana- lyzed for chemical agent vapor content by a standard system, such as the Army's automatic continuous air monitoring system (ACAMS). The proposed concept is to hold the gas and only release it to the atmosphere upon confirmation that it is free of chemical agent. During the development of the SILVER II process, its applicability to many different organic compounds (including explosives, propellants, rocket fuels, pyro- technics, and industrial solvents) was investigated. Disassembly of Munitions and the Removal of Agent/Energetics The transport, receipt, and pre-processing of muni- tions prior to processing with SILVER II are done
41 . ct E. w B 3~L Cal o G) ~0 ~ a== · ,, G) In Ct G) G) cn ~ == C,) G) O s cn ~ _ 1 o `, E O C.) ~1 _ Ct G) .Ba~k ~ ~ oC~ Lo ~ ~ Cod .~ ~ G.) .p Cal c,,- on T G) no G) Ct G) Cal ,, G) f 1 ~ ., ~ ~ G) L) =-_ once Ct o Ct · G) G) C13 s 1 ° ° { ~ 1 ~= Oreo Ad,, . r t ~ ~J to cn ~t ~ Ct ,, I_ G) ~ 1' Ct Cal · ~ Z , G) - o ~ G) ~ o G).cn - 5- Cal o C) o 5- V,
42 ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS using the Army baseline technology modified with ad- ditional material-handling stages at the end of the pro- cess. These stages reduce material size and segregate material for SILVER II processing. The baseline muni- tions disassembly process is described in Appendix C. Rocket Disassembly M55 rockets are sheared into six pieces to generate sections suitable for handling. The six pieces are dif- ferent from those obtained in the baseline process. Sub- sequently, a sheared-parts handling machine performs a number of operations on the sheared sections of the rockets in order to segregate materials for subsequent processing, either in SILVER II reactors or by other treatment technologies. The segregated outputs from the rocket disassembly include: drained chemical agent, as already provided by baseline disassembly a warhead fuze section warhead burster sections, which are further re- duced in size in a rocket shearer to small sections (< 1 inch) for subsequent processing agent warhead sections that have been drained of agent but are still agent contaminated a rocket motor section containing propellant - fiberglass dunnage consisting of shipping/firing tube pieces miscellaneous metal parts, including end caps components from the shipping/firing tubes, tail-fin sections from the rockets, and motor nozzle plates These individual parts are treated separately in subse- quent process units. Prior to treatment, the energetic material is separated from the associated casings. The propellant from M55 rocket motor sections is removed by high-pressure jetting with hot dilute nitric acid recycled from the SILVER II process. High-pressure jetting is directed from below to a vertically oriented rocket motor sec- tion, and the propellant is washed into a sump. The process is carried out in batches in an enclosed cham- ber and is remotely controlled. The remaining metal parts are visually examined for residual contamination, and parts found to contain residual contamination are recleaned. The energetic material that has been re- moved is then mixed with recycled dilute nitric acid to make up a 20 percent (by weight) energetic-in-water slurry. This material is transferred to a continuously stirred interim storage tank from which it is continu- ously fed to the energetics SILVER II reaction circuit. Burster charges and smaller energetic components are reduced in size by shearing to achieve a particle size of less than one inch in diameter. This material is then mixed with recycled dilute nitric acid and fed to the SILVER II reaction process. Whereas AEA origi- nally proposed storing the resultant energetic/metal/ water slurry in an interim storage tank, later discus- sions with the committee indicated that this material would be fed directly to the SILVER II reactor. Projecti/e/Mortar Disassembly Projectiles and mortars are disassembled using the Army's baseline systems without modifications. Burster charges and other energetic components are then reduced in size to less than one inch in diameter and fed to the SILVER II process. Land Mine Disassembly For M23 mines, the Army baseline disassembly sys- tem is used to punch and drain the agent and push out the burster charge. In addition to this baseline process- ing, the mines are sheared into four parts to open the radial initiator charge and expose the energetic Treatment of Chemical Agent The chemical agent drained from the various com- ponents is transferred to an interim storage tank where it is mixed and continually stirred with dilute nitric acid recycled from the SILVER II process. The dilute nitric acid provides the necessary water balance for the elec- trochemical oxidation reactions in the agent SILVER II reaction circuit. It also disperses the agent, thereby increasing the surface area/volume ratio of any gelled agent and provides partial destruction via hydrolysis of the chemical agent. The interim storage provides a buffer volume for the feed of materials to the SILVER II reactors. The design calls for interim storage capac- ity for up to 48 hours of SILVER II operation. The chemical agent/dilute acid mixture is fed continuously
AEA SILVER II TECHNOLOGY PACKAGE to the SILVER II reaction circuits for agent destruction during normal operation. A schematic drawing of the anolyte and catholyte circuits is shown in Figure 3-3. The anolyte circuit con- sists of a glass-lined anolyte vessel in which the re- agents and the agent solution are mixed to start oxida- tion. The vessel is maintained at 90°C (194°F) through the use of a thermal fluid circulating through a jacket surrounding the vessel. The agent material hydrolyzed by the dilute nitric acid is oxidized in the anolyte vessel by the Ag (II) ions, which are reduced to Ag (I) in the process. Carbon dioxide (CO2), oxygen (O2), carbon monoxide (CO), nitrous oxide (N2O), and water are generated in the anolyte vessel. According to the tech- nology provider, NOx is not evolved from the anolyte, but under certain conditions, excess NOx can be present. These gaseous products then flow to the NOx recovery system. The anolyte solution is circulated to the electrochemical cell where the Ag(II) ions are re- generated. Other reagents added to the anolyte vessel include calcium nitrate to precipitate CaSO4 and cal- cium fluoride, silver nitrate solution to maintain silver concentration (when chloride is present, silver chloride will precipitate), and nitric acid. A hydrocyclone be- tween the anolyte vessel and the electrochemical cell prevents solids from entering and potentially blocking the narrow passages in the cell. A continuous bleed of anolyte solution takes place at the hydrocyclone for recovery of silver chloride and nitric acid. The vented gases from the anolyte vessel are passed through a water/glycol-cooled condenser at 0°C (32°F) to condense nitric acid vapor, water vapor, and trace volatile organic compounds. The condensate is re- turned to the anolyte vessel, and the remaining off-gas is sent to the NOx reformer. The catholyte circuit also consists of a stirred glass- lined vessel from which the catholyte solution is circu- lated to the cathode side of the electrochemical cell. The catholyte vessel also has a thermal jacket to main- tain the temperature at 90°C (194°F). In the cathode side of the cell, nitric acid is reduced to nitrous acid, NOx, and water. The NOx is vented from the catholyte vessel to the NOx reformer. A slipstream of the catholyte solution is continuously bled to the silver and nitric Accra recovery system. A make-up input stream of dilute acid to the catholyte vessel maintains the neces- sary concentrations of nitric acid. 43 Treatment of Energetics A mix of sized-reduced propellant material and other energetics and dilute nitric acid is fed directly to a sepa- rate SILVER II reaction circuit via the anolyte vessel. This SILVER II process is similar to the process for treating agent slurries. Fuzes are treated separately from other energetic material. The fuzes are first pretreated in small batches in a reaction vessel with nitric acid, which has been obtained from spent anolyte and catholyte solutions from the SILVER II process for energetics. The tech- nology provider claims that the spent anolyte and catholyte solutions are rich in nitric acid, which at- tacks and completely dissolves the metal of the fuzes and neutralizes the energetics. The resultant liquid material is then evaporated and the dry salt ex- tracted. Sheared mine-body sections are treated in a manner similar to the fuzes, but the effluent from the reaction vessel is directed to the SILVER II cir- cuit for energetics. Treatment of Metal Parts After disassembly, munitions can still contain agent on internal surfaces and in the form of gelled heels. Therefore, metal parts associated with munition disas- sembly are oriented vertically and cleaned by high- pressure liquid jets of hot dilute nitric acid. This pro- cess is carried out remotely in batches in an enclosed chamber. In subsequent discussions, the technology provider indicated that some sort of agitated bed or submerged bath is under consideration as an alterna- tive to high-pressure liquid jetting. The metal parts are then decontaminated in batches inside a material decontamination chamber (MDC). The MDC is part of a sealed heat-treatment circuit and is used to treat batches of metal parts. Air circulates through the MDC, which is heated either electrically or inductively, and the off-gas is extracted, cooled to con- dense any trace agent liquid, and passed through an activated carbon filter prior to recycling back into the MDC. The condensate from the condensers is fed to the agent interim storage tank. The chamber operating temperature is in excess of 1,000°F (538°C), and the metal parts are maintained at this temperature for at least 15 minutes to ensure 5X decontamination.
44 Treatment of Dunnage ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS Both contaminated and agent-free dunnage are shredded, pulped, and mixed with recycled dilute nitric acid. This slurry is temporarily stored in a stirred stor- age tank. Other liquid secondary wastes, such as hy- draulic fluids and decontamination solutions, are mixed with this material. These slurry mixes are then fed into the SILVER II reaction circuit for dunnage. Other solid wastes, such as DPE suits and carbon filters, are also shredded and processed in batches. These materials are treated in the MDC similar to the way metal parts are treated. Process Instrumentation, Monitoring, and Control . The technology provider proposes holding and ana- lyzing gaseous and liquid effluents prior to release from the facility. Liquid streams (e.g., from the evaporator and NOx reformer) are first accumulated in holding tanks to allow sampling and analysis for the presence of agent prior to recycling or prior to shipment off site for disposal. The off-gases vented from the anolyte and catholyte vessels (after scrubbing) are accumulated in evacuated tanks. The tanks are filled to atmospheric pressure; each tank has the capacity to hold the gases produced during approximately 15 minutes of opera- tion. Multiple tanks are proposed to allow for continu- ous operation. As each tank is filled, the gas is sampled and analyzed for agent. If the gas is determined to be agent free, it is vented to the atmosphere. If the gas is determined to contain traces of agent, it is vented to the atmosphere through a dehumidifier and a multistage carbon bed. The following on-line chemical analyses are proposed: · anolyte off-gas composition using gas chromatog- raphy/thermal conducting detector · NOx concentration in off-gas streams · acidity (density and temperature for simple nitric acid/water mixtures) concentrations of chemical agent vapor using ACAMS or another certified analysis Feed Streams be liquids, and the particle size of suspended solids must be smaller than one inch. Suspended solids larger than this could require excessive reaction times in the anolyte vessel. These stringent requirements entail more physical processing of the munitions than is rou- tinely done in the Army's baseline disassembly sys- tem. In addition, materials that contain halogens will increase silver precipitation and necessitate more rapid changeout of reagents. Effluent Streams The process effluents and treatment/disposal strate gies proposed by the technology provider are listed in Table 3-5. The effluent streams include solids (such as agent-free dunnage and 3X decontaminated trash, DPE suits, metal parts, filter candles, and spent carbon), liquids (spent anolyte and catholyte solutions and ex cess nitric acid), and gases from anolyte and catholyte vessels. Liquid bleed streams from the anolyte and catholyte vessels are directed to a nitric acid evaporator in which water, nitrogen oxides, and some nitric acid are evapo rated. The vapors from the nitric acid evaporator are then passed to the NOx reformer. The evaporator bot toms, consisting of a silver nitrate/nitric acid solution, are returned to the anolyte circuit. The NOx reformer receives the vapor effluent from the nitric acid evapo rator and the off-gas streams from the anolyte and catholyte vessels. Pure oxygen is added to the reformer as a reagent. The reformer consists of a reactive distil lation column designed to generate nitric acid by react ing NOx, oxygen, and water. The nitric acid is accumu lated in holding tanks where it is sampled and analyzed for agent prior to recycling to the SILVER II process. From the top of the distillation column, gases consist ing primarily of CO2, CO, N2O, NOx and O2 are di rected through a packed-column caustic scrubber (sodium hydroxide/carbonate/nitrate solution). The scrubber liquor blow-down is accumulated, analyzed for chemical agent, and evaporated. The salts are dis charged as a solid waste. Part of the bottom product from the distillation column (a concentrated nitric acid stream) is recycled, and the remainder is prepared for off-site disposal. The net generation of nitric acid is The requirements for the feed streams to the SIL- attributed to the addition of the calcium nitrate and to VER II reaction circuits are stringent. The feeds must the nitrogen in the energetics.
AEA SILVER II TECHNOLOGY PACKAGE TABLE 3-5 The Process Effluents and Treatment/Disposal Strategies Proposed by AEA for the Silver (II) Process 45 Process Effluent Management Strategy Nonprocess-related inert dunnage Shipped off site for disposal at a hazardous-waste landfill after decontamination using standard (glass, plastic, metal band) decontamination solutions, followed by polishing in the material decontamination chamber. DPE suits Shipped off site for disposal at a hazardous-waste landfill after decontamination as a part of personnel egress procedures, followed by treatment in the material decontamination chamber. Spent carbon Shipped off site for disposal at a hazardous-waste landfill after treatment in the material decontamination chamber. Trash Shipped off site for disposal in a solid-waste landfill. Munition-related metal Decontamination by high-pressure washing followed by treatment in material decontamination chamber to SX. Decontamination solution treated in SILVER II Unit. Nonmunition miscellaneous metal Treatment in material decontamination chamber. Decontamination solution treated in SILVER II Unit. Anolyte solution Nitric acid and water recovered through an evaporator/condenser unit. Remaining solid mixture shipped off site for recovery of silver as silver nitrate. Ultimate disposal of waste from recycling at a hazardous-waste landfill. Catholyte solution Nitric acid from the catholyte solution recovered through an evaporator/condenser unit. Remaining solid material (mostly silver nitrate) shipped off site for recovery of the silver as silver nitrate. See anolyte solution above. Off-gas Treated by caustic scrubber and emitted to the atmosphere. Dilute (1% wt) nitric acid Dilute nitric acid recovered on site from NOx reformer; most reused in plant operations. Excess dilute nitric acid treated on site in a tank treatment system to neutralize it prior to discharge to the local publicly-owned treatment works. Nitrate removal may also be required. Concentrated (71% wt) nitric acid Concentrated nitric acid recovered on site from NOx reformer and reused in plant operations. Acid is generated during treatment of items containing nitrogen (e.g., energetics, mustard, and GB). Excess nitric acid reused off site. Calcium fluoride filter candles Solids from anolyte solution generated during treatment of GB shipped off site for disposal. Silver chloride and calcium Solids from anolyte solution generated during treatment of mustard shipped off site for recovery of silver as sulfate/filter candles silver nitrate. Silver chloride/filter candles Solids from anolyte solution generated during treatment of decontamination solution shipped off site for recovery of silver as silver nitrate. Caustic scrubber waste Dried salts from caustic scrubber shipped off site for disposal at a hazardous-waste landfill. Glass fibers captured on filter Treated in materials decontamination chamber and transported off site for disposal at a hazardous-waste candles landfill. Source: Adapted from AEA, 1997. Another effluent from the process consists of spent anolyte and catholyte solutions. The anolyte solution becomes saturated in metal ions and halogen salts from metal impurities and halogens in the agent. The spent anolyte and catholyte solutions are discharged into holding tanks, and after they are confirmed to be agent free, they are evaporated. The nitric acid and water are recycled, and the dry metal salts are sent off site for recovery of the silver. Wastes from silver recovery ul- timately require disposal in a hazardous-waste landfill. The MDC (material decontamination chamber) is used to desorb traces of agent thermally from a range of solid materials. Munitions-related metals are high-pressure washed and then treated in the MDC to a 5X decontamination level. Nonmunitions-related met- als are also treated to 5X in this chamber. The treated metals are then suitable for release to the public sector. Spent carbon is also treated in the MDC and then shipped off site to a hazardous-waste landfill. Other solid materials shipped to off-site hazardous-waste landfills are: the glass fiber filtrate captured on filter candles, decontaminated DPE suits, residues from off- site recycling of silver nitrate, calcium fluoride/calcium sulfate solids collected from anolyte solutions on filter candles, and dried salts from the caustic scrubber. AEA included a mass balance in the original
46 ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS TABLE 3-6 Process Inputs for SILVER II per 155-mm Projectile Description Total Flow (lb/munition) Details/Comments Organic feed Calcium nitrate Oxygen Sodium hydroxide TOTALa Contaminated metal parts 20.7 12.1 26.6 2.4 61.8 86 Liquid mustard feed to agent plant; solid burster feed to energetics plant; "chipped" wood feed to dunnage plant. Feed to anolyte vessel (dissolved in recycled water to produce the feed solution). Low-pressure gaseous feed. Feed to caustic scrubber (dissolved in recycled water to produce a 20 wt% solution feed to the scrubber). Metal parts not included because they are only decontaminated and not destroyed. Typically the munition casing, etc. aAssumes no net makeup of silver or nitric acid. Source: Adpated from AEA, 1997, and AEA, 1998b. proposal (AEA, 1997) and revisions in the subsequent data-gap report (AEA, 1998a). The technology pro- vider supplied the committee with additional informa- tion on the mass balances for an integrated facility con- sisting of three separate SILVER II units one each for the destruction of chemical agent, energetics, and dunnage. Tables 3-6 through 3-9 provide the process inputs and net (after recycling) outputs for 155-mm projectiles filled with mustard and M55 rockets filled with VX. These estimates assume that regeneration and recycling of spent anolyte and catholyte will be TABLE 3-7 Process Outputs for SILVER II per 155-mm Projectile conducted on site and, therefore, recycled acid will be reused. The precipitated silver chloride is assumed to be recycled off site to regenerate silver nitrate with an efficiency of 100 percent. The silver loss is projected by the technology provider to be less than 1 percent of the silver recycling rate. The technology provider was also asked to supply an estimate of the amount of silver anticipated to be inventoried for operations at Bluegrass and Pueblo, including the total amount of silver circulating in the process, being reprocessed, stored as reserve, and Description Total Flow (lb/munition) Details/Comments Nitric acid Calcium sulfate Water Sodium nitrate Sodium nitrite Carbon dioxide Nitrogen dioxide TOTAL Solid and liquida TOTAL Off-gas Decontaminated metal parts 14.3 9.9 8.8 2.6 2.2 27.3 0.4 37.8 27.7 86 Produced as both a concentrated and dilute acid stream (mass quoted is for pure acid and does not account for any water of solution, which is detailed separately). Solid precipitate removed. Produced from several sources from the plant (e.g., as dilute nitric acid) (mass quoted is for pure water). This mass of sodium nitrate will be contained in the caustic scrubber waste stream. Contained in the caustic scrubber waste stream. Off-gas from scrubber. Off-gas from scrubber. Decontaminated to SX standard. aSilver chloride is recycled as silver nitrate. Source: Adapted from AEA, 1997 and AEA, 1998b.
AEA SILVER II TECHNOLOGY PACKAGE TABLE 3-8 Process Inputs for SILVER II per M55 Rocket 47 Description Total Flow (lb/munition) Details/Comments Organic feed Nitric acid Oxygen Sodium hydroxide TOTALa 62.9 0.4 86.0 9.2 158.5 Contaminated metal parts 44.8 Liquid VX feed to agent plant; solid Comp B burster feed and grain propellant from water jetting to energetics plant; "chipped" wood and fiberglass feed to dunnage plant. Produced by destruction of agent and energetic; when wood is processed no nitric acid is generated; because one of the off-gas components is nitrogen, nitric acid must be added to maintain a constant "nitrogen" balance. Low pressure gaseous feed. Feed to caustic scrubber; dissolved in recycled water to produce a 20 wt% solution feed to the scrubber. aAssumes no net makeup of silver nitrate or nitric acid. Source: Adpated from AEA, 1997 and AEA, 1998b. maintained in any way for use in the process. The information supplied to the committee is included in Tables 3-10 and 3-11 for 155 mm projectiles filled with mustard and M55 rockets filled with VX, respectively. During the operation, the sources of silver-rich output streams are precipitated silver chloride (due to the pres- ence of chloride in the mustard gas) and silver nitrate sludge in the spent anolyte and catholyte solutions. TABLE 3-9 Process Outputs for SILVER II per M55 Rocket The technology provider has estimated that 52,000 pounds of silver will have to be inventoried at Pueblo and 8,000 pounds of silver at Blue Grass. This estimate is based on an assumption of a 10-day supply of stored silver nitrate. The silver requirement for Pueblo is much greater because of the increased production of silver chloride from treatment of larger amounts of mustard- filled weapons, from which there is continuous Description Total Flow (lb/munition) Details/Comments Phosphoric acida Sulfuric acida Lead nitrate Water Sodium nitrate Sodium nitrite Carbon dioxide Nitrogen dioxide TOTAL Solid and liquid Decontaminated metal parts 3.7 3.7 0.2 32.8 9.9 7.9 98.3 10.6 58.2 108.9 44.8 Produced as a result of VX destruction (mass quoted is for pure acid and does not account for any water of solution, which is detailed separately). As above. Small amounts produced as a result of destruction of the lead stearate in the propellant. Produced from several sources from the plant (e.g., as dilute nitric acid); mass quoted is for pure water. Contained in the caustic scrubber waste stream. Contained in the caustic scrubber waste stream. Off-gas from scrubber. Off-gas from scrubber. aProbably disposed of by conversion to calcium salts Source: Adapted from AEA, 1997 and AEA, 1998b.
48 ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS TABLE 3-10 Estimate of Spent Silver for Mustard-Filled 155-mm Projectiles Source Form Mass Per Munition Silver Content Silver from precipitation Silver chloride precipitate 21 lb of silver chloride 75% by weight Silver from spent anolyte Concentrated "sludge" 1.1 lb of silver nitrate contained 64% by weight and catholyte solutions following evaporation within the "sludge" Source: AEA, 1998b. precipitation of silver chloride from the chlorine in the mustard. At Pueblo, the technology provider estimates that the silver contained in the processing systems is 8,850 lb and that the flow rate of silver metal to the plant is 4,340 lb/day. At Blue Grass, the silver con- tained in the processing systems is only 2,040 lb, and the flow rate is 600 lb/day. Start-up and Shutdown Generation of Ag(II) ions depends entirely on the electrical current and stops immediately when the power is switched off. The technology provider claims that the ability to turn the process off rapidly by switch- ing off the electricity provides a safety benefit because it ensures that the reaction is easily controllable. Elec- trical power to the cell can be shut off at any time for example, from safety interlocks at other stages of the overall process. However, the committee notes that oxidation reactions will continue even without electric- ity until Ag(II) concentrations decline, and reactions with nitric acid will proceed even in the absence of electricity. EVALUATION OF TH E TECH NOLOGY PACKAG E Process Efficacy Effectiveness of Munitions Disassembly Although the munitions disassembly process Is based on the Army's baseline disassembly system, some significant differences and additions will require further development, particularly for disassembling rockets and mines. These differences are largely attrib- utable to the need (1) to segregate munition parts and components and treat them in separate SILVER II re- actors, and (2) to further reduce the size of components prior to treatment in SILVER II reactors. Solids must be reduced to a particle size of less than 1 inch in diam- eter to dissolve completely in nitric acid and to oxidize in a reasonable amount of time. The committee found significant barriers to implementing the additional pro- cessing because of the increased complexity of the mechanical processes and the need to ensure proper feed characteristics to the SILVER II reactors. The so- phisticated segregation, material-handling, and size- reduction processes will require either the development of robotics equipment or manual segregation in DPE suits. Manual segregation would be undesirable be- cause of the high hazard level and because performing lengthy work assignments in DPE suits is extremely uncomfortable. The added complexity of robotic equip- ment would require substantial development, which would certainly delay the overall development schedule. The technology provider indicates that visual inspec- tion would be used to determine whether residual ener- getic materials remained after wash out, but the com- mittee has reservations about determining residual contamination by visual inspection. . Effectiveness of Agent Destruction This process can be viewed as an oxidation of organic materials with Ag(II), with electrolytic regeneration of TABLE 3-11 Estimate of Spent Silver Sent for Recycling for VX-Filled M55 Rockets Source Form Mass Per Munition Silver Content Silver from spent anolyte and catholyte solutions Concentrated "sludge" following evaporation 4.2 lb of silver nitrate contained 64% by weight within the "sludge" Source: AEA, 1998b.
AEA SILVER II TECHNOLOGY PACKAGE the silver. Mustard contains volatile low molecular weight chlorinated hydrocarbons that are expected to be oxidized by Silver (II), but this will have to be dem- onstrated. The committee has identified three potential problems that could interfere with agent destruction in a full-scale system. Plugging of the Electrolytic Cell. A hydrocyclone is used in the anolyte circuit to prevent solids from enter- ing the SILVER II cell, but the committee believes that the hydrocyclone may not remove solids to the level necessary to prevent plugging of the electrolytic cell used to regenerate the Ag(II). The plugging can be caused by (1) solids in the agent-contaminated materi- als and (2) precipitates generated in the anolyte vessel that migrate from the vessel to the electrolytic cell. The recirculation stream leaves substantial amounts of sol- ids and precipitates in the anolyte vessel, and the elec- trolytic cell has very small flow channels that appear to be prone to plugging. Impact of Metals on Electrolytic Efficiency. Other metal ions may reduce the electrolytic efficiency of the desired reaction by migrating through the membrane and diminishing the current via useless reactions. The tests conducted to date have been on relatively pure organic chemicals that did not contain iron, copper, alu- minum, or other metals found in munitions. These met- als will all react vigorously with the nitric acid of the SILVER II reagent, causing very large quantities of metal ions to dissolve. The technology provider states that the added metal ions should not affect the reduc- tion/oxidation reactions that destroy the agent and en- ergetics; however, no data have been presented to show this. In fact, iron and other metals found in munitions can exist in many oxidation states. The complex mixture of many metals that will be present during SILVER II treatment of chemical munitions will make predicting the behavior of electrolytic solutions under reduction/oxidation conditions very difficult. Rapid Reaction with Organics. Rapid reactions of nitric acid with organics in the agent and energetic so- lutions could cause process upsets. Rapid reactions were observed by members of the ACW Committee during a bench-scale demonstration of the SILVER II process. That is, the acid by itself is a strong oxidizer, and in the absence of Ag(II) ions, it may initiate or 49 sustain strong exothermic reactions causing the evo- lution of large quantities of gases (e.g., oxides of nitrogen). Effectiveness of Metals Decontamination In discussions with the committee subsequent to submitting the proposal, AEA indicated that some sort of agitated bed or submerged bath would be used for decontaminating metal parts. The committee did not have sufficient information to evaluate this process. The proposed thermal treatment of metals parts in the MDC to decontaminate the metal to a 5X condition appears to be adequate. Effectiveness of Energetics Destruction The technology provider proposed chemical disso- lution of fuzes. However, no data are currently avail- able on the efficacy of this dissolution process. All fuzes are complex units made up of multiple compo- nents and materials. Some contain metals that have been in contact with azides and heavy metals, includ- ing lead. The committee concluded that (1) the pro- posed approach is more complex than conventional techniques of separation and detonation, and (2) a strat- egy and demonstration of the plan for dealing with small amounts of lead azide, antimony, copper, and alu- minum during the dissolution of fuzes in nitric acid would have to be developed. The committee also had concerns about the dissolu- tion of metal parts in an aqueous environment. For ex- ample, aluminum parts in the M55 rocket will generate hydrogen gas when dissolved in acid. The amount of hydrogen generated is uncertain but could be estimated based on the known reactions and thermodynamic properties of reactants and products. The reaction ves- sels must be designed to vent the anticipated amount of hydrogen. Moreover, the cumulative heat release asso- ciated with the exothermic reactions of both metals and energetics must be carefully managed for the fine-par- ticle mix of metals and energetics. Tests completed to date have indicated that very small particle sizes, long reaction times, and intense mixing are required for the destruction of energetics, such as trinitrotoluene (TNT). In initial laboratory tests, flake TNT was not completely destroyed in five
so ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS hours. However, tests with larger amounts indicated much higher destruction efficiencies, and the carbon content remaining was at ppm levels. The committee did not have sufficient data to assess the efficacy of energetics destruction at larger scale. The strategy for scaling up the process to full-scale operation on mix- tures of energetics and metals was not demonstrated to the committee. Sampling and Analysis The technology is amenable to a hold-test-release scheme for liquid and gaseous effluents. Liquid streams are accumulated in holding tanks, where they are sampled and analyzed for the presence of agents prior to recycling or to shipment off site for disposal. Vented off-gases from the anolyte and catholyte vessels are first directed to the nitric acid recovery system and then scrubbed. The off-gas is then collected in an evacuated tank that can hold gases from approximately 15 min- utes of operation. The tank is sampled and analyzed for agent using ACAMS or another certified technique. If the gas is determined to be agent free, it is vented di- rectly to the atmosphere. If agent is present, the gases are vented through a dehumidifier and a multistage car- bon bed to the atmosphere without further analysis. The committee had reservations about obtaining a repre- sentative sample from the tank because revaporization of condensed material on the internal walls of the tank could occur when the pressure is lowered for venting. Maturity Technology Status. The SILVER II process has yet to be operated on a commercial scale for waste treat- ment. The electrochemical cell in the SILVER II pro- cess is used commercially in the chlor-alkali industry. However, the largest pilot-scale tests for waste treat- ment have been conducted using a 4-kW cell consist- ing of a single anode-cathode pair. (The technology provider has proposed a full-scale system made up of 60 cells in parallel. ~ The most extensive tests have been conducted with spent tributyl phosphate dissolved in kerosene, from the Purex process, as the feed material. These tests, which were run continuously, 24 hours per day for up to 14 days, destroyed a total of 150 liters of the feed material. The technology provider has successfully completed laboratory tests on 10-gram batches of agent and has constructed a pilot plant at Porton Down, United Kingdom, that is suitable for tests on 15-liter batches of agent. All of the tests prior to startup of the Porton Down plant had been conducted with only the electrochemical cell component of the agent-destruction system. The Porton Down facility also includes anolyte and catholyte feed circuits, an anolyte off-gas condenser, an NOX reformer system, and a modified version of the combined off-gas treat- ment circuit, including a sodium hydroxide scrubber. The silver management system was scheduled to be tested at Dounreay with the effluent generated from the Porton Down plant. The NRC AltTech report (NRC, 1996a) summarizes the results of a test conducted by the technology pro- vider at Porton Down on 14.62 kg of "as supplied VX," which contained 12.7 kg of agent. The test consisted of a single continuous run of 6.5 days. At the end of the run, no agent was detected in the catholyte solution or in the process residuals. The lower detection limits for VX were 7.6 mg/m3 in the anolyte, 9.2 mg/m3 in the catholyte, and 1.7 mg/m3 in the residuals discharged during the trial. The corresponding volumes were 0.0724 m3 of anolyte, 0.0854 m3 of catholyte solution, and 0.0929 m3 of process residuals. The total residual VX was, therefore, less than 1.5 mg out of an input of 12.7 kg of VX, corresponding to an agent destruction efficiency of greater than 99.99998 percent. The technology provider calculated that the 14.62 kg of "as supplied VX" contained 7.21 kg of organic car- bon. At the end of the run, the total organic carbon remaining in the anolyte and catholyte circuits was 0.816 kg. Therefore, the destruction efficiency for conversion of organic carbon to CO2 and CO was 88.7 percent. The technology provider suggests that further removal might have been possible by continu- ing the operation of the cell after the organic feed was ended. The data-gap report (AEA, 1998a) included addi- tional bench-scale tests (1/35 of full scale) involving the treatment of 100 g of GB at the Boscombe Labora- tory. A 60-W cell was used, and small batches of mate- rial were added. The reaction time was 17 hr. after which the destruction efficiency was greater than 99.9999 percent based on detection limits. The oxida- tion efficiency based on CO/CO2 in the off-gas as com
AEA SILVER II TECHNOLOGY PACKAGE pared to the carbon feed was relatively poor (70 percent). There was no measure of total hydrocarbon levels in the off-gas. Energetic materials were tested in an isola- tion laboratory for a 20 percent slurry of energetic ma- terial in water. Separate runs were conducted with 100 g of TNT in the form of fine particles, 100 g of RDX, 100 g of tetryl, and 100 g of double base propel- lants. In two tests, TNT slurry was run for 42 hr. after which the residual TNT was below detection levels. This corresponds to a destruction efficiency of greater than 99.9999 percent. Scale-up. The committee identified several issues that need to be addressed during the scale-up of the process into a fully integrated system for the wide di- versity of assembled chemical weapons. The key scale- up issues are discussed below. First, the reaction rates and processes are sensitive to temperature, which can be more difficult to control at larger scales. In the committee's opinion, tempera- ture will be difficult to control to prevent localized boil- ing in the cells. The set point for the process is 90°C (194°F). Portions of the process are exposed to high electric currents that can raise temperatures, however, and any blockage that restricts flow could result in lo- calized boiling. This difficulty would add complexity to the scale-up. Second, reaction times for larger sized particles will limit the feed rate. Tests conducted to date have been limited to very small particles. Third, the conversion efficiency of the NOX reformer will depend on the feed rate and composition. Process operation and feed varia- tions cause fluctuations that could lead to performance problems. Fourth, a 240-kW system requires 60 cells in parallel. The committee is concerned about the prob- lems with managing the feed-stream flows to that many parallel cells because of the potential for plugging and localized boiling, which could cause flow imbalances among the cells. A substantial increase in mainte- nance requirements would increase the risk of worker exposure. Fifth, the tolerance of cells to particulate matter, such as very fine silver chloride precipitate and metals that pass through the hydrocyclone, is unknown. How- ever, particles must be kept out of the small passages in the cells. If the hydrocyclone efficiency in removing particles declines at larger size, a series of smaller cy 51 clones in a parallel arrangement (multicyclone) may be necessary. There is also a significant chance of corro- sion/erosion of the hydrocyclone unless the materials for liners are carefully selected. The committee concluded that all five of these scale- up issues will have to be addressed directly in larger- scale units and precommercial integrated-system prototypes. The SILVER II process requires a very high re- circulation rate of the reagent solution between the anolyte reactor vessel and the electrolytic regenera- tion cell. Interruptions in the recirculation stream caused by plugging or corrosion, for example, will prevent the complete oxidation of agent and other organic materials. The proposed full-scale plant represents a signifi- cant scale-up from the existing system. The largest scale system operated to date uses a 4-kW cell, consist- ing of a single anode-cathode pair and a 15-liter reac- tor. In 1996, this system was used to destroy VX at rate of approximately 94 grams per hour. The test cell was operated at currents of between 600 and 1,400 A. Op- eration at the design current of 2,000 A was not suc- cessful because the pressure increased in the anolyte compartment when VX was added. AEA traced the problem to lower than expected efficiency of the NOX reformer, which resulted in the passage of more than expected unreacted O2 and NOX gas through the con- denser and into the scrubber. This increased the pres- sure drop across the scrubber, causing an increase in pressure in the anolyte gas stream. These results illus- trate the types of scale-up problems the SILVER II pro- cess could encounter. In the committee's opinion, these scale-up issues could create serious processing problems in larger scale systems. The uncertainty of scale-up of the SILVER II process units into an integrated treatment facility are serious enough to challenge the ultimate ability of this process to perform at the required level. Robustness The committee has several concerns about the abil- ity of the process to handle nonoptimal feed streams, especially (1) the potential for plugging caused by the accumulation of solids, (2) the effects of metals on the electrolytic reaction efficiency, and (3) the reaction of
52 ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS nitric acid with organics in the feed. Until these issues can be thoroughly investigated, the committee consid- ers the robustness of the process questionable. Monitoring and Contro/ The monitoring and control system involves a rela- tively straightforward application of normal industrial techniques. The transducers for temperature, pressure, flow, and liquid level are commercially available. A centralized computer is used to achieve automatic closed-loop control via control algorithms and opera- tor interface. The complexity of the control systems is consistent with chemical process plants in general. However, the committee is concerned about the ability to determine whether holes have been created in cell membranes. Applicability If the integrated SILVER II reactor system operates as envisioned by the technology provider, it would be applicable to the destruction of all of the assembled chemical weapons in the Army's inventories. Although limited data on the destruction of pure agent and ener- getics in a SILVER II reactor are available, no data are available on treating components from disassembled chemical weapons components in a fully integrated treatment process using SILVER II-based technologies. For this reason, that committee was not able to determine its applicability at this time. The committee did identify several issues (listed below) that should be addressed to ensure that the integrated technology could treat the full array of assembled chemical weapons: · behavior of the SILVER II reaction circuit with high concentrations of metals · effects of various metals on the electrochemical potential potential poisoning of electrodes by trace elements reaction times to destroy energetics and agent components completely · precipitation of silver chloride and recycling of sil- ver from silver chloride materials Process Safety The SILVER II process requires the following unique equipment: a machine for handling sheared rocket parts SILVER II cells for the generation of Ag(II) ions for the destruction of agent and energetics · anolyte and catholyte tanks in which most of the agent and energetic destruction occurs · hydrocyclones to separate solids from liquid flow- ing to the SILVER II cells · nitric acid recovery equipment (NOX reformer and HNO3 recovery evaporator) · MDC for metal parts not dissolved in the SILVER II process and inert secondary wastes (e.g., DPE suits and spent activated carbon) · shredder for dunnage and secondary waste · off-gas scrubbers using NaOH and H2O2 · off-gas tanks for hold-test-release of process gases · oxygen supply system for the SILVER II process The SILVER II processes operate at the relatively low temperature of 90°C (194°F)~ and low pressure (essentially atmospheric pressure), thus minimizing stored energy and reducing process hazards. Nitric acid concentrations are expected to be within safe operating ranges of 4M-12M for anolyte and 2M-6M for catholyte. Higher temperatures (1,000°F [538°C] or more) occur in the MDC, which uses air in a closed- loop recirculation system to evaporate agent from metal parts and transfer any residual agent to a condenser where it is removed as a liquid and returned to the agent feed tank. The MDC operates at near atmospheric pres- sure. Liquid process effluent streams are sampled for completeness of reaction before they are released for acid recovery or other treatment or disposal. A unique hazard for the process is the use of elec- trolytic cells to generate the Ag(II) ions. A unit size for these cells is 4 kW (2,000 amps at 2 V per cell). The plant size is estimated to be four 64-electrode pair cells operating in series with a total operating voltage of 8 V. Worker Health and Safety The SILVER II technology package operates in a batch or semi-continuous mode with verification of agent and energetic destruction prior to release of the process effluent. Electrical energy and the presence of iThe safe operating range is 40°C-120°C (104°F-248°F).
Table 2~1
54 Table 2-1 Throughput Rates Prescribed in the ACWA REP REVIEWOFALTERNATIVE TECHNOLOGIES Processing Rate Processing Rate Munition Agent (munitions/hr) (lb agent/hr) 105 mm projectile HD 100 300 155 HD 100 1,170 155 VX 80 600 155 H 80 1,170 4.2-in mortar HD 50 300 4.2-in mortar HI 50 290 8-m projectile GB 20 280 M55 rocket GB 20 214 M55 rocket VX 20 200 M23 lend mine VX 30 315 Source: U.S. Army, 1997a.
AEA SILVER II TECHNOLOGY PACKAGE metals at concentrations above specified limits. Very little data are available on the characteristics of the solid wastes generated in the process, and the committee is not convinced that proper disposal methods would be available. For example, the high silver content may cause the filter cake to fail TCLP, and the high nitrate content of the filter cake may complicate stabilization. There are several types of effluent streams from the NOx reformer. Some are recycled to the primary reac- tor cycle; others are subsequently processed or must be disposed of. In addition, the scrubber liquor blow-down is accumulated and, after being analyzed for chemical agent, is evaporated and the salts discharged as a haz- ardous solid waste. Some of the middle products from the reformer condenser are recycled to the process, but others (e.g., a portion of the dilute nitric acid) require further treatment. Finally, the bottom product from the NOx reformer is a concentrated nitric acid stream, some of which is recycled and some of which must be dis- posed of. Another effluent is spent anolyte and catholyte solu- tions, which are discharged into holding tanks. After they are confirmed to be agent-free, they are evapo- rated. The nitric acid and water are recycled, and the dry metal salts are sent off site for recovery of silver. Wastes from recycling will ultimately require disposal in a hazardous-waste landfill. The MDC is used for thermal desorption of a range of solid materials. These 5X metals should be suitable for release to the public sector. Other materials will require off site disposal. The gas circulating in the MDC is directed through a condenser and carbon filter. The spent carbon filters will be shipped off site to a hazardous-waste landfill. The fiberglass captured on filter candles after they have been decontaminated in the MDC will also be shipped off site to a hazardous- waste landfill. Air Pollution. Off-gases are generated in a number of locations in the process. The anolyte and catholyte vessels are continuously vented as the organic carbon is oxidized in the anolyte vessel and NO is formed in the catholyte. The process also produces particulates consisting mainly of droplets of liquids and vapor emis- sions from the handling of the munitions. Gases gener- ated from the top of the reformer column are primarily CO2, CO, N2O, NOx, and O2. These gases are directed 55 through a packed-column caustic scrubber (sodium hydroxide/carbonate/nitrate solution). The SILVER II process forms significant quantities of NOx, which will have to be either captured or destroyed during opera- tion. Technology for controlling NOx in process gas streams of the size proposed is commercially available and would be efficient for this application, although the technology provider does not propose it for the full- scale facility. Although the NOx that is collected can be adequately removed, the very large recycle streams will also en- train NOx and transfer it to parts of the process that are not vented to the NOx control equipment. Releases of NOx at unexpected points in the process were observed by members of the ACW Committee during a labora- tory demonstration. Completeness of Effluent Characterization No characterization data is currently available ex- cept from small pilot-scale tests or theoretical mass- balance calculations. Agents and limited decomposi- tion products were sampled and analyzed using gas chromatography/mass spectrometry (GC/MS) in some tests. However, no tests have been conducted to date to define the potential for secondary oxidation and nitra- tion by-products. The amount of carbon monoxide pro- duced is an important indicator of oxidation efficiency and should be monitored. Based on potential chemical synthesis, the committee identified several other po- tential intermediates and incomplete oxidation prod- ucts that should also be investigated. These include nitro- polyaromatic hydrocarbons, alkyl nitrates, intermediate dinitro compounds, hexavalent chromium, nickel carbo- nyl, and zinc. No data are available on the characteristics of the solid and liquid effluents of actual treatments of the components of assembled chemical weapons. Effluent Management Strategy The process effluents and treatment/disposal strate- gies proposed by the technology provider are listed in Table 3-5. The committee has several concerns about effluent management strategy, especially the recycling of 59 lb of concentrated nitric acid per ton of munitions treated. According to AEA, one option for recycling excess concentrated nitric acid is the production of
56 RE VIE WOFALTE^ATIVE TECHNOLOGIES approximated by the molar concentration. Above I.0 M, the activity will deviate progressively from the value of the concentration. Thus, the standard electrode potentials, E ° of the half-cell reactions for the desired electrolysis under standard conditions at 25°C (77°F) would be: Ag ~ Ag +e~ HNO3 + 2 H+ + 2 e~ ~ HNO2 + H2O E°= -~.98 V E° = 0.94 V The overall reaction and standard potential for the electrolysis of the silver nitrate solution are therefore: 2 Ag+ + HNO3 + 2 H+ ~ 2 Ag+2 + HNO2 + H2O E°= -~.04V The electrode potentials at other concentrations are given by the Nernst equation: E = E° + ~ 1~6Q) An where Q represents the standard expression for the Law of Mass Action, Q = [A +~ THEO tH+ ~ Also, T is the temperature in Kelvin, R is the universal gas constant, ~ is the Faraday constant (charge on one mole of electrons), and n is the number of electrons transferred in the reaction. The high concentration of nitric acid used in the SILVER ~ process prevents the electrolysis of water that would occur at a lower potential (-~.23 volts[V]) than the electrolysis of silver nitrate in aqueous solution. For a simple I.0 M silver nitrate solution, He following reactions would take place: 2H2O - O2+4H++4e~ HNO3 + 2 H++2 e~ - HNO2 +H2O For an overall reaction: 2H2O+2HNO3 - O2+2HNO2+2H2O E°=-~.23 V E°= 0.94 V E 0 = -0.29 v These standard electrode potentials are valid only at 25°C (298 K) and at unit activity of all reactants and products. However, the silver (TI) process is normally earned
AEA SILVER II TECHNOLOGY PACKAGE agent and gelled agent from M55 sheared pieces must be tested. 7. The treatment of burster charges and M28 pro- pellant in the SILVER II reactor must be tested, and the material preparation required to ensure reasonable treatment times with no energetic events must be evaluated. This testing must also determine what happens to the lead stearate in the propellant during SILVER II treatment. 8. The process must be developed and tested for the efficacy of submerged-bath dilute nitric acid treatment for metals parts, including the effects of agitation and temperature. 9. The treatment of shredded dunnage material must be tested in a prototype-scale SILVER II reactor. 10. Techniques for controlling particulate matter to prevent plugging of SILVER II electrolytic cell channels must be developed and demonstrated. 11. Materials of construction must be evaluated un- der corrosive and oxidizing conditions. 12. The realistic potential for off-site recycling/reuse of silver salts and concentrated nitric acid must be evaluated, including recyclers' ability to ac- cept, handle, and treat these materials. FINDINGS Finding AEA-1. Significant barriers to the develop- ment of the sophisticated equipment and processes for segregation, materials handling, and size reduction (to reduce materials to less than 1 inch in diameter) must be overcome. Finding AEA-2. Potential problems associated with plugging of the passages in the electrolytic cells will have to be addressed. 57 Finding AEA-3. The proposed chemical dissolution of fuzes is a complete unknown because no data on this process are available. This approach is complex in com- parison to more conventional techniques of separation and detonation. Finding AEA-4. Data are not available to assess the efficacy of the treatment of energetics at larger scales. Finding AEA-5. The ability to obtain a representative sample of gaseous effluents retained in the holding tanks prior to release has not been demonstrated. Finding AEA-6. Several issues need to be addressed during the scale-up of the process into a fully integrated system, including temperature control, reaction times, efficiency of the NOx reformer, cell flow management, efficiency of the hydrocyclone, and the tolerance of cells to particulate matter. These issues are potentially serious enough to create processing problems in larger scale systems. Finding AEA-7. Identifying which corrosion-resistant materials would be compatible with HNO3 and HNO3/HF will require a significant development program. Finding AEA-X. Limiting or controlling reactions be- tween nitric acid and agent and energetics must be dem- onstrated. Finding AEA-9. Conversion of excess nitric acid into ammonium nitrate fertilizer may be complicated be- cause of the potential for contamination and the liabili- ties this would entail. Finding AEA-lO.A large inventory of silver is re- quired for processing of chemical weapons, and find- ing an off-site recycler to accept the potentially con- taminated materials could be a problem.
