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Description of the Pueblo Chemical Agent Destruction Pilot Plant Process

OVERVIEW OF THE PROCESS

In this chapter, the Pueblo Chemical Agent Destruction Pilot Plant (PCAPP) process being designed by Bechtel National, Inc., to destroy the chemical weapons stockpiled at Pueblo Chemical Depot (PCD) is described according to the configuration information available to the committee when this report was being prepared.1

Destruction processes for chemical munitions typically involve the following: (1) transfer and disassembly processes that precede the core processes and which are necessary to acquire and access the chemical agent and energetic materials,2 (2) core processes that destroy the agent and the energetic materials in the munitions, and (3) residuals treatment processes that follow the core processes and decontaminate the munition bodies and other materials associated with the munitions. These processes are accomplished in the following major steps (details on the individual steps are provided in the sections below).

First, during the transfer and disassembly steps, the munitions on their storage pallets or in boxes are transported in ammunition transport vehicles from the depot’s storage igloos to the agent destruction facility. There they are uncrated or unpacked, tested for leakage, and, if the munitions are safe, the pallets and other packing materials are separated from them.

Next, the munitions are disassembled to separate the agent-containing portions from the energetic materials. At PCAPP, propellant that is stored with the projectiles and mortar rounds and not contaminated with agent is to be separated before disassembly of the munitions and prepared for destruction on-site or for shipment to appropriate off-site destruction and disposal facilities.

During disassembly of the munitions, five separate waste streams are produced for further processing: (1) the toxic chemical agent from the munition cavities; (2) the energetic materials, which may include propellants, bursters, igniters, and fuzes, and their associated metal parts; (3) metal munitions casings and their associated metal parts; (4) ancillary wastes or dunnage such as the wooden pallets and boxes and packing materials, most of which are not contaminated with agent; and (5) process offgas streams and air from the facility’s heating, ventilation, and air conditioning (HVAC) system. Ancillary wastes also include demilitarization protective ensemble (DPE) suits, waste lubrication and hydraulic oils, spent activated carbon, and other trash and debris that may be contaminated with agent.

In the core disposal operations that follow disassembly, the chemical agents and the energetic materials are destroyed by hydrolysis processes. At Pueblo, HD or HT mustard agent will be hydrolyzed with hot water and the resulting acidic solution then neutralized with caustic solution. The energetic materials will be hydrolyzed with a hot caustic solution. These primary steps

1  

Except where otherwise noted, background material in this chapter is drawn from U.S. Army (2004b) and the PCAPP intermediate design review in San Francisco, May 19–21, 2004.

2  

Energetic materials or simply energetics are general terms that refer to propellants and explosives as a group.



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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant 2 Description of the Pueblo Chemical Agent Destruction Pilot Plant Process OVERVIEW OF THE PROCESS In this chapter, the Pueblo Chemical Agent Destruction Pilot Plant (PCAPP) process being designed by Bechtel National, Inc., to destroy the chemical weapons stockpiled at Pueblo Chemical Depot (PCD) is described according to the configuration information available to the committee when this report was being prepared.1 Destruction processes for chemical munitions typically involve the following: (1) transfer and disassembly processes that precede the core processes and which are necessary to acquire and access the chemical agent and energetic materials,2 (2) core processes that destroy the agent and the energetic materials in the munitions, and (3) residuals treatment processes that follow the core processes and decontaminate the munition bodies and other materials associated with the munitions. These processes are accomplished in the following major steps (details on the individual steps are provided in the sections below). First, during the transfer and disassembly steps, the munitions on their storage pallets or in boxes are transported in ammunition transport vehicles from the depot’s storage igloos to the agent destruction facility. There they are uncrated or unpacked, tested for leakage, and, if the munitions are safe, the pallets and other packing materials are separated from them. Next, the munitions are disassembled to separate the agent-containing portions from the energetic materials. At PCAPP, propellant that is stored with the projectiles and mortar rounds and not contaminated with agent is to be separated before disassembly of the munitions and prepared for destruction on-site or for shipment to appropriate off-site destruction and disposal facilities. During disassembly of the munitions, five separate waste streams are produced for further processing: (1) the toxic chemical agent from the munition cavities; (2) the energetic materials, which may include propellants, bursters, igniters, and fuzes, and their associated metal parts; (3) metal munitions casings and their associated metal parts; (4) ancillary wastes or dunnage such as the wooden pallets and boxes and packing materials, most of which are not contaminated with agent; and (5) process offgas streams and air from the facility’s heating, ventilation, and air conditioning (HVAC) system. Ancillary wastes also include demilitarization protective ensemble (DPE) suits, waste lubrication and hydraulic oils, spent activated carbon, and other trash and debris that may be contaminated with agent. In the core disposal operations that follow disassembly, the chemical agents and the energetic materials are destroyed by hydrolysis processes. At Pueblo, HD or HT mustard agent will be hydrolyzed with hot water and the resulting acidic solution then neutralized with caustic solution. The energetic materials will be hydrolyzed with a hot caustic solution. These primary steps 1   Except where otherwise noted, background material in this chapter is drawn from U.S. Army (2004b) and the PCAPP intermediate design review in San Francisco, May 19–21, 2004. 2   Energetic materials or simply energetics are general terms that refer to propellants and explosives as a group.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant will be followed by secondary treatment processes to transform the streams resulting from the hydrolysis (hydrolysates) into environmentally acceptable wastes. At Pueblo, biotreatment in immobilized cell bioreactors (ICBs) will be used to treat the agent and energetic hydrolysates. In the residuals treatment processes, metal parts such as the projectile casings, fuze cups, nose closures, and metals separated from dunnage streams are treated by being heated to at least 1000°F for 15 minutes to decompose any residual agent and energetics. This process is called decontamination to a 5X condition.3 The 5X-treated metal parts are considered safe to be released for subsequent disposal or recycling. Low-pressure (<25 pounds per square inch gage (psig)), superheated 1200°F steam will be used as a sweep gas for gases generated during thermal treatment of the metal parts in an inductively heated metal parts treater chamber. Wooden pallets, worker protective suits, and all other nonmetallic wastes that may be contaminated with agent are treated to a 5X condition to destroy the agent and then sent to a suitable disposal site. The decontamination of these materials takes place in a continuous steam treater (CST). The CST is inductively heated and uses low-pressure, superheated 1000°F steam and inert gas to sweep out gases generated during thermal treatment. The Bechtel Pueblo team requested that the Colorado Department of Public Health and Environment (CDPHE) permit sending propellant and dunnage that is not contaminated with agent off-site for appropriate destruction and disposal, provided the Citizens Advisory Commission does not strongly oppose this course of action. All offgases from PCAPP processes, including the offgases from storage vessels used during these processes, are treated before release to the atmosphere. Similarly, all ventilation air from process areas is treated before release to the atmosphere. Offgases from both core processes and residuals treatment processes are treated to ensure that the offgas streams are at or below regulated levels for agent and other contaminants before release directly to the atmosphere. In the following sections, each of the processes being designed for PCAPP is described in further detail. This description is largely based on the initial 30 percent design for PCAPP, along with supplementary information that subsequently became available as this report was being prepared. A process flow diagram is given in Figure 2-1. TRANSFER AND DISASSEMBLY OF MUNITIONS At Pueblo Chemical Depot, chemical munitions are stored on pallets in igloos and are periodically checked for leakers (i.e., leaking munitions). Pallets found to contain leakers are overpacked in specially designed containers and will be processed in a separate campaign after all other munitions have been processed.4 Because PCAPP will operate 24 hours a day, sufficient pallets of munitions will be brought from the PCD storage igloos to the unpack area of the PCAPP energetics processing building (EPB) during daylight hours to permit continued operation at night. Transport from the storage igloos at night or during inclement weather is prohibited. Pallets retrieved from the igloos by forklift are placed in ammunition transport vehicles. These vehicles will be used on a daily basis to transport munitions from igloos to the EPB unpack area, where the transport vehicle airspace is monitored for agent prior to the vehicles being opened. The committee expects that if agent is detected, special procedures and protective equipment will be used to access the vehicle interior, locate and overpack the leaker(s), and decontaminate the vehicle. If it is verified that no agent can be detected in its airspace, the vehicle is opened and the palletized munitions are removed by forklift and delivered to the unpack area, where they are removed from the storage pallets. The 4.2-inch mortar rounds are in boxes with the propellant; the 105-mm and 155-mm projectiles that have been reconfigured (i.e., the propellant has been removed) are palletized. There are also 105-mm projectiles that have not been reconfigured and are packed in boxes with the shell body and the propellant. See Table 1-1 in Chapter 1 and Figure A-4 in Appendix A for a description of the unreconfigured and reconfigured munitions. The unreconfigured 105-mm projectiles and the 4.2-inch mortars in their boxes are moved to the reconfiguration room, where chemical agent detectors are used to verify that the propellant 3   Treatment of solids to a 5X decontamination level is accomplished by holding a material at 1000°F for 15 minutes. This treatment results in material that can be released for general use or sold (e.g., as scrap metal) to the general public in accordance with applicable federal, state, and local regulations. 4   The Bechtel Pueblo team is considering dedicating the disassembly line for 4.2-inch mortars to processing all of the projectile leakers after the mortar campaign, including leakers, is completed.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant FIGURE 2-1 PCAPP process flow diagram. SOURCE: U.S. Army, 2004b.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant does not release agent at concentrations that exceed the short-term exposure limit, in accordance with new criteria for unrestricted release.5 In the reconfiguration room, the uncontaminated propellant, igniters, and primers are removed and, if allowed, will be prepared for off-site disposal. Otherwise, they will be placed in trays for transfer to the energetics destruction processes. At the time that this report was prepared, the Army had not yet obtained a permit to send the propellant off-site for disposal. If a permit is obtained, the uncontaminated propellant will be shipped off-site, but the igniters and primers will be processed on-site. Contaminated propellants and associated munitions will be overpacked and returned to storage for processing with all other contaminated munitions after the processing of all uncontaminated munitions is completed. Following reconfiguration, the unpacked munitions are moved by a horizontal conveyor system from the reconfiguration room to the entrance of one of three explosion containment rooms (ECRs). Munitions that do not require reconfiguration are unpacked and placed on conveyors and moved to the entrance of one of the three ECRs. If a pallet is found to contain a leaker, the pallet will be containerized at the storage igloo in a special overpack that is yet to be designed. The Army estimates that about 0.1 percent (~30) of the unreconfigured stockpile and 0.01 percent (~40) of the reconfigured stockpile will be found to be vapor leakers.6 After processing of the uncontaminated munitions, the overpacked pallets containing leaking munitions will be brought to the EPB unpack area and refrigerated to 0°C for HD and –20°C for HT before processing. Refrigeration at these temperatures will maintain the agent in a frozen state for a minimum of 3 hours to prevent leakage during disassembly (U.S. Army, 2003b).7 The refrigeration unit is to be installed in the EPB unpack area before the processing of contaminated munitions begins. Processing of refrigerated munitions will take place with the same steps as those for uncontaminated munitions, but the necessary additional personal protective gear and agent monitoring will be used. The next step in disassembly takes place at the projectile/mortar disassembly (PMD) machines. The plant is designed with three PMD machines, each in a separate ECR. At the beginning of PCAPP agent operations, one ECR will be dedicated to processing each of the three types of munitions: 4.2-inch mortars, 105-mm projectiles, and 155-mm projectiles. Nose assemblies, fuzes, and bursters are removed by each of the three PMD machines. The PMD machines consist of a commercially available, pedestal-mounted robotic arm and disassembly stands, one for each step in the disassembly process. The robotic arm is used to move the munition from the input conveyor through the disassembly stands, to a tray on the output conveyor. The robotic arm, which permits precise positioning, is computer-controlled, allowing the arm to be walked through the disassembly steps and thereby to “learn” the movements and positions needed. Parts removed from the munitions bodies are placed in trays that are moved from the ECR via conveyors. The newly designed PMD machine, selected as a replacement for the PMD machines used at baseline incineration facilities, is composed of smaller components (robotic arm and disassembly stations). These smaller components can fit through ECR entryways that are in turn smaller than those used at baseline incineration facilities. This change in turn further reduces the required concrete wall thickness and reinforcing necessary for ECR explosion resistance, particularly around ECR openings. This modular design also simplifies maintenance and replacement operations and will simplify the closure of the plant because the modules can be removed from the ECR. As noted above, the key element of the PMD machine design is a pedestal-mounted, multiaxis robotic arm similar to those used in automotive assembly and other manufacturing operations. The disassembly stations are adaptations of technology developed for baseline facilities. AGENT AND ENERGETICS TRANSFER SYSTEMS The agent transfer system (ATS) and energetics transfer system (ETS) are located in the transfer corri- 5   This verification step may be unnecessary if the method of detecting the presence of agent in the storage igloos is deemed adequate. 6   PCAPP briefing by Craig Myler, PCAPP Chief Scientist, to the ACWA Design Committee, Aberdeen Proving Ground, Md., April 13, 2004. 7   Hydrogen gas pressurization can result when mustard agent degrades, thereby forming hydrochloric acid. The acid in turn reacts with the iron of the munition casing to produce ferrous chloride and hydrogen gas. The hydrogen pressurization can cause foaming or frothing of the agent during disassembly, causing the agent to overflow from the casing. This frothing is sometimes called “champagning” (NRC, 2004).

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant dor of the energetics processing building. They are intended to move the agent-filled munitions bodies and the removed energetics from the explosion containment rooms to separate processing areas. In the current design, the 4.2-inch mortar round propellant sheets and the propellant bags containing M1 propellant separated from the projectiles in the munitions reconfiguration area adjacent to the ECRs also will be moved by the ETS to the energetics processing area. The ATS will receive munitions free of energetic materials in trays through a dedicated explosion-resistant door in the ECR that opens into the transfer corridor of the energetics processing building (EPB). The ATS then transfers the munitions to a buffer storage room for feed to the agent processing building munitions washout systems (MWSs) via roller conveyors. The agent-filled munitions are transferred from the ECR to the buffer storage area (tentatively by a remotely operated forklift, but this mode of transport is subject to change depending on the design of the ETS and further design evaluation). In the current design, the energetics separated from munitions in each ECR (bursters, fuzes, and nose assemblies) are placed in trays that are moved on conveyors through an explosion-resistant door dedicated to energetics transfer. Once in the EPB corridor area, the tray is picked up by the ETS. The ETS has elevator mechanisms outside the energetics discharge door of each ECR. These mechanisms raise the tray with energetics to a position for pickup by the ETS elevated monorail system. The tray is then moved to the opposite side of the corridor to the feed chute of one of the two energetics rotary hydrolyzers (ERHs), where the tray is tipped and the energetics are discharged into the ERH. A similar tray elevator and monorail pickup position are provided for trays of mortar propellant and propellant bags containing M1 propellant discharged from the munitions reconfiguration area. The ETS is designed to handle all of the propellants produced in the munitions reconfiguration room, but the PCAPP design team is requesting a waiver from the Army and the CDPHE to permit shipment of all uncontaminated propellant material (propellant bags containing M1 propellant and sheet propellant from the mortars) off-site. At the time this report was being prepared, explosives safety considerations were requiring blast-resistant structures in the transfer corridor and complicating the overhead monorail design of the ETS. Therefore, alternative ETS designs such as pneumatic tubes are being considered. Because both the ETS and ATS operate in the same transfer corridor, the ATS may also be affected by the final choice of the ETS. HYDROLYSIS OF ENERGETIC MATERIALS Hydrolysis of energetic materials begins in either of two ERHs. Each ERH is a continuous-feed unit, 6 ft in diameter and 20 ft long, with an inclined feed mechanism. The ERH rotates at a rate of 4 revolutions per hour and is similar to a rotary kiln in configuration. In the ERH, the feed materials (burster tubes filled with energetics, fuzes, sheet propellant, propellant bags containing M1 propellant, and nose assemblies) are brought in contact with 35 percent caustic (NaOH) at 120°C, which is just below the boiling point (U.S. Army, 2003c). Parts and materials that are not dissolved in the caustic solution move through the ERH in about 2 hours, carried along by the internal helical flights in the rotating ERH. High-pressure water spray from nozzles on a spray bar located on the axis of the ERH washes undissolved materials from the ERH walls and flights. Aluminum in the burster tubes or fuzes is also dissolved by the caustic solution, thereby generating hydrogen gas.8 The output stream from the ERH passes over strainers, where undissolved metal parts and propellant bags are separated from the liquid, dropped on a vibrating conveyor, and then moved to a heated discharge conveyor (HDC), where they are heated to at least 1000°F for 15 minutes for 5X decontamination before being dropped into discharge hoppers for cooling and storage prior to disposal. The HDC and ERH ventilation system feeds all of the reaction gases to the energetics offgas treatment system (OTS). Any undissolved fuzes exiting the ERH are expected to deflagrate on the HDC, which is designed to withstand detonations of these items. The treatment solution that passes through the ERH discharge strainers contains dissolved energetics and some sodium aluminate as well as unreacted caustic. This solution is transferred to energetics neutralization reactors (ENRs), where the hydrolysis of the energetic materials is completed. The hydrolysate is sampled and analyzed for residual energetics before being transferred to buffer storage and then to the immobilized cell bioreactor units. A differential scanning calorim- 8   The Bechtel Pueblo team is considering sending the aluminum-containing parts not through the ERH but directly to the heated discharge conveyor.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant etry (DSC) method has been developed by the Bechtel Pueblo team to determine whether there is any energetic material remaining in the hydrolysate. The absence of an exotherm in the DSC thermogram indicates that there is no component of the hydrolysate that will react exothermically. The detection of any unreacted energetic material, as indicated by an exotherm in the DSC, requires that the hydrolysate be recycled through the ENR. The unreacted energetic materials would not be in sufficient concentration to harm the ICBs. Treat-ability studies have been performed with TNT and tetryl, and neither should be toxic at concentrations that might be inadvertently released to the ICBs. AGENT PROCESSING All agent processing is performed in a separate building, the agent processing building (APB), to lower the risk of agent’s being released if there were a catastrophic explosion in the energetics processing area. Processing the agent in a separate building is expected to lower closure costs by requiring that only one building undergo major decontamination. The munitions bodies, still containing the agent but now devoid of energetics following disassembly in the energetics processing building, are conveyed in trays from the explosion containment rooms through the transfer corridor to the input air locks at the APB-EPB transfer corridor interface. Trays containing either energetics or munitions bodies still filled with mustard agent will be present in the transfer corridor, but the agent and energetics will be handled on separate transfer systems, as previously described. The amount of energetics and agent in the transfer corridor will be limited by operational controls. Removal of Agent from Munitions After arriving in the APB, the munitions (with the bursters and fuzes removed, but the chemical agent still sealed in the body by the burster well) are moved in their trays to one of three munitions washout systems. At each MWS, a pedestal-mounted, robotic arm similar to that used in the PMD machines is used to move each munition from the tray to a weighing station, and then to a cavity access machine (CAM) located in its dedicated containment booth. Each CAM is designed to operate on one of the three different munition types stored at Pueblo Chemical Depot. At the beginning of agent operations, one MWS will be dedicated to each type of munition. The 155-mm projectile MWS will have two operating CAMs and one installed spare. The 105-mm projectile MWS will have three operating CAMs and one installed spare. The 4.2-inch mortar MWS will have four operating CAMs and one installed spare. As the destruction of one type of munition is completed, the MWS dedicated to that munition (as with the PMD machines noted earlier) will be reconfigured to handle 105-mm projectiles. Eventually, all three MWSs will process 105-mm projectiles. The MWS and the associated CAMs were designed to address problems that had been encountered with gelled agent during the processing of mustard agent munitions at the Johnston Island facility (the Johnston Atoll Chemical Agent Disposal System, or JACADS). Munitions are brought in to the MWS stations in trays on a conveyor with the shells pointed upward. For projectiles, the robot picks up a shell and moves it to a weighing station, where its weight is automatically recorded. The shell is then picked up again, turned nose down, and placed in the jaws of a gripper on the CAM. The gripper holds the projectile against a stop on the base end of the projectile while a ram rises up from the bottom of the CAM agent collection cavity to force the burster tube back into the shell. This causes the burster tube to buckle into a “Z” shape, and thus it will not interfere with the draining of agent through the open nose of the projectile. The seal around the nose is designed to contain agent if the agent “champagnes,” or froths, when the cavity is accessed. The agent is gravity-drained from the shell, and the ram is then inserted back into the cavity for washout using a nozzle in the ram head. Warm, high-pressure wash water at 10,000 psi jets through the ram nozzle into the cavity as the shell is rotated to rinse out any gelled agent or residue (FOCIS, 2003a). After completion of this rinsing step, the robot picks up the projectile, tips it to ensure maximum drainage prior to weighing, and then places it in an upright position in the weighing facility to record the weight change resulting from the removal of agent. Finally, the projectile is moved to a tray on the outlet conveyor for removal to a metal parts treater (MPT). If the weight loss of the projectile does not meet or exceed target values, the projectile would be returned to the CAM for further washout, or placed in a reject stand in the MWS area for further evaluation. To access the agent in 4.2-inch mortar rounds, the round is weighed and then inserted into the CAM,

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant which cuts off the base of the round just above the bottom plate. This is done by holding and rotating the body over wheel cutters similar to those in a pipe cutter. The cut-off bottom is dropped into a collection tray, and the liquid agent drains by gravity into a collection tank. Then, residual agent and heels are washed from the munition casing with high-pressure (~10,000 psi at 108°F) water spray through a wand inserted in the munition body cavity (FOCIS, 2003b). Each emptied mortar round is weighed, and the cut-off bases are collectively weighed and the weight averaged to determine the amount of agent removed per shell. The mortar rounds and the collected bases are then placed on a tray on the outlet conveyor for removal to the metal parts treaters. The drained agent from the mortar rounds and projectiles is sent to a settling tank, where the agent, which is only slightly soluble in water, will settle out into an agent concentrate. From the settling tank, the agent and the separated wash water are fed to the neutralization system for processing through different pipelines. Several committee members traveled to the contractor fabrication facility in Pasco, Washington, in May 2004 to view the prototype testing of the munitions washout system. Decontamination of Munitions Bodies The munitions bodies (including internal metal parts and cut-off bottom plates of mortar rounds) are placed in trays and conveyed from the MWSs to one of three metal parts treaters for decontamination to a 5X condition. Other potentially contaminated metal parts are also treated to a 5X condition in the MPTs by being placed in baskets or trays designed to move through the MPTs.9 Each MPT consists of an entry air lock, a process chamber, and an exit air lock. The munitions and metal parts in the trays move on tracks through the MPTs. The interior wall surface of the MPT process chamber is maintained at 1200°F by external induction heating coils. Low-pressure (<25 psig), superheated steam at 1200°F is introduced into the process chamber of the MPT as a carrier gas to move vaporized agent and other gases produced from the 5X decontamination process into the MPT offgas treatment system. The steam may react with the agent and other organics such as paint to form some hydrogen, but the primary means of achieving the 5X condition is through thermal decomposition. Both the entrance and exit air lock chambers are purged to the MPT offgas treatment system with nitrogen before the doors are opened to the process chamber, because the gas mixture in the process chamber could contain hydrogen or other combustible gases. The airspace in the exit air lock will be sampled for the presence of agent before the air lock is opened and the tray is moved out of the air lock. The decontaminated metal will be recycled or disposed of appropriately. If agent is detected in the exit air lock, the tray will be backed into the MPT process chamber for further treatment. One of the MPTs will be larger than the other two (one will be 10 ft in diameter, the others 6 ft in diameter). The larger MPT will be used for big objects during closure of the facility (e.g., a CAM in its containment booth that requires 5X decontamination during facility closure). Hydrolysis of Mustard Agent After washout, the solution of agent and washout water is fed to one of two agent/water separators, where it separates into a lighter water phase and a heavier agent phase. The agent concentrate, normally more than 99 percent agent, is then sent to an agent-concentrate holding tank, and the washout water is pumped to wash-water holding tanks for recycling to the munitions washout system stations. The agent concentrate is fed to one of two agent neutralization reactors (ANRs), which are continuously stirred tank reactors (CSTRs), where hydrolysis with hot water (194°F) will be taken to completion. The outlet stream from the ANR is first collected in buffer storage tanks, which are also CSTRs, and checked for the completion of hydrolysis. Because the resulting hydrolysate is acidic and unacceptable for feed to the immobilized cell bioreactors, sodium hydroxide solution is added until the pH of the solution is in a neutral range. This process and the reaction conditions are identical to those used by the Aberdeen Chemical Agent Destruction Facility for the destruction of the bulk mustard agent stored at Aberdeen Proving Ground in Maryland. After the neutralization is completed, the hydrolysate is sent to an agent hydrolysate tank, where it is stored until further processing in one of the continuous-feed ICBs. The hydrolysate is sampled and analyzed for the presence of residual mustard agent. If agent is detected, the hydrolysate will be returned to 9   These metal parts include strapping from dunnage, DPE metal connectors, and metal parts discarded from maintenance of contaminated equipment.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant the ANRs after hydrolysis of the next batch being processed is completed. BIOTREATMENT OF AGENT AND ENERGETICS HYDROLYSATES Biotreatment has been selected as the secondary treatment process at PCAPP for agent and energetics hydrolysates. The hydrolysates, various process condensates, and additional water are collected in 30-day storage tanks. After sampling to determine the composition of the tank contents, these contents will be mixed with required nutrients and fed to twenty-four 40,000-gallon ICBs for biotreatment. The average residence time in each ICB is expected to be approximately 3.6 days.10 It will require approximately 30 days to acclimate each ICB at start-up. The design team has provided flexibility to accommodate this time period by allowing for the storage of feed water. The bacteria used in this process are immobilized on a support material made of plastic packing rings and an elastomer foam impregnated with activated carbon. The reactor is arranged with three compartments in series. The solution is sparged with air at a flow rate of 600 cubic feet per minute. The ICBs can operate in temperatures ranging from 95°F to 41°F, but ambient temperatures in Pueblo, Colorado, range from 115°F down to –20°F. Therefore, the design will provide appropriate cooling and heating of air and water fed to the ICBs to ensure optimum operating temperatures. Thiodiglycol, the only Schedule II component in the agent hydrolysate, has been reported from testing to be 99.9 percent destroyed (the goal was 90 percent).11 The ICB design is the same as the system used for the earlier ACWA engineering design studies conducted for Pueblo.12 Normally, the bioreactor liquid effluent will be sent directly to the brine recovery system (BRS) for the recovery of most of the process water. Vapor from the bioreactors is collected and sent to the bioreactors’ offgas treatment system for odor control. The BRS consists of two 50 percent capacity trains of equipment. Each train contains a pretreatment steam stripper, a brine concentrator, an evaporator/crystallizer unit, and a solids-dewatering unit, along with related tanks, heat exchangers, and pumps and piping systems. Water conservation is an important consideration for the Pueblo community. The BRS recovers clean water from the ICB effluent for reuse in the process units and separates the solids in pressure filters or centrifuges. The BRSs are designed for a total flow rate of about 200 gallons per minute. Vapors from the evaporator/ crystallizer vapor condensers on each train are combined and flow to the BRS offgas treatment system. The solids from the crystallizer will be sent to an appropriate off-site facility. If necessary, the bioreactor liquid effluent can be fed to two clarifiers, where suspended solid materials (e.g., cells from the ICBs) are separated and collected by a sludge collector. It is expected that the clarifiers normally will not be required. This question is being studied at Battelle, which is a member of the Bechtel Pueblo team, and should be answered prior to facility construction. In each clarifier, a scraper-type sludge collector is provided to collect the underflow sludge and release it intermittently to the thickener. The underflow sludge is fed to two thickeners designed to capture 90 percent of the suspended solids. The thickened sludge is then pumped intermittently to one of two dewatering filter presses for solids removal. Filter cake from the presses is collected in dumpsters and sent for off-site disposal. Overflows from the thickeners and filter presses are sent to the BRS. DUNNAGE TREATMENT All contaminated wood pallets, used DPE suits, and other contaminated nonmetallic waste will be shredded in the dunnage shredding and handling system, and the shredded material will be decontaminated to a 5X condition in one of the three continuous steam treaters. Uncontaminated wood pallets will be sent off-site for disposal if a permit is granted and the Citizens Advisory Commission does not strongly oppose this course of action. Otherwise, the uncontaminated pallets will be treated in the same way that the contaminated pallets are. Table 2-1 summarizes the expected quantity of waste feed to the dunnage treatment system. Potentially contaminated metallic waste will be processed in one of the three MPTs. As shown in Table 2-1, approxi- 10   PCAPP briefing by Craig Myler, PCAPP Chief Scientist, to the ACWA Design Committee, Aberdeen Proving Ground, Md., April 13, 2004. 11   Schedule II components are those agent breakdown products that the Chemical Weapons Convention of 1997 requires to be destroyed because of the potential that they could be reconstituted into agent. 12   See NRC, 2000; 2001b.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant TABLE 2-1 Estimated Quantity of Waste Feed to Dunnage Treatment Waste Type Composition Waste Quantity (lb/round) Wood pallets Wood, both contaminated and uncontaminated. 2.4 (105-mm projectiles and 4.2-inch mortars) 5.0 (155-mm projectiles) Miscellaneous dunnage from nonmunition sources Glass, plastic, wood, paper, packaging materials. Assumed to be 60 percent wood and 40 percent plastic. 0.5 Demilitarization protective ensemble (DPE) materials Chlorinated polyethylene, PVC, latex, butyl rubber. 0.15 Spent carbon from plant heating, ventilation, and air conditioning filters Generated by filter building and offgas treatment systems. 0.3 Waste oils Assumed to be heavy oil for lubrication. Heat content assumed similar to that of kerosene. 0.3 Trash, debris, protective clothing Assumed to be solid, nonmetallic, nonplastic. Treated like wood. 0.2 Spent hydraulic fluid Light oil for hydraulic machinery operation. Heat content assumed similar to that of kerosene. 0.2   SOURCE: Adapted from U.S. Army, 2004b. mately 1.65 lb per round will arise from sources other than wood pallets, and when 105-mm projectiles and 4.2-inch mortars are being processed, these other sources constitute approximately 40 percent of the dunnage feed. The remaining 60 percent of the dunnage feed will be wood pallets, assuming no off-site disposal of uncontaminated pallets. All solid dunnage materials will be shredded prior to being fed to the continuous steam treater. The shredded materials will be mixed with carbon carrier material—either similar to the activated carbon used in the HVAC filters or coconut shell activated carbon—and then fed to the CST. The liquid organic wastes (see Table 2-1) will be mixed with the shredded solid material or the carbon carrier material, presumably as the solid material is fed to the CST. Each CST is designed to process materials at a design rate of 160 lb/hr for wood, 50 lb/hr for plastic and rubber, or 300 lb/hr of granulated activated carbon from spent HVAC filters. Each CST processes only one of the preceding feed materials at a time. For wood and plastic or rubber, carrier carbon is added to maintain an overall feed rate of 300 lb/hr. Mixes of feed materials are not planned. The design of the CST is still under consideration. A unit will be fabricated and tested at the Parsons Fabrication Facility in Pasco, Washington, in late 2004. How-ever, the current CST design consists of two inductively heated chambers, one above the other, as shown in Figure 2-2. The upper chamber is horizontal from the feed end to the discharge end, while the lower chamber is slightly inclined upward from the feed end to the discharge end. As shown in Figures 2-3 and 2-4, each chamber consists of two concentric shells, a chamber shell and an auger shell. An electrical induction heater is mounted on the outside of the chamber shell. The annular space between the shells is filled with a gas, presumably inert or with very low oxygen content. The auger shell containing the auger and its end-mounted drive unit can be withdrawn from the chamber shell on racks (not shown in Figures 2-3 and 2-4). Material is fed to the upper auger shell, which uses a shaft with rotating paddles to move the material to the exit of the auger shell. The material leaving the upper auger shell drops into the inlet of the lower auger shell. The lower auger shell uses a rotating shaft with solid helical flights for material movement. The lengths of the two chambers and the speeds of the rotating auger shafts are set to ensure that 5X decontamination is achieved. Low-pressure (<25 psig), superheated steam at 1000°F is fed countercurrent to the material flow in the upper auger shell. This steam serves as sweep gas for the removal of gaseous decomposition products. Expe-

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant FIGURE 2-2 Two-cylinder continuous steam treater configuration. SOURCE: U.S. Army, 2003d.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant FIGURE 2-3 Primary chamber of the continuous steam treater. SOURCE: Provided by Yu-Chu Yang, ACWA Chief Scientist, July 26, 2004.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant FIGURE 2-4 Secondary chamber of the continuous steam treater. SOURCE: Provided by Yu-Chu Yang, ACWA Chief Scientist, July 26, 2004.

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Interim Design Assessment for the Pueblo Chemical Agent Destruction Pilot Plant rience gained in prior CST testing suggests that steam may react with the wood, DPE suit material, and any agent and other organic materials present, in the first chamber of the CST (NRC, 2001b). However, air may have leaked into the system in prior tests. A nitrogen sweep gas flows countercurrently through the lower auger shell into the upper auger shell and exits that shell with the superheated steamgas mixture from the upper auger shell. The CST offgas flows to the CST offgas treatment system for the destruction of any remaining hazardous materials. Treated solid material, a mixture of char and tar, exiting the lower chamber is collected and cooled in an air-locked bin, where the vapor space is sampled to verify agent destruction. Subsequently, the treated material is released to a hazardous waste disposal site.