Assessment of Supercritical Water Oxidation System Testing for the Blue Grass Chemical Agent Destruction Pilot Plant (2013)

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4 Systemization of the Supercritical Water Oxidation System with the Water Recovery System In 2011 and 2012, the Committee to Review the Water WRS is nonoperational). The WRS includes the following Recovery System for the Blue Grass Chemical Agent De- system components: struction Pilot Plant (WRS committee) reviewed the WRS planned for use at the Blue Grass Chemical Agent Destruc- •  hree SCWO effluent storage tanks where the efflu- T tion Pilot Plant (BGCAPP). The WRS committee’s statement ent will be analyzed to ensure that the total organic of task focused on corrosion and materials of construction. carbon (TOC) concentration is less than 10 ppm In its work, the WRS committee also commented on the (BPBGT, 2013); adequacy of the pretreatment system and the fact that the •  conventional pretreatment system consisting of A reverse osmosis (RO) membranes will be sitting for sev- coagulant and antiscalant addition (dual pumps on eral years before the WRS is systemized. Its report is titled each unit), media filtration (six units), and canister The Blue Grass Chemical Agent Destruction Pilot Plant’s filters (three) prior to the RO units; Water Recovery System (NRC, 2012). •  hree spiral wound RO units (two operational, one T This chapter discusses systemization of the WRS in spare); and consideration of the findings and recommendations of the •  torage tanks used to hold RO permeate for use in S WRS committee. To do this, the chapter first describes the periodically cleaning the RO membranes. WRS and provides a summary of the WRS committee’s concerns, which were reflected in its findings and recom- Figure 4-1 shows the flow of material from the agent mendation. Next, actions taken by BGCAPP in response to and energetic hydrolysis processes, through the SCWO the 2012 WRS report are considered and findings are made process, up to the pretreatment step in the WRS. It also about those actions. This committee then uses the basis of indicates where the cooling tower and steam blowdown is the WRS committee’s findings and BGCAPP’s responses, blended with the SCWO effluent. The dashed arrows indicate together with the results of first-of-a-kind (FOAK) testing of changes recommended by the WRS committee (discussed the supercritical water oxidation (SCWO) system, to discuss in more detail below): namely, two additional RO bypasses, systemization of the WRS and the integrated SCWO and one to redirect blowdown water directly to the tanks holding WRS systems. blowdown water or to the RO reject tank if the water softener fails, and the other to divert softened water directly to RO permeate if water quality allows. OVERVIEW OF THE WATER RECOVERY SYSTEM Figure 4-2 shows the flow of material through the WRS. The BGCAPP WRS will treat and recover water from a The following process performance indicators of the WRS combined feed stream comprising SCWO effluents, cooling operation will be continuously monitored by the facility: tower blowdown, and steam boiler blowdown. Recovered water will be reused as quench water in the SCWO process. •  emperature indication for the feed to the RO units, T The system was designed to operate at 70 percent product •  low indication for the feed to and discharge from F water recovery as permeate and a maximum of 500 mg/L the RO units, total dissolved solids (TDS) in the product water and to en- •  DS concentration (through conductivity monitor- T sure that one full day of SCWO quench water requirements ing) of RO permeate, is stored (to permit continuous SCWO operation in case the •  ifferential pressure across the RO unit (feed versus D reject), 33 

34 ASSESSMENT OF SUPERCRITICAL WATER OXIDATION SYSTEM TESTING FOR THE BGCAPP •  ifferential pressure across the multimedia filters and D Pretreatment canister filters, and The WRS committee’s concerns focused largely on the •  roportional flow ratio and total flow rate indication P pretreatment system design and operation. There was, first for the caustic injection system (BPBGT, 2009). of all, some uncertainty about the solids loading that would arrive at the pretreatment system—mainly the media filters— 2012 NRC REPORT ON THE BGCAPP WATER from the SCWO effluent, especially considering the elimina- RECOVERY SYSTEM tion of the originally planned clarifier. The WRS committee’s specific concern was that the media filtration system would Key Concerns be rapidly overloaded with incoming solids, particularly in the case of H hydrolysates, which are expected to have very The findings and recommendations of the WRS com- high iron particle content in SCWO effluents. Any overload mittee raised several concerns in three main areas: pretreat- and shutdown of the pretreatment system would have a cata- ment, the RO membranes, and the materials of construction. strophic effect on the RO membranes and could ultimately Rather than merely list the WRS committee’s findings and shut down the WRS system for more than a day. recommendations, this committee summarizes their intent Secondarily, the WRS committee was concerned about in this report. Water Blended To RO SCWO Hydrolysis hydrolysate SCWO pre - effluent process storage treatment tanks (3) tank Water Energetics hydrolysis Emergency bypass of RO system Cooling tower and Water steam softener blowdown To RO permeate Spent regenerant to RO reject tank FIGURE 4-1  Flow of material from hydrolysis, through SCWO, up until the pretreatment step in the WRS. The dashed lines show changes recommended by the WRS committee, as discussed in this report. SOURCE: Adapted from NRC, 2012. Antiscalant Coagulant RO units (3) RO figure 4-1.eps permeate From SCWO effluent tanks To RO permeate tanks SCWO Multimedia Canister High- effluent filters filters pressure tank (6) (3) pump RO reject pumps Recycle pump To RO reject tanks FIGURE 4-2  Process flow diagram for the BGCAPP WRS, including the pretreatment and RO system. SOURCE: NRC, 2012. 4-2.eps 

SYSTEMIZATION OF THE SUPERCRITICAL WATER OXIDATION SYSTEM WITH THE WATER RECOVERY SYSTEM 35 the choice of coagulant and whether it would perform ad- Agent Destruction Pilot Plant project staff appear to have equately. Accordingly, the WRS committee discussed risk taken appropriate engineering design measures to safeguard mitigation options for the media filtration system, as well the reverse osmosis membranes from excessive fouling as the option of replacing media filtration with membrane conditions. filtration, which would completely clarify WRS feed water without the use of coagulants and with a smaller footprint. RO Membranes The WRS committee concluded that membrane fouling would not be a significant problem if the pretreatment steps In response to the WRS committee’s concerns, BG- are effective in removing suspended solids from the efflu- CAPP has indicated that the RO membranes will be stored ents to be passed through the RO membranes and also that, according to manufacturer recommendations and that ad- given other feed water quality indicators, the product water equate replacement membranes will be stored on-site at all recovery could exceed the target of 70 percent. times. They have also arranged for the appropriate membrane chemical cleaning agents to be provided by the equipment supplier. RO Membranes The WRS committee’s main concern with the RO sys- Finding 4-2. The WRS committee’s concerns about the tem was the length of time the membranes would be stored storage of the RO membranes between delivery and sys- in place, 3 years. The WRS committee recommended taking temization and their chemical cleaning appear to have been late delivery of the membranes to alleviate this concern. It adequately addressed. also discussed membrane chemical cleaning considerations, as some fouling over time would be inevitable. Materials of Construction In response to the WRS committee’s concerns, BG- Materials of Construction CAPP conducted an array of additional corrosion tests at The WRS committee noted that the materials of con- various salinities and temperatures. The tests were U-bend struction would not be tested for use in the WRS influent weld tests, oxidation reduction potential tests, and cyclic water stream, which was expected to be highly corrosive. polarization tests. The U-bend weld tests were to evaluate The WRS committee recommended that candidate materials materials for stress corrosion cracking. The oxidation reduc- of construction be tested and discussed some tests that could tion potential tests characterized the test solutions. The cyclic be performed to give better insight into the suitability of the polarization tests investigated general and pitting corrosion. selected materials of construction. The WRS committee rec- The materials tested were 316L, 904L, and 2205.1 Based on ognized that the opportunity for representative testing might the test results, BGCAPP has concluded that as far as could be limited prior to the start of operations, so it also recom- be simulated with surrogate waters and conditions, 316L mended the possible use of a duplex alloy, such as 2205, in stainless steel will resist corrosion over the working life of the WRS as a conservative approach. the WRS system for the anticipated operating environment. Finding 4-3. The materials of construction planned for use BGCAPP Response to the 2012 NRC Report in the WRS now appear to have been adequately tested in representative environments. It is now possible to have con- Pretreatment fidence that the planned materials will perform adequately BGCAPP conducted additional analyses and confirmed for the amount of time that the water recovery system will that the design of the SCWO effluent tank would serve as operate and in the anticipated environments. a clarifier. Hence, the WRS committee’s concerns about the pretreatment system design and operation were appropri- SYSTEMIZATION OF THE WRS ately addressed. Given the anticipated residence times for the SCWO effluent in the SCWO effluent storage tanks, the RO Membrane Storage After Systemization majority of particles should settle out of the effluent before the water is fed into the media filters. Given the settlement During systemization, the combined SCWO and WRS of particles ahead of the filters, concerns about the choice system will be tested using simulated blended hydroly- of coagulant may be moot; however, BGCAPP also had the sate. Following systemization, the combined system will equipment supplier research the best available chemical be flushed with fresh water. Following flushing at the end coagulants for use in the WRS as a safeguard. of systemization, the components will sit idle until plant Finding 4-1. Although stable, fouling-free performance can- 1Surajit Amrit, mechanical process lead, BGCAPP, “Water Recovery not be guaranteed ahead of time, the Blue Grass Chemical System Update,” presentation to the committee on January 7, 2013. 

36 ASSESSMENT OF SUPERCRITICAL WATER OXIDATION SYSTEM TESTING FOR THE BGCAPP start-up. This period may last many months. As noted, the Impact of Water Recycling on the SCWO System previous NRC study of the WRS stated concerns about long- Site tap water was used for all testing of the high- term storage of the RO membranes prior to systemization pressure quench flow. During systemization and operations, (NRC, 2012). BGCAPP engineers responded by contacting RO-purified recycle water will be used as the quenching the membrane vendor, which suggested dry storage of the water. The committee explored the impact of switching membranes after delivery for long-term preservation.2 This these input streams when moving from FOAK testing to may not be possible after systemization testing because the systemization. The RO system reduces the salt concentra- membranes will have been used during this testing. tion by a factor of approximately 20-60, yielding 70 percent net volume of recovered water containing no more than Finding 4-4. There is the potential for membrane degrada- 500 mg/L TDS (NRC, 2012). Though the committee could tion between systemization and full plant operation unless not locate data describing the specific values for dissolved care is taken to preserve the membrane. solids in the process water used during FOAK testing, the 500 mg/L target for dissolved solids should not represent a Recommendation 4-1. Blue Grass Chemical Agent Destruc- significant perturbation to the SCWO system. Also, because tion Pilot Plant operators should obtain, review, and follow the prequench concentration of salt and TDS in the effluent is manufacturer recommendations for membrane preservation expected to be 10,000-20,000 mg/L, the anticipated level of between systemization and start-up of plant operations. TDS in the WRS effluent should not have a dramatic impact on the performance of the SCWO quench system. Thus, the Development of Water Balance committee believes that the use of RO permeate in the quench water flow instead of the tap water used during testing does A portion of the permeate from the WRS will be re- not significantly change the process, though “normal” levels cycled for use as quench water in the SCWO system. It is of effluent conductivity may need to be reestablished upon shown that each RO system will produce 61 gal/min (gpm) of systemization using RO permeate. permeate when all three SCWO units are operating (BPBGT, The continued recycling of water through the SCWO 2007). According to the SCWO process flow diagram, ap- quench and the RO system will not continually concentrate proximately 21.5 gpm of permeate will be required for use the salts in the recovered water because the RO system deliv- as SCWO quench water in each SCWO unit. Process water ers water with a specified, constant maximum total dissolved included elsewhere in the system leads to roughly 24.5 gpm solids concentration. Incidental solids such as titanium and from each SCWO unit into the RO (stream 670 in BPBGT, iron oxides do not accumulate in the recycled water as solids 2008), suggesting that the greatest contribution to the water are filtered from the SCWO effluent prior to RO processing effluent is from the quench water (BPBGT, 2008). It appears to preserve RO membrane integrity. to the committee that the water balance for the integrated SCWO/WRS system has not yet been addressed and opti- Finding 4-6. The committee foresees no problems with us- mized. Whether there will be an excess of permeate relative ing the water recovered via reverse osmosis in the SCWO to the required quench water or, possibly, a small deficit is system other than slight changes that may need to be made hard to say based on the sources provided to the committee. to the monitoring parameters. FOAK testing would have provided an excellent opportunity to investigate optimization of the combined SCWO and Recommendation 4-3. The Blue Grass Chemical Agent WRS. It appears that this was not possible, however, because Destruction Pilot Plant project staff should characterize the the two systems are being provided by separate vendors reverse osmosis effluent for each agent campaign. They whose delivery schedules are not coordinated. should then reestablish normal operating conductivities when reverse osmosis permeate is injected (recycled) at the Finding 4-5. The operation of the WRS has not been opti- bottom of the SCWO reactor. mized for use with the SCWO system. Recommendation 4-2. Blue Grass Chemical Agent Destruc- INTEGRATED SCWO AND WRS OPERATIONS tion Pilot Plant staff should optimize permeate generation to The committee noted that SCWO rinse water during match supercritical water oxidation system quench demand. FOAK testing of the SCWO unit was provided by plant water at the contractor’s site on an as-needed basis. The use of a storage tank for RO permeate effectively replaces city water during SCWO/WRS operations. The committee sees no problems in using RO permeate for SCWO quench. Earlier in this chapter, it was reported that the contents 2 Surajit Amrit, mechanical process lead, BGCAPP, “Water Recovery of the SCWO effluent tank would be monitored to ensure System Update,” presentation to the committee on January 7, 2013. 

SYSTEMIZATION OF THE SUPERCRITICAL WATER OXIDATION SYSTEM WITH THE WATER RECOVERY SYSTEM 37 that TOC is below 10 ppm. The previous NRC report on the for more frequent and extensive cleaning (ideally between BGCAPP WRS (NRC, 2012) assumes a TOC level in the campaigns), which could lead to rapid membrane degrada- SCWO effluent tank of <2 ppm, based on the System Design tion and call for premature replacement. Description for the Water Recovery System (BPBGT, 2009).   This was based on the best information available at the time Recommendation 4-4. Blue Grass Chemical Agent Destruc- of that report. FOAK testing of the SCWO system now as- tion Pilot Plant operators should monitor the reverse osmo- sumes that a monitored TOC level of less than 10 ppm will sis membranes and system during systemization testing to exist in the SCWO discharge. This level may be reduced determine if there is any evidence of premature membrane somewhat in the SCWO effluent tanks because cooling tower degradation. If this is observed, then the membranes would and steam blowdown effluent may also be added to the tanks. need to be replaced sooner. This is a minor operational issue However, the FOAK test report also states as follows: that can be handled by keeping a spare set of membranes on-site at all times. The actual set point for effluent diversion to off-spec effluent tank will be determined by finalized permit levels based on allowable effluent TOC for the effluent disposal path chosen. REFERENCES (BPBGT, 2013, p. 73) BPBGT (Bechtel Parsons Blue Grass Team). 2007. SCWO Building Water Recovery: R.O. Unit Process Flow Diagram, Rev. 6, October 2. Rich- This seems to indicate that the SCWO effluent tanks and mond, Ky.: Blue Grass Chemical Agent Destruction Pilot Plant project office. WRS feed may contain up to 10 ppm TOC, or even more if BPBGT. 2008. SCWO Process Building SCWO Process Flow Diagram, permitting allows. These are significantly higher levels than Rev. 9, December 19. Richmond, Ky.: Blue Grass Chemical Agent considered in the WRS report and could cause more rapid Destruction Pilot Plant project office. degradation of RO membranes than envisioned in the WRS BPBGT. 2009. System Design Description for Water Recovery System, report. Rev. 2, July 16. Richmond, Ky.: Blue Grass Chemical Agent Destruction Pilot Plant project office. BPBGT. 2013. Test Report for Supercritical Water Oxidation (SCWO) First- Finding 4-7. Since the final effluent total organic carbon of-a-Kind (FOAK) Test, Preliminary Draft, April. Richmond, Ky.: Blue (TOC) level will be based on permit levels, the WRS feed Grass Chemical Agent Destruction Pilot Plant project office. may have a considerably higher level of TOC than envisioned NRC (National Research Council). 2012. The Blue Grass Chemical Agent in previous reports, and this could lead to more rapid and se- Destruction Pilot Plant’s Water Recovery System (Letter Report). Wash- ington, D.C.: The National Academies Press. vere fouling of the reverse osmosis membrane than originally envisioned in the WRS design. The main concern is the need