Metrics for Successful Supercritical Water Oxidation System Operation at the Blue Grass Chemical Agent Destruction Pilot Plant (2019) / Chapter Skim
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Letter Report
Letter Report
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You requested that the National Academies form a committee to further develop the material in the 2015 report Review Criteria for Successful Treatment of Hydrolysate at the Blue Grass Chemical Agent Destruction Pilot Plant. That report set out criteria for the successful operation of the BGCAPP SCWO system and water recovery system (WRS)
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However, if there were an unexpected amount of insoluble compound or particles in the reactors for some reason -- say, especially severe corrosion resulting in significant amounts of TiO2 in the reactor -- that could result in augmented corrosion/erosion or reactor plugging. The concerns discussed above elevate the possibility that the SCWO reactor may not function in a fashion that is compatible with the overall chemical warfare agent destruction rate needed from the BGCAPP main plant.
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TABLE 1 SCWO and WRS Effectiveness Goals, Sections in Which They Are Considered, and Whether Metrics Are Proposed Metrics Effectiveness Goal Report Section Proposed 1. Reliably feed agent hydrolysate, energetics hydrolysate, and Hydrolysate Feed to the SCWO Yes blended hydrolysate to the SCWO reactors.
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: Corrosion; High-pressure air compressor reliability; Compressor condensate oil-water separation operation; Liquid effluent letdown valve erosion; Solid sulfur heating and mixing in the blend tank; SCWO control system code; TOC analyzer reliability; Preoperational storage; Operator currency and experience gaps; Unacceptable equipment wear and corrosion during operation; Simultaneous maintenance and operation of three reactors, which presents potential safety problems since maintenance personnel would be working near operating reactors; Actual agent hydrolysate and energetics hydrolysate successfully tested on smaller SCWO reactors, but only simulated hydrolysates have been tested on a full-scale unit; Potential variations in hydrolysate feed composition, which may present operating problems; The proper mix of feed additives is complex and is determined using a computer algorithm; Elevated aluminum concentrations in the reactor feed may cause reactor plugging; and Untested blend tank mixing effectiveness.
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and are detailed in the statement of task, as follows: Develop metrics that can be used to determine the success or risks of failure of the BGCAPP SCWO system. These are to be based on the Performance Goals for the SCWO and the WRS, and the Graded Success Scale for Use in Evaluating Overall Operation and Individual Treatment Processes, both in the 2015 report for successful hydrolysate treatment.
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Hydrolysate Feed to the SCWO Reactors This section addresses goal 1 in the list of effectiveness goals in Table 1. The committee interprets this to encompass both the ability to mechanically feed hydrolysate reliably and the ability to feed chemically appropriate hydrolysate (i.e., there are both mechanical and chemical components)
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BGCAPP staff should both verify the validity of the blending procedures, including additive supply to the SCWO feed blend tank, and determine the SCWO tolerance level to variability in the composition of the blended hydrolysate feed streams. Processing Rates, Availability, and Processing Parameters This section addresses goals 2-5 in the list of effectiveness goals in Table 1.1 Experimental operation of the SCWO reactor has demonstrated that acceptable destruction of all organic species can be achieved if the reactor system is operated at 1,150-1,200°F and 3,400 psig with a feed residence time in the reactor of 10 s or more.
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TABLE 4 Proposed Metrics for Processing Rates, Availability, and Processing Parameters Graded Scale Definition Performance RAM 0 All three trains run with a feed rate of 1,000 lb/hr and No impact No impact availability of 76 percent. 1 All three trains run with a feed rate of 1,000 lb/hr and an Minimal impact Minimal availability of between 55 and 76 percent.
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While both of these actions aid in achieving the target aluminum concentration in the SCWO feed, the committee has one concern -- namely, that protocols developed for bench scale synthesis of hydrolysatesimulant feed used for SCWO testing may not scale properly to the generation of blended hydrolysate that will ultimately be used in the larger SCWO blend tank. It is possible that the agent and energetics hydrolysates that comprise the blended hydrolysate feed may exhibit inconsistent mixing that might lead to locally higher aluminum concentrations.
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TABLE 5 Proposed Metrics for Aluminum Concentrations in Hydrolysate Graded Scale Definition Safety Performance RAM 0 Aluminum level is No impact No impact No impact reliably maintained in all blended hydrolysate feed batches. 1 Average aluminum level Minimal impact Minimal impact to Minimal impact to is 200-300 ppm 90 because of safety organic conversion RAM but percent of the time.
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Release Specifications for Total Organic Carbon, pH, and Conductivity This section addresses goal 8 in the list of effectiveness goals in Table 1. The permit level for TOC in SCWO effluent is 50 ppm and, as long as the SCWO reactor operating conditions are maintained within target ranges, this criterion will be met.
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In the event that the on-line TOC analyzers do not provide the on-line time to successfully meet processing requirements -- that is, contributing to less than 55 percent overall SCWO availability -- an alternative methodology to validate the TOC levels of the effluent to meet specifications could reduce any impact on SCWO operations. One such alternative is an appropriate manual sampling program at a frequency to keep SCWO production levels at the 55 percent availability level discussed in the "Processing Rates, Availability, and Processing Parameters" section.
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than the significant impact impact SCWO reactor trains. unless manual sampling and analysis procedures can be developed to meet SCWO performance requirements Corrosion This section addresses goals 9 and 10 in the list of effectiveness goals in Table 1.
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This is also treated in the "Hydrolysate Feed to the SCWO Reactors" section, above. Liner Replacement This section addresses goal 9 in the list of effectiveness goals in Table 1.
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Recommendation 8. BGCAPP staff should seriously consider using thicker thermowells in the SCWO reactors and should explore the possibility of reducing SCWO feed rates while still maintaining adequate availability to not affect BGCAPP main plant operations.
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This means that SCWO operating time accounts for 90 percent of the 333 hr cycle, corresponding to a 90 percent availability. liner, thermowell thermowell thermowell OT OT OT OT thermowell change-out change-out change-out 75H 75H 75H 75H change-out 7H 7H 7H 12H 333H FIGURE 1 Timeline for thermowell and liner change-outs, based on a 90 percent SCWO reactor availability.
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on the graded scale because of the potential compromise to the unit safety envelope. Perhaps more likely is the possibility that an increased corrosion rate would result in lowered processing rates for the hydrolysate, which would compromise agent processing and scheduling success.
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. The WRS will be operated together with the SCWO during 1,200 hr of simulant-based testing that is being planned, which is expected to provide data and operating experience enabling evaluation of the performance and reliability of the WRS.13 TABLE 7 Proposed Corrosion Metrics Graded Scale Definition Safety Performance RAM 0 Maximum liner No impact No impact No impact corrosion rate is <1.1 mil/hr.
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Based on information provided to the committee, employees reportedly expressed concerns about performing maintenance on one of the three SCWO reactors while one or both of the remaining reactors are operating.16 Risks associated with performing maintenance while SCWO reactors are operating can be divided into two categories: working within an idle module while one or both of the other reactor modules are operating, and working outside an idle reactor module while one or both of the other reactor modules are operating. Many methodologies exist to perform risk assessment and management.
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From page 20... ...
line in an external operating reactor module. The major potential hazards and sources of risk when performing maintenance outside the reactor modules while one or both of the other reactor modules are operating include Failure of a SCWO reactor pressure vessel in an operating reactor module; Failure of compressed air lines in an external operating reactor module; Failure of high-pressure IPA lines in an external operating reactor module; Failure of other feed lines in an external operating reactor module; Removal of reactor linings; and Removal of the thermowells.
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Best safety practices would call for the IPA line to be locked out and remaining contents drained within the idle module, eliminating this risk, while the impact of an IPA line rupture within the operational module would be contained within the physical barriers. The SCWO Process Building fire suppression system and the gaseous hydrocarbon detectors on either end of the reactor modules, which can shut down SCWO operations, are expected to provide the required safety envelope in the event of a fire.
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Another potential source of useful information is the lessons learned from prior chemical demilitarization operations, both the baseline program, which used incineration, and operations at the Pueblo Chemical Agent Destruction Pilot Plant. For instance, while the BGCAPP SCWO system is fundamentally different from any operations at baseline facilities, there may be useful experience from those facilities in general industrial process safety and specific situations encountered.
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Recommendation 9. The BGCAPP staff should conduct a more thorough analysis of safe operating procedures for conducting maintenance operations in the presence of operating SCWO reactors; should apply any useful lessons learned from prior chemical demilitarization experience to SCWO operations and maintenance; should ensure rigorous management of the staff as it gains experience, such as leader follow-up checks; and should address concerns about unforeseen safety events to minimize or prevent stop-work safety events.
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2019. Metrics for Successful Supercritical Water Oxidation System Operation at the Blue Grass Chemical Agent Destruction Pilot Plant: Letter Report.
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