Flowsheet Testing for Strip Effluent to Slurry Mix Evaporator Modifications at the Defense Waste Processing Facility

Abstract

Savannah River Remediation plans to add strip effluent to the Sludge Receipt and Adjustment Tank (SRAT) and/or the Slurry Mix Evaporator (SME) during processing in the Defense Waste Processing Facility (DWPF). At the present time, strip effluent is added only to the SRAT, but this flowsheet change is planned to allow more flexibility in processing the large volume of strip effluent produced by the Modular Caustic-side Solvent Extractant Unit (MCU) or the Salt Waste Processing Facility (SWPF).Four process demonstrations of the coupled flowsheet for SRAT and SME cycles were performed using SB8-Tank 40 simulant. These runs were patterned after run SB8-D5 (a previous coupled experiment completed in developing the SB8 flowsheet and utilizing the same sludge simulant, addition of Actinide Removal Product (ARP), and acid addition). Differences from run SB8-D5 included much higher noble metal concentrations and very long strip effluent addition times (equivalent to 38,000 gallons of Strip Effluent, including 30,000 gallons of Strip Effluent added to the SME), which combined to make this a very challenging set of runs.The main difference between the runs was that three strip effluent combinations (original solvent based on BobCalix/nitric acid, new solvent based on MaxCalix/boric acid, and a blend of the two) were used. A fourth run was performed without solvent and using water as the strip effluent solution to see whether the solvent or strip effluent acid had any impact on processing, particularly hydrogen generation.Although allowing a large addition of strip effluent to either the SRAT or SME offers obvious operational advantages, it also requires a longer time at temperature than typical DWPF batches, which may lead to higher hydrogen generation, higher ammonia production, higher formate destruction, lower Reduction/Oxidation (REDOX) Ratio, higher potential for foaming and coil fouling, and higher yield stress and consistency. Although these impacts could be carefully controlled, consistent processing (same sludge, ARP, strip effluent, and decon water volume for each SRAT and SME batch), should lead to consistent product chemistry. Processing at the maximum volumes of strip effluent, whether in the SRAT, SME or both increases the likelihood of the process problems listed above and may require remediation of the SME product with nitric or formic acid to achieve the desired glass REDOX. Due to the high pH of the SME product leading to higher yield stress and consistency, the melter feed pump may have more difficulty feeding to the melter without dilution. Some of the highlights of the testing are summarized below:• The destruction of formate was very high in all runs, but especially high in the two runs with the highest hydrogen generation. The SME formate destruction varied from 29.3 to 70.7% for the four runs, much higher than the 2% measured in a similar run during SB8 blend qualification. This led to a high generation of CO 2 , which could increase the potential for foamovers. • Due to the high anion destruction ra...

White Paper to Justify the Use of Strip Effluent in the Defense Waste Processing Facility During Slurry Mix Evaporator Processing

“…A study was completed by SRNL to evaluate whether the addition of SEFT in the SME cycle would have any influence on nitric-formic Acid Flowsheet CPC processing. 3 This testing was designed to bound all future DWPF processing, so it included high noble metal concentration (HM or H Modified) and high SEFT addition volume (38,000 gallons, 8,000 in SRAT, 30,000 in SME). The report recommended "Based on the testing completed, an endorsement of the flowsheet change for adding strip effluent to the SME is not currently warranted."…”

“…2 The addition of SE to the SME has been previously studied for the nitric-formic acid flowsheet. 3 This study found that due to the long processing time that results from processing increased volumes of SE may lead to higher hydrogen generation, higher ammonia production, higher formate destruction, lower REDOX ratio, higher potential for foaming and coil fouling, and higher yield stress and consistency. As a result of this testing, the addition of SE to SME was not implemented in DWPF.…”

Impact of Salt Waste Processing Facility Streams on the Nitric-Glycolic Flowsheet in the Chemical Processing Cell

“…Testing has been performed for the nitric-formic flowsheet using the SEFT from either the baseline (i.e., BOBCalixC6), the Next Generation Solvent (NGS) (i.e., MaxCalix b ), and the blended solvent systems. 2 Since Sludge Batch (SB) 3, 3 SRNL has performed testing specific to ARP as part of nitric-formic flowsheet testing with simulants. Simulated ARP streams typically added less monosodium titanate c (MST) to the slurry than the SWPF version of AR.…”

“…The first test listed is the evaluation performed for the nitric-formic flowsheet on the inclusion of SEFT material in the SME. 2 Processing difficulties were encountered with heat transfer rod fouling specific to the experimental system that ultimately led to increased hydrogen generation. Lab scale testing simulated a total of 38,000 gallons of SEFT material processed during these cycles split between the SRAT and the SME, for a respectable 80 hour boiling time.…”

“…With the exception of the testing to support sending SEFT material to the SME, 2 Consideration should be given toward testing coupled operation in the shielded cells as part of the qualification. While not strictly required by the DWPF WAC, including PRFT and SEFT material in the qualification of a blend could provide valuable processability information if DWPF employs coupled-only operation.…”