Actual Waste Demonstration of the Nitric-Glycolic Flowsheet for Sludge Batch 9 Qualification

Abstract

For each sludge batch that is processed in the Defense Waste Processing Facility (DWPF), the Savannah River National Laboratory (SRNL) performs qualification testing to demonstrate that the sludge batch is processable. Testing performed by the Savannah River National Laboratory has shown glycolic acid to be effective in replacing the function of formic acid in the DWPF chemical process. The nitric-glycolic flowsheet reduces mercury, significantly lowers the catalytic generation of hydrogen and ammonia which could allow purge reduction in the Sludge Receipt and Adjustment Tank (SRAT), stabilizes the pH and chemistry in the SRAT and the Slurry Mix Evaporator (SME), allows for effective rheology adjustment, and is favorable with respect to melter flammability. In order to implement the new flowsheet, SRAT and SME cycles, designated SC-18, were performed using a Sludge Batch (SB) 9 slurry blended from SB8 Tank 40H and Tank 51H samples. The SRAT cycle involved adding nitric and glycolic acids to the sludge, refluxing to steam strip mercury, and dewatering to a targeted solids concentration. Data collected during the SRAT cycle included offgas analyses, process temperatures, heat transfer, and pH measurements. The SME cycle demonstrated the addition of glass frit and the replication of six canister decontamination additions. The demonstration concluded with dewatering to a targeted solids concentration. Data collected during the SME cycle included offgas analyses, process temperatures, heat transfer, and pH measurements. Slurry and condensate samples were collected for subsequent analysis. Chemical Process Cell (CPC) demonstrations utilizing the alternate reductant flowsheet were performed at an acid stoichiometry of 78.0% Koopman Minimum Acid basis (87.1% Hsu basis) for the SRAT cycle. The scope specified by the technical task request has been successfully completed. Highlights of the testing results are summarized in the paragraphs below. The total solids measurements of the SRAT and SME products were 24.6 and 49.0 weight percent (wt%), respectively, which matched the targets of 25 wt% and 48 wt% acceptably. The consistency and yield stress of the SRAT receipt material fall within the DWPF design basis. The SRAT product yield stress and consistency (0 Pa and 2.8 cP, respectively) are below the DWPF design basis. The SME product yield stress and consistency were 1.0 Pa and 16.0 cP, respectively. The SME product yield stress is below the DWPF design basis. It should be noted that similar rheological properties were encountered during SB5 processing at DWPF. DWPF successfully processed SB5 by implementing process control software to mitigate issues related to the melter feed. This software is still in use at DWPF. Based on the comparison of the iron in the SRAT product and SME product analyses, the waste loading of the SME product is 37.6%. The current DWPF target for waste loading is 36%. Calculations based on several of the other major sludge components (Al, Ca, Mn, Ni, and U) indicated waste loadings ranging from 36....