DWPF Recycle Evaporator Simulant Tests
Testing was performed to determine the feasibility and processing characteristics of an evaporation process to reduce the volume of the recycle stream from the Defense Waste Processing Facility (DWPF). The concentrated recycle would be returned to DWPF while the overhead condensate would be transferred to the Effluent Treatment Plant. Various blends of evaporator feed were tested using simulants developed from characterization of actual recycle streams from DWPF and input from DWPF-Engineering. The simulated feed was evaporated in laboratory scale apparatus to target a 30X volume reduction. Condensate and concentrate samples from each run were analyzed and the process characteristics (foaming, scaling, etc) were visually monitored during each run. The following conclusions were made from the testing: Concentration of the ''typical'' recycle stream in DWPF by 30X was feasible. The addition of DWTT recycle streams to the typical recycle stream raises the solids content of the evaporator feed considerably and lowers the amount of concentration that can be achieved. Foaming was noted during all evaporation tests and must be addressed prior to operation of the full-scale evaporator. Tests were conducted that identified Dow Corning 2210 as an antifoam candidate that warrants further evaluation. The condensate has the potential to exceed the ETP WAC for mercury, silicon, and TOC. Controlling the amount of equipment decontamination recycle in the evaporator blend would help meet the TOC limits. The evaporator condensate will be saturated with mercury and elemental mercury will collect in the evaporator condensate collection vessel. No scaling on heating surfaces was noted during the tests, but splatter onto the walls of the evaporation vessels led to a buildup of solids. These solids were difficult to remove with 2M nitric acid. Precipitation of solids was not noted during the testing. Some of the aluminum present in the recycle streams was converted from gibbsite to aluminum oxide during the evaporation process. The following recommendations were made: Recycle from the DWTT should be metered in slowly to the ''typical'' recycle streams to avoid spikes in solids content to allow consistent processing and avoid process upsets. Additional studies should be conducted to determine acceptable volume ratios for the HEME dissolution and decontamination solutions in the evaporator feed. Dow Corning 2210 antifoam should be evaluated for use to control foaming. Additional tests are required to determine the concentration of antifoam required to prevent foaming during startup, the frequency of antifoam additions required to control foaming during steady state processing, and the ability of the antifoam to control foam over a range of potential feed compositions. This evaluation should also include evaluation of the degradation of the antifoam and impact on the silicon and TOC content of the condensate. The caustic HEME dissolution recycle stream should be neutralized to at least pH of 7 prior to blending with the acidic recycle streams. Dow Corning 2210 should be used during the evaporation testing using the radioactive recycle samples received from DWPF. Evaluation of additional antifoam candidates should be conducted as a backup for Dow Corning 2210. A camera and/or foam detection instrument should be included in the evaporator design to allow monitoring of the foaming behavior during operation. The potential for foam formation and high solids content should be considered during the design of the evaporator vessel.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-96SR18500
- OSTI ID:
- 890169
- Report Number(s):
- WSRC-TR-2005-00142; TRN: US0604655
- Country of Publication:
- United States
- Language:
- English
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