Preliminary feasibility evaluation of a scrubber for removing acid gases and radioactive iodine from a waste vitrification system offgas stream at a government facility.
VITRIFICATION SYSTEM OFFGAS SCRUBBER FEASIBILITY EVALUATION
The client was issued a Request for Proposal (RFP) for designing and fabricating a scrubber to be located at a nuclear materials processing facility. The scrubber is to be used for removing acid gases and radioactive iodine from a waste vitrification system offgas stream. The RFP contained a detailed specification for the requirements of the scrubber that included: inlet stream flow rates, temperatures, pressures, and composition characterizations; scrubber duties; scrubber performance requirements for acid gas and iodine removal; required materials of construction; scrubber height and diameter restrictions; and required scrubber lifetime. The client was unsure of the feasibility of simultaneously meeting all of the listed requirements and contracted Process Engineering Associates, LLC (PROCESS) to execute a preliminary feasibility evaluation of the scrubber. PROCESS constructed detailed computer process simulations of scrubber operation using licensed commercial process simulation software and utilized its knowledge of, and experience with similar systems to reach the following conclusions:
- Although the unit size set forth in the RFP specification will suffice from a pressure drop and acid gas removal standpoint, the requirement for removal of 99% of the iodine cannot likely be met. (PROCESS estimated that 75-90% of the iodine will be removed by the scrubber.) As such, a downstream polishing unit for supplemental iodine removal will be required.
- The requirement for quenching the hot offgas stream in the bottom section of the scrubber is not feasible due to gas high velocities and high temperatures which will result in the loss of mass transfer stages as well as pluggage in the packing where gas quenching is occurring. PROCESS strongly recommended a separate upstream vessel for gas quenching. If a separate unit for quenching is not feasible, PROCESS recommended a carefully-designed spray nozzle system in the scrubber inlet duct for the purpose of completing the majority of the gas quenching upstream of the scrubber.
- The requirement of 316L stainless steel for the vessel is entirely incompatible with the requirement of a 40-year life for the unit. PROCESS recommended Hastalloy C2000 for the vessel and vessel internals.
Subsequent to the initiation of the project, the client reduced the size of the scrubber. PROCESS executed additional process simulations and selected the scrubber packing to help ensure that the scrubber still met mass transfer and pressure drop requirements.
The information was summarized in a letter report and was used by the client in the preparation of a bid for design and fabrication of the unit.
- Governmental radioactive materials processing
- Front end engineering design (FEED)
- Computer simulation
- Radioactive materials processing
- Scrubber design
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