IDAHO FALLS, Idaho - EM’s Idaho Site is preparing to conduct another Integrated Waste Treatment Unit (IWTU) demonstration, focusing on fluidization of the facility’s primary reaction vessel after the project team completed improvements this past year.
The new test follows a 2017 demonstration that successfully tested the IWTU’s redesigned auger-grinder, which transfers treated waste material to downstream processes.
In previous demonstrations, instabilities occurred within the Denitration Mineralization Reformer (DMR), including sudden temperature changes and clumping of bed product material due to lack of carbon dioxide in the vessel. Those conditions are caused by weaknesses in the DMR design and the cohesive characteristics of the waste as it converts to a solid carbonate product. The bed material began to stick together like sand castles, greatly hampering fluidization inside the DMR.
The team redesigned the DMR’s interior from a half-moon to cone shape and replaced the fluidizing gas rails as a result of extensive studies, computer modeling, and the operation of a pilot plant in Colorado. Superheated steam is delivered through many small nozzles to suspend and fluidize the billions of tiny beads in the vessel. During the steam-reforming process, liquid waste is injected among the superheated beads, which are coated with the waste and converted to a carbonate product like the creation of a pearl.
“The pilot plant at Hazen Research underwent these same modifications, so we’ve got a good look at how performance was improved during its operation," said Joe Giebel, chief engineer for Fluor Idaho, EM’s Idaho Site cleanup contractor. “This demonstration run is all about fluidization."
Hazen operated the pilot plant for nearly 100 days in 2017 to assess a wide range of operating conditions and equipment configurations.
Other factors critical to optimum fluidization include the rate at which the waste product is introduced into the DMR and the product particle size. The operating team plans to maintain a 1.5-gallon-per-minute waste feed rate during the demonstration and control the product particles to an average size of 300 microns (about the size of coarse coffee grounds) before transferring them out of the DMR.
The demonstration is scheduled for up to 30 days of waste feed followed by a second run of up to 50 days after performance expectations are met.
The team is focused on determining how effectively the changes improve fluidization, according to Craig Olson, Fluor Idaho IWTU manager. Because the IWTU hasn’t operated for nearly a year due to its modifications, Olson said his team will closely monitor how the system responds to the equipment modifications and process control changes.
Construction of the IWTU was completed in 2012 to treat 900,000 gallons of liquid sodium-bearing waste remaining in the tank farm at the Idaho Nuclear Technology and Engineering Center. Six demonstrations using simulated waste have occurred at the IWTU to test its steam-reforming process. Each run ended prematurely due to equipment problems or process instabilities caused by insufficient fluidization.
Source: U.S. Dept. of Energy, Office of Environmental Management
