Abstract
The Department of Energy is sponsoring the River Protection Project, which includes the design of a facility to stabilize liquid radioactive waste that is stored at the Hanford Site. The Savannah River Technology Center (SRTC) of the Westinghouse Savannah River Company was contracted to develop and test parts of the waste treatment process. One part of the process is the separation of highly radioactive solids from the liquid wastes by precipitation and cross-flow filtration. A cross-flow filter was tested with simulated wastes made to represent typical waste chemical and physical characteristics. This paper discusses the results of a cross-flow filter operation in a pilot-scale facility that was designed, built, and run by the Experimental Thermal Fluids Laboratory of SRTC. The waste simulant had an insoluble solids loading from 2 to 22 wt.%, with particle sizes from 1 to 2 μm and 5 to 10 μm in diameter. The filter contained seven 316L stainless steel sintered-metal tubes in parallel. Each tube was identical, being 1.01 m long, 9.5 mm inside diameter, and membrane thickness of 1.6 mm. The porous tubes were made to capture 95% of particles ⩾0.1 μm. The flow conditions for the test varied: Axial slurry velocities from 3 to 5 m/s and transmembrane pressures (TMP) from 200 to 500 kPa, at a temperature of 298 K. The results showed good separation for the Newtonian slurry with solids loadings of 2 wt.%. Under the flow conditions of a slurry velocity of 3.5 m/s and a TMP of 400 kPa, the observed filtrate flux was 17 cm/h (Volumetric flow rate per filter surface area (cm 3/h/cm 2) was reduced to cm/h for convenience. Other commonly used units for filter flux include: 1 cm/h=10 l/m 2/h=0.0041 gpm/ft 2.); meeting the plant design need of 16 cm/h. As the insoluble solids loading was increased to 22 wt.% the slurry became a shear thinning, thixotropic fluid, with a yield stress of 5.5 Pa and a consistency of 23 mPa s. Despite the changing rheology the filtrate flux continued, but dropped to 2.4 cm/h.
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