Sludge Heel Removal Analysis for Slurry Pumps of Tank 11

Abstract

Computational fluid dynamics methods were used to develop and recommend a slurry pump operational strategy for sludge heel removal in Tank 11. Flow patterns calculated by the model were used to evaluate the performance of various combinations of operating pumps and their orientation. The models focused on removal of the sludge heel located at the edge of Tank 11 using the four existing slurry pumps. The models and calculations were based on prototypic tank geometry and expected normal operating conditions as defined by Tank Closure Project (TCP) Engineering. Computational fluid dynamics models of Tank 11 with different operating conditions were developed using the FLUENT(tm) code. The modeling results were used to assess the efficiency of sludge suspension and removal operations in the 75-ft tank. The models employed a three-dimensional approach, a two-equation turbulence model, and an approximate representation of flow obstructions. The calculated local velocity was used as a measure of sludge removal and mixing capability. For the simulations, a series of the modeling calculations was performed with indexed pump orientations until an efficient flow pattern near the potential location of the sludge mound was established for sludge removal. The calculated results demonstrated that the existing slurry pumps running at 1600 rpm could remove the sludge mound from the tank with a 103 in. liquid level, based on a minimum sludge suspension velocity of 2.27 ft/sec. In this case, the only exception is the region within about 2 ft. from the tank wall. Further results showed that the capabilities of sludge removal were affected by the indexed pump orientation, the number of operating pumps, and the pump speed. A recommended operational strategy for an efficient flow pattern was developed to remove the sludge mound assuming that local fluid velocity can be used as a measure of sludge suspension and removal. Sensitivity results showed that for a given pump speed, a higher tank level and a lower pump nozzle elevation would result in better performance in suspending and removing the sludge. The results also showed that the presence of flow obstructions such as valve housing structure were advantageous for certain pump orientations.