Mixing in Large Scale Tanks: Part III — Predicting Slurry Pump Performance

Abstract

This third in a series of four papers (Parts I–IV) presents the equations used for the initial evaluation of a pump’s ability to suspend solids and extends those equations to establish the minimum local velocity required to suspend those solids. This minimum velocity was used in a finite difference model in Part I to predict the ability of a pump to suspend, or slurry, solids that had settled on the bottom of a nuclear waste tank. To slurry waste, the Advanced Design Mixer Pump (ADMP) discharges a fluid jet that impinges on, shears, and then suspends the waste. Prior to the pump’s installation in a waste tank, the local velocity at a point in the flow required to suspend solids was found from available equations, material properties, and empirical data for similar pumps. Also, the computational fluids dynamics (CFD) model was validated in Part II by comparing it to flow rates measured in a full scale test facility where the ADMP was operated. The CFD fluid model could then be used to predict flow rates throughout the actual waste tank where the pump was to be installed, and the ability of the pump to adequately slurry the waste could be shown. All that needed to be done was to compare the local velocity of the fluid required to shear the waste into suspension to the velocities modeled throughout the waste tank. In short, this paper validates the theoretical and experimental basis for the derivation of a minimum velocity required for the flow stream to shear the waste into suspension. The final installment to this series of papers (Part IV) validates the application of the CFD model, by concluding that a nuclear waste tank is effectively cleaned to the wall throughout most of tank, using the ADMP.

Analysis of Turbulent Mixing Jets in a Large Scale Tank

“…However, studies of the ECR based on measured yield stress and density provide reasonable estimates for both the ECR and the velocity at the ECR required to suspend sludge. A complete discussion of material properties and their relationship to the minimum required velocity of 0.7 m/sec is provided in the previous work [12]. In this work the velocity criterion required for the flow stream to shear the waste into suspension was discussed in detail by the theoretical and experimental basis.…”

“…Two types of materials are identified in Tank 18, both of which are discussed in detail in the previous work [12]. One is particulate zeolite.…”

“…A minimum fluid velocity for suspending cohesive sludge at Savannah River Site (SRS) has been confirmed and established as 0.7 m/sec (2.27 ft/sec). [12] Figure 2 shows that this velocity, 0.7 m/sec, will erode the sludge layer for the particle sizes larger than clay material (about 5 µm).…”

Tank 26 Evaporator Feed Pump Transfer Analysis

“…In the present study, the sludge solids are not scoured unless the liquid velocity is greater than the minimum scouring velocity (V min ) necessary to pick up solids deposited at the sludge layer. For cohesive sludge solids, the minimum scouring velocity is 0.7 m/s (2.27 ft/s) [6,10]. For loosely-packed solid, the minimum scouring velocity is dependent upon several factors, including: flow velocity, particle size, and the density ratio between the sludge particles and the carrier fluid.…”

Tank 32 Evaporator Feed Pump Transfer Analysis

“…For cohesive sludge solids, the minimum scouring velocity is 0.7 m/s (2.27 ft/s) [6,10]. For loosely-packed solid, the minimum scouring velocity is dependent upon several factors, including: flow velocity, particle size, and the density ratio between the particulate and the carrier fluid.…”