Flows hydrocyclones

The reverse-flow hydrocyclone shown in Figure 1.9 is a relatively cheap, compact and versatile device. The basic unit has no moving parts and comprises an inverted conical bottom section attached to a cylinder containing a tangential inlet port. Feed is injected through the port at a mean velocity between 10 and 30 m s whence geometry-induced motion causes the (usually denser) suspended particles to experience centrifugal forces of between... 

Figure 1.9 Cross-section through a reverse-flow hydrocyclone showing the typical flow patterns. The inset photograph (Axsia-Mozley) shows a bank of six cyclones connected to a common feed manifold system.

Fig. 4.25 Counterflow and unidirectional flow hydrocyclones for heavy weight (HW) and lightweight (LW) particles removal.

The vessel design features a Chinese hat-like conical core stopper above the underflow sump, which is there to prevent the vortex from reaching the latter and reentraining the settled soHds. The core stopper is also beheved to stabilize and locate the vortex flow in the vessel. Overflow from the vessel is through a wide cylindrical insert through the Hd, similar to a vortex finder in a hydrocyclone (16), and an optional provision can be made for collecting any floatables in a float trap. 

Fig. 3. Air-sparged hydrocyclone, where A represents the tangential feed that estabHshes swid flow B, the area of small bubbles formed by high shear at the porous wall and C, the outlet for the (D) hydrophilic particles rejected by the swid flow. The (B) hydrophobic particles are in the axial froth flow.

Figure 4.22 Schematic diagram of hydrocyclones, a) Flow pattern, (h) Alternate a.spect ratios adapted for service after Wallas, 1988)...

Theoretical representation of the behaviour of a hydrocyclone requires adequate analysis of three distinct physical phenomenon taking place in these devices, viz. the understanding of fluid flow, its interactions with the dispersed solid phase and the quantification of shear induced attrition of crystals. Simplified analytical solutions to conservation of mass and momentum equations derived from the Navier-Stokes equation can be used to quantify fluid flow in the hydrocyclone. For dilute slurries, once bulk flow has been quantified in terms of spatial components of velocity, crystal motion can then be traced by balancing forces on the crystals themselves to map out their trajectories. The trajectories for different sizes can then be used to develop a separation efficiency curve, which quantifies performance of the vessel (Bloor and Ingham, 1987). In principle, population balances can be included for crystal attrition in the above description for developing a thorough mathematical model. 

Because of the complexity of the flow within hydrocyclones, however, various, largely empirical, methods for prediction of the cut size have been proposed for use in practice, as reviewed by Svarovsky (2000). 

Brayshaw, M.D., 1990. Numerical model for the inviscid flow of a fluid in a hydrocyclone to demonstrate the effects of changes in the vorticity function of the flow field on particle classification. International Journal of Mineral Processing, 29, 51. 

Hydraulic transport, vertical flow 1.96, 210 Hydrocyclones 55 Hygrometer 758... 

Centrifugal force can also be used to separate solid particles from fluids by inducing the fluid to undergo a rotating or spiraling flow pattern in a stationary vessel (e.g., a cyclone) that has no moving parts. Cyclones are widely used to remove small particles from gas streams ( aerocyclones ) and suspended solids from liquid streams ( hydrocyclones ). 

The diameter of a hydrocyclone can range from 10 mm to 2.5 m, cut sizes from 2 to 250 /am, and flow rate (capacities) from 0.1 to 7200 m3/hr. Pressure drop can range from 0.3 to 6 atm (Svarovsky, 1984). For aerocy-clones, very little fluid leaves with the solids underflow, although for hydrocyclones the underflow solids content is typically 45-50% by volume. Aerocyclones can achieve effective separation for particles as small as 2-5 pm. 

The down-comer from the gas/liquid separator that collects the liquid slurry product is connected to the suction side of a moyno-type (Liberty progressive cavity) pump. The pump discharge is connected to a primary separation device (an inertial separator similar to a hydrocyclone). Since the slurry pump is a positive displacement device (i.e., no slurry slippage inside the pump), the total flow... 

The hydrocyclones and high-shear mixers operated throughout the testing. During energetics destruction, no deposits of crystalline material or flow blockages were observed with the hydrocyclones and high-shear mixers in place. 

The existing titanium hydrocyclones are close in design to the units to be provided by the Mozley Company for a full-scale facility in multiple parallel flow units (sometimes called multiclones ). Therefore, the results for the titanium system are anticipated to be similar to those for the Mozley units. 

The flow rate to the hydrocyclones for the full-scale SILVER II unit, based on a 14-mm vortex finder and a 6.4-mm underflow spigot, would need to be approximately 3.2 m3/hr at a pressure of around 3.5 bar. This flow rate should be sufficient to achieve the overflow flow rate of 1.8 m3/hr required to feed the SILVER II cells. As noted previously, the hydrocyclones used in the 12-kW energetics and agent simulant trials for EDS II handled solids at the planned design loading (AEA, 2001a). 

The committee notes that the laboratory tests established operating parameters for hydrocyclone operation that involve careful control of pressures and flows to achieve desired separation efficiencies. No tests were performed to demonstrate the robustness of hydrocyclone operation during the pressure and flow swings that might be expected during normal operations of a full-scale facility. 

Integrated operation of these hydrocyclones has been demonstrated in a three-cell configuration. However, scale-up to 432 cells may present new challenges in flow and pressure management to sustain satisfactory hydrocyclone operation. 

Demonstrations of the scale-up, development, and integration of hardware with real materials of construction must focus on the robustness of the parallel flow in multiple-cell reactors. The issues of cell blockage, hydrocyclone performance, and NOx reformer performance must be addressed. 

The slurry flow management scheme to the cells has large numbers of parallel flow paths through the hydrocyclones and through individual electrode cavities. Upsets in these paths can lead to upsets in the quality and quantity of slurry flowing to the electrode cavities, with possible impact on membrane operation. 

As flow patterns are influenced only slightly by gravitational forces, hydrocyclones may be operated with their axes inclined at any angle, including the horizontal, although the removal of the underflow is facilitated, with the axis vertical. 

The flow patterns in the hydrocyclone are complex, and much development work has been necessary to determine the most effective geometry, as theoretical considerations alone will not allow the accurate prediction of the size cut which will be obtained. A mathematical model has been proposed by Rhodes et alP6), and predictions of streamlines from their work are shown in Figure 1.38. Salcudean and Gartshore137 have also carried out numerical simulations of the three-dimensional flow in a hydrocyclone and have used the results to predict cut sizes. Good agreement has been obtained with experimental measurements. 

Near the top of the hydrocyclone there will be some short-circuiting of the flow between the inlet and the overflow, although the effects are reduced as a result of the formation of circulating eddies, often referred to as the mantle, which tend to act as a barrier. Within the secondary vortex the pressure is low and there is a depression in the liquid surface in the region of the axis. Frequently a gas core is formed, and any gas dispersed in the form of fine bubbles, or coming out of solution, tends to migrate to this core. In pressurised systems, the gas core may be very much reduced in size, and sometimes completely eliminated. 

There have been very few studies of the effects of non-Newtonian properties on flow patterns in hydrocyclones, although Dyakowski et al.,AU have carried out numerical simulations for power-law fluids, and these have been validated by experimental measurements in which velocity profiles were obtained by laser-doppler anemometry. 

Rhodes, N., Pericleous, K. A., and Drake, S. N. Solid Liquid Flow 1 (1989) 35. The prediction of hydrocyclone performance with a mathematical model. 

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