Hydrocyclone efficiency

As expected, a reduction in hydrocyclone efficiency was experienced during the flash-tank pumping trials. With inlet oil-in-water concentrations ranging from 1,000 to 5.000 ppm. the clean-water outlet was around 200 to 300 ppm. 

Mechanical Gleaning. A cleaner is a hydrocyclone device utilizing fluid pressure to create rotational fluid motion (20). Pulp is introduced tangentially near the top of the cleaner. Contaminants denser than water such as chemically treated toner inks and sand migrate toward the outer wall of the cleaner and exit in a separate (reject) stream. For most forward cleaners, optimal ink removal efficiency is obtained at a pulp consistency of 0.2—0.3%. Most forward cleaners deinking efficiency declines at pulp feed consistencies greater than 0.4%. However, a cleaner said to be efficient at 1.2% pulp consistency has been reported (39). 

Lynch, A.J., T. C. Rao, T.C., "Influence of Hydrocyclone Diameter on Reduced Efficiency Curves," International Journal of Mineral Processing, 1, 173 (1974)... 

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. 

The Bradley hydrocyclone has a lower capacity than the Reitema geometry but is more efficient. For the Rietema cyclone geometry the cor-relatins are (Antunes and Medronho, 1992)... 

The methods developed by EBC and others in the late 1990s using hydrocyclones and phase-inversion techniques may be sufficient for separation of the treated oil from the aqueous phase and biocatalyst. However, a cost analysis of such methods may be necessary to determine the economic feasibility. Recent work using hydrophobic membranes, magnetically separable immobilized biocatalysts and other techniques may provide alternate methods for separation of oil and recycling biocatalyst. A comparison of these techniques with each other and the previously investigated hydrocyclone techniques is needed to demonstrate improvements in the separation efficiency. 

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. 

The grade efficiency reflects the properties of the particles exploited in the separation. It is influenced by the nature of the fluid/solid system, and by the operating conditions which determine the magnitude of the separating effect, and the period during which particles are subjected to it. Such details should, therefore, accompany any experimental data on G(d). The concept is widely applied to separations using hydrocyclones as discussed in Section 1.5.4. 

The experimental results reported in this paper demonstrate the ability of a flat-bottom hydrocyclone to separate the coarse fraction of ammonium sulfate crystals from a slurry which contains crystals of a wide size range. It appears that the grade efficiency curve, which predicts the probability of a particle reporting to the underflow of the cyclone as a function of size, can be adjusted by a change in the underflow diameter of the hydrocyclone. These two observations lead to the suggestion to use hydrocyclone separation to reduce the crystal size distribution which is produced in crystallisers, whilst using a variable underflow diameter as an additional input for process control. 

There is a clear need for other size classifiers which combine a high separation efficiency with flexibility and compactness. Hydrocyclones have a small volume, are simple in operation and are standard size classification equipment, for example in closed circuit grinding applications. The recent development of the flat-bottom hydrocyclone, which permits classification in the coarse size range, creates an additional motive to study the use of hydrocyclones for Crystal Size Distribution (CSD) control. Furthermore, throttling of a flat botom hydrocyclone does not necessarily provoke blockage but allows continuous control of its cut size when a controlled throttling valve is used. There is a clear incentive for its use in this application since it may provide an additional process input. 

Definitions. The performance of a hydrocyclone is generally characterised by means of a grade efficiency or Tromp-curve which is the fractional mass recovery expressed as a function of particle size. 

The degree of cell separation is an important parameter to be evaluated in perfusion systems. This can be done through the use of some concepts as cell separation efficiency, grade efficiency, and cut size. These concepts are applicable to any equipment whose performance remains constant if the operational conditions do not change. They are valid, therefore, for equipment such as sedimenting centrifuges, hydrocyclones, gravitational settlers, etc. 

Fig. 3. Separation efficiency of HeLa cells when using a 10 mm Mozley hydrocyclone, a 10 mm Dorr-Oliver hydrocyclone and a 7 mm Bradley hydrocyclone [65]...

Liibberstedt [64] tested three different hydrocyclones for HeLa cell separation a 7 mm Bradley [67], a 10 mm Mozley (Richard Mozley Ltd., Redruth, UK), and a 10 mm Dorr-Oliver (Dorr-Oliver GmbH, Wiesbaden, Germany) (the dimension quoted here is the diameter of the cylindrical part of each hydrocyclone). The best results were obtained with the Dorr-Oliver hydrocyclone (Fig. 3), which produced a cell separation efficiency of 81 % when working at a pressure drop of 300 kPa and a flow rate of 2.8 L min When operating with two 10 mm Dorr-Oliver connected in series (the overflow of the first as feed for the second) at 200 kPa, the global efficiency of the arrangement was 94% [65]. These experimental values confirm the computational fluid dynamics (CFD) predictions that high levels of efficiencies for mammalian cells could be achieved with small diameter hydrocyclones [46]. 

The effective density of separation depends on the particle size and aspect ratio. As the particle size and aspect ratio decreases, the separation becomes more efficient and the offset between separation density and hydrocyclone medium density decreases. This findings suggest that for efficient density separation closely sized fine plastic fractions are required. 

In Hydrocyclones A Solution to Produced Water Treatment, Meldrum presents the basic design principle of a dc-oilmg hydrocy leone. System design, early operational experiences, and test results on a full-scale application in the North Sea are discussed. Oil-removal efficiency was seen to rise with increasing reject ratio up to around 1%, producing acceptable outlet concentrations Early field test results on a tension leg platform in the North Sea are discussed. Preliminary data on a pumped system are also given. 

The reject rate and mlet flow rate provide the means of efficiently controlling the hydrocyclone for optimum performance over a range of conditions. While the other parameters are undoubtedly equally important, they are essentially fixed for a given installation, so we do not have the same degree of control over them, except through careful system design. 

Flow Rate. The inlet flow rate is another key operating characteristic of the hydrocyclone. Typically, as flow rate increases, the efficiency of separation increases and then levels out over the unit s operating range. Further increases in flow will eventually cause the efficiency to drop sharply (Fig 3). 

In summary, from all currently available test data, the four-in-one 33-tnm (1.4-in.] hydrocyclones exhibit high efficiencies over a range of 318 to 1113 m3/d water (2,000 to 7,000 BWPD] per unit, giving a turndown ratio of 3.5 1. The upper limit is considered to be a pressure-drop restriction on available reject rate, not droplet shearing caused by the high flow rate. 

Hence, currently available test data, current separator pressures, and the need for high reject ratios indicate that the hydrocyclones exhibit high efficiencies from 636 to 1590 mJ/d water [4,000 to 10,000 BWPD] per four-in-ooe 60-nun [2.4-tn.J hydrocyclone (single unit times 4). This gives an operating turndown ratio of 2.5 1. The relationship of efficiency vs. flow rate for the 60-mm (2.4-in.] cyclooe is shown graphically in Fig. 3. 

Monitoring the separation efficiency is an important way to evaluate the performance of a given separator. The efficiency concepts described in this section apply not only to animal cell separation, but also to the separation of any particles and bioparticles, such as microorganisms, cellular debris, nuclei, etc. These concepts apply to any separation device whose performance remains constant if the operational conditions do not change. This happens, for instance, in gravity settlers, centrifuges, and hydrocyclones. 

Hydrocyclones are very simple devices and always operate with a flow ratio Rf > 0. They may be easily designed to give a desired separation efficiency (Castilho and Medronho, 2000), and their performance may also be easily predicted (Coelho and Medronho, 2001). In the last few years, it has been shown either theoretically or experimentally that hydrocyclones may be used in animal cell separations (Luebberstedt et al., 2000 Medronho et al., 2005 Elsayed et al., 2006 Pinto et al., 2007) aimed mainly at mammalian cell retention in perfusion bioreactors (Jockwer et al., 2001 Elsayed et al., 2005). 

Elsayed A, Medronho RA, Wagner R, Deckwer, W-D (2006), Use of hydrocyclones for mammalian cell retention - I. Separation efficiency and cell viability, Eng. Life Sci. 6 347-354. 

Solids control for the drilling fluid system An effective way to reduce the volume of drilling fluid waste is the use of solids control. The efficient use of solids control equipment (for example hydrocyclones and centrifuges) in combination with chemical flocculants minimizes the need for makeup water to dilute the fluid system. An enhanced solids control system designed to compliment a specific drilling operation is a very effective waste minimization technique. 

This is a batch size analyzer [33] (Figure 10.1). An extremely dilute sample of milled ore is introduced, at a constant flow rate, to a coarse separator in the form of a tangentially fed cylindrical screen. The coarse fraction is allowed to settle and the fine fraction is further separated with an efficient hydrocyclone into a fine and a very fine fraction. The very fine fraction is discarded and the fine fraction is allowed to settle. The ratio of the times taken to fill the coarse and fine fraction collection vessels to indicated levels can be related directly to the particle size distribution. The cyclosensor has a sensitivity whereby a change of 1.8% passing 100... 

---