Decanters settlers

Decanters are used to separate liquids where there is a sufficient difference in density between the liquids for the droplets to settle readily. Decanters are essentially tanks which give sufficient residence time for the droplets of the dispersed phase to rise (or settle) to the interface between the phases and coalesce. In an operating decanter there will be three distinct zones or bands clear heavy liquid separating dispersed liquid (the dispersion zone) and clear light liquid. 

Z2 = height from datum to heavy liquid overflow, m, 

A rough estimate of the decanter volume required can be made by taking a hold-up time of 5 to 10 min, which is usually sufficient where emulsions are not likely to form. Methods 

The decanter vessel is sized on the basis that the velocity of the continuous phase must be less than settling velocity of the droplets of the dispersed phase. Plug flow is assumed, and the velocity of the continuous phase calculated using the area of the interface  

Equation 10.7 is used to calculate the settling velocity with an assumed droplet size of 150 pm, which is well below the droplet sizes normally found in decanter feeds. If the calculated settling velocity is greater than 4 x 10-3 m/s, then a figure of 4 x 10 3 m/s is used. 

A rough estimate of the decanter volume required can be made by taking a hold-up time of 5 to 10 min, which is usually sufficient where emulsions are not likely to form. Methods for the design of decanters are given by Hooper and Jacobs (1979) and Signales (1975). The general approach taken is outlined below and illustrated by Example 10.3. 

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Design Scope. Stirred vessels, rotor-stator mixers, static mixers, decanters, settlers, centrifuges, homogenizers, extraction colunms, and electrostatic coalescers are examples of industrial process equipment used to contact liquid-liquid systems. Although this chapter emphasizes stirred vessels, the fundamentals of phase behavior are applicable to a broad range of other equipment types. Immiscible liquid-liquid systems are processed in batch, continuous, and semicontinuous modes. 

Gravity Settlers Decanters These are tanks in which a liqmd-liquid dispersion is continuously settled and coalesced and from wriich the settled liquids are continuously withdrawn. They can be either horizontal or vertical. Figure 15-24 shows some typical horizontal decanters. For an uninstrumented decanter the height of the heavy-phase-liquid leg above the interface is balanced against the height of the hght-hquid phase above the interface, Eq. 15-50. 

The ratio of the ionic liquid to the organic phase present in the reactor also plays an important role. A too high level of ionic liquid results in much longer decantation time and causes lower dimer selectivity. To combine efficient decantation and a reasonable size for the settler in the process design, it has been proposed that the separation of the two phases be performed in two distinct settling zones arranged in parallel [38]. 

Horizontal Gravity Settlers or Decanters, Liquid/Liquid... 

Gravity decanter, illustration, 243, 244 Happel/Jordan method, 241 Horizontal gravity, 239 Lamella classifiers, 239 Settler vessel, illustration, 240 Time planning and scheduling, process design, 36... 

In the model simulations, the settling and decanting phase were characterized by a reactive point-settler model. The simulations were carried out using matlab 6.5 simulation platform. A systematic model calibration methodology as described in Fig. 2 was applied to the SBR. Fig. 3. shows the simulation results from the calibrated model. The model predicted the dynamics of the SBR with good accuracy. 

The archetypal, stagewise extraction device is the mixer-settler. This consists essentially of a well-mixed agitated vessel, in which the two liquid phases are mixed and brought into intimate contact to form a two phase dispersion, which then flows into the settler for the mechanical separation of the two liquid phases by continuous decantation. The settler, in its most basic form, consists of a large empty tank, provided with weirs to allow the separated phases to discharge. The dispersion entering the settler from the mixer forms an emulsion band, from which the dispersed phase droplets coalesce into the two separate liquid phases. The mixer must adequately disperse the two phases, and the hydrodynamic conditions within the mixer are usually such that a close approach to equilibrium is obtained within the mixer. The settler therefore contributes little mass transfer function to the overall extraction device. 

The simplest form of extractor is a mixer-settler, which consist of an agitated tank and a decanter. 

Gravity separators can take many shapes and arrangement, depending in part on the characteristics of the waste. Typical design configurations include horizontal cylindrical decanters, vertical cylindrical decanters, and cone-bottomed settlers. 

Figure 8.1b shows a simple gravity settler or decanter for removing a dispersed liquid phase from another liquid phase. The horizontal velocity must be low enough to allow the low-density droplets to rise from the bottom of... 

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