Liquid Spray Columns

When the dispersed phase is the light phase, the constants are similar to those for bubble columns. The case of a heavy dispersed phase can also be handled in a similar manner. 

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A unified approach has been developed for the prediction of transition in multiphase reactors such as gas-hquid bubble columns, liquid-liquid spray columns, solid-liquid fluidized beds, gas-solid fluidized beds, and three-phase fluidized beds. 

For liquid-liquid spray columns Wijffels and Rietema (W17) have studied the combined effect of bulk turbulent flow and the drop motion suspended in it on the intrinsic turbulent viscosity pf. For the contribution of turbulent flow alone they assume that pf is given by k R mw. with k adjusted at 0.0167 from experiment. Numerically, k is the same order of magnitude ask, although smaller, withuo + wl taken here instead of uw. ... 

In regard to axial dispersion in unbaffled bubble-flow equipment like liquid-liquid spray columns, gas bubble columns, or fluidized catalyst beds, a close similarity has been supposed as a result of bubble flow and of turbulence induced by bubbles (B3, M33). Baird and Rice (B3) have assumed that the Kolmogoroflf concept for eddy viscosity in isotropic turbulence is applicable to evaluate E in the unbaffled bubble column under turbulent conditions, concluding that Ezt >s 0.35 in cm-sec units,... 

It is interesting to note that the governing equations for a moving bed are identical with the two phase model of a liquid/liquid spray column which was investigated theoretically by Luss and Amundson ( ). 

Van den Akker (1978) carried out a Hnear stabflity analysis for a liquid-liquid spray column operated with a positive temperature gradient. The leading idea was that local differences in mixture density would give rise to a multiple circulation pattern in a way similar to the multicellular natural convection mode in a vertical slot heated from one side (Elder, 1965 Lee and Korpela, 1983). The only way to find in the Hquid—Hquid spray colurrm... 

Van den Akker HEA Liquid-liquid spray columns hydrodynamic stability and reduction of axial mixing, PhD thesis. The Netherlands, 1978, Eindhoven University of Technology. 

Van den Akker HEA, Rietema K Plow patterns and axial mixing in liquid-liquid spray columns— part 3. The reduction of axial mixing by applying a positive temperature gradient, Trans Inst Chem Eng 57 84—93, 1979a. 

A common liquid chromatography column is somewhat larger in diameter than a nanocolumn. Consequently, the flow of solution along such a column is measured in terms of one or two milliliters per minute, and spraying requires the aid of a gas flowing concentrically around the end of the inlet tube (Figure 10.2c). An electrical potential is still applied to the end of this tube to ensure adequate electrical chaiging of the droplets. 

The sample solution is pumped (e.g., from the end of a liquid chromatographic column) through a capillary tube, near the end of which it is heated strongly. Over a short length of tube, some of the solvent is vaporized and expands rapidly. The remaining liquid and the expanding vapor mix and spray out the end of the tube as an aerosol. A flow of argon carries the aerosol into the plasma flame. 

Thermospray nebulizers are somewhat expensive but can be used on-line to a liquid chromatographic column. About 10% of sample solution is transferred to the plasma flame. The overall performance of the thermospray device compares well with pneumatic and ultrasonic sprays. When used with microbore liquid chromatographic columns, which produce only about 100 pl/min of eluant, the need for spray and desolvation chambers is reduced, and detection sensitivities similar to those of the ultrasonic devices can be attained both are some 20 times better than the sensitivities routinely found in pneumatic nebulizers. 

A sample to be examined by electrospray is passed as a solution in a solvent (made up separately or issuing from a liquid chromatographic column) through a capillary tube held at high electrical potential, so the solution emerges as a spray or mist of small droplets (i.e., it is nebulized). As the droplets evaporate, residual sample ions are extracted into a mass spectrometer for analysis. 

Liquid Dispersion Spray columns are used with slurries or when the reaction product is a solid. The absorption of SO9 by a hme slurry is an example. In the treatment of phosphate rock with sulfuric acid, offgases contain HF and SiF4. In a spray column with water, solid particles of fluorosilic acid are formed but do not harm the spray operation. The coefficient /cl in spray columns is about the same as in packed columns, but the spray interfacial area is much lower. Considerable backmixing of the gas also takes place, which helps to make the spray volumetri-caUy inefficient. Deentrainment at the outlet usually is needed. 

Figure 8.11 Types of reactors for gas-liquid precipitation, (a) bubbling stirred tank, (b) fiat interface stirred tank, draft-tube bubble column, (d) spray column after Wachi and Jones, 1994)...

Direct contact heal exchangers should be considered whenever the process stream and the coolant are compatible. The equipment used is basically simple and cheap and is suitable for use with heavily fouling fluids. For liquids containing solids, spray chambers, spray columns, and plate and packed columns are used. 

Use of w/o-MEs for transport in liquid emulsion membrane separations Perforated rotating disk contactor Spray column Packed column... 

The simplest form of extractor is a spray column. The column is empty one liquid forms a continuous phase and the other liquid flows up, or down, the column in the form of droplets. Mass transfer takes places to, or from, the droplets to the continuous phase. The efficiency of a spray tower will be low, particularly with large diameter columns, due to back mixing. The efficiency of the basic, empty, spray column can be improved by installing plates or packing. 

Liquid-liquid extraction is carried out either (1) in a series of well-mixed vessels or stages (well-mixed tanks or in plate column), or (2) in a continuous process, such as a spray column, packed column, or rotating disk column. If the process model is to be represented with integer variables, as in a staged process, MILNP (Glanz and Stichlmair, 1997) or one of the methods described in Chapters 9 and 10 can be employed. This example focuses on optimization in which the model is composed of two first-order, steady-state differential equations (a plug flow model). A similar treatment can be applied to an axial dispersion model. 

It is difficult to compare the performance of various spray towers since the type of spray distributor used influences the results. Data from Hixson and Scott 33 and others show that KGa varies as G70-8, and is also affected by the liquid rate. More reliable data with spray columns might be expected if the liquid were introduced in the form of individual drops through a single jet into a tube full of gas. Unfortunately the drops tend to alter in size and shape and it is not possible to get the true interfacial area very accurately. This has been investigated by Whitman et a/. 34 , who found that kG for the absorption of ammonia in water was about 0.035 kmol/s m2 (N/m2), compared with 0.00025 for the absorption of carbon dioxide in water. 

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