Mass spray column

Mass Transfer As mentioned earlier, spray columns rarely develop more than 1 theoretical stage due to the axial mixing in the column. Nevertheless, it is necesary to determine what column height will give this theoretical stage. It is recommended by Cavers in Lo et al. Handbook of Solvent Extraction p. 323 and p. 327, John Wiley Sons, New York, 1983 that the following equation be used to estimate the overall efficiency coefficient ... 

Pulsed Spray Columns Billerbeck et al. [Jnd. Eng. Chem., 48, 183 (1956)] applied pulsing to a laboratoiy [3.8-cm- (1.5-in-) diameter] column. At pulse amplitude 1.11 cm 6 in), rates of mass transfer improved slightly with increased frequency up to 400 cycies/min, but the effecl was relatively small. Shirotsuka [Kagaku Kogaku, 22, 687 (1958)] provides additional data. There is not believed to be commercial application. 

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. 

Mass transfer. As in the case of spray columns, it is not yet possible to predict mass transfer rates from first principles. In the absence of any reliable correlations, use may be made of typical values of overall(20,31) and film(32,33) coefficients. A comprehensive summary is given in Perry s Chemical Engineers Handbook 22). 

Spray columns. These are columns fitted with rows of sprays located at different heights. Gas rises vertically, and liquid is sprayed downward at each of these rows. Mass transfer is usually poor because of low gas and liquid... 

The deterministic population balance equations governing the description of mass transfer with reaction in liquid-liquid dispersions present a framework for analysis. However, signiflcant difficulties exist in obtaining solutions for realistic problems. No analytical solutions are available for even the simplest cases of interest. Extension of the solution to multiple reactants for uniform drops is possible using a method of moments but the solution is limited to rate equations which are polynomials (E3). Solutions to the population balance equations for spatially nonhomogeneous dispersions were only treated for nonreacting dispersions (P4), and only a simple case was solved for a spray column (B19). Treatment of unmixed feeds presents a problem. 

The first major decision in the choice of a reactor for gas-liquid reactions taking place in the liquid phase is based on the optimal usage of the total reactor volume, i.e. the choice of the parameter P, which is the ratio of the liquid-phase volume to the volume of the diffusion layer (see Section 8.4.2). When reactions are slow compared to the mass transfer from the gas to the liquid, sparged stirred tanks and bubble columns are preferred, as these reactors have the largest bulk liquid volume. On the other hand, fast reactions for a large part take place in the diffusion layer, so in this case spray columns and packed columns are more suitable. 

Static extraction columns Spray column Baffle column Packed column (random and structured packing) Sieve tray column Deliver low to medium mass-transfer efficiency, simple construction (no internal moving parts), low capital cost, low operating and maintenance costs, best suited to systems with low to moderate interfacial tension, can handle high production rates Petrochemical Chemical Food... 

For example, when mass transfer limits the overall reaction rate, reaction occurs near the gas-liquid interface to make significant liquid volume unnecessary. To minimize the value of jS, bulk liquid volume is minimized, while interfacial area is maximized. As intense mixing and turbulence throughout a large liquid volume would be of limited benefit, the gas-liquid contactor of choice is a packed bed or a spray column as in the earlier TPA hydrogenation reactor example. 

The numerous variables involved in spray-column exchangers have hitherto defied even approximate engineering correlation. Collation and adaptation of the information and experience accumulated in mass-transfer... 

Consider a special case of a spray column, where the temperature of one phase, say the dispersed phase, is constant throughout. This situation is ideally obtained when the dispersed phase is volatile and evaporates while rising in the column. Under ideal operating conditions (no subcooling or superheating), with constant mass flow rate of the dispersed phase. 

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