Spray contactors, design

To determine the required size of an absorption or stripping nrtl, it is necessary to know not only the equilibrium soluhility of the solute in the solvent and the material balance atound the column bas also the rate at which solute is transferred from one phase to the other within the tower. This rale directly affects the volume of packing needed in a packed tower, the degree of dispersion requited in a spray contactor, and (somewhat less directly) the number of trays required in a nay tower. The last effect occurs as a result of the influence of mass transfer rms on tray efficiency which is discussed in a later section. Because of its direct effect ou packed tower design and the importance of this type of contactor in absoiption. this discussion of mass transfer is aimed primarily at the packed tower case. A more detailed review of mass transfer theoty is given in Chapter 2. 

Spray contactors ate particularly important for the absorption of imparities from large volumes of Hue gas where tow pressure drop is of key importance. They are used where materials in the liquid phase (e.g., particles of limestone) or in the gas phase (e.g., droplets of tar) may cause plugging of packing or trays. Other important applications of spray contactors (which are outside the scope of this discussion) include particulate removal and hot gas quenching. When used for absorption, spray devices are not applicable to difficult separations and geueratty are limited to about Four transfer units even with countercurrent spray column designs. The tow efficiency of spray columns is believed to be due to entrainment of droplets in the gas and beckmixing of the gas induced by the sprays. 

Attempts have been made to develop design equations for preformed spray contactors on the basis of a more foudemental approach by considering muss transfer to individual drops. However, this requires a characterization of the drop size distribution, time of flight, and other factors. The approach is useful when test data are not available bat cannot be expected to provide accurate results for commercial equipment because the effects of drop agglomeration, entrainment, wall contact, gas recirculation, drop velocity changes, and other factors are very difficult to model analytically. 

The Nog values can be used to extrapolate test or opoating data on a spray contactor to other systems or conditions. For example, if one spray unit provides 90% removal (2.3 transfer units), it can be expected that two identical units in series will provide about 99% removal (4.6 transfer units). Since coimnetcial spray systems are widely variable, the development of a generalized design approach based on fundamentals is quite difficult. As a result, spray contactors are usually designed on the basis of previous experioice with milar systems. 

Design and development of an electro spray bioreactor was reported and its suitability for biodesulfurization applications was demonstrated [261], Mixing oil with water in large bioreactors requires significant energy input for classical impeller-based reactors. The electro spray bioreactor (ESB) was developed from an emulsion phase contactor... 

Trial Estimates and Converged Flow Rates and Compositions in aU Stages of an Extraction Battery for a Four-Component Mixture 476 Sizing of Spray, Packed, or Sieve Tray Towers 486 Design of a Rotating Disk Contactor 488 Application of Ion Exchange Selectivity Data 503... 

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