Mass exchangers

Interfacial Area The effective area of contact between gas and liquid is that area which participates in the gas-liqiiid mass-exchange process. This area may be less than the actual interfacial area because of stagnant pools where liquid reaches satiiradon and no longer par-dcipates in the transfer process. 

Counter-current rinsing and rinse-water reuse are useful tips for reducing usage. Counter-current contact systems are more efficient in promoting heat and mass exchanges, which are important to gas absorption, extraction, and many types of chemical reactions. 

Srinivas, B. K. and El-Halwagi, M. M. (1994), Synthesis of reactive mass-exchange networks with general nonlinear equilibrium functions. AlChE J., 40(3), 463-472. 

Modeling of Mass-Exchange Enits for Environmental Applications... 

Throughout this bocdt, several mass-exchange operations will be considered simultaneously. It is therefore necessary to use a unified terminology such that y is always the composition in die rich phase and x is the composition in the lean phase. The reader is cautioned here that tiiis terminology may be different ftom other literature, in which y is used for gas-phase composition and x is used for liquid-phase composition. 

In order to determine the size of a multiple-stage mass exchanger, let us consider the isothermal mass exchanger shown in Fig. 2.3. The rich (waste) stream, i. 

One way of calculating the number of equilibrium stages (or number of theoretical plates, NTP) for a mass exchanger is the graphical McCabe-Thiele method. To illustrate this procedure, let us assume that over the operating range of compositions, the equilibrium relation governing the transfer of the pollutant from the... 

Once again, because of the unified approach of this text to all mass-exchange operations it i.s important to emphasize that the symbols G and L will be used to designate the flowrates of the rich stream and the MSA, respectively and not necessarily flowrates of gas and liquid. 

Figure 2.4 A schematic diagram of a multistage mass exchanger.

Alternatively, for the case of isothermal, dilute mass exchange with linear equilibrium, NTP can be determined through the Kremser (1930) equation ... 

The second type of mass-exchange units is the differential (or continuous) contactor. In this category, the two phases flow through the exchanger in continuous contact throughout without intermediate phase separation and recontacting. Examples of differential contactors include packed columns (Fig. 2.6), spray towers (Fig. 2.7), and mechanically agitated units (Fig. 2.8). 

On a y-x (MeCabe-Thiele) diagram, this equation represents the operating line that extends between the points (y/", xj") and (y , x ) and has a slope of Ly/G,. Equation (2.10) has thitee unknowns, yf , Lj and xj . Let us first fix the outlet composition of the waste stream, yf". As depicted by Fig. 2.9, the maximum themetically attainable outlet composition of the MSA, xj", is in equilibrium with y ". An infinitely laige mass exchanger, however, will be needed to undertake... 

Figure 2.9 Nfiniinuiii allowable composition difference at the rich end of a mass exchanger.

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