Absorber design

Use of HETP Data for Absorber Design Distillation design methods (see Sec. 13) normally involve determination of the number of theoretical equihbrium stages or plates N. Thus, when packed towers are employed in distillation appRcations, it is common practice to rate the efficiency of tower packings in terms of the height of packing equivalent to one theoretical plate (HETP). 

In concentrated wstems the change in gas aud liquid flow rates within the tower and the heat effects accompanying the absorption of all the components must be considered. A trial-aud-error calculation from one theoretical stage to the next usually is required if accurate results are to be obtained, aud in such cases calculation procedures similar to those described in Sec. 13 normally are employed. A computer procedure for multicomponent adiabatic absorber design has been described by Feiutnch aud Treybal [Jnd. Eng. Chem. Process Des. Dev., 17, 505 (1978)]. Also see Holland, Fundamentals and Modeling of Separation Processes, Prentice Hall, Englewood Cliffs, N.J., 1975. 

Principles of Rigorous Absorber Design Danckwerts and Alper [Trans. Tn.st. Chem. Eng., 53, 34 (1975)] have shown that when adequate data are available for the Idnetic-reaciion-rate coefficients, the mass-transfer coefficients fcc and /c , the effective interfacial area per unit volume a, the physical solubility or Henry s-law constants, and the effective diffusivities of the various reactants, then the design of a packed tower can be calculated from first principles with considerable precision. 

Inspection of Eqs. (14-71) and (14-78) reveals that for fast chemical reactions which are liquid-phase mass-transfer limited the only unknown quantity is the mass-transfer coefficient /cl. The problem of rigorous absorber design therefore is reduced to one of defining the influence of chemical reactions upon k. Since the physical mass-transfer coefficient /c is already known for many tower packings, it... 

For fast irreversible chemical reactions, therefore, the principles of rigorous absorber design can be applied by first estabhshing the effects of the chemical reaction on /cl and then employing the appropriate material-balance and rate equations in Eq. (14-71) to perform the integration to compute the required height of packing. 

V and L, are found from Equations 9 and 10. The improved procedure is better for rigorous solution of complicated absorber designs. 

Change to a smaller absorber designed for the lower rate, if needed. 

Lowenstein, A.I., andGabruk, R.S., 1992. The effect of absorber design on the performance of a liquid-desiccant air conditioner, ASHRAE Transactions Symposia, pp. 712-720. 

Krausening, in beer making, 3 584 Krebs cycle, 6 632-633 Kremser-Brown method, of bubble tray absorber design, 1 85 Kreysiginone, 2 91... 

The problem presented to the designer of a gas absorption system usually specifies the following quantities (1) gas flow rate (2) gas composition of the component or components to be absorbed (3) operating pressure and allowable pressure drop across the absorber (4) minimum recovery of one or more of the solutes and, possibly, (5) the solvent to be employed. Items 3, 4, and 5 may be subject to economic considerations and therefore are left to the designer. For determination of the number of variables that must be specified to fix a unique solution for the absorber design, one may use the same phase-rule approach described in Sec. 13 for distillation systems. 

In this case, a major source of pollution may be the off-gas leaving the acrylonitrile absorber. Ensuring high recovery of nitriles is desirable, which can be realized by using low-temperature water, as well as an efficient absorber design. Thermal or catalytic oxidation can ensure 99.9% destruction of escaped toxics. The same techniques can be used to complete the incineration of other toxic liquid and solid residues. 

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