Nomenclature E, = activation energy, cal/mol k = forward rate constant, appropriate units k' = reverse rate constant, appropriate units ko = frequency factor from the Arrhenius equation K = equilibrium constant, expressed in terms of concentrations R = gas constant or rate of reaction, expressed as the rate of production of the subscripted component S / V = surface-to-volume ratio, cm-1 t = time, sec T = temperature, O K ( ) = concentration,M Literature Cited Abel, E.,Neusser, E.. Monatsh. Chem., 54, 655 (1929). Altshuller, A. P., etal., Science, 138, 442 (1962). Ashmore, P. G., Tyler, B. J., J. Chem. SOC., 1017 (1961). Beattle, I . R . , Bell, S. W., J. Chem. SOC., 1681 (1957). Bodenstein, M . , Helv. Chim. Acta., 18, 743 (1935). Bodenstein, M . , Z. Phys. Chem., 100, 68 (1922). Burdick, C. L., J . Amer. Chern. SOC., 44, 244 (1922). England, Christopher, Ph.D. Thesis. California institute of Technology,. 1970. Glasson, W. A., Tuesday, C. S., J . Amer. Chem. SOC., 85, 2901 (1963). Greig, J. D., Hall, P. G . , Trans. FaradaySoc., 62, 652 (1966). Greig, J. D..Hall, P. G . , Trans. Faraday SOC.,63, 655 (1967). Guillory. W. A., P h . D Dissertation, University of California, 1964. 85, 1695 (1963). Guillory, W. A.. Johnston, H. S..J. Amer. Chem. SOC.,
Guillory, W. A., Johnston, H. S., J. Chem:Phys., 42, 2457 (1965). Hall, R. T., Pirnentel, G. C., J. Chem. Phys., 38, 1889 (1963). Hasche, R. L., J. Amer. Chem. SOC., 48, 2253 (1926). Hisatsune, I . C., J. Phys. Chem., 65, 2249 (1961). Jones, L. H.,Badger, R. M.. Moore, G. E.,J. Chem. Phys., 1599 (1951). Karavaev, M. M., Skvortsov, G. A,, Zh. Fiz. Khim., 36, 1072 (1962). Leighton, P. A., "Photochemistry of Air Pollutiorl," p 184, Academic Press, New York, N. Y., 1961. Morrison, M. E., Rinker, R . G . , Corcoran, W. H., lnd. Eng. Chem., Fundam., 5, 175 (1966). Smith, J. H., J. Amer. Chem. SOC.,65, 74 (1943) Solc, M., Nature (London), 209, 706 (1966). 5 (1939). Stoddart, E. M.. J . Chem. SOC., Tipper, C. F. H., Williams, R. K., Trans. Faraday Soc., 57, 79 (1961). 77, 2033 (1955). Treacy, J. C., Daniels, F., J. Amer. Chem. SOC., Trotman-Dickenson, A. F., "Gas Kinetics," p 264, Academic Press, New York. N. Y., 1955. Turney, T. A., J . Chem. SOC., 4263 (1960). Usubillaga, A. N., Ph.D. Thesis, University of Illinois, 1962. 53, 1250 (1931). Verhoek,.F. H., Daniels, F., J. Amer. Chem. SOC., Vlastaras, A. S.,Winkier. C. A , , Can. J. Chem., 45, 2837 (1967). Waldorf, D. M., Babb. A. L., J. Chem. Phys., 30, 432 (1963). Waldorf, D. M . , Babb, A. L., J . Chem. Phys., 40, 465 (1964). Wayne, L. G.. Yost, D. M., J. Chem. Phys., 19.41 (1951).
Receiced for review M a y 28, 1974 Accepted September 3, 1974 W o r k reported here was supported in p a r t by E. I. du P o n t d e N e m o u r s a n d Company, t h e S h e l l Companies Foundation, a n d t h e M c C a r t h y F o u n d a t i o n . T h e i r support i s gratefully acknowledged.
A Second Mode of Operating Packed Columns and Wetted Wall Columns L. S. Leung,* Bruce E. T. Hutton, and Donald J. Nicklin Department of Chemical Engineering, University ot Queensland, St. Lucia, 4067 Brisbane, Oueensland, Australia
For a fixed set of gas and liquid rates below the flooding flow rates in a wetted wall column and a packed column, two modes of operation are possible, viz., normal and incipient flooding. The latter has not been reported previously. Methods for stabilizing this mode of operation are described. Both modes can coexist in different sections of the same column. Modification to industrial packed towers to permit operation in the incipient flooding mode are simple and inexpensive. Such modifications permit operation with higher liquid holdup and higher mass transfer rates at the expense of higher pressure losses.
Introduction In a wetted wall column liquid flows down the wall of a tube while gas flows upward through the core. It is generally known that a t a given liquid rate L, stable operation can be achieved a t gas flow rates G up to that corresponding to the onset of flooding. Equations are available (Anderson and Mantzouranis, 1960; Calvert and Williams, 1961; Lockhart and Martinelli, 1949; Wallis, 1969) for predicting liquid holdup and pressure gradient at a given L and G and for predicting the onset of flooding (Cetinbudaklar and Jameson, 1969; Davidson and Shearer, 1965; Wallis, 1961). In this paper we extend the analysis of Nicklin and Koch (1969, 1971) to show that for a given set of L and G below the flooding flow rates, two modes of operation are possible, viz.: normal mode-a stable mode of operation with low liquid holdup and low pressure gradient (as observed in normal operation) ; incipient flooding mode-an unstable mode of operation with high liquid holdup, high pressure gradient, and high mass transfer
coefficients. Operation in this mode has not been reported previously. Simple methods for achieving the "incipient flooding mode" in wetted wall columns and packed columns are described. Operation of a conventional packed column in this mode permits operation with high liquid holdup, high mass transfer coefficient, and high pressure losses. Analysis of Nicklin a n d Koch Figure 1 shows a section of a wetted wall column with a gas flow rate G upward and a liquid flow rate L downward. Consider first the liquid flow. It can readily be shown for a given system that
where r , = liquid-gas interfacial shear stress and t = thickness of liquid film. The form of eq 1 depends on the nature of flow in the liquid. Different forms of eq 1 have been derived by asInd. Eng. Chern., Fundam., Vol. 14, No. 1, 1975
63
I
CUM
AlBC
APBC
LIQUID FLOW
L
A3BC I
I
c
~
-
R
=
7-i =
zi I7
(L1,t)
(L2.t) (L3,t)
L1> L 2 > L3 DEMF’-
Ti = 7: ( G , t )
OR A GIMN G ALLOWING
FCU TM FLOODING IHSTABILITV AT
