Required Report Items

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1. A log-log plot of

P/H vs. V_g with liquid flow as a parameter where

P is the pressure drop across the top and bottom packing sections (separately) of the tower (in H₂O), V_g is the superficial gas velocity [volumetric flow rate (ft³ /sec)/tower cross sectional area (ft² )] and H is the packing height. The slope of the line is the exponent of the correlation:

P = aV_g^b . This equation is valid for two-phase counter-current flow in the packed tower from dry bed conditions to the loading point. The date for the dry beds should be on the same graph.

2. Plots for each packing of DP/H versus G where G is the mass velocity of the gas, lb/hr ft² based on the empty tower cross section. The loading region and flooding point should be identified on the graphs. Liquid flow rate, L, in lbs/hr ft² should be the parameter. Also include the dry bed data. McCabe and Smith should be consulted for additional information.

3. A plot of L versus G for the flooding points obtained in 2 for each packing. A straight line through the origin, for a given design L/G (specified), with a slope equal to L/G will intersect the flooding curve at the maximum L and G for the tower.
4. A plot for each packing section of 1/K_La versus where K_La is the overall mass transfer coefficient (lbmoles ft³/hr) and the other symbols are as defined in Welty, Wicks and Wilson. The equation for the overall mass transfer coefficient in packed towers is:

= 1/mk_Ga+ 1/k_La

where m is the slope of an equilibrium curve (see Welty, Wicks and Wilson). According to the two film resistance theory of mass transfer, the liquid film becomes controlling when the gas is only slightly soluble in the liquid. This is the case for the CO₂-H₂O system. Therefore ~. Also, K_La for packed towers is correlated by the equation:

. Thus a plot of versus should give a straight line that passes through the origin, with a slope equal to 1/a . If the points do not form a straight line which passes through the origin, the exponent .72 is not valid (see Koch et al.). This analysis assumed that the Schmidt number was constant.

5. A plot of K_La versus L/m on a log-log plot for each packing section. Since we have assumed that K_La ~ k_La, the slope of this line is the valid exponent, 1-n in the general equation and a can be calculated from the intercept.
In items 4. and 5., K_La is calculated from the experimental measurements using the equation K_La = N/{HA Dx_lm}, where N is the lb. moles transferred/hr, and A is the tower cross-sectional area, ft² . Dx_lm for counter-current gas-liquid flow is where the subscripts 1 and 2 refer to the top and bottom of the column (or section), respectively. The x's are the mole fraction of CO₂ in the water, and x^* refers to the liquid phase mole fraction of CO₂ in equilibrium with the bulk phase mole fraction of carbon dioxide in the gas.

References

Koch, H. A. Jr., L. F. Stutzman, H. A. Blum, L. E. Hutchings, "Gas Absorption", CEP 45 (11), 677 (1949).

McCabe, W. L. and J. C. Smith, Unit Operations of Chemical Engineering,4th Edition, McGraw Hill Book Company, New York, NY, 1985.

Welty, J. R., C. E. Wicks, R. E. Wilson, Fundamentals of Momentum, Heat and Mass Transfer 3rd Ed., John Wiley and Sons, New York, NY, 1984.

Coker, A. K., "Understanding the Basics of Packed-Column Design for Modern Random Packings," CEP 87 (11), 93 (1991).

Kisler, H. Z. and D. R. Gill, "Predicting Flood Point and Pressure Drop for Modern Random Packings", CEP 87 (2), 32 (1991).

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