Packed towers liquid holdup

Region I, P > 2. Reaction is fast and occurs mainly in the liquid film so C L 0- The rate of reaction = kj aEC i will be large when a is large, but hquid holdup is not important. Packed towers or stirred tanks will be suitable. 

Otake, T. and K. Okada, Liquid Hold-up in Packed Towers, Operating and Holdup Without Gas Flow, Soc. Chem. Engrs. Qapan) 17, No. 7, 176 (1953). 

In comparison with tray towers, packed towers are suited to small diameters (24 in. or less), whenever low pressure is desirable, whenever low holdup is necessary, and whenever plastic or ceramic construction is required. Applications unfavorable to packings are large diameter towers, especially those with low liquid and high vapor rates, because of problems with liquid distribution, and whenever high turndown is required. In large towers, random packing may cost more than twice as much as sieve or valve trays. 

The amount of liquid holdup in the packing is of interest when the liquid is unstable or when a desirable reaction is to be carried out in the vessel. A correlation for Raschig rings, Berl saddles, and intalox saddles is due to Leva (Tower Packings and Packed Tower Design, U.S. Stoneware Co., Akron, OH, (1953) ... 

Liquid residence time in the packed rotor varies as a function of packing depth, packing type, rotor speed, and liquid properties (26). Two basic approaches have been applied to the measurement of liquid in the rotor. The first measure is the average residence time of the liquid within the rotor, and the second is the liquid holdup on the packing. Due to the flow patterns described previously, not all of the rotor packing is wetted and not all of the liquid resides on the packing surface. As a result, average residence time and liquid holdup are distinct measures of liquid flow, contrary to the experience with packed towers. 

Liquid holdup and flooding in.packed towers. Ind. Eng. Chem., 31 435-445. 

Low weight and low liquid holdup. The total weight of the column and the resultant foundation load is low if the weight of the packing and the liquid holdup in the tower are low. The amount of liquid holdup, however, must be sufficiently great to retain an effective driving force for mass transfer. 

The total weight of a dry plate tower is usually less than that of a packed tower designed for the same duty. However, if liquid holdup during operation is taken into account, both types of towers have about the same weight. 

The amount of liquid holdup is considerably less in packed towers. 

Recommendations All existing literature data on gas and liquid holdups for countercurrent flow systems are for packings normally used in absorption towers or gas -liquid reactors. The validity of these data for small packings that would normally be used in gas-liquid-solid catalytic reactions needs to be checked. 

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