Packed absorbers

The interfacial area aj, differs from the packing surface area because the packing is not always completely wetted, so that a fraction of the surface is not active in the mass transfer, or because of the presence of stagnant pockets that are less effective than flowing streams. Shuhnan et al. [1955] have 

Generalized correlation for flooding rates in packed columns. After Lobo et al. [1945]. 

Generalized pressure drop correlation for packed columns with countercurrent flow. Parameter curves pressure drop in Inches water per foot. From Eckert [1970]. 

The parameters Q, Q, and C3 were determined for ceramic and graphitic Rashig rings and ceramic Berl saddles. 

The operational holdup can be calculated from the dimensionless correlation of Buchanan [1967]  

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Fig. 10. Computed rigorous profiles through an adiabatic packed absorber during the absorption of acetone into water (43).

Rate of Mass Transfer in Bubble Plates. The Murphree vapor efficiency, much like the height of a transfer unit in packed absorbers, characterizes the rate of mass transfer in the equipment. The value of the efficiency depends on a large number of parameters not normally known, and its prediction is therefore difficult and involved. Correlations have led to widely used empirical relationships, which can be used for rough estimates (109,110). The most fundamental approach for tray efficiency estimation, however, summarizing intensive research on this topic, may be found in reference 111. 

Rizzuti et al. [Chem. Eng. Sci, 36, 973 (1981)] examined the influence of solvent viscosity upon the effective interfacial area in packed columns and concluded that for the systems studied the effective interfacial area a was proportional to the kinematic viscosity raised to the 0.7 power. Thus, the hydrodynamic behavior of a packed absorber is strongly affected by viscosity effects. Surface-tension effects also are important, as expressed in the work of Onda et al. (see Table 5-28-D). 

Example 5 Packed Absorber, Acetone into Water. 14-14... 

Example 6 Solvent Rate for Absorption Let us consider the absorption of acetone from air at atmospheric pressure into a stream of pure water fed to the top of a packed absorber at 25 C. The inlet gas at 35 C contains 2 percent by volume of acetone and is 70 percent saturated with water vapor (4 percent H2O by volume). The mole-fraction acetone in the exit gas is to be reduced to 1/400 of the inlet value, or 50 ppmv. For 100 kmol of feed-gas mixture, how many Idlomoles of fresh water should be fed to provide a positive-driving force throughout the pacldug How many transfer units will be needed according to the classical adiabatic method What is the estimated height of pacldug required if Hqq = 0.70 m ... 

Mass Transfer Relationships for calculating rates of mass transfer between gas and liquid in packed absorbers, strippers, and distillation columns may be found in Sec. 5 and are summarized in Table, 5-28. The two-resistance approach is used, with rates expressed as transfer units ... 

The hexamine cobalt (II) complex is used as a coordinative catalyst, which can coordinate NO to form a nitrosyl ammine cobalt complex, and O2 to form a u -peroxo binuclear bridge complex with an oxidability equal to hydrogen peroxide, thus catalyze oxidation of NO by O2 in ammoniac aqueous solution. Experimental results under typical coal combusted flue gas treatment conditions on a laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

FIG. 14-6 Relationship between equilibrium curve and operating curve in a packed absorber computation of interfacial compositions. 

Each curve in Fig. 16 represents a constant pressure drop value. Packed absorbers are usually sized to give a pressure drop of 0.25 to 0.50 in. H20 per foot (200-400 N/m2 per meter) of packed depth. Figure 16 is used to determine the column cross sectional area to achieve... 

Figure 9.107 Separation of ATP, AMP, and cAMP by HPLC. Operating conditions 0.01 M KH2PO4 (pH 5.5) buffer with 10% methanol flow rate, 2 mL/min room temperature, yuBondapak Ci8 column packing absorbance at 260 nm. Approximately 10 yug of each component was injected. Sensitivity of detection, 0.5 AUFS. (From Rossomando et al., 1981a.)...

Example 9 HETP of a Packed Absorber McDaniel, Bassyoni, and Holland [Chem. Engng. Sci., 25, 633 (1970)] presented the results of field tests on a packed absorber in a gas plant. The packed section was 23 ft in height, and the column was 3 ft in diameter and filled with 2-in metallic Pall rings. The measured feeds are summarized in the table below. 

To minimize channeling of liquid in packed absorbers and strippers require that the packing be sufficiently small when con5)ared to the column diameter. Small packing, however, will result in a high pressure drop.Treybal [29] specifies that the ratio of separator diameter to the packing diameter should be 15/1. 

A packed absorber column is used to remove sulfur dioxide form an air stream, using pure water as the absorbent. The following data are given ... 

Instant hot and cold packs create aqueous solutions that form exothermically or endothermically and therefore release or absorb heat. A hot pack generates heat when a salt such as calcium chloride dissolves in water that is stored in the pack. The calcium chloride dissolves exothermically. A cold pack absorbs heat when a salt such as ammonium nitrate dissolves in water. The ammonium nitrate dissolves endothermically. 

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