Separation Process Principles- 2n - Seader & Henley - Solutions Manual

6 106 if we ignore holdup hl in the term hl and

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Unformatted text preview: 1.5-inch Berl Saddles, AE units From the above figure, HOG = 0.85 ft. From Eq. (2), lT = 2.57(0.85) = 2.2 ft (b) From Eq. (6-11), (L/S)min = (V/S) K (fraction absorbed) = 240(2.7)(0.98) = 635 lb/h-ft2 (c) Consider the differences between 1.5-inch ceramic Berl saddles (Saddles) and 1.5-inch ceramic Hiflow rings (Rings). In Table 6.8, data are given for the rings, but not for the saddles of the 1.5-inch size. To make the comparison, take the near-1 inch size. Then, the following parameters apply: Packings Saddles Rings FP 110 a 260 261.2 ε 0.68 0.779 Ch 0.62 1.167 Cp 0.628 CL 1.246 1.744 CV 0.387 0.465 Analysis: (c) (continued) Exercise 6.30 (continued) Note that for the NH3-air-water system, the above plot shows that HOG is approximately equal to HG. Therefore, the liquid-phase resistance is small and KL a need not be considered. Consider KGa and HOG: In the above table, values of a are essentially the same. From Eqs. (6-136) and (6-140), 1/ 2 a / a for Rings 0.779 = = 1.07 aPh/a is proportional to ε /a. Therefore, Ph aPh / a for Saddles 0.68 From Eq. (6-133), if we ignore holdup, hL, in the term (ε - hL), and differences in a, then, 14a H G is proportional to ε CV aPh 1/2 1 (0.779) 4 H G for Rings Therefore, = 0.465 (1.07 ) = 1.53 1 H G for Saddles 4 (0.680) 0.387 This ratio should be about the same for HOG . K G a for Rings 1 From Table 6.7, KG is inversely proportional to HG. Therefore, = = 0.653 K G a for Saddles 1.53 Consider pressure drop: The pressure drop is given by Eq. (6-106). If we ignore holdup, hL, in the term (ε - hL), and differences in a, and combine Eqs. (6-99) and (6-110) to (6-115), then, Cp ∆P is approximately proportional to 3 ε However, Table 6.8 does not contain Cp for Berl saddles, so no comparison can be made. Consider Column NOG and height: The value of NOG is independent on packing material. Therefore, the height is shorter for the saddle packing because the HOG is smaller. Consider column diameter: The column diameter is related to the flooding velocity, as given in Fig. 6.36(a). For a given value X, the value of Y is fixed and the product (uo)2FP is a constant. The packing factor for the ceramic Hiflow rings is not given in Table 6.8. However, if a value is extrapolated from data for larger rings, the packing factor for the Rings is much less than for the Saddles. Therefore, the flooding velocity for the Rings will be higher and the column diameter smaller. Consider maximum liquid rate: For a fixed gas velocity, the value of Y in Fig. 6.36(a) is smaller for the Rings because the packing factor is less. Therefore, as shown in the same figure, the value of X is greater for flooding, which gives a larger maximum liquid rate. Exercise 6.31 Subject: Absorption of CO2 from air into a dilute caustic solution with a packed column. Given: 5,000 ft3/min at 60oF and 1 atm, containing 3 mol% CO2. Recovery of 97% of CO2. Equilibrium curve is Y = KX = 1.75X (i.e. mole ratios) at column operating conditions. Assumptions: No stripping of water. No absorption of air. Caustic soluti...
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