Packings liquid-side controlled mass transfer

Other equations for determination of the liquid- side controlled mass transfer coefficient of random packings are presented in Table 23. 

It must be mentioned that a hysteresis in the same range of gas and liquid velocities for flie same packings is to be expect also for the efiective surface area and for the liquid- and gas-side controlled mass transfer coefficients. In Fig. 11 flm hysteresis curves for the liquid-side controlled volumetric mass transfer cocdflcient are presented [7]. 

The liquid phase has also some influence on the gas-side controlled mass transfer. This is becau the presence of liquid reduces the real free cross-section of the packing for the gas flow. The second reason is that the real velocity responsible for the gas-side controlled mass transfer is the relative velocity between the gas and the liquid phases. These eff are relatively small. To take them into account, Zhavoronkov et al. [168] proposed the following equations ... 

The method is developed in two variants differing in the kind of the laboratory column used. In die first one, this is a column with a single sphere [35, 36], and in the second - with a vertical column of spheres [37]. In both oases the mass transfer process is liquid-side controlled absorption. The method accepts that the mass transfer coefficients in a packing and on spheres are the same, and that the effective surfiice of the spheres is equal of dieir geometrical surfiice. Because the mass transfer coefficient depends on the hjrirodynamics of the liquid phase, and die hydrodynamics - on of die form of the packing, the first acceptation is doubtfiil. 

In another paper Benadda et al. [29S] find that the partial mass transfer coefficient for the liquid phase is not defending on the pressure in the interval fiom 0.1 to 1.3 MPa. The investigation was carried out with the same packing and the same column. That is, the pressure is not influencing the liquid-side control processes. 

The hysteresis observed for the prepare drop of Holpack packing (Fig. 10 of Chapter 2) leads to hysteresis of die liquid-side controlled volumetric mass transfer coefficient [30. In Fig. 11, Ch pt 2, the value of KlO at liquid superficial velocity equal to 0.00S7 m /(m s) in the flooding regime versus the velocity wo is presented. 

The comparison of fte liquid-side mass transfer coefficients of Holpack and of the packing of Kolar at equal liquid superficial velocities shows that they are significantly higher for the Holpack. The maximal values of these coefficients are approximately fte same. The comparison of fte gas-film controlled mass transfer coefficients shows also that fte values for fte Holpack at fte same gas velocity are quite higher. The comparison of fte maximal values for both types of packings shows that they are practically fte same. 

In the case that the mass transfer effects are not negligible, the required height of the packed bed is greater than that without mass transfer effects. In some practices, the ratio of the packed-bed heights without and with the mass transfer effects is defined as the overall effectiveness factor (-), the maximum value of which is unity. However, if the right-hand side of Equation 7.47 is multiplied it cannot be integrated simply, since is a function of C, U, and other factors. If the reaction is extremely rapid and the liquid phase mass transfer on the particle surface controls the overall rate, then the rate can be estimated by... 

However, the gas undergoes a solid-body-like rotation and the slip velocity between liquid and gas is in the same range as in a conventional packed bed. Hence, for the cases in which the controlling resistance is on the gas side, the expected size reduction is only about 5-8 times, which is due to the high specific area of the packing. In most distillation columns, the dominant resistance is on the vapor side. To enhance the slip velocity and hence the gas-side mass-transfer coefficient, a rotor with split packing was proposed by Chandra et al. [5]. Its brief description is given below. 

Fig. 150. Pressure drop for one transfer unit (AP/I. HTUg) as a function of the is-side controlled volumetric mass transfer coefficient (Kca) at constant values of the ratio gas velocity-liquid superficial velocity (wo/I). Comparfeon of the new packing wifh some hi Iy efficient packings (Table 49). 1- Eurofiann, W(/L=166.7 w /mh 2- Hiflow ring 50, Wi/L =166.7 m /m 3-Hiflow ring 25, =166.7 m /m 4- Ii lsepao, Wi/L =166.7 m /m 5- Pall-ring 50, w/Z.

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