Countercurrent contactor

The design of countercurrent contactors is considerably simplified when the solvents A and B are not significantly miscible. The mass flows of A and B then remain constant from one stage to the next, and the material balance at any stage can be written... 

A differential countercurrent contactor operating with a dilute solution of the consolute component C and immiscible components A and B is shown in Figure 8. Under these conditions, the superficial velocities of the A-rich and B-rich streams can be assumed not to vary significantly with position in the contactor, and are taken to be and Ug, respectively. The concentration of C in the A-rich stream is and that in the B-rich stream is C-. ... 

Activated carbon is available in powdered form (200-400 mesh) and granular form (10-40 mesh). The latter is more expensive but is easier to regenerate and easier to utilize in a countercurrent contactor. Powdered carbon is applied in well-mixed shiny-type contactors for... 

Countercurrent contactors, design of, 10 757 Countercurrent continuous centrifugal extractor, 10 781... 

Droplet systems rarely exceed a p value of 0.01. At this low level, D in a low-velocity countercurrent contactor can be approximated by Eq. (14-179). 

The holdup is just as important as r/32 in Eq. (12) for specific interfacial area. In a batch extraction it is simply determined by the amounts of each phase added, but in many types of continuous countercurrent contactor it is a complex function of flow rates, drop size, etc. The slip velocity us for countercurrent flow is defined in terms of the superficial velocities U (flow rates per unit cross-sectional area) of each phase,... 

Slater, M. J., A Review of Continuous Countercurrent Contactors for Liquids and Particulate Solids, Brit. Chem. Eng. 14(1), 41 (1969). 

FIGURE 12.57 Flows in a differential section of a countercurrent contactor. 

Instead of stages or plates, transfer units are introduced to represent the separation requirement of a continuous, countercurrent contactor such as a packed column. As will be shown later, theoretical stages can be converted to transfer units for design purposes. Thus, only a summary of transfer unit theory will be given here, since it is usual practice to determine the required stages, as discussed in the previous section, and then convert them to transfer units. The conversion is in order because the mass transfer characteristics of packings are usually correlated in terms of heights of a transfer unit. Thus,... 

Combo leach tend to use countercurrent contactors with time for diffusion and separation in each stage. Sloped diffuser with rotating screw 10 kg/s sugar beets in 2 m diameter. Tower with rotating screw 10 kg/s sugar beets in 0.3-m diameter unit. Trough-scroll ... 

FIGURE 6.1-6 Material belauee diagram for countercurrent contactor. 

For the case of a countercurrent contactor, we envision the arrangement as shown in Figure 8.14. We will consider that both phases are in plug flow, and again we have the irreversible reaction that occurs in phase 2. Since we have the possibility of either gas-liquid or liquid-liquid reaction, we will just number the phases 1 and 2. Now, over dy, we can write the mass balances as... 

An analysis of flow patterns in vertical countercurrent contactors was reported by Govier et al. [G. Govier, B.A. Rodford, and J.S.C. Dunn, Can. J. Chem. Eng., 38, 58 (1957)] and a generalized flow regime chart based on their findings is given in Figure 8.16. 

Tend to use countercurrent contactors with time for diffusion and separation in each stage. 

In this case, 28 mol% of aqueous diethanolamine was used to absorb CO2 (Ma >0, Ra> 0) in the falling-film liquid-gas countercurrent contactor as... 

Figure 14-19 is a flow diagram of the combined Ifpexol concept. In the first step water is separated from the natural gas to allow low-temperature processing in the subsequent steps. This is accomplished by contacting the natural gas feed with a methanol-rich stream in a conventional countercurrent contactor. Methanol, since it is more volatile than water, is vaporized and taken overhead, while the water stream containing as little as 50 ppm of methanol is withdrawn as bottoms. Control of this column to achieve the desired splits of water and methanol while minimizing methanol losses in the water stream is critical to proper operation. 

The use of reactive solvents has a signiflcant advantage over physical solvents, where applicable, because normally the impurity is destroyed or altered by the reaction and does not exhibit a significant vapor pressure over the solution once absorbed. When the liquid phase reaction is irreversible and rapid, which is often the case, a countercurrent contactor is not necessary, and simple venturi or spray scrubbers can provide high efficiency. The design of such equipment is discussed in Chapter 1. 

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