Leaching constant underflow

NUMBER OF IDEAL STAGES FOR CONSTANT UNDERFLOW. When the Operating line is straight a McCabe-Thiele construction can be used to determine the number of ideal stages, but since in leaching the equilibrium line is always straight, Eq. (17.24) can be used directly for constant underflow. The use of this equation is especially simple here because yj = and — Xj. 

Constant Underflow in Leaching Oil from Meal. Use the same conditions as given in Example 12.10-1, but assume constant underflow of N = 1.85 kg solid/kg solution. Calculate the exit flows and compositions and the number of stages required. Compare with Example 12.10-1. 

Countercurrent Multistage Leaching. Countercurrent extraction offers the most economical use of solvent, permitting high concentrations in the hnal extract and high recovery from the initial solid hul utilizing the least amount of solvent. When the amount of solvent removed with the insoluble solid in the underflow is constant, it is convenient to define the ratio... 

We wish to treat 1000 kg/h (wet basis) of meal (D) that contains 0.20 wt frac oil (A) and no benzene(S). The inlet solvent is pure benzene and flows at 662 kg/h. We desire an underflow product that is 0.04 wt frac oil. Temperature and pressure are constant, and the equilibrium data are given in Table 14-2. Find the oudet extract concentration and the number of equilibrium stages needed in a countercurrent leaching system... 

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