In order to remove a desired solute constituent from a solid phase, leaching with a liquid solvent is used. A device is used to bring the solvent into contact with the solid. Thus, the solute is dissolved in the solvent and separated from the solid. When the solvent is water and the solute is an undesirable component to be removed from the solid, the operation is called washing.
A countercurrent leaching system is used in order to extract oil from solid meal using benzene. The process treats 2000 kg/hr of inert solid meal containing 800 kg oil and 50 kg benzene. The inlet flow per hour of fresh solvent contains 1310 kg benzene and 20 kg oil. You can set the amount of the remaining oil in the leached solid from 50 kg to 250 kg. Settling experiments of Badger and McCabe are used. They give data for (kg inert or insoluble solid/(kg oil+kg benzene) in the underflow) versus (kg oil/(kg oil+kg benzene) in the underflow). This data is represented by the blue curve. in the overflow for all values of (kg oil/(kg oil+kg benzene) in the overflow). This means that the overflow is free of inert solid meal.
This Demonstration determines the number of stages for a countercurrent leaching and for various values of the oil remaining in leached solids. Stepping off the stages is done using alternatively one operating line (in magenta) and a tie line (in green). Tie lines verify , which means that two streams leaving a stage have the same oil and benzene content. The operating line is drawn using the difference point represented by the green dot. In addition, the mixing point is calculated and is shown as a cyan dot. The yellow dot represents the inlet solution with = and As expected, it is observed that the number of stages increases as the remaining amount of oil in the leached solid decreases.