Recycle without Chemical Reaction
Recycle of material occurs in a variety of processes that do not involve chemical reaction, including distillation, crystallization, and heating and refrigeration systems. As an example of a recycle system, look at the process of drying lumber shown in Figure 12.6. If dry air is used to dry the wood, lumber will warp and crack. By recycling the most air that exits from the drier and mixing it with dry, the inlet air can be maintained at a safe water content to prevent warping and cracking of the lumber.
Another example, shown in Figure 12,7, is a distillation column used to separate two compounds. Note that a portion of the exit flow from the accumulator is recycled back into the column as reflux while the reboiler vaporizes part of the liquid in the bottom of the column to create the vapor flow up the column. The recycle of vapor from the reboiler and return of the liquid from the accumulator back into the column maintain good vapor and liquid contact on the trays inside the column. The contact aids in concentrating the more volatile components in the overhead vapor stream and concentrating the less volatatile components in the bottom of the column.
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