Beads
Operating methods
There are three basic operating methods for ion exchangers. They consist of batch, column and moving bed operations.
Following is an introduction to each type of system.
Batch operation consists of dumping resin and solution into a tank, mixing and allowing for equilibrium. Solution
is filtered off. Resin is then prepared for the next cycle. This process is limited by the selctivity of the resin under
equlibrium. The total capacity used is due to selectivity.
Column operation is like several batch reactors in series. It is carried out in a row of containers. The purpose of
column operation is to work around the limitation of selectivity. H It is realized that the improvement in each stage
is less than that obtained in preceding one. It can be seen with an unfavorable selectivity there is a need for more
stages (law of diminishing returns). Column operation is analogous to a distallation column and the same
techniques can be applied to analize the process.
Three types of column operations are down flow, up flow and counter flow. Most beds operate with down
flow operation. This is where feed and resin pass down through the resin bed. On the contrary, upflow operation
is when the feed and resin are raised throught a bed. The final flow is counter flow and it consists of the feed
flowing down from the top and the regenerate flows up from the bottom.
Moving beds are the most economical beds of the three. The principle is resin and solution flow through the
system. The resin is contacted counter-currently with the exhausting stream and regenerated stream. The physical
chemistry is similar to fixed bed and can also be thought similarly as a distillation column. The advantages of
operation is there is a continuous product of uniform quality at less space, capital and labor. The problem is a
complexity of the design problem for a operating system.
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