Dow Water & Process Solutions

How to Design an Ion Exchange System

Step 7: Number of Lines

Steps:

Step 1:Regeneration System Selection
Step 2:Selection of Layout and Resin Types (Configuration)
Step 3:Chemical Efficiencies for Different Resin Configurations
Step 4:Atmospheric Degassifier
Step 5:Resin Operating Capacities and Regenerant Levels
Step 6:Vessel Sizing
Step 7: Number of Lines
Step 8:Mixed Bed Design Considerations

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Based on the flow rate and throughput required, the number of lines operating at the same time needs to be defined. The simplest layout with 2 lines (1 in operation, 1 in standby) can be used in most cases. With large plants (> 400 m³/hr or 1800 gpm), however, it may be more appropriate to have 3 lines (2 x 50% in parallel, 1 in standby) in order to reduce system redundancy, optimize flow conditions and reduce vessel sizing. In making a design, it is important to ensure that there is enough time for the standby lines to complete regeneration before they are required to go back on line. The optimum number of lines with minimum redundancy can be calculated using the following formula:

Number of lines =	Run length (throughput) (hrs) + Regeneration time (hrs)
	Regeneration time (hrs)

If the equation predicts a non-integer result, the number should be rounded down to obtain the optimum number of lines. For example, a 10 hour run length with a 3 hour regeneration time gives a ratio of 4.3, so the number of lines with minimum redundancy would be 4.

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