Answer to Reader Question: Impact of Flow on Ion Exchange Resin

Dec. 1, 2008
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I work in power plant 320 MW as a chemist and am responsible for the condensate polishing plant. The inlet flow of the condensate will increase to 520 m3/hour but the design flow is 415 m3/hour.

Q: What is the reverse effect of the flow on the ion exchange resin?

Answer 1:

Check the flow specifications from the ion exchange resin manufacturer. They give typical flow rates on both a volumetric and superficial velocity basis. If you exceed those you may see reduced water quality due to either channeling or kinetic impairment. From Siemens Water Technologies

Answer 2:

The correspondent asked about the effects of increasing the flow through an ion exchange system.

The kinetics of the exchange reaction on resin beds is basically linear over the roughly 25% change in flow rate in this example. Total q12antity of ions exchanged would be roughly proportional to contact time. Increasing the flow rate by 25% without increasing the size of the system decreases the contact time by 25%.

Remember that 415m3/hour is the design rate. There may be a safety factor built in to this number or, on the other hand if the system and resin has lost efficiency due to age or mistreatment it may not be able to achieve even the stated design rate. We don’t know what the present flow rate is. So in the absence of more concrete information about what the system is presently doing we would need to make some assumptions. Assuming that the resin bed is already operating at maximum utilization at the design rate of 415 m3/hour, the effect of increasing the flow rate by 25% would be that the effluent would contain 25% more of the species which the resin bed was designed to exchange out. The fact that the tail end of the bed sees a somewhat more concentrated feedstock might improve this number slightly.

One way to know for sure what actual results to expect, if the arrangement of the system permits, would be to hold back a volume of feedstock equal to several times the amount required to completely fill the exchangers (more is better, I would recommend at least 6 fills to get meaningful results). Then feed that through the system at the higher rate and analyze the effluent.

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