Question

a water purification process in which the water undergoes adsorption and ion exchange processes.

what is the expected effect of flow rate on ion concentration after the adsorption and ion exchange units?

Answer 1

In general, the adsorption and ion exchange process used for the removal of traces of the impurities such moisture, salts, dissolve metal, etc. from the gaseous and liquid feed.

In the separation process, the feed is passed through the bed of material called adsorbent/ion exchange resin where impurities are adhere or capture by the adsorbent. The adsorbent or ion exchange resins are very specific type differs from one process to another process. The selection of adsorbent type depends greatly on the type of impurities present in the feed which need to be removed.

There are many different factors such as concentration of impurities in feed stream, desired concentration of impurities in outlet stream, height of bed of adsorbent or ion exchange resins, effectiveness of resins, resident time of feed, etc. that need to take into account when designing an adsorption or ion exchange system.

The system (Adsorption or Ion Exchange) reduces the impurities to certain level when the feed gas or liquid with specific designed flow rate is passes through the bed.

At the beginning of process, when the adsorbent or resin is pure (vergin) the maximum output flow rate of purified feed can be obtained.

The activity of the adsorbent/resin is decreasing with time due to the accumulation of impurities over the surface of the adsorbent/resin.

At this point, there are two ways to run the process

1). Reduce the flow rate of feed to maintain same outlet concentration of impurities throughout.

2). Maintain constant flow rate and compromise with the level of impurities in outlet stream.

For fixed height of bed of adsorbent/resin, the flow rate is decided on the residence time required by the the molecules of impurities to adsorbed on the surface of adsorbent.

If the flow rate of the inlet feed stream (with specific impurities level) is higher than the designed flow rate limit, then the molecules of the impurities may not get the enough time to get adsorbed into the adsorbent. Resulting, the concentration (level) of the impurities goes up in the outlet stream.