In an ion exchange system, which action would directly increase the hydraulic loading rate (HLR) if the exchanger bed area cannot be changed?

In an ion exchange system, which action would directly increase the hydraulic loading rate (HLR) if the exchanger bed area cannot be changed?

• A. recirculate flow
• B. increase the exchanger bed area
• C. increase the feed concentration
• D. add exchanger vessels in series

Answer: (A)

Hydraulic loading rate is the volume of liquid passing through the exchanger bed per unit area per time. If the bed area cannot change, the only way to increase HLR is to increase the flow rate through the bed. Recirculating flow does just that: it pushes more liquid through the exchanger bed by looping some of the effluent back toward the inlet, so the bed processes a higher volume per unit time while its area stays fixed. This directly raises HLR. Increasing the bed area would have the opposite effect, lowering HLR because the same flow is spread over a larger area. Increasing feed concentration doesn’t directly change the flow rate through the bed. Adding vessels in series changes how the flow is arranged but typically distributes flow across more bed area, not increases it, so it wouldn’t raise HLR.

Hydraulic loading rate is the volume of liquid passing through the exchanger bed per unit area per time. If the bed area cannot change, the only way to increase HLR is to increase the flow rate through the bed.

Recirculating flow does just that: it pushes more liquid through the exchanger bed by looping some of the effluent back toward the inlet, so the bed processes a higher volume per unit time while its area stays fixed. This directly raises HLR.

Increasing the bed area would have the opposite effect, lowering HLR because the same flow is spread over a larger area. Increasing feed concentration doesn’t directly change the flow rate through the bed. Adding vessels in series changes how the flow is arranged but typically distributes flow across more bed area, not increases it, so it wouldn’t raise HLR.