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How can one fix minimum circulation flow and scheme for a pump which is undergoing in revamp, specially when flow is going to reduce after revamp?
 
Answers
02/12/2011 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
I agree that the minimum flow can be obtained from the pump manufacturer data sheets and from the pump performance curve. However running the pump at this rate for any period of time will result in poor reliability... Have you have ever seen the diagram of a reliability curve super imposed on a pump curve?.... If the pump is going to be run at a somewhat steady state the pump should be run at approximately -10% +5% of the Best Efficiency Point (BEP) it should never be run for any length of time below 30% of BEP.... even -20% is pushing it... The impeller can be trimmed or re-sized to achieve this.
29/11/2009 A: G KAMALAKANNAN, Foster Wheeler India Ltd, siddhukamal@yahoo.co.in
Minimum flow is fixed by checking the pump minimum safe flow. You can get this from Pump characteristic curve. Then you can check the process min flow (typically this should be turn down flow, about 50% of rated flow).
Min flow design reqd = Process min flow - Min safe flow.
19/07/2009 A: keith bowers, B and B Consulting, kebowers47@gmail.com
When the new operating condition after a revamp results in flow rate below prudent operation for a piece of equipment, that equipment must either be replaced with appropriately sized unit or modified as necessary to allow it to operate reliably in the new conditions. Since you did not provide any details, it is not prudent for me to guesstimate the best path to achieving the reliability goal.
It may be possible to install smaller internals, or simply trim the impeller diameter of the pump. Installing a minimum flow bypass (automatically self controlled), is likely to be significantly more costly than modifying the pump. It is very poor engineering to plan on always operating with a spill-back or minimum flow bypass active. It not only wastes energy, it unnecessarily complicates the control system and depreciates the overall reliability.