I am evaluating a vendor pump performance curve for a centrifugal pump used in CO2 recovery plant. Pump is circulating lean solution pump to CO2 absorber. My required RATED flow is 308 m3/hr @ 475 mlc. The NORMAL flow is 265 m3/hr.
I have got the offer from a pump vendor (i feel, i should not disclose the name of the vendor...) who has supplied many pumps for the similar service for many clients. Upon seeing the curve i found that for the particular model, vendor has selected the impeller dia such that my rated point comes on best efficiency point. at first look it looks nice...but the problem arises when i see my normal point on the same impeller H vs Q curve. I could see that for the rated condition i.e. 308m3/hr and 475 mlc if i go towards left side of the curve upto the normal flow i.e. 265 m3/hr, the head rise is almost 40mlc. that means that for the selected impeller dia i can get my normal flow at almost 520 mlc. I understand it this way that, for the selected impeller dia and model if i want to operated my pump at normal flow (away from the rated flow) i have to drop almost 4kg/cm2 pressure at control valve.
Now while doing the pump hydraulics, i have kept approx. 0.8 kg/cm2 pressure drop for the rated flow condition for the control valve. It means that the same control valve have to drop 0.8 kg/cm2 pressure at rated condition and 4 kg/cm2 at normal condition. IS IT FEASIBLE???
problem becomes much severe when i further go towards left up to the turndown point which is 156 m3/hr. At this point head rise from rated head is almost 80 mlc (approx. 8kg/cm2). Plz note that at 156m3/hr also, i am still well away from the minimum recirculation flow which is 100 m3/hr.
the head rise from rated head to shut off head is approx. 105 mlc ( apprx 10 kg/cm2).
IN SHORT THE REGION ON CURVE WHERE THE RATED CONDITION IS ACHIEVED IS VERY STEEP.
i want to know
1) IS THERE ANY GUIDLINES OR CODE REQUIREMENT LIMITATION IN HEAD RISE FROM RATED POINT HEAD TO SHUT OFF HEAD??? i have gone through the API 610 there is a limitation of 5% head rise from rated head to shut off head but that is for PUMPS IN PARALLEL, for single pump there is no exact value?
2) what is others experience, can a control valve be designed for such a high range in pressure drop...i guess it is quite difficult.
kindly revert in case any other inputs required to comment on the problem
Awaiting responce from the experience ChE Jedis....
Edited by Jiten_process, 25 June 2010 - 01:04 PM.