Brownfield limitation in design pressure with pumping system

[Sawsan311]

Dear All,

for a system which has a specific design pressure limit and requires revamp with a new pumping system. Do you agree that selecting the pump's impeller size wand hence selecting smaller multiple pump's capacity to achieve the total target demand would contribute in limiting the shut off head of the system. In other words, for a VFD driven large pump, going to high speed range up to an increased capacity per pump (and hence less number of installed pump) would force the system to exhibit higher head towards shutoff and accordingly limit the application of such less number of large pumps to an existing system.

Do you agree that I would rather install smaller capacity multiple pumps which will operate over a smaller rpm range such that HxN2 would be less. Bearing in mind that I still have to fulfill the minimum head to rise to shut off of 10% for pump operating in parallel as per API 610.

thanks

regards,

 

[LittleInch]

Sorry, your'e going to have to provide some numbers here.

I read this three times and still can't understand what you have, what you're trying to do and why it might be better.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Dont know if your assumption is correct. Better to get some quotes from pump vendors. You may be able to get a flatter head rise to shutoff for the larger pump if there is some preference for the larger single pump option.

Other considerations:
Though total CAPEX may be less for the larger single unit, overall availability of the system would be better with the multiple smaller pumps option (theoretically).
Overall footprint requirement for the pumping system may be less for the larger single unit.

If there is some significant benefit in getting some headroom in design pressure in this brownfield application at pump discharge, would suggest installing a 2oo3 voting for PSHH at the source vessel to trip the pump at the MCC through 2 independent trip relays (or similar - talk to electrical engineer responsible for MCC) to avoid using the PSV setpoint on the source vessel for calculating design pressure downstream of the pumps.

 

[Sawsan311]

Thanks All,

Actually my query is simple, I was enquiring about the effect of pump impeller size on the shut off head considering the affinity basic laws. Obviously a larger pump w(specially if VFD driven) would be more aggressive with respect to shut off head than a smaller pump (both having same rated capacity and head), even if both are complying with minimum head rise to shut off as per API 610.

Do you agree?

 

[mk3223]

To consider the number of the pumps for the specific process, it can be based on several factors, such as pump size and availability, process criticality, maintenance, TIC cost, etc., in additional to the shut off head of the pump. One may compare the pro and con of these factors and decide the final number of pumps for operation.

 

[georgeverghese]

Dont think so. There are some pump curves in Perry 6th edition you can take a look at also.