Rerating and Reusing of Existing Pump

Obtain the pump flow/pressure characteristic curve for the impeller speed in question. 430m³/h @497m will be on the curve. What is the head from the curve at 395m³/hr? Once this question is answered, the recommendations can follow.

It's probably got a motor around the 650kW region. What does the drive look like in terms of voltage and starting method? In particular, is it variable speed?

At 522m head, the flow will be a little above 395m³/h, then, although a check with the curve will determine the expected value. Usually, the propsect of a pump over-delivering slightly on flow isn't a huge concern, though it depends on what the pump is doing. If there is a downstream valve that can be modulated a little to trim the flow slightly, then that might do.

First impression suggests, then, that the pump is more-or-less suitable without modification or adaptation to the new duty, though do wait to see what others chime in with. It might be a bit pedantic to quibble over a few m³/h on those figures.

However, the motor looks like it's overloaded. Is it truly running at that operating point, as it gives 563kW at the new operating point ignoring efficiency?

Indeed; the 390KW doesn't sound right at all, unless the liquid has a specific gravity of around 0.6.

Indeed. Not many do - at least, not many that need that order of m³/h do.

250mm/10in or so pipe for water, up to 400mm/16in pipe perhaps for non-conductive flammables (to keep the static buildup in check)? It's going to be thick pipe, too, to cope with the pump delivery pressures.

It would be good to know what the system is doing.

Temperature?

Is it flammable?

Agreed; GA.

If any trim change is required, it would be in the direction of larger impeller OD.
The new KW is slightly less than before, which may work in your favor.

if I was you, throw it away and buy a correctly sized pump to perform the way you want.

Pumps can be re-rated using the "laws of Affinity" and a VFD. However it sounds to me like your client has no idea what he's asking, and you, while I'm sure have an overall idea of pumps etc, by mentioning "impeller trimming" are not really sure how to deliver as trimming the impeller, REDUCES the flow, moving the pump curve to the left.

I would go ask a pump supplier and get their application engineer to design/select the correct pump for you.

Your question will not be answered to its fullest extend giving you the exact answer you require in this forum because we're all to remote from the problem.

The requested head increase is only about 105% of the current rating, so is LIKELY on the pump curve at reduced flow.

If it isn't, an easy fix is to use a VFD run at increased frequency.

The increased frequency will also shift the flow up by 5%. So- you can install a small by-pass line with balancing valve to kill any increased flow by recirculating the overage through the pump. Closing inlet valve to restrict flow will likely cause pump cavitation.

This will use more power (1.05 cubed), so check to see if the existing load is low enough to support that level of power increase. If not, you will need to increase motor HP. Obviously, this is a fix that meets the need, but wastes energy and adds costs.

Comparing the existing operating condition and the envisaged conditions, the pump should be able to meet the revised duty condition, without any modifications to Hydraulics (like impeller trimming etc. Based on the required operating head, I presume that this is a 2 stage double suction pump.

From the S.G figure of 0.44, I presume this must be pumping flammable hydrocarbon like LPG/Naphta. In this process service, slightly higher pumping rate should not be a problem for operation from process angle.

.

Noting the fact that this pump has never been in for years, the concern should be more on the mechanical integrity of the pump. It is imperative that you check the mechanical conditions of the pump (Hydro test of casing, close clearance parts such as wear rings, throat bush, which affect the efficiency, conditioning of pump bearings, replacement of mechanical seals and inspection of flexible elements of the coupling). This calls for reconditioning of the pump. Likewise, motor requires scrutiny of windings, bearings.

For such a flashing hydrocarbon, safety requirement stipulates provision of Dual mechanical seal with supporting flush plan.

So it is not hydraulics, but the mechanical fitness of the pump and motor that needs attention.

King cow Protector

You need the pump's performance curve, you DO NOT trim the impeller(s) to reduce Flow, you trim to reduce Head. The new Rated Flow 395 m3/hr Rated Diff. Head 522.5m may already fall on the pump's performance curve. If not, you may need a larger impeller(s) to meet the lower flow/higher Head requirement, which may also require more Horse Power (KW). The existing impeller(s) may be at full diameter already and you would not be able to increase the diameter. If the new flow/head requirements do not fall on the pump's performance curve or you need larger impeller(s), it may be cheaper to buy a mew pump.