Increasing the Capacity of Seawater Lift Pumps

You need to give more information my friend. At the existing head and flow rate, what kW is required from the motor (running current)?

Do you have a pump speed/torque curve? The pump curve indicating flow and head vs absorbed power?

hi aldego,

have you got a email address so i can send you the operating manual, i think this will help.

thank you

Hi Feato

You can send him a Private Message without him having to broadcast his e-mail address for all shysters to see.

Click on the user name and then click on Send xxxx a message (top right).

Sorry I see he or she or it is a (lasy) guest.

Most probably not with the same equipment.

Your friction losses will be higher and possibly excessive.

for the same pump you may need a oversize / bigger impeller or a faster RPM but your motor may not be enough.

It may be possible to increase the size of the piping but it need to be calculated.

It may be possible to find a bigger pump at an better efficiency (slim chance, but suppliers have been known not to optimize the design).

An inline booster (even on the shore) may also be an proposition.

Whatever is done you have to do NPSH calculations.

Please give more info or consult an expert.

hey hendrik thanks for reply, can i send you more info via email please?

kind regards

paul

Hi Feato

See my above post on how to send PM's.

But rather post the detail here for more members to respond.

The idea of CR4 is that all must be able to learn.

the file is PDF that i want to put on here. But not to sure how to send it.

any clues?

Upload the file to a website and post the link to it here.

having problems uploading the data. will do it tomorrow as ive just finished work.

thank you

<...is it possible within the current design of the pump and motor?...>

Please post a detailed description of the pump and the motor. What is the manufacturer, type, size, motor type, etc.?

<....provide a head/power/efficiency curve for new situation?....>

While the manufacturer can certainly do this via its local technical sales office, the thing that will be absent is the system characteristic curve. The pump operates where its performance curve and the system curve intersect. So the manufacturer will need some idea of the system that the pumped fluids are being despatched to in order to advise properly.

<...what needs to be changed (only pump, only motor or both) to end up with the desired capacity....>

Without seeing the system characteristic curve as well as the pump characteristic curve, it is impossible to say.

Hello Guest

A possibility is to drive it via an inverter at higher speed.

Backcalculating gives pump head about 100m. I suspect this is mostly static so only a small increase in speed needed. Just how much depends on the pump curve, but I'd guess 3-4%, and power drawn goes up about the same. Quite possibly the motor has enough in hand to cover this. On inverter, above 60Hz voltage is constant at 440V (because that's usually maximum volts available from supply) and available power is constant at 200kW.

The motor is probably 440V delta, but if it's 440V star connected you have another possibility. Reconnect it in delta and set up the inverter to supply 254V (= 440/√3) at 60Hz. The motor won't know the difference but current is √3 x higher so check cables OK. At higher frequency increase volts proportional to Hz. Then power also increases proportional to Hz. If the head is all friction (worst case) speed increases to 66Hz to give flow rise 10%, with available power 220kW. Pump shaft power goes up by 1.1³ = 1.33 so you still need to check the details, but in practice (part static, part friction) it won't be that high.

Cheers........Codey

Why is this posted in an ELECTRICAL engineering forum? This is a Mechanical Engineering problem. Although it's entirely possible to increase the flow of the pump by over speeding it using a VFD, there is NO WAY anyone here should recommend that without an ME being involved. There are MUCH bigger mechanical engineering problems here than electrical.

hey

yeah maybe its more mechanical, my fault for putting it in the wrong section. Anyway here is more info.

operating manual for a pleuger submersible pump unit.

TYPE: QN122-2A+MI10-880-2

Electrical Data

Motor Type: MI10-880-2

Motor output: 200kw

Rated voltage: 440V

Frequency: 60Hz

Insulation class: Y, Protection class: IP58 (Water/glycol filled)

Current at full load: 360A

Starting mode: D.O.L

Speed at full load: 3480RPM

Connection: Delta

cos phi at full load: 0.82

cos phi at start: 0.37

efficiency: 0.89

Locked rotor current: 2052 A

Starting time: ca 1.0 sec

Full load torque: 549Nm

Locked rotor torque: 878Nm

Breakdown torque: 1537Nm

Permissible ambient temp: max.35c

Pumping medium water: 1025 kg/m3

Min. water velocity along motor surface: 0.96m/sec.

Motor Curves: MK 0514

Motor starting diagram: MM0514

Hydraulic data (pump at duty point)

Pump type: QN122-2A

Pumping Capacity: 450m3/h

Total head: 9.4 bar

i do have the power supply cable, signal cable info. also the weights and motor filling of the pump unit.

thank you

I'm a ME. Use pump affinity laws, you can change the impeller dia (if casing has extra space) or increase the speed or both.

The change in flow is proportional to speed/dia ratio, and head the square and power the cube of the speed/dia ratio. So to get 10% extra flow you'll need to spped up the motor by 10%, but then the head would also increase by 1.1^2 i.e. 1.21 times.

The increase in flow will lead to increase frictional pressure drop in the piping system, and hence you would need this extra head to keep the flow at same velocity. Alternatively if you don't need the extra pressure, throttle pump discharge valve to bring the pressure to whatever value you require. Also if you trim the impeller it is possible to get the head back to original, but you need to contact the vendor for the exact re-profile

There is also some fat available in current motor power. Your pump needs 117.5kW hydraulic power and assuming efficiency of pump as 85%, the shaft power required is only 138 kW. As you said the motor is 89% efficient, the power drawn is only 155 kW. Give 10% margin and you get a required motor size of 170.5kW.

As you are only increasing the flow by 10% (and not the head), the new power required will be 188 kW. So a standard 200 kW motor will still do the job.

You may have to contact

Read post #11, there is little to add to that; your system is not likely designed to be operating at 100% of its capacity, so I'm sure there is a safe margin to attach a VFD, that extra 10% of frequency increase won't hurt. Besides you get advantage of soft starts and monitoring functions of the drive.

Yahlasit

Thanks Guest!

Codey