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Greetings Members,

Looking forward for your valuable feedback in resolving a centrifugal pump (API type OH2) high power consumption issue. Service media is naphtha.

Problem Statement: Pump is drawing more power at reduced flow rates. Refer attached pump operating parameters. Current discharge flow rate is 96 m3/hr. However, design flowrate is 124 m3/hr. At 96 m3/hr motor current is reaching FLC.

Findings & Observations:

1. Current reported liquid density was checked, and it is averaged to be 720 Kg/cubic m since commissioning.
2. As per the pump performance curve, the pump & motor combination are designed for liquid density of 646 Kg/cubic m .
3. As per the history, the high current is experienced by both the pumps (1 running and 1 stand-by configuration)
4. Motor winding problem is ruled out as the current is balanced in both the motors. 
5. As per condition monitoring observation, the motor & the pumps bearing are healthy and its vibrations are within limit.
   6. Pump was overhauled and internal clearances are within design limits,.  

Members support is requested to identify other potential causes leading to this issue. Please note, operation team informed that there is nothing they can do about the naphtha density. 

------------------------------
Vaibhav Sharma BTech
Reliability Engineer
Saudi Aramco
RAS TANURAH
------------------------------

Sir,

Maybe you can check out the following aspects to confirm, hope it can help you

1.Exclude the physical and chemical properties of the process medium changes
2. No abnormal operation when starting the pump artificially
3. The motor is connected to the pump only by coupling
4. No abnormalities at all seals
5. No abnormality in motor exclusion
6. Mechanical internal parts are in accordance with the design requirements

------------------------------
Yi Sun
惠州市
------------------------------

Greetings, thank you for sharing your feedback. Kindly refer below comments:

Maybe you can check out the following aspects to confirm, hope it can help you

1.Exclude the physical and chemical properties of the process medium changes - Density of the service fluid is more than design limit. This we have identified but operation cant do anything about it
2. No abnormal operation when starting the pump artificially - No abnormality
3. The motor is connected to the pump only by coupling - Yes
4. No abnormalities at all seals - No issues in the mech seal
5. No abnormality in motor exclusion - No issues in the motor circuit
6. Mechanical internal parts are in accordance with the design requirements - YEs

------------------------------
Vaibhav Sharma BTech
Reliability Engineer
Saudi Aramco
RAS TANURAH
------------------------------

Original Message:
Sent: 05-08-2023 06:42 AM
From: Yi Sun
Subject: Centrifugal Pump increased power consumption at reduced flow rates

Sir,

Maybe you can check out the following aspects to confirm, hope it can help you

1.Exclude the physical and chemical properties of the process medium changes
2. No abnormal operation when starting the pump artificially
3. The motor is connected to the pump only by coupling
4. No abnormalities at all seals
5. No abnormality in motor exclusion
6. Mechanical internal parts are in accordance with the design requirements

------------------------------
Yi Sun
惠州市
------------------------------

I am not familiar with naphtha but a few other random thoughts.

With SG increase, you are 1.11 times more BHP to start.

Pump clearances can cause that but you say they have been checked and are correct.

Assume pump turns freely by hand when down and empty.

Check system for any recirculation valves open or leaking by which is not measured flow in system.  Is the flow you list from a flowmeter or from curve or calculation?

Is viscosity in range for design?  Has it changed?

Is issue high power or high amperage?
What is motor voltage?  If line voltage is lower, amps may be higher for same BHP.

Can you check system pressure compared to original design?  Does it match up with your flowrate or motor load?

------------------------------
Randy Riddell, CMRP, PSAP, CLS
Reliability Manager
Essity
Cherokee AL
------------------------------

Thank You Mr Randy for sharing your feedback.

Yes, we identified that the increase in density is one of the reasons of motor overload. operating liquid density from 646 Kg/cubic m to 720 Kg/Cubic m which corresponds to a significant increase of 11.5%

Recirculation valve isn't passing. 

We haven't checked viscosity part

Issue is motor overload trip on FLC (problem is current consumption. Motor is drawing more current even when pump is operated well below rated point. Please refer attached curves.). Current operating point is 96 m3/hr

------------------------------
Vaibhav Sharma BTech
Reliability Engineer
Saudi Aramco
RAS TANURAH
------------------------------

Original Message:
Sent: 05-08-2023 08:47 AM
From: Randy Riddell
Subject: Centrifugal Pump increased power consumption at reduced flow rates

I am not familiar with naphtha but a few other random thoughts.

With SG increase, you are 1.11 times more BHP to start.

Pump clearances can cause that but you say they have been checked and are correct.

Assume pump turns freely by hand when down and empty.

Check system for any recirculation valves open or leaking by which is not measured flow in system.  Is the flow you list from a flowmeter or from curve or calculation?

Is viscosity in range for design?  Has it changed?

Is issue high power or high amperage?
What is motor voltage?  If line voltage is lower, amps may be higher for same BHP.

Can you check system pressure compared to original design?  Does it match up with your flowrate or motor load?

------------------------------
Randy Riddell, CMRP, PSAP, CLS
Reliability Manager
Essity
Cherokee AL
------------------------------

Also since both pumps are doing the same, it is likely a system problem.  Just to make sure, verify the correct impeller is on both pumps.  Same flow but higher system pressure and more HP is required.  Efficiency changes too.

Ok, so taking a quick look at the pump curve I see the following.
At 96m3/hr, 64% eff, 30Kw
At 124 m3/hr, 68%eff, 34Kw
With 11% increase in density that makes up the 4Kw difference and basically they are the same pumping condition power wise.

I don't know what motor size you have so not sure of FLA and any other motor size issues.  I'd check motor voltage too just to make sure.  Low voltage will mean higher amperage for same power.  Check wiring and starter connections.  

------------------------------
Randy Riddell, CMRP, PSAP, CLS
Reliability Manager
Essity
Cherokee AL
------------------------------

Original Message:
Sent: 05-09-2023 11:53 PM
From: Vaibhav Sharma
Subject: Centrifugal Pump increased power consumption at reduced flow rates

Thank You Mr Randy for sharing your feedback.

Yes, we identified that the increase in density is one of the reasons of motor overload. operating liquid density from 646 Kg/cubic m to 720 Kg/Cubic m which corresponds to a significant increase of 11.5%

Recirculation valve isn't passing.

We haven't checked viscosity part

Issue is motor overload trip on FLC (problem is current consumption. Motor is drawing more current even when pump is operated well below rated point. Please refer attached curves.). Current operating point is 96 m3/hr

------------------------------
Vaibhav Sharma BTech
Reliability Engineer
Saudi Aramco
RAS TANURAH
------------------------------


Original Message:
Sent: 05-08-2023 08:47 AM
From: Randy Riddell
Subject: Centrifugal Pump increased power consumption at reduced flow rates

I am not familiar with naphtha but a few other random thoughts.

With SG increase, you are 1.11 times more BHP to start.

Pump clearances can cause that but you say they have been checked and are correct.

Assume pump turns freely by hand when down and empty.

Check system for any recirculation valves open or leaking by which is not measured flow in system.  Is the flow you list from a flowmeter or from curve or calculation?

Is viscosity in range for design?  Has it changed?

Is issue high power or high amperage?
What is motor voltage?  If line voltage is lower, amps may be higher for same BHP.

Can you check system pressure compared to original design?  Does it match up with your flowrate or motor load?

------------------------------
Randy Riddell, CMRP, PSAP, CLS
Reliability Manager
Essity
Cherokee AL

Hi Vaibhav,

Please take under consideration how steep is the efficiency curve of your pump. At reduced flow rate the efficiency is dropping hence the power consumption per 1 cubic meter of fluid is increased in relation to Nominal Flow Rate. Another thing is that you run the pump with more dense fluid than rated one - these are two major factor for power increase.

Cheers from Grundfos

------------------------------
Lukasz Sznajder
Senior Customer Success and Reliability Success manager
Grundfos
Warszawa
------------------------------

Greetings, thank you for your valuable feedback. I agree with you that change in liquid density is one of the reasons for high current consumption but operation can't do anything about it. 

Current operating point is 956 m3/hr. However, rated flow is 124 m3/hr. Kindly refer attached curves.

Is there anything else we can do in this case except replacing the existing motor with higher capacity motor? 

------------------------------
Vaibhav Sharma BTech
Reliability Engineer
Saudi Aramco
RAS TANURAH
------------------------------

Original Message:
Sent: 05-09-2023 07:15 AM
From: Lukasz Sznajder
Subject: Centrifugal Pump increased power consumption at reduced flow rates

Hi Vaibhav,

Please take under consideration how steep is the efficiency curve of your pump. At reduced flow rate the efficiency is dropping hence the power consumption per 1 cubic meter of fluid is increased in relation to Nominal Flow Rate. Another thing is that you run the pump with more dense fluid than rated one - these are two major factor for power increase.

Cheers from Grundfos

------------------------------
Lukasz Sznajder
Senior Customer Success and Reliability Success manager
Grundfos
Warszawa
------------------------------

Hi,
Please check the installation for a protection recycling line back to source (maybe a tank), and flow meter installed downstream of its intersection. If it is the case, you need to consider (add) the flow recycling to balance out for MCSF which is not indicated in performance curve.

------------------------------
Jorge OLIVEROS
Profesional Engineers of Ontario
Stoney Creek ON
------------------------------

Hello Sir,

1. Can you check the check valve for any backflow that cause reduced flow rate.

2. Is the strainer is cleaned or the try to replace the strainer?

------------------------------
Haysen-M Venal CMRP
SAN MIGUEL GLOBAL POWER
2103
------------------------------

Greetings, Thank you for your feedback. Strainer was checked and found clean. What's the relation of strainer mesh size with the motor current consumption?

------------------------------
Vaibhav Sharma BTech
Reliability Engineer
Saudi Aramco
RAS TANURAH
------------------------------

Original Message:
Sent: 05-09-2023 06:29 PM
From: Haysen-M Venal
Subject: Centrifugal Pump increased power consumption at reduced flow rates

Hello Sir,

1. Can you check the check valve for any backflow that cause reduced flow rate.

2. Is the strainer is cleaned or the try to replace the strainer?

------------------------------
Haysen-M Venal CMRP
SAN MIGUEL GLOBAL POWER
2103
------------------------------