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Low performance in centrifugal pump

Low performance in centrifugal pump

Low performance in centrifugal pump

(OP)
Hello!
We are having serious problems with a centrifugal pump, it is overcharged, I mean the operating electric current is higher than the nominal one.
This pump is giving the head of liquid for the flow rate according to the rated condition point but the electric motor input power is higher. The overall efficiency is 35%.
The pump was cleaned and mud was removed.
The operating conditions are:
-higher density fluid
-lower process temperature
-rated suction pressure

I hope you can help us.
Greetings.  

RE: Low performance in centrifugal pump

what is the efficiency (and required duty) specified for? If its water then if your desity incl. mud is higher your duty will be higher - but head (i meter/feets whatever) and flow will be correct.

Best regards

Morten

RE: Low performance in centrifugal pump

(OP)
Pump efficiency: 49% (specified)
Pump output power: 28.7 kW
Density: 0.794 (specified 0.750)
Viscosity: 0.37 (specified)

RE: Low performance in centrifugal pump

Your power input will increase 6%(0.794/0.750 = 1.0586) more because of increased density (more precisely specific gravity). Further, you have increased inefficiency of 14%. So it will not surprise me if you have to supply 20% more power.


Regards,

RE: Low performance in centrifugal pump

  If you had an air-cooled induction motor with a typical efficiency of 90% driving your (specified) 49% efficient pump hydraulics your overall efficiency would be 44.1% Your present 35% (presumably measured) overall efficiency of 35% indicates that you are overpowered by 26% of which 6% is due to the fluid specific gravity increase as cited above. The remaining 20% increase in input power (and running current assuming no power factor change)could be due to either degraded motor efficiency or degraded pump hydraulic efficiency. Your mention of two-phase liquid-solid fluid (mud) pumping suggests that the likely degradation in efficiency is in the hydraulics not the motor. Aside from the pumped fluid density change, pumping solid-liquid mixtures can lead to solids deposition buildup on the blades of the pump impeller which can alter inlet flow incidence angles, create increased drag losses and generally screw up pump hydraulic efficiency.

RE: Low performance in centrifugal pump

Only for the efficiency decrease from 49% to 35%, your power consumption will go up 29%. And since the efficiency is not at your calculated point, the pump is actually running at a different working point - probably lower pressure and higher flowrate. This can also increase the horsepower.
When I size the motor of a pump, I always take a check of the curve end (low pressure and high flowrate), make sure motor is big enough if the operating point swifts.

RE: Low performance in centrifugal pump

I note you have a lower process temperature. This will normally cause an increase in viscosity. Increasing viscosity can significantly increase power draw with only moderate reductions in head and flow.
Suggest you research the change in viscosity due to the lower process temperature and the need for this lower temperature. The densities you give suggest a hydrocarbon liquid, so the effect could be significant.
Or fit a bigger motor if the pump will take it.

Cheers

Steve McKenzie

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