minimum flow bypass

[edko]

A boiler feedwater motor for the deareator in a unit that the RTD's increase in temperature when the pump's minimum flow bypass is opened. These are VFD motors, but are operated at full speed when the minimum bypass is opened on low discharge pressure. Why would temperature increase?

 

[BigInch]

Arn't you reducing the net flow of cooler water into the boiler when some flow in the pump is recirculated in the bypass?

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

A better question is what use is the VFD, if it operates at full speed when the bypass is opened?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JJPellin]

If I understand your question, you are asking why the windings in your motor are running hotter when you increase bypass flow. If I have interpreted this correctly, then the answer in easy. When you open the bypass, the total flow produced by the pump increases even if the flow going to the boiler may decrease. If the total flow increases, then the pump is doing more work. More work requires more motor horsepower. If the horsepower goes up, then the motor may run a little bit hotter. Please correct me if I have misunderstood your situation.

I am confused by the last part of your post. You say that the bypass opens when the discharge pressure is low. Normally, I would expect the bypass to open when the discharge pressure is high; indicating a low net flow from the pump. If the discharge pressure is low, this would suggest higher flow from a centrifugal pump and no need for minimum flow bypass. We need more details to understand what you are describing.



Johnny Pellin

 

[BigInch]

Yes. It was a confusing question. I thought the process was heating, not the pump/motor.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[dabluffrat]

Why is the bypass opened on low discharge pressure?

Did you know that 76.4% of all statistics are made up...