Pump Min. Flow Recycle Heat Gain

[LAche81]

Hello All,

I have a question I was hoping you guys could help out with.

I'm installing a new 5300barrel/hr pump that will be used for two services. The first will have a required flow of 5300barrel/hr and the second will have a required flow of 1500barrel/hr. We are limited on nozzles off the tank, so we are planning to route the min flow recycle line back to the pump suction. Since we are recycling 3800 barrel/hr through the min flow line for the second service, I am worried about heat gain though the recycle line since we can not use the fluid in the tank as a heat sink. How would I go about calculating what the potential heat gain will be? They will only use the pump for the second location during outages, however, this could be for a period of 1-2 days.

Thanks

 

[Pumpsonly]

You did not mention what type of pump and the operating head.
If it is centrifugal, you will not need to recycle the 3800Barrel/hr You can throttle the discharge valve until the minimum allowable flow of the pump. If it is still too much, then you recycle the difference.

 

[bimr]

If a pump is rated 60% efficient, that means that 40% of the power is being converted to heat. In a normal temperature stabilized pump, running at its best efficiency point, (B.E.P.) the temperature rise within the pump is calculated from the following formulas:


Centigrade Rise:

((BkW-WkW)*14.34)/ (Flow in l/m*Specific Heat)

Where:
BkW = Break kW from pump curve
WkW = Water kW = (Meters * Liters/Min)/6000
14.34 = Conversion from kW to kilocalories

http://www.mcnallyinstitute.com/01-html/1-04.html

The lowest flow that a pump can operate at without compromising mechanical reliability is the "Minimum Stable Flow". For most pumps, this is more of a limiting factor than minimum thermal flow. Minimum thermal flow often does become a critical factor, especially when dealing with volatile liquids , and it should always be checked when evaluating a pump system.

Calculating Minimum Continuous Thermal Flow

http://www.lawrencepumps.com/newsletter/news_v03_i1_Jan06.html

 

[BigInch]

You're not going to want to pump at absolute minimum flow for more than 15 to 20 minutes. Look for minimum stable flow, probably around 20% of pump's BEP flow. Calculate temperature gain via bimr's links to see if you can dump back into suction, or have to go back to the tank, or ... add a cooler.

From "BigInch's Extremely simple theory of everything."