Calculating NPSHA
Calculating NPSHA
(OP)
On a stripper tower, does the vessel pressure equal to the vapor pressure of the process?
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RE: Calculating NPSHA
RE: Calculating NPSHA
rmw
RE: Calculating NPSHA
Least that's how I understand it.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Calculating NPSHA
RE: Calculating NPSHA
See thread798-129328: NPSH calculation question for a reasonably good discussion.
RE: Calculating NPSHA
To spare me the agony of reading (and actually trying to understand) the 50 some odd responses to that thread, would you mind just nodding your head one way or another here? Just this once. If I'm wrong, I promise I'll read, reread and understand every response in your ref.
If I don't deserve the star, I don't want it.
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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/
RE: Calculating NPSHA
To BigInch, you're not wrong.
One of the items I recall in that thread refers to the fact that saturated water at a higher temperature (and pressure) with about the same NPSHA causes less cavitation damage than cold water.
The proposed reason can be exemplified when comparing water at 10oC vs water at 90oC. It is a bit exaggerated, anyhow...
The specific volume of saturated steam at 10oC is 45 times larger than that at 90oC. The latent heat at 90oC is just about 92% of that at 10oC.
Therefore to produce at 90oC the same volume of vapor bubbles than at 10oC one needs to add about 41 times the heat.
Since the residence time of the liquid at the lower pressure zone inside the pump is very short, the net resulting effect is a lower cavitation intensity at 90oC due to a lower volume of imploding bubbles.
The other point was that raised by Mr Montemayor on adding an inert (hardly dissolvable) gas on top of a liquified petroleum gas (also in equilibrium, e.g., saturated) to improve the normally very low NPSHA values.
Plus a lot of good advice by others...
I hope this short message saves you time in reading the whole thread.
RE: Calculating NPSHA
rmw
RE: Calculating NPSHA
BTW, missed with the towel.
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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/
RE: Calculating NPSHA
rmw
RE: Calculating NPSHA
The question posted by Smackavelly didn't refer to any particular fluid. And the answer should be no. When calculating the NPSHA, the vessel pressure is generally higher than the vapor pressure of the stripped liquid to be pumped.
I said generally, since there are occasions when chemical reactions may produce "volatiles" in the stripped liquid e.g., thermal cracking, obliging to quench the "bottom" liquid to a lower "safer" temperature level.
In fact, the very reason to use stripping, i.e, to inject a gas (steam, nitrogen, etc.) is to reduce the pressure (at a given temperature) against which one wishes to eliminate -the more vaporizable- fractions originally present in the liquid.
RE: Calculating NPSHA
rmw, be sure to let me know if the local supply runs out. In the meantime have all you want... and enjoy. If they have white Rioja, grill a lobster.
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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/
RE: Calculating NPSHA
In the first case the vessel pressure is higher than the vapor pressure, but in the second case the vessel pressure and the vapor pressure are the same.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Calculating NPSHA
What katmar has added regarding reboiled strippers is absolutely correct. It merits a star. The question still remains what was Smackavelly's intention when asking about stripping.
The only comment I have (following the OP's question) is that the "vessel pressure" which is equal to the "vapor pressure of the liquid" is not necessarily the column's top pressure but the one at the reboiler. The difference is generally due to the ΔP caused by the column internals (packing, trays, etc.).
RE: Calculating NPSHA
Smackavelly are you happy?
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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/
RE: Calculating NPSHA
Thanks to all for your interesting comments. I wonder, Smackavelly, are you there? I can not hear you.
RE: Calculating NPSHA
RE: Calculating NPSHA
How do you deal with the rejection?
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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/
RE: Calculating NPSHA
RE: Calculating NPSHA
RE: Calculating NPSHA
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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/