5 replies to this topic

[Dave Morgan]

Hydrogen gas is purposefully added to the suction of the feed pumps for a boiling water reactor. The concentration of gas (2 ppm to 3 ppm) is equivalent to ~5 psi/ppm hydrogen gas overpressure at the temperature of the feedwater (393F). Does this pressure need to be added to the fluid vapor pressure to establish a suction pressure trip setpoint that will maintain the Net Positive Suction Head Required for the pumps?

In this case, the vapor pressue of water at feed pump suction pressure is ~229 psia, and the equilibrium pressure (water vapor plus H2 gas) would be ~239 psia. In effect, the pressure trip setpoint would be increased by ~10 psi of that determined using the water vapor pressure. Is this increase in setpoint necessary? If not, why not?

[pleckner]

There has been a number of articles written on the subject of dissoved gas and the effect on pumps. The main goal is to show how to calculate a pseudo NPSHA just as you are trying to do. So in a nut shell, you are approaching the problem correctly. My only regret is that I don't have them readily available to get you a reference. I'll see tomorrow.

[Dave Morgan]

Thanks. It's good to know I hadn't wandered too far from reality. References would be greatly appreciated.

[pleckner]

References:

"Cope with Dissolved Gases in Pump Calculations", Chemical Engineering Magazine, October 1993

"Effects of Entrained Air, NPSH Margin, and Suction Piping on Cavitationin Centrifugal PUmps", Pumping Technology, June 1998

"Accounting for dissolved gases in pump design", Chemical Engineering Magazine, July 26, 1982

"Inert gas in liquid mars pump performance", Chemical Engineering Magazine, July 3, 1978

"Pumping Liquids Loaded with Dissolved Gas", Chemical Engineering Magazine, July 1998

[Dave Morgan]

Thank you so much for the references and for your help.

[pleckner]

You're welcome. I'm glad to have been of help.