Adding nitrogen to Boiler

[ScottI2R]

Hi All,
In my latest position with my company, I get to deal with some hot water boilers we use to heat chemical tanks. These run around 30-40 psi at 220-280 degrees F. I was told that we add 15-30 psi nitrogen into the supply lines to prevent the water from boiling into steam in the pipes (which cavitates the pumps and rattles the pipes to death). My question is straight out this: How does the addition of nitrogen keep the water from boiling? I would think it would just be easier to run the boilers at a higher pressure.

Thank in advance for any comments

Scott

I really am a good egg, I'm just a little scrambled!

 

[quark]

Even if I consider 40psi as gauge pressure then your temperature is close to saturation. So, boiling happens at places where the pressure reduces. That is the reason we have to run the system at higher pressures than saturation pressure. Nitrogen blanketing the feed tanks is one option (you maintain nitrogen at certain pressure, so entire system gets pressurised).

Otherwise, how do you propose to increase the pressure?

 

[Compositepro]

Pressurized nitrogen is used in the vapor space of expansion tanks in steam systems. It prevents oxygen from entering the system and provides some pressure at the lowest pressure point in the system. There is generally very little flow through an expansion tank.

 

[ScottI2R]

Quark, First thank you. I always got pressure increases when adding water to the x tank. Makes sense. Even though the max working psi of these things was 150 psi, we always keep them below 60 because the old heaps tend to leak much above that. Maybe the lower pressure could be required due to the capabilities of the rest of the system which I have no specs on.

Compositepro-So you are saying that it is just used as a pressure boost system wide, and at that point it would seem we could use Helium or Argon instead. The point being that we just happen to be using Nitrogen,is of no importance as a choice of gas. Correct?

Thank you
Scott

I really am a good egg, I'm just a little scrambled!

 

[quark]

The choice comes from the cost. Nitrogen is the cheapest of all inert (to some extent) gases.