Condensation of CIP steam in tanks & pressure equipment 2

[Whe]

Are there any good ways to calculate the rate of condensation of steam in a tank due to a cold inlet flow of water or other liquid, through an inlet pipe in the roof?

The water can fall several metres to the floor of the tank. There is no spray nozzle, just the open pipe.

The rate of condensation affects vacuum protection.

 

[sshep]

Whe,
The simplest and most conservative model is by energy balance using the inlet water flow rate and resulting in a single mixed (vapor and liquid) tank temperature. The steam condensed sets the make-up flow. The enthalpy of the make-up air can probably be ignored for simplicity, although as it will be heating up perhaps it could be credited to small advantage.

This approach will likely give a large vacuum breaking requirement for a your water flow, but direct contact heat transfer is very effective so if your tank is filled with steam (i.e. 212F, 14.7psia) you want to be certain that you do not underestimate- such a situation has collapsed much equipment. Even though you feel that there should be able to credit the fact that you are not "spraying" the water in, when it splashes against the floor and spreads out there will be plenty of surface area to condense your steam, and it is this initial condition which will set the vacuum breaking requirement.

As a fully steam filled tank may not be your situation, a more detailed description may result in alternative rationalizations- i.e. give us some more detail.

best wishes,
sshep

 

[katmar]

This is a very difficult situation to analize rigorously. If you compare your situation with a direct contact condenser, where the droplets fall about 2 metres and in that time they achieve thermal equilibrium with the vapor, you can get a feel for the speed at which you can destroy a tank.

I accept that in the direct contact condenser the liquid stream is deliberately broken up into droplets by a nozzle or a perforated plate, but it would still be very quick with a water stream as it broke up during its fall.

When we tried to do this analysis on a recent project we came up with such large vacuum breakers that we elected instead to install temperature interlocks to the water feed valves, and also micro-switches on the manhole covers. This meant that it was "impossible" to put cold water into a tank before it had cooled down, and that the open manhole would allow some venting if there was a problem. So far it has worked....



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