Emergency water line purge with compressed air/gas

[Icecoffee]

Hi all,

I would like to ask for advice for the following issue...

My project is a process cooling water for equipment in our plant and this problem applies to cryogenic equipment...

The process water is delivered to the equipment which has internal cooling coils, if there is a power failure/water stoppage, water can remain stagnate in the coils and will freeze up (therefore expand and rupture the coils), I am trying to find a way to deal with this emergency situation.
I am wondering if say, injecting plant compressed air (90 psig) /nitrogen (60 psig) into the water lines (all about 3/8" to 3/4") and try to "push out/purge" the stagnate water is something possible, and if so, how do I calculate how much cfm air/gas, pressure, and how do I install this? (three way valves at inlet and discharge...?)
Any suggestions and advise will be greatly appreciated.

 

[BigInch]

Of course that might be a possibility, but wouldn't it be soooo much easier to use gravity and install drain valves?

You might also just allow the cooling water to run its circuit at a much reduced flowrate. Just a little velocity will prevent freezing in many situations.

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For your compressed air solution, you'll need to look at the pressure needed to lift your water from the air injection point to the highest point in the path you will use to clear your water.

I would use a conventional 2-way valve to introduce the air. Why 3-way? Will you still want to have water upstream of the injection point, or something?
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If I were you, I'd seriously take a look at adding those drain valves.

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"Pumping systems account for nearly 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/

 

[Icecoffee]

Hi BigInch,

Thanks for you input.

The thing is... the internal coils have paths such that it is not drainable so gravity would not solve the whole problem; currently I have installed drain valves on the return side.

well the reason I mentioned 3-way valve is that I thought about having to introduce air "in-line" with the water lines, such that during an emergency (and no operators around), system can introduce air automatically and "blow out" the remaining water in the line... (does this make sense to you?)

 

[BigInch]

Something in my nature doesn't like the idea of introducing air into a water system. Most of the time, trapped air is creating a problem and you're looking for ways to remove it. Once air gets into a system, its not easy to ensure that it all gets out. And, would such a system guarantee that water is indeed positively removed or has some remained to form freeze plugs at critical moments. Probably not, without some sight glasses.

If drainage isn't possible, I'd much rather have some means to recirculate and guarantee that problem areas remain above freezing temperatures. I think recirculation could be the overall best choice.

**********************
"Pumping systems account for nearly 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/

 

[dicksewerrat]

I think you buy a standby generator to kick on when line power fails. Then the circulation will continue.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[AcesHighJoker]

Ice, I believe you are suggesting using a 3 way valve so you can run liquid through the gas valve? Is that what you are suggesting?
You would likely run into a problem with sealing materials, it would be much safer to run a water valve on one side of the setup and an air valve on the other. If you're not worried about contamination running shop air at 90psi should blast water out of a system like you describe so fast that anyone around will likely jump out of their skin. (Think super soaker at 23psi vs 90psi and unlimited(virtually) volume...