Method for Steam pressurization accident calculation

[lharsch]

I would like some advice on methods to use to calculate steam pressurization accident scenario. The end result is to size a pressure relief device for safety. I am pressure casting metal using water cooled induction coils

System:
Vacuum Chamber - 8.3ft^3
Heat Source - Crucible at 1000 C, diam=4inches
Induction Heating Coils ~ 0.75 inch away from crucible, water cooled at 2-5 gpm, 0.5in diameter copper tubing

I believe that the likely accident scenario is a pinhole in the copper line spraying on the hot crucible.

I have done some research and have found information on Liedenfrost Temperature methods may be applicable.

 

[TangoCleveland]

You want to be conservative when sizing relief devices. Use your entire 5 gpm water converting to steam at whatever pressure you have in the copper coil. A manufacturer should be able to size a valve to relive that quantity of steam. 5 gpm x 8.33 lb/gal x 60 min/hr = 2499 lb steam per hour. You'll also need to know what the maximum allowable working pressure (MAWP)of your vacuum chamber is, if that's where the steam is generated. The MAWP will give you the required relieving pressure.

Larry

 

[chicopee]

I do not believe that the cooling coil made of copper should be generating steam. Copper tubing is not design for steam but can be designed to carry hot water.
Your pressure relief valve ( for hot water) should be sized for releiving capacity normally expressed in btu/hr and set pressure expressed in psig. No temperature setting is required since your are not protecting a hot water storage tank? So heat input to the cooling coil and a safe design pressure of the tubing have to be determined. You may also need a flow switch in the cooling coil to shut down the heat source in the event the coolant flow is interrupted.

 

[lharsch]

The copper coil does not contain steam. the coil contains water used to remove excess heat from the copper coil during the induction heating process. The copper is used to carry the RF power that is used for induction heating of my metal inside the crucible. The accident scenario is if there is an unexpected leak in the coil, causing the <100C water to potentially spray out onto the hot (1000C)crucible, thereby generating steam, that could then overpressurize the vacuum chamber. The pressure relief device is for the overpressurization of the vacuum chamber.
The chamber itself is designed to a MAWP based on the process of pressure casting with the appropiate safety factors. The copper cooling line is also designed based on the internal line pressure and flow, and there are interlocks in place to stop power if there is no water flow.
We are still in the design phase, so none of this is built yet, but I am analyzing accidents so that the system is bounded and safe.

 

[TangoCleveland]

There are extensive guidelines in API RP 520 Parts 1 and 2 for determining relief valve sizing scenarios. Steam generation from hot process fluids is one that we use all the time. You can order copies at

http://apistandardsonline.api.org

Larry

 

[lharsch]

Thanks Tango,
I will look those standards up.