Flash Tank

E.D.

Upon inspection of a job site, I would like to know what size relief valve should be appropriate on a high pressure 6" std. ASME flash tank. Here are the criteria:

The existing relief valve seemed to be small and is only capable of reliefing 150 lbs/hr steam with a 1/2" relief vent line that is connected to the main 2" vent line. Incoming to the Flash tank are 2 high pressure steam traps( 3/4" F&T, at 150 psi)and 2 low prssure steam traps( 3/4"F&T, 10-15 Psi. A 2" line on the top and or out of flash tank is connected to the low pressure steam supply (10-15 Psi).

Also, just curious to know if it is ok to connect the low pressure traps and high pressure traps to the same flash tank?

Eric

Something is very wrong

Based on your describtion

1. Stop and isolate imediately.

2. One of your high pressure traps must be failed.

3. If your low pressure traps into flash tank are modulated they will not work. Because they will be less than your low pressure steam vent connection 15 psig.
Your flash tank is always at your low pressure steam pressure, If vent is truely connected to LPS. Only gravity will allow flow from low pressure traps. At 150 you will start to backpressure your low pressrue traps and your lowpressure steam header.

4. What is your vessel rated to? What is your relief valve setting? 150?

Eric

wait

I thought your tank was operating at 150 psig currently, missread.

If you are just evaluating PSV then you need to do calculations based on failed open orifice sizes on F&T traps.

I would not connect Low pressure traps to this vessel to the fact that condensate will back up if you have a high pressure trap failure.