4 replies to this topic

[kybele39]

Hello Experts,

 

We are trying to come up with a sizing method for a PSV located on the shell of a water bath heater. Theater has a two process coil in it and one the coil heating medium has a really high pressure.

 

We assume the pin hole diameter is 0.25inches and we calculated the mass flow rate will pass through this hole. The process gas in the coil passing through into glycol water mix. The glycol-water temperature is 250F. And the shell is filled with this solution.

 

My questions are

 

1. What are the phenomena occuring at the pinhole and in the bath? 

 

2. The process gas in the process coil is at the 1900psig pressure and at the 100F temp. The heater shell is pressurized at 40psig at 250F. When the gas starts leaking into bath fluid (glycol/water mix) is the process gas actually cooling? (at the pin hole, the gas temperature shows -77F at the 40psig bath pressure. )

3. If the gas is not cooling enough due to the bath temperature, then when the pressure equals to bath pressure and finally reaches the set pressure, the PSV will open?

4. Should the PSV sizing base on the bath fluid expansion due to pressure increase taking the reliving flow equal to gas mass flow that is calculated from the pin hole? Or should we base on the gas expansion due to the temperature increase from 100F to 260F? 

 

I will appreciate if you input with your expertise.

 

Thanks,
Kybele

 

 

 

[Bobby Strain]

A strange query. Unless the gas tubes are welded pipe as in a double pipe exchanger, ASME code requires that protection must be provided for the shell for a high pressure tube rupture. This means gas rate through 2-tube size holes.

 

Bobby

[kybele39]

Hello Bobby,

 

Thank you. One thing, I have not written above is that the pinhole size already given us by the customer as 0.25inch.

 

My main question is what happens when the gas start going into glycol water mix? Is there a solubility in the mix? How is the PSV will lift?

Is the gas will start changing its volume based on the new pressure and temperature of 40psig and 250F?

 

Thanks,

Kybele

[Bobby Strain]

I wouldn't touch this with a ten foot pole!

 

Bobby

[Bayo Alabi]

Water bath heaters do usually have an Expansion Tank with a Fill Hatch on the shell. This is usually the case. Check if you have this arrangement. If so, you do not need a pressure/vacuum protection in case of tube rupture as the gas is vented to the atmosphere. In addition, if there a contraction if liquid inside the shell, the same Expansion Tank/Fill Hatch will admit atmospheric gas into the shell for vacuum protection.