17 replies to this topic

[shahidulislam48]

Hi,

 

I have a system that contain Ethylene Oxide. The system is shown in the following drawing.

 

A PSV is attached at the outlet of the ON/OFF valve whose set pressure is 3.5 Barg. It has been recommended that the PSV has to be sized on Fire Case basis. As in the case of Fire case vapor will form after some few moments of liquid relief. But there is no significance of giving vapor in return line which contains liquid fluid. So it can be assumed that PSV will release liquid in return line. 

 

And the required flow is calculated by considering volume of vapor generated by the fire according to section 5.15.3.3, API STD 521.

But I have been facing dilemma whether to select liquid sizing equation or vapor or gas sizing equation for calculating area?

 

Any suggestion is highly appreciated.

 

 Drawing1.pdf   86.02KB   54 downloads

[fallah]

Hi,

 

At first, appears there is a safety issue; if the PSV is to be installed for tank protection there should be no obstacle such as not CSO/LO valve and on/off valve between the tank and PSV...

[Saml]

It is not clear what are you trying to protect.

It is protecting the line  for the simultaneous event of automatic valve closing and fire?

[navneet2109]

Check out the drawing, I've commented on that. May be it help.

But the detail given by you was not sufficient.

 

With regards

Navneet

Attached Files

•  Drawing1.pdf   141.55KB   32 downloads

[Fletch]

The discussion in API is more related to multi-component mixtures or ones that result in vapour generation when heated to the reliving conditions.

In these instances one needs to ensure that the orifice allows the liquid being pushed out by generated/expanding vapour.

In these scenarios, both methods should be used check which case is governing (especially if its a plug of liquid being displaced) or use a two phase method.

 

If you can take your fluid to relieving conditions and show that there is no vapour being generated i.e. liquid release, then you don't need to consider vapour aspects.

 

I think your sketch has clouded the question, but as the others have highlighted it doesn't look right.

I don't think its protecting the tank as the PSV is discharging back on itself... so its protecting something "upstream" at p-4?

Fire case always consider blocked in case, so closure of automatic valve is valid (and makes mild sense if the outlet of the PSV is routed around the valve.

Again like Fallah mentioned, ensure valves in relieving path (in and out) don't restrict the release (e.g. valve back to tank).

This looks like more like a thermal release case as it is shown.

[shahidulislam48]

Hi,

 

Thanks everyone for yours valuable feedback.

 

I would like to clearly describe the situation with the new uploaded drawing.

 

Liquid that have been trapped between ON/OFF valve and V-2 valve, have to be relieved due to overpressure scenario (Basis: Fire Case ...Recommended). There is another PSV for the overpressure protection of tank. Hence this mentioned PSV is to protect from overpressure region between ON/OFF valve and V-2 valve. It is important to mention that  V-1 valve will remain opened.

 

From the suggestion of Fletch, I would like to mention that at relieving condition fluid state remains in liquid phase as the relieving temperature is below the saturation temperature.

 

I would also like to point out an example to understand this scenario as we use PRV in cooling water return line to be compared with this one.

 Drawing1.pdf   91.62KB   35 downloads

 

Many Thanks.

Shahidul

Edited by shahidulislam48, 01 February 2017 - 10:07 AM.

[navneet2109]

Hi,

 

Thanks everyone for yours valuable feedback.

 

I would like to clearly describe the situation with the new uploaded drawing.

 

Liquid that have been trapped between ON/OFF valve and V-2 valve, have to be relieved due to overpressure scenario (Basis: Fire Case ...Recommended). There is another PSV for the overpressure protection of tank. Hence this mentioned PSV is to protect from overpressure region between ON/OFF valve and V-2 valve. It is important to mention that  V-2 valve will remain opened.

 

From the suggestion of Fletch, I would like to mention that at relieving condition fluid state remains in liquid phase as the relieving temperature is below the saturation temperature.

 

I would also like to point out an example to understand this scenario as we use PRV in cooling water return line to be compared with this one.

Drawing1.pdf

 

Many Thanks.

Shahidul

You uploaded the same drawing without any detail.

at least tell us working press/temperature of tank.

from my side answer is same which I've already given.

Your PSV size would 3/4" / 1" (This is based on Liquid expanding due to temperature increase but no phase change)

[shahidulislam48]

 

Hi,

 

Thanks everyone for yours valuable feedback.

 

I would like to clearly describe the situation with the new uploaded drawing.

 

Liquid that have been trapped between ON/OFF valve and V-2 valve, have to be relieved due to overpressure scenario (Basis: Fire Case ...Recommended). There is another PSV for the overpressure protection of tank. Hence this mentioned PSV is to protect from overpressure region between ON/OFF valve and V-2 valve. It is important to mention that  V-2 valve will remain opened.

 

From the suggestion of Fletch, I would like to mention that at relieving condition fluid state remains in liquid phase as the relieving temperature is below the saturation temperature.

 

I would also like to point out an example to understand this scenario as we use PRV in cooling water return line to be compared with this one.

Drawing1.pdf

 

Many Thanks.

Shahidul

You uploaded the same drawing without any detail.

at least tell us working press/temperature of tank.

from my side answer is same which I've already given.

Your PSV size would 3/4" / 1" (This is based on Liquid expanding due to temperature increase but no phase change)

 

Hi,

 

The tank pressure is 2.3 barg and temperature is -5 degC.

 

Although the PSV has nothing to do with the tank. It has to protect the mentioned pipe portion from overpressure.

 

If PSV size is 3/4" / 1" then what could be the orifice size as I didn't manage to get any orifice designation that matches with the mentioned size.

 

Thanks.

Edited by shahidulislam48, 01 February 2017 - 06:31 AM.

[flarenuf]

greetings
I am totally confused here

you say the PSV is to protect the line between on/off valve and V2 in case of fire.

you also say  " ..V2 valve will remain opened"

 

so the portion of line between on/off valve and V2 isn't blocked in

 

do enlighten us please

thanks

[shahidulislam48]

Sorry my mistake V-1 valve will remain opened and valve V-2 will remain closed.

[mirandomka]

3/4"X1" will be typically screw type.
That's why it's not in API 526 (standard for flanged type PSV).

[shahidulislam48]

Thanks mirandomka for your information.

[navneet2109]

May be this helps

Attached Files

•  Untitled1_001.jpg   334.67KB   1 downloads

[navneet2109]

 

Hi,

 

The tank pressure is 2.3 barg and temperature is -5 degC.

 

Although the PSV has nothing to do with the tank. It has to protect the mentioned pipe portion from overpressure.

 

If PSV size is 3/4" / 1" then what could be the orifice size as I didn't manage to get any orifice designation that matches with the mentioned size.

 

Thanks.

 

 

 At this press and temperature the ethylene oxide will not become in vapor form. 

i am assuming your line is cold insulated. am i right??

[shahidulislam48]

 

 

Hi,

 

The tank pressure is 2.3 barg and temperature is -5 degC.

 

Although the PSV has nothing to do with the tank. It has to protect the mentioned pipe portion from overpressure.

 

If PSV size is 3/4" / 1" then what could be the orifice size as I didn't manage to get any orifice designation that matches with the mentioned size.

 

Thanks.

 

 

 At this press and temperature the ethylene oxide will not become in vapor form. 

i am assuming your line is cold insulated. am i right??

 

Yes. you are.

 

I have checked your last post with the attached pics. I had also thought about that.

But the problem is my sizing basis is Fire Case. I have calculated the required capacity as it is done on the case of fire case and used that flow to calculate area for liquid relief. Is it valid or allowable?

You might have a look on the attached file.

 APIfgg.jpg   315.91KB   3 downloads

Edited by shahidulislam48, 02 February 2017 - 03:55 AM.

[navneet2109]

 

 

 

Hi,

 

The tank pressure is 2.3 barg and temperature is -5 degC.

 

Although the PSV has nothing to do with the tank. It has to protect the mentioned pipe portion from overpressure.

 

If PSV size is 3/4" / 1" then what could be the orifice size as I didn't manage to get any orifice designation that matches with the mentioned size.

 

Thanks.

 

 

 At this press and temperature the ethylene oxide will not become in vapor form. 

i am assuming your line is cold insulated. am i right??

 

Yes. you are.

 

I have checked your last post with the attached pics. I had also thought about that.

But the problem is my sizing basis is Fire Case. I have calculated the required capacity as it is done on the case of fire case and used that flow to calculate area for liquid relief. Is it valid or allowable?

You might have a look on the attached file.

APIfgg.jpg

 

In my point of view its not necessary to design fire case psv at pipe. Normal TRV will work.

 

Refer this link it might help.

http://www.cheresour...re-case-piping/

[shahidulislam48]

Thanks for your concern.

[shahidulislam48]

Hi,

 

Is there any equation that I could use to calculate required capacity that will flow through 3/4"x1" TRV?

 

Thanks.