12 replies to this topic

[Amin Va]

Hi folks,

 

I have faced the attached schematic in one of the projects.  There is PSV located on the test separator inlet line. This PSV relieves a two phase HC flow to the Pop Tank and there is a liquid seal with the surface located above the inlet line nozzle to the Pop Tank. We use the same inlet line connection to pump the liquid to the recycle pumps, to truck out the liquid or to receive liquids accumulated in Flare Knock-out Drum by a pump. My question is what is the purpose of this liquid seal and can we remove this seal if it is unnecessary?

 

Thanks in advance,

Best

Attached Files

•  photo-4.JPG   82.85KB   6 downloads

[Bobby Strain]

If your sketch is correct, there is a disaster waiting to happen. Maybe you should check your sketch.

 

Bobby

[fallah]

Amin,

 

Please specify if the tank equipped with a free vent. As per the sketch appears it has, but it should be confirmed...

[Art Montemayor]

I think Bobby Strain has a very valid and important point.   I still have a big problem trying to understand and read your "sketch" - even when I "zoom" it up to maximum.  Why don't you take the required time and draw a reasonable and readable sketch so we can all be sure of what you have.  Show all pumps involved with the flow rates.

 

What is a "POP tank"?

[Amin Va]

I don't know how to attach another picture. There is no "attach" button anymore. It is appreciated if  someone help me.

Edited by Amin Va, 17 August 2014 - 06:04 PM.

[fallah]

Amin,

 

Click on the "More Reply Options" botton in adajacent of the "Post" botton and you will see a window below which you can find a botton for action to attach the file(s)...

[Art Montemayor]

Amin:

I sent you the following detailed instructions last week through my message service - where you requested it.  Have you read it yet?   Are you still having problems?   You haven't replied, so I don't know. 

1. I assume you want to start a new thread.  On the Forum Page, click on the black button that is titled “Start New Topic”;
2.  You will get a full editor window where you write your post;
3.  At the bottom of the Editor window, you will see the instructions “Attach Files” with a button directly below it that is titled “Choose Files….”.  Click on this button and you will gain access to your drives where you have your file stored.
4.  Select your file from your drive and click the “Open” button to load it onto your post.  At this point the file is uploaded, but it is not attached to your post yet.  You can see it at the bottom of the Editor window.  To the right-hand side you can see the commands: Add to Post | Delete.
5.  Click on the button that says “Add to Post” after the file is uploaded and it will then be attached to your post at the point where you left the cursor pointed.   I always leave my cursor pointed two spaces below the body of my post.
6.  Once your attachment is attached to your post, click on the black button at the bottom titled “Post New Topic”.

Art Montemayor

[Amin Va]

Thanks very much Fallah for your guidance.

Thanks a lot Art. I actually read your message and replied however I am not sure why you didn't receive it. Anyways, now I learnt how to do it.

 

I attached a higher quality picture of the sketch.

 

Fallah: As you mentioned there is a 6" vent on the Pop Tank. I performed a calculation and confirmed the vent size for the worst case relief scenario. 

 

Art:  In Canada, it is common to tie the PSVs into a tank which is open to atmosphere and is called Pop Tank (or sometimes Relief Tank). I have seen this arrangement in some of the projects that I have worked on. In this case, PSV on the inlet line to the test separator is connected to Pop Tank because it contains both liquid and gas. Since the liquid flow rate is quite high we need a very big Flare Knock out Drum. However, by connecting this PSV to Pop Tank we can save costs by having a smaller FKOD. 

 

 

Let me clarify my question. In the sketch as you see there used to be a connection from the Pop Tank to 

a recycle pump which used to recycle the Pop Tank liquids back to the process. Now this line is demolished. My guess is that the liquid seal was related to an issue with this connection. In the even of PSV release from the test separator, a two phase flow will be generated and will fill the connection line to the Pop Tank. In the absence of liquid seal, the gas portion of this two phase flow might travel to the recycle pump suction (considering that  PSV and Recycle Pump share the same nozzle connection) and get trapped there.  However in the presence of liquid seal, if the seal liquid level is higher than pump suction, it will prevent the gas from being trapped in pump suction line.  Since the recycle pump line is demolished now I think we can remove the liquid seal.

 

I just would like to know whether anyone has faced a similar arrangement before and whether there is any justifiable reason for the presence of liquid seal in the Pop Tank?

 

Thanks,

 

Amin 

Attached Files

•  0282_001-2.pdf   66.55KB   41 downloads

Edited by Amin Va, 22 August 2014 - 02:44 AM.

[fallah]

Amin,

 

You fail to specify if the vent on the pop tank is free vent...

 

Anyway, i think if there is simultaneous PSV relief and recycle pump operation, the gas portion of PSV relief can travel to recycle pump suction line either the liquid seal is existed inside the tank or not. Of course, if there isn't such simultaneous operations the liquid seal is necessary to provide needed liquid level on recycle pump suction...

 

Now if the recycle line is demolished, appears the liquid seal for providing liquid level on pump suction is meaningless but it might be necessary to keep the liquid level from being subject to atmosphere through the ove flow line if the vent on top of the tank isn't a free vent...

 

One more question: If the recycle line is demolished how the liquid inside the tank be extracted from now on?     

Edited by fallah, 22 August 2014 - 05:23 AM.

[Amin Va]

Hi Fallah,

 

As you mentioned, it is a free vent to atmosphere and now they are going to truck out the liquid from the Pop tank. The truck out connection is shown on the sketch.

 

 

Best,

 

Amin

[fallah]

Amin,

 

Ok, then it could be said that the liquid seal doesn't relate to over flow line and it only relates to keep a liquid static head on the pump suction line. Therefore, now the recycle line is demolished but appears the liquid seal should still be kept if truck out the liquid is going to be done by pump...

Edited by fallah, 23 August 2014 - 01:44 AM.

[Amin Va]

Thank you very much Mr. Fallah.

[explosion]

Just a comment for the use of liquid seal. As per ISO 16852 a liquid seal is also defined as:

Liquid product detonation flame arrester - flame arrester in which the liquid product is used to form a liquid seal as a flame arrester medium, in order to prevent transmission of a detonation.

Note: there are two types of liquid product detonation flame arrester for use in liquid product lines: liquid seals and foot valves

• liquid seal flame arrester - flame arrester designed to use the liquid product to form a barrier to flame transmission
• foot valve flame arrester - flame arrester designed to use the liquid product combined with a non return valve to form a barrier to flame transmission

So maybe the intention here was related to flame transmission also ?

Regards,

explosion