4 replies to this topic

[ddftr]

Dear Sirs,

 

Here I have some doubt regarding the design of loop seal of an atmospheric flash tank. This flash tank is an intermittent boiler blow down tank which is generally collect all drains from boiler ( saturated liquid) and  then flashed in this drum and vented out from top of this drum. The overflow and drain is normally taken to the hot effluent drainage system.there is one drip pump attached with the tank to recovered the condensate for further use.

 

Now for one of our latest project I have found that the flash tank overflow line is attached with a loop seal (shown in p&ID) while checking the design of it I'm little confused regarding the height of the loop seal.

Here I'm attaching the snap shot of the P&ID and my understandings for your comments and kind review.

 

My question is how to decide the height of the loop seal? Is there any guideline or standard regarding this?

 

 

Please help me here to clear my confusions.

 

Attached Files

•  Drain Tank.jpg   100.44KB   13 downloads

[ddftr]

Hi all,

I have prepared an excel for sizing the above seal. But I'm having trouble to understand the use of lower part of this seal. From my point of view this part is for vacuum pressure inside the tank. Please provide your views and comments on this subject. Please help me to understand the sizing calculation of the "U" seal clearly.

 

With Best Regards,

 

Attached Files

•  DESIGN OF LOOP SEAL FOR FLASH TANK.xls   438KB   63 downloads

[Saml]

It is almost impossible to read into the P&ID you posted and understand what it is other than a educated guess. The resolution is low.

[ddftr]

Here is a PDF of the P&ID.

Attached Files

•  a_001.pdf   561.66KB   70 downloads

[prengr]

Hello.

 

As i know, the seal loop is generally applied to below two cases.

1. to keep liquid level

2. to block between two different system

 

In this case, above no.2 may be applicable.

For example, in any over pressure case of Steam Condensate Flash Drum(SCFD), condensate can go into drainage system if there is no seal loop.

And, we can assume vacuum condition of SCFD. Any fluid from drainage system can go into SCFD if there is no seal loop.

But, because this SCFD is open system, i think above two cases (overpressure and vacuum) might be impossible in SCFD.

Hence, the seal loop is nor required because of above reasons.

 

However, i can guess one thing why the seal loop is required on overflow line.

It is to avoid contamination of steam condensate against any vapor from drainage system.

For this purpose, we need to know the differential pressure between SCFD and drainage system. As i know, normal pressure of drainagne system is normally ATM.

Hence, this seal loop is required to provide just slight pressure (like 2m H2O) due to similar pressure of two system.

 

This is my understanding.

If you have any different opinion, please share it.