11 replies to this topic

[canhhienfamily]

Dear all

In my plant, some air fan coolers  (AFCs) or water coolers are isolated by valves. For example, AFCs on the overhead line of the main column of CDU unit, each AFC is isolated by inlet and outlet valves. 

However, AFCs and water coolers on the overhead of main column of FCC unit have no isolation valve. If any failure (tube leak, broken,..), the unit must be shutdown.

Some reasons to explain for the design of FCC without isolation valves for exchangers as mentioned above are: pressure drop issue, potential leak at flanges of valves,...

Please be noticed that AFCs and coolers in series,  there are 8 banches of cooler in parallel. Historical operation showed that the external tubes of coolers are severely corroded due to deposite, many tubes need to be replaced.

Some opinions request to install insolation valves at each cooler, then we can isolate for maintenance if required.

Other opinions do not agree because of pressure drop or potential leak issues.

My question is: Is there any philosophy of isolation for coolers as my case? With isolation valves or not based on what?

Thanks and best regards

[ecas]

 The installation of butterfly isolation valves in the water coolers is very common. The pressure drop of the butterfly valves 100% open, is practically 0.

[canhhienfamily]

My concern is for hydrocarbon side, not water side.

[shvet1]

...

My question is: Is there any philosophy of isolation for coolers as my case? With isolation valves or not based on what?

...

Talking of a fractionation column it is a normal practice do not provide isolation valves for reboiler(s) and condenser(s). The purpose is fractionator, reboiler(s), condenser(s) and reflux drum will be a on common pressure system with no valves betwwen them. Valve(s) between a pressure safety valve and a vessel it protects is not allowed by pressure vessels codes. If one will provide isolation valves for fractionator's condenser/reboiler a separate pressure safety valve will be required for reboiler or reflux drum respectively. 

Situation you described is common in process industry. I have been involved many times in discussions like "isolation vs pressure relief" for air coolers and heat exchangers because each option has pros and cons. Sometimes "isolation" benefits wins (mostly "car seal opened" or "locked open" with means against falling down of internals), sometimes "pressure relief" benefits wins.

Imagine a situation when an air coller has individual valves for isolation of each bundle. Each bundle is a presssure vessel which has to be protected by a pressure relief. Each bundle has to have a separate pressure safety valve for pressure relief in case of external pool fire (like many or other proosible cases). Or this air cooler can be protected by a pressure relief valve (rather big with huge capacity) on fractionator overhead or reboiler.

Edited by shvet1, 12 March 2020 - 12:30 AM.

[Sharma Varun]

As such a sketch of the system always helps. 

• If the column and downstream system is designed for turndown say the exchangers are designed for 60:60 or 50:50 than you may have isolation across parallel exchangers or air cooler tube bundles. It is common to provide isolation valves for parallel condensers or if the exchanger can be taken out for maintenance in a running plant. 

• Safety wise if there is a common relief valve case for the overhead system, you can not provide isolation valves. LO arrangement might not be acceptable as per your policy.

[Sharma Varun]

One more reason why isolation valves were avoided is usually overhead line sizes are huge and thus call for very heavy isolation valve placement.

[breizh]

Hi,

To me if you have to shut down the unit for maintenance  no need to install isolation valves . For safety purpose you need  to install blind plates .

 

Can you share a drawing or PID for a better answer ?

 

Breizh

[Sharma Varun]

Hi,

To me if you have to shut down the unit for maintenance  no need to install isolation valves . For safety purpose you need  to install blind plates .

 

 

Breizh he is looking for maintenance of these exchangers in a running plant, i.e. without taking shutdown

[breizh]

Hi Sharma Varun ,

I do understand  and request a PID to assess . To me isolation is key and valves are not sufficient !

Breizh 

[canhhienfamily]

  I has found two configurations as follows:

1. Air fan cooler on the overhead line of crude distillation column (12 banks) with isolation valves at the inlet and outlet of each. During PSV study they considered column , overhead line AFC and accumulalator is an open communication.

2. Water coolers following AFCs on the overhead line of FCC unit without isolation valve.

[shvet1]

  I has found two configurations as follows:

1. Air fan cooler on the overhead line of crude distillation column (12 banks) with isolation valves at the inlet and outlet of each. During PSV study they considered column , overhead line AFC and accumulalator is an open communication.

2. Water coolers following AFCs on the overhead line of FCC unit without isolation valve.

Different designers/licensors = different practices

What is your question? 

Edited by shvet1, 17 March 2020 - 11:45 PM.

[canhhienfamily]

I just want to share what I found. As Shvet1 mentioned, I understand that even different practices but both of them are acceptable.