Hi everyone,

I have been dabbling with the utilization of area margin Vs fouling resistance on shell and tube heat exchangers for some time now. I haven't seen any trend acrosss industry although some of customers are asking to use area margins instead of fouling resistance. Having said that, most customers continue to prescribe fouling resistance and i am in habit of using the same owing to concerns of over specification with area margin.

In applications where we have good experience (like amine reboilers or lean rich amine exchangers, in my case), we know what should be % area margin if we were to stop using fouling resistance. 

So, repeating my question, is it better to use fouling factor or area margin? I can appreciate its not a simple answer, but hopefully you guys can throw light on nuances of it. 

Ps: I did see HTRI is prescribing use of area margin.

http://dc.engconfint...atexchanger2005

It's accepted practice to use both. Fouling factors should be based on experience. Margins are used in addition to assure performance. Engineering companies typically use margins based on service. Owners can do whatever they wish, as long as they assume responsibility. I've worked for both. This practice makes the design transparent. Sometimes an allowance will be made for a higher flow, i.e. X 1.1.

Bobby

Edited by Bobby Strain, 18 April 2019 - 04:58 PM.

Hi,

I have used them all

1) Fouling factor

2) Flow margin (generally 10%)

3) Excess surface area (generally 10% for normal heat ex and 20% for reboilers)

Having said that, this was mentioned in the Equipment Design Criteria of the project.

Discuss with you Client/Principal Engineer. I guess, they will help you more in reaching a conclusion than the people in this forum

Edited by Chemitofreak, 19 April 2019 - 05:55 AM.

https://www.eng-tips....cfm?qid=288801

hi ,

You may consider the link above . Different people different opinion .

Good luck 

Breizh 

Thank you all for responding to my question. Since the short answer from you all is anything is okay as long as the user knows what they are doing. I agree on that in general. 

But I was hoping to get  to bottom of why would someone use fouling factors if a % surface area is adequate? isn't that easy? 

At risk of being repetitive, i will re-phrase :  I believe only end user will have enough data and knowledge about their fluids to specify a fouling factors. Anyone else (EPC or exchanger vendor), using fouling factors from TEMA or GPSA would use a "standard" value.  

PS: My question is not specific to a particular project, therefore a general one. Although i do not expect specific answer to general question, any insights on how you tend to approach the problem will be useful. 

You want to adhere to accepted practices.

Bobby

I've had my problems with applying fouling factors and heat transfer area over-design in my design years.  Read the attached documents and they may be of some help.

 No Fooling - No Fouling by Charlie Gilmour(The Article).docx   2.93MB   856 downloads

 No Fooling - No Fouling by Charlie Gilmour(Eng-Tips Thread).doc   63.5KB   735 downloads

The fouling factors specified in TEMA or GPSA are based on experience and these are not just some values. These are tried and tested values hence used across the globe.

There is no problem in using excess surface area without fouling factor, but there might be a risk, the question is who wants to take risk in a million dollar or billion dollar project.

Every one goes for a conservative design unless he/she has hands on experience of the said system