8 replies to this topic

[el pivas]

Hi everyone;

can someone please tell me how to calculate efficiency and fouling in heat exchanger (including air coolers ). I was doing a temperature survey across some exchanger, I have the inlet and outlet temperatures for both cooling and process side. I also have the exchangers designed data and will like to calculate the fouling and effciciency.

thanks very much in advance

[Root]

Hi,

Fouling factor is calculated during heat exchanger design face and added as required heat-transfer margin.

cheers
Toor

[djack77494]

Fouling factors are empirical factors developed to allow for successful design and operation of heat transfer equipment. They are not absolute immovable values but instead represent an adjustable parameter that will permit acceptable heat transfer to occur over a reasonable period of time. They are determined based on experience.

If you are operating an exchanger that, let's say, heats a heavy hydrocarbon stream using a hot light hydrocarbon stream, several things are known about the rate of heat transfer. Initially, you have a clean exchanger and heat transfer will be great. But performance will soon start to decrease. It will drop quickly at first, but will then slow down. It will continue to drop over time. Generally the operations should be designed so that the performance will be acceptable for some period of time. After that, the plan is to take the exchanger off line and clean it, thus restoring it to nearly its original condition. Simplistically, the fouling factor is the adjustment that allows you to calculate what the heat exchange will be just before the exchanger is cleaned. If the designer uses too small a ff, then frequent cleanings will be required to maintain acceptable performance. Operations will not be happy with that. If the ff is set too large, more expense will be incurred in buying a larger than required exchanger. Other problems may also ensue. The project people will not be happy. I believe that our knowledge to accurately predict fouling over time is rudimentary (nearly non-existant). The phenomenum is extremely non-linear. A thin layer of deposit may greatly inhibit heat transfer while a much thicker deposit will have only a slight effect. My advise is to refer to published tables to get your ff.

[Root]

Djack,

I attended HTRI training course for Heat exchanger design and trouble shooting, as per trainer, for gas processing units no need to put FF but for Hydrocarbon and petrochmicals FF is depend on nature of process.

I have experience for Heat Exchanger efficiency is coming down very slowly also and then maintain for many year (4 years).

Could you bit explain why happen like this.
Thanks
Toor

[djack77494]

I have experience for Heat Exchanger efficiency is coming down very slowly also and then maintain for many year (4 years).

Let me initially state that I am certainly NOT a expert in heat transfer. There are many types of fouling and many mechanisms for explaining it and its impact on heat transfer. Perhaps the common is fouling of services involving hydrocarbon fluids. Here a thin layer of deposit may slowly form on the surfaces of your heat exchange equipment. Deposition is dependent on many factors, but for a given service I'd guess that temperature is often the most important variable. A very thin deposit acts to significantly inhibit heat transfer while a much thicker deposit will have only slowly worsen this effect. Thus a newly cleaned heat exchanger typically quickly drops in performance before reaching the point where performance declines almost level off.

[Art Montemayor]

In my humble opinion, the best and most practical discussion on the subject of fouling in heat exchangers was carried out by Charlie Gilmour during his tenure as chief engineer for Union Carbide. One of his outstanding papers on the subject is considered by me to be so important that I couldn't bear to see it crumbling away in my paper engineering files, and so I took a couple of days and typed out the entire paper into a Word document.

I am attaching a copy of this work so that all engineers reading this post can learn and admire the ingenuity of engineering masters such as Charlie. Charlie is no longer with us, but I am sure he would have loved to share his knowledge with all of you. Enjoy and learn how really unimportant it is to use a fouling factor. Simply learn how to really design a heat exchanger, and you won't need a fouling factor in most cases.

[Art Montemayor]

All:

Please excuse my omission of this attachment from the previous post.

The file is so large that it took longer than usual and the time ran out before it was attached.

I hope all students reading this thread take the time and effort needed to thoroughly read and study this classic explanation on how to deal with heat exchangers prone to fouling. You will never regret the effort and it will be a success story for you when you get the opportunity to apply everything that Charlie Gilmour writes and recommends.

Attached Files

•  No Fooling - No Fouling by Charlie Gilmour(The Article).zip   2.92MB   207 downloads

[Root]

Hi, Art

Thanks for posting a good article on fouling.

Toor

[S.AHMAD]

Hi,

Attached please find note on heat exchanger fouling monitoring method that I have prepared sometime ago.

Hope that note helps.

Attached Files

•  HEAT EXCHANGER FOULING.pdf   128.6KB   134 downloads