fouling factor in heat exchanger 2

[16613]

Hi every body
I hope to get my response from your knwoledge.
I want to calculate efficeincy of plate heat exchanger five years after startup.
It's clear efficeincy reduce in during time because U(overall heat transfear cofficient)decrease.
decrease of U due to fouling factor(the amount of fouling factor is depend of tempreture,velocity,time work).
but i don't know how determine this factor by actual data in the plant.
Now any body has information about this,please help me.

Thanks.

 

[TBP]

You need 'U' to calculate surface area. If you have all of the other delta-P and delta-T data, and surface area - which should be on the nameplate or in the documentation - then you can just back-out the value of 'U' with some basic algebra.

I try - without anything even approaching complete success - to get plants to install local themometers & pressure gauges on the HX connections during initial installation, and record some base-line info when things are new, and clean. This lets everyone verify that things are working properly and allow for some troubleshooting in the future. The production problems and the amount of time wasted by not having some basic data is often unbelievable.

Sometimes fouling is an issue, but much of the time other factors have come into play. I'm looking at one company's steam to process water HX installations now where things just don't work properly anymore. Why? Because somebody rolled through and sold them on the idea of removing their perfectly good boilers (running at 125 PSIG) and relacing them with low pressure boilers running at 12 PSIG. (The payback on that project, in and of itself is doubtful, but what's done is done.) Unfortunately, what "Moron & Associates Engineering Ltd" didn't do, was look at the impact this greatly reduced steam pressure would have on the plants' distribution piping, temp control valves, steam traps, and last but not least, the HEAT EXCHANGERS. Everything is now WAY too small. There should be criminal offenses on the books - "attempted steam" and/or "conspiracy to commit steam". Punishment should be severe.

 

[abeltio]

16613,
if i understand correctly you want to "predict" the U five years from now.

TEMA gives typical fouling resistances for different fluids... provided that the HE is cleaned once a year... the U should be restored to near clean condition once a year... therefore you can use the values suggested by TEMA and go happy.

cheers.

saludos.
a.

 

[AggieCHEN04]

Moron & Associates Engineering is a good company. I've been at this company for over 20 years and I can guarantee that MA&E had good cause to change out those boilers!

 

[epoisses]

16613 - make a trend of (T in - T out) * flowrate on either side of the HX (there must be at least one side where MA&E has put TI's AND a flow meter, or else you can rent a clamp-on flowmeter) and see how fast it goes down. Check if composition and (if gas) pressure have remained constant, if yes the problem appears to be fouling. ("Appears to be" because you might also have leaking tubes).

 

[16613]

I appreciate of allof you that response to my helping ask.
for calculating fouling factor ,i face to actual data in the plant .if i want to make a trend of( T in - T out) * flowrate on either side of the HX ,i have one problem(flow rate is not constant)and trends of Q and U don't go down therfore i can't calculate how fast it goes down.
what can i do?
too,
(Dear abeltio;i can't find any thing in that adders,why?)


thanks

 

[rmw]

16613,

Some comments you might find interesting on your topic begin on page 32 of the article linked below.

http://www.aiche.org/uploadedFiles/CEP/Issues/2005-12/120531.pdf

rmw

 

[vpl]

16613:

What parameters can you measure? And what information do you have from initial installation?



Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[16613]

we can measure the input and output temperatures and mass of cold and hot stream in plate heat exchanger. (Mass of streams isn’t constant therefore we can’t know the losses of heat based on fouling)

 

[vpl]

16613

It seems you should have enough information to calculate the fouling, if you use an average mass flow (for example, record the flow every minute for a hour or two, then calculate the average.)

There are some good (but expensive) heat exchanger calculation programs where you could enter your data and find the fouling. You can also make a spreadsheet and do it yourself. If you're a member of the Electric Power and Research Institute, they have a book on testing heat exchangers (TR-107397) which contains guidance on how to compute the fouling factor.

If you want to do it yourself, I can lay out the process for you to follow (I'm a bit crunched for time now so would have to do it later). Then it's a matter of taking the data, entering it in, and crunching through the numbers.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[16613]

Thank you very much for attention to solving my problem.
For your information, I draw the average mass flow rate and temperature per day. Then I use from Q=m*Cp*?T and calculating Qc and Qh and we can calculate fouling factor by this formula: (1- Qc/Qh). (Of course I think).

Now if draw graph of (1- Qc/Qh) versus time (step time is one day), we should recognize the time of cleaning (high fouling factor). But there is a problem: this graph (that draw by actual data in the plant) is very unknowable and unpredictable.
(Dear Mr.Patricia Lougheed I like to know your guidance on how to compute the fouling factor)