7 replies to this topic

[mosa]

Dear All,

I have a set of process data and old spare heat exchanger(was for hydrocarbon services).Now i want to utilise the old exchnager for new service and data sheet(water service) .I checked the new duty and new Design Pressure/Temperatureof new process data and found to be less than the old exchanger data sheet details.Now my questions are ,

1. Is it suffcient to check only adequacy of duty and Temperature and pressure details ?
2. If not, what are the other things to be checked ? like pressure drop, U, fouling resistance etc
3.Is it necessary to carry out detail rating of exchnager by an exchnager specialist to ensure the integrity of exchanger is unaffected in all terms.

I appreciate that if anybody can provide me spreadhseet calculation ( MKS units) to carry out new exchnager design and also check adequacy of exisiting exchanger for new process duty.( and ) step by step procedure how to carry out existing exchanger rerating for new process data sheet and what limits we have check like pressure drop, velocity,U, etc etc

Please note i have some basic knowledge of heat transfer theory and calculation,k howver to put in proper perspective i request above help.


Regards
mosa

[Zauberberg]

Hi Mosa,

Posting a spreadsheet is not very likely option: there are many types of heat exchangers available, although I believe you are referring to the most common E-shell type. Excel worksheets and corresponding calculation methods are different for various types of exchangers.

The procedure for performing rating calculations can be found in heat transfer textbooks, "Process Heat Transfer" by D.Q. Kern being my favorite.

The basic concept is to check whether you have sufficient surface area for the new duty/service, based on re-calculated film coefficients. It's very similar to standard design procedure. Then, after finishing the thermal performance check, you should focus on mechanical issues: vibration, impingement protection, expansion joints (in case of fixed tubesheet) etc. Fur such purposes you can use one of the sophisticated softwares available in the market: Hetran/HTFS, HTRI, and others.

Looking at the overall picture, you need to check: surface area requirements, available pressure drop, mechanical issues, and suitability of given material of construction.

Good luck,

[GREGORY]

Hi Mosa,

If you want, i could help you to do that job.

On the basis of all the data you have regarding your exchanger and your process i will run a computation with HTRI software to check the performance of your exchanger under desired operating conditions.

My e-mail: greg_lemeur@hotmail.com

Gregory

[djack77494]

Now my questions are ,
1. Is it suffcient to check only adequacy of duty and Temperature and pressure details ?
2. If not, what are the other things to be checked ? like pressure drop, U, fouling resistance etc
3.Is it necessary to carry out detail rating of exchnager by an exchnager specialist to ensure the integrity of exchanger is unaffected in all terms.

mosa,
Checking the duty and "temperature and pressure details" (not sure what you mean by that) will NOT be adequate. It sounds as if your new service is unrelated to the old service. It's a completely new design. The new duty, temperatures, pressures, and flowrates will bear no relationship to the old.

In question 2 you are getting closer to the required approach. If you can do a new process design, then you should be able to develop the needed duty, the temperatures, pressures, pressure drops, and flowrates. From this, you (or preferably a heat exchanger specialist) can recommend (or evaluate) and exchanger configuration, estimate fouling factors, and calculate U and required surface area. This should give you a pretty good idea of whether or not you can use the existing exchanger(s). By all means, have your work checked/confirmed by a specialist.

[mosa]

Dear Jack

I have attached the detils of old&unused exchnager and new process data to get better idea about my reuirement.

Earlier the exchanger was in hydrocarbon srevice and now it is intended to use for water/water exchanger.I have checked the newduty,new design temperature and pressure and found to be less than data sheet details.To proceed further, what are the other things to be checked and what factors we should keep altering to achieve say recommended velocity in shell and tube, delta P etc etc.

If anybody could help me to indicate in steps or spreadhseet (MKS units) atleast in terms od U,Velocity,delta P,fouling resistances etc it works good.Then we can think about vibration,baffle etc etc.

My email address momsalih01@yahoo.co.in
Regards
mosa

Attached Files

•  exchnager_details.xls   25KB   1039 downloads

[Art Montemayor]

mosa:

You have, based on what you have described, a very benign service proposed for a rather over-rated heat exchanger unit. Yet you are soliciting help – and it has to be in MKS units.

As has been pointed out, all you have to do is follow an example rating given by D.Q. Kern in his book, "Process Heat Transfer", and you have your answer(s). If you have "some basic knowledge of heat transfer theory and calculation, k", then this should be a piece of cake for you and you could develop your own spreadsheet application.

If you have any problems, if will probably be in the physical condition of the unit. It might have sustained some corrosion and might need to be de-rated for service. All it has to withstand is 75 psig.

I would put the pressurize blowdown water in the tubeside and since the flow rate is so relatively small, you might have to make various tube passes – maybe 4 or 6. You may also have to plug off some tubes to increase the velocity. You should come out with a "U" of approximately 100 to 125 Btu/hr-ft2-oF.

You haven't told us your scope of work. If your intention is to exchange as much heat as possible, then you shouldn't have any trouble with this over-sized exchanger.

[mosa]

Dear ART,

Thank you for your kind advice and i proceeded hand calculation to get the grip of understanding.However, still i need some help to close out my understanding.
Earlier i had posted my exchanger details and worked out results are following

1. New Duty is 0.2mmkcal/hr which is much less than data sheet duty.Hence as a prliminary step, i can proceed for further calculation

IS MY APPROACH CORRECT ?

2. I had put high pressure fluid in tube side and low pressure in shell side.

IS IT OK ?

2. The calculated(new) overall (S&T)dirt factor is 0.064 m2hrC/Kcal but the old exchanger data sheet dirt factor IS 0.0012m2hrC/Kcal .

NOW WHAT SHOULD I CONCLUDE AND WHAT ADJUSTMENT I HAVE TO MAKE TO REDUCE THE CALCULATED VALUE OR SHOULD I LEAVE LIKE THIS ?

3. Calculated Delta P shell side - 0.23 psig

Shell side is very low as normally it should be 5 to 10 psig.So what should i do now to increase the velocity in sHELL SIDE ? OR should i leave like this

4. Calculated Delta P tube side - 10.22 psig

Tube side seem to be acceptable- Any comment ?

5. Calculated overall U is 75 Btu/hrft2F which is less than recommended one

The recommneded is 150 to 200 Btu/hrft2F.
AM I CORRECT ?NOW WHAT SHOULD I DO? SHOULD I LEAVE LIKE THIS OR I HAVE TO adjust some parameter to MEET THE RECOMMENDED U value ?

6. Calculated Tube side(High pressure fluid) velocity is - 0.2 m/s for 196 U tubes with 3/4"OD &2 PASS

The velocity is very much less than the recommeded one 1.5 to 3 m/s

TO get the recommended velocity i have to plug 140 tubes.
Now if i have to run my exchanger with only 50 tubes, WHAI IS THE NEXT STEP I SHOULD DO?

IS MY UNDERSTANDING AND APPROACH IS CORRECT?

i THINK I HAVE PUT MY UNDESTANDING AND APPROACH AS AS FAR REASONABLY OK AND I THINK OTHERS HAVE ALSO UNDESTOOD WHAT IS MY INTENTION.

PL IF ANYONE WOULD PROVIDE ME STEP BY STEP PROCEDURE ( ALTHOUGH KERN HAD ADDRESSED EXTENSIVELY BUT STILL TO TUNE TO MY UNDERSTANDING THIS FORUM HELPS A LOT) OR SPREADSHEET IN MKS UNITS IT WILL BE LOT MORE HELPFUL.

ART, I ONCE AGAIN APPRECIATE FOR YOUR ADVICE AND HOPE TO CONTINUE THE SAME.IF YOU COULD HELP ME FURTHER YOU CAN SEND ME ANY GUIDELINES TO ME EMAIL ADDRESS momsalih01@yahoo.co.in

Regard
mosa

[Art Montemayor]

Mosa:

The following is what you posted today in this same Forum, in another post. PLEASE STOP MAKING DUPLICATE POSTS OF THE SAME TOPIC. Read our Forum Guidelines. I am deleting the other, recent post because you continue with the same topic. -- Art Montemayor.

"Dear guys

I had earlier posted under the same title,however i am reposting again here. I have an existing and unused exchanger to be rated for new service and presented the results below

1. New Duty is 0.2mmkcal/hr which is much less than data sheet duty. Hence as a prliminary step, i can proceed for further calculation
IS MY APPROACH CORRECT ?

2. I had put high pressure fluid in tube side and low pressure in shell side.
IS IT OK ?

2. The calculated(new) overall (S&T)dirt factor is 0.064 m2hrC/Kcal but the old exchanger data sheet dirt factor IS 0.0012 m2hrC/Kcal .

NOW WHAT SHOULD I CONCLUDE AND WHAT ADJUSTMENT I HAVE TO MAKE TO REDUCE THE CALCULATED VALUE OR SHOULD I LEAVE LIKE THIS ?

3. Calculated Delta P shell side - 0.23 psig
Shell side is very low as normally it should be 5 to 10 psig. So what should i do now to increase the velocity in sHELL SIDE ? OR should i leave like this

4. Calculated Delta P tube side - 10.22 psig
Tube side seem to be acceptable - Any comment ?

5. Calculated overall U is 75 Btu/hrft2F which is less than recommended one
The recommneded is 150 to 200 Btu/hrft2F.
AM I CORRECT ?NOW WHAT SHOULD I DO? SHOULD I LEAVE LIKE THIS OR I HAVE TO adjust some parameter to MEET THE RECOMMENDED U value ?

6. Calculated Tube side(High pressure fluid) velocity is - 0.2 m/s for 196 U tubes with 3/4"OD &2 PASS
The velocity is very much less than the recommeded one 1.5 to 3 m/s

TO get the recommended velocity i have to plug 140 tubes. Now if i have to run my exchanger with only 50 tubes, WHAI IS THE NEXT STEP I SHOULD DO?

IS MY UNDERSTANDING AND APPROACH IS CORRECT?

i THINK I HAVE PUT MY UNDESTANDING AND APPROACH AS AS FAR REASONABLY OK AND I THINK OTHERS HAVE ALSO UNDESTOOD WHAT IS MY INTENTION. PL IF ANYONE WOULD PROVIDE ME STEP BY STEP PROCEDURE (ALTHOUGH KERN HAD ADDRESSED EXTENSIVELY BUT STILL TO TUNE TO MY UNDERSTANDING THIS FORUM HELPS A LOT) OR SPREADSHEET IN MKS UNITS IT WILL BE LOT MORE HELPFUL. IF ANYONE COULD HELP ME FURTHER YOU CAN SEND ME ANY GUIDELINES TO MY EMAIL ADDRESS momsalih01@yahoo.co.in

Regards
MOSA"