11 replies to this topic

[Araboni]

Hi all
I have a problem on exchanger design. I designed two exactly similar exchangers (as per attached HTFS outcome) , in 1^st one tube is carbon steel , but the 2^nd one tube is stainless steel. Off course the thermal conductivity of CS is somehow 3-4 times more than that of SS , but the HTFS calculation exhibits no differences in heat transfer performance as you can also see in attached TEMA sheets.
On the other way, in practice we built both two exchangers , and tested in plant (Polypropylene plant) to cool an stream of unreacted propylene gas from reactor(carrier gas which is 98% propylene). It is really surprising that in CS exchanger , outlet T of tube side is 40 ^oC (in compliance with design), whereas in SS exchanger , it is 58 ^oC.
please note that in both cases , all other conditions such as cooling water flow, temp, ... were the same.
Could anybody inform me of my problem?

Attached Files

•  EA-2030 tube SS-316.pdf   51.95KB   47 downloads
•  EA-2030 tube SA-179.pdf   52.8KB   37 downloads

[srfish]

Because of the lower thermal conductivity of SS you would not expect the gas to cool as much in that heat exchanger as it would in the heat exchanger with CS tubes. But for the SS exchanger to cool only to 58C means there is something else going on besides the difference in metalurgy.

[Himanshu Sharma]

Please be sure that cooling water is free of chlorides otherwise stainless steel will corrode like anything and there will be holes and cracks in the tube.

This may well explain the reason for exchanger non-performance in case of SS tubes.

[breizh]

Hi ,
At site :
Can you check the Delta P on your equipment (shell and tubes) and compare the 2 HX ? Did you check your equipment ( temp probe , valve opening on Cooling water , ...) ? All are well calibrated !
Fouling could be also a reason .
Breizh

[Araboni]

Himanshu
I have already checked , and was informed that the chloride content of cooling water is 100 ppm and I believe that this is not so corrosive for SS.

[Araboni]

Breizh
Everything is the same and no differences we have when using SS than CS exchanger. We tested this issue more than 5 times and in either cases , tube side of CS one cools down to 40 ^oC , whereas for SS one , it cools down to min 58 ^oC.

[breizh]

Did you check the drawings ( as built or construction) ? Did you inspect the equipment ? You may have pipes tubes plug or baffles missing ,....

Something may be different from your expectation .

Breizh

Edited by breizh, 08 July 2012 - 03:56 AM.

[Araboni]

Breizh
I have myself double checked the drawing, you know we have just one drawing for both exchangers, nothing is deviated, except MOC. Even after they were constructed/fabricated, we inspected them and were satisfied their compliances/conformation with drawings. In fact I , for my interest , just did such a test to see what happen when we change material of tube from CS to SS, while keeping all geometrical features the same. Moreover when we dismantled both coolers, and deeply checked their integrals, no blockage or plugging, ..took place.

[Araboni]

dear all
attached , please find the spec of cooling water flowing in shell side of both coolers.

Attached Files

•  cooling water analysis 7.07.2012.pdf   87.64KB   23 downloads

Edited by Araboni, 08 July 2012 - 01:22 AM.

[sheiko]

Araboni,

I believe there is possibly a construction error.

If construction & precom/com check lists and punch lists have not been created, filled and checked, then you may have missed something...

[Anup Paul]

Araboni,

Since you confirm that there is no fouling and no construction error, then request you to kindly verify the properties of carrier gas.
Properties that you have used in HTFS and actual may be different.

From the datasheet, it is clear that required U is only 218 W/m2K where as actual U (clean) for CS is 312 ND FOR SS is 304 W/m2K.
Since you are getting outlet temperature more that 58 C means you actual U is less than 218 W/m2K.

This can be due to fouling or error in construction or due to change in fluid property.

[Shivshankar]

Araboni,

Hope attached document help you.

Regards
Shivshankar

Attached Files

•  HEAT EXCHANGER PERFORMANCE MONITORING_R11.pdf   58.36KB   48 downloads

Edited by Shivshankar, 09 July 2012 - 05:01 AM.