14 replies to this topic

[CSNK]

Dear All,

 

As per TEMA guidelines, which kind of shell and tube heat exchanger is best suitable for cooling water serivce.

 

I am using HTRI software for my thermal checking but not sure of which type of shell geometry to be used.

 

Can i go for TEMA - AES type or is there any guidelines in cooling water service.

 

Please reply.

 

Regards,

[meetyourmaker]

Any TEMA type exchanger may be used. I have seen all type of exchangers used for cooling water service. Are you designing a new exchanger or rating an existing one. If you are rating an existing exchanger then you can find out from the datasheet what type of exchanger is used in the plant and enter details in HTRI accordingly . If you are designing one then you have to first decide the fluid allocation and what type of rear head is required? I must know more details about your system to decide whether AES is the corrrect choice.

[CSNK]

I am having viscous liquid at around 110 Deg C which needs to be cooled to 66 Deg C

with the help of cooling water at 32 Deg C inlet temperature.

I designed with the help of HTRI (BEU) by putting viscous liquid in shell side and CW in tube side.

I am able to achieve final temperature of 66 Deg C.

 

Now my concern is that when we can go for cooling medium as cooling water, is
it acceptable in my case since inlet temperature of hot fluid is as high
as 110 Deg C.

[thorium90]

Hot fluid inlet temperature of 110C is ok. What is the CW out temperature? It shouldnt be more than 50C. What are the values you get from the HTRI? Like the pressure drop, heat transfer coefficients, velocities etc.

Edited by thorium90, 16 February 2013 - 08:02 AM.

[meetyourmaker]

your selection seems fine to me, viscous fluids should be in the shell side and cooling water should work fine for this application.Try to limit the outlet temp of cooling water to below 45 deg C.

[gegio1960]

chicks,

according to the few info you've given (mainly missed: foulings, viscosities of the viscous fluid), the selected BEU should be the most economical choice.

Chemical cleaning should be provided.

Erosion damages could occur in the u-bends in high tube side velocity applications.

Maybe a quite high number of baffles is needed to increase the velocity in the shell side and, consequently, the overall U.

No big problems about the temperatures: if you've to go to 66°C, the process stream is not too much viscous (very viscous fluids are normally taken at higher temperatures and tempered water is used instead of CW); in case that's not true, you should improve the situation with an equicorrent heat exchanger (and so you couldn't use U tubes).

These are only few speculations in absence of a process data sheet. 

Good luck

 

This Heat Exchanger Animation comes from www.temaindia.com..... Ok, it's an AEU but it's coloured!   

Edited by gegio1960, 16 February 2013 - 01:16 PM.

[Art Montemayor]

gegio1960:

 

Nice animated heat exchanger drawing!

 

However, you need some homework on your TEMA types.  What you depict is NOT an AEU.  It is an AES:

 

A = a channel with removal cover;

E = a one-pass shell;

S = an internal floating head with a backing device.

 

U = U-tube bundle.

[gegio1960]

yes, sorry!

[Adil Akbar]

Can anyone explain to me what is

-Expanded tube to tubesheet joint

-Seal weld tube to tubesheet joint

-strength weld tube to tubesheet joint

 

along with pictures and in what cases they are used.

[mvp]

1. The process side is being cooled from 110 to 65 C. An air cooled exchanger can easily do the job; No need to worry about CW fouling.

2. If you still wanted to use CW (Cooling water), ensure you do not exceed skin temperature of 60 C; to avoid accelerated fouling. To achieve this you may need to ensure adequate CW flow.

3. Flud allocation: If your process is less fouling than CW, you can place it on the shell side.

4. Typically CW is on the tube side (hot fluid in the shell), ensure adequate CW velocity 2 to 2.5 m/s (4 to 7 ft/s)

5. Given that the fluid is viscous, you may find it very difficult to acheive a good Heat transfer coefficient in a tubular exchanger; try a spiral plate exchanger; adjust the gap of the process side and CW side, to get a good HTC at a reasonable pressure drop.

Good Luck

[Atttyub194]

Good day!

1. There a lot of missing information which can lead to proper decision for selecting the type of exchanger ., however, I will try to elaborate  the parameters to some extent.
2. In industry , you may find BEM, BEU, BET,AES,NXN, NEN BFU, DEU type exchanger for cooling water service.
3. It is obvious that the tube side can be cleaned mechanically, but the shell side if need to be cleaned , must be cleaned chemically as the bundle is fixed. Therefore, it will be difficult to put a dirty fluid i.e. fluid containing solids or substances which can be accumulated on shell side with U tube bundle.Also,  use of internally or externally packed floating head designs for volatile or toxic shell side fluids can not be recommended
4. In lethal or explosive applications, it is common to place the critical fluid inside the tubes, regardless of other considerations. In such cases shell and tube exchangers are typically specified with high-alloy materials and/or polished surface finish. Mechanical and electropolish techniques are also acceptable some times or exchangers can be manufactured with clad tube sheets in large diameters and solid in smaller diameters.Thus, the decision to put cooling water on tube or shell side totally depends on pressure rating, corrosivity,cleanliness of the process fluid.
5. The decision of what type of channel head you require depends on pressure of the fluid to be put in. For example if the pressure of process fluid is higher typically greater than 40 bar then the obvious choice for channel head is D type. The type of channel head is dependent on the pressure or service condition of the process fluid if placed on tube side. Accordingly, the first obvious reason for going from straight type bundle is the acceptable thermal expansion between shell and tube material
6. Shell and tube exchangers can also be manufactured with “A” type heads where access to the tube side without disturbing any connective piping  is required.
7. As indicated by mvp , typically CW velocity  of 2 to 2.5 m/s (4 to 7 ft/s). This is required especially to avoid the risk of MIC ( Microbiological Induced Corrosion). You may lower the velocity to 1.7 m/sec for carbon steel and 1.5 m/sec for Stainless Steel. However, this need a very careful review of your system. If you need further details please refer your cooling water chemical supplier  or alternatively please check GEO&G site for a very good presentation on this subject
8. Regarding queries about tube expansion , rolling seal welding and strength weld following may be noted. However, this depends totally on industrial practices followed, despite the fact you will find lot a literature indicating that grooving with expansion is sufficient with respect to mechanical strength. One such paper is Reliability Study of Hydraulically expanded tube to tube sheet joints published by ASME in 2006. However, if my friends ask my opinion , I would go as follows, however, the following recommendations do not to supersede any recommendation by process licenser   :
   1. Non flammable service  expanded with groove and rolled ( steam , lube oil etc)
   2. Expanded with groove and rolled and seal welded upto pressures 30 bar
   3. Strength welded for lethal, hydrogen and high pressure service
9. I would suggest that members like anukar / kalkaa should also share their experience. They seems silent on the subject
10.  In the end, if I have to make the selection then I  would have suggested the following 
    1.  TYPE : BEM
    2. TEMA : Class C
    3. Cooling Water : On shell  Side
    4. Tubes: Twisted or Tube with insert by Cal Gavin or similar company  to optimize heat transfer area

Hope the above information will help

 

Best regards and God Bless You

 

Ahmed Attyub

[feihong21314]

thanks for your repl!y

[Art Montemayor]

Although Attyub194 is known for his constructive, experienced, and accurate posts, I have to correct the following statement:

 

“Therefore, it will be difficult to put a dirty fluid i.e. fluid containing solids or substances which can be accumulated on shell side with U tube bundle.”

 

ALL U-tube construction heat exchangers are capable of having their U-tube bundle removed.  Otherwise, they couldn’t be practically and economically fabricated.  Because of this inherent U-tube bundle feature, it is possible to remove the bundle from the shell and clean it mechanically out in the open and not treat the bundle with chemical solutions while it is inside the shell.  If fouling is expected or anticipated for the service it is always wise to specify square pitch for the tubes – which allows for external mechanical cleaning.

 

However, having said the above, it is also important to bear in mind WHAT type of fouling is anticipated.  For example: in a prior 1985 U-tube heat exchanger installation that I inherited, the outlet cooling water on the exchanger shell side was specified to be 125 ^oF.  At this outlet temperature, the cooling water solids – mostly carbonates – precipitated out and formed a solid block.  It was virtually impossible to physically pull the U-tube bundle out of the shell and I had to cut the shell in sections to salvage the U-tube bundle.  I welded on a new shell later, after mechanical cleaning.  The point here is that cooling water should not be allowed to heat up above 120 ^oF – especially where the cooling water has dissolved solids.

 

It is the responsibility of the designer (and NEVER the responsibility of the Computer program – even HTRI) to ensure that the heat exchanger complies with all of the project scope – especially the characteristics of both fluids and their properties.  In doing so, it becomes common place to be able to select the proper, best heat exchanger selection and orientation.

 

 

[99thin]

very useful information. thanks a lot for this.

 

thanks

99thin

[Atttyub194]

Nice to see your Picture Art

 

Best regards

Ahmed Attyub