TEMA AES Design

[Angsi2]

For a high temperature/pressure application, if BEM design is found to be acceptable (within stress limits), would there be any incentive in using a AES design if BEM could do the job?

What I've 'heard' is that AES could be prone to internal leakage (thru its internal floating head), not to mention it being expensive. Anyone here has any direct experience (design & mainteannce) of AES exchangers?

Any input will be appreciated.

 

[muld0020]

This question is hard to answer in a general sense. The thing with high pressure temp designs is that you will most likly require an expansion joint on the BEM. The floating design (AES) eliminates this problem. Depending the expansion joint these can range from low cost flanged heads to thin wall bellows type (very expensive). Depending on what processes are being run on the shell and tube sides will also matter (if a high alloy inner head is needed). The pull through head has the extra ring/flange/head to deal with which adds cost, and this may or may not be significant based on material required and size. It is also much easier to design a floating bundle compared to the expansion joint and is probably more reliable if the vessel is highly cycled at high temperatures. Anyway, it is best evaluated on a case by case basis.

 

[TJOrlowski]

If your shell-side temperature and pressure are less than 400F and 200 PSIG, and your shell-side fluid is non-corrosive, you may consider a type AEP or BEP configuration. It's been my experience that there are less problems with gaskets vs. type S units.

If you have > 200 PSIG shell-side pressure and/or temperature, or corrosive fluids - there are too many factors to consider when choosing beween a type S floating bundle and a type M fixed bundle. Is your only concern initial capital cost? Is the unit highly cycled? How often are you going to be doing maintenance, and of what measures/operations will the maintenance consist? How much would repairs and replacement parts cost on one configuration vs the other?

As muld0020 pointed out, case by case evaluation is almost always the way to go when doing cost-benefit. One-size-fits-all rules tend to cause more problems than they solve.

-TJ Orlowski

 

[Angsi2]

muld0020: For the purpose of discussion, assume that the stresses can be contained by the fixed tubesheet design i.e. say BEM type.

TJOrlowski: Assume that cyclic service is not a factor. More often that not, at least in the offshore oil and gas industry, if the service fluid temperature exceeds a certain limit, the process engineer, almost always as a rule of thumb, specifies a floating head design. These configuration than goes onto the P&ID and the mechanical engineer than finds himself stuck with it. The fact is, no mechanical calculations were performed to verify or confirm if fixed tube sheet design could accomodate the stresses. It would seem like an overdesign, more capital cost investment with a floating head, which is also a little more mainteance intensive. In my view, I dont think a floating head is preferable if a simple fixed tube sheet or a U-Tube design could do the job.

Any comments?

 

[TJOrlowski]

If process engineers are specifying type S heat exchangers across the board, but it could be advantageous to explore using other configurations on a per-application basis, I don't see why you wouldn't weigh other options - if there is the will and the way to do so.

In my view, best practice is to submit all of your project specifications to an experienced shell & tube manufacturer with thermal and mechanical design capabilities. Most manufacturers will ask the right questions to determine the right configuration for the application.

-TJ Orlowski

 

[Angsi2]

TJ I agree with your final recommendation. In fact I've done that before and found that manufacturers do advise the use of fixed heads if found suitable after considering its service, mechanical stresses, maintenance requirements etc.

But still, I get a lot of defensive arguments from the process engineers over their selection and thought maybe there are more reasons to it that what I'm aware of, and that's why I raised it.

Thanks.

 

[muld0020]

The main thing with the fixed tubesheet design is that you can not access the shell side of the bundles (BEM). If you are talking petrochemical or process plant cleaning the bundle is usually important. If you are talking closed cooling water on the shell side then it's not. The "S" shell allows you to remove the bundle and clean it, the BEM does not. So depending on your process fluids and expected fouling it may be very advantageous to specify AES vs BEM.

 

[Angsi2]

muld0020: Agree with your comment regarding the SS fluid and its fouling conditions.

 

[silebilee]

AES classified in TEMA is internal floating head exchanger which is used wildly in petroleum refineries. This type of exchanger is commonly used for high temperature with fouling fluid application.
Also, it is highly recommended used in the leakage risk process as the floating head intenal flange equipped.

 

[LCeballos]

I am agree with silebilee. AES type exchanger are very common in oil refineries. In spite that at the beginning could be some expensive (floating head, back up ring, shell cover larger than other types) you must be to have present other issue, the maintenance.AES type its maintenance is very easy and faster than other types, in fact, you can remove tube bundle, clean it, check all internals, easily.
In oil industry "Time is money".
I am from Venezuela. Near of 80% of tube & shell HE's in our refineries have designed as AES type.

Regards.