9 replies to this topic

[jitendraprocess]

I am designing Shell & tube heat exchanger in which shell side having gas at pressure 86 kg/cm2g & temp. 45 deg C same gas after passing through chiller cools up to 4 deg C pass through tube side to cool feed gas.

In this case for this high pressure which type of front head & rear head should i choose?

for high pressure if i choose D as front head then for combination which type of rear head i choose?

please guide.

[Art Montemayor]

Your description in English is very confusing and does not make sense because of your grammar. The best and most accurate way to describe your heat exchange application is with an Excel spreadsheet sketch. I simply can’t determine which fluid (gas?) is in the shell and tube side. You tell us the pressure of one fluid, but you don’t tell us the pressure of the other one.

Please furnish a good, clear sketch of the application so you can obtain good, positive comments and guidance.

[jitendraprocess]

Thanks for your valuable reply.

Please find attached herewith schematic sketch for query posted earlier.
In that, i am designing HE E-104, E-105, E106
In this case, for this high pressure application which type of front head & rear head should i choose?
For high pressure if i choose D as front head(High pressure clouser) then for combination which type of rear head i choose?

Please see attached file
Please guide.
Thanks

Attached Files

•  20120628114738224.pdf   70KB   623 downloads

[srfish]

On the basis of the sketch where the heat exchangers are in countercurrrent flow, I would use a type NEN heat exchanger. At the high design pressure required gaskted joints can be a problem. The NEN type eliminates a double gasketed joint like you would have with a BEM type. There would be only one gasketed joint per exchanger end. The type D exchanger end is used only at higher design pressures than what would be required here..

[Art Montemayor]

As I expected, the sketch you furnish tells us all a lot of information that it necessary and vital for a recommendation. You are using refrigeration to drop out liquids from a lift gas. However, you fail to fully explain what liquids you are dropping out in your separator. I have to assume you are condensing associated water vapor in the lift gas.

You also do not tell us the flow rates, so we are unable to get an idea of the size of these exchangers. This is an important point because it has an impact on the type and cost of TEMA shell and tube exchangers that I believe you are contemplating on applying. You also fail to advise what type of design (TEMA?) and I have to assume you mean TEMA. Am I correct?

If you are dropping out condensed water, I would caution you on the temperature approach that you are using. Your refrigerant is well below the freezing point of water and I must also assume that you are aware of that. I don’t know how you can avoid formation of water ice in your evaporator.

The type of TEMA design I would recommend is the same that I recommended in the last project I led that handled 115,00 kg/hr of natural gas at 100 barG. That type was a BEU.

I also mention here that your sketch has an error in that the incoming “wet” gas is at 86.1 kg/cm²g and 45 ^oC while the outgoing drier gas is at 86.4 kg/cm²g and 29 ^oC. The gas must undergo a pressure drop through all the exchangers and separator; it can’t have a pressure increase. I would also check for any temperature crosses in the two precoolers.

[jitendraprocess]

Yes, higher hydrocarbon like C5, C6, C7 & some water vapor are condensing component.
In sketch, outlet gas pressure is 84.4 kg/cm2g @ 29 deg C.

Thanks all of you for your valuable reply.

Dear srfish,

Why NEN type please explain elaborately. In NEN thickness may be high so impact on cost. Am i correct?

Dear Art,

Sir, As you tell BEU is used earlier but here we may use BEM
Reason 1) BEU cost will be more
2) Here there is no large temp difference so why U type rear head we used?

Please guide.
Awaiting your valuable reply.

[Art Montemayor]

Jitendraprocess:

The reasons a BEU was recommended were:

• The cost was considerably LESS. There is only one tube sheet and one head employed as compared to two (and we are dealing with rather thick tube sheets and heads).
• There are much less joints to account for and, consequently, less potential leakage. Our application was on an offshore platform. All tube joints on the tube sheets were expanded and seal welded. All we had was one gasketed head flange joint on the tube side.
• There was no need for inspection or cleaning in the tube side since we had rather clean natural gas. Therefore, a very expensive, heavy, and leak-prone “D” type head was averted. The “D” head not only is leak-prone, it is very, very, heavy and costly.
• The individual, high-alloy U-tube hairpins were subcontracted to a specialty tube bending contractor and were much more economical than the straight-tube construction. Our shell side was seawater, so bundle removal was much more facilitated with a U-tube design. There are more reasons to select a U-tube design than just bundle thermal expansion allowance. Additionally, today it has become commonplace to be able to mechanically clean out internally a U-tube assembly in-place – especially when using 1” OD tubes. This is no longer the problem it once was. Unless there are strong reasons for having to look straight-through the tubes, I would not employ a BEM design - or two heads – in a high natural gas pressure application.

[srfish]

jitendraprocess,

Art gave good reasons for not considering a "D" type head.

If you do not have a length limitation the most economical selection is a single long counterflow type NEN heat exchanger This reduces the number shells and keeps the diameter size down. Both of these factors reduce the cost.

[jitendraprocess]

Thanks all of you for given very valuable reply.

[Dipankarc84]

Dear Art,

In the sketch provided by Jitendra the approaches at the hot and cold ends of both exchangers (E-104 and E-105) are 16 deg C ((20 - 4) C at cold end of E-105, (33 - 17) C at intermediate and (45 - 29) C at hot end of E-104). I wanted to understand why you are asking to check for a temperature cross when the approaches seem to be considerably wide?

In case there are chances of temperature crosses, my second query is, why do you recommend a BEU type exchanger which is essentially a 1-2 pass exchanger and chances of pinching are much more probable compared to a 1-1 pass or a multi-shell configuration?

Regards
Dipankar