4 replies to this topic

[masino]

Dear members

Hi

 

I have question on differences between BKU and BKM TEMA.

 

I am working on ethylene plant energy saving project.

 

There are two types of chillers (BKU and BKM)

 

Process description.

 

Both of them have -27C operating temperature and 1.4kg/cm2(g) operationg pressure.

This is the shell side process condition (propylene refrigerant).

 

Tube sides of each HX have hydrocarbon fluid (vapor phase) and then condensed fully(BKM) or partially(BKU).

 

Which factors affect the choice between BKU and BKM?

 

i appreciate for your advice in advance

 

Yours

[Art Montemayor]

 

Masino:

 

I offer the following comments to your post --

"There are two types of chillers (BKU and BKM)"

WHERE, specifically, are these two types to be found - In your operating ethylene plant?

I personally have never seen a BKM type of kettle – and I don’t think I’ll ever see one.  The reason for this can be surmised in the attached workbook.

 

"Tube sides of each HX have hydrocarbon fluid (vapor phase) and then condensed fully (BKM) or partially (BKU)."

I don’t understand your description.  If the shellside contains the refrigerant, then the tube bundle must be flooded with LIQUID refrigerant (by rational definition of a kettle), and NOT vapor.  Additionally, how (or why) are you only “partially” condensing in the tubes of a BKU kettle?

 

Await your response.

   Kettle Reboiler Types.xlsx   16.35KB   1370 downloads

[ColinR33]

It depends on what industry you are in, I have designed,built and put into operation a fairly large number of NKN and BKM chillers for gas processing, along with lots of BKU style chillers.  While what Art's workbook states regarding BKM style chillers is true in that they don't allow for as much thermal expansion of the tubes and the bundles cannot be removed for cleaning, in gas processing plants this is often not an issue as the temperature differentials are not that great (typically a 5 degree F temperature of approach) and the differential expansion between the bundle and shell is not significant, allowing the use of fixed tubesheets.  Also, on the tube side at least it is easier to clean the tubes as they can be rodded out mechanically, something you cannot do very easily with a U-tube (usually not an issue as the gas is typically quite clean with a fairly low fouling factor.  On the shell side we use refrigerant grade propane, so very clean service and cleaning is only very rarely, if ever, required.

 

As to BKM vs BKU?  Depends on the service, temperature differential (back to the thermal expansion thing), how dirty the tube and shell side fluids are, capital cost, etc.  Sometimes a U-tube design is impractical as you are limited in tubesheet to tangent length by the maximum tube length (usually 40'-48' overall tube length from our suppliers, so TS/Tan length will be less than half this - remember to take the length of tube used up by the return bendinto account!) and the diameter starts to get too large compared to length.  Going with a BKM style you can go to a 40'-48' TS/TS length which can result in a much smaller diameter vessel with usually lower cost.  I have also put BKM styles with 2-pass bundles into service with success.  Many of these have been operating for 20 years or more.  Hope this gives you a bit more insight.

 

Cheers,

Edited by ColinR33, 02 August 2013 - 04:00 PM.

[masino]

@Art Montemayor

 

At first, I appreciate for your time and advice.

 

This is NCC plant.

BKM is used for ethylene refrigerant condenser and ethylene fractionator condenser

 

each tube side has C2 refrigerant and C1/C2 hydrocarbons

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BKU is used for wash tower trim condenser.

 

on tube side, there is hydrocarbon charge gas including small amount of water content

 

as for partiall contensing matter, I made a mistake and not clearly understand the terminology.

 

some of vapor HC remain vapor, not turning into liquid and then I describe this as partiall condensing in the tube.

 

I should take care of dealing wiht word selection more.

 

Yours

[masino]

@ColinR33

 

I apprecaite for your advice and sharing experience.

 

for the dimention issue

 

(mm unit)

 

BKM (1700/2400 (ID)    12000(L))

BKM (900/1500   (ID)      9000(L))

 

BKU(1500/2000 (ID)        6000(L))

BKU(1350/1650(ID)         6000(L))

 

As you explained above, BKM is possible to have more margin in length.

 

I realized that selection of TEMA type is interrelated with so many factors that I should not focus only on specific issue, but deal with

various factors and discriminate which factor governs the operation.

 

Yours