Hello All!!

Well , can anyone give me some insights on Vertical Reboiler modelling in Caesar?

I need to discuss some important issues such how to model, say, 3000 tubes each of dia D?

Should i model one combined rigid element with dia 3000D?

What about other associated aspects?

Prompt response will be appreciated?


Thanks!!

SJ

“One of the most responsible things you can do as an adult is to become more of a child.”

Your question is too fundamental for this forum. Ask your supervisor for some training.

For what purpose? A reboiler will not be designed to piping codes. Using PVElite is probably more appropiate.

MoverZ!!

If you don't have anything to say , please don't give feckless advise!!

I'll really appreciate this!!

I know from whom to seek advise!!


Thanks,

SJ

Perseus !

Thanks for responding!!

Well , I'm aware of how to model a reboiler in Caesar. But the only doubt I've is about the modelling of the tubes. As you know , there are a large no. of tubes (my case more than 2700) in a reboiler but some engineers model it as pipe element with total dia equal to the dia of each tube multiplied by the no.

However , I feel that modelling a reboiler as a piping element with OD same as that of the equipment & modelling a rigid element from the fixed tubesheet with total dia equal to the dia of each tube multiplied by the no. to take care of the rigidity because of the tube bundles is a better approach.

Which one is more accurate?

Thanks,

SJ

“One of the most responsible things you can do as an adult is to become more of a child.”

What is your purpose in modeling the exchanger?

I typically model a reboiler at the OD of the reboiler with a wall thickness of several inches to insure a stiff representation of the cylinder and a reasonable graphical representation. I usually set the density of the metal to zero and include a rigid element at the CG of the reboiler and set it at the operating weight of the reboiler so that the support springs can be correctly sized. Local flexiblity at the nozzle connections is done via WRC or Nozzle Pro FEA.

What (TEMA) type of heat exchanger? Get the data sheet and study the info. Get the specification and verify the nozzle loads that were submitted in the inquiry. TEMA assumes that nozzle loads are negligible unless specified. See RGP-RCB-10.6.

Look at the first 12 pages of TEMA. You should spend a little time reviewing the geometry. Briefly, some exchangers have fixed tubes at both ends with (or without) a shell expansion joint. Others have floating heads, pull through floating heads, U Tubes, etc.
There are both vertical and horizontal reboilers. A fixed tubesheet exchanger with SS tubes and a CS shell with expansion joint will expand at the SS rate. This could be from tube process fluid conditions or from shell fluid conditions. Many owners limit fixed tube length to 24 ft. A floating head tubesheet will expand at the shell expansion rate for shell nozzles and at the tube rate for pull nozzles.

Next, study the operating temperatures, then the design temperatures. The design temperatures could have come from the design temperature of an upstream piece of equipment. Then consider the possible displacements of the nozzle that you are modeling.

Steam on the shell side can be turned off. Discuss this with your process engineer. Ask about the possibility of having mixed modes and then adjust your load cases.

You haven’t asked, but including equipment nozzle flexibilities will give a more accurate calculation. Remember to include them at both pieces of equipment before suggesting piping revisions. Ed mentioned this earlier.

Bill Edasi

Great answer Bill. You do the Forum good...

Thanks Bill & Ed for your help!!I did go through your advise deeply & got answers for many of my queries!!

I've some more unresolved queries!! In case, we go for an expansion joint in the shell (for high temp system with both tubesheets fixed), what about the pressure thrust as the bellow is untied? Will it be taken care by the fixed tubseheets?Or should the piping be designed to take care of it??

Further, there are some vendors who give a seismic /wind stopper for their equipment.How to take care of the loads that will be experienced by this stopper?I checked with my Equipments engineer & he's of the opinion that their domain is limited to equipment.This has to be taken care by Civil.Equipment engineer just transfer the location of the stopper & Civil calculates the reactions & submits to equipment engineer to check whether the equipment is safe against these loads. What's the normal design procedure followed??If I want to trasnfer the load to Civil, how should I do this?

What about tube modelling?As you know , there are a large no. of tubes ) in a reboiler but some engineers model it as pipe element with total dia equal to the dia of each tube multiplied by the no.

However , I feel that modelling a reboiler as a piping element with OD same as that of the equipment & modelling a rigid element from the fixed tubesheet with total dia equal to the dia of each tube multiplied by the no. to take care of the rigidity because of the tube bundles is a better approach.

Which one is more accurate? Edward , is my method correct too??

Thanks in advance!!!

Thanks,

SJ

“One of the most responsible things you can do as an adult is to become more of a child.”

I get the feeling that you're trying to answer questions that aren't in your remit. I would typically expect nozzle displacements associated with equipment or at least the fixed point and basic equipment dimensions & materials.

Concerning your reboiler, the stiffness is modelled with the dia. approximation method because it tends to have a high enough value that some error wouldn't affect the solution, this is going to be the stiffest element in your system. Remember there are material and manufacturing tolerances so you don't always have to get the 'perfect' solution. Therefore tube modelling is unnecessary and your project manager may not like his hours being used this way. (But what does he know ;-)

On the other hand doing more detailed analysis for a control is useful, let us know what you find.

Concerning the bellows, you should be told what degrees of freedom they provide but I would expect them to be tied, there's no reason why they shouldn't be as far as I can see.

Hello Perseus!!

Thanks for your response..!!

Pertaining to the bellows , the bellows are untied.So my concern still stands tall...!!

What about pressure thrust?

Are the fixed tubesheets suppose to hold this or should the piping be designed for this?

My equipment engineer is coying away from this answer!!

How do you take care of this case?

Help me out guys!!

Thanks...!!

SJ

“One of the most responsible things you can do as an adult is to become more of a child.”

Sounds like you need a new equipment engineer. He is the one that should be determining the need for a bellow in the exchanger and should understand when and why one is needed.

You should not see any pressure thrust in the piping system, the tube bank attached to fixed tubesheets at each end will effectively act as your tie-rods.

Thanks Ed!!

Well , it seems like this is the only option left for me to recommend the exile of my equipment engineer!!

He is also naive on the design of seismic/wind stopper . These guys jsut pass the baton to CIVIL/Vendor. For this too , they say that it is CIVIL domain. We just check the equipment shell for local stresses using base shear concept.

It seems like that i should only worry about the equipmnet modelling & the piping loads.I was also of the opinion that in case of untied bellow , the fixed tubesheets should take care of the pressure thrust!

Seems like I'm reaching to some conclusion!!

Thanks,

SJ

“One of the most responsible things you can do as an adult is to become more of a child.”