14 replies to this topic

[dpp]

A thermosyphon reboiler is to be checked for its adequacy in HTRI. The enthalpy & other properties values are generated from KBC petrosim. and the same was specified in the HTRI.

The enthalpy values generated in the KBC petrosim are having a negative sign before them. I understand that it is something to do with the reference state considered.

My question is ... How should i incorporate these values in HTRI.? What is the Reference sate considered in HTRI.? Whether my negative enthalpies shall be accepted or not by HTRI?

I tried running the HTRI with the negative enthalpies.. The run was converged.. but i get a warning message " A negative latent heat has been calculated for cold fluid at isobar no. 2 at 5th increment. Check ur heat relaease data"

Help me out pls.

[Padmakar Katre]

Dear,
What if you run HTRI with positive duty? Have you compared the outputs of these two cases. As far as the sign of the duty is concerned it is w.r.t. the thermal state of the fluid. That is for cooling/condensing side it will be positive (Heat imparted to the system) and negative in case of hot fluid as the heat is extracted from the system. Please seek some HTRI expert opinion for further understanding.

[dpp]

Dear,
What if you run HTRI with positive duty? Have you compared the outputs of these two cases. As far as the sign of the duty is concerned it is w.r.t. the thermal state of the fluid. That is for cooling/condensing side it will be positive (Heat imparted to the system) and negative in case of hot fluid as the heat is extracted from the system. Please seek some HTRI expert opinion for further understanding.

Thanks... I need some guidance reg. rating of a reboiler. (horizontal thermosyphon reboiler.)Appreciate your help

[Jiten_process]

@dpp

i have recently done some design and rating of kettle reboilers on HTRI. i dont know what you mean by horizontal thermosyphon. As to my understanding thermosyphon reboilers are always verticle.

Please mention your problem i can try to help you out...

As far as negative enthalpy value is concern, i have also got to see such values but that is because of base property of model used. We dont know the base condition (refrence temp and pressure of that reference temp.) it takes in their model. See attached image of HTRI case...i think you are confused with the same type of case.

Attached Files

•  NEGATIVE_ENTHALPY.xls   143KB   83 downloads

[dpp]

Thanks jiten.....there are horizontal thermosyphon reboilers.....in use....i just need to know what s the procedure for rating the reboiler.....should we assume the exit vapor fraction...or shud we assume the circulation rate.....is there any procedure for rating the reboiler.....any softare document...?

[dpp]

jiten can u just tell me the procedure of rating ur vertical thermosyphon reboiler in HTRI at least....

thanks

[Jiten_process]

jiten can u just tell me the procedure of rating ur vertical thermosyphon reboiler in HTRI at least....

thanks

well, i assume here that you know rating procedure for shell and tube h.e. on htri. what extra we need to do for verticle thermosyphon is as below

spcify process data for shell and tube side fluid. now here since you are doing rating dont initially put outlet vapor fraction for tubeside (boiling) fluid. instead you have to specify required head (in reboiler tab) based on actual layout in your plant. (even if you specify outlet vapor fraction, HTRI will override it and will recalculate if you have specified required head value)

Also in reboiler tab if you specify inlet pressure location at column nozzle then you have to specify the piping details also (assume u know where to put in in HTRI input) which is recommended since you want to present actual condition that you have.

Now you have to check the outlet vapor fraction calculated by htri as per process requirement.

Hope above will help u...

[dpp]

jiten can u just tell me the procedure of rating ur vertical thermosyphon reboiler in HTRI at least....

thanks

well, i assume here that you know rating procedure for shell and tube h.e. on htri. what extra we need to do for verticle thermosyphon is as below

spcify process data for shell and tube side fluid. now here since you are doing rating dont initially put outlet vapor fraction for tubeside (boiling) fluid. instead you have to specify required head (in reboiler tab) based on actual layout in your plant. (even if you specify outlet vapor fraction, HTRI will override it and will recalculate if you have specified required head value)

Also in reboiler tab if you specify inlet pressure location at column nozzle then you have to specify the piping details also (assume u know where to put in in HTRI input) which is recommended since you want to present actual condition that you have.

Now you have to check the outlet vapor fraction calculated by htri as per process requirement.

Hope above will help u...

[narendrasony]

Dear Jiten,
Can you please tell how to design a new vertical thermo-syphon re boiler manually, what should we fix : Exit vapor fraction or circulation rate? And is there any guideline for fixing exit vapor fraction for a given service? I think once static head and the re-boiler I/L O/L piping pressure drop are decided, then both exit vapor fraction & circulation rate will be fixed after trial and error. I suspect multiple solutions may result for the same head. Please tell me if I am correct and how to do it?

Regards
Narendra Kumar

[Jiten_process]

Dear Jiten,
Can you please tell how to design a new vertical thermo-syphon re boiler manually, what should we fix : Exit vapor fraction or circulation rate? And is there any guideline for fixing exit vapor fraction for a given service? I think once static head and the re-boiler I/L O/L piping pressure drop are decided, then both exit vapor fraction & circulation rate will be fixed after trial and error. I suspect multiple solutions may result for the same head. Please tell me if I am correct and how to do it?

Regards
Narendra Kumar

Dear narendra

I havent done vetical thermo-syphon design manually nor i am well versed with thermo-syphon design. i always rely on sophisticated software like HTRI so far. Now to address your question, i would say it also depends on the layout and piping limitations if you have any in your plant otherwise you can specify outlet vapor fraction (that should be in range of 0.15 - 0.35) and find out required head (driving head) requird to achieve that vapor fraction. Substract the inlet and outlet piping and nozzle pressure drop and see how much head is left to be given. Adjust your plant layout such that the verticle distance between column liquid level and reboiler inlet side tube bundle would be slightly higher than the required head that you end up calculated. But the selected vapor fraction is fixed by column's process design.

Instead you can fix the required head that you have in actual and see how much vapor fraction you can achieve but in any case column process requirement should not be overlooked. Also we should keep one thing in mind that thermo-syphon design is very much critical as far as smoothness of column operation is concern and design should be deeply evaluated before finalising it.

I am also searching for some good literature/guidlines for designing thermo-syphon reboilers, request to members if anybody can share.

Hope it might help u somewhat
good luck...

[narendrasony]

Dear Jiten,
Thanks for your prompt reply.
I fully agree with you that both design and smooth operation of thermo-cyclone re-boiler are very critical and it is to be handled with utmost care.
Now, for a given available head and re-boiler we can find out the vapor fraction & circulation rates as you mentioned.
But for a new re-boiler design, don't you think that for a given available head you may still fix the vapor fraction...re-boiler sizing (No of tubes of a pre-selected diameter) will then depend on these two parameters and piping configuration. Can we select any vapor fraction in the recommended range of 0.15-0.35 or there any guidelines to narrow down our choice?
Requesting more insight to all.

Regards
Narendra Kumar

[DarrenO]

If you are using the latest version of Petro-SIM (v3.2) then you could run HTRI directly inside Petro-SIM and not have to worry about transferring data yourself. This can be done a number of ways: you can export the streams from inside the column flowsheet and use a Cape-Open operation to link to HTRI, or if you have the latest version of HTRI's software (v6) then the HTRI solution method links directly into the Petro-SIM heat exchanger operation. The software should then take care of exporting data correctly for you.

[Jiten_process]

Dear Jiten,
Thanks for your prompt reply.
I fully agree with you that both design and smooth operation of thermo-cyclone re-boiler are very critical and it is to be handled with utmost care.
Now, for a given available head and re-boiler we can find out the vapor fraction & circulation rates as you mentioned.
But for a new re-boiler design, don't you think that for a given available head you may still fix the vapor fraction...re-boiler sizing (No of tubes of a pre-selected diameter) will then depend on these two parameters and piping configuration. Can we select any vapor fraction in the recommended range of 0.15-0.35 or there any guidelines to narrow down our choice?
Requesting more insight to all.

Regards
Narendra Kumar

Dear Narendra

I have already stated what you are asking. i dont undertand your confustion now. Its better if you start new thread with specific case and all the relevant data and tell all where exactly you are facing problem. Rather than talking generalise best way is to talk with live example.

hope u agree with this...

[dpp]

If you are using the latest version of Petro-SIM (v3.2) then you could run HTRI directly inside Petro-SIM and not have to worry about transferring data yourself. This can be done a number of ways: you can export the streams from inside the column flowsheet and use a Cape-Open operation to link to HTRI, or if you have the latest version of HTRI's software (v6) then the HTRI solution method links directly into the Petro-SIM heat exchanger operation. The software should then take care of exporting data correctly for you.

Darren,

i m using Petro sim 3.2...good to know that i can run htri inside petrosim.....well...i need one more detail....I tried to simulate a column.....i need a thermosyphon...reboiler....but by default ...i m getting a kettle type reboiler...in petrosim...
The problem with this is that petrosim treats the Kettle type reboiler as a stage...and seprates the liquid from vapor in the reboiler.....hence the boilup in this case is only a vapor....

I would like to know if is it possible to use a thermosyphon type reboiler in petrosim....and i wud be glad if u cud tell me that it cud be linked with HTRi...

I m new to these softwares....so pls. forgive me...if i have asked something stupid...

[DarrenO]

I m new to these softwares....so pls. forgive me...if i have asked something stupid...

I'm new to answering these sorts of questions on forums, so please extend me the same courtesy

Let me first say that you might want to take this up with KBC's support as I am starting to hit the limits of my knowledge - typically thermosyphon reboilers are simulated by returning the boilup and liquid from the reboiler back to the column with the vapour going back to the stage above that which the liquid returns to. You then draw the column bottom product directly off the bottom tray of the tray section.

Then exporting those streams from the inside of the column to the outside allows you to connect them up to a rigorous heat exchanger linked to HTRI so you can then rigorously rate the reboiler all within the same simulation file.

I hope this is clear, feel free to ask more questions if I am only confusing you - but you might get better quality help from KBC directly (software@kbcat.com).