14 replies to this topic

[karun]

Dear,
can anybody tell which is the most suitable method for calculation of relief load for a distillation column PSV
1. manual heat balance.
2. dynamic simulation.
and why?

Thanks
karun

[JoeWong]

Karun,
Welcome...

Your question is just too general and whoever answer you by saying which method is most suitable may be specific to certain system and particular experiences. I am afraid you will have no answer for this question. Answer to this question form a book...i guess.

[karun]

Joe thanks for ur reply.
for not wasting time i am sending u a PFD for my system.
hope u can help me out.
If u need anything else what i have done, just ask.

Thanks
karun

Attached Files

•  PFD_Depropanizer.pdf   117.79KB   771 downloads

[JoeWong]

Karun,

Generally a manual steady state estimation is adopted. However, latest API Std 521 allow dynamic studies for estimation. Whenever relief is excessive and uncontrolled, it is allowed to use Instrumented Safety Protective function and dynamic analysis to analyse and estimate relief load.

Although you have submitted the PFD, you still have not shown what you have done, what you have considered, what your specific questions, etc. Hope you can come with specific question.

[CMA010]

Dear,
can anybody tell which is the most suitable method for calculation of relief load for a distillation column PSV
1. manual heat balance.
2. dynamic simulation.
and why?

Thanks
karun

The following Hydrocarbon Processing article seems to favor dynamic simulation:

"Dynamic Simulation Improves Column Relief-Load Estimates", C. Depew & J. Dessing, Hydrocarbon Processing, December 1999.

There are a lot of different approaches and methods to estimate column relief loads but i have yet to find a reference that compares them to an actual relief load. Would make a great phd project.

[karun]

Joe,
This PFD is developed by me.The whole design and controls have been decided by me. In all the total front end engineering design is done by me.
For manual calculations u just need to know stream conditions ( temp., Pressure, flow, enthalpy) , properties ( latent heat) , composition , reboiler & condenser duties and column controls, if u agree.
Ok for all these values i will send u a hysys file.

But Joe my Quesn. is still not answered. How will i know my relief is excessive and uncontrolled ? When i calculate relief load manually my load comes out to be double if i check for a UOP system.

Thanks
karun

[JoeWong]

Joe,
This PFD is developed by me.The whole design and controls have been decided by me. In all the total front end engineering design is done by me.
For manual calculations u just need to know stream conditions ( temp., Pressure, flow, enthalpy) , properties ( latent heat) , composition , reboiler & condenser duties and column controls, if u agree.
Ok for all these values i will send u a hysys file.

I don't necessary need your HYSYS file.

But Joe my Quesn. is still not answered. How will i know my relief is excessive and uncontrolled ? When i calculate relief load manually my load comes out to be double if i check for a UOP system.
Thanks
karun

I wouldn't be able to guess if i don't know

- how much knowledge and experience you have in pressure relief and disposal system design.
- the design philosophy of you pressure relief system.
- detail process of your system.
- which PSV you are talking
- what scenario you are discussing
- have you done your scenario analysis
- ambient condition
- what is the significant of Instrumented Safety protective system
- any HIPPS
- any depressuring
- any credit taken for relief
.
.
.

This forum is a place for engineers to communicate and share information and experiences. But i am afraid no one in the forum will be able to do your or your consultant works without knowing the detail. I guess no one will spend their valuable time to do your works.

Safety is one the critical issue shall be handled in proper manner and can not be tolerated. From the question that you answer, i am strongly suggest you obtain a experience engineer to assist you or engage third party consultant to assist you.

[karun]

thanks Joe,
sorry if u felt bad.

[JoeWong]

I don't feel bad. Hope you understand what i meant

[sheiko]

See also:

- Bradford, M. and D. G. Durrett, "Avoiding common mistakes in sizing distillation safety valves," Chemical Engineering, July 9, 1984
- Kister H.Z., Distilllation Operation, McGraw-Hill, Chapter 9 "Distillation Overpressure Relief", page 229, 1990
- Nezami, P.L., "Distillation column relief loads Part 1 and 2," Hydrocarbon Processing, April and May, 2008
- Rahimi Mofrad S., "Tower pressure relief calculation," Hydrocarbon Processing, September, 2008

[karun]

thanks sheiko

[sheiko]

QUOTE (karun @ Jan 19 2009, 04:53 AM) thanks sheiko

Attached are some of the above mentionned articles if interested (as somebody asked me in private). That's all i have.

Attached Files

•  art1.pdf   103.76KB   1776 downloads
•  art2.pdf   132.82KB   1409 downloads
•  art3.pdf   126.85KB   1326 downloads

Edited by sheiko, 22 August 2009 - 08:25 AM.

[karun]

Thanks again Sheiko,
i will read these articles and if face any problem will ask you.
karun

[amit bansal]

Thanks again Sheiko,
i will read these articles and if face any problem will ask you.
karun

In fact, i am not really familiar with all the strategies proposed in these articles, so maybe it is wiser to ask your supervisor, forums or even the authors (as i usually do)...

Good luck!

thank you very much..........

Thank you sooo much