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3

Propylene-Propane Splitter Control


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#1 Vegeta

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Posted 02 September 2022 - 12:32 PM

Team, 

 

I am working within a petrochemical project where there is a propylene-propane splitter.  The suggested control loops by one engineering party are shown in the attached file with some preliminary values. I have some doubts about some loops and these in particular are: 

 

  • The feed flow control is adjusted according to the level in the overhead accumulator.  It is usually set as either a simple flow control or cascaded with the level in the feed tank. 
  • The tower pressure is adjusted via split range control: hot vapor bypass and throttling the off gas.  Isn't one enough (preferably the throttling of off gas)? 
  • The level in the tower bottom is adjusted according to the heat duty of the reboiler via the low pressure steam flow control valve.  Isn't it better to control the tower bottom level via the flow of the propane flow? also, isn't it better to control the bottom temperature via the steam flow (I don't see any control of the tower temperature in the scheme)? what about the control of steam condensate level in the reboiler shell?   
  • Is it a good idea to have a pressure throttling valve at the motive stream of the ejector? is it going to be able to reach the fuel header pressure of the boiler? 
  • I heard once that it is not a good idea to put a throttling valve against a positive displacement pump.  Here, there are three flow control valves against the propylene supply pump to the reactors.  Aren't these valves redundant as each reactor is supposed to receive an equal flow and the shall have similar operating pressure (more or less)?

 

I appreciate any exchange of ideas, feedbacks, and suggestions. 

 

If you need any additional information, please let me know. 

 

 

Regards, 

Attached Files


Edited by Vegeta, 02 September 2022 - 12:34 PM.


#2 Bobby Strain

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Posted 02 September 2022 - 01:00 PM

The controls look strange to me.

 

Bobby



#3 breizh

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Posted 02 September 2022 - 08:30 PM

Hi,

I encourage you to study the material attached. 

Write down the philosophy of the process control  and let the E&I engineer do his/her  part .

Make it easy to understand for the operators. 

 

https://www.research..._fig1_305111152

 

 

Good luck

Breizh 



#4 Bobby Strain

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Posted 03 September 2022 - 01:22 PM

Can you provide feed composition and type and number of trays in the column? Has this system been installed? If not, what is the status of the project.

 

Bobby


Edited by Bobby Strain, 03 September 2022 - 01:23 PM.


#5 horatorres

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Posted 06 September 2022 - 08:48 PM

https://www.research..._fig4_254470476

 

From google, this is a logical process control for C3/C3?= splitter. Search in the web

 

Horacio



#6 Vegeta

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Posted 11 September 2022 - 07:25 AM

Can you provide feed composition and type and number of trays in the column? Has this system been installed? If not, what is the status of the project.

 

Bobby

 

Sorry for being late in getting back to this discussion...

 

The top feed is 99.5 wt.% propylene and the balance is propane.  

The lower feed is a recycle from the process and it is 98 wt.% propylene, 1.5 wt% propane, 0.3 wt% water, and the balance is lights like methane, ethane,..etc. 

There are around 100 trays and all are valve trays.  The feeds are at the 5th and 50th trays. 

 

If you need any additional information, please let me know. 

 

 

Regards, 



#7 Bobby Strain

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Posted 11 September 2022 - 09:28 AM

The flow rates in the drawing suggest a pilot plant scale. Are the flows really this low? What is the top tray number? I am surprised that you can use valve trays in such a small column.

 

Bobby






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