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Reboiler With A Hot Oil Jacket

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#1 bmicky


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Posted 05 April 2020 - 05:09 AM


We are designing a pilot batch distillation unit, which consists of a small 40L jacketed reboiler.
We are considering to install the electrical heating element below the bottom of the reboiler in a sealed jacket filled with a thermal oil.(the simplified sketch is attached).In order to increase heat-transfer,the oil into the jacket is continuous circulate through the jacket.
The reboiler's design pressure is 3 barg and it will be designed based on the ASME Code.
I would like to ask you following questions regarding the jacket's process design:
1. How can the oil's thermal expansion inside the jacket be considered. If the jacket's total volume must include the additional oil thermal expansion volume? Is it feasible to combine in the jacket both oil operation volume + expansion volume,given the fact the oil is heated and circulated through the same jacket?
2. How the max.operation/design pressure of the jacket can be defined?
3. If the jacket should be defined as a pressurized vessel and therefore protected by a PSV? Or the jacket can be defined as atmospheric vessel equipped with a breather valve?
Attached File  Oil Jacket.jpg   123.29KB   0 downloads
Thanks in advance, Mike

#2 PingPong


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Posted 07 April 2020 - 12:55 PM

Unless the jacket contains a big enough gas volume the pressure in the jacket would become gigantic when the oil is heated and therefor the jacket will require a PSV to protect it, and relieve the expansion when necessary. You can avoid the PSV to open during normal operation by installing a sufficient big expansion bellow in the oil piping.


But I really don't understand why anybody would design such a complicated system to provide heat to the bottom of a column.

Change the design: delete the jacket and pump, and insert a suitable heating element directly in the column bottom liquid.

#3 breizh


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Posted 07 April 2020 - 11:55 PM


To add to the other comments , a specification/operation sheet for thermal fluid (paratherm) where you can read the expansion volume ( about 10% for 100 c) . 

Additional volume must be considered to take account the expansion together with a PSV where the discharge should be routed to a safe location (catch pot) . 

Regarding the circulation pump  it should be a centrifugal pump , more robust /reliable than an air diaphragm pump .


my view


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Edited by breizh, 08 April 2020 - 12:13 AM.

#4 bmicky


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Posted 08 April 2020 - 08:49 AM



Thanks for your recommendations.


An option to use a heating element installed directly in the reboiler was checked in the past.The biggest problem is to find a electrical heating element which is certified for the hazardous area (Class 1 Div.1), the heating fluid is n-pentane. 


Thank you, Mike

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