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Creating And Maintaining Pressure In A Column
#1
Posted 24 March 2016 - 02:18 AM
#2
Posted 24 March 2016 - 04:38 AM
Hi,
In brief:
The pressure in a distillation column is normally created by a reboiler and is maintained by heat removal from the overhead product through a back pressure controller normally located at upstream of overhead condenser...
#3
Posted 24 March 2016 - 08:08 AM
Hi ,
Consider the resource attached .
Breizh
#4
Posted 24 March 2016 - 08:37 AM
You are missing the very important basics of Chemical Engineering by not knowing (or taking into account) the fact that it is the VAPOR PRESSURE of the various components being distilled inside the column that produces the operating pressure of the operation. Additionally, as Fallah has pointed out, the heat energy added at the reboiler raises the temperature - and, consequently, the vapor pressure.
In a distillation process you are dealing with liquids at their boiling points - which means that these liquids are saturated and, as such, generate a saturated vapor pressure while boiling. Engineering involves the practical application of the physical sciences. The distillation process is an engineering application of Physical Chemistry.
#5
Posted 24 March 2016 - 09:49 AM
Edited by p_stark95, 24 March 2016 - 09:50 AM.
#6
Posted 24 March 2016 - 12:15 PM
Hi,
It's not necessary in all cases a reboiler to be pressure source, a thermal (electrical) element can do the job in an autoclave as well ; also a compressor or pump can be the pressure source...
In a distillation column the operating pressure should not exceed the feed pressure...
Edited by fallah, 24 March 2016 - 12:38 PM.
#7
Posted 24 March 2016 - 02:50 PM Best Answer
As Fallah indicates, the feed pressure has nothing to do with setting the distillation column (or a reactor, or autoclave) pressure. It is the vapor pressure of the internal components that you are seeing in any pressure gauge that is on the vessel. IT HAS NOTHING TO DO WITH THE FEED'S PRESSURE.
As Fallah states, all you should be concerned about with regards to the feed to the column is that its pressure is high enough to OVERCOME the vapor pressure that already exists inside the column. Otherwise, it simply won't enter the column ..... the fluids in the column (that exist at a higher pressure) will backflow into the feed line and upstream!
The same conditions exist in a reactor or autoclave. You may not be introducing direct reboiler energy, but you are facilitating either a reaction or another source of energy that raises the vapor pressure(s) or generates a gas product and subsequently raises the internal pressure (which is usually controlled by a back-pressure control valve on the vessel's overhead vapor stream). The basic philosophy is that you must furnish a source of energy (either as a chemical reaction or externally applied with heat exchange in a reboiler - or electric element, as Fallah states) and be able to regulate and control that introduced energy. There are some processes where a pressurized inert gas blanket is kept over a liquid reaction, but these are very rare - and understandably difficult to control safely.
I think your problem is conceptual and due to a lacking of knowing or understanding the physical processes taking place. This is either a lack of good teaching or a lack of thorough and detailed study into the matter, the basic science applied, or exposure to the actual processes in an engineering lab or in an actual industrial process.
#8
Posted 24 March 2016 - 09:23 PM
Edited by p_stark95, 24 March 2016 - 09:28 PM.
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