Dephlegmater and reflux coils are not the samething

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acfixer69
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Dephlegmater and reflux coils are not the samething

Post by acfixer69 »

I read posts over and over using the terms a same thing. They are not and are not to be driven the same way. With a reflux coil a full knock down is required as the column is open above it and the idea is to send the condensed vapor down the column to re vaporize with the new vapors coming up the column. With a dephlegmater the whole purpose is to have a partial reflux with quick response to adjustments and only fill the plate below it. Some vapor passing is not a bad thing as it is passed to the product condenser as fores and is tossed anyway. I read a post today which lead me to start this topic. Sub-cooling vapor in a packed column not a good thing if it is excessive. It wastes energy and water. It can cause a bit of smearing also if power is raised to increase take off rate.
I feed water to my dephleg with the product condenser water output. This way the vapor escaping my dephleg during stabilization is guaranteed to be knocked down and I am sure i am not sub-cooling my column.
cayars
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Re: Dephlegmater and reflux coils are not the samething

Post by cayars »

You could certainly use a coil in a sealed CM column, think dimroth, as well as cross sectional tubes, tube(s) in shell or outside shell around the vapor tube holding coolant. Each of these methods done correctly could do full to minimal reflux as all vapor is routed to the product condenser. So in this case you actually would control them all basically the same, controlling the amount of water/coolant with a valve. Using any of those methods and you have a dephlegmator. The dephlegmator would be used to completely knock down all vapor to stabilize the column before takeoff to condense the heads for example.

A dephlegmator is just a device used to partially or fully condense vapor. The vapor stream flows vertically upwards and the condensate (condensed vapor) runs back down under the influence of gravity. They can be built numerous ways to achieve the vapor cooling.

What you must have is an open/unrestricted system so pressure doesn't build up. That can be an opening at the top of the column for something like a boka that CAN have it's takeoff sealed (with a valve), to a CM that can have a sealed column feeding the product condenser that must remain open (no valves) and unrestricted. While it's not common you could use all the same methods as the CM still to knock down the vapor for a boka.

In any reflux still you will typically fully reflux to start out with (no difference) before you start to take off product, so I'd disagree with one being only partial vs other fully refluxing. You'll start out similar on any reflux still. How you take off the product is different of course and the amount of reflux needed. For example a VM still can take off product under full reflux but a CM still will not produce product under full reflux and the cooling needs to be adjusted to allow product through the dephlegmator after stabilization.

What I think you're really getting at is the difference in the way you run a LM, VM or CM still vs the actual mechanism used to condense the vapor.
Programmer specializing in process control for ExxonMobil (ethanol refinery control), WT, Omron, Bosch, Honeywell & Boeing.
More than a decade working for NASA & FAA Tech with computer code used on Space Shuttles and some airline flight recorders.
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acfixer69
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Re: Dephlegmater and reflux coils are not the samething

Post by acfixer69 »

No I said what I meant to say doesn't matter type of either. :silent:
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Saltbush Bill
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Re: Dephlegmater and reflux coils are not the samething

Post by Saltbush Bill »

I fully agree with what you are saying AC, it annoys the hell out of me when i see the two words used in an interchangeabe way, as if they are the same thing.
Using the wrong terms for the wrong things just leads to confusion for all involved, new and old alike.
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Saltbush Bill
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Re: Dephlegmater and reflux coils are not the samething

Post by Saltbush Bill »

A bit more light reading to add to this thread. viewtopic.php?f=87&t=78276
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