Vapor speed, reflux condenser size, power input

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MtRainier
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Vapor speed, reflux condenser size, power input

Post by MtRainier »

I'm trying to get my head around the parameters needed to maximize reflux at a given desired takeoff rate.

I have a 5kW immersion heater that I can adjust the power on, a 6 inch tall dephlegmator with lots of open space, and a column that's 4 inches wide packed tightly with stainless scrubbies. I'd like to take off around two liters per hour.

I can monitor the temperature of the water coming out of the reflux condenser. If I run the power at around 1000W, there is not much total heat getting up to the condenser and the water temp needs to be very hot in order to let any product through. I just trickle a little water through the condenser.

If I turn the power up to around 3000W there is much more heat in the vapor getting to the condenser, so the water temp coming out of it is lower despite the higher amount of heat being dropped.

I suspect the answer lies in the vapor speed calculation somehow and the inner surface area of my reflux condenser, but don't know what to take into consideration. I found rad14071's vapor speed calculator here, but I don't understand how to apply the number it gives.

I was tempted to just open up the water to the reflux wide and start turning up the power to see when it hits the point where vapor gets past no matter how much water I put in. Then it would be blowing vapor right past it. Then I can start turning down power until no product comes out and that would be my maximum power. Then I can start turning down cooling with the needle valve until I get product out at the rate I want.

Is that a reasonable approach or does running at such a high power with a high vapor speed let un-redistilled product to just blow straight up the column packing and make it out at some point?
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Re: Vapor speed, reflux condenser size, power input

Post by Setsumi »

MtRainier wrote: Sat Jun 12, 2021 7:32 am I was tempted to just open up the water to the reflux wide and start turning up the power to see when it hits the point where vapor gets past no matter how much water I put in. Then it would be blowing vapor right past it. Then I can start turning down power until no product comes out and that would be my maximum power. Then I can start turning down cooling with the needle valve until I get product out at the rate I want.
myself think that is the way. then again i rather take off slower, heads and tails have a way to mess with my product.
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OtisT
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Re: Vapor speed, reflux condenser size, power input

Post by OtisT »

Hi MtRainier

With a CM rig, I would not worry too much about the temp of water output from you condenser. The output temp will be what it is, based on other factors. Here is a simplified version of tuning to get you going.

First I would verify that your Dephlag can knock down all of your heat. Open up your dephlag full flow and crank the heat to full power and verify that no vapor is passing the condenser.

Next turn down coolant flow slowly until you start seeing some vapor pass, then increase the cooling flow slightly until you are back to 100% reflux.

If your column is flooding at full power, back the power down slowly until you are not flooding. Some folks here recommend you run with a slight amount of flooding. You may not see any flooding at all with your 4” column.

Run the column at 100% reflux for 5-10 minutes to let it reach equilibrium.

Monitor vapor temp at the head and slowly decrease your cooling flow until you reach your desired output rate. Your vapor temp will tell you if you are pulling off product too fast for your column to keep up with.

Remember that when adjusting heat/cooling, do so in small increments and be sure to give the system time to react to your changes. Packing with a higher mass require more time for adjustments to propagate through the system than lighter packing. I.e. your column of scrubbies will react to and settle down from changes much faster than a column packed with marbles or rocks.

Hope this helps,
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MtRainier
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Re: Vapor speed, reflux condenser size, power input

Post by MtRainier »

Thanks, Otis.

This is very helpful. I'll try the trick with full flow through the dephleg and see how much power I can put in there until I get output. seems like it should change a bit throughout the run as the ratio of ethanol to water in the boiler changes and the boiling will require a little more energy for the same amount of vapor generated as the run goes on.

I don't ever flood the packing on this 4 inch column. I put a plate at the very bottom with bubble caps in it to kind of hold up the first level of scrubbies to get it started out. I assume if I was going to flood I'd see it in that bottom flute section for sure, but I don't. I guess that bubble plate with 1/4" of liquid on it does qualify for a "slight amount of flooding" though.

I have a batch of SSS that I've kind of been playing with trying to see what I can really do with this. It's on it's third run through the packed column with dilution afterwards. I'm not really doing cuts aside from fores as I use the same liquid over and over to tune the operation.
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Re: Vapor speed, reflux condenser size, power input

Post by kimbodious »

Flooding in a reflux column is a top down situation. Flooding occurs when the condensate from the reflux condenser builds up on top of the packing. You might not be able to pick up that you are flooding by looking at the plate at the bottom of the column.

PrairiePiss describes it well here https://homedistiller.org/forum/viewtop ... =1&t=42984
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MtRainier
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Re: Vapor speed, reflux condenser size, power input

Post by MtRainier »

kimbodious wrote: Sat Jun 12, 2021 2:35 pm Flooding in a reflux column is a top down situation. Flooding occurs when the condensate from the reflux condenser builds up on top of the packing. You might not be able to pick up that you are flooding by looking at the plate at the bottom of the column.

PrairiePiss describes it well here https://homedistiller.org/forum/viewtop ... =1&t=42984
Thanks. I'm not flooding the top. I can see it.
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