Cooling coil wasn't working well enough, fixed and graphed

Distillation methods and improvements.

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binoscope
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Joined: Thu Nov 16, 2017 1:42 pm

Cooling coil wasn't working well enough, fixed and graphed

Post by binoscope »

I recently built a new boka. 2000w copperhead stills boiler, 50mm x 1100mm copper main tube, sight glass then a standard boka head with about a 150mm long double wound 6mm copper cooling coil.

This is my new creation
IMG_20171112_175929small.jpg
Love watching the sight tube in action
IMG_20171112_175556small.jpg
I was having issues with cooling in that even at 4 litres a minute with almost cold cooling water coming out I was seeing vapour out the top just enough so I could see a very small amount condense then vaporise immediately. All through the run I could get small smells of ethanol. I was outside on a very windy so and the amounts were small so I continued, so it was a considered risk. The point of this post is about what I did to fix it and some real measured results that surprised me.

I decided that the issue was probably the vapour was flowing directly through the centre of the coil to the vent hole. I decided to stuff the middle with a rolled up piece of copper mesh 60x140mm rolled into a tightish cylinder then pushed into to lower half of the middle of the coil. So the vapour had to flow mostly now up the very outsides or between the two layers of the coil at least until half way when they could flow back to the middle again.

The mesh inside the bottom of the coil
Extra packing
Extra packing
I did some graphs of the flow rate vs both outlet water temperature and the temperature that the very top of the coil just inside the vent holes both with and without this extra packing. This was just done with water BTW. The results were amazing to me.
vent_temps.jpg
the green and blue lines are as expected, they are the cooling water outlet temp (input water was 18.5 deg C) it is simply there is X amount of heat to get rid of and increasing the flow lowers the temp. However that may be useful as gives an idea about the temp of the reflux liquid (possibly)

The red line is without the packing, I was seeing vapour at the exit holes at all flow rates. So this is why I was getting a bit of vapour during my run

The purple line is the vent temperatures after I put in the packing down the lower half of the middle of the coil. At flow rates greater than 1 L/Min I had a 20 deg C lower temperature (compared to without the packing) at the top of the column inside the outlet vents! Actually only at flow rates less than about 0.5 L/Min did I see any sign of vapour at the vent at all, so my issue is solved. I know people have said that mesh packing around a coil helps but I'd never seen anyone try to quantify it like this graph does. I could also see a knee at the 1L/min mark. This is with water so possibly I will repeat some of this with a real wash to map top end temps against flow rates for ethanol as well.

This begs the question is there an optimum way to place packing around a coil to increase its efficiency? I only did this one simple change and made a massive difference to the efficiency, what other subtle things are there to learn?

I'm also thinking about another graph that also plots the reflux liquid temperature vs all of the above as I have heard that the closer the reflux ethanol is the re-vapourizing the temperature as it returns to the packing the better? To make this I was thinking of just running with water with the takeoff valve wide open and measuring the temperature of the distillate and mapping this to water flow etc.

Anyways hope this is interesting to someone out there :-)
BugHunter
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Location: Bay Area, California

Re: Cooling coil wasn't working well enough, fixed and graph

Post by BugHunter »

Very nice data. Thanks for sharing it.
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Kareltje
Distiller
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Joined: Tue Feb 09, 2016 4:29 pm

Re: Cooling coil wasn't working well enough, fixed and graph

Post by Kareltje »

I second that ^^^^
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