Problems running VM

Vapor, Liquid or Cooling Management. Flutes, plates, etc.

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Matt64
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Re: Problems running VM

Post by Matt64 »

Thanks for the comment. The column is 64mm ID and the ball valve is 3/4" connected to 15mm copper pipe. Are you saying that this will choke the vapour too much even with the valve fully open?
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Re: Problems running VM

Post by Matt64 »

bunny wrote: Tue Aug 30, 2022 6:58 am
Yummyrum wrote: Tue Aug 30, 2022 2:45 am Regarding the column height . Can't comment from experience on that but concencus is that anything over 20:1 height to diameter is no gain
There is also a consensus that anything over 20:1 height to diameter can add to take off speed. However, I don't know how to figure this.
What sort of take-off speed could I expect from my very tall 64mm ID column?
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Re: Problems running VM

Post by bunny »

Matt64 wrote: Tue Aug 30, 2022 7:07 am What sort of take-off speed could I expect from my very tall 64mm ID column?
It's not the height of the column that's your problem. It's the tiny take off tube setting your RR way high and holding you back.

I'm not expert on this but if you are using a valve to control the vapor, you need to get the take off tubing diameter similar to the main column so you can actually adjust the RR and take off rate.

Sooner or later the VM designers will check in with some solid info.
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Re: Problems running VM

Post by Salt Must Flow »

Matt64 wrote: Tue Aug 30, 2022 7:07 am
bunny wrote: Tue Aug 30, 2022 6:58 am
Yummyrum wrote: Tue Aug 30, 2022 2:45 am Regarding the column height . Can't comment from experience on that but concencus is that anything over 20:1 height to diameter is no gain
There is also a consensus that anything over 20:1 height to diameter can add to take off speed. However, I don't know how to figure this.
What sort of take-off speed could I expect from my very tall 64mm ID column?
I'd guess you should be able to get nearly 3 lpm takeoff rate. I'd use a 1" vapor takeoff valve, ideally a gate valve. Gate valves give you extremely precise and repeatable control. My 3" easily gets 3.2 lph at 50% power (2750W). I suspect I might be able to push it faster, but I haven't really tried yet.

Get yourself a Borosilicate Graduated Cylinder and you can easily calculate your takeoff rate. This was a necessity for me when keeping notes, bumping up power, measuring takeoff rate and testing ABV to see if the % drops.
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Re: Problems running VM

Post by Yummyrum »

I don't see a problem at all with the take off valve size .
Large valves were desired by those that wished to use them for stripping runs where 1:1 reflux ratio was still only as good as you can get . However , if you are wanting Nuetral or Azeo then you will be running with a reflux ratio closer to 10-20:1

So having a 3/4" valve on 2" column is quite in the ball park .

I use a 1.25" valve on my 4" and it's almost open when I use 4 plates under it because I'm needing a low RR.
When I stick it on 2metres of packing , it's Barely half open because I'm running with a high RR.

When I use that valve on my 2" VM which narrows to the same diameter (1.25" ) at the take off , the valve is barely cracked open in use . Here are pics of how little the valve is open . You can see on the handle I have marked the "just closed" and where it is normally running on the 2" still . The first pic is looking inside the valve to get a visual of how little open are there is at normal operating point on that 2" still .

The mark to the right is closer to where it sits on the 4" packed still .It is obvious that if the valve is large , it's operation is finicky where as if it is smaller , you have more wiggle room
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Matt64
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Re: Problems running VM

Post by Matt64 »

That's great thanks - I will stick with the valve and give stainless SPP a go. This still will only produce vodka, as stripping is carried out in a separate alembic still.

Cheers,
Matt
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Re: Problems running VM

Post by Matt64 »

OK, I finally got time to retest my column again. Now filled with stainless SPP instead of plates.

Warmed up and with temperature by the take-off valve sitting around 75°C, left it for a time to balance but when the vapour take-off valve was opened, no output at all, so I gradually increased the heat bit by bit. Increased this over about an hour but still nothing until the heat input was creating sufficient upward vapour flow that the column must be flooding (which I obviously do not want). Then the distillate came over but of course way too fast and all the separation was gone.

Is it my column design or its operation that is at fault? Is it possible for the SPP packed column to be too tall for the vapour to exit in a controlled manner?

I am clearly not understanding the physics involved here, so would appreciate any input. Thank you!
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Re: Problems running VM

Post by Yummyrum »

What sort of power are you running Matt ?
2kw is pretty much a ball park for most 2” Packed reflux stills . Much less won’t create enough reflux to be able to take off at a reasonable rate . Much more than 2kw will result in flooding .

Typical takeoff rate should be around 1l/hr .

If you can add a sight glass above the packing and below the take off , it sure will help you work out if its flooding or not .
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Re: Problems running VM

Post by Matt64 »

Yummyrum wrote: Thu Jan 19, 2023 3:23 am What sort of power are you running Matt ?
2kw is pretty much a ball park for most 2” Packed reflux stills . Much less won’t create enough reflux to be able to take off at a reasonable rate . Much more than 2kw will result in flooding .

Typical takeoff rate should be around 1l/hr .

If you can add a sight glass above the packing and below the take off , it sure will help you work out if its flooding or not .
We are propane fired, so have plenty of power if needed. There is a sight glass at the base of the column and when I had brought the column up to temperature, I reduced the power down low. Temp in the pot was 78°C and 75°C at the top of the column and I could see dripping down from the packing through the port hole at the base of the column.

In order to get any flow at all from the take-off valve, I needed to increase the power to such an extent that the vapour drops were being forced up, not dripping down. So, I concluded that the column was now flooding and the amount that came over the take-off valve seemed to validate that thought.

The temp at the top of the column was sitting around 75°C and the reflux condenser sits about 1" above that. I just don't understand why I am getting no vapour exiting the take-off valve at all, unless I increase the gas so much that the column is flooding. My column is either super sensitive, or else I have a fundamental design or operational flaw that I need to resolve :?
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Re: Problems running VM

Post by OtisT »

Are you by chance running water only? Water vapor rises at 1 atmosphere while alcohol vapor will sink. If you are testing with water, I could see you getting little to no product output under 100% reflux with the VM valve slightly open. Cranking up the heat would create a little more pressure and would push some vapor on to your PC but most will still go up.
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Re: Problems running VM

Post by haggy »

I have three observations.

First, your reflux condenser may be oversized. Your RC heat transfer area is about 1.5 ft^2, where normal area for even a 4" column is about 0.5 ft^2. For a 35% pot ABV at 2000 watts, your RC needs about 0.5 L/min or less coolant water flow to condense the vapor off the top even if not taking any vapor off the side. A higher water flow rate than 0.5 L/min will subcool the condensed reflux liquid.

What is your RC coolant water approximate flow rate? Try to reproduce the observed RC water flow rate stream and measure it.

If much greater than 0.5 L/min, subcooled reflux liquid is hitting the top packing. Maybe that cooling is reducing the top vapor rate and stopping the vapor take-off. A sight glass at the top would really help understand the problem. You could insert a small section with a sight glass in it.


Second, we need to know the power (watts) the your gas burner is providing. Then we can relate it to other reflux columns. Here is a way to determine the approximate watts from the gas burners.

Put 20 liters of water in the boiler. Measure the start temperature ( TS ) of the water. Set the burner at a low value and heat up the boiler. Measure the time in minutes it takes to heat it up until it boils at 100 C. Repeat this for 3 different settings of the burner ( low- middle -high ). Then the watts generated for each burner setting and 20 Liters of water is found from this equation:

watts = 1397 * ( 100 -TS ) / min Time

Wait, I just saw that you have a 250 L pot. Very big for a 2.5 " column. How many liters do you charge each run with? So maybe you should start with 50 L instead of 20 L for the test. Use 3492 instead of 1397 in the equation.



Third, with 35% ABV in the boiler the start boiling temperature should be 84-85 C, not the 78 C you measure. Some error in that reading. Maybe we should question the top temperature reading also. Have you ever tried to run a mash ( about 10% ABV ) only in the pot?


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Re: Problems running VM

Post by OtisT »

OtisT wrote: Thu Jan 19, 2023 10:09 am Are you by chance running water only? Water vapor rises at 1 atmosphere while alcohol vapor will sink. If you are testing with water, I could see you getting little to no product output under 100% reflux with the VM valve slightly open. Cranking up the heat would create a little more pressure and would push some vapor on to your PC but most will still go up.
Adding more questions for you Matt after looking at the pics of your rig..... Does your thermometer probe extend into the column? If so, does it have a drip shield to prevent liquid reflux from raining on the probe?

****

I’m just trying to square all the symptoms. All that plate/packing conversation aside, if you have alcohol vapor in your column being refluxed by your RC and your VM valve is open, I can’t think of any reason why you don’t get alcohol product output.

Here is what I think is going on:

You are running with water only in the boiler. You won’t get product output from a VM running water only because water vapor is too light.

The reason why you see 75c below the RC is you have liquid water reflux raining on the probe, so you are not measuring vapor temp which would be near 100c for water vapor.

The reason you get lots of product output at very high power is because the column has finally flooded to the top and it is just pouring liquid from your column to your VM port.

Just a guess, but it’s the only thing I can think of that explains your wonky symptoms.

You could put this theory to bed if you answer the question about what you are running in your boiler.

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Re: Problems running VM

Post by Matt64 »

OtisT wrote: Fri Jan 20, 2023 1:09 pm
OtisT wrote: Thu Jan 19, 2023 10:09 am Are you by chance running water only? Water vapor rises at 1 atmosphere while alcohol vapor will sink. If you are testing with water, I could see you getting little to no product output under 100% reflux with the VM valve slightly open. Cranking up the heat would create a little more pressure and would push some vapor on to your PC but most will still go up.
Adding more questions for you Matt after looking at the pics of your rig..... Does your thermometer probe extend into the column? If so, does it have a drip shield to prevent liquid reflux from raining on the probe?

****

I’m just trying to square all the symptoms. All that plate/packing conversation aside, if you have alcohol vapor in your column being refluxed by your RC and your VM valve is open, I can’t think of any reason why you don’t get alcohol product output.

Here is what I think is going on:

You are running with water only in the boiler. You won’t get product output from a VM running water only because water vapor is too light.

The reason why you see 75c below the RC is you have liquid water reflux raining on the probe, so you are not measuring vapor temp which would be near 100c for water vapor.

The reason you get lots of product output at very high power is because the column has finally flooded to the top and it is just pouring liquid from your column to your VM port.

Just a guess, but it’s the only thing I can think of that explains your wonky symptoms.

You could put this theory to bed if you answer the question about what you are running in your boiler.

Otis
Just to confirm that I was running 50 litres of 35% ABV wash in the still. It wasn't a full boiler as I just wanted to run a quick test on the packed column.

There isn't a shield above the temperature probe. That's a good point that I should fix.

I just can't work out why I can't get any output from the vapour valve unless I crank the heat up high and then all it's doing is flooding the column.

The 2" column is too narrow for the boiler but it's what I have.
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Re: Problems running VM

Post by bunny »

Matt64 wrote: Mon Jan 23, 2023 3:44 am
OtisT wrote: Fri Jan 20, 2023 1:09 pm
OtisT wrote: Thu Jan 19, 2023 10:09 am Are you by chance running water only? Water vapor rises at 1 atmosphere while alcohol vapor will sink. If you are testing with water, I could see you getting little to no product output under 100% reflux with the VM valve slightly open. Cranking up the heat would create a little more pressure and would push some vapor on to your PC but most will still go up.
Adding more questions for you Matt after looking at the pics of your rig..... Does your thermometer probe extend into the column? If so, does it have a drip shield to prevent liquid reflux from raining on the probe?

****

I’m just trying to square all the symptoms. All that plate/packing conversation aside, if you have alcohol vapor in your column being refluxed by your RC and your VM valve is open, I can’t think of any reason why you don’t get alcohol product output.

Here is what I think is going on:

You are running with water only in the boiler. You won’t get product output from a VM running water only because water vapor is too light.

The reason why you see 75c below the RC is you have liquid water reflux raining on the probe, so you are not measuring vapor temp which would be near 100c for water vapor.

The reason you get lots of product output at very high power is because the column has finally flooded to the top and it is just pouring liquid from your column to your VM port.

Just a guess, but it’s the only thing I can think of that explains your wonky symptoms.

You could put this theory to bed if you answer the question about what you are running in your boiler.

Otis
Just to confirm that I was running 50 litres of 35% ABV wash in the still. It wasn't a full boiler as I just wanted to run a quick test on the packed column.

There isn't a shield above the temperature probe. That's a good point that I should fix.

I just can't work out why I can't get any output from the vapour valve unless I crank the heat up high and then all it's doing is flooding the column.

The 2" column is too narrow for the boiler but it's what I have.
Your column is 2.52" id
Your built in RR is : 0.5/2 x 0.5/2 x 3.14= 0.19625; 2.52/2 X 2.52/2 x 3.14= 4.985; 4.985/0.19652= 25.40 with the valve wide open

If we assume your thermometers are relatively accurate, your 75c at the top of the column appears to be too low to function properly.
My guess is your SPP has not fully heated up yet and is not steaming 78*+ vapor to your RC.
It appears your 2.8m column is also not insulated and you are losing lots of heat.
If you are seeing a small amount or liquid passing through your site glass I would suggest this is passive reflux.
When you gradually increased the heat did the 75c move up ?

How full did you fill the SPP?

As a starting place,I'm going to suggest you remove the top 6 inches of SPP and stuff a scrubby on top of the stacked SPP.
This should keep the reflux from flashing and boiling up and out your takeoff.


First insulate the column if it isn't already.
I don't know how your old plates heated up, but I do know SPP are very slow to heat up compared to scrubbies.
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Re: Problems running VM

Post by Salt Must Flow »

Matt64 wrote: Mon Jan 23, 2023 3:44 am I just can't work out why I can't get any output from the vapour valve unless I crank the heat up high and then all it's doing is flooding the column.
This is very strange. It makes me wonder if you would get proper vapor output if you installed something like a 'centering collar' just below your reflux condenser. My hypothesis is that it may create a slightly higher pressure at the top of your column and cause vapor to be forced out of the vapor takeoff.

This is the type of centering device I use and it works great to direct reflux straight down through the center of my sight glass. Those petals can be bent to create more or less restriction which I suspect would affect the pressure at the vapor takeoff.
Centering Plate.jpg
I have a 3" column and I made the VM head with a 2" tee. The vapor takeoff is a 2" x 1-1/2" concentric reducer connected to a 1" gate valve. I deliberately used a 2" tee thinking it 'might' create a higher pressure zone, but I don't know if it does provide any benefit other than lower cost for parts.
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Re: Problems running VM

Post by Sporacle »

:D From someone who has never run a VM, but has run a CCVM.
Personally I would return to scale.
Go back to a 20:1 or slightly better ratio for your column, pack it with one of the packings recommended here. I use copper mesh.

I'm saying this because when you use a column of this height (20:1) then there are literally hundreds of people who have done the exact same thing.

You should be able to get 96ish at a touch under a litre per hour (based off CCVM numbers)

Once you have that dialled in you can scale up, it may be as simple as breaking your column into three parts and adding some ferrules. This will give you the ability to add height as you understand how the still runs.

Just my two cents, I think you need to get a base reading from a know design prior to going outside the common design parameters
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Re: Problems running VM

Post by StillerBoy »

Matt64 wrote: Thu Jan 19, 2023 2:59 am Warmed up and with temperature by the take-off valve sitting around 75°C, left it for a time to balance but when the vapour take-off valve was opened, no output at all, so I gradually increased the heat bit by bit. Increased this over about an hour but still nothing until the heat input was creating sufficient upward vapour flow that the column must be flooding (which I obviously do not want). Then the distillate came over but of course way too fast and all the separation was gone.

Is it my column design or its operation that is at fault? Is it possible for the SPP packed column to be too tall for the vapour to exit in a controlled manner?
The column is flooding because of improper packing holder, and improper power management.. nothing to do with the value size.. if a column floods it is because it's holding distillate from returning back..

But are assuming the column is flooding.. how do you that.. if the column was really flooding, there would be distillate either coming out of by the valve (if opened) or over the top of the column..

I've run a VM (old style) 2" x 38" packed with SPP on a 1/2" valve, with no issue of flooding or no vapors coming out..

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Re: Problems running VM

Post by bluefish_dist »

Mars, I like that still head. Looks a lot like mine.

Back to the problem at hand, have you tried running with no packing? Would verify if the problem is due to the packing or if it’s a base still issue.

Btw this is 6” down to 4, then down to 3”.
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Re: Problems running VM

Post by Matt64 »

Thanks for all the input.

The SPP sits around 4" below the vapour take-off valve at the moment.

The day I ran the test was very cold at around 0 - 4°C ambient. The top of column temperature did reach 77.3°C when the power was increased but that much power was pushing the reflux liquid back up the still and eventually caused it to flood and rise over into the take-off valve.

The column isn't insulated.

The column is in two parts, so I will try taking off the upper section to reduce the height. This will approximately half the height of the column but I will measure the two parts to confirm. I will rerun the test to see if I can get vapour out of the valve with the reduced height.

I am working on the assumption that reduced height will need less power input in order to get the vapour to the top of the column and hopefully out of the vapour valve.

We did test the lower part of the column originally (with the plates) on a small 10 litre test still. The problems started occurring when we scaled up, moving the column to the larger still and increased the height in search of greater purity. Hopefully with stainless SPP, the original height will be sufficient.

The goal is a smooth high purity vodka from the 35% ABV barley wash.
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Re: Problems running VM

Post by Matt64 »

Just measured the lower half of the column at 1.4 metres.

Packed with SPP, is that likely to be enough to achieve the smooth high purity vodka that I am looking for?

Thanks,
Matt
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Re: Problems running VM

Post by bunny »

Matt64 wrote: Tue Jan 24, 2023 3:31 am Just measured the lower half of the column at 1.4 metres.

Packed with SPP, is that likely to be enough to achieve the smooth high purity vodka that I am looking for?

Thanks,
Matt
Probably yes. However the rate of collection is going to be a lot less than you hoped for due to your 25.4 to 1 RR.
What size spp are you using?
Have you insulated your column?
Did you check if your column is draining properly?
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Re: Problems running VM

Post by kimbodious »

Get right back to basics. Forget about thermometer readings. Feel where the heat is getting up to on the column. Likewise feel where the coolth from the Reflux Condenser is coming down to. You’ll never get output if your RC is creating a cold area below the offtake.

Start your run with the valve open and fiddle with heating power and coolant flow until you are confident you are getting reliable output (it won’t be highest purity). Then you can start getting fancy with putting your column in to equilibrium, again feeling where those thermal boundaries are.

+1000 on the column insulation once you are confident you have got the basics sorted.
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Re: Problems running VM

Post by Sporacle »

100% with Kimbo, just get back to basic distillation and insulate your column, don't worry about anything else. Let the heat and reflux do its thing
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Re: Problems running VM

Post by OtisT »

bunny wrote: Tue Jan 24, 2023 7:47 am
Matt64 wrote: Tue Jan 24, 2023 3:31 am Just measured the lower half of the column at 1.4 metres.

Packed with SPP, is that likely to be enough to achieve the smooth high purity vodka that I am looking for?

Thanks,
Matt
Probably yes. However the rate of collection is going to be a lot less than you hoped for due to your 25.4 to 1 RR.
What size spp are you using?
Have you insulated your column?
Did you check if your column is draining properly?
Matt, 1.4 meters of SPP is more than enough packing height to get the best separation you can achieve on a 2” column. Any taller won’t buy you any speed or quality improvements.

Matt’s bottleneck for collection speed, assuming he figures out how to get vapor to the top of his column, is the diameter of his column. Column diameter determines how much power can be applied and still have a chance of getting good separation. There is some variation on this max power, dependent upon the packing used, but max power will be around 1500w.

The 3/4” valve is more than adequate size for a 2” column. With power limited by the 2” column diameter, you will find a good RR and produce a clean product with the VM valve open only a small amount.

Otis
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Re: Problems running VM

Post by bunny »

OtisT wrote: Tue Jan 24, 2023 6:02 pm
bunny wrote: Tue Jan 24, 2023 7:47 am
Matt64 wrote: Tue Jan 24, 2023 3:31 am Just measured the lower half of the column at 1.4 metres.

Packed with SPP, is that likely to be enough to achieve the smooth high purity vodka that I am looking for?

Thanks,
Matt
Probably yes. However the rate of collection is going to be a lot less than you hoped for due to your 25.4 to 1 RR.
What size spp are you using?
Have you insulated your column?
Did you check if your column is draining properly?
Matt, 1.4 meters of SPP is more than enough packing height to get the best separation you can achieve on a 2” column. Any taller won’t buy you any speed or quality improvements.

Matt’s bottleneck for collection speed, assuming he figures out how to get vapor to the top of his column, is the diameter of his column. Column diameter determines how much power can be applied and still have a chance of getting good separation. There is some variation on this max power, dependent upon the packing used, but max power will be around 1500w.

The 3/4” valve is more than adequate size for a 2” column. With power limited by the 2” column diameter, you will find a good RR and produce a clean product with the VM valve open only a small amount.

Otis
Otis:

We must be looking at different set-ups.
In Matt64's first post he clearly states his column has a 64mm id(2.5")
In his 10th post he reiterates 64mm column id,(2.5") 3/4 ball valve, and the pipe coming off his valve is 15mm (presumable 13mm id- 1/2").
These sizes are easily visible on his picture below:
image.jpeg
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Can you tell me what RR you believe he will have with the valve wide open?
What kind of collection rate in ml/hour should he get?
What kind of collection rate should he get with the valve open only a small amount?

"Any taller won't buy you any speed or quality improvements."
I personally am leaning away from your statement above and leaning towards "der wo's" and "Odin's" views here:
viewtopic.php?p=7507268#p7507268
I haven't seen anything convincing written on that subject since the above from 2016.
Please direct me if you know of any.

I think Matt64's biggest problems that need to be solved before he can move forward are the column drain/flooding issue and the insulation.
Since this is supposed to be a neutral machine I would switch to LM. (But that's all I ever use :D)
OtisT
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Re: Problems running VM

Post by OtisT »

I’m just basing it on my practical experience running something of similar size for a few years. I don’t recall the production rate, but it can be found somewhere here on HD. Regardless, it was painfully slow which is why upgraded to a 3” column and more recently, 4”.
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Matt64
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Re: Problems running VM

Post by Matt64 »

Thanks to everyone who has input and made suggestions!

We go again.

I removed the top half of the column, leaving the lower 1.5m section. This is filled with 125cm of SPP with a scrubber top and bottom of the SPP and a 10cm gap from the top of the packing to the 1/2" vapour take-off valve above it. Replumbed it and ran again.

Still to do is: column insulation and a drip guard above the temperature probe that sits opposite the vapour take-off valve.

Filled the pot with 50 litres of 30% ABV barley wash, left the vapour take-off valve open (no equilibrium stage) and warmed it all up.

Good news: We have distillate exiting the column and filling the parrot :D

So then I ran a series of tests with the vapour take-off valve at different settings to measure flow rate and also worked out the maximum gas setting I could use before the draining liquid was forced back up the column, potentially flooding it. I will do a separate test to calculate this setting in kWh of gas.

During the test, I collected just over a litre of distillate in total, so never got past the heads stage.

I have pulled together all the data in this spreadsheet. Hope it makes sense if interested.
Test Feb 1, 2023.xlsx
Vodka column test data
(13.32 KiB) Downloaded 36 times
With the vapour port open settings, I had these flow rates:
Initially open full: 750ml per hour
Closed for gas input testing and then reopened by half: 424ml per hour
Opened to 3/4: 679ml per hour
Opened fully: 923ml per hour

Just a reminder that the boiler is 250 litres and the column is 64mm internal diameter.

Does a litre an hour seem about right? That makes for a very long run!

One thing I could not rationalise is that the temperature below the reflux condenser started dropping when the vapour take-off valve was closed by half, from initially being fully open. Temperature started rising again when the vapour valve was being opened again.

The pot temperature is measured in the lid and with the boiler only being partially filled, the analogue temperature probe was about 80cm above the liquid level.

The level of coolant needed to keep the reflux condenser stable was about 40 seconds per litre. Mains water here is about 10°C. That's a lot of water, approx 99 litres for 1 litre of distillate per hour. Water currently costs here 32 Pence per hectolitre.

Now that we have some output, my next step will be to run again with 160 litres of 30% ABV wash and cut the distillate. I am expecting approximately the cuts to work as follows. Do they sound about right?
Vodka cuts
Vodka cuts
image.png (5.88 KiB) Viewed 644 times
Final question - how long should I expect the equilibrium stage to take? I had worked on the basis of 2 hours but with 2 hours warmup of the still charge, that's a big chunk of the day gone before collection starts.

Thanks again for your input.
Matt
----------------------------------------------------
UK Distilled Spirits Producer NRU/D/03/19
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Re: Problems running VM

Post by greggn »

Matt64 wrote: Thu Feb 02, 2023 6:29 am
One thing I could not rationalise is that the temperature below the reflux condenser started dropping when the vapour take-off valve was closed by half, from initially being fully open. Temperature started rising again when the vapour valve was being opened again.

The slower takeoff rate created a higher reflux ratio and allowed the more volatile fractions to stack in the top of the column.
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Re: Problems running VM

Post by StillerBoy »

Matt64 wrote: Thu Feb 02, 2023 6:29 am One thing I could not rationalise is that the temperature below the reflux condenser started dropping when the vapour take-off valve was closed by half, from initially being fully open. Temperature started rising again when the vapour valve was being opened again.
+1 on what "greggn" stated..

What the temp probe indicated was that the ABV of vapors or vapor behavior occurring.. the drop in temp indicate a higher purity of the alcohol.. and increase in temp indicates/causes a reduction of alcohol purity..

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Re: Problems running VM

Post by OtisT »

Hi Matt,
Agree with stillerboy and Greggen. Seeing the temp drop by reducing the VM opening shows that you should not be running with the valve fully open and you don’t need a bigger opening.

The top of column temp can also answer your question about column equilibrium as well as help you learn what your max power should be for that column.

1) Get it producing at 100% reflux and watch your vapor temp rise until it stabilizes. If your temp is too high such that you are not fractioning/separating well, reducing power will improve that separation and your vapor temp will go down. Reduce power slowly and in small increments and watch your temp drop with each change. High mass packing like SPP, rocks or solid ceramic rings will take longer to react to changes in power compared to low mass packing like copper mesh. Note how long it takes for the change to fully propagate. Keep doing this and there will come a point when your temp no longer drops with a reduction in power. This is close to the max power level you should run at for the best separation.

2) Once your power is set and your temp is stable, open your VM port a small amount and wait to see product output and any change in vapor temp. If no change in vapor temp, open a bit further and wait to see the results. Keep doing this until your vapor temp rises as a result of opening the valve more. Close it back down to the previous setting and you should be set for getting your best ABV at the fastest takeoff rate for that level of separation.

There are caveats to what I wrote above, but it is the basics as I see them.

So the short answer for how long does it take to equalize you column is however long it takes for your vapor temp to stabilize at your desired power level. For me, 10-15 minutes is plenty of time.

Otis
Otis’ Pot and Thumper, Dimroth Condenser: Pot-n-Thumper/Dimroth
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