Problems running VM

[Matt64]

Probably a daft Idea , but what about a bank of smaller stills .
A 50 litre keg with a 3” column pumps out over 2l/h of high. Quality and can be easily run in a day . Get 4 of these and you’d be making 10 L/H easily .
And they don’t need a 2 Story warehouse and a staircase to adjust .

Not such a daft idea! I was thinking that I could even bolt on a second column running parallel to the first. That should double output. Add two more to treble it etc..

My numbers seem out though. I was getting 1 l/h from my 2.5" column and yet you are getting 2l/h from a column just 1/2" wider. Sorry if I have missed the detail in previous posts, but how tall is your 3" column and what size is the takeoff valve?

[bluefish_dist]

Not such a daft idea! I was thinking that I could even bolt on a second column running parallel to the first. That should double output. Add two more to treble it etc..

My numbers seem out though. I was getting 1 l/h from my 2.5" column and yet you are getting 2l/h from a column just 1/2" wider. Sorry if I have missed the detail in previous posts, but how tall is your 3" column and what size is the takeoff valve?

A 2” should do 1l/hr easily. A 3” has double the area of a 2”, so it should do 2l/hr as the save velocity. Your 2.5” should probably run around 1.6l/hr vs the 1l/hr you are getting. If you can’t run that fast, it is probably a function of how many plates or the length of the packed section.

[Matt64]

A 2” should do 1l/hr easily. A 3” has double the area of a 2”, so it should do 2l/hr as the save velocity. Your 2.5” should probably run around 1.6l/hr vs the 1l/hr you are getting. If you can’t run that fast, it is probably a function of how many plates or the length of the packed section.

Packed section too tall, or not tall enough?

[bluefish_dist]

A 2” should do 1l/hr easily. A 3” has double the area of a 2”, so it should do 2l/hr as the save velocity. Your 2.5” should probably run around 1.6l/hr vs the 1l/hr you are getting. If you can’t run that fast, it is probably a function of how many plates or the length of the packed section.

Packed section too tall, or not tall enough?

Not tall enough. If you want faster with high proof, taller and larger diameter are the way to get that. Taller alone should get you 50% faster. The taller the column, ie more plates, the less reflux you have to run to hold a given abv. This is true until you get to about 40 plates based on what I have read. So for scrubbies, that’s about 160” of packing.

[Matt64]

Not tall enough. If you want faster with high proof, taller and larger diameter are the way to get that. Taller alone should get you 50% faster. The taller the column, ie more plates, the less reflux you have to run to hold a given abv. This is true until you get to about 40 plates based on what I have read. So for scrubbies, that’s about 160” of packing.

OK, thanks. Current section is 1.5m (with 1.25cm packed) and I can add another section to double that height. I have some pipe insulation arriving next week, so will extend, insulate and run again. The issue I had last time when running at full height, was no output from the column when running low wines. I only had output when running the shorter column.

Ambient temperature was very low (close to 0°C), so I hope that insulation will fix the issue and allow for output at the top of the taller column. Take-off valve on this taller section is 3/4".

Will let you know how I get on.

[bluefish_dist]

Being that cold and no insulation, you could have had so much passive reflux that there was no output. That’s really extreme case as most here don’t run anywhere near that cold. Still make sure it’s not plugged as you don’t want to be making a pressure vessel.

[Matt64]

Being that cold and no insulation, you could have had so much passive reflux that there was no output. That’s really extreme case as most here don’t run anywhere near that cold. Still make sure it’s not plugged as you don’t want to be making a pressure vessel.

We just seem to have had a lot of cold here while I have been running. Looking forward to spring

[haggy]

Matt,
Here are some more thoughts on what is happening in your 2.5" column.
First - part of a post from kiwidistiller:

VM operation instructions.
Post by kiwistiller » Sat May 29, 2010 9:55 pm

DRAFT - suggestions and improvements welcome. Thanks to Hookline for some suggested changes.

Right, some long awaited VM operational instructions. Bear in mind that this is just how I run my VM ------

Cooling Setup:
Run your coolant through the bottom of your product condenser, out the top, then into your coil. Don't run it too fast - the water should be exiting fairly warm (45-50 º C / 115-120 º ). Obviously, don't run the cooling too slow either, no one likes ethanol vapour billowing out the top of the still. The reason for not running the cooling flat out is that you may actually overcool the surroundings of the condenser, which will extend the effective condenser length down into your column. In extreme cases this will reduce your takeoff speed by condensing product in the takeoff chamber.

So,
I think the above is what is going on in your reflux condenser (RC) . I mentioned this in a post earlier here, Jan 19. The 1.4 ft^2 area in your RC is 2.5 times larger than needed. And you run 1.5 L/min cooling water through it. If you run the 10 deg C water directly to the RC ( not to PC then to RC ) , that is a lot of cooling.

And you got to the 1.5 L/min rate because your top temperature after the RC was increasing 25C and up. But 25C is a low temperature and what is it measuring, the surroundings, metal? You need to measure the exit water temp from the RC. Run at a lower gas burner setting (inner ring at half power?) and see what flow rate gives an exit cooling water temperature of about 40-50 deg C. Observe your top temperature when you slowly reduce the cooling water rate, it can go up to 50 -60C and still should not be vapor. BUT, do not let it get above 70 C - close to what would be vapor - and do not get vapor out the top.

Also,
We need to know the power (watts) delivered to the pot. Can your propane burner run at 2500 watts for your 2.5" column?
When you up the power and see in the bottom sightglass the liquid being carried upward, that is open column flooding and I estimate it would take about 5000 watts power to do that ( burner inner ring on full ). You gradually reduce power to allow the draining but not too much, so you could be running just under 5000 watts. That would be way too high for a 2.5" column. And a high pot watts leads to high vapor upflow. That combined with a low take-off rate gives a high reflux ratio which has been discussed here by bunny.

The pot power (wattage) determines the vapor upflow rate in the column - and the take-off valve and piping determine the exit vapor flow. The vapor up minus vapor takeoff is the vapor to the RC which is condensed to a liquid which flows down the column. If you subcool this liquid too much, as kiwi states above, you may actually overcool the surroundings of the condenser, which will extend the effective condenser length down into your column. In extreme cases this will reduce your takeoff speed by condensing product in the takeoff chamber. This may be why you previously saw no take off sometimes when the valve was open.

And,
About the observation that the temperature below the RC decreases when you reduce or shut the take-off valve completely. I agree with greggn that it could be the slower takeoff rate created a higher reflux ratio and allowed the more volatile fractions to stack in the top of the column ( higher ABV which boils at a lower temperature).

But, here is another possibility of what could be happening. More cold liquid comes down from the RC and this is what reduces the temperature. ( as kiwi states above )


In summary,
maybe it is the RC cooling that is not right, too much. You might try some tests at lower gas burner levels and gradually reduce the RC cooling water flow rate and see what happens. Observe the top temperature, should be OK below 70 C. As long as vapor is not coming out the top, it must all be condensed. You should measure the exit cooling water temperature and see if you can get to 40-50 deg C. Do not allow vapor out the top. Your 1.5 m, insulated column should be run.

Keep trying to determine the power (watts) that you are using. Try to calibrate the gas burner settings.

[kimbodious]

Great explanation Haggy. Matt, you can check this is or isn’t happening by carefully feeling where the heat is on the outside of the column.

[Yummyrum]

Great explanation Haggy. Matt, you can check this is or isn’t happening by carefully feeling where the heat is on the outside of the column.

Was thinking of typing just that Kimbo . The head will normally be so hot you can't touch it. So will the bottom half of the RC shell . The top half of the RC shell will still be hot , but you can touch it without too much bother

[Matt64]

When I ran it last, I did run with slower coolant rate. Just checked my notes and they say coolant was running at 80 seconds per litre (still a lot of water, given the distillate output).

Coolant goes in bottom of product condenser and exits at the top, feeding to the bottom of the RC. Where it was exiting at the top, it was quite warm to touch at the top of the RC.

From reading through all the input above, the cold ambient temperature plus too cold RC could both have been factors in zero output from the taller column.

It's not a problem to run the coolant slower but I was trying to find a balance where the temperature above the RC was stable and not steadily increasing. The temperature above the RC was around 25°C but the water temperature exiting the RC was much higher than this. I need to get another thermometer to measure the actual coolant temperature at exit.

Hopefully a combination of column insulation and slower coolant feed will improve the situation with the taller column.

I am running on gas and still need to calculate the real kWh being used. This is complicated by the pot not being insulated at the moment. It looks very nice but a lot of heat is being lost from the copper surface.

Are there any numbers on litres of coolant used, per litre of distillate output, for different diameter columns - 2.5" v 3", 4", 5" etc? I am wondering if (all things being equal in terms of power input) doubling the distillate output, doubles the coolant rate needed, or if there are coolant savings per litre of distillate (or maybe the opposite) by increasing the diameter of the column?

Column size, output and power-in looks something like this from the info in this thread (packed column). It would be interesting to be able to add in the coolant per hour number:
2" = 1l/hr output and needs 1500-1800w, coolant needed =
3" = 2l/hr output and needs 3000w, coolant needed =
4" = 4l/hr output and needs 6000w, coolant needed =
6" = 8l/hr output and needs 12000w, coolant needed =

I realise that I am probably oversimplifying it and that there are many factors, such as column height, packing and reflux etc that make a coolant flow needed quite variable but it would be interesting to know if going from a 2" to 3", for example, doubles the coolant flow needed.

Will report back once I have run the taller insulated column again.

Thanks to everyone for your input!

[bluefish_dist]

Coolant will have to remove all the power being put into the boiler minus environmental losses. It will be split between product condenser and reflux condenser. To calculate heat removed, you need to know volume of water and the temperature change. Imho not something worth calculating. Input power would be easier. Weight your tank, run 5 min, weigh again, that’s how much gas was used in 5 min, convert to amount of gas consumed by density, then convert to btu’s and then multiply by .3 as gas heat is only about 30% efficient.

[OtisT]

Hi Matt. As bluefish stated, the total amount of cooling needed is proportional to the total amount of heat you put into the system minus environmental heat loss which can be minimized with insulation. Column diameter does not impact this.

My system uses just a hair over 3 liters of cool water per minute to fully knock down 5000 watts. I believe my environmental heat loss is less than 500 watts. My system is insulated.

Otis

[OtisT]

I guess I should add the the output temp of cooling water was warm, so I could get by with a bit less than 3 lpm and the result would be hot output water.

[haggy]

For what it is worth, I have developed some charts to help us understand Matt's VM still operation better.

So, we know that the cooling water ( CW ) passes through the PC first, then to the RC. It is heated up in both condensers by the vapor condensing ( the major factor ) plus some subcooling. The amount of condensed vapor in the RC is the amount L that travels down the column. The amount of condensed vapor by the PC is the measured distillate product D in L/hr. And V = L + D. where V is vapor traveling up the column. And Reflux Ratio RR = L / D . And L = D * RR

How to Construct a Chart of the CW Flow and CW Del T
We can calculate the V at several pot power watts. (later) We will use an initial pot ABV of 32% for this. Then for each value of the watts and D, we can get a RR and L. So, for theses watts and D, we can find the amount being condensed in the RC ( which is L ) and in the PC (which is D). From the amount condensed, the heat given off ( Q, watts ) in each case can be calculated.

Next, the CW flows through and is heated up an amount ( Del T ), the temperature rise in each Pc and RC. The CW energy balance equation for each case is; Q = m * cp * Del T
where m is the CW flow - cp is the water specific heat - Del T is the CW temperature rise
We calculate Del T in each, for PC and RC, add them up and get the total Del T of the CW. We construct a chart and compare this with measurements early in the run to find the effective watts of the run.

So,
By measuring the total temperature rise Del T of the CW through the two units ( PC and RC ) and measuring the amount of CW flow L/min, you can determine from the following charts the effective power (watts) of the run and then find the RR. This should be done early in the run since the initial pot ABV of 32% is used.

The charts to use to find the effective watts for a VM operation are plotted two different ways:

Before, we never really knew what Matt's effective watts and RR were in his runs. Now, we can get a better fix on these numbers. The accuracy of this approach should be close enough, ballpark anyway. We get the watts from the charts and get the RR from the watts and distillate rate as shown below.

The column diameter was not used to generate the above charts. But we know the operating range of watts for each column diameter, so look in that range for the column being studied. The charts might be good for many different VM columns where the pot charge is about 32% ABV.


Next Run CW Flow
For Matt's 2.5" column, it would be best to start at about 1.1 L/min CW flow and see what the CW Del T is. If the CW Del T is low, then you can reduce the CW Flow to 0.75 L/min and even lower in steps. With 10 C inlet CW temperature, about a 30-40 C CW Del T is a good target. Use the charts to find the effective watts.


Another crazy observation
If you look throughout the HD posts for VM column builds, you will find that most ( 90%+) of them have the distillate exit connecting pipe line diameter the same diameter as the column or the vertical reducer from the column. Many use a T with the same pipe diameter on all 3 sides. One side is for the RC, the other for the distillate take-off. That way you get a minimum RR of 1 and higher distillate flow rates.

Matt's exit pipe from the 2.5"column is about 1 inch. So maybe there is no way that he can get a low RR as Bunny has pointed out. According to one of DAD300 posts, Re: 3" VM still - take-off port dimension/stepdown Questions, the lowest RR Matt can get is about 6.5. But that may be ok for getting a high ABV, but it will reduce the distillate flow rate. A modified take-off build with the same distillate exit pipe diameter as the vertical column or a reducer pipe could help get higher distillate flow rates.


A Table to Look At
Here is one of the tables I generated to construct the charts. It is for a D distillate of 1 L/hr and shows what increased watts will do to the V, L, RR and to the Exit CW temperature and CW Del T early in the run. The basis is a VM still with the pot at a 32% ABV charge.

Finally, ( if you are still reading this ), here is how to get RR:
You can find the VM still Reflux Ratio RR of a 32% pot ABV run by either knowing the watts used or getting the watts ( or KW ) from the above charts, then using the above table or chart below to find a value for V. Then you subtract the observed distillate flow rate D from V to get L ( all values in L/hr). RR is then L/D.

Here is the chart for V in L/hr vs the effective KW for a 32% charge ABV ( or close to this ABV ). Also a line for a 10% wash charge ABV.