Is anyone running a continuous still? With the knowledge out there from the oil industry using them for a hundred years and the efficiency they have by reusing heat from exchangers and condensers I'm surprised more don't use them.
I've run distillation units for years so maybe it just seems easier for me.
And I wish there was a easy program for design out there then what we have.
Most of your big distilleries use continuous stills. What you have to remember is that they aren't optimal for smaller distilleries who don't work around the clock or don't produce the same spirit all day long or don't have the ability to always have enough fermented to run.
For many smaller distilleries running batches is preferred.
Still Dragon makes a great continuous still - ask Stumpy.
The issue is mash production. 2,000 gals per day / 10,000 per week is a lot of mash for a small distillery to cook and ferment.
You also need manpower, barrels and cash flow to sustain the process to get to market.
I have 2 continuous stripping stills that I built. An experimental one that runs on 1.5 Kw electric and will strip about 400 litres of beer per day. A larger one strips about 2,000 litres a day. Very efficient with energy use and zero cooling water required. Beer feed is used as condenser coolant, so the beer enters still at close to boiling point requiring very little energy to raise the last few degrees. Hot overflow of the spent beer is also used to heat the input beer which increases the flow rate. Surplus heat from the overflow produces high grade hot water.
The larger continuous runs on used fryer oil so my running costs are almost negligible.
I will probably never get time to build it, I would love to build a continuous fractionating column with quite a few take-off points ( like petroleum stills) That way I could blend different cuts back at various ratios to create unique flavour profiles.
Reply:4 hours ago, PeteB said:
I''d love to see a picture of your 400 liter/1.5KW stripping still as well.
I love to see how different people do these stripping stills and your's seems quite effecient!
Pete, I would like to see pictures of your big stripping still. How many plates does it have?
Reply:On 4/20/2020 at 2:23 PM, Mverick160 said:
I haven't forgotten to post photos and diagrams, just too busy just now to do it properly this week.
I'm currently building a whisky column (on a budget) at the moment. The plan is to distill grain in.
I am aiming for a feed rate of between 420-480 litres per hour.
I had the main copper column is fabricated in 4mm copper. It's made up of two 2400mm sections. Overall it measures 5400mm / 300mm. And will hold 12-14 trays? I am aiming for a 70-73% abv spirit.
I'm planning the trays will be perforated with 6mm? holes and 50mm? downcomers. If anyone has advice on the percentage of hole area to surface area I should be aiming for that would be helpful.
I've just managed to find second hand a 3000mm / 110mm heat stainless steel exchanger. The tube stack is 15 x 12.5mm. I plan to counter flow the spent wort (360-420 litres per hour at 95+ degrees celsius) scavenged from the column sump via mono pump to preheat the incoming fresh wort. I'm not sure what to expect the temperature of the fresh wort to be coming out of the exchanger at but I'm guessing the heat exchanger is oversize. So if someone who is more clever than I knows how to work that out I would appreciate your math skills.
The next on the list of things to do is to spec the size of a second steam feed heat exchanger to boast the fresh wort temperature from the heat recovery exchanger before it is delivered into the top of the column. Feel free to add any of your suggestions here as well.
The demethanizer will be 3000mm / 100mm column packed with ceramic structured packing.
I haven't done any drawings that are worth sharing.
@Modernity I would be wary of using perforated trays if you are going to be distilling grain in. If you are going to make the trays into a removable cassette then that could work if you need to clean them. Maybe wait for @PeteB to post his photos and diagrams to see how he did it. He and I discussed using very simple splash trays before he built his first column, and he came up with a very innovative way of installing the trays but I have not seen what he finally built.
If you do go with the perforated trays be generous with your downcomer sizing. I like to allow a downcomer residence time of 10 seconds, based on the full volume of the downcomer. If your tray spacing is around 300 mm then it would be better to install a 3” downcomer. I also prefer D shaped downcomers. You can make these easily by splitting a 6” pipe in half longitudinally and then welding in a plate to seal the straight part of the D. Half a 6” pipe has double the area of a 3” pipe, but is still only 3” wide.
Some references for downcomer design also specify a maximum velocity, but this only comes into play with large hydrocarbon columns that can have +3 ft tray spacings.
The hole area (perforations) is much harder to calculate. I found this reference that states
% Hole Area:
This is the ratio of hole area to bubbling area. The default practice is to target a hole area of 8 to 10 % of bubbling area for pressure services. The acceptable range for percentage hole area is 5 % to 15 %. However for some critical services, we can go % hole area up to 17-17.5 % provided that weeping is under control. Hole areas below 5 % are not used.
Despite their claim that hole areas of less than 5 % are not used I designed a column that uses 2.9 % and has been running very stably 24/7 for 33 years. That column was a bit unusual in that it had a very high liquid to vapor ratio and I had a lot of pressure drop to play with. For your stripper you will also have a relatively high liquid to gas ratio and I would guess that it will need 6 to 8 % open area, but that really is just a guess.
If the hole area is too small it will unnecessarily limit the capacity of the column, and if the hole area is too large the trays will weep and their separation power will be low. Rather than taking the risk of deciding on the hole area yourself it might be better to buy trays from a supplier with a track record and who offers a guarantee. (I am not touting for business – I do not supply equipment or consulting services.)
Reply:22 hours ago, meerkat said:
For a column of 300 mm ID you definitely do not want to go for the split flow design you have shown. It is unnecessarily complex and restricts the bubbling area. I have seen single pass trays of 2 m diameter working very well, even back in the days of bubble caps.
I have never seen a downcomer with perforations at the bottom. You want the flow down the downcomer to be as unimpeded as possible, especially if the liquid is not totally clear. I would leave the bottom of the DC totally open.
The residence time is calculated as DC volume divided by volumetric flowrate. Your flowrate of 480 l/h (actually a bit less because some goes out as vapor) is equivalent to 0.000133 m3/s going down the DC and for an 80 mm ID pipe 300 mm long the volume of the DC is 0.0015 m3. If you divide m3 by m3/s the m3 cancels and you are left with seconds, so that is why it is called a residence time. Here we get 11.3 seconds - a nice safe number.
The downcomer does not run full. Typically the level in the downcomer would be 30 to 50 % of the tray spacing. So the true time that the liquid spends in the downcomer is 3 to 5 seconds, but this is enough for the bubbles to disengage, thus avoiding vapor being carried downwards when it should be going upwards. The reason the level in the downcomer backs up is because the pressure on any tray has to be a bit higher than on the tray above it to force the vapor up through the tray and this pressure holds the liquid in the downcomer back. There is also a small pressure drop as the liquid flows under the downcomer and onto the tray.
The diagram below, from Peters and Timmerhaus, shows a variety of different tray types but I like these simple downcomers
Here they have shown segmental downcomers where the column shell forms the outer part of the downcomer but this is difficult to fabricate in smaller columns and it is more usual to weld a pipe or D section into the tray to achieve the all-round seal.
A very important aspect shown in this diagram is the sealing of the bottom downcomer in the base of the column. For a tray to function properly the vapor must not flow up any of the downcomers. The bottom tray seals first and then the seal is achieved in turn on each higher tray until all the DCs are sealed. Imagine the column at start-up with the bottom DC sealed by the liquid in the pot. When boiling starts in the pot the vapor cannot flow up the bottom DC and it flows up through the perforations in the first tray. The bottom of the DC from the 2nd tray will not be sealed with liquid yet and vapor will flow up this DC, as well as through the perforations of the second tray. But because the vapor flowing up through the bottom tray prevents any liquid from weeping through the holes the liquid will accumulate on the bottom tray until it can overflow the weir into the downcomer. As long as the downcomer projects above the tray more than the gap between the tray and the bottom of the DC from tray 2, when the liquid gets to a height sufficient to overflow into the downcomer it will have sealed the bottom of the next downcomer. Now all the vapor from tray 1 goes through the perforations in tray 2 and the same process allows the next downcomer to achieve its seal.
30 mm is a reasonable height for the weirs, but maybe a bit on the high side. They cannot be too low because (as explained above) they must be higher than the gap at the bottom of the downcomer so that the tray can seal the bottom of the DC. The higher the weir, the higher the liquid level will be on the tray. The higher this level the higher the efficiency of the tray, but also the more easily the tray will weep. It's all a trade-off between the competing factors.
Reply:On 5/4/2020 at 2:08 AM, meerkat said:
Reply:On 4/21/2020 at 2:26 AM, DrDistillation said:
Reply:On 5/3/2020 at 3:11 PM, Modernity said:
Reply:On 9/9/2020 at 9:35 AM, Alex_Sor said:
Reply:52 minutes ago, Oldguy said:
Reply:46 minutes ago, Alex_Sor said:
Reply:On 5/2/2020 at 2:30 PM, meerkat said:
Reply:39 minutes ago, Oldguy said:
Reply:10 minutes ago, Alex_Sor said:
Reply:19 minutes ago, Oldguy said:
Reply:9 hours ago, Alex_Sor said:
Reply:2 hours ago, PeteB said: