Preheater/Thumper

[SaltyStaves]

Built a preheater to save me time and energy in the distillery.

The vapour pipe was brazed together and assembled in two halves inside the keg, with the last join being soft soldered in situ (which was a challenge to do through a 4" hole!)

I added a 4" ferrule to the top and a 1" ferrule which can be used for the condenser and a drain port on the bottom so I can get every last drip out and into the main boiler as quickly and efficiently as possible.

I have a mini gin still that uses 1" ferrule accessories, so I had the expansion chamber already and I built a smaller condenser for that still too.
The plumbing had to be overhauled to accommodate the two condensers.

Had my first proper run with it yesterday (an Apple Brandy wash). Three charges to strip, so two charges went through the preheater.
It is going to take me a while to work out how to run this setup. The bottom of the charge remains cool for most of the run, but by the end, its too hot to touch. Insulation for the boiler and drain pipe will need to be added before winter gets here. With the expansion chamber in place, the preheater did not produce a foreshot. Without it, it produced more than a foreshot... So I'm going to have to learn by experience as to how much to expect based on the charge.

If the preheater is charged from the start of the run, the vapour collapses and pools in the vapour pipe. This creates surging that makes foreshot collection very difficult and erratic. Once the charge in the preheater is up to temperature, the collection becomes much smoother. I will have to experiment with it.

Doing three strips in a day would usually result in my cooling water being too hot for a fourth strip. I'm happy to say that yesterday, the water was not even tepid.

The thumper setup is still to come.

[NZChris]

A very nice looking setup Salty.

The vapour tube needs to have fall to avoid pooling and smearing.

I put mine as close to the bottom as possible and haven't noticed it heating from the top down, but that could be because I've never run it without lagging.

To save on cooling water, I always charge the preheater before the main pot gets up to temperature.

I highly recommend automating the cooling water flow to the Liebigs to control the condensate out temperature.

[SaltyStaves]

It was designed with fall in the vapour tube, but on execution I wasn't able to maintain the desirable positioning and I decided that unsweating the solder wasn't going to solve the problem. Long term it might be a deal breaker and I'll have to cut out the vapour tube and unions. I'll live with it for now and see how it goes. I'm not worried about smearing as I won't be doing spirit runs with the preheater inline.

The lagging will certainly help and I think I can help heat the very bottom by having some copper draped over the heat pipe and touching the bottom of the keg.

[NZChris]

It was never my intention to do spirit runs in the preheater, but I have done a half full one while running the last strip. There was far more alcohol coming from the preheater than there was from the strip

[SaltyStaves]

I didn't mean doing a spirit run in the preheater, I meant having the preheater in line during a spirit run.
For spirit runs I can just attach the liebig to the lyne arm as usual and bypass the preheater completely.

If I were to leave it inline (but empty) it would smear the spirit run. Fortunately its not a big problem to bypass it.

[NZChris]

Is your preheater tube straight or a loop?

[SaltyStaves]

Its a loop. The second pic I posted must not be clearly conveying it. I'll have to take some more.

[NZChris]

There is a small bit of uphill in mine that has been annoying me for thirty years

[Kareltje]

It took me some time to understand the contraption, but I think I start to understand it and it is impressing.
Several details I would not have thought about, among them the expansion vessel and the fact that foreshots are produced during preheating.

Very nice, thank you for sharing this. And thank NZChris for the professional remarks.

[SaltyStaves]

Hopefully this internal shot helps clear up some of the confusion. Vapour enters from the left side and exits the right.

[NZChris]

The last run I did got a 150ml foreshot plus 400ml of low wines before it went into the main boiler. I'd had 6l too much to fit into both vessels for two strips, so shot additions into the main boiler as I took off low wines.

If the strips are mismatched, you have the option of charging the vessels to maximise the takeoff from the preheater. There is nothing to stop you running different washes in each vessel and I have done it. You might have to spend a little longer cleaning up the main pot and lyne arm etc. during the changeover if you are worried about a flavor mismatch carrying over.

[SaltyStaves]

Being able to add a valve to the main boiler for shooting would be worth having indeed. Think I might add that to the projects list.

[NZChris]

I shoot using the same valve that is used when filling from the preheater.

[SaltyStaves]

It was designed with fall in the vapour tube, but on execution I wasn't able to maintain the desirable positioning and I decided that unsweating the solder wasn't going to solve the problem. Long term it might be a deal breaker and I'll have to cut out the vapour tube and unions. I'll live with it for now and see how it goes.

Well it turns out I can't live with it in the short term either.

[NZChris]

With that diameter tube, you might get enough heat transfer without having a loop.

[NZChris]

If it makes it easier, the tube doesn't have to come out opposite to the entry and anywhere convenient will do. Mine exits at about 100 degrees from the entry because there was an existing hole I could use.

[SaltyStaves]

My original plan was something like this.

If you can imagine the two 'candy canes' having a piece that joins them together. There was also a very slight decline from entrance to exit.
When it came to assembly, I decided that the difficulty in soldering two joints in situ would be highly risky and it was better to braze that middle joining piece to one of the candy canes. That is where I came unstuck and the two parts didn't meet where I wanted them to.

I think my original plan is doable. I just have to be better with the execution.

[NZChris]

Is there a way you can solder it outside the vessel then insert it?

Mine was 1/2" tube so I had enough flex to be able to fit it after I shaped it. Yours looks like it might have slightly more flex than a crowbar

[SaltyStaves]

The only entrance is a 4" hole at the top of the keg and the tubing has to be assembled near the bottom. So no. No chance in hell.
3/4" so yeah, it needs more than a bit of coaxing.

[NZChris]

I had enough trouble fitting mine through a 12" hole

[SaltyStaves]

Version 2.0

Very minimal pooling and mostly smooth takeoff. This has a very slight downward angle, but there is still a bit of liquid that pools in it after shutdown, which I have to blow through before I put the heat on again (otherwise it will dilute my foreshot and huff until it clears).

The problem I now have is that significantly more of the bottom remains cold, as the gap is now bigger. I've been playing with putting copper in various shapes and sizes, but the difference is not significant. The fastest configuration to heat the bottom was putting lots of off-cut copper tube.

Biggest problem was vapour collapse as the additional copper pieces were cooling the heat pipe in one or more spots.
I think agitation of the cold layer may be the only viable option.

[NZChris]

Does it really matter for stripping runs?

Unless the preheater is producing a large amount of product before recharging, I doubt it's a problem. In my experience, they don't. My last strips didn't produce a single drop from the preheater because the must wasn't very warm after an EC1118 grape ferment.

The last time I got a decent foreshot off my preheater was from a quite warm baker's yeast fermented rum.

If you want to do a spirit run over a stripping run, you might have a problem.

[SaltyStaves]

Its a problem if the top 3/4 gets hot enough to take off fores with the bottom 1/4 barely warmer than ambient. That seems to be the pattern now, because with the bottom layer remaining cold, its like running a much smaller charge with the same amount of energy.

It makes fores collection incomplete, so it pushes the problem down the road and takes more time out of the day.
I've got the expansion chamber and some additional lengths of copper that I can add to delay any product take off, so I don't have to build a reflux condenser for it, but if I can move the cold layer, then I think I'd be able to bring the whole charge up to temperature at a much more uniform rate and it seems like the best outcome.

[NZChris]

Without going to the trouble of dismantling stuff, I measure mine at 18mm from the bottom of the worm to the bottom of the preheater. If there is a stratification problem, I've never noticed it.

[SaltyStaves]

Do you have a flat bottom vessel? This keg is concave, so there is a dead zone.
In the old configuration, 2L of wash would be below the pipe. Its now more like 5L.

[NZChris]

Flat in the preheater. Less than 1.5l below the lowest point in the worm.

[Chauncey]

An agitator of some kind seems like it would help with the stratification

[SaltyStaves]

I'll have a play with drawing off the cold layer mid-run and pouring it back in to the top of the vessel. Shouldn't need to do it more than once. Luckily the drain valve is at the lowest point, so all of the cold liquid would be displaced.

[NZChris]

A small PTC element under the lowest point might be enough to induce some circulation in the stagnant layer. Hair straighteners from charity shops are a cheap source of them.

[SaltyStaves]

I have one I can try easily enough. Just have to find a way to attach it securely.