Wash preheat using latent heat

[Peaty Jones]

IMG_6791.jpeg

I’ve been thinking about how to make better use of the waste heat from the condenser during a stripping run.

Let’s say I have 90 L of 5% ABV wash at 20°C, and I split it into three 30 L batches.

For the first 30 L stripping run, I end up with approximately 10 L of 15% ABV low wines.

That means I have recovered approximately:

10 L × 15% = 1.5 L of pure ethanol

With ethanol having a density of about 0.789 kg/L:

1.5 L × 0.789 kg/L = 1.18 kg ethanol

The remaining ~8.6 kg is water.

If we assume that this entire amount has been vaporized and then condensed in the condenser, the approximate condensation heat is:

Ethanol:

1.18 kg × 840 kJ/kg ≈ 990 kJ

Water:

8.6 kg × 2250 kJ/kg ≈ 19,350 kJ

So the total is approximately:

990 + 19,350 = 20,340 kJ

or:

20,340 / 3,600 ≈ 5.65 kWh

Obviously, I wouldn’t want to heat the next batch all the way to 100°C using the condenser cooling water. Once the cooling water gets too hot, it becomes less and less effective at condensing the vapor. I think around 50°C would be a sensible point to stop using the closed cooling loop and switch to fresh tap water.

For example, heating 60 L of wash from 20°C to 50°C requires approximately:

60 kg × 4.0 kJ/(kg·°C) × 30°C = 7,200 kJ

or:

7,200 / 3,600 = 2.0 kWh

So the condenser waste heat could theoretically provide enough energy to raise the 60 L from 20°C to 50°C.

With a 3 kW heating element, 2.0 kWh would otherwise take:

2.0 kWh / 3 kW = 0.67 h ≈ 40 minutes

So, in an ideal system, recovering the condenser heat could reduce the heating time of the next 60 L batch by approximately 40 minutes.

My idea would therefore be to run the condenser cooling water in a closed loop through a coil immersed in the next batch. Once the wash has reached around 50°C, I would stop using the closed loop and switch back to fresh tap water for the actual condensation.

I actually noticed the potential of this idea when I was using a closed cooling loop with a coil and plain water. The amount of heat transferred to the cooling water was surprisingly significant. However, I haven’t actually tested this setup in practice specifically for preheating a wash/mash for the next stripping run but i dont see why would it be any different.

And of course, the recovered heat doesn’t necessarily have to be used only for preheating the next batch. If needed, there are plenty of other ways to make use of several kWh of low-grade heat for example, preheating water for another process. But for preheating the next batch, there is more than enough heat available.

I have seen breweries use this kind of setup to get all the used energy in use again with heat exchangers.

[MooseMan]

This is something I've done a fair bit Peaty, along with a few others on the forum, and it works really well.

I use a wort chiller coil from my beer brewing days, in a bucket of the next wash to be stripped (Pic below) and it cuts off loads of heating up time. The hot water comes out of the condenser, through the coil and out to either the drain or to another vessel for cleaning, watering the garden etc.

I also as you mentioned, use the hot water from the condenser, most commonly to set up my next ferments while I'm stripping.

IMG_20230524_180920_433.jpg

If you search "Pre heat" you'll turn up lots of results here.

[Yummyrum]

Your thinking correct Peaty . There are a number of ways to do it .
Moose did similar to your idea but didn’t recycle the cooled water back to the Condenser .

Another way to do it is to have the actual condenser coil in the next wash to be heated . Like a Charentyne Still . In this configuration , the latent heat is given directly to the wash . These stills still have an auxillary condenser to take over when the pre-heated wash gets to hot to be effective .Tbis is Saltystaves version

viewtopic.php?p=7561148#p7561148

IMG_4790.jpeg

I tried another version . I pumped the next wash through the condenser . Similar thing , the heat is directly transferred to the wash , rather than into the coolant , then back to the next wash . A double heat transfer .

viewtopic.php?p=7586183#p7586183

IMG_4789.jpeg

What this showed me was pretty much as you predicted . That at the critical speed of pumping the wash through the condenser .
, it would barely but just condense the stripped wash and the wash that was pumped through the condenser was so hot it was at the point of evaporating .
It was a critical juggling act to get the speed just fast enough to condense the vapour and not have the next wash too hot .

And yes , had to switch over to tap water to finish the run . But as you predicted , the next wash was ready to run and it took longer to drain the boiler and refill it than it took to get it boiling.

I think your method is a lot more manageable .However , I believe it is not as efficient due to having the heat have to pass two times .IE , once i to the coolant and then into the next wash .

[Peaty Jones]

It was wort chiller which i also used in the closed loop system also. I also tried two wort chiller system where i pumped the heat from the leftover wash but i have to say that the condenser is way more powerful because of the latent heat energy. The temperature of the leftover wash starts to drop and the next batch rises so the temperature difference gets smaller and the power of it gets low -> thus it gets slow even though you could theoretically get quite a lot energy from it. Considering there would be 20l of that leftover @ 100C and you pump the heat so that its 50C in the end, there would be 20l x 50C x 4kJ/ (kg C) = 4000kJ which is approx 1.1 kWh.

If you dont mind the hazzle, all that heat from every run (latent heat and specific heat) could be put to use even in next mashing water and such also.

This is something I've done a fair bit Peaty, along with a few others on the forum, and it works really well.

I use a wort chiller coil from my beer brewing days, in a bucket of the next wash to be stripped (Pic below) and it cuts off loads of heating up time. The hot water comes out of the condenser, through the coil and out to either the drain or to another vessel for cleaning, watering the garden etc.

I also as you mentioned, use the hot water from the condenser, most commonly to set up my next ferments while I'm stripping.

IMG_20230524_180920_433.jpg

If you search "Pre heat" you'll turn up lots of results here.

[Peaty Jones]

Hi Yummyrum,

I agree and thats why the amount of water in the closed loop should be at minimum so the amount of energy charged to it is low but for the purpose of heating the next batch there is more than enough energy available so it doesnt matter that much. Circulating the wash would be much more efficient but i just dont like the idea of circulating it in my clean condenser.

Ill have to take a look of these threads you linked, thank you

Your thinking correct Peaty . There are a number of ways to do it .
Moose did similar to your idea but didn’t recycle the cooled water back to the Condenser .

Another way to do it is to have the actual condenser coil in the next wash to be heated . Like a Charentyne Still . In this configuration , the latent heat is given directly to the wash . These stills still have an auxillary condenser to take over when the pre-heated wash gets to hot to be effective .Tbis is Saltystaves version

viewtopic.php?p=7561148#p7561148

IMG_4790.jpeg

I tried another version . I pumped the next wash through the condenser . Similar thing , the heat is directly transferred to the wash , rather than into the coolant , then back to the next wash . A double heat transfer .

viewtopic.php?p=7586183#p7586183

IMG_4789.jpeg

What this showed me was pretty much as you predicted . That at the critical speed of pumping the wash through the condenser .
, it would barely but just condense the stripped wash and the wash that was pumped through the condenser was so hot it was at the point of evaporating .
It was a critical juggling act to get the speed just fast enough to condense the vapour and not have the next wash too hot .

And yes , had to switch over to tap water to finish the run . But as you predicted , the next wash was ready to run and it took longer to drain the boiler and refill it than it took to get it boiling.

I think your method is a lot more manageable .However , I believe it is not as efficient due to having the heat have to pass two times .IE , once i to the coolant and then into the next wash .

[Username]

Whenever I do more than one stripping run I'm using cooling coil in the 2nd wash.

As above an immersion chiller from beer brewing days, but a self build with 3 separate copper coils for efficiency

I will always have to remove the coil before the end of the run to avoid evaporation, I'll re direct the flow when the wash hit's 60C

It's a big saving on time and free energy, winner, winner

[Peaty Jones]

Actually i noticed this while i was trying to use this closed circulation just for the condensing purpose alone. We have subzero temperatures here in the winter so its quite easy to get ice during that time. Moisture from the air freezes on the outdoor unit of the air-source heat pump, causing ice to build up. The unit periodically removes this ice through a defrost cycle. I have this 65l plastic tub under it and i just grabbed it with me. It had about 50l of ice in it and i added about another 10l of water in it. At the end of the stripping run all that ice had melted and the water was about 50-60C. Based on that i calculated that defrosting that 50l of ice + rising the temperature of that 60l of water it has given about 30 MJ which corresponds to 8,33kWh. To me that was
quite impressive.

[higgins]

I've been preheating my second and third stripping charges for about 3 years now. After the 1st stripping run I have to pump the leftover stillage out of the kettle, so I decided to run it thru a coil in the bucket of the next still charge. I can easily get it up to 140F/60C before adding it to the kettle without using any water from the PC. I use tap water in my PC and collect it in a barrel (for cleaning up, etc).

[Peaty Jones]

Collecting it for cleaning is a good way of using that for sure. I have also tried to get the leftover heat from the leftover wash but in my case it wouldn’t serve the purpose of getting things done faster. What im looking for is getting the whole stripping run faster and the condenser does it WHILE distilling and it does it very fast.

Lets say id use the heat from the leftover wash i would need to do it after stripping the first run and what i have as leftover in the still is 20l @ 100C. If i want to transfer that heat to the next batch which is 30l @ 20C they would balance in 52C and even to that it would take forever because the power of the heat exchange gets lower and lower when the temperature difference between them get narrower. It even could be more spent time during this than to heat it with a element.

But dont get me wrong, theres plenty of energy to harvest from the leftover for something other and put it in use. Also its almost free and doesn’t add your electricity bill

Ill start to make a list here for the things to use all that leftover energy (from the condenser and leftover wash):
-Preheating next batch
-Preheating mashing water
-Cleaning water

Can anyone think of anything else?

I've been preheating my second and third stripping charges for about 3 years now. After the 1st stripping run I have to pump the leftover stillage out of the kettle, so I decided to run it thru a coil in the bucket of the next still charge. I can easily get it up to 140F/60C before adding it to the kettle without using any water from the PC. I use tap water in my PC and collect it in a barrel (for cleaning up, etc).