In an effort to turn my 16 hour days into 12-14 hour days, I am considering preheating my fermented mash overnight. If I were to heat and hold a mash at 150 degrees overnight, would it be necessary to run the condenser (at full reflux)? I suspect that as the temp rises, the rate of alcohol evaporation will accelerate, so even at this temp I will have vaporized some of the higher alcohols? What would be the maximum safe preheat temperature without needing to run the condenser?
If you can automate your still to heat up / hold a temperature overnight, you should also be able to automate your condenser to run when necessary, and shut off when it's not needed, right?
A 2-4 hour heat up time sounds excessive to me. Perhaps it might be easier to beef up your heat input? Another area that many stills seem to be undersized is in the condenser. Would a larger condenser cut some time out of your shifts?
At Santa Fe Spirits, we run a 1000 liter Carl still at about 4 hours per batch for stripping runs, double that for spirit runs. This number would be a little larger if we didn't use a heat exchanger to pre-heat our mash. Would that work with your process?
We take our 180 deg F consenser water (stored in a holding tank) and cool it down to about 70 deg with a heat exchanger that heats up our mash from 40 deg F to 150 deg F as we fill the still. By the time the still is full, it's boiling. We rarely dump cooling water down the drain since we re-use it after the heat exchange.
Even though the heat exchanger and holding tank weren't cheap to install, the energy, water, and labor savings will show us a return on investment in less than 2 years.
Some food for thought...
P.S. if you hold a temperature below 140 deg F, you'll start getting some bacterial souring, butyric acid souring in particular. Yuck.
My heating system is lacking BTU's. I currently use a glorified hot water heater to heat my stills. I do vacuum distillation, so I don't need a lot of heat during the process, but heating up is too slow. I'm adding more power, but I have single phase and approaching my panel limit already (time to upgrade that too).
I like your heat exchange system, it sounds very efficient. My production is currently too sporadic to take full advantage of that type of set-up. Long term, I would like to do the same.
So in the short run, I'm considering two possibilities: 1. use my current system and let it slowly heat overnight, or 2. increase my hot water tank to 125 gallons and preheat it to 200 degrees so that I have a larger thermal mass ready to heat the mash in the morning. Neither option costs much, but #1 just makes me a little nervous!
A small braized plate heat exchanger (Mcmaster calls them "space saving") might work for you, depending on the solids content of your mash (you don't want to clog it). You could eliminate lots of the worry of your overnight heating by heating water, not mash, then exchange the heat from the water to your mash in the morning. You wouldn't be taking full advantage, but you'd be sleeping better...
Your setup sounds like it might have an all around low heat differential when you're exchanging heat. The first thing that happens is that your hot water reservoir gets it's temperature knocked down, then you're fighting to heat that back up, while all the while you're cooling it off too. Going to a process with a higher temperature differential, like a plate heat exchanger, might help a lot.
If 125 gallons at 200 degrees (or 168,000 BTU assuming that you take your hot water from 200 degrees to 32 degrees... a generous estimate) is all of the heat that you need, it sounds like you could use a pretty small heat exchanger with a flow rate in the realm of 3 gallons per minute to get your mash heated up in well under one hour.
Incidentally, mcmaster isn't the cheapest place to buy one, but I had to link to something, right?
The key point of brazed plate exchanger use is that it won't tolerate any solids or material that can possibly coat (foul) the passages.
If the excahnger becomes fouled in the slightest, there will be practically no heat exchange and a sizable pressure drop for the pump to overcome.
I have too much solids in my wash. I may try immersing a simple 3/4" or 1" copper coil in my hot water tank. With a thermometer fitted on the hot side, I could adjust the flow to preheat my mash. Same concept as the heat exchanger mentioned above, but less likely to clog - I hope!
If you've got a 3/4" copper coil, you might also consider encasing it in a 1.5" (or thereabouts) pvc hose so that you could counterflow your hot water against your mash. Probably better heat exchange that way.
What's the volume and temperature differential (i.e. total BTU) that you're trying to heat up, anyway? I'm curious how much hot water might be required...
My temperature differential will be 70 degrees maximum - usually a little less. I have been running 100 gallons at a time, but I want to step up to 200 gallons.
A counterflow heat exchanger could be more effective and easy to make, but I'm not sure PVC is rated for 200 degrees. Stainless or copper would still be simple to come up with.
Sounds like you've got just over 100k BTU to come up with. If you've got the space and the cash for the materials, maybe a simple tube-in-tube would be even simpler than a coil (and way easier to clean).
20' of 3/4" or 1" copper pipe would give you around 4 or 5 square feet of heat exchanging surface area, respectively. Double that for a 40' long U shape. It would probably be easier to stick the straight 3/4" pipe inside of another straight 1.25" or 1.5" pipe than dealing with coils.
I'm not exactly sure which side of the HEX you'd want to flow your product through, or exactly how many square feet of surface area would be required for your application (maybe you could even get away with a 1/2" tube inside of a 1" tube). I want to say that you'll want to flow your mash through the larger tube, and your hot water through the smaller one.
Maybe MG Thermal could help with the details?
Not to sidetrack the post to much, but you run a 1000 ltr still and don't put much cooling water down the drain? I understand that you use the very hot post condenser water to run through a HX but where does it go from there? We use that water for mashing and some cleaning but we still dump plenty of cooling water down.
We dump about 4-5X as much water as we reuse, something I'd really like to change. It's stressing our water and sewer bill as well as our grinder pumps (below grade for sewer) and it just seems bad. I've been toying with the idea of a closed loop cooling system in some fashion but don't have it worked out yet.
I'm also impressed by Nick's water/heat conservation. I plan to incorporate similar methods over time. I use closed loops for cooling and heating. My only "running" water comes from two 1100 gallon holding tanks which I have filled as needed by a local spring water supplier. One tank holds mash water and the other holds cooling/process water. I have a cooling loop running underground into a heat sync in a cooling pond. It works fine for my current limited production, but I'll need to expand it, drill a well, or move at some point.
The only water I dump is cleaning water.
I understand that you use the very hot post condenser water to run through a HX but where does it go from there?