Condenser Water Heat Recovery

I'm playing around with recovering heat from condenser water and I have a 3"x10" shotgun hooked up to the hot output from my 6"x48" product condenser. Hot water is going in the top of the 3"x10" and hot water is going out the bottom of the 3"x10". My fermented wash I'm trying to heat up goes in the bottom cold and comes out the top cold. The 3"x10" is extremely hot to the touch.

The 3"x10" seems to be doing next to nothing and I was thinking of getting a 3"x20" shotgun to it, but I'm concerned it will just end up doing twice next to nothing.

I'd really expect more heat exchange to be happening. Obviously the temp of the output wash is going to be highly dependent on the flow rate, but the fact that the condensing water still is blistering hot after leaving the 3"x10" is disappointing. Maybe a shotgun out of copper would be better, but copper is a PITA to keep clean.

I'm thinking a tube in tube heat exchanger might be another option but most of them are pretty ugly (rubber and copper) and not really well suited for hanging in the air.

Ideas?

Comments

  • I’m guessing what I need is another 6“ x 48“. But, seems like the continuous set ups are able to usefully HX without a huge heat exchanger.

  • edited August 2018

    What is the wash flow rate through the 3"x10"?

    I'm guessing, realistically based on the tiny tube side volume, we're talking very low single digit gallon per minute.

  • I use a coiled coaxial HX, I have .5 ton to 3-ton models, most have about a 10' path... they also have a convoluted(twisted ) inner tube that creates turbulence...

    in 20 minutes, I can dump 100gal of fermented wash down the drain (lowering from 210 to 120F) and pump 90-100gal fermented wash into a holding tank going from 80 to 160F.

    the units can be had on a per/lb basis if you know a scrapper that takes down large AC units...

    here is the post with a video

  • @grim said: What is the wash flow rate through the 3"x10"?

    I'm guessing, realistically based on the tiny tube side volume, we're talking very low single digit gallon per minute.

    I haven't measured it, but I'd guess 1-2 gallons per minute. Its a pretty thick grain in rye mash so it doesn't move too fast.

  • @CothermanDistilling said: I use a coiled coaxial HX, I have .5 ton to 3-ton models, most have about a 10' path... they also have a convoluted(twisted ) inner tube that creates turbulence...

    You were the inspiration for my tube in tube comment. I've never seen a AC unit using a tube in tube though at least here in MI and what you have is bigger than I've ever seen. Make that in stainless (at least the exterior) with 1.5" triclamp fittings and you'd have a winner.

  • Units I use are for large rooftop chillers, I have stainless tri-clamps brazed with silver solder, and the inside is copper, which is perfectly acceptable for wash... The actual better version of this is the ladder-type chiller commonly used in dairy.. (search for dairy heat exchanger - but you are talking thousands or even tens of thousands of dollars, not a hundred bucks to a scrapper... but they will handle solids, I saw one in use back when ADI was in Louisville, on the tour of Kentucky Artisan Distillery, the distillery that makes jefferson ocean..

  • edited August 2018

    I've tried for years to find a tube-in-tube switchback style dairy cooler.

    You can find them, but they tend to be huge. I couldn't find anything shorter 20 feet long, because, apparently, sanitary tube readily comes in 20 foot lengths, and that's an economical length to make the things.

    Resale on the things tend to suck, and industrial resellers sit on them for years, but those guys will sit on something until it rots to the ground before they sell it cheap.

    Couple of vendors are now making small versions of them, but I don't see how a couple 5' lengths are going to do very much (talking single-pass mash cooling).

  • I do have a 60’ long tube in tube (2” inside 3”) that I built for the purposes of cooling mash, but it wouldn’t be terribly convenient to use in this case. Trouble is if I spend 1/2 hour hooking things up to save 1/2 hour in heat up for the next batch by preheating with condenser water, I haven’t gained much. I’m giving it more thought though.

  • @grim said: I've tried for years to find a tube-in-tube switchback style dairy cooler.

    You can find them, but they tend to be huge. I couldn't find anything shorter 20 feet long, because, apparently, sanitary tube readily comes in 20 foot lengths, and that's an economical length to make the things.

    Resale on the things tend to suck, and industrial resellers sit on them for years, but those guys will sit on something until it rots to the ground before they sell it cheap.

    Couple of vendors are now making small versions of them, but I don't see how a couple 5' lengths are going to do very much (talking single-pass mash cooling).

    I saw one about 8' long with maybe 8 levels in @smaug 's warehouse when we picked up my 8" condenser... looked nice...

  • edited August 2018

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  • Question: If I had 900 litres per hour @ 85C of spent wash leaving a continuous column what temp would I be able to get 1000 litres per hour @ starting temp of 18C up to in a heat exchanger?

  • To do this, one needs to establish the "overall heat transfer coefficient" and herein lies the problem because it can only be guestimated until you have a working model. In otherwords the result can be way out from reality.

  • edited June 18

    Here is an ASPEN model who's numbers are relatively accurate in practice.

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  • @Modernity_Column said: Question: If I had 900 litres per hour @ 85C of spent wash leaving a continuous column what temp would I be able to get 1000 litres per hour @ starting temp of 18C up to in a heat exchanger?

    Your spent wash will be 100C unless you left a LOT of alcohol in it...

    900L/hr is 15L/min, It is mostly water, so it is about 1KG per liter

    46 degrees C is assuming a 50% HX efficiency...

    Bottoms heat exchanger                  
    HX efficiency                 50    %           
    bottoms temp into HX         100.00 Deg. C          
    bottoms temp out of HX        40.00 Deg. C          
    Temp delta                    60.00 Deg. C
    bottoms rate out              15.00 liters/min     900.00   liters/hr
    bottoms rate out(weight)      15.00 kg/min         900.00   kg/hr
    energy out                  3763.77 kJ/min      225826.05   kJ/hr
    energy recovered            1881.88 kJ/min      112913.03   kJ/hr
    beer feed rate in             16.70 l/min         1002.00   l/hr
    beer feed rate in(weight)     16.46 kg/min         987.32   kg/hr
    beer feed temp                18.00 Deg. C          
    beer temp out of HX           46.00 Deg. C          
    % turned to steam              0.00 %
    

    if you search this forum for 'cooling water required', I have shared this spreadsheet here before..

    If you get a better(longer, larger) HX, and bring the outlet temp down lower than 40, and get more efficiency, you can get a bunch more out, but 112KJ/hr is a lot of energy savings...

  • Thank you both, I wish I had a head for that kind of math. With the above result; 1000 litres of 10% abv @ 46 degrees C. How much energy would I need to bring this 46 degrees C wort, at a rate of 1000 litres per hour to 85 degrees C feed in temp, in a rims heating tube/reboiler setup?

  • To do the work that the boiler HX can do with direct electric heat:

    P(kW) = E(kJ) / t(s) --> so 1kW = 3600kJ/hr (there are 3600seconds in an hour)

    112913kJ/hr = 31kW

    now that is at 50% and only cooling to 40C.. there is more kW to be had at a small expense, but the returns decrease as you get closer to the max... which I guess is 80kW if you have a 100% efficient HX and you cooled to 20C

  • Thank you this is a great help.

  • @CothermanDistilling said: To do the work that the boiler HX can do with direct electric heat:

    P(kW) = E(kJ) / t(s) --> so 1kW = 3600kJ/hr (there are 3600seconds in an hour)

    112913kJ/hr = 31kW

    now that is at 50% and only cooling to 40C.. there is more kW to be had at a small expense, but the returns decrease as you get closer to the max... which I guess is 80kW if you have a 100% efficient HX and you cooled to 20C

    One more question: What would the surface area of HX tubing need to be to achieve a 100% efficiency in theory?

  • Probably approach infinity.

  • @grim said: Probably approach infinity.

    that is 100% correct..

    just buy bigger, longer and more, the SD stuff like chillers are modular... you will find all sorts of uses for them :-)

  • The only downside of going oversize, as I see it, if I am distilling grain-in, is that the solids may start to settle to the bottom of the HX because of the lower flow rates in bigger/oversized HX'ers. Or am I thinking too narrow here?

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