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Closed loop cooling for 300 gal still

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Hi, all

I am trying to figure out if we can get by with a small chiller (e.g. 5 ton or less) and a big tank of cold water. Our water rates are quite high and we live in a village where everyone is very concerned about water consumption, so using a one pass system where we dump hot water down the drain won't really fly. Can someone out there check my numbers, since I'm really not sure if any of my assumptions make sense?

For mash cooling:

Assume we need to cool 300 gallons of mash (assume same thermal properties and density as water) from 150F down to 90F or so for pitching. This should use about 150,120 Btu (300 gal * 8.34 lb/gal*60F). If we use cold tap water (at 50F) and let it heat up on average to about (100F), we would need an empty tank big enough to hold 360 gallons of hot water, which we could use for mashing, cleaning, etc. Alternatively, we could use a small chiller to cool the water down overnight and start in the morning with 360 gallons of water at 50F.

For condensing our stripping still:

Assume we are producing low wine with 60% alcohol, starting with 300 gallon of wash at 10%. This should yield a maximum of 50 gallons at 60%ABV (20 gallons of water and 30 gallons of alcohol). The energy to condense is 8100 Btu per gallon for water and about 2400 Btu per gallon of ethanol. Therefore, condensing the vapour should take about 234,000 Btu. We'll need a little extra cooling to bring the temperature of the condensate down from about 180 to 70F, this should take about 45,870 Btu (50 gallons * 8.34 lb/gal * 110F). Our total cooling requirement is, therefore about 280,000 Btu. This would require about 668 gallons of water (assuming it starts around 50 and we let it warm up to 100F). 

If we cool the 668 gallons of 100 F water overnight (e.g. 12 hours) back down to 50F, we should need about 23,213 Btu/h or roughly 2 tons. 

Obviously, we would need multiple tanks and/or do some careful scheduling of our mashing and stripping. Does any of this make sense?

Thanks in advance for your feedback!

Mark

 

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We had a lot of great help from G&D Chillers. We went with an oversized reservoir that the spent cooling water returns to, as opposed to a separate tank. That way the returning hot water won't effect the temperature of the reservoir as much due to the sheer size of it. All the while a twin seven ton glycol chiller is cooling said reservoir, and will continue to do so overnight until it reaches a pre-determined temperature. Basically, it was more economical to have an enormous reservoir as opposed to a more powerful chiller unit.

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We have a closed loop system that uses our pond as the cooler. Most of the time it's great but we are at it's limits now.

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You will need a very large reservoir to serve a 300 gal strip run with a 5 HP chiller.

In addition, you will have a tough time keeping any fermenters and getting back to setpoint to chill mash.

It is much better to go to an 10 ton chiller and 600 gal reservoir.

Good luck and if you need a trouble free air glycol cooler to precool chilled return water, give me a shout. For the electric cost of a second pump and fan motor, it will save you kwh and have payback in less than a couple years, depending on your weather.

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Mark,

 

If your tap water is 50 F then simply use the condensers as hot water heaters and reclaim the hot water in 2 plastic tanks for all of your cleaning and mashing needs.  You should be able to use all of your condenser water that way. 

If your agitator is strong enough, you can add cold water to a really thick mash for the first crash cool and use your chiller with a tube in tube for the 2nd crash cool.

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We run roughly in the same ballpark.

Our tank is a little more than 2x the still volume, we run 4.5 tons.

As long as we pre-chill the tank to 50f, we can make it through a run.  If the tank starts warm, say 75f, we can not make it through a run, even with the chillers on.  The tank and chiller can not keep up with a fast strip - but this might be due to our product condenser size (need to be significantly larger with a slower flow rate).  The chillers easily re-cool the tank by early morning.  

On the mash cooling, I think you are optimistic, the delta-t is significantly smaller.  As soon as the tank starts to warm, the cooling time will start dragging out substantially (unless you have a massive heat exchanger).  I would imagine you'd need 3x the mash tun volume, just to keep the coolant temperature low.

Our fermenter chillers are separate from our still chillers, for exactly the reason MG mentions.

We would have went larger, but we don't have 3 phase.  We'll eventually put dry coolers on the roof, since we live far enough North to be able to cool air temperatures for half the year.

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I have supplied 5 HP chillers for 300 Gal pot stills, but more often than not, the customer is running a strip, so the load is much hotter an usually wind up supplying a 10 Ton instead, a couple fermenters are enough to make a 5 HP lacking. I really don't like chiller return water to get beyond 70F continuously, 75F continuously and you're asking for trouble on hot Summer days, overheating refrigerant compressors.

I am supplying a chiller plus a hybrid air cooler on a large mash load (85 tons) down South right now and wound up selecting a 40 T hybrid cooler (runs like a cooling tower only dry circuited) on the first stage cooling and a 60 ton chiller on the 2nd stage rather than a 100 ton chiller.  Much more KW friendly and will allow a second mash run in the future.

I have two types of dry or hybrid coolers, one very simple and the other like the hybrid variety which uses a water spray in the summer. Paybacks about 2 years or less. 

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MG Thermal you are always good for practical matters. There are a lot of ways to optimize chiller loads and I am with you on not wanting the return water temp above a certain critical threshold. This is for sure necessary. The thing that boggles my mind about everyone attempting to save dollars on first cost, is the idea of a cooling media supply that drifts higher during the run which in my view is fully unacceptable. If you want a rock solid process your condenser cooling fluid needs to be at a " constant." It does involve, not doing things on the ultra cheap to make this happen but you do not have to continually adjust your prcess due to a lack of the correct temperature media. This will take away instantly the chasing of certain variables that lead to inconsistency. It will allow you to focus on your process, instead of chase the lack or necessary cooling BTUs. Batch cooling really only is a time game. It does not give you more of the cooling BTUs in real terms that you may be short on.

 

Star

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Thanks, Star!

It's a tough thing to get through some clients that running a strip requires almost double capacity what a pot run will require- and just because you have oodles of tank capacity, doesn't mean successive strips and mash coolings will have you run out of tank capacity because the chiller was sized marginally or the boiler is over capacity and will try to do the strip in 3 hrs and your cooling was sized on 6 hrs.  

Lately it seems to be common to have larger mash runs, more than twice the strip run volume and here is where a hybrid cooler can keep your chiller size down to the size of the run volumes and fermenters.

Unequal size of batches will make tanks hot such that there isn't enough remaining to control a number of fermenter. 

Like everything, best be wary of loads that are far apart in the calculations.

 

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We have a closed loop w/ a 211 gallon still, 2-211 gallon fermenters (sized for 6), a 10 chiller and a 850 gallon holding tank. It has worked excellent since installed.

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Curious what type of tanks everyone is using for cold water reservoirs?  

We currently have a 300 gallon stainless tank with a built in stainless coil we feed the glycol from the chiller through .  We wrapped it with a layer of rubber foam insulation, but its hardly what one would consider properly insulated.  Tank was purchased used for salvage company.  We need to upgrade to a larger reservoir (probably something along the lines of 600 gallons)  Seems like there are options for insulated plastic water tanks, but they don't have heat exchanges, etc.   

Just curious if anyone has found a good solution.

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Poly Tank - chillers directly cooling the water.  We only cool to 50f, so no need for glycol.  We get some condensation on hot humid days, but 50f is a good balance for us.  

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18 hours ago, Silk City Distillers said:

Poly Tank - chillers directly cooling the water.  

The chiller we have is glycol, so I dont think this is an option for us, unless we change chillers.  Might need to start hunting for a brewers bright tank, as they typically have both jackets and insulation.  

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7 minutes ago, HedgeBird said:

The chiller we have is glycol, so I dont think this is an option for us, unless we change chillers.  Might need to start hunting for a brewers bright tank, as they typically have both jackets and insulation.  

You need to add a small plate exchanger and second pump. Put globe valves on discharge of pumps so you can balance flow on HTX.  I have pix from one of clients, if you want to email me, I'll send them over.

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2 hours ago, MG Thermal Consulting said:

You need to add a small plate exchanger and second pump. Put globe valves on discharge of pumps so you can balance flow on HTX.  I have pix from one of clients, if you want to email me, I'll send them over.

This is basically what we would need to do to convert our Glycol circulating chiller to a water circulating chiller?  I assume your thinking a cross flow type plate exchanger and can see how that would address the problem, but with the complication of an additional pump.  (basically adds a cross flow plate exchanger and circulating pump, but eliminates the need for a jacketed cold water tank)  This would also allow us to still run some things (fermenters perhaps) directly with glycol..  Makes sense.

 

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Yep, that's the deal. The water pump side is your feed to still and the chiller pump can feed the fermenters.

This way you can shut off the process pump and just run the chiller pump at night (like now with these hot days and nights).

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If I'm running my chillers at 50f set points - what's the difference between water and glycol?

Both cause corrosion without inhibitors - arguable that uninhibited glycol is far worse due to decomposition.  Yet, I know plenty of brewers running uninhibited glycol.  Every day we talk about people using their condensers to heat straight water, or just use city water for cooling.

What's the benefit of running sub-freezing temperatures and using glycol?  My jackets and condensers all operate just fine with 50f coolant.

Good luck controlling a dephlegmator with sub-freezing coolant - all it takes it a tiny PID/Control upset, and the column goes full reflux with  sub-cooled reflux - a serious PITA.  Having to feed the dephleg coolant through the product condenser to temper it seems like a major compromise, because it links control of both condensers.  Trying to run high reflux and slow product rate will almost always result in overcooled product (wasted energy).

Sure, warmer coolant likely needs higher flow rates, get it.  But water is a better coolant than glycol mix, so it's got slightly better heat transfer, which likely reduces the necessary flow rate.

I have city water plumbed into my cooling system, so if my chillers fail, or I run out of capacity, I can just backup with regular water, with no worry about losing glycol down the drain.

I mean, if I was running lagering tanks, I get it.  If I was using the chillers to cool a cold box, I get it.  If I had an undersized coolant reservoir, thus need to run a lower temperature to increase my cooling capacity, I get it.  If my fermenter jackets were minimal, I get it.

My Rotovap chiller runs at -25c fixed, so that's running glycol/water, so I get it.

What am I missing?

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2 hours ago, Silk City Distillers said:

What am I missing?

Probably the fact that our chiller is located outside and subject to freezing temperatures so requires glycol.  Even if it was inside, I also am not familiar enough with this stuff to know if we could take the chiller we have, that is currently running sub-freezing glycol and just change its temperature set-point to 50F and swap the glycol for water. My assumption is/was that making that change is not an option??

2 hours ago, Silk City Distillers said:

What's the benefit of running sub-freezing temperatures and using glycol?  My jackets and condensers all operate just fine with 50f coolant.

No one has suggested running glycol to the still or mash tun, only the fermenters.  Currently the still and mash tun are plumbed to the cold water tank (our temp set to about 45F), and this is what MG mentions doing.

Your points are probably all valid for someone setting up their system from scratch, but I am using an existing chiller purchased and used by a brewery in my building..

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Yeah, moving to roof-mounted dry coolers is going to be a big shift for us.  We would need to do closed-loop glycol and HX to the existing water system, or bite the bullet and shift.

Our chillers are inside - great during the winter.  Awful during the summer, especially with 100f degrees expected this weekend.

Don't mind me, I like to argue.

 

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Hedge,

More often than not, clients just fill the whole inside portion with water (treated) which simplifies it.

The only reason glycol is added is to: 1) prevent winter free-ups, and 2) if you want to chill water below 45F, many manufacturers tell you to.

Tapping off the glycol line allows you to lower the glycol temperature- handy for chill filtering- but you must valve the line off so the sub-freezing  glycol doesn't pass through the heat exchanger (if you have one) and freeze the water in the water loop of the heat -x.

You certainly can have the chiller set lower, again depending on whose you have, but you should be able to get to 40F by adding glycol and re-setting thermostat.

"Raw" water is often used in critical situations as a backup, only, situation like at hospitals, but it needs to have a rugged filter to keep silt out of the loop which will inevitably end up inside the chiller evaporator.  If you have a chiller that has a "coil inside a tank" design, this is not as critical because the water is outside of the tubing, settling in the tank.

 

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For a 5 ton chiller, a brazed plate exchanger is about $900, new.

Obviously there are a lot of used plate and frames out there, you just have to set flows.

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For such a small chiller, if you can set it under a roof vent to take hot discharge air off it outside, you should be able to use it indoors unless it would be really close to any ethanol vapor- thats a no-no.

The chiller should not suffer too much with glycol at the same temperature output, you may need a little more flow on the glycol to offset the friction loss and inherent loss from glycol thermo properties.

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When electricity is $0.41/kw hr and Water $0.05/gal, with a 500 gallon still, 78F water temps, would it work best with a 10 tonne chiller, bore a hole and create a chilling water option for the condenser? Year round air temps 95 F to 75F. Ideas? Fermentation of molasses.

 

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