Effects of Pre-Cooling the water on Freezing Times

Hi all,
I came across this yesterday suggesting that by pre-cooling the water to 10C, the OP was able to reduce freeze times.

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At couple of plants, I had incorporated a smaller refrigeration unit to bring the temperature of water being filled in the cans to 7 to 10oC. That had improved the timing of freezing, thus increasing the production.

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However the thread doesn't say how much actual freeze time was shaved off .

Then I came across this today:

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If 288,000 Btu are required to make one ton of ice, divide this by 24 hours to get 12,000 Btu/h required to make one ton of ice in one day. This is the requirement for the phase change from liquid to solid — to convert water at 0°C (+32°F) into ice at 0°C (+32°F). As a practical matter, additional refrigeration is required to take water at room temperature and turn it into ice.
To be specific, one ton of refrigeration capacity can freeze one short ton of water at 0°C (32°F) in 24 hours.

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http://www.powerknot.com/what-is-a-t...igeration.html

So ~24 hours to state change given water temp of ~0C. Our current plant takes 48 hours to freeze water. I am looking at some chillers that can reduce water temp down to 0.5C and their power requirements is half that of the Ice Block plant. If we added a water chiller to the system, would it effectively reduce the freeze times close to half, while reducing our cost of production, thanks to the higher efficiency of the water chillers? If not half, roughly what kind of freeze time reductions can we expect?

Sounds too good to be true. Am I missing something here? Whats the catch?

aakbar,
Check download, see page 90 gives some indication of producing more ice with colder water.

http://www.vogtice.com/wp-content/up...ice-Manual.pdf

I don't see any reason for being surprised.
Everyone who works with ice machines knows that, the colder the supply water, the shorter the ice cycle.

Some machines though are working with timers so it's only about the temp of the ice.

What is the current water temp being put into the cans?
In your first post you asked what 6X6 and 8X8 stood for. That is the bore and stroke of each the cylinders in the compressors.

The latent heat of freezing the water is still the biggest part of refrigeration load, the sensible load above freezing is minor by comparison, but pre chilling entering water will have gains, nothing close to halving whole cycle. But all dependent on seasonal water supply temperatures. Adding ice banks rather than chillers to pre chill make up water will decrease block ice freeze rate. You reduce power consumption and still get 0.5 C ish water for refilling block ice containers.

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Originally Posted by RANGER1

aakbar,
Check download, see page 90 gives some indication of producing more ice with colder water.

http://www.vogtice.com/wp-content/up...ice-Manual.pdf

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Thanks mate! Very helpful. It seems going from 90F from 50F seems to increase capacity in the ~15-20%. Nothing to sneeze at.

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Originally Posted by NH3LVR

What is the current water temp being put into the cans?
In your first post you asked what 6X6 and 8X8 stood for. That is the bore and stroke of each the cylinders in the compressors.

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Current temp is between 17-22C depending on time of the day. The water is supplied from a water tank on the roof top and in 40C ambient, it gets a little warm during the day.

Thank you for the information on the bore and stroke. They are all 2 cylinder compressors.

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Originally Posted by Magoo

The latent heat of freezing the water is still the biggest part of refrigeration load, the sensible load above freezing is minor by comparison, but pre chilling entering water will have gains, nothing close to halving whole cycle. But all dependent on seasonal water supply temperatures. Adding ice banks rather than chillers to pre chill make up water will decrease block ice freeze rate. You reduce power consumption and still get 0.5 C ish water for refilling block ice containers.

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You are quiet right about not having enough gains to half the freezing time. This morning I poured some water in a stainless steel container and set it in the freezer section. Bringing it to about 1C took around an hour or so but to actually freeze it solid took more than 4 hours. So yeah. My initial estimates were overly optimistic. The other problem I am anticipating with the water chiller option is managing the cold water flow. There are times during the summer when our daily demand is close to 28,000 gallons and that too in a short period of time when we harvest the ice and re-fill the tanks. So we kinda need all that water in a short period of time and then nothing. I suspect the kind of chiller that can keep up with that kind of demand is going to end up costing way more than the cost savings in this case.

I am intrigued by the ice banks suggestion. Are they the same as thermal storage tanks? How would one go about implementing them in an ice block factory? Our peak electric tariff is from 7PM-11PM. Rest is all off-peak.

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Originally Posted by aakbar

Thanks mate! Very helpful. It seems going from 90F from 50F seems to increase capacity in the ~15-20%. Nothing to sneeze at.

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AAkbar,
Those figures are from a tube ice machine so not entirely accurate for your block ice, but an indication it does something. Tube ice cycle around 8-20 minutes depending on set up.
What temperature is the brine used for freezing ice?
How cold is the ice when removed from mould.?

Hi AAkbar,
Ice banks are tanks with pipe grids inside that chill the water and form ice on tubes, basically run system 24/7 to reduce power consumption, a demand water chiller would be large and will supply water at +5.5C.
There are also falling film chillers eg Chester Jenson set up above water make up storage tank, continuously circulating.
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Originally Posted by RANGER1

AAkbar,
What temperature is the brine used for freezing ice?
How cold is the ice when removed from mould.?

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Ranger1, 2016 was the first year I ran the ice block plant. I measured the brine temp during the season and it showed -0.7C. I don't think that it should be at this temp for optimum performance. I've been told it should be between -10 to -15

I never even thought to measure the ice temp. Shouldn't it always be closed to 0C?

Attachment 14444

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Originally Posted by Magoo

Hi AAkbar,
Ice banks are tanks with pipe grids inside that chill the water and form ice on tubes, basically run system 24/7 to reduce power consumption, a demand water chiller would be large and will supply water at +5.5C.
There are also falling film chillers eg Chester Jenson set up above water make up storage tank, continuously circulating.
.

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Thanks!

Aakbar,
I agree brine should be -10 to -15 deg C, it will help reduce freeze time, but if frozen to quick ice will not be as clear.
Refrigeration system will work a bit harder, but temp you measured, was it at beginning, middle or end of freezing period?
Brine should also be checked for freezing temperature as well as good circulation with pump.
Brine solution could be diluted over time.
I like those old machines you have, as go forever.
I wonder though if they are working 100%, have they been checked in the last couple of years.
Usually check suction & discharge valves.

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Originally Posted by RANGER1

Aakbar,
Refrigeration system will work a bit harder, but temp you measured, was it at beginning, middle or end of freezing period?

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The way our Ice Plant works, we harvest half the capacity of one tank everyday. So if the brine pool has a total of 300 blocks in it, we harvest a max of 150 every 24 hours. The system takes 48 hours to freeze water into ice so I guess it's a continuous cycle with no beginning or end.

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Originally Posted by RANGER1

I like those old machines you have, as go forever.
I wonder though if they are working 100%, have they been checked in the last couple of years.
Usually check suction & discharge valves.

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You're right. They do go on forever. I am just not sure how efficient they are anymore given their old design. We sent one of those to the service center for repairs this year. We'll get it back by February.