Vat cooling cost 1

[AlexDO]

Hello,
I want to calculate the cost of the cooling process and see if this is the right way to do it. Assuming the cost per KW at $0.15
I need to cool 12 vats of milk from 175 F down to 90 F. Each vat has 1500 gallons of milk.
Total BTU per vat = 1500*8.6*0.92*85=1,008,780
Total TR=1008780/12000=84,065
Total KW=84,065*3.51=295,06
Total cost=295*0.15=$44.25
Total cost for 12 vats=44.25*12=$531 per day
Is this right?

 

[MJCronin]

Homework problem ????

MJCronin
Sr. Process Engineer

 

[dvd]

Put some units in your equations- unitless equations indicate laziness and slopiness to me. How does time enter into this? Do you want to do this in two hours or two weeks?

 

[IRstuff]

How does time enter into this? Do you want to do this in two hours or two weeks?

For that matter, is 2 hours even a doable thing without stirring? Also, need to consider thermal losses if this process takes a few hours.

Also, your numbers are possibly a bit sloppy. Density of milk should be more like 8.6 lb/gal. You're using a mixed unit version of specific heat that has kcal/kg/degC, but you're using Imperial density and temperature. That is why you need to have units in your calculations.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[MintJulep]

At least some of your arithmetic is wrong.

 

[pierreick]

Hi,
I don't think this is the right forum, heat transfer is more appropriate.
How do you intend to cool down your milk? A process description is needed.
You may want to study the material underneath.

https://nzifst.org.nz/resources/unitoperations/httrapps.htm

Pierre

 

[LittleInch]

AlexDO,

You are messing about with units here.

you don't appear to have grasped the difference between POWER - kW and ENERGY kWh (i.e. 1kW for one hour)

Also I can't be bothered to check all your figures so please list them in consistent units, either BTU, BTU/hr, lbs, TR etc or kW, Deg C, etc.

You're also ignoring any heat input for ambient conditions or efficiency of the chillers or any idea how long this operation is planned to take.

My BOAFP calc is less than yours.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AlexDO]

Hi Guys
Thank you for your replies, and sorry for the confusion.
I am trying to determine the total amount of energy that needs to be removed from the milk and the cost associated with this process. I want to cool down one jacketed vat of milk 1500 gallons from 175 degrees Fahrenheit to 90 degrees Fahrenheit. The vat has a mixer that mixes the milk during this process. Also, there is an incoming cold water coming to the jacket at 36 degrees Fahrenheit
1500 gallons
Milk has a density of around 8.6 pounds per gallon
0.92 specific heat (Btu/(lb oF)
Delta T 85 degrees Fahrenheit
I am using a sensible heat formula to find the total amount of BTU that has to be removed q = mcΔT
Total BTU per vat = 1500*8.6*0.92*85=1,008,780
How do I convert this energy to find the cost of electricity used for this process?

 

[LittleInch]

Well in a very simplistic sense you're on the way.

I get a little more total energy but not a lot.

Now you need to decide how long you want to allow for this operation. Say one hour?

So I get that to be an average of 300kW of heat rejection.

If your COP for your chiller unit is lets say 2 to allow for other losses / inefficiencies etc that's 150kW of electrical power needed.

So 150 kWh x 0.15 $/kWh = $22.5.

But the heat transfer rate might not be even over time and to start with your unit won't be able to maintain your 36F incoming chilled water supply as your chiller will just be overloaded or your supply water reduced. Also you will need to circulate the milk in the Vat.

And then expend money keeping it cool.

And tis requires perfect insulation of your vat which doesn't exist.

But that gets you in the ball park I think? Anywhere from $20 to 50 per vat is as good as you're going to get before getting into specifics.

If you want it faster than an hour then there are possible issues about how fast you can cool a vat using an external jacket as the area for heat transfer is relatively small. And an hour might be optimistic - haven't bothered to check the heat transfer rate as I don't know the dimensions of your "vat"




Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AlexDO]

Thank you so much LittleInch,
I don't really look at the timeline of the cooling process but want to be at least a 1 - 2 hours window.
The project I am working on is to justify the VAT cooling process compared to HTST milk pasteurization. I want to understand the savings on the cooling side of it.

 

[LittleInch]

There may be physical issues which mean the vat system doesn't work as well as another system so the devil is in the detail. As the milk cools the heat transfer rate to the outer jacket falls so temperature won't fall as fast at the end which might be important?

I don't know a lot about milk cooling but think there are other hygiene issues to think about warm milk....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pierreick]

Hi,
You should study the supportive documents shared with you or ask support from a chemical engineer.
Good luck.
Pierre

 

[IRstuff]

I don't see HTST as a cost-driven choice; it supposedly preserves taste and color, but it's supposedly also the dominant approach for pasteurization. The heating is supposedly on the order of seconds, so its "rapid cooling" is likely in the minutes regime, so not something that could be easily done in a vat.

The flash heating and cooling would seem to entail high sunk cost, irrespective of its marginal cost.

Note that HTST temperature cycle is roughly, heat to 160F for 15-30 seconds and rapidly cool to 40F over a time period I've not been able to find, but I assume it's comparable, since it's a continuous process using heating and cooling plates in the processor.

This makes the vat approach much less productive than the HTST approach, but UHT and HTST are basically standard and supposedly have crazy-long shelf lives, even at room temperature.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[LittleInch]

HTST seems to use regeneration modules where the hot liquid warms up the cold liquid before the heating and cooling sections thereby saving energy. The vat system doesn't seem to have this?

Overall I'm not sure what savings there are here.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AlexDO]

Hi guys,
Thank you for your replies. Yes, the HTST system uses a heat regeneration module in which 80-90 % of energy is recovered compared to the vat pasteurization process. The hot pasteurized milk preheats the incoming cold milk in the regeneration section. Also. there is no cooling required to have a 90 degrees Fahrenheit outlet temperature for the fermentation stage. Heat energy and cooling energy are the cost savings.

Thank you all.

 

[IRstuff]

From

https://cms.agr.wa.gov/WSDAKentico/...de.pdf?/308-PasteurizerOperatorStudyGuide.pdf

it looks like the minimum time to heat is 30 minutes. That would require 590 kW of power. Because the heat comes from the exterior jacketing in the form of steam, you'd need a truckload of agitation to minimize boiling of the milk. There are thermal losses in the jacketing as well as in the steam generation process which have to be accounted for.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm