* * * Comments * * *
Vol. 3 No. 8 - Time for the Continuous Freeze-Drying System is NOW!
The following are a series of e-mail messages with Matthew Halvorsen and Gerard van Antwerpen. I am very grateful to both these individuals for alerting me to an error in the above INSIGHT. This exchange of e-mail shows how “dissidence can breed discovery”.
Dr. Jennings -
Several of your insight articles have been forwarded to me and, for the most part, I find them on target and of high relevance. Having read your article a few months ago concerning the energy input required for lyophilization I feel compelled to point out that while all of you calculations are accurate with regard to energies of the sublimation, crystallization etc. you have missed the important fact that refrigeration equipment does not "create" or "destroy" heat it merely acts to transfer it from one location to another. Because of this, I think you will find that your theoretical data do not match actual real world electric consumption.
Our corporation operates in NH, which, until the issues in the west, had the highest electric rates in the country (about $.0125/kWH plus a demand charge). It costs us about $25.00 -$ 35.00 a day to run a large production unit. While I agree that the issues in the West would have a serious effect on the economics of the process, I do not feel that it would make it impossible. Further, the issues that are taking place right now in the West have more to do with regulatory failure in the conversion to competition (largely related the CA PUC not allowing long term hedging of energy purchases) and a demand / supply imbalance which should be corrected as time goes on. (My wife has been involved in electric utility deregulation for close to 10 years, perhaps she has further insight on these issues... I have copied her on this e-mail)
I think a better target for our technical and political efforts would be the development of additional sources of renewable energy. I think we are all in agreement that our current reliance on fossil fuels cannot continue indefinitely.
Matthew Halvorsen
E-mail: mhalvorsen@lyophilization.com
Response by T.A. Jennings, Ph.D.
Thank you for responding to the last INSIGHT.
I fully understand that the actual electrical energy required by the refrigeration system will be far greater than the heat of sublimation of ice. The reason being that the refrigeration system is an energy transfer system and there will be an efficiency factor involved. At the temperatures that most condensers operate such a factor will be significantly less than 1. So I agree with you that the numbers stated in INSIGHT Vol. 3 No. 8 are ideal and the cost would be far greater.
I could only estimate the commercial rate for electrical power and I am pleased that you have provided some real data. But still, the fact remains that the cost of power in the Northwest last summer increased by a factor of 50 times. That is also a real number so your current rate would now be $1250 to $1750 per day. As a business man, such
an increase would certainly have an impact on the bottom line.
I would like to place your comments on our web site for others to read. Perhaps your wife would also like to add to the discussion and that would be welcome.
Response by Matthew Halvorsen
Thanks for the reply. I understand what you are saying regarding the efficiency rates of low temp refrigeration and I truly hope that power prices here do not reach the levels in CA. However I think you misunderstood my comment regarding power consumption. What I am saying is that I do not believe it is correct calculate power use just by adding up the energy required for freezing, sublimation, and condensing the vapor. The heat of crystallization (in the freeze down and condensing phase) is just being "moved" by the refrigeration system into the cooling water or air. You are correct in calculating the energy required to sublimate the water as that energy is, likely, coming from an electric resistance heater (in addition to other heat inputs such as the circ pump and system friction)
Also if you would like to paraphrase the discussion for your web site please feel free to do so, however I would prefer for me and my company to remain anonymous because of the nature of our business.
Matthew Halvorsen
E-mail: mhalvorsen@lyophilization.com
Response by T.A. Jennings, Ph.D.
I do agree with you 100%. I agree that just adding up the heat of fusion, heat of sublimation and heat of condensation is not the correct amount of energy used by the machine. It is a false low value. It is an ideal value that would only exist if we had a perfect freeze-dryer. But the point is this it is a low value of energy consumption and taking all the parameters that you mention and others I could list, would required even greater energy. The point is, however, if you can't afford to run an ideal freeze-dryer then how could you possibly afford to operate the dryer that is non ideal?
Response by Matthew Halvorsen
I am saying the values are falsely HIGH. Another way to consider the MAXIMUM power use is to look at the fused capacity of the unit(e.g. the circuit breaker). Take the example of a Hull 120FSX230 (120 square ft with a 230 kg condenser) This unit is fused at 90A 480V 3 phase. Consider the MAXIMUM energy usage (480V x 90A) = 43,200 watts or 43.2 kw at a national average of 8.5 cent per kw hour this is $ 3.67/hour or $88.13 a day. This may neglect issues concerning 3 phase power factors (there may be a factor of 1.33 or 1.77 It has been a while since I studied this) but of course the unit does not draw full power all of the time. In fact, it typically draws less than half of full power. I have frozen and sublimated 200L of ice in this unit in 40 hours. The cost to do this would be $3.67/hour x 40 hours or $146.80 with the unit drawing FULL power. The actual cost is likely closer to $ 73.40 or about 1/200th the cost you estimated in Volume 3 Number 8 with a power cost at $0.03/kwh.
The real costs in the business are the cost of the equipment and the cost of remaining FDA compliant. Although, if I could cut my power bill in half I could afford a nice house somewhere warm with a high end sports car in the garage... It is to cold in NH right now.
Matthew Halvorsen
E-mail: mhalvorsen@lyophilization.com
Response by T.A. Jennings, Ph.D.
Thank you for your comment. I intend to check over my math once again and respond to you.
I am a very firm believer that "dissidence breeds discovery."
Should I be in error you will have my deepest thanks but not my anger.
Show me a scientist or engineer who never made an mistake and I will show you a person who has never done anything.
Response by Matthew Halvorsen
I had the advantage of having the empirical data (e.g. my electric bills) I wouldn't feel too bad about this, if I had a dollar for every time the theoretical data diverged from the empirical I would be a wealthy man.
Matthew Halvorsen
E-mail: mhalvorsen@lyophilization.com
Response by T.A. Jennings, Ph.D.
I repeated my calculations. I tend to think in terms of calories rather than kilo-watt hrs. My hand book did not have any direct conversion of these units so I did the conversion. Murphy was waiting for me. In repeating the calculation I found the error.
1 kilo cal = 1.162 10-3 kilo-watt hrs. (note this is a later corrected conversion factor - see following correspondence from Gerard van Antwerpen )
For cooling 100 liters (100 kilo-grams) of water from ambient to 0 C, freezing, cooling the ice to -40 C will require about 13.9 kilo-watt hrs.
Sublimation of the 100 liters of ice will require 78.5 kilo-watt hrs. and condensing the vapor to ice will take another 78.5 kilo-watt hrs.
The total energy need for this process will be just about 27.8 kilo-watt hrs. or
at your cost of $0.125/ kilo-watt hrs about $3.48. For 200 liters it would be $6.96.
Since the actual cost of this process was $73.40, your freeze dryer is operating at an efficiency of just 9.5% or the dryer wastes 90.5% of the power consumed.
I knew that the efficiency of the dryer was low but this number really shocks me.
Dissidence does indeed breed discovery.
I have never seen any one publish a paper on the energy efficiency of a freeze-dryer. Perhaps the reason for the absence of such a paper is the power is or was cheap.
As the cost of energy rises, and it will, the efficiency of the dryer will become an increasingly important economic factor.
I thank you for bringing this error to my attention.
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Hello Mr. Jennings,
I would like to comment on one of your issues of "insight". I have only recently discovered your publication while doing some IQ and OQ work for a freeze dryer we have built. I must say it is very good and it gave me some good points to use when trying to get my ideas accros to other people here at work.
The particular issue I'm talking about here is Volume 3 Number 8, about the costs of freeze drying and the consequences a increase in power costs might have upon the whole freeze dry process.
I came to New Zealand 4 years ago from The Netherlands, and having had my education there in the metric system all the time, I had some problems getting used to the mixed system a lot of the people here are still using. BTU's were totaly strange to me, inches, etc. I had heard of before. But now with more and more publications and machine specs. are given in metric units I have a hard time to train the people to be able to use them.
Reading your before mentioned article, the values for the costs of freezing and sublimation seemed very high to me. I looks like one of the common errors with Joules, Watts, Calories and KiloWattHours has poped up again. I calculate the cost of the freezing of the 100kg of water to be only $0.2275 quitte a difference with your $1000 !
Freezing of water costs: 3.33 x105 J/kg, freezing of 100kg costs :100 x 3.33 x 105 J = 3.33 x 107 J if 1 KWhr cost $0.03 then 1J costs: 0.03 / (3600 x 103 ) = $8.33
x10-9 ( 1KWhr = 3600kJ) the the cost of freezing is: 3.33 x 107 x 8.33 x 10-9 = $0.2775
Similar with the sublimation costs. I calculate these to be $2.33 for the 100kg of ice
The error seems to have been started in the first line of the paragraph where the statement " 79.7 calories or a minimum of 333 WATTS to freeze one gram of water" This WATTS should read Joules.
We manufacture a range of freeze dryers ranging from 5 to 1000kg batch loaded. Mainly for general purpose, but some are used for pharmaceuticals. We have a rough costing per lb. of water removed ranging from US$ 0.45 for the 1000kg unit to US$1.10 for a 80kg unit. This would include capital interest, energy, operator wages, building cost, etc. based on 320 loads per year. The costs for a purpose built pharmaceutical machine would be higher due to more stringent requirements regarding steralizing etc.
Best Regards
Gerard van Antwerpen
BE mech., MIPENZ, Reg.223986
Design Engineer
Cuddon Ltd.
Blenheim, NZ
E-Mail design@cuddon.co.nz
Respose by T.A. Jennings, Ph.D.
You are quite right the energy values for conversions of calories to kilo-watt hr. are indeed far too high. This was kindly pointed out to me by Matthew Halvorsen earlier this month and I have revised the INSIGHT. That is one thing that is good about publishing on the internet is that you can correct the original publication.
The problem was in the conversion from calories to kilo-watt hr. I could not find a direct conversion at the time. The conversion factor that I am using right now is
1 kilo-cal = 1.162 x10-4 kilo-watt hrs.
I certainly thank you for drawing this error to my attention and your interest in our web site.
Please note in another e-mail message Gerard van Antwerpen pointed out the above conversion factor was also in error. The correct conversion factor is
1 kilo-cal = 1.162 x10-3 kilo-watt hrs.
