What goes around comes around

[shogun7]

Carbon dioxide (CO2, or R-744) as a refrigerant seems to be making a comeback. The reasons are simple: It’s plentiful, inexpensive (about$1 per pound) and it’s accepted under environmental regulations everywhere in the world. CO2 is natural as it’s found in abundance in Earth’s atmosphere, and every animal on Earth, including the human population, replenishes the supply with every exhaled breath. So what caused CO2 to lose out as a refrigerant if it had the advantages of being cheap and plentiful? In a word, pressure. The CO2 cycle’s high-side pressure can be as high as 800 psia in a subcritical cycle. Transcritical cycles, applicable to heat pumps and other close-coupled commercial refrigeration applications, rise above the critical point (1,070 psia), and can easily reach 1,500 psia. So what’s the prognoses in jolly old Europe?

Zu antworten, dass quesion wir den cristal Ball von Adolf fragen und dann Zeichen iterpretation des Wetters dass als eine Obstructinist-Antwort, nes Papa bekommen müssen?

[Peter_1]

Zu antworten, dass quesion wir den cristal Ball von Adolf fragen und dann Zeichen iterpretation des Wetters dass als eine Obstructinist-Antwort, nes Papa bekommen müssen?

Was that meant as German Shogun? You mixed Spanish, French and perhaps some German. Probably translated wit some sort of Babelfish automatic translator.
What is the meaning of this if I may ask?

[Andy]

Shogun
R744 is a good refrigerant to use and very usefull never mind the fad that is going on at present. We are using it extensively in large distribution centers for supermarket, pumped R744 in the coldstores and volitile secondary in the chills (pumped liquid off the cascade condenser returning to the R744 liquid receiver/surge vessel and liquid and vapour for re-cooling by the high temp R717 plant). Pipe sizes are smaller on the wet returns and comparable on the liquid lines, recir rates are low and pressure drops on pipe runs very low. We are lucky in a way with our defrost systems, in that we have a patented hot gas generator and don't have to trash the compressors at 45 barg discharge to have hot gas for defrost.
We have also just completed a plate freezing plant on R744 and the results are even better than hoped for. Evporation is lower than R717 and cost per ton of product frozen is also lower, with very good batch freezing turn around times.
Any R744 plants up and running in your part of the world yet?

Kind Regard. Andy

[chemi-cool]

hi andy.

do you buy R744 or have the equipment to separate it from the air?

out of curiousity, how much do you pay for a ton?

the reason I ask is because I maintain CO2 tanks farm that stores a few hundred tons of the liquid.

we use R404a to keep it -25C and under 22bar.


chemi

[Andy]

Hi Chemi-cool
we buy de-hydrated R744, mostly by road tanker, although it is available in cylinders, price well less than a £ per kilo, much less.
Kind Regards. Andy

[shogun7]

Peter, I as practicing my German because I am French

Andy, I have no direct experience with CO2 so I was wondering what pressures you work with and does certified people weld the piping. With those kinds of pressures I would think one must be doubly cautious. Do you find leaks as less of a significant problem as compared hydrocarbon refrigerants? Does your equipment operate in the subcritical and/or the transcritical cycles.

[Andy]

Hi Shogun

Andy, I have no direct experience with CO2 so I was wondering what pressures you work with and does certified people weld the piping. With those kinds of pressures I would think one must be doubly cautious. Do you find leaks as less of a significant problem as compared hydrocarbon refrigerants?

pressures are depandant on what part of the system you are working on. Highest pressure would be the defrost lines with a design pressure of 52 barg and a strength test to 56 barg. Your discharge would be somewhere in the region of 40 to 45barg and your compressor suction about 15 barg for deep freeze conditions.
Welding standards are very similar to NH3, (probably ASME 8 equavilent) with low temp astm 333 grade B (could be A) used. Good pipe work is good pipe work, much more is expected of process chemical pipe work than refrigeration, so the standards we work to as an industry are much higher than we require, to catch the higher standards required for process chemical.
We don't run transcritical, our system is simply a cascade system, which looks and operates much like a pumped nh3 system. You could say the cascade condenser is much like a closed flash intercooler in operation, except two different refrigerants interface there, NH3 evaporation is similar to an interstage evaporation say -5 to -15 deg C, with the R744 condensing maybe 4 to 6 deg c higher, dependant on cascade condenser design.
Hope this helps, keep the questions comming
Kind Regards. Andy.