liquid CO2 injector for dry ice machine (how does it work) 2

[NZBen]

I have a picture of an inlet to a small asco dry ice machine and Am trying to figure out how it works. I think I may have it figured but am wondering if anyone else can shed light on it's pluming for me and why it's arranged in such a complex manner the image is found here :

http://farm1.static.flickr.com/231/499206428_cabdc2b0e0.jpg?v=0

Thanks

 

[Montemayor]

Ben:

I see that you are still trying to make Dry Ice with someone else's flawed ideas. I had to try to make seven of these New Zealand "clunkers" work to produce pellet-shaped, food-grade, Dry Ice in 1985. Like most of the others who tried the same thing, I also failed. I wound up scrapping everyone of them and getting substantial, well-engineered machines to do the job. However, this experience drove me to develop and patent my own design of food-grade, pelletized Dry Ice which solved the bulk, food-grade production of Dry Ice.

The whole idea of the machine you describe "evolved" in New Zealand and not in Switzerland. The best I can guess is that Asco (a Swiss company) bought out the local New Zealand company that was making these pounding machines that were attractive only in initial capital costs. These machines failed to produce un-contaminated Dry Ice and I could not seriously recommend them for the food industry - nor for any steady-state flow process for that matter of fact. There are a lot of people in down-state Illinois who would turn purple and run for the hills if you told them they had to operate these machines.

I know exactly how the flawed thinking was attempted as an application for a Dry Ice pelletizer. It would take many paragraphs to explain it to you (and I don't know for what purpose), so I won't attempt it here.

Good Luck in whatever you are trying.

 

[NZBen]

I have my own system which works well, but I was wanting to know how this other system works it looks more complex than mine and was thinking there might be some cleverness to it - solely relating to the snow formation not the machine itself (my machine is a fully stainless hydraulic machine). I'd just like to know how it works for sake of knowing - I'm not about to buy one. It does seem very difficult to get a straight answer out of anyone on this site tho.

 

[dcasto]

Thanks Montemayer, as a curious type, what was the principle the spril tube/ejector/exchanger looking thing was suppose to work.

 

[NZBen]

Maybe no one knows the mysteries that lie beneath the theory of the spiral tube/ejector/exchanger device I got a theory but not too sure how true it is (and i've not really had much time to look at it so I'm prolly way off track) - my theory is that the liquid CO2 begins to spiral around the spirally thing, and gas gets drawn off through the little tubes that look like spokes (tho they do look a bit too small to do the job) there may be a restriction between the spiral pipe and the junction of where the other pipe merges in which would create a pressure diff to enable the gas to be drawn off. The rest of the tubing am guessing allows the snow to coalesce into bigger clumps (one would think that might cause a blockage).

I've never pulled one of these apart or spent any time near one - montemayor had seven so hopefully he's pulled one apart and knows whats inside or how it works?

 

[Montemayor]

Ben:

I just got back from a quality-time vacation with my grandchildren in Tucson, Arizona (where I posted my comments above) and can now spend some time responding to your basic question – and to dcasto’s curiosity.

I don’t know your age, but you would have to be at least 40 years old to have some in-depth knowledge of the Dry Ice business in New Zealand and especially about the Carbonic Industries’ Pelletizer machine and, therefore, be able to relate to what I am about to explain. Carbonic Industries, I believe, was the name of the company that developed and marketed the original (& existing design depicted n your photo) dry ice Pelletizer in New Zealand. Asco, a Swiss company, I believe has acquired Carbonic Industries since around 1990 or later.

The reason I have to mention the machine’s history is to explain to you why you are finding it difficult to logically understand how the machine works. The machine was first known by me around about 1965 when my company, Liquid Carbonic, became interested in the idea of pellet dry ice. Up to that time, Liquid had pioneered the industrial production of dry ice and the story I got while I was working for them in International Operations was that the “Kiwi” machine made pellets rather than the then conventional 10”x10”x10” blocks that everybody knew. There were marketing and distribution advantages to the pellet shape – although it also carried its inherent trade-offs and disadvantages. Liquid Carbonic bought and tried these machines out; since Liquid Carbonic was the largest producer of Dry Ice world-wide, they decided to develop their own Pelletizer. Their version, although better and much bigger than the Kiwi, also had the same basic flaw(s) in trying to process the solid snow: constant plugging-up of the system. This has been the main and common flaw of these type of machines (as well as other bad features) and the reason I patented my own design.

I worked (or tried to work) with the Kiwi machines and I found that they were not operational under a constant, steady-state production demand. I even had representatives of Carbonic Industries come to the USA and try to make them work under the basic design scope of work – and the result was a failure to comply with the basic scope of work. I made a lot of the basic engineering heat and mass calculations around the entire process and my conclusions were that the machines couldn’t meet the requirements due to mechanical and process shortcomings. They would work – but only on a “mom & pop” type of batch operation, and then only for a short time before requiring mechanical attention and un-plugging. The NZ representative agreed with my calculations and my conclusions. The whole matter went into Federal Court as a law suit and I testified as an expert witness on all the details for a duration of approximately 8 to 10 months.

I know exactly what was being attempted by using a helical (not a spiral) coil. My thoughts on this were accepted and confirmed by the NZ reps when they visited my operations in the US. The helical idea was to try to segregate the produced snow from the vapor and lead the solid product into the snow compression chamber where it would be subjected to continuous pounding of a brass piston. The idea was (& is) basically a naïve way of engineering a process. There were no NZ calculations or documented engineering. In fact, the only calculated and empirical solid to revert vapor quantities revealed during the entire time that I was involved were my data.

I can assure you that unless you are a degreed and experienced engineer with in-depth mechanical knowledge in semi-cryogenic processing, you will not understand all the engineering and data that I have on this process and machine. Suffice it to say that recovering the revert -100 ^oF vapors from this machine is next to impossible and not credible due to constant mechanical and process problems. The inability to recover revert vapors makes the machine impractical and totally un-economical. I don’t believe Asco would try to market this original Pelletizer machine under the scope of continuously recovering the revert vapors. If they do, I wish them all the luck in the world because they would need it. I am not casting stones or speaking badly of anyone or any design here – just stating engineering facts and actual historical facts. (You will note from the Asco website that the actual mechanical machine is not shown or divulged) The only dry ice Pelletizer machine that I’ve known to make successful, food-grade, and acceptable product is the Tomco hydraulic design – and even that design has a limitation on engineering design and capacity. But at least it works continuously and one can recover the revert vapor. One major and factual result of my findings was that the Kiwi machine produced, from time-to-time, dry ice pellets contaminated with brass metal shavings resulting from the constant pounding and metal-to-metal contact within the compression chamber – something I would never allow or accept.

I told you it would take many paragraphs to explain what you ask; it would take several tomes to discuss all the points of successfully making food-grade, economical pelletized Dry Ice. I have tried to give you a fair preview of the industry that you have aspirations to get involved in and I hope that you have obtained a good idea of the difficult and expensive problems that you have to overcome to be successful in it. It ain’t easy and it takes a lot of experienced engineering. If you don’t have a proven, experienced background in engineering, you will suffer.

 

[NZBen]

Thanks Montemayor - the reason I'm curious about these machines is that they are what my competitors are running (funnily enough the one shown in the pic does have an asco revert recovery machine hooked upto it) being that they are my competitiors machines I wanted to know their short comings. Do you know their conversion rate? How long do they run before they pug up? etc?

I'd never so much as seen an ice machine when I built my one, but just built it out of dead reckoning and it seems to be reasonably successful, tho I'm still ironing out little issues at the moment- the problem with working a full time job and trying to start into business at the same time (anything takes forever to do). Will send you some pics and details if yr interested.

Hope you enjoyed yr vacation away

BUt any info you're wanting to give me would be greatly received

 

[dcasto]

Are the processes: The Joule Thomson effect and the the Hilsch effect?

 

[Montemayor]

dcasto:

The basic thermodynamic process employed in converting liquid CO₂ to solid CO₂ snow is a constant enthalpy one. The entire process can easily be depicted and plotted on a T-S diagram for CO₂.

The main, unique diference (& the major headache) from other adiabatic expansions is the separation of the solid from the vapor phase. The properties of the CO₂ snow are such that it is a very difficult and troublesome operation. The resultant conversion to the solid state yields a subsequent ratio of approximately 50% vapor and solid and the recovery of the revert vapor is essential for economic operation. The entrainment of solid snow in the revert vapor is a constant hazard for downstream recompression equipment while also plugging up the process and making heat exchange between process streams difficult and impractical. Experienced, empirical engineering techniques acquired through hands-on operation and experience have historically proven to be the main resolution to making the process viable and workable.

 

[dcasto]

Montemayor, I was asking about the specific device with the helical coils, does it work like a vortex sheading (Hilsch effect) to allow a separation of the soilds from the fluid phase based on density difference combined with the JT cooling (delta H = 0).

 

[Montemayor]

dcasto:

I was describing the specific helical coil which, as I mentioned, was expected to produce a gas-solids separation using the circular flow as a means of stimulating separation - which it doesn't. Although the device seems to work for a while, it eventually plugs up with persistant dry ice snow which is very troublesome due to the ability of the solid snow flakes to bind together mechanically.

The free adiabatic expansion of liquid CO₂ is irreversible and definitely not a Joule-Thomson expansion. James Prescott Joule did his pioneering research on the expansion of real gases and was later joined by William Thomson (Lord Kelvin) to formally define the theory and the effect of free expansion of high pressure real gases. One of the outstanding results of this research was the Joule-Thomson inversion temperature – a point that defines where the free isenthalpic expansion of real gases results in either a lower temperature or a higher temperature for the expanded gas product. The adiabatic expansion of liquid CO₂ - like the expansion of conventional liquid refrigerants (ammonia, Freons, etc.) - is not described nor taken into account by the J-T effect. However, as you indicate, both the liquid free adiabatic expansion and the J-T effect are isenthalpic processes.

The Hilsch Tube, as you probably well know, is a unique device in that it seems to employ the J-T effect with compressed air, except that it produces both a hot expanded stream and cold expanded air stream simultaneously.