This is one of my ongoing ideas so I thought I would share it here. I have looked on the internet for similar ideas and found nothing close. So this is a 100% original idea as far as I know.
The idea.
(See diagram below)
Using extremely low temperature for drying a refrigerant charge. in a self contained loss less system. You could do the same thing using dry ice to cool a refrigerant tank, but that requires the out gassing of a lot of CO2 and it couldn’t be operated continuously (well hard to operate continuously that is).
The moisture holding capability of a refrigerant goes down as temp goes down. The main reason I am posting this is another thread I seen
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(Had to clip three URL's because of the 15 post rule for new people....)
That would mean that I could dry propane to 3PPM with that type of unit. If I go down to <-40C at around 0PSIG That is within refrigeration specs.Quote:
Temperature ppm saturated level in liquid propane
-40C 3ppm
-30 5
-15 13
+6C 44
+15 75
+30 173
+45 360
How good it would do on R134a, R22, and the others depends on the saturated water content of those refrigerants at low temp. I don’t have that info on hand, and I can’t find it on the web. If anyone has access to it and would like to post it, I would be very grateful.
If you send the refrigerant through a cycle that reaches that temperature it will percolate out the moisture in the form of ice in the cryo tank.
The basses of my project is an old vacuum flask designed for LOX that was in an old portable medical oxygen respirator.
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Max operating of the flask in the original application is 30 PSIG at a real cold temp!!!!!! Original capacity was 3 pound of LOX.
If a person had access to a larger pressure rated vacuum flask you could hold a large amount of refrigerant standing in the unit while being dried.
I would like to get a hold of one of the LOX reservoirs/filling stations that went with the above unit.
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That would be a good basses for a low temp project.
The intended normal operating pressure in my application is 0 PSIG. (around -42C for R290)
30PSIG relief valve will be left in place.
Cycle basics. The compressor pulls vapor off the top of the tank, and runs it though a compressor at high pressure to condense it. And it is dropped in pressure through a regulator and then a capillary tube which sticks into the cryotank. Some of the liquid will flash off as gas cooling the rest to -42C and depositing it in the tank.
The cryo regulator will regulate the pressure of the cryotank to about 0 PSIG. If the pressure is below 0 PSIG and the condenser is empty then the regulator will open up fully letting uncondensed gas back in to main tank. basically turning it into an open cycle. If the pressure increases it will hold up the refrigerant in the condenser and force some of it to liquefy before entering the cryotank and adding to the cooling effect. The cryo regulator is basically a normal externally equalized expansion valve with the sensor bulb cut off, which puts the valve reference point at 0 PSIG. The valve is set to zero, or close to zero superheat. Input is the output of the cycle condenser. eq port is hooked to the vapor space of the cryo tank. outlet is hooked to the input of the cap tube. The regulator will maintain the vapor space at 0 PSIG. the output pressure will be held higher than 0 PSIG provided by the cap tube restriction. the liquid refrigerant will not drop to full 0 PSIG (and reach lowest operating temp) until it leaves the cap tube end, which is in the cryo tank. That will reduce unwanted heat pickup from the surrounding atmosphere.
The heat exchanger at the intake/outlet of the cryotank will help supercool the refrigerant in the cap tube useing the heat uptake of the cold refrigerant gas/liquid mix leaving the tank to increase cycle efficiency.
The cycle evaporator is to warm the gas/liquid mix coming out of the tank to make sure that all the liquid evaporates before entering the cycle compressor.
When the cryo tank becomes full, the level will auto regulate by the fact that the liquid will start coming out the outlet (when the liquid level reaches the intake of the outlet port) which will vaporize in the evaporator and it will basically dump all the incoming liquid refrigerant back out of the tank that come in. When you see the evaporator icing up solid then the tank is full.
When you have the refrigerant in the tank you can let it set there and run while the moisture slowly percolates out of the liquid in the tank(and freezes into ice in the tank). The gas/liquid coming in through the cap tube will agitate the liquid in the tank to stop it from stagnating.
The trap is for purging any incondensable gas that gets into the system. It should have a sight glass in the column to monitor liquid level in the trap. To maximize purging efficiency. (To avoid purging liquefied refrigerant.)
The liquid pickup leg in the tank is for injecting the refrigerant back into the system, or storage bottle.
It goes through the evaporator which vaporizes the liquid at room temp so it can go through the injection compressor. The injection compressor brings the gas pressure back up to system pressure to reintroduce it back into the system. It can go straight in as gas. Or it can be run through the condenser to liquefy it before injection. Like when you want to put it into a tank and minimize tank heating from condensation.
When the job is done, and you have pumped the cryotank down, then you have to remove the moisture out of it after it’s internal temperature comes above freezing. That is what the purge isolation valves are for. shut them off when you are done pumping down the system. After the tank warms up, purge the tank of water with dry nitrogen. or dry air. The water will go to the bottom of the tank that is why you use the liquid leg for the purge output.
The two compressor bypasses are used for capacity control. when you want to reduce the output of the compressor in a specific application. And it allows for easy restart of the compressor after loss of power. Shut off the purge isolation valve between the cycle evaporator and the cryotank. then open up the cycle bypass valve to eq the pressure across the cycle compressor for easy restart. Then close bypass valve and reopen the purge isolation valve once the cycle evaporator has pumped down to cyrotank operating pressure(to prevent pressure backlash into the cryotank and popping of the relief valve).
Same basic method with restarting the injection compressor.
The outer loop is for running the dry refrigerant through the injection system and back into the tank to dry out the injection system in case water get into some how.)
The two gauges on the condensers are for watching condensing pressure. If it goes too high, crack open the bypass for that system to allow the condenser to catch up.
The system could be strapped onto an operating refrigeration plant and pull refrigerant off the plant, dry it, and re-inject it. It could run until the refrigerant charge in the plant has been dried to satisfactory levels.
If you was building the system for just that type of operation, then you could simplify the cryo dryer system greatly. I will post a diagram of a basic system for that later.
Another idea. You could increase the efficiency of it by packing the tank with steel wool or something to increase the surface area for the ice to form on.
Does the system sound useful, or is it another one of my stupid ideas?
I have had the parts on hand, and have been intending to build it for a long while, if I can just get my lazy butt in gear.
PS, if decides to start making them and selling them in the thousands, for big $$$$ please remember to pass some of that green this way. I need the money!!!!!!!!!! :D
Good day!
