Making Big Dry Ice Blocks With Low Pressure CO2
Hyperspace Pirate 17:54
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In this video I'll demonstrate how I made large blocks (up to 360 grams) of CO2 by freezing them in a container with low pressure CO2 and a refrigeration system rather than the typical method of discharging room temperature high pressure CO2 in liquid phase through a porous mold.
The Carbon Dioxide in this video was made with baking soda and vinegar, and sent through a chiller at -35C to remove residual moisture before being pumped into a pressure pot that was cooled between -60C to -70C. The pressure pot is cooled by a mixed-gas joule-thomson cycle using a 15/35/50 blend of Butane/Propane/Ethylene respectively. The unloaded temperature is about -75C, but with a thermal load it typically runs somewhat warmer. The evaporator coil sits in a bath of alcohol to act as heat transfer fluid to chill the 2-liter pressure pot. Initially I used 70% isopropyl alcohol, but found that it froze solid, so I ended up using 96% ethanol instead, which remained liquid at the working temperature of the chiller.
The pressure pot is only rated for 8 bar or about 115 psi of pressure, which is dramatically lower than the pressure needed to liquefy CO2 at room temperature (around 60-70 bar), which is why the chiller is needed. During pumping, the CO2 pressure in the pot went up to around 140 psi (9.7 barG), but ultimately settled right around 100 psi (6.9 barG), which corresponds to a temperature of -46C. This is somewhat higher than the working temperature of the chiller, because only the bottom third of the pressure pot is in contact with the supercooled alcohol bath, so while the bottom of the pot is close to -70C, a thermocouple near the top consistently read about -25C, so the average temperature was somewhere in between, thus the -46C.
The compressor was originally from a 12,000 BTU R-22 unit, and pulled around 700 watts, with a discharge pressure around 380 psi (26 bar), and suction around 40 psi (2.8 bar). Because of the counterflow heat exchanger used in the joule-thomson cycle, the vapor returning to the compressor was at room temperature, and there was inadequate cooling for it, causing the case temperature to go as high as 130C during operation. This definitely shortened the life of the compressor, but so far it's still running.
Once the CO2 freezes at the bottom of the pressure pot, the pot can be depressurized, and the frozen block can be removed. This is different from the standard method of making dry ice, where high pressure liquid is discharged into a porous mold or a large container where the "snow" is pressed into a block. This method creates a continuous solid, and has a relatively high yield (over 70%). Unfortunately, it's extremely time consuming, so a better method would probably just be to use a single stage vapor-compression chiller to drop a vessel to -20 to -30C and accumulate liquid CO2 at a moderate pressure then discharge it the regular way.
Music Used:
Kevin MacLeod - George Street Shuffle
Kevin MacLeod - Groove Groove (This is the one from Kerbal Space Program)
In this video I'll demonstrate how I made large blocks (up to 360 grams) of CO2 by freezing them in a container with low pressure CO2 and a refrigeration system rather than the typical method of discharging room temperature high pressure CO2 in liquid phase through a porous mold.
The Carbon Dioxide in this video was made with baking soda and vinegar, and sent through a chiller at -35C to remove residual moisture before being pumped into a pressure pot that was cooled between -60C to -70C. The pressure pot is cooled by a mixed-gas joule-thomson cycle using a 15/35/50 blend of Butane/Propane/Ethylene respectively. The unloaded temperature is about -75C, but with a thermal load it typically runs somewhat warmer. The evaporator coil sits in a bath of alcohol to act as heat transfer fluid to chill the 2-liter pressure pot. Initially I used 70% isopropyl alcohol, but found that it froze solid, so I ended up using 96% ethanol instead, which remained liquid at the working temperature of the chiller.
The pressure pot is only rated for 8 bar or about 115 psi of pressure, which is dramatically lower than the pressure needed to liquefy CO2 at room temperature (around 60-70 bar), which is why the chiller is needed. During pumping, the CO2 pressure in the pot went up to around 140 psi (9.7 barG), but ultimately settled right around 100 psi (6.9 barG), which corresponds to a temperature of -46C. This is somewhat higher than the working temperature of the chiller, because only the bottom third of the pressure pot is in contact with the supercooled alcohol bath, so while the bottom of the pot is close to -70C, a thermocouple near the top consistently read about -25C, so the average temperature was somewhere in between, thus the -46C.
The compressor was originally from a 12,000 BTU R-22 unit, and pulled around 700 watts, with a discharge pressure around 380 psi (26 bar), and suction around 40 psi (2.8 bar). Because of the counterflow heat exchanger used in the joule-thomson cycle, the vapor returning to the compressor was at room temperature, and there was inadequate cooling for it, causing the case temperature to go as high as 130C during operation. This definitely shortened the life of the compressor, but so far it's still running.
Once the CO2 freezes at the bottom of the pressure pot, the pot can be depressurized, and the frozen block can be removed. This is different from the standard method of making dry ice, where high pressure liquid is discharged into a porous mold or a large container where the "snow" is pressed into a block. This method creates a continuous solid, and has a relatively high yield (over 70%). Unfortunately, it's extremely time consuming, so a better method would probably just be to use a single stage vapor-compression chiller to drop a vessel to -20 to -30C and accumulate liquid CO2 at a moderate pressure then discharge it the regular way.
Music Used:
Kevin MacLeod - George Street Shuffle
Kevin MacLeod - Groove Groove (This is the one from Kerbal Space Program)
Category (YouTube): People & Blogs
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