Method and system for making carbon dioxide snow

Claim 1

A method for making CO2 snow which method comprises supplying liquid CO2 from a storage vessel at high pressure to a tank and expanding said high pressure liquid CO2 at said tank to a lower pressure lower temperature liquid plus vapor and thereby providing a desired reservoir of said low temperature liquid CO2 in said tank, withdrawing vapor from said tank and compressing said withdrawn vapor for return to said storage vessel, periodically repressurizing said low pressure liquid CO2 to a higher pressure and transferring said repressurized high pressure low temperature liquid CO2 to expansion means whereat it is expanded to CO2 snow and vapor, said low temperature high pressure liquid CO2 producing CO2 snow in an amount more than 50 weight percent of said transferred liquid CO2, and maintaining a pressure of at least about 100 psia. on the feed side of said second expansion means between said periodic repressurizing of said low temperature liquid CO2 in said tank to positively prevent the formation of solid CO2 on the feed side of said second expansion means.

Claim 2

A method for making CO2 snow which method comprises supplying liquid CO2 from a storage vessel at high pressure to a tank and expanding said high pressure liquid CO2 at said tank to a lower pressure lower temperature liquid plus vapor and thereby providing a desired reservoir of said low temperature liquid CO2 in said tank, withdrawing vapor from said tank and compressing said withdrawn vapor for return to said storage vessel, initially establishing a reservoir of liquid CO2 in said tank at a temperature above -70* F. and then intermittently lowering said pressure within said tank below about 75 psia. to cause formation of successive layers of solid CO2 at about the surface of said liquid CO2, resulting in the creation of CO2 slush in said tank, and periodically pressurizing said CO2 slush to a higher pressure and transferring said higher pressure CO2 slush to expansion means whereat it is expanded to CO2 snow and vapor.

Claim 4

A system for making CO2 snow which system comprises a storage vessel for holding liquid CO2 at high pressure, a tank, first conduit means for supplying liquid from said vessel to said tank, first expansion means in association with said tank for expanding said high pressure liquid from said first conduit means to lower pressure lower temperature liquid plus vapor, means for controlling the passage of liquid through said first expansion means to obtain a desired reservoir of said low temperature liquid in said tank, a compressor, means connecting the intake of said compressor to a location in said tank wherein said vapor resides, second conduit means connecting the discharge of said compressor to said storage vessel, Second expansion means for expanding the liquid to CO2 snow plus CO2 vapor, means for pressurizing said reservoir of liquid CO2 in said tank to a high pressure substantially above that of the liquid after passing through said first expansion means, and third conduit means for supplying said pressurized liquid CO2 from said tank to said second expansion means whereby CO2 snow is created by passage therethrough.