Clean Surface produces DioXice dry ice pellets in their Leicester facility from liquid CO2. The pellets used for blasting purposes are 3 mm diameter, but start out as long strands as they exit the extrusion die.
First, liquid CO2 is allowed to decompress into CO2 snow in a cylinder behind the extrusion die. A hydraulic ram then pushes the snow through the die and compacts it into solid dry ice.
Dry ice is a very weak material so when it comes out of the die it soon breaks up as it falls into the insulated transport container, which placed under the die.
|325 kg Dry Ice Insulated Container
Dry ice is unstable under ambient conditions and will, from the moment it is produced, do its best to return to CO2 gas. This is called sublimation, which is a particular characteristic of Carbon Dioxide, and it means that there is no liquid phase when a solid “melts”. It simply sublimes directly from a solid into a gas, and this is why dry ice can be used as a cleaning agent.
The immediate sublimation of dry ice means that it must be stored in a way that prevents its sublimation as much as possible. It can be kept indefinitely at 18 bar or below –78.6 deg C, but unfortunately either is impracticable, especially during transport.
When packed in well insulated containers a shelf life between one and two weeks can be achieved. The actual time will depend on the ambient temperature, how often the box is opened and the rate of use. A good guide is don’t expect more than a week in summer, but in winter it will be more.