How Dry Ice is Made
Dry ice is made by taking pressurized Liquid CO2 (LCO2) and allowing it to expand into the natural atmosphere. This causes the LCO2 to expand into both a gas vapor and solid snow. The snow is then either compressed to form blocks or compressed and extruded to form pellets or nuggets. The equipment required to make the dry ice includes a Liquid CO2 tank and a Pelletizer or Block maker.
About CO2: Physical Properties
Carbon dioxide is a colourless gas and natural byproduct of breathing. Its density at 25 °C is 1.98 kg/m³ (0.123 lbs/f³), about 1.65 times that of air. This means that CO2 gas displaces oxygen (the CO2 will sink to the floor and the Oxygen will rise above it). It is important therefore to handle or store CO2 (whether solid or gas) in well-ventilated locations (liquid CO2 needs to be stored in sealed and pressurized vessels in order to prevent any phase change). As it is fully oxidized, it is not very reactive and, in particular, not flammable.
At temperatures below −78 °C, carbon dioxide changes directly from a gas to a white solid called dry ice through a process called deposition. Liquid carbon dioxide forms only at pressures above 5.1 atm; at atmospheric pressure, it passes directly between the solid phase and the gaseous phase in a process called sublimation. The chart below shows the phase changes of Carbon Dioxide.
Properties:
Types of Dry Ice
Dry Ice Snow: looks like regular snow. It has a very high sublimation rate compared to pellets, nuggets and block or slabs. Dry Ice Snow requires less complex equipment to produce, but has very short shelf life.
Dry Ice Pellets: The standard 3 mm (1/8") blasting pellets look like rice. These high-density pellets are mainly used for dry ice blasting but they also are increasingly being used by some food processors who have found value in the slower sublimation rate and smaller size.
Dry Ice Nuggets: Nuggets typically range in sinze from 6 mm (1⁄4") to 19 mm (3⁄4") in diameter. Dry ice nuggets are typically used for packaging and shipping be it food or aluminum parts for Aerospace. High-density nuggets have a longer shelf-life and better transportability than "regular" dry ice nuggets as their increased mass takes longer to sublimate.
Dry Ice Slabs: The 19 mm (3/4") dry ice slab is predominantly used by the airline catering industry, though some other companies use them for shipping.
Dry Ice Blocks: Block dry ice is today being used for dry ice blasting (Cold Jet patented block-shaver technology) but historically, block dry ice was made for shipping/packaging or simply keeping things cool for a period of time. Standard block sizes vary from country to continent, but larger blocks are produced so that they may be cut to size if needed.
High-Density Pellets
High-density pellets are created using specialized pelletizers that extrude a homogenous CO2 pellet as opposed to the "regular" pellets, which result from compacted snow. While the sublimation rate remains the same for High-density and regular ice, high-density ice will take longer to sublimate completely as there are more dry ice particles per square inch than regular ice. High-density dry ice has improved transportability and a longer shelf life than "regular" dry ice pellets or CO2 snow, as well as increased aggression for blasting applications.
The images above show high-density dry ice being extruded. Regular ice, being less dense and therefore more brittle, would break off much sooner after extrusion.
Note: High-pressure does not equate to high-density.
Cold Jet Dry Ice for Blasting
The dry ice media used for blasting comes in two forms: pellets (3 mm or smaller) or blocks. The standard 3 mm pellet allows for a more aggressive clean as the particles blasted tend to be larger and more irregularly sized. Shaved block dry ice produces much finer and more consistently sized particles allowing for more delicate surfaces to be cleaned without damage. Blasting with Dry Ice
Cold Jet Dry Ice for Shipping
Dry ice nuggets, block, pellets or slabs are being used for shipping (food products, aluminum parts or biological products). Dry ice slabs are predominantly used by airline caterers; pellets are typically used for smaller packages over shorter distances whereas nuggets are used to ship larger packages over longer distances. Shipping with Dry Ice
Cold Jet Dry Ice for Food Processing
Dry ice is a yeast retardant. It is also bacteriostatic and fungiostatic and is excellent for removing biofilm. Meat processors and bakers use large quantities of dry ice for these properties. The Dry Ice is mixed in calculated doses into the mixers to keep the mixes cool, preventing the growth of bacteria and fungi and, in the case of baking mixes, to slow the leavening process. Dry Ice pellets are being used instead of direct LCO2 injection because their amount and weight are easier to control and the process is simplier and safer. As it is a dry product it does not add water to the mix.Food Processing with Dry Ice
Cold Jet Dry Ice Production Equipment
Cold Jet's dry ice pelletizers have been scientifically engineered by the dry ice industry's leading engineers and experts to offer the greatest level of reliability available and the highest density extruded dry ice obtainable. With our expansive made-to-order and customizable product line that is easy to implement and meet every need, Cold Jet continues to set the standard for dry ice production everywhere with ongoing reliability, customer support and product innovation.