After the CO2 vapor is absorbed out of the process gas stream,
it is sent to the CO2 plant where it is condensed into a liquid
form under pressure. The liquid is then sent to the ice plant.
In the ice plant the liquid is sent to various machines where
it is depressurized. When this happens, some of the liquid changes
into a solid form resembling snow(dry ice), the rest changes back
into a gas and is vented out the chamber and sent to the recycle
skid. The snow is then pressure-packed into a solid form. It is
either formed as a 240 lb. block using the presses shown to the
left, or as a small pellet using the pelletizers.
The large blocks of CO2 are cut to various sizes
pieces, ranging from 8 lbs. to 60 lb. blocks. Some of the pieces
are then sent through an automatic sealer which wraps them in
a plastic bag. The pellet CO2 pieces are collected in plastics
bins which hold approximately 1300 lbs. of ice pellets. Midwest
Carbonic produces about 125 ton a day of CO2, and averages about
31,000 ton of dry ice and 43,000 ton of liquid CO2 yearly. CO2
has an ambient temperature of -109 F, and can cause severe "freeze"
burns if it comes in contact with skin. The vapor off of CO2 also
displaces the oxygen in surrounding air, and should only be handled
in well ventilated areas.
Since a large potion of the liquid CO2 used to make dry ice
turns back into a vapor, Midwest recaptures the vapor off of the
presses and pellet machines and passes it through a recycling
system. Here the vapor is compressed then cooled, causing the
vapor to return to a liquid form. Without recycling the unused
vapor, it takes about 10 tons of liquid CO2 to make 3 to 4 tons
of dry ice. By recycling the unused vapor, Midwest can get about
8 tons of dry ice for every 10 tons of liquid CO2. CO2, liquid
or solid, is mainly used as a coolant in shipping or storage processes
of refrigerated items.
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