Carbon dioxide at ambient conditions exists in gas form and mix uniformly with air. CO2 produced or generated during chemicals manufacturing generally released into atmosphere through chimney. However, recent technologies develop carbon dioxide capturing processes they are not yet implementable in full scale. Most of the technologies are still at the theory and some of them not succeed due to the economy and energy balance failure. From most of the technologies dry ice manufacturing method is recommended to the manufacturing plants that produce carbon dioxide as by-product in excess quantity at high pressure. For example in urea production industry CO2 is produced in excess per process cycle, as it is available at the process pressure of 20 Mpa and 130 oC. By throttling method, the pressure is reduced to atmospheric pressure, which leads to the physical state change of CO2.
Dry ice manufacturing process diagram
A flow diagram here shows the pattern of the carbon dioxide flow in dry ice manufacturing unit. Initially a cooler is used to decrease the temperature of pressurized gas to ambient temperature by means of cooling water. The outlet stream of cooler drops to the temperature around 40oC. An expander than reduce the pressure by 3.9 Mpa (throttling through the nozzle) which leads to phase change of the CO2. Both gas and liquid phases of CO2 at equilibrium are further cooled to temperature of 4 oC using chilled ammonia. The equilibrium mixture is fed to separator to collect the liquid CO2. The liquid stream is further throttled to atmosphere pressure and fed to snow tower to convert liquid CO2 to solid-state dry ice (-10oC). The equilibrium gas from the snow tower and separator is removed and vented into atmosphere.