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What is CO2?
Carbon dioxide is the combination of two atoms of oxygen joined with a single atom of carbon. Its chemical formula CO2, is almost as well-known as that of water, H2O, and it is frequently referred to by its formula rather than its name.
In nature’s chain of life, the mutual dependence of plant and animal life is maintained through the link of carbon dioxide. Every time we breathe we release this gas, which plants need for life. Through the process of photosynthesis, the plants separate the carbon from the oxygen. In turn, plants release the pure oxygen, which we need to survive. We reverse the process, and by combining the oxygen with carbon from the foods we eat, produce carbon dioxide again.
CO2 is a colourless, inert gas approximately 1 ½ times heavier than air and 0.03 % is present in the earth’s atmosphere. It is odorless, has a sweet biting taste (soda water) and is highly stable (difficult to separate).
It is produced in varying amounts by the common process of combustion of fuels high in carbon content. The most common source of fuel for combustion is oil which, when mixed with the correct proportion of air, burns to produce around 15 % CO2 in the flue gases of a CO2 plant. After combustion has taken place, the CO2 can be separated from the flue gases and, through a simple process, made available for the many commercial purposes to which it can be applied.
CO2 can exist in three forms:
- in gaseous form: for the beverage and food industries
- in liquid form: in a storage tank under pressure
- in solid form: called dry ice (for cooling, blasting etc.)
Gaseous CO2 can be liquefied under pressure provided its temperature is below 31 °C (87,8 °F), this temperature being referred to as the CRITICAL POINT. If compressed and cooled below the critical point, a colourless fluid, approximately the same density as water, is produced.
CO2 will remain in the liquid form as long as its temperature remains below the critical point but will return to the gaseous state if its temperature rises above this point, regardless of the pressure applied.
Liquid CO2 can be stored indefinitely at high pressure or Low pressure as follows:
High Pressure CO2
High pressure liquid CO2 is produced by compressing the gaseous CO2 in multistage compressors to pressures in the neighbourhood of 69 bar (1000,76 psi) pressure, then cooling it to around 18 °C (64,4 °F). It is customarily filled into specially constructed steel cylinders. Like water, liquid CO2 can be weighed, and this is the normal form of measuring it.
Low Pressure CO2
Low pressure liquid is an alternative method of storing CO2 and is produced either by expanding high pressure CO2 to a lower pressure or by refrigeration. It is held in specially constructed storage tanks, heavily insulated and equipped with refrigeration units to hold the internal tank pressure at or below 21 bar (304,58 psi) and -18 °C (-0.4 °F) temperature. Pressure switches are incorporated to control the refrigeration units and safety mechanism and electrical alarms are fitted to release the tank pressure and raise an alarm in the event of refrigeration malfunction.
Low pressure liquid CO2 (sometimes referred to as “bulk”) is transported to one place from another in insulated road tankers or trailers (or, in some countries, by rail tank wagons), the liquid being simply transferred from mobile to static tank by pumping or gravity feed.
Unlike water, carbon dioxide cannot exist in the open air in liquid form. It must be held under pressure or refrigeration (or a combination of both) to remain in the liquid state.
Solid CO2 (customarily known as “DRY ICE”)
Dry Ice is the product of processing liquid CO2 . If the pressure of liquid CO2 is suddenly released, a proportion of that liquid will change to the solid state (becoming dry ice “snow”) and the remainder will revert to gas (revert gas). When the snow is compressed under hydraulic or mechanical action, blocks or pellets of dry ice are formed. The revert gas (gaseous CO2 ) can be readily reclaimed and converted back to liquid by recompression and reliquefaction, thence returned to the dry ice block machine or pelletizer for further processing.
The temperature of dry ice is -79 °C (110,2 °F) and in the atmoshere it will pass directly from the solid to the gaseous stage, leaving no moisture or trace of its presence except the cold.
CO2 is our life
Many generations - and individual lifetimes! - of experience have perfected ASCO‘s ability to provide the most complete and best matched CO2 system available.
From the CO2 production or recovery plant to to storage, dry ice blasting, cylinder filling, dry ice making and even dry ice wrapping, it‘s all ASCO. This ability to provide matched components benefits ASCO clients as they can comfortably develop and grow their business without changing suppliers.
Having the largest range of CO2 and dry ice components also enables ASCO customers to make full use of the versatile nature of CO2 and its vast number of uses, thus gaining maximum value from the product. For example a soft drink bottler could easily develop an extra cash flow business from surplus CO2 (or excess plant capacity) by adding ASCO dry ice equipment and / or cylinder filling gear to supply CO2 to other users.
ASCO‘s website provides details of their most up to date CO2 and dry ice plants. All ASCO equipment is space efficient, designed for easy operation maintenance and engineered for maximum reliability and life. Component materials are selected to balance capital cost and plant longevity and from the flue gas oxygen sensor on the plant to the level indicator on the CO2 storage tank all controls are effective, logical, clear, and linked to a PLC.
ASCO‘s technology, combined with a wide range of CO2 equipment, makes it easy for their clients to mix and match components and thus tailor their CO2 / dry ice system from the one shop.
Significant new ASCO CO2 plant sales to Africa, South America and the Middle East indicates that many bottlers, brewers and merchant CO2 companies prefer working with a single supplier and that supplier is ASCO. Let our life add life to your Business.
From liquid CO2 into dry ice
Carbon Dioxide has 3 physical states of gas, liquid and solid which depend on temperature and pressure.
The relationship between the 3 states is shown on the pressure-temperature phase diagram beside.
Where does CO2 come from?
CO2 is derived from a number of sources including combustion of carbonaceous fuels, fermentation, natural wells, and as a by-product of industrial processes such as ethylene oxide and bioethanol production and ammonia synthesis.
The Solid State (Dry Ice):
Below the triple point (5.18 bar, - 56.6 °C) (7'512,96 psi, - 69,88 °F) CO2 can only appear in its solid and gaseous state. Dry ice is the common trade name for solid CO2 . At atmospheric pressure it has a temperature of approx. -79 °C (-110,2 °F). The solid CO2 changes directly into its gaseous state. This evaporation (sublimation) does not leave any residues. Dry ice is non-toxic, non-inflammable, inert, without smell and bacteriostatic. It is white and has a density of approx. 1'500 kg/m3 (93,64 lb/ft3) in its compact state. Dry ice is an ideal refrigerant which qualifies especially well for various applications. It has a high cooling capacity and heat transfer is very high when in direct contact with the cold material.
ASCO has the best range of dry ice machines for dry ice production.
The Liquid State:
Within a temperature range between -56.6 °C (-69,88 °F) and 31 °C (87,8 °F) and pressure greater than 5.2 bar and less than 74 bar (1'073,28 psi) respectively CO2 is in its liquid state except at very high pressures. This means that, below 5.2 bar (754,20 psi), CO2 exists only in its solid or gaseous state. At 5.2 bar (754,20 psi) and - 56.6 °C (- 69,88 °F) all three states (solid, liquid and gas) are present. This is called the triple point.
The critical point of CO2 lies at a temperature of approx. 31 °C (87,8 °F) and a pressure of approx. 74 bar (1'073,28 psi). Normal CO2 liquid can only be formed at temperatures below 31 °C (87,8 °F). Above the critical point there is no physical difference between the liquid and gaseous phase. This supercritical state is also called „Fluid“. The liquid state is important for the storage and transportation of CO2 as well as during cooling and freezing applications. During release of the liquid CO2 to atmosphere a temperature of -79 °C (-110,2 °F) is reached. This is associated with a high cooling capacity due to the evaporation heat which is extracted from the environment when releasing the liquid CO2 .
The Gaseous State:
CO2 gas has a density of approx. 1.9 kg/m3 (0,12 lb/ft3) at atmospheric pressure and +15 °C (+ 59 °F). CO2 has many unique and beneficial features which make it valuable in the preservation of packaged food, in explosion and fire protection, in pest control and as protective gas in inert-gas-welding. In all these applications it is important for the CO2 gas to drive out and replace the atmospheric oxygen. Moreover, CO2 gas is used for enriching the atmosphere in greenhouses, in storing fruits and vegetables and for pH control when treating potable and waste water.