USING GASES
Producing, packaging and transporting gases
USING GASES
Producing, packaging and transporting gases
By the Editorial Team
Though most gases literally come out of thin air, they are nevertheless highly valuable – not only for the manufacturer, but above all for the users. The value-added chain also requires solid engineering, however.
Gases are used in countless processes for an extremely wide variety of purposes. Regular readers of our Magazine Gases for Life, the magazine for industrial gases, already know many of them. Some gases – nitrogen, for example – are used for cooling and inertization; oxygen’s applications include, among other things, raising combustion efficiency; noble gases are used in welding and in laboratories. Wherever gases are used, they are an indispensable part of the process in question.
The boiling point trick What most gases share in common is their source: the atmosphere. The air we breathe is a gas mixture. In order to be able to use these gases, we must first eliminate contaminants such as water vapor and then, in an air separation unit (ASU), use cryogenic rectification to separate the components. This method takes advantage of the different boiling points of the elements involved. By alternating between compression and decompression, the air is cooled to very low temperatures. In the process, one gas after the other transitions to liquid form as soon as the temperature drops below its respective boiling point. The liquid can be draw off, while the remaining gases are cooled down even further. The main components of air – nitrogen and oxygen – are extracted in large quantities in this way. The noble gases argon, neon, xenon and krypton are also recovered in significantly smaller quantities.
Pressure swing and source of natural gas Nitrogen and oxygen can also be produced in gaseous form with far less technical effort and energy consumption. Vacuum pressure swing adsorption (VPSA) units use membranes to separate these two gases from one another. However, the purity is lower than with air separation units.
But not all gases come from the air. Industrial helium, for example, is obtained from sources of natural gas containing helium. Some streams of this fossil fuel contain up to 16 % by volume of the lightest noble gas. Carbon dioxide is produced from several different sources, such as the combustion of fossil fuels, fermentation, and natural underground springs, and also as a byproduct of chemical processes such as ethylene oxide production, ammonia production and ethanol fuel production. Hydrogen and acetylene are produced in chemical plants.
Complex packaging Because gases are necessarily volatile, the “packaging” of these products is no mean feat. To hold useful quantities in anything approaching reasonable package sizes, they must first be compressed. Steel cylinders freshly filled with gas are under 200 to 300 bar or more pressure. For average consumption cylinders in bundles have become established. Larger quantities are carried in liquid form in special tank cars. When transporting gases in such containers, distance has frequently a major impact on cost. That’s why gas markets are always regional. Especially with nitrogen and oxygen, the quantities significantly restrict the economical delivery range. Its radius generally extends just a few hundred kilometers. Supply by pipeline is possible only over short distances. Pipelines serve plants within the same industrial zone where the ASU is also located. And with major consumers, we can also flip the script: Messer installs air separation units or vacuum pressure swing adsorption units on the grounds of the consumer and supplies surplus gases to other customers in the region.
