Cryogenic separation
The term cryogenic refers to the science of very low temperatures. Cryogenic
separation uses the different temperature related properties of the gas species to
separate them from each other. In biogas upgrading, the technique is used to create a
gas or liquid containing mostly methane and lighter hydrocarbons. An example of a
process schematic of a cryogenic upgrading plant is shown in Figure 5. The process
starts with the compression of the biogas to approximately 80 bar. Several different
heat exchanger steps are used to progressively cool the biogas to a lower temperature,
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allowing for the CO2 to be liquefied and separated. A simpler construction used in this
master thesis work can be seen in Figure 15.