Production of liquid biogas, LBG, with cryogenic and conventional upgrading technology - Description of systems and evaluations of energy balances

The aim of this master thesis is to evaluate energy balances for the production of liquid biogas, LBG.LBG can be produced in two main ways and these are by means; cryogenic upgrading technology andconventional technologies connected with a small-scale liquefaction plant. A third alternative is to injectbiogas into the gas grid and then liquefy a part-flow at a pressure letdown station.The cryogenic upgrading technology is based on differences in condensation temperature for differentcompounds, and by chilling biogas, impurities and CO2 can be separated from CH4. When using thistechnology also liquid CO2, LCO2, comes as a by-product, which could be used in external applications.With one of the two main ways it takes between 0.8-1.8 kWh/Nm3 clean biogas to produce LBG. If theenergy is expressed in primary energy, this energy consumption corresponds to 12-23 % of the energycontent in the product. The net energy consumption is affected by the disposal of waste heat and use ofLCO2 in external processes while CH4 losses have a small influence.The production of LBG is more energy intensive than the production of compressed biogas but in somesituations the product is more valuable since the biogas becomes available for more customers.