Method and system for the production of liquid biogas

A method for production of liquid biogas (LBG), said method comprising:

• inflow of crude gas comprising mainly methane and carbon dioxide;
• removal of trace elements being at least one of hydrogen sulphide, siloxanes and VOC's from the crude gas, which is performed through at least one activated carbon filter;
• wherein a biogas compressor is arranged subsequent to said at least one activated carbon filter;
• a first heat exchanger for heat exchanging with water is arranged subsequent to the biogas compressor;
• and
• at least one dryer is arranged subsequent to said first heat exchanger;
• dehumidification;
• particle purification by mechanical filtration for the production of a treated biogas;
• separation of carbon dioxide from the treated biogas;
• condensation of the treated biogas with a low content of carbon dioxide, for the production of LBG with a carbon dioxide content of maximum 100 ppm, wherein the separation of carbon dioxide from the treated biogas;
• and
• condensation of the treated biogas with a low content of carbon dioxide are performed via alternatively heat exchanging so that the separation of carbon dioxide from the treated biogas is performed so that carbon dioxide is frozen and then separated off via sublimation,
• wherein a cascade cooling system is used in which compression is performed in at least one reciprocating compressor, and
• wherein the cascade cooling system comprises at least two heat exchangers being a second heat exchanger and a third heat exchanger, and which cascade cooling system is connected to a cooling water loop and a heating water loop, which cascade cooling system is arranged subsequent to said at least one dryer.