Biomethane is a renewable and effective substitute for natural gas and can be used in a versatile manner. However, for the transportation of biomethane to the customer conventional upgrading plants are bound to an available connection on the local gas grid. Inspired by enabling decentralized biogas upgrading, the CC TEVT has developed the concept of the Three Phase Process for the production of liquid biomethane (LBM; also called bio-LNG). Since LBM has a 600 times higher energy density than biomethane at atmospheric conditions, it can be easily transported on the road system via trucks.
The main step of the upgrading and liquefaction process is CO2 separation. The Three Phase Process is based on CO2 desublimation (direct phase change from a gas into a solid) by cooling the gas in a special separation column. The solidified dry ice is afterwards melted at -56 °C and absorbs energy from the incoming biogas to cool it. Thus, the overall energy demand of the process is reduced. The liquid CO2 is then used as refrigerant for other pre-cooling purposes or can be sold as high valuable by-product (dry ice). Finally, the upgraded biogas with a purity of over 99.9% is liquefied in a low-maintenance refrigerator.