Product Description

CO2 Liquefication

With the increased use of biogas in the form of biomethane, carbon dioxide can now be effectively harnessed as a by-product of biogas upgrading. The combination of feeding the upgraded methane into the gas grid and using the by-product CO2 makes it possible to operate biogas plants with virtually no emissions and no losses. In this way, a major contribution can be made to reducing greenhouse gas emissions in the fuel and energy sectors. It also creates local synergies with CO2-consuming industries.

Biogas plants are source of biogenic (biomass based) CO2 and are part of the natural short carbon cycle, which starts with extraction of atmospheric CO2 through photosynthesis. As companies seek to reduce their carbon footprint and demonstrate their commitment to sustainability, the demand for biogenic CO2 is rising, as well as new applications in production of fuels, chemicals and building materials.

For the plants with biogas to biomethane upgrading, the process includes the collection of gaseous CO2 from biogas, its purification and liquefication. A synergy effect with the upgrading is that methane in the raw CO2 stream can be brought back to the upgrading plant resulting in a methane yield of almost 100%.

When engineering this system for biogas plant, multiple recirculations and interfaces have to be considered and coordinated to prevent accumulation of undesired components, make the most of the synergistic effects and reduce the emissions to a minimum.

Whether you are considering investing in biogas plant or seeking to expand current biogas business (existing CHP or RNG production), we will be happy to help you effectively utilize your CO2 stream. Contact us directly at



Reference Projects

In the recent assignment for Krieg & Fischer engineering team, CO2 liquefication will be implemented alongside installing a biogas upgrading system for two already existing biogas plants owned by LSW Energie GmbH, energy distribution network operator in North Germany.

Bioerdgas Isenhagen

  • Location: Germany, start of operation mid 2024
  • Gas utilization: 750 Nm³/h of biomethane, 1,1 t/h liquefied CO2, dry-ice production
  • Particularities: integration of the biogas upgrading and CO2 liquefaction with two pre-existing biogas plants, waste heat utilisation

The project will replace the existing biogas processing plant and involves the installation of a biogas to biomethane upgrading and CO2 liquefaction plant producing food-grade quality CO2. 1,400 Nm³/h of biogas will be sourced from two existing plants that use renewable raw materials and manure and from a nearby wastewater treatment plant (200 Nm³/h of biogas from potato processing waste). These three biogas flows will be integrated into the processing plant to produce 750 Nm³/h of biomethane, which will be fed into the local natural gas network.

The separated CO2 will be liquefied, stored temporarily on site, and sold. Production of liquefied CO2 will be about 1,1 t/h. It is also planned to implement a Dry-Ice production of 1.000 t/a. The proximity allows otherwise emitted Off-Gas to be reliquefied in the liquefaction plant

The plant complies with all relevant regulations, including EU regulations, DIN standards, safety rules for biogas plants, operational safety regulations, and WHG and DVGW regulation.

Krieg & Fischer engineering team carries out the integration of the biogas upgrading and CO2 liquefaction with the pre-existing biogas plants, determining suitable biogas extraction points, purification and function of the gas system, as well as using waste heat and coordinating between multiple heat and electricity consumers. CO2 liquefication consumes quite a bit of electricity (0,21 kWh/kg liquid CO2) and at the same time produces heat that comes from the compressor. So, part of the biogas is used at the existing CHPs that will supply the plants on site with electricity.

Waste heat from the biogas upgrading and CO2-liquefaction plant’s compressors will be used to heat the digesters. The remaining heat needed for the digesters will be supplied from CHPs. Excess CHP heat is used for heating in the nearby villages.


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