Multi-stage centrifugal CO compression train
Cooling
Inert gases with some CO to vent
Dry, low pressure gaseous CO feed
Feed gas precooler
Liqui er
Overhead condenser
Flash separator
2-stage screw or reciprocating Ammonia compression train
Distillation column
Reboiler
Liquid CO subcooler
Cooling
Cooling
Liquid CO insulated storage
Figure 1 CO 2 liquifier with ammonia refrigeration cycle
it requires minimal additional Capex and Opex (see Figure 1 ). CO 2 from biogas upgrading is used as a local, diversified source of commercial CO2 . For example, Bright Renewables has installed food- grade liquid CO 2 production plants at the biogas facilities in Heek and Brandis, Germany. CO 2 from bioethanol Bioethanol is the most significant liquid biofuel worldwide by production volume. It is produced during the fermentation of sugary broths on an industrial scale. The process is like making a hop-free beer from grain, then distilling it to make whisky. In Asia and the Americas, the most widely used crops for bioethanol production are maize and sugar cane. Rice, sorghum, and cassava are also used in secondary quantities. In Europe, these crops are generally replaced by wheat and sugar beet. Corn ethanol fermentation yields a high-purity CO 2 stream, which is readily liquefied. This is a common CO2 source in the US and is also used in Europe. For example, Messer France has exploited a bioethanol CO 2 source at Vertex Bioenergy at Lacq. Demand for biogenic CO 2 Since 2020, a vibrant VCM has emerged. This exists in parallel to regulated costs of CO 2 emissions through national taxation programmes and emissions trading schemes.
The main buyers of CDR certificates in the Voluntary Carbon Registry (VCR) are cash- rich consulting firms and US-based mega-cap tech companies. Their vision is to offset the CO 2 emissions from their business activities. This is a cost-effective route to ‘net-zero’ for these knowledge-based sectors because their greenhouse gas emissions are diffused. Other industrial sectors with higher-intensity point- source CO 2 emissions can capture and sequester CO 2 at a lower cost. The VCM prizes biogenic CO 2 for its ability to permanently remove CO 2 from the atmosphere. Biogas monetisation with CDR Capture and sequestration of biogenic CO 2 is one of the favoured methods to generate high-quality CDR certificates. For example, in November 2025, the German clean-tech start-up Reverion signed an agreement whereby Frontier (a trader of CDR certificates) will purchase 96,000 tonnes of CDR certificates for $41 million. This values each tonne of removed CO 2 at $427 (circa €370). Reverion has developed a technology to convert biogas to heat and power. Its process does not require CO 2 to be separated from the biogas prior to entering its equipment. Plus, it produces a high-purity biogenic CO 2 stream ready for low-cost liquefaction. Considering that €370 per tonne must cover the full value chain cost and that the cost of transportation and sequestration from Germany
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