Photo: Colourbox

CO2 as a valuable byproduct from biogas

Wednesday 01 May 19
by Morten Andersen


Philip Loldrup Fosbøl
Associate Professor
DTU Chemical Engineering
+45 45 25 28 68
Upgrading of biogas into methane mainly implies removal of CO2 from the biogas. A project at DTU Chemical Engineering strives to make use of this CO2.

CO2 is generally perceived as a greenhouse gas, but can actually be a valuable raw material. For instance, sparkling water and soft drinks are produced by dissolving CO2 in water, forming carbonic acid (H2CO3). Also, CO2 is in high demand for welding and a range of other industrial processes.

The scope of the project “BioCO2”, coordinated by Associate Professor Philip L. Fosbøl from Applied Thermodynamics – Center for Energy Resources Engineering (AT CERE), DTU Chemical Engineering, is to capture CO2 during production of biogas and turn it into a product of commercial value.

“For some years now, production of biogas from manure and other agricultural waste products has caught on. Biogas can be upgraded into methane. This upgrading both increases the energy value of the gas and allows for storage of excess gas in the high-standard Danish storage system for methane,” explains Philip L. Fosbøl.

Biogas contains roughly 35 per cent CO2. Removal of this CO2 will upgrade the biogas to methane.

“Unfortunately, it is not possible to use the CO2 from biogas upgrading directly for the various industrial purposes where CO2 is in demand. If things were that simple, utilization of this CO2 would already be in place. Each of the purposes in question have their own specifications, but generally the requirements for purity are very high. It is a key challenge in the project to meet these specifications in an economically feasible way,” says Philip L. Fosbøl.

"It seems realistic that methane from upgrading of biogas can substitute 5-7 per cent of the current energy consumption in Denmark. If further biomass becomes available, this number could go even higher in the future"
Philip L. Fosbøl, Associate Professor

A portable plant is under construction
BioCO2 is a 3-year effort sponsored by the EUDP program under the Danish Energy Agency. Besides DTU Chemical Engineering, the Danish Gas Technology Center (DGC) and Pentair are partners to the project. The Danish branch of Pentair, located in Fredericia, specializes in plants for amine-based capture of CO2.

Together, the BioCO2 partners are to build a portable plant to demonstrate the technology. The plant will be constructed at the premises of DTU Chemical Engineering. After completion it will be installed for periods of operation at two different locations. One location is Mølleåværket, a sewage management plant operated by Lyngby-Taarbæk Forsyning, and the other is a biogas facility at Fyn operated by Nature Energy.

“We want to see the technology operated both at a facility with biogas production based on sewage, and at a facility with production based on manure from farms,” says Philip L. Fosbøl.

Contributes to Danish energy policy
Besides the new production of high-quality CO2, Philip L. Fosbøl stresses that BioCO2 will contribute to fulfilment of the ambitious Danish policy on sustainable energy:

“It seems realistic that methane from up-grading of biogas can substitute 5-7 per cent* of the current energy consumption in Denmark. If further biomass becomes available, this number could go even higher in the future. Hopefully, BioCO2 will contribute to this development by making biogas upgrading more economically attractive both to farmers and to biogas plant operators.”

Although high-quality CO2 is the main focus of BioCO2, the upgrading of biogas into methane is also revisited.

“Developing a better way to produce CO2 from the upgrading is important, but obviously one needs to ensure that this doesn’t harm the quality of the methane. We need to ensure that the methane quality stays within specifications both for the sake of private consumer safety, and as a precautionary measure for avoiding danger of explosions at industrial facilities,” Philip L. Fosbøl explains.

Continuing efforts in carbon capture
While capture of CO2 at biogas facilities is a relatively new activity at DTU Chemical Engineering, capture of CO2 from coal-fired power plants has been the subject of vast research efforts over the latest decades. This is known as CCS (Carbon Capture and Storage).

“For some years now, it has not been possible to achieve Danish public funding for research in CCS. However, we have maintained activity in the field through extensive participation in research projects funded by the EU with academic and industry partners from a range of European countries,” says Philip L. Fosbøl.

He notes that despite Danish energy policies moving away from coal, CCS remains highly relevant to the Danish society:

“Just like we have invested significant resources into development of photo voltaic and wind turbines technologies, we should invest in CCS. This not in order to keep our coal facilities afloat but because in a sustainable scenario we will still need to produce goods which are bound to emission of CO2. We cannot just stop using steel, cement, medicine, paper and similar types of welfare goods which rely on processes which emit a noticeable amount of CO2.”