Carbon Dioxide

Carbon Dioxide (CO₂) acts as a greenhouse gas in the Earth's atmosphere and thus contributes to global warming in the long term. Carbon Capture (CC) is given great importance in the current discussion about reducing these greenhouse gas emissions to be able to achieve the goals of the Paris Agreement. To reduce global CO₂ emissions, CO₂ should no longer be seen as a waste product but as a raw material in a wide variety of applications and become part of the circular economy.

A distinction can be made in the capture of CO₂, between direct capture from the atmosphere by means of direct air capture (DAC) and the capture of CO₂ from the exhaust gas of power plants and other facilities. In the case of DAC technology, there are various methods to reduce the CO₂ concentration in the atmosphere by means of geoengineering and to slow down global warming (climate change mitigation) such as amine scrubbing, absorption by sodium hydroxide or membrane separation, among others. However, all these methods have the disadvantage of very high capture costs. Therefore, the implementation of CC to reduce greenhouse gases tends to consider the direct capture at power plants. In order to reduce CO₂ emissions in power plants, various processes have been developed. These are roughly divided into three areas.

1. The post-combustion process describes the extension of flue gas purification in a power plant by CO₂ capture in the outgoing flue gas. Similar adsorbents and absorbers as in the DAC process are used.
2. The separation of CO₂ in the pre-combustion process is mainly used in gas and coal-fired power plants. During this process, carbon monoxide is converted to CO₂ by water vapour with a water-gas shift reaction and removed from the process before combustion.
3. A third possibility for low-CO₂ power generation is the so-called oxyfuel process, in which combustion is not carried out in an air atmosphere but with pure oxygen. Thus, after flue gas cleaning, the flue gas consists only of water vapour and CO₂ and can be separated without any problems. The issue with this process lies in the provision of the pure oxygen. Since the separation of the ambient air is costly, the pure oxygen for this process can also be provided from an electrolysis plant.

The main difference between DAC and point source capture is that DAC processes reduce the CO₂ content of the atmosphere. With point source capture, CO₂ neutrality of the plant is usually achieved through the integration of CC. However, this depends on the further handling of CO₂.

One possibility is storage (CCS- carbon capture and storage), for example through sequestration in pure form in depleted gas deposits or special rock strata, thus removing part of the CO₂ emissions from the cycle. However, this is only the case for biogenic fuels, while for fossil CO₂ the carbon balance remains unchanged with the help of CC. However, since storage is strongly dependent on geographical conditions and a renewed leakage cannot be ruled out at the present time, research is also being conducted on the mineralisation of CO₂. This process is analogous to natural rock formation and only involves a small risk. In addition to storage, the utilisation of CO₂ is also being focused on (CCU - carbon capture and utilisation). In various processes, new products can be created by incorporating carbon dioxide. For example, the addition of CO₂ and hydrogen in a power-to-X plant offers the possibility of producing hydrocarbons in a regenerative way. Further applications can be found in the chemical industry for the production of synthetic compounds, in the production of urea, in greenhouses or as a basis for building materials.

As a third and indirect possibility of CO₂ use, so-called bioconversion processes can be mentioned in this context. These can be used to technically convert organic waste into stable carbon compounds (e.g., by means of pyrolysis or HTC). This biochar/plant carbon is more difficult for microorganisms to access, so that further natural degradation to CO₂ is interrupted. By incorporating the charcoal into soils, CO₂ is removed from the atmosphere in the longer term, while at the same time plant growth and the binding of CO₂ are promoted by means of photosynthesis.

We are happy to support you in the integration of a process into your planned plant as well as in the expansion of your existing plant. Thanks to our know-how in the planning of incineration plants with waste gas purification, we can assist you in all planning phases, from the initial idea and approval to implementation and commissioning.

Are you considering whether the expansion of your plant is worthwhile? We would also be happy to prepare a CO₂ balance for your current plant and support you in the assessment.

Figure 3: CO₂ cycle

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