Carbon Capture

In order to achieve climate neutrality in the industrial sector, processes are also needed to deal with unavoidable emissions.Through carbon capture, CO2 can be separated from industrial waste gases and from the atmosphere.

The use of fossil-based energy sources in many industrial processes causes emissions of the greenhouse gas carbon dioxide (CO2), which is harmful to the climate. Work is ongoing to reduce these emissions by using renewable energies and a range of different technologies. Nevertheless, certain process-related CO2 emissions will remain unavoidable – particularly in the cement and lime production industries. It is therefore important to find a solution, which contributes towards climate neutrality despite greenhouse gas emissions, to deal with these processes and others that cannot be made carbon neutral in the medium term.

Carbon Capture, or the separation of CO2, offers a means of handling the problem. Under this process, carbon dioxide is extracted either directly from the atmosphere (Direct Air Capture) or from industrial waste gases. In the first case, the ambient air is passed through a filter which removes most of the CO2 from the air. Facilities of this type are already in use. Depending on the application, the extraction of carbon dioxide from industrial waste gases is based on various processes, whereby a distinction can be made between pre-combustion-, post-combustion- and oxy-fuel combustion processes. Carbon capture from industrial waste gases is more efficient than direct air capture due to the higher concentration of CO2 in industrial waste gases.

In the case of pre-combustion, the harmful CO2 is captured before the energy from the fuel is used. To achieve this, hydrogen and CO2 are produced from the fuel, e.g. coal or natural gas, by treating it with steam at a high temperature. The CO2 is then captured and the hydrogen remains available as a carbon-free substance for energy production.

The so-called blue hydrogen produced in this way can serve as a provisional solution to establish a hydrogen economy until the required quantities of hydrogen can be supplied in full using renewable energy sources.

Carbon Capture in hydrogen production

In contrast to pre-combustion, in the case of the post-combustion process CO2 is captured after the fuel is burned. Examples of post-combustion techniques include calcium looping and amine scrubbing, both of which can be used not only for capturing CO2 after combustion but also for avoiding process-related CO2 emissions.

Calcium Looping: in the case of calcium looping, following the industrial production process, quick lime is brought into contact with the flue gases at a temperature of 650 degrees Celsius in order to bind the CO2 and separate it from the remaining components of the waste gas. As a result of absorbing the CO2, regular lime is formed, which is then in turn burned to release pure CO2 and the burnt lime is reused in the separation process. There are potential applications for calcium looping in the cement industry in particular, since this process takes place at high temperatures and lime is in any case used in cement production.

Amine scrubbing: in the case of amine scrubbing, flue gases produced during combustion processes flow through a washing column, which is a kind of chemical washing machine. At the same time an amine solution, which has a similar effect to a solvent, flows from the other direction and absorbs the CO2, thus separating it from the gas. The washing solution charged with CO2 is regenerated by means of heating, which drives out the CO2. The washing solution can then be reused. This process is also suitable as a retrofit solution for a wide range of processes, in part due to the lower temperatures required.

CO2 separation from flue gas

The oxy-fuel combustion process is based on burning fossil fuels, e.g. natural gas or coal, with pure oxygen. Since, in contrast to conventional combustion with air, this process takes place in a nitrogen-free atmosphere, steam and CO2 are formed almost exclusively. By subsequently condensing the steam, it is possible to obtain CO2 that is virtually pure. The oxy-fuel combustion process primarily offers potential for the cement industry and biogas power plants, making it possible to capture carbon dioxide and reuse it in a climate-friendly manner or store it, and at the same time avoid nitrogen oxide emissions, in contrast to conventional processes.

The afore-mentioned technologies currently remain at different stages of development – some are still undergoing testing, others are already in use. In addition, the frequent absence of infrastructure for the subsequent use of the captured CO2, the partial lack of market maturity of the respective processes and the disputed issue of the storage of CO2 still constitute barriers to wider industrial application. Criteria such as the availability of infrastructure and processes, but also loss of efficiency, costs, purity of the captured CO2, environmental impacts and the efficiency of carbon capture will be decisive in future in terms of which techniques prevail for industrial use in the various fields of application. Since CO2 emissions are expected to continue to occur for the long term, however, these kinds of processes for capturing and reusing CO2 will be essential for paving the way to the energy transition in any event – despite the high level of energy consumption that is required for using these technologies and the barriers that remain.

Increase in the concentration of CO2 in flue gases by means of combustion with oxygen

The CO2 captured using the various techniques can subsequently either be used as a raw material for a range of different industrial processes (Carbon Capture and Utilisation – CCU for short) or it can be stored (Carbon Capture and Storage – CCS for short).

In the case of carbon capture and storage (CCS, also known as sequestration), the captured CO2 is permanently stored in underground storage facilities at great depth (1,000 to 4,000 metres). For this purpose, deep saline aquifers, coalbeds and depleted oil and gas reservoirs onshore and under the seabed are used. As a result of the pressure that prevails at great depth, the carbon dioxide is compressed, becomes much denser and is permanently bound, so that it is virtually impossible for it to re-emerge.

In the case of further utilisation of the CO2 in industrial processes, the commodity is used as a raw material. CO2 is therefore available as a renewable resource instead of one that is fossil-based. Innovative applications make its material use possible in the areas of basic chemicals, fuels, and fertilisers, as well as in the production of methanol and polymers (plastics). This allows the life cycle of the carbon to be extended and any leakage is avoided for the time being. 

Info booklet

With information about the initiative, the participating stakeholders, technologies and solutions for a climate-neutral industrial sector.

Info booklet