Climate protection

In Germany, the production of one tonne of cement is associated with around 600 kg of CO₂ emissions - of which roughly two thirds can be attributed to raw material-induced process emissions and only one third to fuel emissions. The total CO₂ emissions of the cement industry in this country currently amount to roughly 20 million tonnes, or approximately 2% of national CO₂ emissions. But how does CO₂ occur in the cement production process?

The first stage of cement production involves the extraction of limestone in quarries and its comminution and subsequent burning at temperatures of 1450 °C in rotary kilns to produce cement clinker. The chemical properties which are responsible for the performance of the cement and the great stability of the concrete in which it is used are formed in this process. In the course of burning, process-induced CO₂ occurs during calcination of the limestone to form quick lime, a preliminary stage of cement clinker, on the basis of the following chemical reaction: CaCO₃ → CaO + CO₂.

The German cement industry has reduced its specific emissions per tonne of cement by around 22% since 1990. This progress can essentially be attributed to the following measures:

• Increased thermal and electrical energy efficiency thanks to a variety of process engineering improvements
• Replacement of fossil fuels by alternative biomass-containing fuels with a smaller carbon footprint
• Use of alternative pre-calcined raw materials
• Efficient utilisation of emission-intensive cement clinker as intermediate product in the cement

It is however apparent that the limits of conventional CO₂ reduction measures will soon be reached: For example, the thermal efficiency of cement plants is now already close to the technically possible maximum and progress made with regard to electrical energy efficiency is often more than offset by increased power consumption - for instance due to the demand for finer ground cements, more technically sophisticated exhaust gas filtration or CO₂ reduction measures. A further reduction in the clinker content of cement would be technically feasible, but is dependent to a considerable extent on the availability of suitable alternative raw materials such as blast furnace slag, fly ash or burnt clay.

In terms of the goal of achieving a climate-neutral society by the second half of this century, the enormous challenge facing the cement and concrete value chain will be to reduce both energy and process-induced CO₂ emissions to "zero" if at all possible. In addition to some new CO₂-efficient raw materials for clinker, cement and concrete production, this will require above all innovative technologies which will fundamentally alter the production processes and concrete construction work. It is imperative to develop these future solutions "today" to ensure their prompt readiness for implementation on an industrial scale and with economic operation.

For this reason, the cement manufacturers in Germany have for many years now been performing intensive research and work on various approaches in addition to the "conventional" reduction measures explained above to further drastically reduce the CO₂ intensity of cement production. To do so, it will be essential to exploit the full CO₂ reduction potential at every stage of the value chain: clinker - cement - concrete - structure - demolition. This primarily includes:

• The use of innovative, particularly CO₂-efficient types of cement such as CEM II/C and CEM VI and the advancement of concrete technology required for this
• The intelligent, resource-preserving utilisation of concrete in structures
• CO₂ absorption in the concrete (recarbonation)
• The development of new types of mineral binder
• Technologies for carbon capture, transportation, utilisation and storage in suitable and safe geological formations

In full awareness of the scale of the challenge posed by climate protection, the German cement manufacturers have been working hard for years under the auspices of VDZ and the European Cement Research Academy to further enhance the reduction options available today and also to develop new technologies. It has become apparent that carbon capture at the cement plant and its subsequent utilisation and storage (CCU, CCS) will have a crucial role to play in the process of decarbonisation. Following completion of a wide range of studies and research projects, the cement industry is now in a position to perform carbon capture trials on an industrial scale (e.g. oxyfuel and post-combustion technologies). Other possible ways of capturing carbon in the production process are currently being tested in the course of several pilot projects in Europe or are at the planning stage.

A further approach involves the use of new types of mineral binder, which could be produced on the basis of a different raw material composition and requiring less energy input. Work on this is however still at the development stage and at present it is not apparent whether or not these new binders would be capable of replacing cements on a large scale. This is due on the one hand to the highly limited availability of some of the raw materials required and also because of the technical properties which, at least from today's point of view, are only likely to be suitable for extremely specific building applications. With regard to the CO₂ balance, new binders also have to stand comparison with innovative cements such as CEM II/C or CEM VI, which are basically already available now, are likewise highly CO₂-efficient and lend themselves to a far wider range of applications.

The cement industry will not be able to shoulder the burden of extensive decarbonisation of the cement and concrete value chain on its own. It will require support from mechanical engineers, concrete manufacturers, the building industry, planners and architects. A suitable political framework will also be necessary to permit the competitive production of low-CO₂ cements and concretes in Germany whilst at the same time allowing a market to develop for these products.

This applies in particular to the widespread economical use of carbon capture technologies at cement plants. Many other conditions have to be fulfilled alongside technical feasibility. On the one hand, the process is exceptionally power-intensive and thus expensive. Which means there is a need for appropriate subsidies to make economical operation possible in practice. On the other hand it will not be possible to successfully implement this transformation without the necessary infrastructure – for CO₂-free power consumption throughout and the transportation of CO₂ and hydrogen for example. And finally the people on site, and society in general, will have to be prepared to support and accept the technical and economic changes for the transformation to a climate-neutral society to ultimately be a success for all concerned.