The catch4climate project
Project Overview
1Why was Mergelstetten selected as the location for the project?
All sites within the consortium that were considered suitable for the Pure Oxyfuel pilot plant were evaluated by a team of experts from all consortium partners. The key reasons for the consortium’s decision to select Mergelstetten were the availability of a designated construction area covered by a development plan, the site's excellent transport connections, and its favourable logistical accessibility for potential oxygen suppliers. At the same time, significant synergies can be achieved with the existing SCHWENK cement plant at the site. These benefits relate primarily to the supply of raw meal and fuels. Both pulverised hard coal and alternative fuels can be sourced via short logistical routes, thereby minimising the number of required lorry movements.
2When will the plant be commissioned?
The pilot plant is expected to be commissioned in summer 2026.
3Um wieviel verteuert sich der Zement durch das Oxyfuel-Verfahren?
The production of cement clinker using the Oxyfuel process requires significantly more energy, particularly electricity for extracting pure oxygen from the air and for liquefying the captured CO₂. As a result, the production process inevitably becomes more expensive. Public studies conducted between 2014 and 2018 estimate that clinker production costs could increase by approximately 40%. However, the actual extent of the cost increase cannot currently be determined with certainty and is one of the aspects that the pilot project aims to investigate.
4How many million euros will the project cost in total?
Taking into account the total investment and operating costs, the overall project budget amounts to approximately €130 million.
5How can long-term competitive advantages be achieved?
According to current studies, the expected range of CO₂ avoidance costs is between €40 and €90 per tonne of CO₂ (including CO₂ capture and processing at the cement plant). The actual costs depend heavily on the technology and process selected.
Current studies indicate that the Pure Oxyfuel technology selected for the catch4climate project could achieve CO₂ avoidance costs in the range of €40 to €50 per tonne of CO₂. This cost advantage forms the basis of the expected competitive benefit of the Pure Oxyfuel technology, which enables significantly easier separation, processing, and subsequent utilisation or sequestration of CO₂ emissions from the clinker-burning process.
6How is CO₂ pricing taken into account?
Due to its low production capacity, the pilot plant does not participate in the European Union Emissions Trading System (EU ETS). Instead, CO₂ price surcharges under the German Fuel Emissions Trading Act (BEHG) must be paid for the fuels used. These charges form part of the plant’s operating costs.
7How does this process affect the CO₂ price per tonne?
The Oxyfuel process itself does not affect the amount of CO₂ generated during the clinker-burning process; rather, it ensures that the CO₂ is produced in a highly concentrated form. CO₂ emissions to the atmosphere are only avoided once the CO₂ has been captured through subsequent processing steps, such as purification and liquefaction.
For future large-scale Oxyfuel plants, this means that there would be a reduced demand for CO₂ allowances within the EU Emissions Trading System (EU ETS). At least in theory, this could contribute to downward pressure on the price of CO₂ allowances.
For future large-scale Oxyfuel plants, this means that there would be a reduced demand for CO₂ allowances within the EU Emissions Trading System (EU ETS). At least in theory, this could contribute to downward pressure on the price of CO₂ allowances.
8Does clinker quality actually improve with the Oxyfuel process?
This question is being investigated extensively as part of the project and represents a further element in assessing the benefits of the Pure Oxyfuel technology. To this end, trials will be carried out at the pilot plant to evaluate the potential for improving clinker quality.
9Will every cement plant require a kiln system operated using the Oxyfuel process in the future?
If the pilot project proves successful, the Oxyfuel process represents an excellent option for capturing highly concentrated CO₂ from exhaust gases and thereby contributing to the cement industry’s transition to carbon neutrality. In principle, existing kiln systems can be retrofitted to operate using the Oxyfuel process, or new kiln systems can be constructed specifically for this technology. However, alongside the Oxyfuel process, the global cement industry is also testing other technological alternatives aimed at achieving carbon neutrality. At present, it is not possible to predict which of these innovations will ultimately become the dominant solution. Nevertheless, the Oxyfuel process is expected to offer the lowest operating costs among the competing technologies.
10Is the project worthwhile from an energy-efficiency perspective?
The associated CO₂ capture process requires significantly more electrical energy than the conventional production process, with the majority of the additional demand arising from oxygen production. In the case of the pilot project, however, this additional energy consumption occurs at the oxygen supplier’s facilities rather than at the plant itself.
In addition, the Oxyfuel process also requires somewhat more fuel energy. This is due to factors such as increased heat radiation resulting from smaller cross-sections in the gas ducts and the fact that the heat from the fired clinker cannot be used to preheat the combustion oxygen in the same way that conventional kiln systems use clinker heat to preheat combustion air.
In addition, the Oxyfuel process also requires somewhat more fuel energy. This is due to factors such as increased heat radiation resulting from smaller cross-sections in the gas ducts and the fact that the heat from the fired clinker cannot be used to preheat the combustion oxygen in the same way that conventional kiln systems use clinker heat to preheat combustion air.
11Is it also the goal to use 100% alternative fuels?
The use of alternative fuels in the cement industry, particularly those containing biogenic components, makes it possible to reduce the consumption of fossil fuels to a corresponding extent.
12Would it be worthwhile to focus on environmentally friendly fuels?
With regard to the planned use of 100% alternative fuels, the highest possible level of resource conservation in fuel use is achieved. The clinker-burning process enables the thermal utilisation of fuels without generating residual waste. Unlike municipal waste incineration plants, no ash or slag requiring disposal in landfill is produced. As a result, the process makes a significant contribution to environmentally responsible thermal recovery and resource efficiency.
13Why is research being conducted into capturing CO₂ from exhaust gases?
The goal of achieving climate neutrality in Europe and Germany by 2045 provides the framework for the necessary technological developments and transformation processes, including those within the cement industry. According to the CO₂ Roadmap of the German Cement Works Association (VDZ), so-called CCUS technologies (Carbon Capture, Utilisation and Storage) are expected to make a significant contribution of more than 50% towards reducing process-related CO₂ emissions on the path to climate neutrality. Among the available options for capturing CO₂ from the clinker-burning process, Pure Oxyfuel technology is considered to have the potential to be the most economically viable solution. For the cement industry, this makes the technology highly promising and a key element in achieving climate neutrality and meeting long-term policy objectives.
Plant Technology
1Does the plant require a large amount of electricity?
Avoiding CO₂ emissions is highly energy-intensive, regardless of the technology selected. For the CO₂ capture plant in combination with the Pure Oxyfuel process, the specific energy consumption is expected to be approximately 120–150 kWh per tonne of CO₂ purified and liquefied.
2What exhaust gas cleaning technologies are used in the Oxyfuel kiln system?
The flue gas leaving the preheater cyclones must be treated in accordance with the emission requirements of the German Federal Immission Control Act (BImSchG), the Technical Instructions on Air Quality Control (TA Luft), and the 17th Federal Immission Control Ordinance (17th BImSchV). This takes into account the fact that the composition and pollutant concentrations of the kiln exhaust gas change as a result of using a different oxidant (pure oxygen instead of ambient air). Compared with conventional kiln systems, the flue gas cleaning technology is therefore being further developed.
The following exhaust gas cleaning technologies are planned:
• The flue gas stream leaving the preheater will be dedusted using a high-temperature-resistant filter.
• The low-dust flue gas will then be directed to an SCR (Selective Catalytic Reduction) unit for catalytic NOₓ reduction. The SCR unit represents the second stage of flue gas denitrification, following the kiln-integrated SNCR (Selective Non-Catalytic Reduction) system used for non-catalytic NOₓ reduction. • Potentially higher SOₓ concentrations in the flue gas have made it necessary to install a dedicated flue gas desulphurisation system. As part of its overall design, this system also contributes to the reduction of mercury emissions. Therefore, an additional wet scrubber is planned for flue gas treatment at this pilot Oxyfuel kiln plant. To date, this has generally been regarded as an unconventional solution within the cement industry.
The following exhaust gas cleaning technologies are planned:
• The flue gas stream leaving the preheater will be dedusted using a high-temperature-resistant filter.
• The low-dust flue gas will then be directed to an SCR (Selective Catalytic Reduction) unit for catalytic NOₓ reduction. The SCR unit represents the second stage of flue gas denitrification, following the kiln-integrated SNCR (Selective Non-Catalytic Reduction) system used for non-catalytic NOₓ reduction. • Potentially higher SOₓ concentrations in the flue gas have made it necessary to install a dedicated flue gas desulphurisation system. As part of its overall design, this system also contributes to the reduction of mercury emissions. Therefore, an additional wet scrubber is planned for flue gas treatment at this pilot Oxyfuel kiln plant. To date, this has generally been regarded as an unconventional solution within the cement industry.
3How is CO₂ captured?
The CPU (CO₂ Processing Unit), or CO₂ gas treatment unit, combines several coordinated process steps for the separation and liquefaction of CO₂ from the exhaust gas stream. First, the gas is passed through a gas scrubber, where it is cooled, partially dewatered, and salts are removed. The gas is then treated, for example, by means of an alkaline scrubbing process under pressure to remove nitrogen oxides and sulphur oxides. Following this, the gas is dried using a fixed-bed adsorber. The dried gas is subsequently separated in a high-pressure rectification column operating at very low temperatures. This process divides the gas into liquid CO₂ and gaseous fractions consisting of oxygen, nitrogen, argon, and residual CO₂. Note: The yield of liquefied CO₂ (the “capture rate”) also depends on the CO₂ concentration in the feed gas entering the CPU. Achieving a higher capture rate is closely linked to maintaining a high level of kiln availability over time and a high degree of CO₂ enrichment in the process gas.
4Where exactly is the CO₂ captured within the process?
The CO₂ is captured after the exhaust gas cleaning stage (which is required to comply with the emission limits of the 17th BImSchV) and before the gas is released through the stack.
5What is the energy cost of CO₂ capture? How high is the energy demand for CO₂ separation?
The primary objective of this project is to achieve the highest technically possible concentration of CO₂ in order to optimise the design of a large-scale CPU both in terms of energy consumption and capital investment costs.
The pilot plant represents the first step in redesigning the clinker-burning process further upstream in the technical process chain, thereby enabling an optimal CO₂ concentration at the inlet of the subsequent process stage.
In general, there is a direct relationship between lower CPU energy consumption and a higher degree of CO₂ enrichment at the CPU inlet. (It should be noted that the specific electrical energy demand of a CPU, regardless of its design, will exceed that of the kiln operation.) Therefore, the focus of the research project is on evaluating the process performance of the new kiln system. Determining the level of CO₂ enrichment achieved and the extent of its variability is one of the project's objectives, as this information is required for the appropriate sizing of the other plant components. Based on existing studies, a large-scale plant can be expected to require a specific electrical energy consumption of approximately 120–150 kWh per tonne of CO₂. Reference:
A. Darde et al., “Air separation and flue gas compression and purification units for oxy-coal combustion systems”, Energy Procedia 1 (2009) 527-534 V. Hoenig, et al. „ECRA CCS Project –Report about Phase III. Technical Report TR-119/2012“, Düsseldorf / Germany, 2012 K. Koring, „CO2-Emissionsminder-ungspotential und technologische Auswirkungen der Oxyfuel- Technologie im Zementklinkerbrennprozess“; Schriftenreihe der Zementindustrie, Heft 79, 2013
The pilot plant represents the first step in redesigning the clinker-burning process further upstream in the technical process chain, thereby enabling an optimal CO₂ concentration at the inlet of the subsequent process stage.
In general, there is a direct relationship between lower CPU energy consumption and a higher degree of CO₂ enrichment at the CPU inlet. (It should be noted that the specific electrical energy demand of a CPU, regardless of its design, will exceed that of the kiln operation.) Therefore, the focus of the research project is on evaluating the process performance of the new kiln system. Determining the level of CO₂ enrichment achieved and the extent of its variability is one of the project's objectives, as this information is required for the appropriate sizing of the other plant components. Based on existing studies, a large-scale plant can be expected to require a specific electrical energy consumption of approximately 120–150 kWh per tonne of CO₂. Reference:
A. Darde et al., “Air separation and flue gas compression and purification units for oxy-coal combustion systems”, Energy Procedia 1 (2009) 527-534 V. Hoenig, et al. „ECRA CCS Project –Report about Phase III. Technical Report TR-119/2012“, Düsseldorf / Germany, 2012 K. Koring, „CO2-Emissionsminder-ungspotential und technologische Auswirkungen der Oxyfuel- Technologie im Zementklinkerbrennprozess“; Schriftenreihe der Zementindustrie, Heft 79, 2013
6To what extent do the storage and transport of CO₂ pose risks? Risk assessment for CO₂.
CO₂ is an industrial gas that is used, for example, as an inert gas for fire and explosion protection, as a purging gas, or as a shielding gas to prevent unwanted reactions. The liquefaction of gases using high pressures and low temperatures, as well as their storage and transport under these conditions, must be carried out in compliance with the relevant safety standards.
Air Quality Control
1What other substances (besides CO₂) are released into the atmosphere through the exhaust stack? What does the exhaust gas consist of?
The technical report on air pollutants describes and forecasts the future emissions of the plant as accurately as possible. In general, emissions from the clinker-burning process arise from the combustion process itself, the process technology employed, and the composition of the raw materials and fuels used.
Emission limits apply to: the following components: • Nitrogen oxides (NOₓ), • Carbon monoxide (CO), • Dust, • Sulphur oxides (SO₂), • Ammonia (NH₃), • Chlorides and fluorides (HCl, HF), • Organic compounds (TOC), • Benzene, • Mercury (Hg), • Trace elements, and • Dioxins/furans. The Oxyfuel process also affects the emission levels of the aforementioned components due to its different process technology. As a result of the lower exhaust gas volume flow, emission concentrations are higher; however, the total emission loads per tonne of clinker are comparable to those of conventional kiln systems. The emissions are therefore monitored by measurement on a regular basis and, for the most part, continuously, just as they are in conventional kiln systems. In addition, state-of-the-art exhaust gas cleaning technology, in accordance with best available techniques, is employed. Furthermore, an air pollutant dispersion modelling study is carried out to assess the immissions that can be expected in the surrounding area as a result of the plant. The pilot plant is designed, constructed, and operated in such a way that safe and environmentally compatible operation is ensured at all times.
Emission limits apply to: the following components: • Nitrogen oxides (NOₓ), • Carbon monoxide (CO), • Dust, • Sulphur oxides (SO₂), • Ammonia (NH₃), • Chlorides and fluorides (HCl, HF), • Organic compounds (TOC), • Benzene, • Mercury (Hg), • Trace elements, and • Dioxins/furans. The Oxyfuel process also affects the emission levels of the aforementioned components due to its different process technology. As a result of the lower exhaust gas volume flow, emission concentrations are higher; however, the total emission loads per tonne of clinker are comparable to those of conventional kiln systems. The emissions are therefore monitored by measurement on a regular basis and, for the most part, continuously, just as they are in conventional kiln systems. In addition, state-of-the-art exhaust gas cleaning technology, in accordance with best available techniques, is employed. Furthermore, an air pollutant dispersion modelling study is carried out to assess the immissions that can be expected in the surrounding area as a result of the plant. The pilot plant is designed, constructed, and operated in such a way that safe and environmentally compatible operation is ensured at all times.
2Why do you say that, in the end, nothing will be emitted from the plant?
The long-term objective is to increase the amount of CO₂ captured from the exhaust gas stream. As a result, progressively less kiln exhaust gas would be emitted into the environment via the main stack. If the entire kiln exhaust gas stream were directed to a CO₂ capture facility, only the dedusted cooler exhaust air would ultimately remain as an emission source. However, the actual extent of CO₂ capture achieved within the pilot project will only become clear as the project progresses. The primary aim of the research project is to demonstrate that complete CO₂ capture is fundamentally possible when using the Pure Oxyfuel production process.
3How does the pollutant composition change when using 100% oxygen?
The use of pure oxygen combustion affects the emission levels of the components listed above under No. 31, such as NOₓ, due to the different process technology involved. The higher gas temperatures may lead to an increased conversion of available nitrogen into NOₓ. On the other hand, the overall amount of nitrogen present in the system is significantly lower, meaning that these effects may partially or completely offset one another. In addition, changes in kiln operation between reducing and oxidising conditions can influence the emission levels of SO₂ and TOC (Total Organic Carbon). Emissions of these components are continuously measured and monitored during operation.
Due to the lower exhaust gas volume flow, pollutant concentrations in the exhaust gas are generally higher than in conventional cement kiln systems. However, the emission loads per tonne of clinker are comparable to those of conventional kiln systems, as ultimately no more pollutants can be emitted than are introduced into the clinker-burning process through the raw materials and fuels used.
Other Questions and Comments Regarding the Project
1What is the situation regarding climate protection projects like this elsewhere in the world, for example in Asia?
As a result of the Paris Agreement, climate protection projects are currently being carried out all over the world. A key focus is the development and testing of new technologies, such as the Oxyfuel process, which, if successful, can subsequently be deployed in many other countries, including those in Asia. The partners of the CI4C consortium operate internationally. Following successful testing within the catch4climate (C4C) project, Oxyfuel technology will be available for implementation at their sites worldwide.
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