Reducing Carbon Footprint in Cement Plants – A Comprehensive Overview of Capture and Storage Options

Dr S B Hegde
Professor, Jain University, India and Visiting Professor, Pennsylvania State University, United States of America

I.              Introduction

The cement industry, while essential for modern infrastructure development, is also a significant contributor to global carbon dioxide (CO2) emissions. As the world seeks to address the challenges of climate change and move towards a more sustainable future, finding effective solutions to reduce greenhouse gas emissions from cement production has become a paramount concern. Carbon capture and storage (CCS) technologies offer a promising avenue to mitigate CO2 emissions from cement plants, ensuring a more environmentally responsible and sustainable approach to cement manufacturing.

This paper explores a range of suitable and feasible processes for carbon capturing and storage specifically tailored for cement plants. These technologies have the potential to significantly curb CO2 emissions by capturing the carbon released during the cement production process and either storing it securely or finding beneficial uses for the captured CO2. The goal is to enable cement manufacturers to align their operations with global climate objectives while continuing to meet the world's infrastructure demands.

This paper highlights various CCS methods, considering both post-combustion and pre-combustion capture techniques. Post-combustion capture involves the removal of CO2 from flue gases after cement clinker formation, while pre-combustion capture entails capturing CO2 before combustion by converting fuel into a mixture of hydrogen and CO2. Moreover, we will explore innovative approaches such as oxy-fuel combustion, mineral carbonation, chemical looping combustion, and biomass co-firing with CCS. Each process offers distinct advantages and challenges, making it crucial to assess their feasibility and applicability in cement production settings.

Also, an attempt has been made to explain the potential of mineral carbonation, where CO2 is chemically transformed into stable carbonate minerals using readily available waste materials. This process not only mitigates emissions but also offers the possibility of incorporating carbonated products back into the cement manufacturing process, closing the carbon loop and reducing reliance on traditional raw materials.

The integration of these carbon capturing and storage technologies into cement plants requires careful consideration of factors like energy efficiency, cost-effectiveness, scalability, and compatibility with existing infrastructure. Safety, regulatory compliance, and public acceptance are also essential aspects that must be addressed to ensure the successful implementation of CCS in the cement industry.

 Through a comprehensive understanding of these technologies and their potential synergies, the cement industry can play a pivotal role in advancing the global effort to combat climate change and pave the way for a more sustainable future.

II.            Feasible Carbon Capturing Technologies

1.Post-Combustion Capture:

Post-combustion carbon capture technologies involve the extraction of CO2 from the flue gases emitted during the cement production process. Among the prominent methods is the utilization of amine-based absorption, where a solvent, often amines, selectively absorbs CO2 from the flue gas stream. The captured CO2 is subsequently separated from the solvent, compressed to a supercritical state, and transported for storage in suitable geological formations or repurposed for other industrial applications.

Despite its effectiveness, post-combustion capture may require significant retrofitting of existing cement plants to accommodate the additional equipment and capture processes, making it essential to evaluate the economic viability and energy penalties associated with implementation.

2.Pre-Combustion Capture: Pre-combustion carbon capture involves converting the fuel used in cement kilns (such as coal or natural gas) into a mixture of hydrogen and CO2 through gasification. The CO2 is then separated from the hydrogen-rich gas stream, providing an additional supply of hydrogen, which can be utilized as a cleaner fuel for cement kilns, reducing the overall carbon intensity of cement production.

Pre-combustion capture presents an opportunity to capture CO2 at a higher concentration, making subsequent capture and storage more efficient. However, like post-combustion capture, it requires modifications to the cement plant's infrastructure and integration with gasification processes.

3. Oxy-Fuel Combustion: Oxy-fuel combustion is a process where pure oxygen is used instead of air during cement kiln combustion. The resulting flue gas primarily consists of CO2 and water vapor, facilitating the direct capture of CO2 without the need for extensive separation from nitrogen. The captured CO2 can be stored or utilized, and the water vapor can be condensed and recycled back into the cement production process.

Oxy-fuel combustion is an attractive option as it allows for relatively straightforward implementation in existing cement plants, providing a feasible pathway for capturing CO2 with minimal infrastructure modifications.

4. Mineral Carbonation: Mineral carbonation offers a unique approach to carbon capture by utilizing waste materials, such as steel slag and cement kiln dust, to capture CO2 through a chemical reaction with metal oxides. This process converts CO2 into stable carbonate minerals that can be used as potential raw materials in cement production, thereby closing the carbon loop and achieving a circular economy approach.

Although mineral carbonation shows promise, further research is required to optimize the process, improve reaction rates, and identify suitable waste materials for large-scale implementation.

5. Chemical Looping Combustion: Chemical looping combustion (CLC) relies on metal oxides as oxygen carriers to transfer oxygen from air to the fuel. This results in a flue gas stream consisting primarily of CO2 and water vapor. The CO2 can be readily separated and stored, while the metal oxide can be regenerated and reused in the process.

CLC is a conceptually appealing option for CCS, but its application in cement plants necessitates thorough evaluations of its technical feasibility and economic viability.

6. Biomass Co-Firing with CCS: Co-firing cement kilns with biomass, such as agricultural residues or wood waste, presents a carbon-negative option for cement production. The biogenic carbon content in biomass is considered carbon-negative, offsetting the emissions from cement production. Combining biomass co-firing with CCS enhances this carbon-negative effect, as the remaining CO2 emissions from biomass combustion can be captured and stored.

However, the availability of sustainable biomass feedstock and the associated logistics should be carefully assessed for successful implementation.

As the global community intensifies efforts to address climate change, integrating carbon capturing and storage technologies into cement plants represents a crucial step towards achieving carbon neutrality in the cement industry. Each of the processes explored in this paper offers unique advantages and challenges, making it imperative for cement manufacturers to assess the most suitable and feasible options based on their specific circumstances and operational requirements.

To ensure successful adoption, cross-industry collaborations, government support, and technological advancements will be pivotal in ushering the cement industry towards a more sustainable and environmentally conscious future.

III.           Integrated Carbon Capture and Utilization (CCU):

In addition to carbon capture and storage, cement plants can explore the concept of integrated carbon capture and utilization (CCU). CCU involves capturing CO2 emissions and converting them into valuable products, thereby offering economic incentives alongside emission reduction. Several CCU pathways hold potential for cement plants:

a.    CO2 Mineralization:

 CO2 can be reacted with calcium and magnesium-rich materials, such as steel slag or waste concrete, to form stable carbonate minerals. These carbonated minerals can be utilized as supplementary cementitious materials, providing a dual benefit of carbon sequestration and improved cement properties.

b.    CO2 in Concrete Curing:

 CO2 can be injected into concrete mixtures during curing to promote faster and more efficient carbonation, leading to the carbonation of calcium hydroxide to form calcium carbonate. This process consumes CO2 and enhances the strength and durability of concrete.

c.     Carbonation for Aggregates Production:

CO2 can be utilized in the production of aggregates by carbonating industrial waste materials, such as steel slag or fly ash, to enhance their properties and reduce their environmental impact.

IV.          Safety and Regulatory Considerations:

The successful integration of carbon capture and storage technologies in cement plants requires meticulous attention to safety and regulatory considerations. The storage of captured CO2 in geological formations necessitates stringent risk assessments to prevent any potential leaks or hazards. Adherence to local, national, and international regulatory frameworks and best practices is essential to ensure the safe and responsible operation of CCS facilities.

V.            Financial and Policy Support:

The implementation of carbon capture and storage technologies in cement plants often entails significant upfront capital investments. To encourage widespread adoption, financial incentives, subsidies, and supportive policies from governments and international organizations can play a crucial role. Carbon pricing mechanisms and emission reduction targets can incentivize cement producers to invest in CCS and promote sustainable practices.

VI. Collaborative Research and Development: 

Advancing carbon capture and storage technologies for cement plants requires collaborative research and development efforts involving academia, industry, and government agencies. Investment in research and technology development can lead to innovations, cost reductions, and improved efficiency of CCS systems, making them more accessible to cement manufacturers worldwide.

VII. Most Suitable Process for the Cement Industry

Considering the nature of cement production and the existing infrastructure, oxy-fuel combustion is often considered one of the more suitable processes for carbon capture in the cement industry.

Oxy-Fuel Combustion:

In oxy-fuel combustion, pure oxygen is used instead of air during the cement kiln combustion process. This results in a flue gas stream consisting primarily of CO2 and water vapor, making it easier to capture CO2 without the need for extensive separation from nitrogen.

o   Compatibility with Existing Infrastructure: Oxy-fuel combustion can be relatively straightforward to implement in existing cement plants with some modifications to the combustion process. It allows for a gradual transition to a low-carbon process without requiring a complete overhaul of the plant.

o   High CO2 Concentration: The flue gas from oxy-fuel combustion has a high CO2 concentration, making the subsequent carbon capture more efficient and cost-effective.

o   Reduction of NOx Emissions: Oxy-fuel combustion can also lead to a reduction in nitrogen oxides (NOx) emissions, which are a common environmental concern in cement production.

o   Experience in Other Industries: Oxy-fuel combustion has been successfully demonstrated in other industries, such as power generation, providing valuable insights and learnings for its implementation in the cement sector.

Challenges:

o   Oxygen Supply: Providing a reliable and cost-effective source of pure oxygen can be a challenge, and it requires additional infrastructure for oxygen production and supply.

o   Energy Requirements: Oxy-fuel combustion can consume more energy than conventional combustion processes, which may impact overall energy efficiency.

VIII. Conclusion:

 The integration of suitable and feasible carbon capturing and storage processes in cement plants offers a promising pathway to mitigate greenhouse gas emissions and align the cement industry with global climate goals. Each CCS technology presents unique opportunities and challenges, and the choice of the most suitable approach should consider factors such as plant-specific infrastructure, available resources, and local regulations.

As governments, industries, and society collectively prioritize environmental sustainability, the cement sector's commitment to adopting carbon capture and storage technologies will play a pivotal role in shaping a more sustainable future. By actively embracing and investing in these innovative solutions, cement manufacturers can take significant strides towards reducing their carbon footprint and driving the transition towards a low-carbon and environmentally responsible cement production industry.

While oxy-fuel combustion is considered one of the more suitable carbon capturing technologies for the cement industry, it is essential to conduct a comprehensive feasibility study at the individual cement plant level. Other carbon capturing technologies, such as post-combustion capture and pre-combustion capture, may also be viable depending on specific site conditions and economic considerations. Each technology has its advantages, and the optimal choice will depend on the cement plant's unique circumstances and long-term sustainability goals.

Ultimately, successful implementation of any carbon capturing technology in the cement industry requires careful evaluation, collaboration with experts and stakeholders, and ongoing support from governments and industry leaders to achieve the desired carbon reduction targets.

References:

1. IEA (International Energy Agency) and CSI (Cement Sustainability Initiative), "Technology Roadmap: Low-Carbon Transition in the Cement Industry," 2018. Available online: https://www.iea.org/reports/technology-roadmap-low-carbon-transition-in-the-cement-industry
2. European Cement Research Academy (ECRA), "Carbon Capture in the Cement Industry - Comparative Study of Providing Oxygen for Combustion in Cement Kilns," ECRA, 2019. Available online: https://ecra-online.org/fileadmin/user_upload/documents/Publications/ECRA_CCU_Report_2019.pdf
3. European Cement Research Academy (ECRA), "Carbon Capture in the Cement Industry - Technologies, Progress, and Costs," ECRA, 2020. Available online: https://ecra-online.org/fileadmin/user_upload/documents/Publications/ECRA-CCS_Report_2020_final.pdf
4. Global CCS Institute, "CCS in Industry - Cement," 2019. Available online: https://www.globalccsinstitute.com/resources/industry-reports/ccs-in-industry-cement/