Carving the way with carbon capture

The cement industry, while essential for modern infrastructure development, is also a significant contributor to global 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 article explores a range of suitable and feasible processes for CCS 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 article 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, innovative approaches will be explored 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 CCS 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.

Feasible carbon capturing technologies

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 utilisation 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.

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 utilised 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.

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 vapour, facilitating the direct capture of CO₂ without the need for extensive separation from nitrogen. The captured CO₂ can be stored or utilised, and the water vapour 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.

Mineral carbonation

Mineral carbonation offers a unique approach to carbon capture by utilising 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 optimise the process, improve reaction rates, and identify suitable waste materials for large-scale implementation.

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 vapour. 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.

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 CCS technologies into cement plants represents a crucial step towards achieving carbon neutrality in the cement industry. Each of the processes explored in this article 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.

The second half of this article will be available on 09 November.

About the author

Dr S B Hegde is a seasoned and accomplished cement industry professional with over three decades of experience, both in India and internationally.

Currently, he holds the position of professor at Jain University, India and also serves as a visiting professor at Pennsylvania State University in the US.

With a proven track record of leadership positions in reputed major and multinational cement companies, he is a recipient of the prestigious ‘Global Visionary’ award for his contributions to the Cement field.

Read the article online at: https://www.worldcement.com/indian-subcontinent/07112023/carving-the-way-with-carbon-capture/