Sand destined to the manufacture of cement in a quarry

Analytical solutions for the safe and efficient CO₂ storage in the cement industry

Mon 18 Sep, 2023

Analytical solutions for the safe and efficient CO2 storage in the cement industry

If the cement industry were a country, it would come after China and the U.S. in terms of CO2 emissions. Or to put it in figures: With a global production volume of 4.5 billion tons of cement per year, the cement industry emits around 2.8 billion tons of CO2, accounting for around 8% of total greenhouse gas emissions worldwide.1

These CO₂ emissions, which are generated during cement production, cannot be avoided in principle, as they are based on a natural chemical reaction of the raw material and fuel emissions: The raw material limestone is converted into clinker at temperatures of up to 1,500 °C (calcination process), releasing large quantities of CO2.

Restricting the cement industry itself is also not realistic; after all, cement is necessary as a binder for concrete wherever construction is taking place. Even projects to promote climate protection, such as the construction of rail lines, energy-efficient buildings, etc., cannot do without cement as an important building material.

There are some approaches to reduction, such as the use of waste heat, a reduction in the proportion of clinker, new manufacturing processes, the use of substitute fuels and recycling of concrete. However, these are not sufficient to achieve climate neutrality.

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CO2 capture and storage for a climate-neutral cement industry

A promising alternative is to filter CO2 out of exhaust gases before releasing it into the atmosphere. Captured CO2 can then either be stored, e.g., in rock or in the seabed (CCS - carbon capture and storage), or captured, transported, and further utilized, e.g., as a raw material to produce polymers, fuels and building materials (CCU – carbon capture and utilization). Thus, once captured, the CO2 can be transported and either stored or reused as a raw material for the production of polymers, fuels and construction materials.

The following carbon capture concepts are therefore considered an important approach:

Carbon capture and storage (CCS)

For this, CO2 is captured, processed, compressed, and transported to a storage site, e.g., underground (rock or seabed). CO2 can be captured either from the atmosphere or directly from emission sources during fossil fuel use in industrial processes or power generation.

Carbon capture and utilization (CCU)

CO2 is captured, transported, and reused, e.g., as a raw material to produce polymers, fuels, or construction materials.

Carbon capture, storage, and utilization (CCUS)

This approach encompasses all variants of CCU and CCS. CCUS allows the high CO2 concentrations generated by industrial activities to be captured and used effectively. This method therefore has a key role to play in decarbonization.

The potential of carbon capturing

By using these approaches to capture carbon at various stages of the cement manufacturing process, cement manufacturers can significantly reduce their emissions. Each of these processes has its advantages in terms of cost, feasibility, and efficiency.

Pre-combustion capture

involves capturing of CO2 before it is released during the cement production process. By converting fossil fuels into a mixture of hydrogen (H2) and CO2, the CO2 is separated and can be stored, while H2 is used as a fuel for the cement process. Pre-combustion capture is considered more energy-efficient than post-combustion, but it requires additional investment into equipment and processes.

Post-combustion capture

is the most widely used to date. Specialized equipment such as chemical solvents or membranes is used to separate and capture CO2 from cement plant flue gases after combustion, which can then be stored or utilized in other processes (CCUS).

For this purpose, chemical processes are used, such as amine gas treating, also known as amine scrubbing. The flue gas is contacted with an aqueous amine solution. Amine reacts with CO2 and removes it in large proportions from the gas stream during the absorption process. For the desorption step, the amine/CO2 solution enters the regenerator where it is heated to recover the CO2 from the scrubbing solution.

In this process, it is important to find the right ratio between absorption power and heating power. If less heating is used in the final CO2 desorption process, costs are saved, but there is also the risk that more CO2 will remain in the amine solution and subsequently also in the flue gas, because of reduced absorption capacity.

To find the optimum between absorption performance and required heating power, monitoring of CO2 loading in the amine solution is important and must be measured regularly. These measurements can be conducted by different methods, like Raman spectrometry or conventional titration. As well online monitoring of CO2 concentrations in the flue gas by NDIR (non-dispersive infrared) sensors is applied.

However, TIC (total inorganic carbon) measurement is much more suitable to evaluate CO2 absorption rates in amine solutions and to monitor the CO2 capture processes. The advantage is that there is no interference when thermal processes change the amine solution properties by aging due to thermal stress, like there is with spectrometric methods. The TIC parameter is simply measured by acid treatment of the sample. This converts carbonates and hydrogen carbonates into CO2, which is easily removed from the acid solution by a gas purge and quantified by an NDIR detector within the analytical device. The multi N/C 2100 S and multi N/C 3100 from Analytik Jena are predestined for this purpose, offering an accurate, automated, and reliable method for the CO2 monitoring in amine absorption solutions. (see AppNote)

Oxy-fuel combustion

involves burning fuel with pure oxygen instead of air, resulting in a concentrated stream of CO2 that is easier to capture and store. Oxy-fuel combustion can be integrated into cement kilns, allowing for more efficient carbon capture process. 

Carbonation

or carbonatization represents another approach to CCU. CO2 and minerals react to form carbonates which can then be used, e.g., for concrete recyclables and improve their strength. Here, separated CO2 is used, old concrete is recycled. To optimize the carbonation process and to record the CO2 uptake rate (see AppNote), the fully automatic TIC determination with the multi EA 4000 is an excellent choice.

Calcium looping

is using calcium oxide (lime) to capture CO2 from the flue gases of cement plants. The process utilizes a loop where calcium oxide reacts with CO2 to form calcium carbonate (limestone), which is then calcined to release the captured CO2. Calcium looping has shown promising results, but it is still at the research and development stage.

Direct separation of CO2

The direct separation of CO2 from cement plant flue gases is using various techniques such as membranes or adsorbents. It has the advantage of potentially lower energy consumption and smaller infrastructure requirements, but it is still under development and faces technical challenges. 

The capture and recovery of CO2 for reuse by converting it into valuable products with the aim of achieving carbon neutrality is an important topic in industrial research and the development of innovative technologies. Facilities for CO2 capture and storage can be installed in the cement industry to remove the CO2 from the flue gas and subsequently allow purification, liquefaction, and storage. 

Benefits of carbon capturing in the cement industry

Implementing carbon capturing technology in the cement industry offers several advantages, including: 

  • Reduced greenhouse gas emissions and carbon footprint  
  • A sustainable cement production by minimizing CO2 emissions without compromising the quality or functionality of the cement 
  • Ensuring compliance with emission regulations and avoiding potential penalties or restrictions 
  • Carbon utilization, e.g., for producing building materials, or even creating valuable chemicals  

While carbon capturing technology holds great promise, several challenges need to be addressed. These include the high cost of implementation, the need for infrastructure development, and efficient process control. Also here, TIC monitoring can contribute significantly.  

As technology advances and awareness grows, the cement industry is increasingly investing in research and development to overcome these hurdles. There are the first countries e.g., Switzerland, rewarding utilization of carbonated recycling cements in the building industry by refunding carbon tax.  

Outlook

As global efforts to combat climate change intensify, carbon capturing in the cement industry emerges as a crucial solution, paving the way for a greener and more sustainable future. By implementing these various methods, cement manufacturers can significantly reduce greenhouse gas emissions while ensuring the production of sustainable cement. TIC measuring methods as shown above enable a reliable and efficient monitoring of carbon capture and utilization processes.  

Read our e-book on the analysis of cement and other building materials and learn about powerful methods that can be used to reliably implement the carbon storage approaches presented.

1 cf. Germany 2022 754 Mio. metric tons – Umweltbundesamt

Downloads

TIC Determination in Amine Scrubbing Solutions for Efficiency Control of CO2 Emission Reduction from Fossil Fuel Combustion (EN)

Application Note

Open PDF

Determination of CO2 Absorption Rates in Cement and Concrete Recycling by Automated Solids TIC Measurement (EN)

Application Note

Open PDF

Analysis of Building Materials: C/S/Cl and Metals Determination in Cement and Related Materials (EN)

Brochure

Open PDF

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