Introduction: The Cement Industry’s Carbon Challenge
Cement is the backbone of modern infrastructure, but it comes with a major environmental cost. According to a recent study from the World Economic Forum, global cement manufacturing accounts for roughly 6 % of the world’s total CO₂ emissions. And with global production projected to increase from around 14 billion m3 to 20 billion m3 by mid century, decarbonization is high up on the agenda. One of the most promising solutions: carbon capture technology.
Contents
Why Cement Production is Hard to Decarbonize
We have in a previous article explained more about cement production and how the CO₂ emissions arise, both from the heat generation and from process emissions. We recommend to read that blog to get a primer on the challenges at stake and possible solutions. In short, emissions cuts in cement production is particularly challenging due to:
- Unavoidable process emissions: About 60% of the CO₂ comes from the chemical reaction during limestone calcination, making emissions unavoidable.
- High-temperature energy demand: Cement kilns operate at extreme temperatures, requiring large amounts of energy that are difficult to electrify.
- Scale & cost challenges: Carbon capture must be both technologically and economically viable to be widely adopted.
Carbon capture options for cement
There are many solutions being pursued in parallel to reduce the emission intensity of cement production. One that stands out in particular because of its ability to drastically decarbonize the overall site is carbon capture. For a while, we thought carbon capture in cement is all the same approach. Until we dug deeper and realized that it’s more complicated.
Let’s look at each approach in more detail, as it relates to cement. This is all based on our overall breakdown of the different basic capture technology types being developed in the industry.
Post-Combustion Capture
Post-combustion capture in cement aims to capture CO₂ from the exhaust gases from the cement kiln. It is illustrated below to the right from the European Cement Research Academy, and works as follows:
- Flue Gas Conditioning: The exhaust gases from the cement kiln are cooled and cleaned to remove particulates and other impurities.
- CO₂ Separation: A solvent (e.g., amine-based) or alternative capture technology (e.g., membrane, calcium looping) is used to absorb or separate CO₂ from the gas stream.
- Regeneration: This step also depends on whether a solvent or alternative capture technology is applied. In essence, it’s about releasing the CO₂. In the case of a solvent-based approach, the CO₂-rich solvent is heated to release pure CO₂. Once the CO₂ is released, it is then purified and compressed for transport, storage (CCS), or utilization (CCU).
Norcem’s Brevik project in Norway with post-combustion capture from SLB Capturi is a great example of this approach. A video of the latest status of this project, currently under construction is here. With a capture capacity of 400 000 tonnes of CO2 pr year, and scheduled to go into operation in 2025, this is a trailblazer for others to follow.
Oxyfuel Combustion
Oxyfuel combustion is a CO₂ capture technology for cement production that replaces regular air with pure oxygen in the kiln and precalciner. This results in a flue gas that is mainly CO₂ and water vapor, making CO₂ capture easier and more efficient. It is illustrated below to the right from the European Cement Research Academy and works as follows:
- Oxygen Supply: An air separation unit (ASU) produces high-purity oxygen, which replaces the nitrogen-rich air normally used in combustion.
- Oxyfuel Combustion: The kiln and precalciner burn fuel in an oxygen-rich environment, leading to more efficient combustion and a higher concentration of CO₂ in the exhaust gas.
- Flue Gas Recycling: To control temperature and heat transfer in the kiln, part of the CO₂-rich flue gas is recirculated, reducing energy demand and NOₓ formation.
- CO₂ Purification and Compression: The remaining flue gas, which consists mostly of CO₂ and water vapor, is cooled and dried. The CO₂ is then purified and compressed for transport, storage (CCS), or utilization (CCU).
Holcim’s Obourg cement plant in Belgium is currently under construction and is a great example for an oxy-fuel capture plant in cement. The project is called Go4Zero, with Air Liquide delivering the oxy-fuel capture technology. This project has an annual capture capacity of 1,1 million tonnes of CO2 and is scheduled to go into operation in 2028.
Inherent process capture
But wait – there’s more! An alternative approach is also gaining traction, and we place this in the category of inherent process capture. In the case of cement, this is about separating the heat source from the processing of raw materials. By heating the kiln on the outside, the emissions from heating (typically low CO₂ concentration and relatively speaking harder to capture) are separated from emissions from the inherent process (higher concentration and easier to capture).
This is exactly what LEILAC (Low Emissions Intensity Lime and Cement) from Calix is doing, and which is being deployed at several sites. A conceptual image of LEIAC is shown to the left, and a neat time lapse video on the bottom. LEILAC is being investigated several places, among them at the Boral cement plant in New Berrima in Australia.
Where’s the market for capture technology in cement going?
Now that we’ve reviewed the different approaches, it’s interesting to see what’s happening in the market. For that, we turn to CaptureMap and its data on more than 1200 different capture projects that we’ve categorized.
We’ve shown the data for capture technology in cement in three ways. The first figure gives a breakdown of capture technology, by number of projects. The second is the same categorization, now shown by capture capacity. While the shares between the figures vary slightly, the main takeaway is that post-combustion is the capture technology leading the way. That said, both oxy-fuel and inherent process capture also play a role. It’ll be interesting to watch the evolution of these market shares in the time to come.
Not all of these projects are of the same size. About a third (47 of the 133 capture projects) are categorized as pilot/demo, meaning much smaller projects of limited duration, typically to test out technology. Comparing what’s commercial scale and what’s in pilot/demo, we find that while the # of projects and capture capacity are certainly different, the relative distribution of the projects between the capture technologies is pretty similar.
Beyond the number and capture capacity of each technology approach, it’s also important to understand how far ahead things are progressing with regards to implementation. The third figure above looks at the same 133 capture projects and 49mtpa of capture capacity for cement. This time, however, we’re breaking down the data by engineering stage. Anything in yellow is in feasibility stage, meaning pre-FID (final investment decision). Bright green signifies EPC (being built), and dark green is in operation.
The take-away from this figure is that while post-combustion has the largest capture volume under development, it’s actually oxy-fuel that has the largest capture volume under construction. And it’ll be real good to see some dark green bars soon, with sites in operation.
Conclusion & Call to Action
Global cement production is a significant source of CO₂ emissions, and decarbonization is crucial. Various carbon capture technologies are being explored, including post-combustion capture, oxyfuel combustion, and inherent process capture. Post-combustion leads in the number of projects and capture capacity, but oxyfuel has the largest volume under construction. Pilot/demo projects are common, and the implementation status shows real progress with several projects in the EPC stage. 2025 should be the year when we see the first of these larger scale projects coming into operation.