Reduce greenhouse gas emissions – know your processes

As more and more emissions are released and warms the Earth’s atmosphere, global non-government organisations (NGOs) and policymakers are uniting to limit the release of these unwanted greenhouse gases. In response, cement plant operators are seeking innovative ways to maintain healthy production levels and simultaneously reduce their CO₂, NO_X and other emissions. This often requires in-depth knowledge of production processes, as well as adjusting existing cement manufacturing lines and cement composition.

 

The complexity of the cement production process from start to finish is a labyrinth of scorching temperatures, numerous chemical reactions, lightning-fast heating & cooling and at times hard-working catalysts.

The heat is on

In cement manufacturing, clinker production demands the most energy and emits the greatest amount of CO₂ into the atmosphere. Clinker is produced at a sizzling 1,450 °C (2,640 °F), a crucial point for certain chemical reactions to occur.

 

With such a high energy intensity, it makes sense to focus optimisation around clinker production to lower overall energy consumption and reduce CO₂ emissions. Of course, it is not the only place where improvements can be made. Decreasing the clinker to cement ratio by substituting clinker with other materials is just one proven way of doing so. This practice is aptly named clinker substitution.

 

 

Passing the strength test

Using clinker substitution to reduce CO₂ emissions is increasingly being considered by many cement plant owners. Typical cement composition is 95% clinker, with gypsum making up the remaining amount. By substituting clinker with a comparable material, cement plant owners can achieve impressive environmental gains and align with global efforts to reduce CO₂ emissions.

For a material to be deemed suitable for clinker substitution, its compressive strength, tensile strength and water absorption are must-have characteristics. With cement being used to construct buildings and bridges, its composition needs to be able to withstand, for example, the devastating effects of an earthquake.

 

Strict cement strength standards affect the decision to adopt the practice of clinker substitution. For instance, the European cement standard, EN 197-1, outlines methods of testing cement to determine its strength. These standards, and others like it, may be viewed as roadblocks for considering clinker substitution. It isn’t as difficult as it seems, though, especially with a team of cement processing experts ready and willing to help.

Just as strong

So, what is considered a good substitute? Many cement plants around the globe making sustainability-oriented upgrades are turning to clay calcination. Some recent examples are shown in South America and the Philippines, where clay is readily available and suitable for clinker substitution. Certain parts of Brazil are also abundant in clay that has the stamp of approval for calcination.

 

As with all things novel, it’s fair to be sceptical. And with such strict standards outlining required strength and other characteristics, why change something that has worked well since cement production began?

 

It’s about balancing the profitability of the cement plant with taking ownership of the environmental footprint of the business. The effects of climate change are felt across the world – fast becoming a reality in many people’s everyday lives. A readily available solution that the industry can use today is clay calcination as a tried and tested method.

 

 

Clay can make your day

For many cement plant owners, some points need to be considered before committing to clay calcination for clinker substitution. Firstly, it is ideal that the cement plant is located close to a clay quarry. Transporting large quantities of clay over long distances defeats the overall purpose of lowering CO₂ emissions.

 

Secondly, a heat source is required for clay calcination. Temperatures of around 700-800°C will suffice, and it is feasible to reuse old equipment like rotary kilns. However, it’s not a simple feat. The heat balance needs to be just right throughout the entire process to produce gas hot enough for calcination. Skaarup’s team of technicians test clay samples at their labs in Denmark and India. She says: “Once the clay has been activated, the lab team can test it for strength and other desirable characteristics. It needs to meet the applicable standards before we pass it.”

 

Another consideration is that clay naturally has a red-brown hue, which would mean the environmentally friendly cement will not be the typical grey or white colour. Of course, the colour does not impact the strength of calcined clay.

 

 

Swiss spotlights sustainability

An intensive research project called the LC3 project is currently being undertaken by the Swiss government. The project finances sustainability projects within the cement industry. One of the projects explores the composition of limestone and clay, as well as the potential of widespread adoption of Limestone Calcined Clay Cement (LC3). A typical flash calciner can be used to make LC3. Skaarup comments: “I think that within two years, the EU standards will adapt to fit the widespread use of LC3 cement. India’s standards are expected to change this year. Hopefully, this will be the beginning of change in the industry where clinker substitution becomes the norm.”

The bigger picture

 

While clinker substitution is one way of helping to reduce emissions, there are certainly other parts of the process that can be targeted. For example, the grinding process, which requires considerable amounts of electrical energy. The widespread adoption of energy-efficient technologies, such as vertical roller mills and hydraulic roller presses, in place of traditional ball mills should be encouraged. 

The complexity of the cement production process is nuanced and a lot needs to be done before embarking on small- and large-scale projects to lower process emissions. Laying down plans now will help prepare cement plants for a sustainable future as well as for the people they are serving. Emission standards are only going to become stricter as governments around the world work to mitigate the effects of industrialisation on the environment.