Clay Calcination

Cement producers around the world are pursuing clay calcination projects as part of efforts to reduce the carbon intensity of their cement. But how best to implement these projects depends on a range of site-specific factors. It’s also true that not all clays are suitable for calcination. Ensuring success therefore requires a partner with advanced process and equipment engineering skills. A partner like KHD.

Calcined clay: the options

We have developed our clay calcination solutions from proven components for best possible energy efficiency and quality control. We offer two technology routes, flash calciner and rotary calciner, and will partner with you to deliver the best solution for your technical and business requirements.

Clay calcination technology – Flash Calciner

Flash Calciner

Ideal for greenfield projects, our flash calciner delivers cost-effective clay calcination, including for very sticky clays and clays with up to 40% moisture.

Flash calciners offer very precise process control: ours achieves temperature control accuracy to within plus/minus 5°C. This results in a much more reactive clay, which facilitates maximum clinker substitution rates. In contrast, clay calcined in a rotary kiln is lower quality and thus achievable clinker substitution rates are typically much lower.

During the flash calcination process, pre-ground clay is heated rapidly and held at temperature for a short time, before being rapidly cooled. It is thus more heat and fuel efficient that the longer rotary kiln process. Hot waste gases from the calciner are also used to dry the raw clay, further reducing heat consumption.

Both our flash and rotary kiln processes have been optimized to deliver a calcined clay similar in color to ordinary Portland cement – without any additional processing.

Our flash calciner incorporates familiar components of clinker production, alongside a state-of-the-art flash calciner. The process begins with our proven impact hammer mill to crush, deagglomerate and dry the feed material. This material is preheated in a high-efficiency cyclone before dropping into the flash calciner – the heart of the process. It is here that the clay is calcined – or dehydroxilated if you prefer the technical term. The flash calciner is also a proprietary KHD equipment and ensures best possible levels of productivity and performance. The activated clay is then cooled in cooling cyclones with cooling air recovered for raw material drying. The cooled clay is then transported to silos or straight to the finish mill separator for blending with cement.

The flash calcination process contains few rotating parts, reducing and simplifying maintenance needs.

Clay calcination technology – Flash Calciner

Flash Calciner – Flowsheet

Ideal for greenfield projects, our flash calciner delivers cost-effective clay calcination, including for very sticky clays and clays with up to 40% moisture.

Clay calcination technology – Flash Calciner

Flash Calciner – Performance Data

Is the clay calciner for you? Check out the performance data below.

Production Capacities250 tpd up to 5000 tpd
Adjustable Temperature Range650 °C up to 900 °C
Feed Moistureup to 40 %

Clay calcination technology – Rotary Calciner

Rotary Calciner

Based on the familiar principals of clinker production, rotary calciners have been proven in operation for many years at South American installations.

Retrofitting an existing rotary kiln allows you to re-use existing infrastructure and thus offers a lower-CAPEX option than flash calcination.

Clays are crushed and dried before being fed into the kiln for calcination. Depending on the characteristics of the clay, a number of options are available for the initial material preparation stage, including impact hammer mill and roller crusher/roller mill with box feeder. Our experts will support you to select the equipment most suitable for your applications. After calcination is complete, the hot clay is cooled before final grinding in the cement mill. Again, a number of options are available when it comes to cooling, including rotary drum quencher, screw cooler, and cyclone cooling.

Both our flash and rotary kiln processes have been optimized to deliver a calcined clay similar in color to ordination Portland cement – without any additional processing.

Clay calcination technology – Rotary Calciner

Rotary Calciner – Flowsheet

The rotary calcination process runs on similar principals to those of clinkerization. Which is not really surprising, given it uses much the same equipment. View the flowsheet to understand how we adapt this familiar system to produce a quality calcined clay.

Clay calcination technology – Flash Calciner

Rotary Calciner – Performance Data

Is the clay calciner for you? Check out the performance data below.

Production Capacities250 tpd up to 2000 tpd
Adjustable Temperature Range650 °C up to 900 °C
Feed Moistureup to 40 %

Key solutions

Thoroughly modern clay calcination solutions

Whether opting for a flash calciner or rotary kiln, some issues present a common challenge for clay calcination systems. These include color control of the final product and the use of alternative fuels. But when you work with KHD, neither are a problem.

Key solutions

The color conundrum

A historical issue with calcined clay has been the unwanted reddish hue of the final product, which results from the oxidation of iron in clay. But thanks to our intelligent process control, both our flash calciners and rotary calciners produce material that is the same color as ordinary cement – without additional processes. The result is a more credible clinker substitute.

Key solutions

Alternative fuels

Combining clay calcination with alternative fuels offers the chance to extend the sustainability advantage. However, the relatively low temperatures involved in clay calcination raises the risk of incomplete combustion. Impurities within the fuel and unburnt fuel particles may thus pass through to contaminate the final product. To prevent this, both our flash and rotary calcination processes can be combined with our alternative fuel combustion chamber. This creates a high-temperature combustion zone, where the fuel is completed combusted, so no unwanted residues enter the product.

For more advanced alternative substitution rates, we can also incorporate a Pyrorotor® into the clay calcination process. This innovative solution ensures complete combustion of very low-quality alternative fuels, allowing up to 100% substitution rates to be achieved.

Why clay calcination?

Lowering carbon emissions and more: the benefits of clay calcination

The process of turning limestone into clinker is responsible for about 60% of cement-related carbon emissions. These process emissions are also much more difficult to abate than those associated with electricity or fuel consumption, as they are an unavoidable consequence of the chemistry of clinkerization. Reducing the amount of clinker in cement is thus a key strategy when it comes to delivering Cement beyond Carbon. Calcined clay (or metakaolin) is a pozzolanic material that can be substituted for clinker in the same way as other supplementary cementitious materials (SCMs), such as blast furnace slags and fly ashes, which have long been used in cement production.

Like clinker production, clay calcination requires heat. But there is a huge different in scale: in the cement kiln temperatures reach over 1500°C, whereas clay is calcined at 650-850°C. Calcined clay production thus consumes less than half of the specific thermal energy of clinker production. Even more importantly – and unlike limestone – calcining clay does not release CO2. This eliminates those process emissions that are intrinsic to clinkerization and so difficult to abate. As a result, the carbon intensity of calcined clay is significantly lower than clinker: in fact, estimates suggest that replacing up to 40% of clinker with calcined clay would eliminate up to 40% of cement-related CO2 emissions.

In addition to these sustainability benefits, calcined clay offers a lower CAPEX route to increase cement production compared to a new clinker line, while in regions with limited limestone resources, it offers a lower-cost and environmentally responsible replacement for imported clinker. And by expanding the availability of SCMs beyond traditional sources, such as steel production and coal-fired power, where supply is likely to decrease over time, calcined clay increases the supply of these important materials.

Why KHD?

Your partner for clay calcination

Here at KHD, we are an established partner to the cement industry with a long tradition of innovation. Our technologies have shaped the modern cement plant and driven the industry forward in terms of productivity, efficiency, and environmental performance. Our clay calcination solutions fit perfectly into that tradition. Based on tried and tested equipment and our deep process and plant engineering expertise, we are your reliable clay calcination partner, able to provide a flexible solution that best fits your needs and preferred technology route.

So wherever you are on your clay calcination journey, reach out to a KHD expert today at claycalcination@khd.com or just hit Get In Touch and complete the contact form. And let’s build the future of cement, together.

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