Clay Calcining Technologies

Clay Calcining Technologies

For the production of ‘Green Cement’

With cement production responsible for approximately 8% of man-made CO2 emissions, several countries are adopting strict policies for greenhouse emission reductions.

One of the ways to reduce CO2 emissions caused by cement production is to replace clinker with Supplementary Cementitious Materials (SCM) such as calcined clay to produce what is known as ‘green cement’, named for its environmental benefits. Other key benefits include lower fuel consumption and lower capital costs.

At FCT, we have put together a specialist team who have successfully commissioned a combined 12 plants around the world for calcined clay cement. Eight of these plants were brownfield, and 4 were greenfield projects.

With proven experience in this growing industry, we have the necessary experience to evaluate and suggest the most suitable production method for each individual project. Our expert knowledge has shaped the development of two proprietary technologies for clay calcining: FlashCalx™, a suspension calciner, and RotaCalx™, a rotary kiln calcining solution.


A suspension calciner than can be installed with a mill or in an integrated plant.

FlashCalx™ combines the flexibility to use the least expensive and most readily available fuels, with the environmental and economic benefits of using flash calcining technology for sustainable cement production.

Available in standard sizes to optimize engineering and shipping costs, FlashCalx™ has a minimum footprint and can easily fit in new or existing plants with customization options available to suit different moisture contents, fineness and fuel types.

 Existing equipment may be re-usable, such as a pre-heater tower, and in some cases, a dryer-grinder may be required depending on the moisture composition of the material. For such cases, a state-of-the-art hot gas generator will be installed, offering extreme fuel flexibility for liquid, gaseous, solid and alternative fuels without need for grinding.

Fuel usage: 450-600 kcal/kg (depending on raw material mineralogy)

Fuels: Oil, gas, petcoke (1 to 10mm), mineral coal (0 to 10mm), wood chips (10 to 30mm), biomass (including wood pellets, wooden briquettes, sugarcane bagasse and others), refuse derived fuels (RDF)

Key benefits:

  • Lower overall energy consumption

  • Quick set-up with a calcination time of just seconds

  • Low thermal inertia with limited refractory lining

  • Precise temperature control for highly reactive pozzolan

  • Only one grinding system is required

  • Static system results in less maintenance

  • Lower rate of under- or over- calcination

  • Quick return of investment


Based on a traditional rotary kiln. Suitable for either greenfield or brownfield projects.

FCT offers supply of new kilns and equipment, or alternatively, can match parts of old kilns or dryers with new equipment to complete the design and supply of a clay calcining plant. The re-use of an existing burner, hot gas generator, gasifier and other parts will reduce the associated capital expenditure.

Key benefits:

  • New or existing equipment

  • Drying and calcination in a single unit

  • Burner or combustion chamber

  • Utilization of de-commissioned machinery

  • Fast track

  • Easy operation

  • Broad range of fuels, with multi-fuel firing possible

  • Allows for coarser feed granulometry

  • Suitable for clays with higher moisture content

Producing Green Cement Using FCT Calcined Clay Technologies

Identifying the best calcined clay technology for different scenarios

Producing green cement using FCT Calcined Clay Technologies

Additional Materials

‘A Focus on Flash Calcining’ by Joel Maia and Pedro Ladeira, published in International Cement Review (Jan 2021)

Download article

Read the FCT Calcined Clays Technologies brochure

Download brochure

Frequently Asked Questions

Clay deposits tend to be very heterogeneous, but typically clays used as pozzolans range from 50% to 65% SiO2 and 17% to 38% Al2O3. After activation, several types of clay can be used including Illite, Kaolinite, Montmorillionite, and calcined kaolinitic clays among others.

There are different methods to mitigate the reddish hue caused by the iron content in clay, to create the more traditional grey colouring cement producers are used to working with.

Two common methods are maintaining a reducing zone during cooling, using fuel injection close to the kiln discharge or in the cooler and/or injecting fuel mixed directly with the raw clay. However, both methods are counterproductive and increase the plant specific production.

Drawing on our team’s experience and specialist expertise in clay calcining, FCT has developed a proprietary solution for colour control using our FlashCalx™ technology, which involves the addition of inorganic modifiers and does not increase fuel consumption or emissions.

Each method has its own advantages and disadvantages, depending on factors unique to the project. A study should be undertaken to evaluate projected costs and benefits specific to the plant.

FCT is one of the only companies who offer both flash calcining and rotary kiln solutions. We can conduct an unbiased analysis to help clients select the most appropriate method to produce high quality activated clay.

To ensure high quality output, FCT collaborates with associated laboratories to perform Thermogravimetric/Differential Scanning Calorimeter and Reactivity tests, among others, to assess project viability. FCT has access to pilot plants in Europe and in the Americas, while industrial scale tests can also be performed in a 10tph unit in Europe.

The process includes:

  1. Raw material investigation considering reactivity, colour, activation temperature, moisture and other factors
  2. Pilot plant tests and trial LC3 cement testing
  3. Plant scale production of calcined clay and bulk cement plant trials
  4. Concept plant design and operating conditions, budget pricing
  5. Clay calciner design, supply, commissioning, and support