How Kilns Create Cement

Cement is one of the most widely used and trusted building materials in the world – and it wouldn’t be available in such huge quantities if not for the work of rotary kilns.  Cement is fundamentally made up of limestone and clay, heated and ground into a fine uniform powder which can then be liquefied later.

Let’s take a look at how this is done in modern kilns.

How Cement Is Made In A Rotary Kiln

Originally, when the process was first developed, manufacturers used the “wet kiln” process.  This involved pouring in a slurry of clay, limestone, and water.  While the process was easy to set up, it required an absolutely enormous rotary kiln to be effective – at least 200 meters long.  This is because all the moisture in the mix required huge amounts of heat just to vaporize the water, while also having very poor heat transfer properties.

So, the “dry kiln” process was created instead. 

As the name suggests, this process does not require the initial “meal” of clay and limestone to be wet.  However, it does require the meal to be pre-heated.  So, the pre-cement starts in a large tower, going through a multi-stage heating process until it’s already at around 900 C.  This helps convert the limestone into calcium before it even reaches the kiln.

Once the heated dry meal enters the rotary kiln, it is rotated as it moves downhill towards the kiln’s heat source.  This continues the calcination process, while also breaking down the limestone and clay into smaller particles.  Eventually, the mixture reaches the bottom of the kiln, the hottest part, and then drops out into a receptacle.

This receptacle is generally a cooling system, using conveyor belts and rapid airflow to cool down the mixture, which is now called clinker.  Once the clinker is thoroughly cooled, it’s ready to be mixed with water and become cement.

The major advantage of this process is that the kiln can be far shorter – usually only around 70m long.  So, factories can install twice as many kilns in the same area that would be needed for wet processes, greatly increasing output.

The Vital Role of Kilns in Cement Production

The kiln is the heart of the cement-making process. Raw materials like limestone, clay, and sand must be heated to extremely high temperatures in a kiln to produce cement clinker. Kilns provide the intense heat needed to initiate the chemical reactions that convert the raw materials into clinker.

Rotary Kilns and Vertical Shaft Kilns

There are two main types of kilns used in cement production – rotary kilns and vertical shaft kilns. Rotary kilns are large tilted cylindrical tubes that rotate, heating the raw materials as they pass through the kiln. Vertical shaft kilns are upright cylindrical vessels where raw materials move downward through the kiln. Both kiln types reliably produce high-quality cement clinker.

Environmental Considerations with Kiln Operations

Operating cement kilns presents environmental challenges, including air emissions control and energy use. Strict regulations govern allowable emissions from cement kilns. Emissions are minimized through technologies like dust collection and exhaust gas treatment. Energy efficiency is also critical, with heat recovery systems helping reduce consumption.

Kiln Technology Company – The Rotary Kiln Manufacturer You Can Trust

If your processes rely on a rotary kiln, you need good rotary kiln manufacturers on your side to help with any problems that arise. Kiln Technology Company is one of the country’s foremost sources of kilns, spare parts, and repair/installation services.

When you need assistance with your kiln, contact us!