How Concrete Is Created in An Industrial Kiln

Concrete is one of the most popular, common, and affordable building materials in the world – and it’s thanks to industrial kilns.  Modern operations can create concrete in huge quantities easily, and concrete can even be recycled, due to well-understood processes for creating concrete mixes within a large kiln.

Here’s how it happens.

How An Industrial Kiln Processes Cement

1 – Preheating

Modern processes for creating concrete begin by pre-heating the raw materials, called raw meal.  The meal is made primarily of clay and limestone, but one of the key elements of cement manufacture is that the limestone must be calcinated – removing CO2 within the mix.

So to begin, the meal is heated to a temperature just a bit below that of the kiln itself – around 800°C.  This is typically done in a cyclone preheater, where the meal is fed into a vertical cylinder with high airflow to heat the particulate clinker evenly.

2 – Precalcination

After the raw meal is heated, it goes into a chamber called a precalcinator.  This extends the heating process and begins releasing CO2.  One common method is to mix the meal with pulverized coal, heating it until the coal combusts, sending that energy directly into the raw materials.   This prepares the meal for its time in the kiln.

3 – Into the industrial kiln

After precalcination, the meal has already lost much of its CO2 content, so its time in the kiln can be relatively short.  Its temperature is raised even higher – up to 1300-1450°C – which burns off the rest of the CO2 and completes the calcination process.  This is a significant improvement over older methods of calcinating concrete, which required long stays in gigantic kilns which could be 200m in length or more.

Once the meal reaches the bottom of the kiln, chemical processes have converted it into tricalcium silicate – the main ingredient in common concrete.  This is also called clinker.

4 – Cooling

Finally, the clinker falls into a chamber below the kiln to be cooled.  This is generally accomplished with airpower for low energy costs.  Once cool, the clinker is ready to be mixed with other additives and packaged as ready-to-mix concrete.

How Rotary Kilns Transform Raw Materials

Rotary kilns are tilted cylinders that rotate to heat up and convert raw materials into clinker for making concrete. The kiln is inclined at a slight slope and rotates 1-3 times per minute. As material moves through the kiln, it reaches temperatures up to 1500°C.

Achieving the Right Reactions Through Precise Temperature Control

The kiln uses various temperature zones to drive the chemical reactions needed to produce clinker. Temperatures must reach at least 1400°C to initiate clinker formation, but not exceed 1500°C. Operators carefully control the kiln’s speed and heating elements to maintain optimal temperatures.

The Critical Role of Quality Control

Quality control is essential throughout the kiln process. Raw materials are continually tested and monitored. The kiln atmosphere and interior temperatures are also regulated. Finally, the produced clinker is analyzed to ensure it meets specifications before being used in concrete production. Strict quality control results in consistent, high-grade clinker.

Proper kiln operation transforms raw materials into high-quality clinker, the essential ingredient that gives concrete its binding properties. Careful temperature control and quality assurance are critical to create clinker that will produce strong, durable concrete.

Kiln Technology Company is one of the country’s leading providers of industrial kilns, installation, repairs, and associated parts and supplies.  Contact us for Kiln component reconditioning and kiln spares.