Technology Roadmap Low-Carbon Transition in the Cement Industry

partly in the kiln. Here, the chemical decomposition 
of limestone into lime and CO
2
typically emits 
60-70% of the total CO
2
emissions. Fuel combustion 
generates the rest of the carbon emissions. 
Approximately 65% of all fuel is burnt in this step of 
the process, in plants with precalciner technology.
6. Producing clinker in the rotary kiln 
The precalcined meal then enters the kiln. Fuel is 
fired directly into the kiln to reach temperatures 
of up to 1 450°C. As the kiln rotates (about three 
to five times per minute), the material slides and 
falls through progressively hotter zones towards 
the flame. The intense heat causes chemical and 
physical reactions that partially melt the meal into 
clinker. The reactions in the kiln include completion 
of the calcination of limestone that has not taken 
place in the precalciner and emission of CO
2
from 
other CO
2
combined minerals. The CO
2
released 
from the raw materials during production is referred 
to as “process CO
2
emissions”.
7. Cooling and storing
Hot clinker from the kiln is cooled from over 
1 000°C to 100°C rapidly on a grate cooler, which 
blows incoming combustion air onto the clinker. 
The air blowers use electricity and heated blown air 
circulation to improve thermal efficiency. A typical 
cement plant will have clinker storage between 
clinker production and the cement grinding 
process. Clinker may be loaded onto transportation, 
and can then be traded or further processed into 
cement.
8. Blending
Clinker is mixed with other mineral components 
to make cement. All cement types contain around 
4-5% gypsum to control the setting time of the 
cement. Slag, fly ash, limestone or other materials 
can be interground or blended to replace part of the 
clinker. This produces blended cement.
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9. Grinding
The cooled clinker and gypsum mixture is ground 
into a grey powder, known as Portland cement 
(PC), or ground with other mineral components to 
make blended cement. Ball mills have traditionally 
been used for grinding, although roller presses and 
vertical mills are often used in modern plants due to 
their greater energy efficiency.
7. The described process steps reflect the cement production 
process that is most commonly adopted. The order of blending 
and grinding process steps could be reversed.

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