Technology Roadmap Low-Carbon Transition in the Cement Industry

2. Overview of cement manufacturing
Figure 1: Cement manufacturing
Note: A dry-process kiln is shown with a precalciner and multistage cyclone preheater, which is considered state-of-the-art technology. 
The modelling results used for the analysis in this roadmap include steps 3-10 of the above figure.
Source: IEA and WBCSD (2009), 
Cement Technology Roadmap 2009: Carbon Emissions Reductions up to 2050
, www.iea.org/publications/
freepublications/publication/Cement.pdf. 
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Prehomogenization
and raw meal grinding
Crushing
Preheating
Precalcining
Clinker production
in the rotary kiln
Cooling and storing
Quarries
Blending
Cement grinding
Storing in
the cement silo
Quarrying
raw materials
Technology modeling scope
KEY MESSAGE: Cement manufacturing involves multiple steps.

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2. Overview of cement manufacturing
1. Quarrying raw materials 
Naturally occurring calcareous deposits, such as 
limestone, marl or chalk, provide calcium carbonate, 
which is a key ingredient for cement. They are 
extracted by heavy duty machines from quarries, 
which are often located close to the cement 
plant. Small amounts of other materials, such as 
iron ore, bauxite, shale, clay or sand, may also be 
excavated from deposits to provide the extra iron 
oxide, alumina and silica needed in the chemical 
composition of the raw mix to meet the process and 
product performance requirements. 
2. Crushing
The quarried materials are crushed, typically to less 
than 10 centimetres in size, and are transported to 
the cement plant.
3. Preparing raw meal
Raw materials are mixed to achieve the required 
chemical composition in a process called 
“prehomogenisation”. The crushed material is then 
milled to produce a fine powder called “raw meal”. 
The chemistry of the raw materials and raw meal is 
monitored and controlled, to ensure consistent and 
high quality of cement.
4. Preheating and co‑processing
A preheater is a series of vertical cyclones through 
which the raw meal is passed. During this process, 
the raw meal comes into contact with swirling 
hot kiln exhaust gases moving in the opposite 
direction. Thermal energy is recovered from the 
hot flue gases in these cyclones, and the raw meal 
is preheated before it enters the kiln. The chemical 
reactions therefore occur quickly and efficiently. 
Depending on the raw material moisture content, 
a kiln may have up to six stages of cyclones with 
increasing heat recovery at each stage. The raw 
meal temperature is raised to over 900°C.
Cement production can co-process wastes and 
by-products generated from other industries and 
municipalities, as materials for the raw mix or as 
fuels for pyro-processing. Wastes and by-products 
vary widely in nature and moisture composition. 
They may need sorting, shredding and drying 
before feeding into the cement kiln.
5. Precalcining
Calcination is the decomposition of limestone 
into lime. It takes place in a “precalciner” in most 
processes. This is a combustion chamber at the 
bottom of the preheater above the kiln, and is