In 2023, the cement industry generated around 2.27 billion tonnes of CO2 equivalent (CO2e) emissions, representing approximately 3.71% of the global 61.15 billion emissions (Source: Climate TRACE).

Cement production involves three key stages: First, limestone and other raw materials are quarried and blended. Next, this mixture is processed and heated to high temperatures to create clinker, which may be partially replaced with calcined clay. Finally, the clinker is ground with gypsum and additional additives to produce the final cement product. This final grinding can happen in so-called integrated plants where the clinker is also produced or in independent grinding plants.

Reminder: Transport emissions and emissions from raw material mining/quarrying are excluded from the CBAM scope.

What are the main CO2 emission sources in the cement industry?

Most emissions during cement production occur during clinker production in the kiln system, both from fuel consumption and, more significantly, from the calcination of limestone, which releases CO₂ during thermal decomposition of calcium carbonate at about 900°C (Calcium carbonate [CaCO₃] → Calcium Oxide [CaO] + Carbon Dioxide [CO₂]). The proportion in the raw materials of carbonates other than CaCO3 is generally very small.

Calcined clay is covered by the EU CBAM. This material can be used as a supplementary cementitious material (SCM) to partially replace clinker.

Calcined clay production involves grinding kaolinite, then heating it to 600-800°C in a calciner, causing dehydroxylation that releases water vapor. After cooling, the material undergoes final grinding. The process requires thermal energy and electricity for grinding and material handling, generating emissions primarily from fuel combustion and power consumption.

Note: Other clays falling under CN code 2507 00 80 which are not calcined are assigned embedded emissions of zero.

Cement clinker is covered by the EU CBAM. The clinker production process (pyro-processing) consists of several steps.

Raw materials such as limestone, clay, bauxite, and iron ore, are crushed, mixed, and milled into "raw meal" under chemical control. The powdered meal passes through cyclone preheaters where hot exhaust gases coming from the kiln raise its temperature before entering a precalciner where limestone decomposition begins, converting calcium carbonate (CaCO3) to calcium oxide (CaO), also known as quicklime.

In the rotating kiln, fuels (such as coal, petroleum coke, gas, oil and alternative fuels) heat the material to around 1,450°C, where calcium oxide reacts with silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3) to form the silicates, aluminates and ferrites that constitute the clinker. Main fossil fuels used in Europe are coal and petroleum coke. The clinker is then rapidly cooled. The actual thermal energy demand for different kiln systems and sizes is around 0.003 - 0.0065 TJ/tonne of clinker.

During this process, cement kiln dust (CKD), containing partially calcined material and CO2, is captured from kiln exhaust gases.

Grey and white clinkers may be produced depending on temperature and raw material purity, though the EU CBAM makes no distinction between them.

Note: The exact configuration and sequence of these production steps may vary depending on the specific installation. Moreover, some installations may use either wet, semi-wet, dry, or semi-dry processes. In wet kilns, raw materials (often with high moisture content) are ground with water to form a slurry, while in dry kilns, materials are ground into powder. The difference is relevant in the context of carbon emissions due to the higher energy efficiency of the dry process, which might correlate with lower-carbon cement.

A variation on the clinker production process may be with permanent geological storage, i.e., carbon capture and sequestration (CCS).

Where do emissions come from?

This production process generates CO2 emissions from limestone decomposition and the combustion of both kiln and non-kiln fuels.

Cement production consists of grinding clinker with gypsum and other constituents such as limestone, granulated blast furnace slag (from steel production), natural or artificial pozzolanas, or calcined clay. Depending on the specific mix, this produces different types: Portland cement, blended cement (containing Portland cement and other hydraulic constituents), or other hydraulic cements. Large cement plants produce around 4,000 tonnes of cement per day.

Grinding occurs either in integrated facilities (where clinker is produced) or in separate grinding plants. The process generates emissions from fuel used for material drying and electricity consumption.

The embedded emissions of the cement clinker and calcined clay (if used in the process) must be added.

An integrated cement plant is a facility that performs both clinker production and cement grinding.

Aluminous cement is produced similarly to Portland cement, but uses bauxite (aluminum-rich) and limestone as raw materials instead of the typical limestone-clay mix.

Unlike Portland cement production, which requires separate clinker formation and then grinding with gypsum, aluminous cement is produced in a single fusion process where the molten material is cooled and ground directly into cement. As such, it is regarded as a good with no relevant precursors (simple good) under the EU CBAM.