CBAM Cement Calculation: How to Compute Embedded Carbon for Clinker and Cement
CBAM cement calculation centres on two emission sources: the calcination of limestone (chemically unavoidable) and the combustion of kiln fuels. The clinker substitution rate — how much cement is made of clinker versus supplementary cementitious materials (SCMs) like fly ash, slag, or limestone — is the dominant lever in cement actuals. This page walks through the calculation.
CBAM Cement Calculation Formula
For cement and clinker under CBAM Annex I:
SEE_cement = (SEE_clinker × clinker_factor) + (SEE_grinding × electricity)
Where the clinker factor is the proportion of clinker in the finished cement (typically 0.65–0.95). The clinker calculation is the dominant component:
SEE_clinker = (Calcination_emissions + Fuel_emissions + IE_electricity) ÷ Clinker_output
Calcination Emissions — The Unavoidable Component
Calcination of limestone (CaCO3 → CaO + CO2) releases approximately 0.525 tCO2 per tonne of clinker. This is a chemical emission, not a fuel emission, and cannot be reduced by switching fuels or improving energy efficiency. It is the floor of cement embedded emissions and the reason cement is one of the hardest sectors to decarbonise.
The only ways to reduce calcination emissions are: (1) reduce the clinker fraction in cement by substituting SCMs, or (2) capture and store the CO2 from the kiln (CCS — not yet at commercial scale in most cement plants).
Fuel Emissions — The Dominant Variable
Kiln fuel emissions vary widely by fuel mix:
- Coal-fired kiln: 0.30–0.40 tCO2 per tonne of clinker
- Petcoke-fired kiln: 0.32–0.42 tCO2 per tonne of clinker
- Natural gas-fired kiln: 0.18–0.25 tCO2 per tonne of clinker
- Alternative fuels (waste-derived, biomass): 0.10–0.30 tCO2 per tonne of clinker depending on substitution rate and biogenic share
Total clinker actual emissions therefore range from approximately 0.65 tCO2/t (gas + alternative fuels, modern dry-process kiln) to 0.95 tCO2/t (coal, older wet-process kiln).
Clinker Substitution — The Cement Calculation Lever
For cement, the clinker substitution rate is what differentiates a CEM I (95–100% clinker) from a CEM II/III (lower clinker, higher SCM content). For the same output tonne of cement:
- CEM I (95% clinker): SEE ≈ 0.78 × clinker SEE
- CEM II (~80% clinker): SEE ≈ 0.66 × clinker SEE
- CEM III (~50% clinker, slag-rich): SEE ≈ 0.42 × clinker SEE
For non-EU producers shipping to the EU, switching from CEM I to CEM II/III where the application allows can deliver 30–50% reductions in CBAM-relevant embedded emissions without changing kiln operations.
Frequently Asked Questions
What CN codes does CBAM cement calculation cover?
CBAM Annex I covers cement under CN code 2523, including clinker, Portland cement, aluminous cement, and other hydraulic cements. The calculation in Annex III applies across these codes.
What is the unavoidable component of cement emissions?
Calcination of limestone releases approximately 0.525 tCO2 per tonne of clinker. This is chemical, not fuel-related, and cannot be reduced without CCS or clinker substitution.
How does fuel mix affect the CBAM cement calculation?
Fuel mix is the largest controllable variable. Switching from coal/petcoke to natural gas reduces fuel emissions per tonne of clinker by approximately 35–50%. Alternative fuels with biogenic content reduce them further.
Does the clinker substitution rate help with CBAM?
Yes — significantly. A CEM III with 50% clinker has approximately 42% of the embedded emissions of a 100% clinker product per tonne of cement. Switching to lower-clinker cements where the application permits is one of the highest-leverage CBAM interventions for cement producers.
Are co-processed waste fuels treated as zero emissions?
Only the biogenic share of co-processed alternative fuels is treated as zero direct CO2 emissions per Annex III. The fossil share is counted at standard emission factors. Producers must document the biogenic fraction to claim the deduction.
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