How do I calculate process CO2 from limestone or dolomite calcination?
Multiply the tonnes of each carbonate heated by its purity and by its IPCC emission factor: 0.43971 t CO2 per tonne of calcium carbonate, 0.47732 for dolomite, 0.52197 for magnesium carbonate. Then multiply by the share actually calcined. This is Scope 1 process CO2, counted separately from the fuel burnt in the kiln.
The formula
Process CO2 (t) = carbonate consumed (t) x carbonate fraction x emission factor (t CO2 per t carbonate) x fraction calcined.
The factors in Table 2.1 of the IPCC 2006 Guidelines, Volume 3, Chapter 2, are stoichiometric: they come from molecular weights, so they hold anywhere. CaCO3 0.43971, MgCO3 0.52197, CaMg(CO3)2 0.47732, Na2CO3 0.41492, all in t CO2 per t of pure carbonate.
Where each input comes from
- Carbonate consumed: purchase invoices adjusted for opening and closing stock, or weighbridge records of what entered the kiln.
- Carbonate fraction: the supplier's chemical analysis or your own lab assay, as CaCO3 and MgCO3 percent. Do not assume 100 percent; Indian limestone grades vary widely.
- Fraction calcined: 1.0 unless you can show unburnt carbonate in the product or dust. If you lose kiln dust that is only partly calcined, its CO2 is lower; IPCC gives a correction for this.
- Output check: you can also work back from product. Each tonne of CaO formed releases 44.01 / 56.08, about 0.785 t CO2.
Which uses count and which do not
- Count: lime burning, clinker making, glass batch (limestone, dolomite, soda ash), limestone or dolomite flux in a blast furnace or steel furnace, carbonates in ceramic clay that are fired, and limestone used to scrub sulphur from flue gas.
- Do not count: limestone used as a filler or aggregate that is never heated, or CaO bought in as lime, whose CO2 was released at the lime maker.
- Do not double count: if a stack monitor already measures total CO2, do not add the calculated process CO2 on top.
How to report it
Report process CO2 as its own Scope 1 line, next to combustion CO2 from coal, petcoke or gas in the same kiln. CBAM monitoring for cement treats them as separate source streams, and a fuel switch cuts only the combustion part.
Worked example: a lime kiln, one month
- Limestone fed: 1,000 t, assay 92% CaCO3 and 3% MgCO3
- CaCO3: 1,000 x 0.92 x 0.43971 = 404.53 t CO2
- MgCO3: 1,000 x 0.03 x 0.52197 = 15.66 t CO2
- Total at full calcination: 420.19 t CO2
- With 98% calcined: 420.19 x 0.98 = 411.79 t CO2, Scope 1 process emissions
The coal or petcoke burnt in the kiln is added separately from fuel invoices. The assay and calcination fraction are illustrative; use your own lab results.
What Senseible does here
Senseible reads fuel invoices, so the coal, gas or oil burnt in the kiln is calculated from them. It does not calculate the carbonate share: process emissions are calculated only when you supply the measured data, such as tonnes fed and assay.
Sources: IPCC 2006 Guidelines, Volume 3, Chapter 2 Mineral Industry Emissions, Table 2.1, GHG Protocol Corporate Standard
Last reviewed 2026-10-16.