# How do I calculate process CO2 from limestone or dolomite calcination?

Canonical: https://senseible.earth/answers/process-co2-from-limestone-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.

- [CO2 per tonne of clinker](https://senseible.earth/answers/co2-per-tonne-of-clinker-calculation)
- [Cement carbon accounting](https://senseible.earth/industries/cement)
- [Ceramics carbon accounting](https://senseible.earth/industries/ceramics)

Sources: [IPCC 2006 Guidelines, Volume 3, Chapter 2 Mineral Industry Emissions, Table 2.1](https://www.ipcc-nggip.iges.or.jp/public/2006gl/), [GHG Protocol Corporate Standard](https://ghgprotocol.org/corporate-standard)

Last reviewed 2026-10-16.