# Does a flue gas desulphurisation unit add CO2 at a coal power plant?

Canonical: https://senseible.earth/answers/fgd-limestone-co2-power-plant

Yes, a little. Wet limestone scrubbers release the carbon in the limestone: 0.44 tonnes of CO2 per tonne of limestone, or about 0.69 tonnes per tonne of SO2 removed. It is small next to the coal, but it is a real process emission and should be reported, along with the scrubber's power use.

## The chemistry

Limestone (calcium carbonate) reacts with SO2 and oxygen to make gypsum and releases CO2. Each 100 kg of carbonate gives 44 kg of CO2.

## What to report

- Process CO2: tonnes of limestone used x purity x 0.44.
- Electricity for fans, pumps and mills inside the unit, already in auxiliary consumption.
- Gypsum sold to cement or board makers carries no share of the CO2.

## Scale

For typical Indian coal with low sulphur, the scrubber adds well under 2 percent to the plant's CO2, but leaving it out understates Scope 1.

## What Senseible does here

Senseible reads fuel, electricity and freight invoices into a dated, fingerprinted record per site, so each figure you send a buyer can be traced back to the documents behind it.

- [Limestone calcination CO2](https://senseible.earth/answers/process-co2-from-limestone-calcination)
- [Coal power CO2 per kWh](https://senseible.earth/answers/coal-power-plant-co2-per-kwh-heat-rate)
- [Fly ash allocation](https://senseible.earth/answers/fly-ash-from-power-plant-carbon-allocation)

Sources: [IPCC 2006 Guidelines, Volume 3 Industrial Processes](https://www.ipcc-nggip.iges.or.jp/public/2006gl/), [IPCC 2006 Guidelines, Volume 2 Energy (fuel defaults)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-10-21.