Sulphite Lyes (Black Liquor)
Reviewed by Afonso Firmo, Co-Founder & Director · Updated 7 July 2026
Sulphite lyes (black liquor) has an emission factor of 7.19 kg CO₂-e per tonne combusted (NGA Factors 2025) — the lowest solid fuel factor. Calculate here.
Emission Factor Value
7.19 kg CO₂-e/tonne
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Estimated emissions
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Fuel combustion emissions are reported under Scope 1. Calculated as quantity × 7.19 kg CO₂-e per tonne (12.4 GJ/t × 0.58 kg CO₂-e/GJ CH₄ + N₂O, NGA Factors 2025 Table 4). Biogenic CO₂ is zero-rated and reported separately.
Official Source & Citation
This emission factor is sourced from the Australian National Greenhouse Accounts Factors 2025 , Table 4 — Solid fuels and certain coal-based products, published by the Department of Climate Change, Energy, the Environment and Water (DCCEEW).
Citation: DCCEEW (2025). Australian National Greenhouse Accounts Factors 2025. Commonwealth of Australia. Available at: https://www.dcceew.gov.au/climate-change/publications/national-greenhouse-accounts-factors-2025
Notes
Derived from NGA Factors 2025 Table 4: energy content 12.4 GJ/t × combined Scope 1 emission factor 0.58 kg CO₂-e/GJ ≈ 7.19 kg CO₂-e per tonne. Sulphite lyes (black liquor) is the spent pulping liquor burned in recovery boilers at pulp and paper mills. It is a biomass fuel: the CO₂ emission factor is zero (biogenic CO₂ is reported separately) and the 0.58 kg CO₂-e/GJ covers methane and nitrous oxide only — the lowest combined factor of any solid fuel in Table 4. No Scope 3 upstream factor is estimated. 1 tonne combusted = 7.19 kg CO₂-e.
Calculation Example
If your pulp mill's recovery boiler combusted 10,000 tonnes of sulphite lyes during the year:
| Working | Result |
|---|---|
| 10,000 t × 7.19 kg CO₂-e/t = 71,900 kg CO₂-e | 71.9 tonnes CO₂-e (Scope 1) |
Every kraft and sulphite pulp mill runs on a fuel it makes itself: black liquor, the spent pulping liquor burned in recovery boilers to raise steam and recover chemicals. In the NGA tables it appears as sulphite lyes — and it carries the lowest emission factor of any solid fuel, a rounding error next to the coal it displaces in a Scope 1 inventory.
Low is not zero, though, and NGER still wants the methane and nitrous oxide counted. Here is the 2025–26 factor with worked examples you can verify in a Scope 1 and 2 calculator.
Quick Verdict
Sulphite lyes (black liquor) carries a combined Scope 1 emission factor of 0.58 kg CO₂-e per gigajoule under the NGA Factors 2025 — the lowest of any solid fuel in Table 4. At an energy content of 12.4 GJ per tonne, each tonne combusted produces about 7.19 kg of CO₂-equivalent. As a biomass fuel, its CO₂ is biogenic and zero-rated; the reportable factor covers methane and nitrous oxide only. The pulp mill operating the recovery boiler reports these emissions under Scope 1. Values come from Table 4, published by DCCEEW for the 2025–26 reporting year.
How to Calculate Sulphite Lyes Emissions
Emissions (t CO₂-e) = Quantity (t) × Energy content (12.4 GJ/t) × Emission factor (0.58 kg CO₂-e/GJ) ÷ 1,000
Worked Example 1: Large recovery boiler burning 50,000 tonnes
An integrated pulp mill fires 50,000 tonnes of concentrated black liquor over the year. Using the per-tonne factor:
50,000 t × 7.19 kg CO₂-e/t = 359,500 kg CO₂-e
359.5 tonnes CO₂-e (Scope 1)
Worked Example 2: Smaller mill burning 10,000 tonnes
A regional mill’s recovery boiler consumes 10,000 tonnes of liquor solids.
10,000 t × 7.19 kg CO₂-e/t = 71,900 kg CO₂-e
71.9 tonnes CO₂-e (Scope 1)
Worked Example 3: Energy-based records of 25,000 GJ
A mill’s energy accounting attributes 25,000 GJ to black liquor firing.
25,000 GJ × 0.58 kg CO₂-e/GJ = 14,500 kg CO₂-e
14.5 tonnes CO₂-e (Scope 1)
How Sulphite Lyes Compare to Other Solid Fuels
| Fuel | Energy content (GJ/t) | Scope 1 EF (kg CO₂-e/GJ) | kg CO₂-e per tonne |
|---|---|---|---|
| Sulphite lyes (black liquor) | 12.4 | 0.58 | 7.19 |
| Dry wood | 16.2 | 1.2 | 19.44 |
| Green and air-dried wood | 10.4 | 1.2 | 12.48 |
| Bagasse | 9.6 | 1.4 | 13.44 |
| Charcoal | 31.1 | 6.3 | 195.93 |
| Bituminous coal | 27 | 90.24 | 2,436.48 |
NGER and AASB S2 Reporting
Recovery boiler combustion is reportable under NGER: mills above the thresholds report the CH₄ and N₂O to the Clean Energy Regulator using this Table 4 factor, with biogenic CO₂ disclosed separately outside the total. The same figures carry into your AASB S2 climate disclosure, where clean segregation of biomass and fossil fuel lines keeps the audit straightforward.
Related Emission Factors
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Disclaimer
This page is provided for general information, not professional or compliance advice. The factor shown is reproduced from the official publication cited above, and while we work to keep it current, government factors change — the publication is always the authoritative source.
- Before using this value in any formal reporting — including under the National Greenhouse and Energy Reporting Act 2007 — confirm it against the current official publication and the methods specified by the Clean Energy Regulator.
- NetNada is independent of the Australian Government, DCCEEW, and the Clean Energy Regulator. Government data is Crown copyright, Commonwealth of Australia.