How do I calculate the carbon footprint per tonne of container glass, including soda ash and limestone in the batch?

Add three parts and divide by tonnes of good glass: CO2 released from carbonates in the batch (soda ash, limestone, dolomite), CO2 from the fuel burnt in the furnace and lehrs, and CO2 from the electricity used. More cullet in the batch lowers both the carbonate CO2 and the melting fuel.

Batch carbonate CO2

Each carbonate gives off CO2 when it melts into glass. Use the stoichiometric factors in the IPCC 2006 Guidelines, Volume 3, Chapter 2: soda ash (Na2CO3) 0.41492 t CO2 per tonne, limestone (CaCO3) 0.43971, dolomite (CaMg(CO3)2) 0.47732, all per tonne of pure carbonate.

Multiply the tonnes of each carbonate charged by its purity from the supplier's analysis, then by its factor. Use tonnes charged to the furnace over the period, from batch house records, not tonnes bought. This is Scope 1 process CO2.

Furnace fuel and electricity

• Fuel: litres, kg or scm of natural gas, furnace oil or LPG burnt in the furnace, feeders, forehearths and annealing lehrs, times the fuel factor. Scope 1.
• Electricity: kWh from the discom bill for compressors, IS machines, batch house and any electric boosting, times the grid factor (0.710 kg CO2 per kWh, CEA CO2 Baseline Database version 21.0). Scope 2.
• Keep process CO2 and fuel CO2 as separate lines. A fuel switch cuts only the fuel line.

What cullet does to the number

Cullet is glass already formed, so it carries no carbonate. Replacing half the raw batch with cullet roughly halves the batch carbonate CO2. Cullet also melts with less energy than raw batch, so furnace fuel per tonne falls as well.

State the cullet ratio you used and whether the cullet is your own rejects or bought from outside. Your own rejects go round again, which is why the divisor must be good glass packed, not glass melted.

What a buyer's product footprint adds

The steps above give your factory's own emissions per tonne. A cradle-to-gate product footprint under ISO 14067 also includes the emissions of making the raw materials, mainly soda ash, plus inbound transport and packaging. Soda ash is energy intensive to produce, so ask your soda ash supplier for its footprint per tonne rather than leaving it out.

Worked example: one month at a container furnace (illustrative)

• Glass melted: 3,000 t at 50% cullet; good glass packed: 2,700 t
• Soda ash: 330 t x 0.41492 = 136.92 t CO2
• Limestone: 200 t x 0.43971 = 87.94 t CO2
• Dolomite: 150 t x 0.47732 = 71.60 t CO2
• Batch carbonate total: 296.46 t CO2
• PNG: 390,000 scm x 2.05 kg CO2 per scm = 799.50 t CO2
• Electricity: 600,000 kWh x 0.710 kg CO2 per kWh = 426.00 t CO2
• Total: 296.46 + 799.50 + 426.00 = 1,521.96 t CO2
• Per tonne of good glass: 1,521.96 / 2,700 = 0.56 t CO2

Batch quantities, gas and power use are assumptions for the arithmetic, with carbonates taken as pure. Use your own batch sheets and assays. Raw material production upstream is not included.

What Senseible does here

Senseible reads your PNG, furnace oil, LPG and coal invoices (PNG 2.05 kg CO2 per scm, furnace oil 2.97 kg per litre) and your electricity bills at 0.710 kg CO2 per kWh, with the factor and source on each line. Work out the batch carbonate CO2 from your batch records and assays with the IPCC factors above, and keep it as its own line.

• Process CO2 from limestone calcination
• Financing a glass furnace in Firozabad
• How scrap rate affects carbon per unit
• PNG emission factor

Sources: 2006 IPCC Guidelines, Volume 3, Chapter 2 Mineral Industry Emissions (Table 2.1 and section 2.4 Glass production), 2006 IPCC Guidelines, Volume 2 Energy, CEA CO2 Baseline Database

Last reviewed 2026-10-17.