How do I calculate emissions per tonne for a heat treatment shop?

Question

Senseible · Accepted Answer

Add a month's furnace electricity, LPG or PNG and any methanol carrier gas, convert each to CO2 with its factor, and divide by the tonnes treated that month. Electricity at 0.710 kg CO2 per kWh and LPG at 2.98 kg CO2 per kg usually make up nearly all of it. Electricity for furnaces, washers, tempering ovens and compressors: kWh x 0.710 kg CO2. LPG or PNG burnt in radiant tubes or endothermic gas generators: kg x 2.98 for LPG, scm x 2.05 for PNG. Methanol cracked as carrier gas: its carbon leaves as CO2 when the gas burns at the furnace door, 44/32 = 1.375 kg CO2 per kg methanol. DG diesel during power cuts: litres x 2.68. Purchased nitrogen and quench oil are Scope 3 purchases, not Scope 1. Add them only for a cradle to gate product figure. Carburising runs long cycles at high temperature; annealing and tempering use far less energy per tonne. If one figure covers everything, a buyer of tempered parts pays for someone else's carburising. Meter each furnace line if you can. If not, share energy by furnace hours times rated kW, which is a physical basis that ISO 14067 accepts, and state it. A job shop that bills per kg can quote the same figure per kg: divide the per tonne result by 1,000. The principal records it in its Scope 3 Category 1 as a purchased service. Give the month or year it covers and the process, for example 'gas carburising, case depth 0.8 to 1.0 mm'. Dividing by tonnes invoiced instead of tonnes through the furnace, which hides rework. Counting the LPG cylinder purchases of the month when stock has changed. Use consumption. Leaving out the endo gas generator because it is not a furnace.

How do I calculate emissions per tonne for a heat treatment shop?

What goes into the figure

Splitting between processes

Quoting to a principal

Common mistakes

Worked example: one month at a job shop

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