Biomass gasifier or LPG for a small furnace or dryer: which has lower emissions?

A biomass gasifier usually has far lower reported Scope 1 emissions than LPG, because the CO2 from burning biomass is biogenic and reported outside the scopes. Only its methane and nitrous oxide count, a small fraction of LPG's CO2. The claim holds only if the biomass is residue or sustainably sourced, and the gasifier's blower power still counts.

How each fuel is counted

• LPG: 2.98 kg CO2 per kg burnt (IPCC 2006 default), all fossil Scope 1, plus very small CH4 and N2O.
• Biomass through a gasifier: the CO2 from the producer gas flame is biogenic. The GHG Protocol asks you to report it separately, outside Scopes 1, 2 and 3.
• CH4 and N2O from biomass combustion are counted in Scope 1, using IPCC 2006 stationary combustion factors and a named GWP set.
• Electricity for the gasifier blower, feeder and gas cleaning is Scope 2; diesel for a backup DG is Scope 1.

Compare per unit of useful heat, not per kg

A gasifier system loses more energy between fuel and product than an LPG burner: char, tar and sensible heat in the gas. Work out the biomass needed for the same useful heat using the efficiency of each system, then apply the factors. A lower efficiency raises the biomass tonnage and the CH4 and N2O, but rarely enough to close the gap with LPG.

When the biomass claim weakens

• Wood cut from land that is not regrowing: buyers and assurers may question a zero fossil figure without evidence of sustainable sourcing.
• Biomass carried long distances by truck: transport diesel belongs in Scope 3 and grows with distance.
• A gasifier running poorly, with high tar and unburnt gas venting, which raises methane.
• A dryer where product quality needs clean heat and LPG is kept as backup; count the LPG you still buy.

What to keep as evidence

• Biomass purchase invoices with tonnage and type, such as rice husk, wood chips or briquettes.
• Supplier declarations on where the residue or wood came from.
• Moisture content tests, since wet biomass carries less energy per tonne.
• Any LPG still bought, and electricity bills for the gasifier connection.

Illustrative dryer using 20,000 kg LPG a year

• LPG CO2: 20,000 x 2.98 = 59,600 kg CO2; its CH4 and N2O add about 52 kg CO2e
• LPG energy: 20,000 kg x 47.3 GJ per t = 946 GJ; useful heat at 80% burner efficiency = 757 GJ
• Gasifier at an assumed 60% system efficiency: 757 / 0.60 = 1,261 GJ of biomass, about 81 t of wood at 15.6 GJ per t
• CH4: 1.261 TJ x 30 kg per TJ = 37.8 kg x 28 (AR5 GWP) = 1,060 kg CO2e
• N2O: 1.261 TJ x 4 kg per TJ = 5.0 kg x 265 (AR5 GWP) = 1,337 kg CO2e
• Gasifier Scope 1: about 2,400 kg CO2e, against about 59,650 kg CO2e for LPG; biogenic CO2 of about 141 t reported separately

System efficiencies are assumptions. Calorific values (LPG 47.3 GJ per t, wood 15.6 GJ per t), the wood CO2 factor (112 t per TJ) and CH4 and N2O factors are IPCC 2006 defaults; the wood factors for manufacturing combustion stand in for producer gas. Add Scope 2 for the gasifier's electricity.

What Senseible does here

Senseible calculates LPG CO2 at 2.98 kg per kg from your purchase invoices and keeps each invoice as the source, so a switch shows up month by month as LPG tonnage falling. Keep the biomass invoices, supplier declarations and the gasifier's electricity bills with the same record.

• Biomass or waste fuel in a boiler
• Morbi coal gasifier vs natural gas
• Biomass fuel supplier evidence
• LPG emission factor

Sources: 2006 IPCC Guidelines, Volume 2, Chapter 2, Tables 2.2 to 2.5 (stationary combustion CH4 and N2O factors), GHG Protocol Corporate Standard (biogenic CO2 reported outside the scopes), IPCC Fifth Assessment Report, 100-year GWP values (CH4 28, N2O 265)

Last reviewed 2026-10-18.