Is biomass really carbon neutral? The honest answer

Biomass fuel gets called "carbon neutral" constantly. The phrase is partly true and partly misleading. Here is which is which.

What carbon neutral actually means here

A tree absorbs CO2 from the air as it grows and releases it when burned. The same carbon cycles through a loop roughly as long as the tree's life (about 25–35 years for a rubber tree).

Coal releases carbon too, but carbon locked underground for millions of years. Burning it adds new carbon to the system rather than circulating what is already there.

The difference is the length of the cycle, not the CO2 released per burn.

At the stack, wood actually emits more CO2 per unit of heat than coal (IPCC 2006 defaults: 112,000 for wood against 94,600 kg CO2/TJ for bituminous coal). What differs is the cycle: regrowth reabsorbs the carbon.

Two conditions that have to hold

Carbon neutrality is not automatic. It depends on two things.

Replanting. Cut without replanting and there is nothing left to absorb what was released.

Counting the energy spent along the chain. Transport, chipping, and above all drying for pellets all consume energy. The further fuel travels, the more of the carbon advantage it gives back.

That second condition is why distance from feedstock matters, and not only for freight cost. Fuel shipped across a continent delivers less carbon benefit than fuel produced two hours away.

Advantages that are measurable

Low sulphur. Wood contains tens of times less sulphur than coal, cutting SO2 and acid rain.

It uses material that would be burned anyway. Roots, branches and leaves left after rubber replanting are otherwise burned in the open, which emits far more particulate than a controlled furnace.

Money stays regional. Income goes to growers and hauliers nearby instead of leaving with an import bill.

Limits worth accepting

Lower calorific value per ton. Wood chips run about 2,200 Kcal/Kg against roughly 6,300 for imported coal (DEDE figure). You need nearly three times the tonnage for the same heat.

More storage. Follows directly from the above.

Potassium-rich ash. Lower fusion temperature, so furnace temperature has to be controlled to avoid slagging.

Trace heavy metals. Wood contains small amounts of arsenic, cadmium and mercury, which is why the ENplus pellet standard caps them (arsenic ≤1, cadmium ≤0.5, mercury ≤0.1 mg/kg).

Supply tied to agriculture. Volume and moisture shift with the season and the replanting cycle. Stock planning matters more than with fossil fuel.

Where it pays and where it does not

It pays when the plant sits near the feedstock, has yard space, and runs a boiler rated for high-moisture solid fuel.

It does not yet when haul distance is long, when space forces pellets for the entire load while coal stays cheap, or when the boiler was built specifically for pulverised coal.

Whether it pays for you is a calculation from your furnace spec and your actual distance, not from a general principle.

See the method and conversion conditions on the replacing coal with biomass page, or send us your spec at +66 92 392 2292.

Sources

• US EPA, AP-42 §1.6 Wood Residue Combustion in Boilers
• ENplus, ST 1001 Requirements for companies
• ERIA, Chapter 2 rubberwood supply
• IPCC, 2006 Guidelines Vol.2 Ch.2 Stationary Combustion
• กรมพัฒนาพลังงานทดแทนและอนุรักษ์พลังงาน, รายงานสถานการณ์พลังงาน ม.ค.–มิ.ย. 2568