What is a biomass wood pellet?

How energy dense sustainable biomass wood pellets can help us generate the renewable electricity we need to reach net zero. The 4th post in our series ‘Powering to net zero’.

Drax
Drax
Aug 20 · 3 min read

Since humans first lit a log fire, we’ve been using biomass to generate energy.

But nowadays we can use biomass for heating or to generate renewable bioenergy at a much greater scale than ever before. How? By compressing organic materials such as wood, sawdust and by-products from the forestry industry into pellets.

However, by compressing organic matter like wood, forest residues and sawdust into energy-dense pellets, the resulting biomass can be used for heating or renewable bioenergy generation at a much greater scale.

Why are pellets so powerful?

Biomass wood pellets have a much greater energy density than biomass in its natural form. This means they can store more energy than an equivalent amount of the raw biomass of which they’re made.

In its natural state, wood (and sawdust and wood chips) is not very energy dense. In fact, it’s much less dense than other materials commonly used as fuels, including uranium, diesel or coal.

But when we condense something like sawdust into a tiny pellet, the biomass we’re left with has much greater energy density than the forestry residues from which it’s made. Add to that the fact that biomass wood pellets are very low in moisture, then you have a fuel that experts call a ‘high combustion efficiency’ — which is significant when it comes to generating power.

Even better, biomass wood pellets can help us power towards net zero carbon emissions. That’s because provided the forests biomass is sourced from are sustainably managed, and that the trees naturally regenerate or are replanted and regrown within a human timeframe, the biomass pellets sourced from them are classified as renewable.

How do we make biomass wood pellets?

Biomass pelletisation plants gather together low-value wood that is not suitable for other industries — like construction or furniture. This could be anything from the materials left over from timber that has been processed in sawmills, misshaped branches or even sawdust itself.

At the pelletisation plant, this wood is first turned into small chips. They are screened to ensure consistent quality and then heated until the residue contains less than 12% moisture. After that, it is reduced to a fine powder, and subjected to intense pressure to create energy-dense biomass wood pellets.

How are biomass wood pellets used to generate power?

Biomass wood pellets are used to generate electricity in much the same way as coal. This means that existing coal-fired power stations can be upgraded and given a new life generating renewable power.

The pellets are transported by huge conveyors from giant storage facilities to pulverising mills. There, they are transformed into a fine powder, which is then blown into the power station’s boiler. The steam this process produces drives the turbines which power the generators and produce electricity.

Biomass pellets — the facts

  • Biomass pellets generate much less carbon than coal.
  • Wood pellets are almost four times more energy dense than fresh wood or wood chips — with an energy density of 11 gigajoules/m3, compared to 3 gigajoules/m3.
  • Biomass pellets can achieve up to an 85% combustion efficiency.

Drax

Short stories from Drax, enabling a zero carbon, lower cost…