When biomass in the form of wood pellets is burned in coal plants, it produces environmental benefits within about twenty years when compared to electricity produced using regular fossil fuels. If the pellets are made of wood residue or from trees in thinning forests, climate benefits can be achieved within six years. The sort of wood used is very important, according to a recent study by the University of Utrecht, which was published in the CB Bioenergy journal.
Several European countries, including the Netherlands, import wood pellets from the south east of the United States to burn in power plants to generate electricity. Wood pellets are made of compressed wood grains and are about three centimetres in size. They are usually made of timber that is too small to handle with lumber from thinned forests, or so-called wood residue - wood that remains after felling or in sawmills after processing. Often the use of larger logs for pellet production is economically unviable as these strains of timber deliver more for use in construction.
Saving CO2 emissions
If the CO2 that is released during the combustion of wood pellets is compared with the CO2 generated from trees throughout their lifespan, there is a CO2 saving of around 70% when compared to fossil fuels. Approximately 30% of the emissions that exist are due to the production and the transport of the pellets. However, there are more factors to consider. For example, wood that is not processed into pellets can rot or be processed into paper, and after some time can also release greenhouse gases. Therefore, it is important to see how long it takes for reductions in CO2 emissions from the burning of wood pellets for power, and thus what the climate benefits are compared to an alternative future for timber.
Energy scientists from Utrecht University, Radboud University and Oak Ridge National Laboratory in the United States contend that electricity from wood pellets leads to climate benefits within zero to 21 years. This means that the burning of wood pellets leads to less CO2 emissions in in 21 years than leading alternative destinations for timber in which the electricity is derived from fossil fuels. When residues or thinned wood are used to make the pellets, climate benefits can be achieved within zero to six years.
Cut from the right stuff
"In particular, the use of wood residues and thinned wood leads to rapid climate benefits, faster than found in previous studies," says Floor van der Hilst, Energy scientist at Utrecht University. "Provided that the pellets are pressed and cut from the right material, the use of wood pellets to replace coal in coal-fired plants quickly leads to CO2 emission savings, and therefore to climate benefits."
Hanssen, S. V., Duden, A. S., Junginger, M., Dale, V. H. and van der Hilst, F. (2017), Wood pellets, what else? Greenhouse gas parity times of European electricity from wood pellets produced in the south-eastern United States using different softwood feedstocks. GCB Bioenergy. doi:10.1111/gcbb.12426