Biomass accounts for 10% of global primary energy supply (56 EJ of in 2012) and provides three times more energy than all other renewable energy sources, combined. Biomass is becoming more important as a power station fuel to reduce CO2 emissions from coal-fired power stations.
There is potential to convert much of the world’s coal-fired fleet to cofiring biomass. Coal power exceeds 1800 GWe, of which half is in China, and 36 GWe currently uses solid biomass as a secondary fuel. More cofiring could help curb CO2 emissions from fossil-fuelled plants across the world. The question is: is there enough biomass in the world to supply sustainably such large-scale consumption of biomass?
Wood pellets are a successful and fast growing internationally-traded biomass commodity. Wood (and straw) pellets are more energy dense and easy to transport than traditional wood chips. The biomass pellet market reached 25 Mt/y in 2013 and is growing rapidly, and becoming more sophisticated. International trade is now common, especially as the heating values and moisture contents of pellets can be similar to some high moisture coals that are traded. Most processed wood pellet fuels are sourced in North America for power plants in Europe.
Extending cofiring at rates of 5-10% to the world’s coal-fired fleet would cause a major increase in demand for wood pellets. Meeting such a demand would offer opportunities and challenges for the entire biomass supply chain, not least for global forest resources.
In his latest report for the IEA Clean Coal Centre, World forest and agricultural crop residue resources for cofiring, Paul Baruya reviews current understanding of world biomass resources. He identifies global and regional resource figures for wood in the form of residues and waste by-products from the forestry industry and discusses the broad issues that affect forest resources worldwide. It is important that the sustainability of forest and agricultural industries is at the forefront of all biomass for energy projects. As a result, the report takes a cautious approach, and does not include crops that are dedicated for energy use, or assume that a whole tree is used for pellet manufacture unless it is felled for thinning and fire protection purposes. Only material that would otherwise by discarded is considered; some of this material is already utilised in heating boilers.
Currently there is 60 GWe of power capacity globally that is designed for biomass and waste; solid fuels account for almost two thirds of this. Large-scale conversions from coal-fired units of around 600 MWe to 100% biomass units are being undertaken in Denmark and the UK.
Published research suggests that the world biomass supply could reach 100-200 EJ/y but optimistic estimates can be as high as 1200 EJ depending on the wide variety of assumptions made on sustainable practice, land use and other factors. The lower estimate of 100 EJ/y is equivalent to 5800 Mt/y of biomass (wood equivalent).
Biomass for cofiring is sourced from residues from existing forestry, sawmilling, and agricultural activities. Recent research from IRENA suggests that forest residues could supply 21 EJ/y of biomass, and agricultural residues supply 13 EJ/y. These alone account for a third of the future world biomass supply.
Residues arising from forest management are a substantial resource suitable for processing into cofiring pellet fuel. Paul Baruya’s analysis suggests there is 14,218 Mt of wood residue within managed forests worldwide. The 14,218 Mt of potential residue contains around 177 EJ of imputed energy. Russia has the largest land area covered in both productive and total forest. North America is the largest producer and exporter of wood pellets; resources in Canada could be underestimated.
While the global resource for residue is abundant in the world’s managed forests, the amount that is produced and available in any year is in direct correlation with the actual output from the forestry and milling industries. The conservative calculations carried out by Paul suggest that there could be 1090 Mt/y of residue (14.2 EJ/y in wood pellet equivalent) from current industrial roundwood and cereal crop production. This residue resource is almost three times current demand for primary biomass in the power and heat sector, and more than double the total biomass demand worldwide.
By 2030, IRENA estimates that 37- 66 EJ/y of agricultural residues and waste and 27 – 43 EJ/y of forest products and forestry residues could be available. With a current supply of 8.9 EJ/y of wood residues and 5.4 EJ/y from agricultural residues, there is a great deal more unexploited potential yet to be realised through improved harvesting, crop yield performance and land use and forestry management.
A 5% cofiring scenario for the world’s fleet could create a biomass demand from subcritical coal plants operating at midload to baseload of 235 Mt/y. This is around a fifth of the annual residue resource from roundwood and straw, and a fraction of the 14,219 Mt/y of residues present in the world’s productive forest as calculated by the IEA CCC.
Other sources of residue will include the millions of hectares of forest that are not clearly designated for productive use and so were not included in this assessment. Municipal and industrial wood waste could also provide biomass. Agricultural residue potential is substantial, but heavily dependent on infrastructure to collect, bale and transport the material.
Clearly, there is an abundance of biomass resources worldwide. The cautious approach to calculating residues by Paul Baruya still shows a residue potential far above the demand that could be created through cofiring biomass at a rate of 5-10% in the world’s coal-fired power fleet.
Europe’s power market has already demonstrated that biomass sources need not be restricted to local suppliers, but in a dense pelletised form, these fuels can be transported from North America. The potential for waste and residue from the global forestry and agricultural sectors to supply the world’s coal-fired power stations is considerable. If production is practiced sustainably, a proportion of the world’s coal can be replaced with biomass and make considerable savings in CO2 emissions while benefitting from the infrastructure that exists for power generation and transmission for large coal-fired plant, without damaging the operation of the power stations.
The report World forest and agricultural crop residue resources for cofiring CCC/249 by Paul Baruya, 66 pp May 2015 is avaiis available for download from the IEA Clean Coal Centre Bookshop http://bookshop.iea-coal.org.uk/site/uk/clean-coal-technology-research-reports. Residents of member countries and employees of sponsoring organisations can download the report at no charge after a one-off registration.