There are many items to include when considering the sustainability of biomass for cofiring, some of them hard to quantify. Sustainability has environmental, economic and social dimensions. The focus of this study is on the greenhouse gas (GHG) emission aspects of sustainability.
The reduction of GHG emissions achieved by substituting biomass for coal depends on a number of factors such as the nature of the fossil fuel reference system, the source of the biomass and how it is produced. Relevant issues in biomass production include the energy balance, the GHG balance, land use change, non-CO2 GHG emission from soils, changes to soil organic carbon and the timing of emissions and removal of CO2, which relates to the scale of biomass production.
According to the Intergovernmental Panel on Climate Change (IPCC), certain current systems and key future options, including the use of biomass residues and wastes, are able to deliver 80 – 90% emission reductions compared to the fossil energy baseline. Policies encouraging the development of forest biomass energy have generally adopted a view of biomass as a carbon neutral energy source because the carbon emissions were considered part of a natural cycle in which growing forests over time would re-capture the carbon emitted by wood-burning energy facilities.
However, burning biomass increases the amount of CO2 in the air, just like burning coal, oil and gas, if harvesting the biomass decreases the amount of carbon stored in plants and soils or reduces ongoing carbon sequestration. The IPCC considers that deployment levels of biomass for energy could reach a range of 100–300 exajoules (EJ)/year by 2050, compared with the present use of biomass for energy of about 50 EJ/year.
Generally, solid biomass can be cofired at rates of up to 10% (thermal) with minimal impact on the workings of a coal-fired power plant. Cofiring is a relatively efficient way to use solid biomass. Biomass cofiring benefits from the infrastructure that is in place for large-scale coal combustion.
Life cycle analysis (LCA) is used to quantify the environmental impacts of products and services. LCA can be used to quantify the GHG emission savings of bioenergy, by comparing the bioenergy system with a reference fossil energy system. However, large ranges of GHG emissions and emissions saved are given from LCA studies of similar bioenergy systems. LCA analyses require significant effort. Thus, it would be sensible to direct the effort towards confirming the accuracy of the more significant emission sources. The overall yield and any land use change are often crucial parameters, while emissions associated with indirect land use change are complex and limited with regards to forestry residues for biomass cofiring. One disadvantage of LCA is that it does not take account of the timing of emissions, which is a serious limitation in its adequacy for assessing bioenergy systems.
The need to secure the sustainability of biomass production and trade in a fast growing market is widely acknowledged by various stakeholder groups, and setting standards and establishing certification schemes are recognised as possible strategies that help ensure sustainable biomass production and trade. Various stakeholder groups have undertaken a wide range of initiatives as steps towards the development of sustainability standards and biomass certification systems.
Standards for biomass sustainability
There seems to be a general agreement that it is important to include economic, social and environmental criteria in the development of a biomass certification system. A proliferation of standards for biomass sustainability exists, which differ from one country or region to another. It can be argued that further coherence in biomass certification systems, possibly through the promotion of international agreements and standardisation is needed. There is a lack of standards for the sustainable production of biomass at the international level. The EU raised the issue of standards in 2010, but a policy has not yet been published.
The FSC and PEFC have set widely-used and well-recognised standards on sustainable forestry but they do not include an assessment of the GHG impacts of forestry. While industry awaits national and international guidance on sustainable biomass, many organisations are developing their own criteria and certification schemes. By this route standards can be developed for different types of biomass source and means of production, as there is such variety. It may mean that strong standards with more credibility emerge and become more widely recognised. Such a process may take no longer than the emergence of an international agreement that may be unwieldy, and not appropriate for every situation.
Some countries have started to develop biomass certification schemes, including Belgium, the Netherlands, the UK and to some extent, Brazil, Germany, Canada and the US. The EU does not yet have sustainability standards for solid biomass, although they are expected. Many national policies relate to targets or incentives to stimulate the use of renewable energy sources. The systems in Belgium and the UK have the reduction of GHG emissions for sustainable biomass feedstock as the main criteria. The Netherlands and the UK have developed a wider set of principles including environmental, social and economic criteria. Certification is not the goal in itself, but the means to an end. It can be one of the policy tools used to secure the sustainability of biomass. Setting up good practice codes and integrating sustainability safeguards in global business models may also be effective ways to ensure this.
Towards sustainable and carbon neutral biomass
It is widely assumed that biomass combustion is inherently ‘carbon neutral’ as it only releases carbon taken from the atmosphere during plant growth. However, this assumption results in a form of double-counting, as it ignores the fact that using land to produce plants for energy typically means that this land is not producing plants for other purposes, including carbon otherwise sequestered. A concern is that if bioenergy production replaces forests, reduces forest stocks or reduces forest growth, which would otherwise sequester more carbon it can increase the atmospheric carbon concentration. If bioenergy crops displace food crops, this may have repercussions for food production, if crops are not replaced and may lead to emissions from land use change if they are.
Biomass for cofiring is not as clear-cut carbon neutral as say wind or solar power, but it is reliable. It is not intermittent and it takes advantage of the massive infrastructure that is in place for coal-fired power generation. Most biomass used in cofiring is from forestry residues and thinnings, so has a low environmental impact. It is important to consider biomass use from the landscape rather than from the stand perspective. Generally forests are managed on a rotation, so as one stand is felled the others are at various stages of regrowth, so if anything, the whole forest will be accumulating carbon. In the southeast US, one of the main sources of biomass for the EU, the total forest cover is increasing. Biomass for pellets is replacing the falling demand for pulp and paper. If the demand for biomass for cofiring increases, there may be an overall increase in forest cover to supply the biomass, and hence an increase in carbon storage. It is unlikely to compete with land for food production, due to market economics.
Biomass can be sustainable and can be carbon neutral, but there are many factors that must be considered, measured and certified, before it can be declared so.
The full report “Sustainability of biomass for cofiring” by Deborah Adams, communications manager at the IEA Clean Coal Centre, is available from the IEA Clean Coal Centre bookshop.
Written by Deborah Adams.
Edited by Jonathan Rowland
Read the article online at: https://www.worldcoal.com/special-reports/10022014/the_sustainability_of_biomass_cofiring_coalnews_491/