The rapid expansion of the market for biomass pellets has brought an increasing focus on safety issues along the entire pellet supply chain, from production to storage and final use. At the first International Workshop on Pellet Safety, in Fügen, Austria, in March 2013, the two most intensely debated topics were safety issues related to pellet storage and pellet production, followed by human health and safety, safety in transport and handling of second-generation pellets. There is good reason for this concern. Pellets are highly combustible and estimated to be 100 times easier to ignite than coal. A pellet fire at a power station in Essex, in the United Kingdom in 2012 knocked parts of the plant offline for six months.
In 2000, the European Commission issued a mandate to the European Committee for Standardization (CEN) to prepare standards for solid biofuels. In total 38 standards for solid biofuels were published,1 covering terminology, fuel specification and classes, quality assurance, sampling and sample preparation, and analysis of the physical, mechanical and chemical properties of solid biofuels. A number of organizations and EU-financed projects are working to develop guidelines that will form the basis for European standards related to pellet quality assurance and safety. The European Pellet Council (EPC), one of the co-organizers of the Fügen workshop, coordinates the ENplus quality certification system, for which a dedicated organisation - PellCert – was set up and funded under the Intelligent Energy Europe programme. The EPC believes that sustainability requirements are key to securing large scale-investments in the biomass sector, and that the ENplus certification scheme could include such sustainability criteria.
This work is being augmented by other EU-funded projects. The FP7-financed SafePellets project (Safety and quality assurance measures along the pellets supply chain) aims to support international standardization work by developing a set of guidelines for the safe production, handling, and storage of pellets from different sources. The project aims at providing solutions to ensure consumer protection by developing preventive measures to avoid off-gassing of toxic substances during storage and by providing technical solutions to safely remove off-gasses on demand. Furthermore, SafePellets deals with the problems of self-heating and spontaneous ignition of stored pellets. The project is developing preventive measures to avoid fires in storage and provide guidelines to improve fire safety. Moreover, Sweden’s Firefly AB, which is a member of the project’s consortium of 15 SME-industry partners and research institutes, plans to develop new sensor solutions to detect fires and off-gases in pellet storage facilities.
A SafePellets project report has outlined some of the inherent risks involved in working with wood pellets, specifically those related to the storage, production, transport and handling issues highlighted in Fügen. With respect to storage, most research was carried out for small scale users. Generally, domestic pellet storage is subject to the same risks as those experienced by producers and wholesalers. However, large pellet storage facilities are usually equipped with temperature and CO detectors to locate self-heating processes and fires as quickly as possible. Furthermore, employers are generally well trained and aware of possible risks. In contrast, knowledge about possible risks and appropriate handling of these risks is less common among small scale users, which can result in fatal accidents.
Fresh pellets (within the first three months after pelletizing from fresh wood) seem, under certain circumstances, to bear a higher risk for off-gassing and self-heating, and the risk of fire tends to be greater in large warehouses. The larger the storage capacity is, the higher the risk of spontaneous ignition of the fuel because the ratio of surface area to volume decreases. In the event of incipient smouldering the temperature rises quickly and may cause the pellets to ignite. The auto-ignition temperature is dependent on the quality of the pellets and is influenced by the same factors that cause off-gassing. Spontaneous combustion reactions are therefore more frequent immediately after pellet production than in pellets that have been stored for a long time.
The project report outlines the current standards and guidelines governing pellet safety and, perhaps more importantly, it identifies problem areas that are not covered by existing standards. It appears that so far adequate solutions have been found only for high-quality pellets. The report stresses that increased focus should be given to the fact that pellets are a fuel and should be handled with the same care as oil or gas. In particular, inexperienced users need to be informed about the potential health risks from gas emissions.
Given that that freshly produced pellets seem to have a higher emission potential than pellets stored for a certain period, the project recommends that a minimum storage period be put in place for pellet producers, in order to reduce the risk to users further down the line. Furthermore, the report recommends setting a fixed value for the temperature to which fresh pellets should be cooled before being stored. Only the ENplus certification system currently contains the requirement that the temperature of pellets should not exceed 40°C before delivery to the end-consumer – there is no comparable regulation for pellet fabrication sites.
The participants in the Pellet Safety Workshop in Fügen identified limited knowledge of the underlying reasons for some safety risks as one of the main problems facing the pellet industry. By aiming to address this knowledge gap, SafePellets will increase the safety of pellet supply and storage, thereby increasing consumer confidence and strengthening the feasibility of European supply chains for biomass, which was one of the challenges set forth in the Biomass Action Plan. Ultimately, by helping create a sustainable European pellet market, SafePellets is contributing to the overarching goals of increasing Europe’s energy security and diversifying its energy supply.
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