PELLETS Bioenergy International PS1 2015 23 Health and safety first Industrial and private consumers use pellets on account of its economical and environmental benefits. Biomass may be renewable and sustainable but this does not mean it is by default safe and harmless to deal with. Ensuring and maintaining good operational, occupational and third party health and safety practices at all times is a key concern. IT IS PERHAPS SELF-EVIDENT THAT PELLETS, a densified thermal fuel made from combustible organic materials, are designed to release thermal energy when used. Being made from combustible particles, health, fire and dust explosion hazards are always a potential risk across the industry value chain. Incidental learning curve Each activity or process has its own set of specific issues. Research and experience over time have shaped the ways in which to deal with them. A particular challenge arises when something new or unfamiliar is introduced to the process-often giving rise to a whole new set of issues that needs to be addressed. Large industrial-scale production, handling, storage, shipping and combustion of pellets are, in this respect, new and unfamiliar processes. According to Yves Ryckmans, Chief Technology Officer for Laborelec GDF-Suez, an R&D cooperative company within the Belgian GDF Suez Group, there have been at least 15 serious fires, explosions and carbon monoxide (CO) poisoning incidents with biomass and pellets, during the period 2004 to 2010. These have occurred at pellet plants, storage silos, vessel off-loading as well as at combustion plants. Some have been dramatic like the Tilbury power station fire in the UK in 2012 causing substantial collateral damage and even a sharp drop in the pellet spot price. Dust a devious hazard The more finely divided the combustible material is, the easier it is to ignite and the more explosive it will become. Even with the best-designed and operated production processes, very fine dusts from these operations risk provoking fire and explosion. This results from the ignition of a combustible substance in a material (dust, gas or vapour) when mixed with oxygen in the air. When this takes place inside a confined space such as storage silo, the rapid rise in pressure could cause a potential explosion in milliseconds, placing personnel and property at risk. Other potential areas of explosion risks include the milling, drying and extraction systems as well as various conveyors and transfer points. Contrary to common perception wood pellet dust has higher risks associated with it than coal dust. Whilst explosiveness in terms of lower explosion limit (LEL) is the same at 30 g/m3, pellet dust still contains 75 to 80 percent volatile matter; over double that of coal. This is compounded by the fact that wood has much lower minimum ignition values. This means that the explosion effects of wood dust compared to coal are more severe with higher explosion pressure and almost twice the pressure rise speed. A dust layer as little as a few mm in thickness will act as a fuel source on for instance, an overheated conveyor bearing, an ignition source. Such rapid combustion of small particles leads to a rapid increase in temperature that in turn leads to a rapid expansion of air, a blast wave which, if it occurs in a confined space, is an explosion. The real danger is if the blast wave from the primary explosion stirs up additional residual dust deposits into the air initiating a secondary explosion that can be disastrous. Off-gases the silent hazard A much less spectacular yet potentially lethal hazard is the risk of carbon monoxide CO poisoning in pellet storage spaces. Several incidents with fatalities have occurred in conjunction with discharging of pellets from vessels at port facilities, Rotterdam in 2002 and Helsingborg in 2006. Another accident happened at sea last July as persons onboard a vessel carrying a shipment of pellets from Russia to Denmark entered the cargo hold. The accident is still under investigation. In recent years at least four fatali- Sharing know-how in pellet production and storage safety, Lennart Jansson, CEO, Firefly (left), which recently gained FM approval for its spark detection and extinguishing systems, and Terrol Bateman, European Head, Dome Technology. Yves Ryckmans, Chief Technology Officer for Laborelec GDF-Suez, discussing health risks for staff, associated with long-term exposure to wood dust that pellet producers need to be aware of, such as allergies or ethmoid bone cancer. ties have occurred in pellet storage bunkers and silos (Germany 2010, Ireland 2010, Switzerland 2011, Sweden 2014) for much smaller volumes than a cargo hold. The Irish case was reportedly a seven tonne storage room for a domestic boiler. Further reading The health and safety issues associated with pellet storage is an area with limited research, in particular the understanding of the processes that occur and how best to prevent, detect and mitigate the effects. A comprehensive handbook “Silo Fires – Fire extinguishing and preventive and preparatory measures” authored by Henry Persson from SP Technical Research Institute of Sweden, published in 2012 by the Swedish Civil Contingencies Agencies (MSB) is available in English. Another report “Health and Safety Aspects of Solid Biomass Storage, Transportation and Feeding” published in 2013 by IEA Bioenergy Task 32 gives an insight into relevant issues. A three-year EU research project, SafePellets, supporting the development of quality assurance and safety measures in relation to self-heating and offgassing, along the biomass pellet supply chain is well underway. 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Bioenergy nr 1 - 2015
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