Controlling Dust Explosions at Waste & Recycling Plants

Any industry which handles fine organic dusts is at risk of these materials burning and exploding. Every year, premises are severely damaged or destroyed by dust fires that usually start in dust extraction and waste conveying equipment. Just a few burning embers entering a dust collector, bin or silo is enough to trigger a dust explosion which would typically lead to fire. What does it take to cause an industrial explosion? A fire or explosion results from ignition of a combustible material (dust, gas or vapour) when mixed with oxygen in the air. When this takes place inside a process or storage enclosure, the rapid rise in pressure could cause a potential explosion in milliseconds, placing personnel and property at risk. Most materials handling, processing and storage equipment is not designed to resist the pressure of an expanding flameball which proceeds below the speed of sound in air – known as a deflagration. Prevention and protection measures An explosion risk assessment will typically recommend that a series of protection measures be implemented. These range from investment in protection equipment to improvements in housekeeping to eliminate the build-up of deposits of combustible dust which may accumulate on beams in the factory. These may be disturbed by a primary explosion in the process equipment and result in a more severe secondary explosion. Bespoke spark detection and extinguishing systems for the waste management industry are designed to detect sparks, glowing embers and hot particles that might become the ignition source for a fire or explosion if allowed to travel on through pneumatic ductwork and conveyors towards other material handling equipment. Such systems can be used in all sectors of waste management, including biofuel plants, recycling facilities and in industries where there is wood waste e.g. from shredding or pelleting. The equipment is used to protect the out feed of hammer mills, grinders and shredders which, in turn, prevents the propagation of secondary fires and explosions further into the process, such as within conveyors, cyclones, dust collectors and storage bins and silos. Using infra-red detectors, systems recognises the radiated light emitted from sparks, glowing embers and hot particles travelling past the detection point, and activates control circuits. The greatest sensitivity occurs when these sensors are employed in a dark area such as closed ductwork, although optional daylight detectors are also available for use on open conveyor belts and for applications where light is likely to be visible. In addition to preventative solutions, there are systems for protection, should an explosion occur. Chemical isolation systems can cut off an explosion and prevent it from affecting interconnected processes. If unprotected, the ductwork and piping, as well as all the connected vessels and equipment, are at risk. This is used in combination with explosion protection equipment on each vessel, bin, or dust collector and could include chemical suppression, explosion venting or indoor venting. Regulations, codes and standards Because of potential health problems, laws exist to ensure employers in the EU protect their workers from being harmed by dangerous substances in the workplace, which includes risks related to dust. Employers must carry out risk assessments, and take steps to ensure they prevent or adequately control exposure. ATEX is the name commonly given to Directive 94/9/EC. This provides the technical requirements and the relevant conformity assessment procedures to be applied before placing equipment and protective systems intended for use in potentially explosive atmospheres on the European market. Kevin Spiess is EMEA sales manager for Explosion Protection at BS&B Safety Systems Read More Plasma Arc FCC Catalyst Recycling to Benefit from Asian Boom Dr. Tim Johnson explains why plasma arc recovery technology could be set to benefit from Asia's growing appetite for materials and chemicals. Brazil's Incoming E-Waste Recycling Regulations Explained Stella Consonni offers a brief on Brazil's first national waste management legislation (PNRS) and its impact on the country’s WEEE infrastructure. UK Waste & Recycling Industry Could Save £12m PA with Mobile Apps UK Waste companies could save £12m a year by recording disposal data on mobile phones according to Graham Whistance, member of the Environment Agency Business Advisory Group.