Bucket conveyors are commonly used to vertically transport materials in many industrial processes. How typical bucket conveyors accept, move and discharge material makes this equipment type more prone to dust explosions than other conveyor types. This is especially true for centrifugal bucket conveyors, where the higher rate of speed contributes to increased dust creation and greater risk of an explosion. In this blog, we focus on continuous bucket conveyors as an equipment type, and examine how good equipment design can control potential ignition sources to reduce the risk of bucket conveyor dust explosions.
What Causes Bucket Conveyor Dust Explosions?
A dust explosion occurs in a bucket conveyor when combustible dust accumulates in sufficient concentration within the enclosed space of the conveyor and is exposed to an ignition source. Since the ignition source is the trigger which sets off the explosion, controlling the possible sources of ignition through good equipment design can reduce the risk of an explosion ever occurring.
What Sources of Ignition can Cause Continuous Bucket Conveyor Dust Explosions?
There are multiple possible sources of ignition for an explosion to occur within a continuous bucket conveyor. These sources are outlined in a guidance document for EU ATEX Directives that cover equipment used in potentially explosive atmospheres, published by the UK Solids Handling and Processing Association (SHAPA). Some of the ignition sources identified by SHAPA can be present in continuous bucket conveyor systems. They include:
- Hot material particles resulting from local chemical reactions or friction as the material is conveyed.
- Mechanically generated sparks from friction, impact and abrasion processes.
- Ingress of foreign materials between moving contact surfaces of the conveyor.
- Thermite or other exothermic chemical reactions. For example, impact between rust present on the conveyor and the conveying of light metals (i.e., aluminium and magnesium, and their alloys). In the conveying of light metals such as titanium and zirconium, friction of these materials against a hard surface may also create sparks.
- Electric sparks created from electric circuits used on machine controls.
- Discharge of accumulated static electric charge within the conveyor. Static charges may arise from friction as material is moved through the conveyor, most likely occurring as material is loaded into and discharged from non-metallic buckets.
How can the Sources of Ignition Within a Bucket Conveyor be Addressed and Controlled?
Intelligent design and construction of a continuous bucket conveyor can address many of the ignition sources identified above and significantly reduce the risk of a dust explosion occurring. TipTrak™ Monocoque and PEC bucket conveyors from UniTrak have the following features which suppress ignition sources and mitigate the risk of an explosion:
- Fully enclosed and gas-tight sealed designs. TipTrak™ Monocoque conveyors feature a fully enclosed and sealed gas-tight design. A variety of options are available, including explosion relief panels. PEC conveyors feature a fully enclosed, but not gas-tight, design. PEC and Monocoque units permit safe handling by mitigating the risks associated with product dusting and any resulting fugitive dust emissions that may result in an explosion. Direct connection to the plant dust collection system can be easily made with either model.
- Explosion proof drive motors. The drive motors used on TipTrak™ PEC and Monocoque units meet all requirements for tools and fixtures intended for use in potentially explosive atmospheres as defined in EU Directive 94/9/EC (ATEX), or as of April 20, 2016 of the EU Directive 2014/34/EU (ATEX). These explosion-proof motors can be used in categories 2 and 3, in gas zones 1 and 2, and in dust zones 21 and 22.
- Fully conductive drive assemblies. TipTrak™ PEC and Monocoque units can be supplied with a continuous electrical ground path that prevents the accumulation of a static electric charge.
- Explosion relief vent panels. These panels provide additional safety and protection in the event of a dust explosion.
- Rubber beltchain, polymer interlocking buckets and joint strips. TipTrak™ PEC and Monocoque units come equipped with a rubber anti-static beltchain which reduces the risk of sparking or heat buildup that could occur with a metal drive chain. Interlocking polymer anti-static buckets and joint strips reduce static charge build up and prevent spillage of material as it moves through the conveyor.
- Stainless steel frame construction. TipTrak™ Monocoque conveyors can be supplied with full stainless steel construction to eliminate the build-up of rust and prevent sparking.
If you are seeking a continuous bucket conveyor for use in potentially explosive application, TipTrak™ Monocoque units can reduce the risk of bucket conveyor dust explosions. To find out more about TipTrak™ Monocoque bucket conveyors, or any of our other fine bulk solids conveyors, please contact our sales team directly.