Applications where a continuous bucket elevator is used to move a flammable or explosive material often require the conveyor to be filled or purged with an inert gas. In these applications, the use of an inert gas within the elevator is a further precaution to prevent ignition or explosion of the material being conveyed. To enable operation with an inert gas, fully sealed and gastight bucket elevators are required for these applications.
How do gastight bucket elevators work?
Gastight bucket elevators can be filled or purged with an inert gas to prevent unwanted chemical reactions from occurring with the material being conveyed.
An inert gas is a gas which does not undergo a chemical reaction under a set of given conditions. Because of their non-reactive properties, inert gases can prevent undesirable chemical reactions, such as fires or explosions, from taking place. Examples of inert gases are nitrogen, argon, helium, and carbon dioxide.
Unless they are of open tube design, bucket elevators are “closed systems”. Fires and explosions which can arise within bucket elevators require the presence of four elements: combustible material or dust present in sufficient concentration; an enclosure (the elevator casing); oxygen; and an ignition source. In a dust explosion, an ignition source causes concentrated dust within the elevator to rapidly combust, creating enough heat and expanding gases to breach the conveyor enclosure.
Filling or purging a continuous bucket elevator with an inert gas is a fire and explosion prevention measure. Filling the elevator enclosure with an inert gas reduces the oxygen concentration and prevents the atmosphere within the elevator from coming into the explosive range. Purging the elevator by flushing it with an inert gas can help prevent the formation of an ignitable atmosphere within the conveyor, reducing the risk of a fire or explosion.
To enable the operation of a bucket elevator with an inert gas, the conveyor must be designed with a gastight casing. This ensures that the inert gas present within the elevator can be kept at sufficiently high concentration, without any leakage or emission to the surrounding environment. Equipment manufacturers ensure gas-tight operation through the use of gaskets and other mechanical seals to fully close the joints of the elevator’s frame sections and casing panels, preventing the escape of any gas.
Applications which require the use of gastight bucket elevators
Critical service applications involving the conveying of materials which can ignite, spontaneously combust, or explode are those where the use of gastight bucket elevators must be considered.
Particular attention should be paid to materials which create explosive dusts when moved, or which have a propensity to spontaneously combust. As noted above, the presence of combustible dust in sufficient concentration with an elevator constitutes a real explosion hazard. Materials which can spontaneously combust are another threat – these materials can auto-ignite through self-heating. A gastight bucket elevator can address both of these risks by reducing to a safe level the concentration of oxygen which is needed to fuel the explosion or fire.
Some examples of applications which can benefit from the use of gastight bucket elevators are the following:
- Chemical processing and production
- Sulphur refining and processing
- Explosives and ammunition production
- Fertilizer production
- Pistachio nuts (these nuts are highly flammable when stored in large quantities and are prone to self-heating and combustion)
TipTrak™ Monocoque gastight bucket elevators from UniTrak
TipTrak™ Monocoque gastight continuous bucket elevators from UniTrak have the following features for conveying materials in critical care applications:
- Fully enclosed and gastight sealed designs. TipTrak™ Monocoque conveyors feature a fully sealed gastight design. These conveyors support fill or purge operation under with an inert gas. Oxygen sensors are available to monitor the concentration of oxygen within the elevator.
- Explosion proof drive motors. The drive motors used on TipTrak™ 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™ 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.
- A rubber beltchain drive and joint strips, with polymer interlocking buckets. TipTrak™ Monocoque units come equipped with a rubber anti-static beltchain which reduces the risk of sparking or heat buildup that can occur with a metal drive chain. Interlocking polymer anti-static buckets and rubber 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.
TipTrak™ Monocoque gastight bucket elevators are used in many facilities worldwide to safely convey hazardous materials. To learn more about the advantages of TipTrak™ Monocoque bucket elevators for applications in your facility, please contact the UniTrak sales team.