Many facilities are using continuous bucket elevators to convey dusty materials. Whenever dusty materials are being conveyed, concerns arise about the risk of an explosion or fire. In previous blogs, we have discussed how intelligent equipment design and operation can greatly reduce the risk of a dust explosion occurring within a bucket elevator. In this blog, we look at the closely related topic of safely conveying flammable solids in a bucket elevator with minimal risk of a fire occurring as the material moves through the conveyor.
What are flammable solids?
Flammable solid materials are those that can ignite easily and burn rapidly. The US Department of Transportation identifies three major categories of Hazmat Class 4 flammable solids:
- Division 4.1 (Flammable Solids) is the most diverse category. Materials that can engage in exothermic reactions without oxygen, combust with friction alone, or are self-reactive fall into this category. Common examples include sulphur and desensitized explosives.
- Division 4.2 (Spontaneously Combustible) includes materials such as activated carbon that can ignite without a specific ignition source. This category includes pyrophoric and self-heating substances.
- Division 4.3 (Dangerous When Wet) items are those which emit a flammable gas and become fire hazards when exposed to water. Aluminum powder and magnesium are common examples of materials within this category.
What precautions are needed when conveying flammable solids in a bucket elevator?
Clearly, the number one precaution to take when conveying flammable solids in a bucket elevator is to ensure that there are no sources of ignition present as the material moves through the conveyor. Potential sources of ignition within a bucket elevator include the following:
- A spark created by the discharge of static electricity which can build up within the conveyor.
- Heat created by the friction of moving parts.
- Misaligned or slipping belts or chains.
- Worn or failed internal bearings.
While ignition sources can exist within a bucket elevator, upstream feeding equipment can also represent a potential source of ignition. For example, if the elevator is being fed with material from a dryer, discharging excessively hot material into the elevator can allow heat to build up within the conveyor to a dangerously high level.
Conveying flammable solids in a bucket elevator: equipment design considerations
Equipment designers and manufacturers can take several preventive measures to help operators safely move flammable solids with a bucket elevator. These include the following:
- Fully sealed or enclosed units. Fully sealed or enclosed units have several advantages. Firstly, in the event of material catching fire within the elevator, the fire is contained. Secondly, sealed or enclosed units prevent the ingress of moisture into the conveyor, which can be an ignition source when “dangerous when wet” materials are being moved.
- Full grounding and anti-static buckets. This prevents the accumulation of static electric charge within the elevator as it is operated.
- Bearing temperature monitoring. Temperature monitoring sensors detect overheated bearings.
- Speed monitoring. Speed monitoring sensors detect any belt slippage.
- Belt misalignment monitoring. Sensors detect any misalignment of the conveyor drive belts or chains.
- Nitrogen purge. Operating the bucket elevator under a purge of nitrogen gas flushes out oxygen that is essential for combustion to occur.
- Flameless vents. While not preventive in nature, these allow for the safe flame-free venting of any combustion which might occur within the conveyor.
TipTrak™ Monocoque (fully sealed) and PEC (fully enclosed) continuous bucket elevators help facilities to safely move flammable materials. TipTrak™ Monocoque and PEC units can be fully customized for flammable solids applications, significantly reducing the risk of a fire occurring while the material moves through the elevator. In addition, fully sealed Monocoque units support operation with a nitrogen purge. To find out more about how TipTrak™ bucket elevators can service your flammable solids applications, please contact our sales team directly.