Using a bucket elevator to convey metal powders
Q: We process metal powders, which we know can be combustible. We use a bucket elevator to convey them in one area of our plant. What kind of safety measures do we have to use with the elevator?
As you mention, some metals can be potentially explosive. Aluminium, for instance, has a minimum ignition energy (MIE) of about 1 millijoule in the worst case scenario and a Kst (dust deflagration index) value going as high as St 2 or even St 3 (classification system indicating a very high risk of explosion). Iron and iron-resin mixtures, such as copier toner, give similar figures, making it unadvisable to handle these products in a bucket elevator.
In fact, a bucket elevator is one of the worst types of equipment you could choose in terms of explosion history and potential because the fuel (the metal powder) and oxygen—two of the key ingredients in an explosion—are present. Combine that with metal dust that’s likely dispersed in the air and you have an ideal explosive situation.
If you do stick with the bucket elevator, making your powder inert using nitrogen gas is the only safe solution. To do this, you’ll need to install additional hardware for containment — rotary feeders or other sluicing systems — and the elevator will need to be completely gas-sealed. Without more detailed information on the nature of your product and process, it’s difficult to give a more detailed answer.
I’d advise consulting an expert on dust explosion prevention and protection to determine the explosion characteristics of your mixture and evaluate your process. Often the best solution isn’t to add hardware and safety devices but to make changes in your process .
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