Dust Explosions

 Dust Explosions

Selecting a Conveyor to Minimize Risk

For the coffee roasters and processing companies using conveyor systems, some ground and powdered materials are ignition sensitive in specific concentrations, particularly when exposed to static electricity discharge.

A key concern is conveyor system connection points such as inlets, outlets, and storage bins. Here, the dust concentration can become sufficiently high for a deflagration to occur with accidental exposure to an ignition source, such as static electricity, a spark, flame, or even high heat or friction.

One solution for coffee roasters is selecting a conveyor, such as a tubular drag conveyor, that conveys powdered material more slowly and gently. Tubular drag conveyors are enclosed systems that utilize a coated, flexible stainless-steel drag cable pulled through on a loop.

Because tubular cable conveyors do not suspend transported powders within high-velocity airstreams like pneumatic conveyors, this imparts “less energy” into the conveyance, which reduces dust explosion risk.

Unlike other conveyor systems, tubular cable conveyors operate on low horsepower with less heat and friction.

With tubular cable conveyors, solid circular discs (flights) are attached to a cable, which pushes the product at low speed through the tube without the use of air, reducing the potential for dust cloud formation and preserving product integrity. The systems can convey up to 2000 cubic feet per hour (56m3/hr.) of powders, granules, etc., with numerous layouts using multiple inlets and outlets.

Minimizing Dust Accumulation

When it comes to minimizing the risk of dust explosions in coffee roasting and processing, even gentler enclosed tubular conveyor systems are not all the same given the two options: chain or cable.

For example, with tubular drag chain conveyors, the entire chain is directly immersed within the powders conveyed so coffee dust and particles can remain trapped after cleaning. With tubular cable conveyors, the cable has about 80% less area exposed than the surface area of the chain. Further, the cable is nylon sealed, preventing debris and dust accumulation within the cable strands.

Another way to mitigate coffee dust accumulation is through sufficient cleaning to remove any potential powdered debris between batches. For this, tubular cable conveyor systems typically offer more options for dry and wet tube cleaning to remove accumulations of dust and residue.

To minimize dust explosion risk with coffee roasting and processing, tubular cable conveyors should be engineered in conformance with EHEDG (European Hygienic Engineering and Design Group) hygienic standards so that they’re entirely free of

crevices, ledges, and dead spots where coffee dust and particles can reside. Surfaces should be designed to be convex, rounded, or inclined to 45 degrees to prevent powder and dust residue.

Given the variety of conveyor choices and powdered ingredients that must be conveyed during coffee processing, the potential risks warrant a careful examination of the available equipment options and system design in consultation with experts.

Systems that eliminate potential ignition sources, convey material with less force, and otherwise reduce the risk of dust explosion can help coffee roasters and processors protect their employees, production, and brand.

by Karl Seidel

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