Dust Suppression in Cement and Aggregate Loading

A loading bay in a building materials plant frequently handles both ends of the material spectrum. Coarse aggregate is dusty because of the fines it carries and the air it drags with it; cement, lime and fly ash are dusty because they are powders.

The controls that work on one are wrong on the other. Water applied to aggregate is routine and effective; water applied to cement starts hydration, and a loading spout with a wet deposit inside it becomes a blocked loading spout. Conversely, enclosure and extraction are the right answer for powder and often impractical for a high rate aggregate stream.

Plants that install one system for the bay therefore end up with a compromise that controls neither material well, and the usual symptom is a visible plume on one product and a blockage on the other.

Both materials also carry respirable crystalline silica in most cases, which means the exposure limit applies to the loading operator regardless of which product is being handled.

Two defined duties in the design, with the powder loading enclosed and extracted and the aggregate loading suppressed, even where they share a bay and a structure.

No water path to cement or lime at any point, including spray drift from the aggregate side and washdown.

Operator exposure measured, since the respirable fraction applies to the person in the bay whichever product is loading.

In food ingredient handling the first question is whether a duct can reach the point at all, because suppression installed where extraction was possible gives away a recoverable product.

The duties are separated first, on paper. Which products load at which position, at what rate, and with what control. A shared structure is fine; a shared control system usually is not.

Powder loading is then designed as an enclosed column: a telescopic spout with an outer dust skirt, a seal to the vehicle hatch, and extraction of the displaced air to a filter. The volume to extract is the air the material displaces plus the air it drags with it, which is a calculable figure rather than a guess.

Aggregate loading is designed around slowing the stream and adding moisture where the specification allows. A suppression hopper or cascade arrangement reduces the energy available to loft fines, and sprays or fog deal with what remains.

Then the water is kept away from the powder side deliberately: separate drainage, no shared sumps that can be hosed towards a cement spout, and a washdown procedure that names what must stay dry.

• Loading duties separated by product and position, even within one bay.
• Powder loading enclosed with a telescopic spout, dust skirt and vehicle seal.
• Extraction volume calculated from displaced plus entrained air.
• Aggregate loading slowed by suppression hopper or cascade before water is added.
• Water paths, drainage and washdown designed to keep the powder side dry.
• Operator exposure to respirable silica measured in the bay.

• Product mix at the bay and whether powders and aggregates genuinely share a position.
• Loading rate, which decides between enclosure and slowing the stream.
• Moisture tolerance of each product, which is zero for cement and lime.
• Vehicle types and whether a reliable seal to the hatch is achievable.
• Respirable silica content and the operator exposure that follows.
• Drainage and washdown arrangement, which is how water usually reaches the powder side.