Dust-free Loading in Grain and Feed Terminals

Loading is the largest single dust release on most grain terminals, for a simple reason: the rates are enormous and the fall is long. A ship loading spout moving thousands of tonnes an hour entrains a great deal of air, and all of it escapes at the hold with the fines in it.

The dust that escapes does not go away. It settles on the gantry, the conveyor structures, the quay and the equipment, and in this industry that layer is the mechanism behind the serious incidents. A terminal that cannot keep its structures clean has a hazard independent of any individual vessel.

Rate changes the available solutions. At truck and railcar rates a telescopic spout with extraction is the standard and works well. At ship loading rates the air volume to extract becomes impractical, and the answer shifts to reducing the generation rather than capturing the result.

And the extraction filter, where there is one, holds the finest grain dust on the site, which makes it a vessel that needs protection and isolation.

Loading arrangements matched to the rate: enclosed spouts with extraction at truck and railcar rates, cascade or slowing arrangements at ship loading rates.

A filter protected and isolated on the basis of the collected dust, with the vessel strength verified.

Housekeeping designed in: access to the surfaces that collect, a cleaning method that removes rather than redistributes, and an interval that reflects what the loading actually releases.

At a mineral terminal the fines content and the moisture specification decide, and a long free fall left in place while water is added controls nothing.

Rate decides the principle. Telescopic spouts with an outer skirt and integrated extraction suit trucks and railcars: the spout follows the fill level, the skirt contains the displaced air, and a modest extraction takes it to a filter.

At ship loading rates cascade chutes do the work instead. The material is decelerated in stages so it arrives with far less entrained air and far less energy to loft fines, which is the only practical control at those volumes.

Where extraction is used, the volume is calculated from the displaced air plus the entrained air rather than estimated, and the filter is then protected: explosion data from the collected dust, vessel strength verified, venting where the location allows it, and isolation in the inlet duct.

Housekeeping is then designed rather than assumed. The structures that collect dust are identified, access is provided, and the method is vacuum rather than compressed air, because compressed air moves the layer instead of removing it.

• Telescopic spout with skirt and extraction at truck and railcar rates.
• Cascade or staged deceleration at ship loading rates, where extraction is impractical.
• Extraction volume calculated from displaced plus entrained air.
• Filter protected on collected dust data, with vessel strength verified and inlet isolation.
• Housekeeping access designed for the structures that actually collect dust.
• Vacuum cleaning rather than compressed air, which redistributes the layer.

• Loading rate, which decides between extraction and staged deceleration.
• Vehicle or vessel type and whether a seal or skirt can be made to work.
• Dust explosion characteristics of the collected dust.
• Filter location, which decides whether conventional venting is available.
• Housekeeping access to gantries, structures and quay surfaces.
• Emission limits at the site boundary, where a terminal is close to neighbours.