Dust Collection in Building Materials Plants

The quantities here set the problem. Crushers, mills, kilns, conveyors, silos and load out points each generate dust, and at plant throughputs the air volumes needed run into very large figures. Every cubic metre per second has a capital cost, an energy cost and a maintenance cost, so the difference between an enclosed source and an open one is not a detail.

The dust is abrasive and often hot. Ducts, fans and filter housings wear; filter media chosen for an ambient duty fail on hot kiln or clinker cooler gas; and condensation in a cement system builds a deposit that sets.

The health question applies throughout. Respirable crystalline silica in quarry and cement dust carries an exposure limit, and the fraction that matters is invisible. A plant can be visibly dusty and compliant, or visibly clean and not.

And a great deal of the equipment is outdoors or in open structures, which makes capture harder and weather a design input.

Dust collection is usually sized from air volume and filter area. In a cement or lime plant the gas temperature and the moisture decide which medium survives that air at all.

Sources enclosed so the air volume is as small as the duty allows, because the volume drives the capital cost, the energy and the wear.

Ducts, fans and filters specified for abrasion and for the real gas temperature and moisture, with wear parts identified and a condensation case considered.

Respirable silica exposure measured on people, with the controls judged against that rather than against appearance.

In food production the same system is sized from the capture velocity at each source rather than from fan capacity, and the allergen matrix decides whether ductwork may be shared at all.

Enclosure is the first and biggest decision. An enclosed transfer point or crusher needs a fraction of the air of an open capture arrangement, and at these volumes that difference pays for a great deal of sheet metal.

Gas conditions are then established honestly: temperature at each source, moisture content, and whether the dew point can be reached anywhere in the ductwork or the filter. Cement systems that condense build a hard deposit, so insulation, heat tracing or a minimum operating temperature become part of the design.

Abrasion is designed for with duct velocities that keep material moving without eroding, wear protection at bends and at the fan inlet, and a discharge arrangement under the filter that is itself specified for the abrasion.

Exposure monitoring then runs alongside. Personal sampling for respirable silica at the positions where people actually work shows where the controls need to be, and it is the only basis on which the system can be said to be adequate.

• Sources enclosed to minimise air volume, which drives capital, energy and wear.
• Gas temperature and moisture established per source, with the dew point case examined.
• Insulation, tracing or a minimum operating temperature where condensation is credible.
• Duct velocities and bend protection specified for abrasive dust.
• Filter discharge arrangement specified for abrasion, not inherited from a standard design.
• Personal sampling for respirable crystalline silica, with controls judged against it.

• Air volume, which follows from how well the sources are enclosed and drives the whole cost.
• Gas temperature and moisture at each source, including kiln and cooler gas.
• Abrasiveness, which sets duct velocity, wear protection and discharge design.
• Crystalline silica content and the exposure limit it brings.
• Condensation risk, since set deposits in a cement system are difficult to remove.
• Outdoor exposure and weather along the duct route.