dry blower

A dry blower is a portable separation device that uses a motorized fan to create an air stream powerful enough to carry away fine dust and lightweight particles while heavier material falls and collects. The operator feeds raw pay dirt, gravel, or ore into the top of an inclined screen or hopper. As material slides downward, the blower pulls air horizontally across the falling particles, ejecting light waste (fines, clay dust, and lighter rock) out the side while denser gold-bearing material and stones drop into collection bins below.

These machines are most common in small-scale and artisanal gold mining, particularly in alluvial operations where pay dirt has already been extracted by sluice or pan. A typical dry blower might process 0.5 to 2 cubic meters of material per hour, depending on particle size distribution and moisture content. The air speed is usually adjustable via throttle or fan blade angle, allowing operators to tune separation for different ore grades and compositions. Some models use a gasoline engine (commonly 5 to 15 horsepower), while others run on electric motors powered by site generators.

Moisture in feed material causes the biggest operational problem. Even slightly damp fines will not blow away cleanly and instead clump together, reducing efficiency and blocking the screening surface. For this reason, dry blowers work best on naturally dry alluvial deposits or on material that has been sun-dried first. Wet ores and oxidized copper or tin ores require alternative concentration methods such as wet gravity tables or flotation cells.

Variants and placement in the milling sequence

A dry blower sits downstream of initial washing and screening but upstream of final refinement stages. Some operations use it to produce a coarse concentrate that still contains 10 to 30 percent waste stone and light minerals, which then goes to a gravity table, jig, or panning station for final upgrading. More advanced dry blowers include a trommel or vibrating deck in front of the blower stage, allowing them to remove large rocks before air separation begins. Portable models are standard in small mines because they need no water supply and require minimal infrastructure; fixed installations in larger mills are rarer because water-based recovery methods typically yield better grades with lower dust emissions.

The term "dry blower" emphasizes the waterless nature of the process, distinguishing it from wet gravity separation methods. It is sometimes called a "winnower" in older texts, though that term now applies mainly to agricultural grain cleaning. Dust control is a practical concern: operators should use respiratory protection and aim to position the discharge chute away from populated areas. The waste stream (blown-off fines) often carries valuable fine gold, so some miners recirculate it through secondary recovery equipment rather than discarding it.