Coal Dust and Quenchers

First let us review the facts on explosions.

Explosive dusts have lower and upper explosive concentrations. An explosion can only occur if the following is true. Assuming we have outside air with 20% oxygen being used to ventilate the mill, it is probable that the outlet from the hammer-mill will be between the upper and lower explosive limit concentrations. Between these limits if there is enough energy in the spark that ignites the dust, an explosive flame front will be triggered and move along the duct toward the ventilation outlet and presumably toward a dust collector, and, we are assuming this is to be a fabric (baghouse) collector. Determining the upper concentration limit is very difficult. The lower explosion limit is around 30 grains per SCFM for combustible dusts like coal. Once an explosive flame front is ignited the normal procedure is to put explosion vents in the ducts and collectors.

The action of Quencher spark arrestor.

Our Quencher spark suppressor works by changing the flow in the duct to turbulent flow. During laminar flow the spark can be carried for extremely long distance as the spark travels with a layer of air which insulates it. When turbulent flow is induced, the spark is immediately cooled so it lacks sufficient energy to start a fire or trigger an explosive front. Most insurance underwriters require explosion venting of the duct systems and dust collectors. The way of achieving this conversion from laminar to turbulent flow is by slowing the air down to lower the power consumption of the conversion device. The conversion device thoroughly mixes the dust laden gas stream with propeller type fixed vanes to extinguish the spark(s). To rid the potential low velocity build up of coal dust in the spark arrestor, it is periodically boosted in air stream speed to sweep the dust into the collector. This uses a compressed air propelled stream identical in design to that of a reverse pulse jet collector with time durations similar to that in those dust collectors. This the “Booster - Duct Cleaner” option is offered with the Quencher spark arrester.

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