Air permeation units

Diamondback Technology's air permeation unit can speed up powder flow rates as much as 1,000 times over that of powders without air permeation. Carefully controlled air injected at critical positions in the hopper replaces air lost when powder is stored. This prevents an in-rush of air from the hopper outlet that would otherwise limit solids flow. The APU controls both the maximum air pressure and the amount of air flow injected, producing a consistent powder flow rate that prevents flooding, flushing and limiting rate conditions.

• Eliminates feeder starvation when used in conjunction with an arch-breaking Diamondback Hopper
• Enhances a Diamondback Hopper's ability to break arches in solids that set up with time
• Eliminates flow problems with powders such as fly ash, ground ore, powdered polymers, fine dry coal and coke, talc, titanium dioxide and other pigments, cement, sawdust, flour, alumina and powdered metals

• Material-specific factory setting
• Complete manifold and tubing for direct hookup to Diamondback Hopper APU ports
• Available with two, four, six or eight injection ports
• Special clean-out nozzles for periodic APU port cleaning
• Installation, operation and cleaning manual

Understanding air permeation

When powders flow in converging hoppers, the powder compacts as the solids contact pressure changes. This increases the bulk-specific weight. If the hopper has a vertical bin section above it and the bin is full, the highest level of compaction in the hopper is at the transition between the vertical bin and the converging hopper. This compaction compresses and pressurizes the air in the voids between the powder particles. The pressure gradient from the pressurization expels some of the air from the top of the bin. As the solids flow in the converging hopper, powder expands, often to a value less than atmospheric.

At the outlet of the hopper, atmospheric air rushes in to negate the low pressure in the voids. This on-rush of air creates an upward force that retards solids flow. A solid moving surface forms at the hopper outlet from which the powder slowly rains in small clumps. This is called a limiting rate condition. The worst-case limiting rate occurs when solids sit in the bin and air pressure at the maximum solids contact pressure (at the top of the hopper) reduces to atmospheric.

The actual limiting rate will vary from the expected solids flow rate, after a powder deaerates in the bin, to a total flushing condition, depending on how fast the bin is filled and how long it stands after filling before initiating flow.

The APU injects missing air in the voids that would otherwise be filled by air rushing in from the bottom of the bin outlet. If the missing air is totally replaced, the solids flow rate can reach a very fast speed. For a powder, this can be several orders of magnitude higher than the maximum expected flow rate.