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Pneumatic conveying refers to the moving of solids suspended in or forced by a gas stream through horizontal and/or vertical pipes. Low pressure conveying is used to collect and convey dust and waste over short distances as required. A material handling fan produces high volumes of air under low pressure. High-pressure conveying is used to transport material such as chips, shavings or sawdust over greater distances. A positive displacement blower provides smaller volumes of air under high pressure.
High-pressure conveying systems are used extensively in the North American wood products industry with over 1,500 systems currently operating in Canadian mills alone. These systems have delivered cost effective fiber handling solutions in sawmills, board and panel plants and pulp mills.
A high-pressure pneumatic conveying system consists of the following number of components:
Blower Package
A positive displacement blower is selected to deliver the required volume of air to ensure efficient movement. Power consumption is determined by the air volume and pressure requirements of the line and not the size of the blower. Allied supplies complete blower packages, including inlet and outlet silencers.
Feeder
Rotary airlock feeders are rotating, star-like emptying devices located at the bottom of a collector to control material flow. Standard wood chip feeders are designed with a hard-chromed bore and hard-surfaced rotor tips that shear against a top, and sometimes, a bottom knife. Allied’s feeders are compatible with other high-pressure system components.
Tee-Injector
A tee-injector is installed below the feeder, and is the most common way to introduce material into the conveying pipeline. This allows several feeders to be connected in sequence and reduces the need for more than one high-pressure system.
Diverter Valves
Two-way or three-way diverter valves allow multiple routing distributions. Manually operated valves are practical in smaller applications. Motor operated automatic valves are used in hard to reach locations and when the diverter is used frequently.
Elbows
Heavy round-formed elbows are satisfactory for small systems or systems with non-abrasive materials. Higher tonnage or abrasive materials require replaceable flat-back elbows. For more remote elbow locations in a high abrasive situation, a more durable wear plate material is justified.
Discharge Devices
Target boxes are most practical for green or wet material. High efficiency cyclone collectors are used to separate material from air on dry materials and baghouses are used on dusty materials. Chip deflectors or pile builders control the direction of the discharge to selected areas. These can be mounted on adjustable booms to reduce fines separation on chip piles.
Unloading Devices
There are many types of bins and unloading devices that can be incorporated into a high-pressure system. Railcar loading or wigwag stations are used to minimize shipping costs. A well-designed wigwag pneumatic loader maximizes compaction, by feeding chips laterally and length-wise across a stationary boxcar, resulting in up to 20% lower shipping cost.
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