Pneumatic Conveying

BCE pneumatic conveying provides material transport systems where a powder or granular material is moved from one place to another down a pipeline by means of a pressure differential. BCE pneumatic conveying systems are generally categorized as either dilute-phase or dense-phase. Dilute phase is normally under 12 lb material per lb of air and assumes that the material is suspended in the air stream. Dense phase operates at an air velocity below the material's saltation velocity and typically includes a high-pressure blow tank to force the slug of material into a line and booster air at regular intervals to keep it moving until it reaches a receiving vessel. Dense phase conveying can have material ratios up to 100-to-1 and can convey material very long distances. This discussion will be limited to dilute-phase pneumatic conveying systems, which are commonly used with dust collectors.

Dilute-phase pneumatic conveying systems can transport material by either positive pressure or vacuum. Both systems will have the following four basic components:

• The pressure blower or mechanical exhauster, to move the gas-solid mixture.
• The material intake valve
• The pipeline
• The dust collector

In a positive-pressure system, a pressure blower is upstream of the pipeline, designed to pressurize the pipeline so that the material is conveyed to a receiving vessel. The receiving vessel is typically a silo on top of which a bin vent filter is located. The pressure at the end of the line is low enough for a standard low-pressure dust collector to be used. In order to feed material into the line, a pressurized material feeder is often used at each pick-up point. The flow rate in the line is significantly higher at the "no-load" (air only) condition; therefore, the dust collector needs to be sized accordingly. The upstream line pressure can be 50-70 psig and therefore can convey for much longer distances than a vacuum system.

In vacuum conveying, a mechanical exhauster is located downstream of the dust collector to pull material through the system. Since the dust collector is at the end of the line, it will see the maximum vacuum, which could be greater than 15" Hg. Therefore, this dust collector (also called a filter-receiver) must be a special design to handle the high vacuum as well as a very high inlet dust loading perhaps on the order of 2000-5000 gr/ft³. If the material is abrasive (such as fly ash), a rotary valve may not be suitable to feed the material across a high pressure differential. In that case either a double dump valve or vented transfer hopper with isolation valves may be indicated to discharge the material and allow continuous operation.

BCE has extensive experience in designing pneumatic conveying systems and we look forward to assisting you with selecting the right equipment for your system.