Pneumatic Conveying in Food Production

A pneumatic line puts air in intimate contact with the product for the whole of its length, and plants routinely specify that air by pressure and volume alone. Blower air carries whatever the intake drew in; compressed air from an oil lubricated machine carries oil mist unless it is removed; and air that is not dried brings moisture to a powder that may be hygroscopic.

All three reach the product directly. An oil carryover in a flour line is a contamination that is difficult to explain and harder to clean up.

Velocity is the second issue and it is the one with the visible symptom. Food powders agglomerate, coat and break, and all of those are undone by speed. A line designed on a convenient velocity turns agglomerated instant powder back into fines and takes the coating off a snack.

And the line is a food contact surface of considerable length. Joints, bends, diverters and the receiving filter all have to be cleanable to the plant standard, and on a shared line to the allergen standard.

Conveying air specified as a food contact utility: a dew point, a filtration standard, and an oil free guarantee where the compressor type requires one.

A velocity derived from the product rather than from the pipe, with the rise in velocity along the line accounted for so the far end stays inside the limit.

A line that can be cleaned to the plant and allergen standards, with the method written and the shared line in the matrix.

In pharmaceutical production the leak direction decides the concept, because pressure conveying makes every seal a containment device while a vacuum line keeps the product inside when it fails.

Air treatment is specified with the system rather than after it. Drying to a defined dew point where the powder is hygroscopic, filtration to a stated grade at the point of entry, and where oil free operation is required, a compressor type that guarantees it rather than a filter that is supposed to catch it.

Velocity is then set from the product. Robust powders tolerate dilute phase; fragile, agglomerated or coated products need dense phase, and the damage onset velocity comes from a trial. A stepped pipeline holds that limit at the far end, because air expands as pressure falls and the last bends run fastest.

Cleaning is designed into the line: crevice free joints, bends that can be removed or inspected, no dead legs at branches, and a drain at low points if the line is wet cleaned, with a drying step afterwards.

Then the receiving end: a filter that is protected against explosion on the basis of the collected dust, and a decision on whether the collected fines return to the product.

• Air dried to a defined dew point and filtered to a stated grade at entry.
• Oil free compressor where oil free operation is required, not a filter relied on to catch it.
• Velocity set from a product trial, with the damage onset velocity as the limit.
• Stepped pipeline so the limit holds at the receiving end.
• Crevice free joints, inspectable bends and no dead legs at branches.
• Receiving filter protected on collected dust data, with a decision on returning the fines.

• Air quality requirement, which follows from the product and the food safety case.
• Hygroscopicity of the powder, which sets the dew point.
• Fragility and coating, which set the velocity and therefore dilute or dense phase.
• Cleaning regime, dry or wet, and the drying that follows.
• Allergen matrix for a shared line.
• Dust explosion characteristics of the powder and the collected fines.