Bulk Bag Discharge in Food Production

A bulk bag holds a tonne of powder above an open process, and everything that makes it convenient also makes it difficult.

The bag is soft, so it deforms as it empties and the spout moves. The powder bridges inside the liner, which stops the flow with the bag still half full. And the moment of untying the spout is the moment dust is released at the operator's face.

In a food plant two more constraints arrive: the station has to be cleanable to the plant standard, and where allergens are involved the liner and the station have to be segregated or verifiably cleaned between products.

A station that empties the bag completely, without the operator reaching into the flow and without a dust cloud at the connection.

In practice that means three things: the bag is supported so it collapses inwards as it empties, the spout is connected before it is opened, and the station can be cleaned in the time the plant has between products.

Sieving after the station as a routine step, because the bag and its liner are the most likely source of foreign material in the plant and a shed fragment reaches the process intact.

In mineral processing the governing figure is the respirable silica fraction, which is invisible: capture judged by appearance passes while the dangerous part is still airborne.

The bag arrives on a pallet and is lifted into a frame, either by hoist or by forklift depending on the building.

The spout passes through a seal into the receiving hopper and is clamped before it is untied. That order matters: a spout untied outside the seal releases dust that the extraction then has to chase.

Extraction at the connection point keeps the operator's breathing zone clear while the bag is open. The volume is set by the opening and the face velocity needed to hold the dust in, not by the size of the station.

As the bag empties, it needs help. Massaging paddles or a vibrating frame work the powder down the walls of the liner, and a bag that is supported at the corners collapses inwards instead of forming a bridge across the spout.

Bag variation is the detail that defeats otherwise good stations. Liner type, spout length and bag dimensions differ between suppliers and between deliveries, and a frame built around one supplier's bag means that a change of supplier becomes a change of procedure, usually an improvised one at the station.

• Connect first, open second.
• Extract at the opening, not at the room.
• Support the bag so it collapses inwards.
• Leave the last of the powder a path to the outlet.
• Sieving after the station, since the bag and liner are the main foreign body route.
• Frame and spout arrangement able to take the full range of bags in the supply.
• Changeover time measured against the allergen plan rather than estimated.

• Flow behaviour of the powder, measured rather than assumed: it decides whether massaging is optional or essential.
• Hygienic standard required, which decides the surface finish, the seal design and whether the station can be wet cleaned.
• Allergen matrix: shared stations need either verified cleaning or dedicated contact parts.
• Headroom in the building, which decides between hoist and forklift loading more often than preference does.
• Bag variation: liner type, spout length and bag dimensions differ between suppliers and the frame has to take all of them.
• Explosion characteristics of the powder, which decide whether the station and its extraction need protection.
• Sieve position and mesh, chosen for liner fragments as well as for product lumps.