Mechanical Conveying in Battery Material Plants

Mechanical conveying appears in battery material plants where the material is too cohesive or too abrasive for comfortable pneumatic transfer, or where a gentler handling is wanted for a granulated precursor.

It brings two problems. The first is contamination: flights, chains, buckets, liners and bearings wear, and metallic debris in a cathode material is counted in parts per million and rejected at that level. The reflex of specifying a harder material for longer life makes the contamination problem worse rather than better.

The second is the atmosphere. These powders are handled at low dew point, and a conveyor enclosure has shaft penetrations, inspection hatches and an inlet and outlet. Every one of them can admit humid plant air, and the enclosure is usually at or below ambient pressure, which makes that the natural direction.

And the powder is harmful. Nickel and cobalt compounds have low exposure limits, so opening the machine, clearing a blockage or changing a liner are containment operations rather than routine maintenance.

Wear surfaces selected against the element by element contamination limits, positioned out of the product path where possible, and with debris that is tolerable where it is not.

An enclosure that holds its atmosphere, with inward leakage specified at the operating pressure difference rather than inferred from an outward figure.

Maintenance procedures written for a harmful dust, with extraction at the point of work and a defined cleaning method.

In a chemical plant the same conveyor is decided at the shaft seal, which is the containment boundary and not a wear part, whatever the maintenance schedule calls it.

Material selection for contact surfaces is the first step, done against the contamination specification rather than against service life. Ceramic and polymer liners, non ferrous or coated flights, and sometimes the deliberate acceptance of a shorter life in a tolerable material.

The enclosure is then sealed against the room. Shaft seals specified for inward tightness, hatches with proper gaskets rather than dust covers, and a vent to dry gas rather than to the plant. Where the process allows, holding the enclosure slightly above ambient with dry gas removes the problem entirely.

Bearings and drives sit outside the product space, which helps contamination, containment and the ignition source list at the same time.

Finally the maintenance is designed. A blockage will be cleared and a liner will be changed, and both mean opening a machine full of a harmful dust. Extraction at the point of work, a defined cleaning method and a written procedure belong with the equipment specification rather than in a manual written afterwards.

• Contact surface materials selected against the contamination limits element by element.
• Wear surfaces positioned out of the product path where the design allows.
• Shaft seals and hatches specified for inward tightness, with the vent to dry gas.
• Enclosure held slightly above ambient with dry gas where the process allows.
• Bearings and drives outside the product space.
• Blockage clearing and liner changes designed as containment operations with extraction.

• Metallic contamination limits per element, which usually decide the contact materials.
• Dew point requirement and the inward leakage the enclosure permits.
• Exposure limits of the materials, which set the maintenance and cleaning arrangements.
• Abrasiveness of the material, which sets the wear rate and therefore the debris rate.
• Whether a closed pneumatic transfer could do the job, which removes the wear surfaces entirely.
• Product fragility, where a granulated precursor has to arrive intact.