Mechanical Conveying in Chemical Plants

Mechanical conveying is chosen in chemical plants where pneumatic transfer is unattractive: a material too abrasive to blow, too cohesive to fluidise, or a duty where the air volume would be a problem for containment or for an inert atmosphere.

What it brings instead is a shaft penetrating an enclosure. That seal is the containment boundary, it wears, and when it fails the result is a release of a product that may be toxic, corrosive or sensitising rather than merely dusty.

Compatibility is the second constraint. Trough, flights, liners, seals and lubricant all contact the product, and the cleaning agent between campaigns is usually the harshest thing they will see. A conveyor specified for one campaign product can be destroyed by the wash.

And the machine is electrical equipment in a classified area. The drive, the local isolator, the speed monitor and the bearing temperature sensors all have to be suitable, and the maintenance happens under permit, which limits how often a seal can realistically be inspected.

A machine whose shaft seals have a stated performance, a known wear life and a defined behaviour on failure, with monitoring where the consequence justifies it.

Wetted parts verified against every product and cleaning agent in the campaign plan, at temperature, with the wear parts identified and stocked.

The complete assembly certified for the area it stands in, and a maintenance interval that is achievable under permit conditions.

A grain and feed plant sizes the same equipment against the peak intake rate during harvest, and the elevator that carries it needs alignment and speed monitoring to stay a conveyor rather than an ignition source.

The shaft seal concept comes first because it is the containment design. A packed gland for a nuisance dust, a purged seal where exposure matters, a double seal with a monitored interspace where it matters a great deal, and in each case a defined action when the seal or the purge fails.

Compatibility is then worked through as a matrix: every wetted component against every product and cleaning agent, at temperature. This step often changes the machine, because the choice between a stainless trough, a lined one and a polymer flight is made here rather than on throughput.

Where the atmosphere matters, the enclosure is designed for it. A conveyor can be purged with nitrogen, which is far cheaper than inerting a pneumatic line, and that is sometimes the reason a mechanical machine is chosen in the first place. The purge then needs a monitor and a stated failure case.

Finally the assembly is certified complete and the maintenance plan is written against permit reality. A seal that needs weekly inspection in a classified area will not get it, so the design has to tolerate the interval the plant can actually keep.

• Shaft seal concept chosen from the exposure limit, with a defined action on failure.
• Compatibility matrix across products, temperatures and cleaning agents for every wetted part.
• Enclosure purged where an inert atmosphere is needed, with monitoring and a failure case.
• Complete assembly, including drive and instruments, certified for the classified area.
• Bearing temperature and speed monitored where they are credible ignition sources.
• Maintenance interval set to what permit conditions allow, with the design tolerating it.

• Exposure limit of the products, which sets the shaft sealing concept.
• Chemical compatibility of trough, flights, liners, seals and lubricant, including cleaning agents.
• Inert atmosphere requirement, which can be the reason mechanical conveying is chosen.
• Area classification for the whole assembly.
• Abrasiveness and temperature, which set wear parts and clearances.
• Achievable maintenance interval under permit conditions.