Gypsum Powder

Handling calcined gypsum means handling a material that is waiting for water.

Hydration starts in the air

Humid conveying air, a leaking vent filter or condensation on a cold silo wall is enough to begin the reaction.

The first sign is usually not a blocked silo but lumps in the product and a slow loss of setting performance at the board line.

• Dried conveying air and sealed, vented silos.
• Insulation where condensation on the inside wall is credible.
• Filter cleaning that actually removes the cake rather than compacting it.

Temperature

Stucco arrives hot from calcination, and hot powder aerates, then consolidates hard as it cools in the silo.

The design basis has to include the hot inlet condition and the cooled, consolidated outlet condition, because they are not the same material from a flow point of view.

Discharge and feeding

Mass flow geometry with a generous outlet and a mechanical discharge aid gives the most reliable result.

Loss-in-weight feeding into the mixer needs a stable, deaerated inlet; a flooding gypsum feed produces a board thickness problem before anyone sees a flow problem.

Cleanout

Any set material has to come out mechanically, which means access hatches, planned downtime and a safe method statement rather than a person with a bar.

What to establish before buying equipment

• Inlet temperature and the cooling profile inside the silo.
• Flow function for the consolidated, cooled powder.
• Dew point of all air in contact with the product.
• Access for cleanout and the planned frequency.

Gypsum powder consolidates quickly and reacts with water, and both matter in storage.

Stucco in particular is hot, cohesive and chemically thirsty: any moisture it meets starts a setting reaction that no vibrator will undo.

• Keep the silo sealed and the vent air dry; this is a chemical requirement, not a comfort.
• Expect consolidation over a weekend and size the outlet for the stood condition.
• Watch the temperature of freshly calcined material; a hot bed draws moisture in as it cools.

Cohesion and build-up drive the design.

A plain cone is unreliable; a live bottom or aerated discharge is normal. Surfaces that stay wet or cool are where the first crust forms, so the geometry matters as much as the discharge aid.

• Live-bottom or aerated discharge specified with the vessel.
• Dry conveying air with a stated dew point.
• Access for cleaning: a set deposit has to be removed mechanically.

Gypsum is not combustible, and the controls are respiratory and chemical.

• Capture at the source; the dust is fine and irritating.
• Eye and skin protection, particularly with freshly calcined material.
• Confined space discipline: a set deposit on a silo wall can collapse as a slab.

Where the product contains crystalline silica from the process, the respirable fraction is a regulated exposure and the declaration decides the controls.