Material
Hydrated Lime
Answer in brief
Hydrated lime is cohesive, light and caustic, and it rewards every design shortcut with a blocked outlet.
It bridges over small openings, coats walls, and reacts with carbon dioxide and moisture from the air it is stored with.
- Give it a generously sized outlet and a mechanical discharge aid.
- Keep storage air dry and the silo sealed.
- Protect operators, because the dust is alkaline and damages eyes and skin.
Reviewed October 21, 2026 · Updated October 21, 2026
Handling challenges
Hydrated lime is cheap to buy and expensive to handle badly.
It is one of the most cohesive bulk powders in common industrial use, and plants that size its silo like a sand silo find out quickly.
Flow behavior
Low bulk density, fine particles and a plate-like shape give the powder high internal friction and a strong tendency to arch.
- Outlet diameters derived from measured flow function, usually much larger than intuition suggests.
- Mechanical discharge aids such as bin activators or screw dischargers rather than vibration alone.
- Steep, smooth hopper walls with a liner selected from measured wall friction.
Air cannon and vibration retrofits are common, and they are usually evidence that the outlet was undersized from the start.
Carbonation and set
Calcium hydroxide reacts with carbon dioxide and water vapour, and the product is a hard deposit on silo walls and in the filter.
Sealed silos, dried venting air and a filter cleaning regime that actually removes the cake keep this from becoming a demolition job.
Feeding into a process
Flue gas treatment and water treatment both need a stable feed rate, and a cohesive powder makes that harder than the controller suggests.
Loss-in-weight feeding with a properly conditioned inlet, short residence time and flexible connections that do not transmit vibration gives repeatable dosing.
Operator protection
Alkaline dust causes eye and skin injury and irritates airways, so enclosure, local extraction and personal protection are specified together rather than one substituting for another.
What to establish before buying equipment
- Flow function and wall friction measured on the delivered grade.
- Bulk density range from aerated delivery to consolidated storage.
- Expected storage time, which drives the carbonation case.
- Required dosing accuracy and turndown at the process.
Material behavior
- Flowability
- Poor, cohesive
- Abrasiveness
- Low to moderate
- Cohesiveness
- High; arches over small outlets
- Moisture behavior
- Reacts with moisture and carbon dioxide, forming hard deposits
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