Clinker handling: hot, abrasive, unforgiving

Clinker is the one material in a cement plant that has already been through the worst the process can do, and it reaches the handling equipment still carrying most of that energy. It comes out of the cooler as hard nodules with a fines fraction: hot enough to damage a belt, abrasive enough to cut through unlined steel, and chemically ready to react with the first water it meets. The equipment between the cooler and the cement mills is chosen for survival first and cost second.

What is clinker, as a bulk material?

Form

Nodules from a few millimetres to several centimetres with a fines fraction and occasional larger lumps; the crusher at the cooler discharge sets the top size.

Temperature

Commonly in the region of 100–200 °C leaving the cooler, and much hotter during cooler upsets. Design for the upset, not the nominal figure.

Bulk density

Commonly quoted in the region of 1.2–1.5 t/m³ loose. Porosity and fines content vary between kilns, so measure your own.

Abrasiveness

Very high. The clinker minerals are hard and the nodules are angular; every surface the stream slides on is a wear part.

Angle of repose

Indicatively in the 30–40° range when dry; fines and any moisture raise it. Measure it on the clinker you make.

Water

Reacts. Free lime and the clinker minerals hydrate on contact with moisture, forming lumps and crusts and losing reactivity. Storage and transfers must stay dry.

Dust

Alkaline, abrasive and irritant fines, made continuously as the nodules rub together.

What makes clinker so hard on equipment?

Three things arrive together. Heat softens belt covers, expands chains and pans against their clearances and cooks the grease out of bearings. Abrasion removes steel from every surface the stream touches at speed — chute walls, pan edges, bucket lips, liner plates — and fastest where the material is hottest. And the fines find every gap: they pack into chain joints, blind the seals on idlers and pulleys, and settle as a grey layer on every horizontal surface. Any one of these is manageable. The combination is why clinker lines are built from heavier, slower, simpler equipment than the tonnage alone would suggest.

• Cooler upsets — a cooler that loses its bed sends clinker downstream at temperatures the conveyors were not chosen for; the line has to tolerate the upset long enough for the kiln to be brought back.
• Lumps and coating — kiln rings and coating fall off in pieces the discharge crusher may not fully reduce; chutes and elevator boots have to pass them or stop cleanly.
• Fines and moisture — where dust meets condensation or rain it hydrates into a crust that narrows chutes and hoppers over weeks.

Which conveyors survive it?

The pattern in most plants is the same: the hottest, lumpiest duty straight off the cooler goes to a pan or apron conveyor, the vertical lift goes to a chain bucket elevator, and belts appear only once the clinker has cooled and the route is long enough for a belt to pay. The note on centrifugal versus continuous discharge explains why the slow, continuous-discharge chain elevator is the usual choice for clinker.

Belt covers deserve a specific warning. Heat-resistant grades exist, but the rating is for the material temperature at the belt surface under steady running, and a cooler upset can exceed it for long enough to harden and crack the cover. Where a belt runs near the cooler, the temperature interlock upstream is part of the belt specification. Every transfer into and out of these machines is where dust and spillage will be made; the pillar note on transfer point design applies unchanged, with the addition that every impact surface needs a liner and every liner needs a replacement route.

How should clinker be stored?

Clinker goes into silos, into covered halls with a loader or a reclaimer, and into domes; the choice is about volume, footprint and how the reclaim is done. What all three share are problems that come from the material rather than the structure. Filling from height segregates nodules from fines and throws dust, so a distribution device or a lower drop reduces both. Reclaim through a single outlet leaves most of the contents stationary, and stationary clinker with a little moisture hydrates into a crust that breaks away in slabs later. The pillar note on bridging, ratholing and mass flow explains why, and what multiple outlets, steeper cones and liners do about it; for clinker the practical answer is usually several reclaim points, abrasion-resistant liners in the cone, and a fill-and-reclaim regime that turns the contents over.

What do we check on an existing clinker line?

• Liners — thickness at the impact zones of every chute, the elevator boot and the silo cone; holes appear from the inside out, so measure rather than look.
• Chains — elongation and pin wear on pan conveyors and elevators, sprocket tooth profile, and the tension arrangement at the tail.
• Temperature history — what the cooler has actually delivered over the last year, from the logs, against what the belts and bearings were specified for.
• Seals and bearings — grease condition and seal integrity on anything near the cooler; fines in the grease are the beginning of the end.
• The cooler transfer — the crusher discharge chute, the drop height and the spillage under the first conveyor; this is the transfer that fails first.
• Dust — where the grey layer is thickest tells you which hood, seal or filter is not doing its job.
• Hydration — crusts in the silo cone and hopper walls, and lumps arriving at the mill feed.

The data that decides most of this — top size after the crusher, fines fraction, real temperature range, bulk density as stored — is described in the note on the properties that decide the design. Our conveying systems service covers this stretch of a cement line, from cooler to silo to mill feed, and the cement duties in the Flow Finder list the equipment types involved.