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Mill Ventilation

How fast the gas is actually moving through your mill. Too slow and the ground material never leaves — it stays in, gets over-ground and coats the balls. Too fast and you blow coarse material out before it is finished. The balls take up most of the cross-section, so the speed depends on how full each chamber is, not just on the fan. Press MEASUREMENTS to type your mill in.

Why this matters now

Clinker reduction, high electricity prices and tighter cement specifications put the grinding circuit under pressure. The fastest gains usually come from finding the real constraint before changing equipment or operation.

What this tool helps decide

Check whether gas actually sweeps the mill and whether diaphragm area or false air is limiting drying, transport and separator performance.

What subscription adds

Build a connected grinding audit: save every mill separately, reload previous measurements, compare changes over time and issue an editable report for the plant team.

Connected to the industry conversation around clinker-factor reduction, grinding energy, blended cement and quality control reported in World Cement, CemNet and Global Cement.See process-tool plans

Gas through your mill

Shared with your other tools. Diameter, chamber lengths and tape readings are remembered in this browser, so this tool and the volume loading tool always describe the same mill.

The mill

Mill inside diameter Inside the lining, in metres.

First chamber lengthMetres.

First chamber — distance down to the balls Millimetres, from the lining at the top to the top of the balls.

Second chamber lengthMetres.

Second chamber — distance down to the balls Millimetres.

The gas

Gas flow leaving the mill Cubic metres per hour, including any auxiliary dust collection.

False air to add Per cent. Leave at 0 if your measured flow is taken at the mill outlet and already includes the leaks. Only raise it if you measured before them.

Ball charge swell Per cent. The charge lifts and expands when the mill turns. Typically 3 to 5.

Diaphragms and output

Intermediate diaphragm open area Per cent of the mill cross-section that is actually slot.

Outlet diaphragm open areaPer cent.

Cement leaving the mill Tonnes per hour, for the air-per-tonne figure.

SPACE THE GAS HAS TO PASS THROUGH

HOW FAST IT IS MOVING

C1 free area

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C2 free area

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C1 how full

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C2 how full

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C1 gas speed

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C2 gas speed

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Mill average

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Gas flow used

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Int. diaphragm speed

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Outlet diaphragm speed

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Air per tonne of cement

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Verdict

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What this means for your mill

The speed depends on the charge

Half of this calculation is how full the mill is. If the tape reading is wrong, the gas speed is wrong with it.

Re-check the charge

How the numbers are worked out

Free area. π/4 × D² × (1 − (how full + swell)/100) — the mill cross-section minus what the balls occupy. The charge lifts and expands when the mill turns, which is what the swell allows for.

Gas speed. flow ÷ 3600 ÷ free area. Straight from your own mill-sweep.js, with the same 1.0 to 1.5 m/s band.

Run twice, once per chamber. Your file uses one loading figure for the whole mill. The same gas goes through both chambers, but each leaves a different area free above its own charge, so the speed differs. The mill average is weighted by chamber length.

Diaphragm speed is flow divided by open slot area — the definition of velocity, not a model. There is no fitted coefficient anywhere in this tool.