Circulating load closed circuit crushing

What actually circulates in a closed circuit

Circulating load closed circuit crushing starts with separating two flows that arrive at the same chute. In a closed circuit the screen oversize returns to the crusher, so the machine sees more than the fresh feed. That difference is the circulating load, and the total flow into the crusher is fresh feed plus return.

The load is stated as a percentage: returned mass divided by fresh feed, multiplied by one hundred. The ratio is not a defect but part of the design, since the whole purpose of closing the circuit is to guarantee top size. The trouble begins when the ratio grows without anyone watching it.

Measurement: finding the ratio

The most direct route is mass measurement: the tonnage on the return conveyor divided by the fresh feed tonnage. With two belt weighers the ratio can be read straight off the instruments. Without weighers, screen analysis takes over: samples of fresh feed, crusher discharge and screen undersize are taken, and the balance is built by comparing the percentages passing a chosen aperture. The method only means something when several samples are drawn during steady running, never from a single grab in an unsettled shift.

Screen efficiency comes out of the same samples. The common expression is E = β(α − θ) / (α(β − θ)) × 100, where α is the share of material finer than the aperture in the feed, β the same share in the undersize and θ in the oversize. When efficiency drops, material that has already reached product size fails to pass and is sent back to the crusher. This is the most frequent and most wasteful source of circulating load: the machine grinds again what did not need crushing.

Symptom, cause, measurement, action

How excess recirculation eats capacity

A crusher fills against the total flow it receives, not against the fresh feed. As circulating load grows, the share the machine can give to new material shrinks; the plant keeps running while hourly saleable output falls. The same happens on belts and screens: the return line sits permanently at full load, drive components carry material that needed no crushing, and energy per tonne climbs. Wear takes its share too, because every tonne crushed twice tires the jaws, blow bars or mantles one more time.

The settings that rebalance the circuit

There are four levers and their order matters. The screen side is corrected first: correct aperture, proper inclination and even feed spread recover efficiency. The crusher setting is reviewed next and opened so the machine does not manufacture more fines than the product needs. Third, fresh feed rate is matched to the circuit, since overfeeding always accumulates on the return line. Capacity investment comes last: adding screen area or a stage. Reverse this order and new equipment simply repeats the same imbalance at a larger scale. For the stage that sets final product size, the choice of tertiary crusher feeds directly into the recirculation ratio.

Keeping the record

Circulating load is a tracked ratio, not a one-off measurement. Fresh feed, return tonnage, crusher current and product fractions go onto the same shift form. When the ratio drifts upward, the cause is usually gradual wear, and gradual wear is invisible without a time series. The articles under plant efficiency tie these records to shift performance.

Frequently asked questions: circulating load closed circuit crushing

What is the correct circulating load

There is no single correct figure; it depends on circuit design, material and target product. What carries meaning is not the absolute value but its movement over time in one plant.

Should the target be zero recirculation

No. Closing the circuit exists to guarantee top size, and zero return means oversize is escaping through the screen.

Is a belt weigher essential for measurement

Not essential, but fastest. Without one, the balance is built from screen analysis, which is slower and must be repeated under steady operating conditions.