Quarry Comminution & PGNAA

Before raw milling can homogenize the mix, the quarry must reduce meter-scale boulders to centimeter-scale crusher product. This comminution chain — drilling, blasting, primary crushing, secondary crushing — is the first and most energy-intensive stage of size reduction in the cement plant.

Bench drilling uses rotary or down-the-hole (DTH) drills to create a grid of boreholes, typically 100–200mm diameter and 10–15m deep. ANFO (Ammonium Nitrate / Fuel Oil) is the standard blasting agent — cheap, safe to handle, and energy-dense at ~3.7 MJ/kg.

Blast design controls fragmentation size distribution. Over-blasting creates excessive fines (wasting energy); under-blasting leaves boulders that choke the primary crusher. Modern quarries use electronic delay detonators to optimize fragmentation and minimize vibration.

Gyratory crushers handle the largest feed (up to 1.5m) with continuous compressive action — the mantle oscillates against a concave bowl, breaking rock by compression. Jaw crushers use a periodic toggle action, ideal for smaller throughput or harder rock.

Primary crushers reduce run-of-mine limestone from ~1m to ~100–150mm. The product is then conveyed to secondary crushing or directly to the raw mill feed stockpile.

Impact crushers use high-speed rotors with blow bars to shatter rock by impact — ideal for softer limestone and producing cubical product. Cone crushers compress rock between a mantle and concave, better for harder, abrasive materials.

Secondary product target: 80% passing 25mm, ready for raw mill grinding.

Prompt Gamma Neutron Activation Analysis (PGNAA) analyzers sit on the conveyor belt between the crusher and the raw mill. A californium-252 or neutron generator bombards the material with neutrons. The rock's atomic nuclei absorb neutrons and emit characteristic gamma rays, which the analyzer reads to determine the elemental composition in real time.

Unlike X-ray fluorescence (XRF), which analyzes a small lab sample, PGNAA reads the entire material flow on the belt — providing continuous, representative chemistry data. This feeds the raw mix control system, which adjusts feeder proportions to maintain target oxide ratios.