The cool fix inside scorching cement mills: ultra-fine water sprays and ultra-clean water

Cement grinding is high-energy work; roughly 50–70% of the input energy can become heat in the mill. Without active cooling, mill outlet temperatures can overshoot the process window. Industry guidance targets a cement discharge temperature of about 90–115 °C (Cement Plant Operation Handbook). Below ~90 °C, gypsum added to control setting stays too wet and weakens cement; above ~115–125 °C, gypsum over‑dehydrates and can trigger flash or false set (Handbook) (VEL). One plant report notes that exceeding 125 °C triggers excessive gypsum dehydration and altered setting behavior (VEL).

That’s why modern ball‑mill circuits inject water for evaporative cooling—pacing cement temperature into the 90–120 °C band (VEL) (Handbook). The approach is widespread: Christian Pfeiffer cites more than 100 ball mills worldwide fitted with its INJECTOR water spray system (Christian Pfeiffer). Case studies also show installing a water spray can increase mill capacity by stabilizing temperature—one performance project explicitly added a water spray system to enable higher throughput (Global Cement).

Evaporation as a heat sink

Water injection removes heat via the latent heat of vaporization (energy absorbed when liquid turns to vapor). One analysis determined roughly 2.1×10^3 L/h of water would be needed to hold cement under 115 °C in a typical mill (Scribd report). In practice, injection rates are on the order of a few liters per tonne of cement. As Cohrs emphasizes, even dry‑process plants must use water to cool hot gas streams in mills and pyro‑process stages (CementEquipment). In short, water sprays convert excess grinding energy (heat) into vapor that is swept out of the mill, holding the outlet in the optimal range (Handbook) (VEL).

Water purity and cement chemistry

Because injected water eventually mixes with the cement, water purity is critical. Any minerals or contaminants can accumulate in the cement or on mill internals. Un‑evaporated water can hydrate cement on liners or screens, causing false set or build‑ups (Handbook). Vendors also caution that ventilation air must be ample so no section drops below the dew point (VEL).

Water quality should meet or exceed concrete‑mixing standards. Indonesian SNI 7974:2018 (adopting ASTM C1602) caps mixing‑water impurities: chloride below 500–1000 ppm and sulfate below 3000 ppm (SNI/ASTM). By analogy, cement mill spray water should be at least as clean. Using demineralized or potable‑grade water prevents extra ions from entering the cement; high sulfate or chloride in the water could increase cement SO₃ or Cl⁻ content unexpectedly, and hardness minerals (Ca²⁺, Mg²⁺) can precipitate as scale. In practice, plants often pipe in softened or deionized water for injection. Where hardness is the concern, a softener helps limit Ca²⁺/Mg²⁺ before the spray line.

When low total dissolved solids (TDS) are required, deionization via a demineralizer is a common route, and polishing steps with a mixed‑bed can further minimize residual ions. For systems built on resins, specifying the right ion‑exchange resin protects water quality and the mill from scaling or deposits. If water quality is poor, any residual liquid can react with cement phases (e.g., hydrolyzing C₃A) and degrade downstream performance; injection water must be low in salts and organics, adhering to standards like SNI 7974/ASTM C1602 (SNI/ASTM).

To keep nozzles clear, plants pair clean water with filtration. Magotteaux describes modular systems with filtered pipes; using a cartridge filter upstream of the spray manifold helps keep particles out of small orifices. In higher‑pressure services, stainless steel cartridge housings provide robust containment without contaminating the water.

Atomization and nozzle placement

Effective cooling depends on fine, well‑distributed spray. Nozzles are typically air‑assisted or high‑pressure to create very small droplets. Standard liquid nozzles produce droplets of 300–4000 μm (micrometers), whereas modern pneumatic air‑atomizing nozzles yield 20–100 μm; EXAIR data show air‑atomizing nozzles can produce median diameters as low as 20–50 μm (EXAIR). Turning up air pressure (or turning down liquid pressure) in these nozzles shrinks droplet size (EXAIR). VEL highlights adjustable‑orifice nozzles and compressed‑air‑fed atomizers so the spray can be tuned (VEL).

Placement matters. Common practice is to inject just behind the diaphragm (the internal partition) into the second chamber, where fines generate heat. The Handbook notes: “where maximum cooling is required, the best effect is achieved by spraying at the diaphragm concurrently into the second compartment” (Handbook). Pfeiffer’s Injector system likewise offers an intermediate diaphragm lance for second‑chamber injection and provides multiple versions of the water injection systems (Christian Pfeiffer). Depending on circuit conditions, water can also be fed at the mill inlet or first chamber (Christian Pfeiffer) (Christian Pfeiffer). Magotteaux similarly describes spraying into either the first or second chamber—via inlet, outlet, or diaphragm—depending on mill type (Magotteaux). Multi‑nozzle manifolds or ring nozzles are used so cascading balls and fines are enveloped by spray from all sides.

Controls, enclosures, and purge

Water injection units are typically packaged with pumps, regulators, and controls. Magotteaux’s modular system includes a heated enclosure (to prevent freezing), water tanks, frequency‑controlled pumps, filtered pipes, and one or more spray nozzles directed into the mill; rotary feed‑through seals allow injection into central‑shaft mills without leaking (Magotteaux) (Magotteaux). Precise flow control is achieved by motorized, PLC‑regulated control valves that adjust spray to track mill temperature; when spray is off, compressed air purges the nozzles to keep them clean (VEL).

Ventilation and dew point balance

Spray design must align with mill ventilation. Air flow needs to be high enough—typically ~1–2 m/s in the free cross‑section, up to 5–6 m/s in air‑swept mills—so all injected water vapor is carried out (Handbook). Systems are tuned so added humidity does not condense in ducts or filters; as VEL emphasizes, ensure “the temperature does not drop below the dew point anywhere in the pipes, dedusting filter, etc., after the mill” (VEL).

When the atomization is fine, placement is strategic, water is mineral‑free, and ventilation is balanced, sprays evaporate within the mill heat balance—avoiding cement hydration while maintaining target temperature. The result preserves product quality and can enable higher throughput (Handbook) (VEL). For durable, clean injection water and reliable hardware, supporting equipment—from steel filter housings to upstream resin units—helps hold the line on temperature and purity without introducing new variables into the grind.