Evaporative water injection keeps mill temperatures in the sweet spot, but only if the spray is ultra‑pure. Grinding aids then take the heat off further by lifting efficiency and shortening residence time.
Most of the electrical energy fed to cement mills turns into heat. Left unchecked, that heat dehydrates gypsum and shifts cement chemistry, degrading performance (christianpfeiffer.com) (ftr.com.tr). So plants install water injection systems—sprays that evaporate on contact—to pull temperatures back into the safe zone.
Suppliers frame it simply: in ball mills and VRMs (vertical roller mills), water injection is “the easiest and most effective way” to control temperature because grinding “converts a high percentage” of power into heat (christianpfeiffer.com). Nozzles—often at the mill inlet, outlet, or intermediate diaphragm—inject a controlled flow that evaporates instantly, absorbing heat and holding the outlet at a preset target (magotteaux.com).
Metering matters. Plants typically meter spray with a dedicated control skid; pairing the skid with an accurate dosing pump helps maintain the target flow and steady mill outlet temperature.
Evaporative cooling parameters and limits
In practice, water injection keeps mill outlet temperature around ≈90–120 °C so gypsum remains stable. Above ~125 °C, gypsum starts to dehydrate and cement characteristics change; below ~90 °C, product can become too wet and sticky (ftr.com.tr).
Flows are small relative to throughput. Guidance for a multi‑chamber mill suggests limiting spray to ~3% of fresh feed—about ~1% in the first chamber and 2% in the second—to avoid over‑saturation (scribd.com). One case‑study design calculated a ~2,100 L/h spray rate to hold the outlet below 115 °C (pdfcoffee.com). Systems such as Magotteaux’s MillCool run this control automatically to a preset temperature (magotteaux.com).
There’s a downstream bonus. Evaporative cooling lowers gas temperature, shrinking gas volume and reducing the load on ID fans (induced‑draft fans) and dust collectors (worldcement.com).
Ultra‑pure water as a process requirement
Industry practice is unequivocal: use only deionized or demineralized water for injection, because any dissolved salts or metals in the spray end up inside the cement. Even traces of chloride or sulfate in mixing water can later nucleate harmful phases or accelerate steel corrosion; concrete mixing‑water standards (ASTM C1602) explicitly limit chloride, sulfate, alkalis, and total dissolved solids (TDS, a measure of dissolved ions) (m.wje.com). One reference notes that mixing‑water chloride should not exceed ~0.3–1.0% of cement mass in ordinary reinforced concrete, with much lower limits in prestressed concrete (globalspec.com).
By analogy, plants treat spray water to very low conductivity, with heavy‑metal ions essentially zero. Indonesian cement plants often rely on reverse‑osmosis or demineralization to produce <500 mg/L TDS (and typically ≪100 mg/L) for critical uses (scribd.com). An RO train such as a brackish‑water RO system is commonly paired with high‑purity distribution where needed.
Demineralized water production is also standard; a packaged demineralizer can provide low‑TDS water when RO brine or source quality makes ion exchange economical. Plants often polish permeate for critical points with a mixed‑bed unit to reach ultra‑low residual ions before injection.
A case in point: Holcim’s Cilacap plant filters river and seawater via RO; the resulting fresh water—about 40% yield—has TDS <500 ppm and is used for process cooling and even potable needs (scribd.com). This illustrates the effort taken to supply ultra‑clean water across a site, often via integrated membrane systems scaled for industrial duty.
The water balance also has a local dimension. Indocement reports its new Pati plant in Java will add more than 600,000 m³/year of storage through reservoirs and flood capture, bringing total local capacity to roughly ~2.1 Mm³—ensuring reliable availability for small, high‑quality process uses without depleting community water (kalbar.antaranews.com).
The bottom line on purity is explicit: only high‑purity water should be sprayed into mills—small impurities (chlorides, sulfates, heavy metals, etc.) can measurably weaken cement. Studies show saline mixing water can cut concrete strength by 10–30% depending on salt level (pdfyar.com), so injection water must meet or exceed potable‑quality standards (often better than municipal water).
Grinding aids as a temperature lever
Grinding aids (GAs—chemical additives dosed onto clinker) control temperature indirectly by boosting grinding efficiency. These polar organics—amines, glycols, and related molecules—adsorb on fresh particle surfaces, neutralizing electrostatic charges and preventing agglomeration (nbmcw.com). The result: higher circulating load and throughput for the same power, shorter residence time, and less total heat build‑up.
Output gains are material. One supplier cites production increases “up to 25%” with appropriate GAs (khm.sika.com). In VRMs, tailored GA formulations have enabled tests with higher capacity and noticeably reduced vibrations and classifier pressure drop, ΔP_mill (mill pressure drop) (globalcement.com) (globalcement.com).
In one such test at ~4,100 cm²/g Blaine (a cement fineness measure), dosing a new GA produced “remarkable” reductions in required water injection and mill vibration (globalcement.com). Lab and pilot work echo the scale: adding just 0.5% GA by clinker weight yielded “remarkable” efficiency gains in a pilot mill (nbmcw.com).
Dietrich (2018) reported a modified VRM circuit with GA that cut specific energy and ΔP_mill; Table 3 summarized the effect: compared to a blank test, the GA case delivered higher production, lower required water addition, and lower mill power draw (globalcement.com). Plants typically meter such additives with precise skids; a compact dosing pump simplifies accurate GA delivery to the feed chute or mill table.
The operational implication follows: investing in high‑performance GAs can reduce reliance on water cooling—cutting frictional heat at the source and allowing lower spray rates, sometimes eliminating spray in specific circuits (khm.sika.com) (globalcement.com). In Indonesian plants (as globally), this supports product quality while saving on water processing. For context, a typical Indonesian cement requires <800 mg/L chloride in the final cement for durability; minimizing any chloride intake via injection helps ensure compliance without costly desiccants (globalspec.com).
Operating recipe and outcomes
The combined playbook is straightforward: run minimal, high‑grade water spray to hold the mill outlet in the 90–120 °C band while preserving gypsum stability (christianpfeiffer.com) (ftr.com.tr), and deploy targeted grinding aids to lift output by 10–25% while cutting energy and residence time—lowering the need for sprays (khm.sika.com) (globalcement.com).
Making that work hinges on the water plant. Producing a small but steady stream of ultra‑pure injection water—via RO and demineralization—keeps contaminants out of the cement matrix while stabilizing mill thermals, a task well suited to modular RO, NF, and UF membrane systems integrated with site utilities.
