In raw material grinding, a few hundred grams of additive per tonne can reduce kilowatt‑hours and raise output within minutes. The data show consistent 5–15% energy cuts and up to 25% productivity gains.
Cement manufacturing is an electricity guzzler, consuming about 110–130 kWh per tonne of cement, with roughly a quarter of that — around 25–35 kWh/t — spent just on raw material grinding (NBM&CW; PMC). One study pegs a raw mill’s specific energy consumption (SEC) at ~25.5 kWh per tonne of raw feed (ResearchGate), while a survey of Chinese lines (2014–2019) found raw mill energy averaged ≈25.2 kWh/t (MDPI).
At this scale, shaving even ≈0.5 kWh/t matters. That’s why chemical grinding aids — organic agents that disperse particles to stop them sticking — have become a standard lever to raise throughput and pull down kWh/t.
Surface chemistry and mill dynamics
Grinding aids (GAs) are typically organic amines, glycols, phenols and related chemistries. Their core job is surface‑chemical: they adsorb on fresh fracture surfaces, lower particle surface energy, and neutralize surface charges so fines do not re‑agglomerate or coat the media and liners (NBM&CW; NBM&CW). The dispersion effect means more of the mill’s power breaks rock instead of polishing it, fluidizing the charge and typically boosting circulating loads (NBM&CW).
In vertical roller mills (VRMs), lower inter‑particle friction stabilizes the bed, eases de‑aeration, and improves bed permeability — enabling higher feed with lower pressure drop (ΔP) and reduced vibration (Sika). Effects show up fast: once dosing starts, benefits are seen within 10–20 minutes — increased ΔP and sound are quickly eliminated (Sika). In long‑residence ball mills, GAs mainly keep fines from coating the balls, preserving grinding rate as fineness rises (NBM&CW).
Throughput and specific energy gains
Plant trials repeatedly show tangible performance. Typical dosing at ≈0.02–0.05% by mass of feed cuts power draw by 5–12% and raises output by 3–10% in ball‑mill circuits (CementL). VRMs, already efficient, see smaller kWh gains — ≈3–8% reductions — but often larger throughput increases, with reports of “up to 5–15%” (CementL).
Vendors cite “up to 25%” productivity in cement grinding when formulations are properly tuned (Sika). In one pilot VRM test, GA addition raised clinker feed from 123 to ~150 kg/hr (~+22%) and increased product specific surface from 340 to ~388 m²/kg, while vibration fell from ~8.6 to 2.6 mm/s and a pack‑set index (a measure of bed compaction) dropped from ~23 to ~2 (Sika).
Lab work underscores the potential: at 0.06% amine‑ or glycol‑based GA, grind rate jumped, delivering 16–72% higher fineness per unit time versus blanks (ResearchGate). Bench‑scale tests found ~350–460 g/t of GA cut cement grinding SEC from ~27.9 to ~24.4 kWh/t (~10–12% drop) under fixed conditions, and small‑lab trials tend to underestimate full‑scale gains: SEC reduction was roughly twice as large at industrial scale (ResearchGate; ResearchGate).
Summing up the field experience: many plants report ~5–15% energy savings and similar output gains at ≈0.02–0.05% dosage (CementL), while specialized formulations can deliver ~20–25% throughput boosts (Sika; Sika). Dropping a raw mill SEC from ~25.5 to ~23 kWh/t saves ~2.5 kWh/t (~10%) while producing 10–20% more raw meal per hour — and saving even ≈0.5 kWh/t at scale is substantial (ResearchGate). These trends have grown more important as Indonesian and global producers push for lower‑carbon, more efficient operations.
Raw mix dependence and product choice
There is no one‑size‑fits‑all GA. Each plant’s raw mix (limestone hardness, clay content, moisture) and equipment setup differs, so selection is empirical (Sika Indonesia). Screening typically starts with water‑soluble amines, glycol ethers, polyglycol esters, sulfonates and similar chemistries in a small mill on the actual feed (NBM&CW).
Dosage ranges and diminishing returns
Effective dosage is low: 0.01–0.15% of solids by mass is the usual range, with many successful trials at ~0.02–0.05% — about 200–500 g per tonne of feed (ResearchGate; CementL). Some vendor notes cite efficiency at 0.5% dosing (NBM&CW; NBM&CW), but raising above ~0.1% usually shows steeply diminishing returns or quality issues.
Injection hardware and calibration
Grinding aids are typically metered as liquids onto the raw material before it enters the mill — for example, sprayed on the feed belt or bucket elevator (CemMate). Feed temperature should be below ~80 °C to avoid evaporating organics (CemMate). Accurate metering matters: a dedicated dosing pump is set by a simple relation — Qv = (M × q × 1000) / (ρ × 60) — where Qv is the pump flow in mL/min, M is mill feed rate in t/h, q is target dose (%), and ρ is additive density in g/cm³ (CemMate). Large plants often use loss‑in‑weight feeders for continuous dosing (control error <0.1%) (CementL); smaller operations may rely on timed batch pumps. Stable, uniform dosing is critical.
Mill set‑up and steady‑state checks
When a trial begins, other settings stay fixed initially. Run to target fineness or ΔP, let the GA reach steady‑state (VRM effects emerge within ~15 minutes, per Sika), then observe: ΔP and vibration typically drop and allowable feed rises. Separator speed and ventilation are adjusted slowly to hold product quality constant, while power draw and throughput are recorded. Dosing is increased stepwise — e.g., by +0.01–0.02% — until gains plateau or fines/pack‑set issues appear.
Key metrics and product quality
- Throughput (t/h) at fixed mill power or fixed fineness.
- Specific energy (kWh/t): a lower SEC at the same output, or more output at fixed kWh.
- Fineness: maintain sieve/Blaine (Blaine is specific surface area) to avoid masking energy savings by over‑grinding.
- Mill internals: VRM ΔP (bed pressure drop), mill and motor current, vibration, and a pack‑set index (semi‑quantitative bed “stickiness”). GA addition can raise ΔP initially as fines circulate, but at steady control it often allows operation at lower ΔP at the same fineness (Sika). Vibration should drop (as in Sika’s data, Sika), and lower pack‑set is a positive signal.
- Cement quality tests: setting time and strength. GA often improves early strength slightly by increasing surface area and dispersing cement particles, but final properties must be verified (NBM&CW).
Safety and regulatory considerations
Safety Data Sheets govern handling; in Indonesia, chemicals may fall under Hazardous/Poisonous (B3) classifications if flammable or toxic. Proper pumps and ventilation are required; many modern GAs are biodegradable with low volatility, while older amine adducts can be volatile — avoid spraying near hot surfaces. No specific Indonesian law bans cement grinding aids, but plants must comply with emissions and effluent permits.
Plant trials, baseline economics
Case outcomes vary with raw mix and mill. One plant saw ~0.035% of a glycol–amine blend lift raw mill output ~8–10% while cutting kWh/t by ~6% (CementL). Another reported 400 g/t delivering ~12% more throughput and 9% lower energy use (CementL). In small VRM tests, a 0.5% dose produced a 20–25% throughput jump alongside a ~70% vibration reduction (Sika). In all cases, the optimal continuous dose landed far below 0.1% — typically a few hundred grams per tonne.
Implementation framework for managers
- Lab and pilot tests: candidate GAs are screened on the actual raw mix at constant energy or fineness; the steepest grind‑rate vs. dose wins early trials (ResearchGate).
- Dose trial: initial plant injection at ~0.02–0.05% of feed, with pump calibration per Qv = (M × q × 1000) / (ρ × 60) and dose confirmed by sampling (CemMate).
- Observation: throughput, motor load, ΔP, and product Blaine are tracked while separator and ventilation hold quality to baseline.
- Optimization: dose is increased stepwise until gains plateau; typical optima are well below 0.1% (ResearchGate).
- Metrics: a clear energy‑saving case is targeted — for example, original flow and fineness held with 5–10% lower kWh/t — while strength and setting time confirm standards.
- Economic check: net benefit is the saved power and higher clinker production minus additive cost; many plants see payback in weeks or months.
- Documentation: GA brand, dosage, injection point, and measured outcomes are recorded for repeatable optimization.
Across sites, the pattern holds: the right additive at the right dose can raise mill output ~10–25% and cut energy use ~5–15% (Sika; CementL).
Sources and technical basis
Figures and mechanisms cited here draw on authoritative literature and industry data (NBM&CW; PMC; MDPI; Sika; CementL), manufacturer and industry technical reports (NBM&CW; Sika; CementL), and pilot trials (Sika). All figures above are drawn from these peer‑reviewed and industry sources.
