How to Configure a Cement Grinding System: Vertical Roller Mill vs Ball Mill with Roller Press

The grinding system is the power black hole of a cement plant — in industry experience the grinding steps (raw meal plus cement) typically take around sixty percent of overall specific power, and cement grinding is the larger share. So the first decision in designing a grinding station is not which brand of mill, but which technical route: closed-circuit ball milling, roller press plus ball mill combined grinding, or vertical roller mill finish grinding. After 40 years serving the cement industry since the 1980s, the lesson at Grand Heavy is that pick the wrong route and every later optimisation pays interest on that mistake; pick the right route and ordinary equipment runs great numbers. This guide sets out the boundaries of the three routes, one decision table, and the classic lesson of a small station chasing a vertical mill it could not justify.

Photo: wear castings — rollers, liners and media for grinding systems, judged by cost per tonne

I. The Three Main Routes: Structure and Boundaries

Route 1: ball mill closed circuit (tube mill + high-efficiency separator)

• System: tube mill (multi-chamber, diaphragms + liners + graded media) + high-efficiency separator (vortex or combined) + elevator + pneumatic conveying or air slides;
• Strengths: a century of validation, wide material tolerance, every maintenance team knows it, cement particle shape close to spherical (water demand friendly); media grading is the soft optimisation lever — see the grinding ball selection guide;
• Boundary: the crushing mechanism sets a floor on power — material is lifted and dropped countless times, a high share of wasted work, system specific power clearly higher (industry experience range; calibrate on site); noisy, large footprint.

Route 2: roller press + ball mill combined grinding

• System: roller press (high-pressure inter-particle crushing) + disagglomerating or V-selectors + ball mill (finish) + high-efficiency separator; by how the work is split there are pre-grinding, mixed, combined and semi-finish modes;
• Strengths: inter-particle crushing is far more efficient than ball mill tumbling — the hard coarse work goes to the press, the mill only polishes, system power drops markedly; existing ball mills are reused, retrofit investment far below a full vertical mill line;
• Boundary: the roller surface (tyre) and side plates are the core wear parts — their life and upkeep directly decide system availability; a failed roller surface stops the heart of the system.

Route 3: vertical roller mill finish grinding

• System: vertical roller mill (rollers + table + hydraulic loading) + integral separator + dust collection, drying, grinding, classifying and conveying in one machine;
• Strengths: bed grinding plus negative-pressure operation gives the lowest power of the three; strong drying (handles wet supplementary materials), small footprint, low noise, short flowsheet;
• Boundary: high upfront investment; roller tyres and table liners are high-value wear parts whose life tracks material abrasiveness (see the VRM roller guide); hydraulic maintenance demands are higher than a ball mill; at small scale the investment per tonne turns ugly.

Common disciplines: on any route, feed stability (size, moisture, tonnage — conveying reference in feeder and conveyor selection) and separator efficiency (return fineness, stable product specific surface) are the shared lifelines. Mill selection logic is covered in the grinding mill comparison guide; classification discipline for ore circuits in grinding circuit configuration.

Photo: VRM roller tyre inspection — the tyre life ledger is the second battlefield of grinding cost

II. A Field Lesson: The Small Station That Chased a Vertical Mill

A cement grinding station in the hundreds of thousands of tonnes per year came to consult: two tube mills in closed circuit, specific power on the high side. The owner had toured the new vertical mill finish-grinding line of a large plant and came back wanting a full conversion. We ran the four-factor check:

• 1. Metered system power audit: main drive, fans, separator, elevator and conveying all metered — a sizeable share of the high power turned out to be uncontrolled separator returns plus high in-mill ventilation resistance, not route at all;
• 2. Payback arithmetic: a full vertical mill line (civil works, dust collection, electrics) costs heavily, while the absolute power saving at the scale of this station was modest — payback far beyond normal equipment renewal cycles; financially untenable;
• 3. Material structure: supplementary materials were mostly dry fly ash, little slag and not very wet — the strongest card of the vertical mill, drying, was essentially unused; paying full price for an advantage you cannot use;
• 4. Existing assets: both tube mills were in good condition — scrapping them was a waste, and they are the ready-made finish stage of a combined grinding route.

Conclusion: the right answer was not a vertical mill but a roller press pre-grinding retrofit. Result: the existing ball mills stayed as the finish stage, a roller press plus V-selector took the coarse work up front, system specific power fell close to vertical-mill territory, investment was a fraction of a full conversion, and payback ran about a year. Separator return control and in-mill ventilation were fixed in the same campaign, removing that non-route share of the bill.

The mirror case is just as real: a large station burning plenty of wet slag that, to save capital, insisted on ball mill closed circuit plus a dryer — the drying step became the new bottleneck and power and heat both suffered. So the lesson stated in full: routes have no good or bad — once scale, supplementary moisture, power price and existing assets are fixed, the answer surfaces by itself.

III. Route Decision Tables (Save These)

Table 1: the three routes compared

Table 2: four-factor route decision

Table 3: common configuration errors

How to account for wear parts in total is covered in limestone wear parts cost optimisation — the cost-per-tonne-not-price discipline applies fully to grinding systems.

IV. Insider Gotchas

• System power swapped for main-drive power: fans, separators, elevators and conveying are all big consumers — comparison must use kWh/t system values; the nameplate is one slice of it;
• The neighbour test: their scale, blend, power price and legacy assets differ from yours — route decisions are calculated, not copied;
• Roller surface upkeep is the lifeline of combined grinding: press efficiency decays gradually; without metering and accounting you will not see it — surface profile belongs on the check sheet;
• Cheap VRM tyre trap: same-size tyres differ in price by tens of percent and even more in life — judge by yuan per tonne of product, verify material reports on receipt;
• Specific surface superstition: higher surface does not equal better strength — particle size distribution (the 3 to 32 micron fraction) is the core; excess fines push water demand up;
• Drying sized on annual average moisture: check capacity against the blend of the wettest month — the rainy season is the real test;
• High in-mill temperature met with more air and water spray: check media grading and material flow through chambers first; symptomatic fixes spiral.

V. When Not to Touch the Route

• System power already near industry-best: if the numbers are healthy, leave it — but confirm the basis first (system vs main drive);
• A media regrading or liner change: that is operation optimisation and maintenance, not route selection;
• Low power price + small scale + dry blend: the absolute saving is small and payback too long — doing nothing is optimal;
• But re-decide when: power price rises sharply, the blend shifts to wet slag, capacity must step up, ball mills reach end of life, or the product mix shifts toward high-blend cements.

Three actions: 1. Run a metered system power audit (sub-metering of drives, fans, separators, conveying) to establish the true baseline; 2. Run the four-factor decision table (scale / supplementary moisture / power price / existing assets); 3. Build the wear part cost-per-tonne ledger — on every route, tyres, liners and media are the second battlefield of grinding cost.

FAQ

• Q: VRM finish grinding has the lowest power — should everyone go vertical? A: No. The advantage must be amortised by scale — at small scale the payback rarely closes; and with mostly dry fly ash the drying advantage goes unused. Decide with the four factors (scale / supplementary moisture / power price / existing assets).
• Q: I have existing ball mills — how do I cut power and raise output? A: If mill condition is good, a roller press pre-grinding or combined grinding retrofit comes first — keep the mill as finish stage, let the press take the coarse work; investment is a fraction of full replacement with short payback. If the mills are end-of-life, re-decide as a new build.
• Q: Is there still room in ball mill closed circuits? A: Yes. Media grading, chamber internals (liner forms, diaphragms), separator efficiency (return control) and in-mill ventilation, all optimised together, still squeeze power out of a ball mill — but the mechanism sets a floor below the other two routes.
• Q: What to watch after a roller press retrofit? A: The roller surface and side plates are the lifeline — surface profile on periodic inspection, overlay repair on wear schedule; the disagglomerator or V-selector state directly decides feed-size stability to the mill and belongs on the same checklist.
• Q: How to buy VRM tyres without being burned? A: Judge by cost per tonne of product, never price alone — a cheap tyre with half the life costs far more in unplanned downtime; verify material certificates on receipt and keep a life ledger. Details in the VRM roller guide.
• Q: Is higher specific surface always better cement? A: No. Strength depends on particle size distribution (the 3 to 32 micron fraction is core); chasing surface alone just over-grinds — power up, water demand up, blend space squeezed.
• Q: Wet supplementary materials but no appetite for a vertical mill? A: There is a ladder: external drying (dryer or dryer-crusher), separate weighing of wet and dry streams into the mill, capacity checked against the wettest month. But with heavy sustained wet slag, separate slag grinding (VRM) plus blending is usually the better answer.
• Q: What does Grand Heavy offer for grinding systems? A: Grand Heavy supplies ball mill liners and media, VRM tyres and table liners, roller press surface overlay repair and whole-line configuration advice — a supplier in the systems of CNBM and Conch Cement, with cost-per-tonne life ledger service as our signature.

VII. Final Verdict

Cement grinding route selection comes down to one phrase: routes have no good or bad, only fit — once scale, supplementary moisture, power price and existing assets are fixed, the answer surfaces by itself. Three disciplines: 1. compare in system kWh/t, never nameplate power; 2. existing ball mills deserve a roller press combined grinding look before any full replacement; 3. judge wear parts by cost per tonne of product and keep life ledgers on roller surfaces and tyres. Foshan Grand Heavy Trading Co., Ltd. has built mining and cement wear parts expertise for 40+ years, holds 20+ patents, partners with Central South University and Guangdong University of Technology, and is certified as a National High-Tech Enterprise [To be added: certificate number]. We serve CNBM, Conch Cement and clients across 6 overseas markets with 24-hour response from Guangzhou, Foshan and Changsha. Send your scale, blend structure, power price and equipment list for a route-match assessment.

Grand Heavy — Routes have no good or bad; the four factors decide!