Energy consumption in clinker production is rarely reduced by one isolated modification. In this case, a cement producer combined mechanical upgrades with operating and maintenance changes across the full production line. The result was a 2.85 kWh/t reduction in overall specific electricity consumption for clinker production.
The plant operates a Φ3.5 m × 56 m modern dry-process kiln rated at 1,700 t/d. Its raw-material grinding system uses a HRM2800 vertical roller mill, while pulverized coal is prepared in an Φ2.6 m × 7.5 m air-swept coal mill.
Following commissioning in April 2008, the line reduced its overall clinker-production power consumption from 65.32 to 57.90 kWh/t. Further reductions then became difficult. A new optimization program therefore examined the line as an integrated system, focusing on material size, wear condition, feed stability, grinding-media loading, false-air ingress, compressed-air demand and electrical monitoring.
After a kiln upgrade increased output in February 2023, the existing PCF1818 limestone crusher could no longer comfortably meet the production requirement. The grate gap was enlarged from the original 28 mm to 42 mm to raise crusher throughput, but the proportion of limestone at or below 30 mm fell to only 70.1%. When the grate frame was not adjusted promptly or became blocked, lumps of 65 mm or larger could enter the raw mill.
To restore feed-size control, the plant connected an idle 1,000 × 1,200 fine crusher in parallel with the limestone conveying system. The unit had a 110 kW motor and a design capacity of 80 t/h. After the change, the share of feed at or below 30 mm exceeded 92%, averaging 93.9% from April through July 2024, while oversize lumps of 65 mm or more were eliminated from the mill feed.
The HRM2800 originally used high-chromium cast-steel roller tires and grinding-table liners. Once wear reached a defined limit, the components were reversed or rebuilt by offline hardfacing. Reconditioned surfaces required a relatively long run-in period, during which mill output was lower and vibration was higher.
During the overhaul, the plant installed ceramic-composite roller tires and table liners. The new wear surfaces required almost no run-in period. Reported wear fell from 5.0 mm in the 2023 baseline to an average of 1.2 mm from April through July 2024. Because the roller tires and table liners wore more uniformly, mill vibration also decreased. Instantaneous operating current fell from approximately 85-88 A to below 80 A, and the mill ran with little perceptible vibration at site.
Frequent clay bridging and feed interruptions affected both raw-mix chemistry and the power consumption of the raw-grinding process. The problem was aggravated by the humid climate. During off-peak mill hours, the plant modified the clay proportioning bin: the angle between the lower cone and the vertical was reduced from 40° to 21°, the outlet was enlarged from 0.7 m × 0.6 m to 1.0 m × 0.8 m, the inner surface was lined with anti-stick polymer sheets, and three pneumatic flow-aid devices were installed near the discharge opening. These measures sharply reduced blockages and feed interruptions.
The air-swept coal mill performs both grinding and drying. When throughput is low, the first step is to determine which duty is limiting: inadequate grinding is normally reflected in coarse pulverized coal, whereas inadequate drying is reflected in excessive product moisture.
In 2023, the incoming raw coal had relatively high moisture, so drying capacity - not grinding capacity - was the principal bottleneck. Adding more grinding media did not address the cause. At the highest media loading, main-motor energy use reached 445 kWh per operating hour, throughput did not improve, and specific power consumption for coal preparation rose to 37.9 kWh/t.
After the 2024 overhaul, the plant progressively reduced and regraded the media charge. Throughput decreased slightly, but the specific energy requirement fell steadily, reaching 31.50 kWh/t in July 2024. The change illustrates why media loading should be based on the actual grinding-versus-drying constraint rather than increased by default.
Coal-mill operating performance after the grinding-media reduction
| Period | Motor energy (kWh/h) | Throughput (t/h) | Specific power (kWh/t) | Moisture: raw / product (%) | Residue on 0.08 mm (%) |
| 2023 avg. | 402.9 | 15.70 | 35.75 | 11.0 / 2.4 | 3.7 |
| Apr. 2024 | 370.1 | 15.43 | 33.89 | 11.7 / 2.3 | 3.1 |
| May 2024 | 367.0 | 15.27 | 33.79 | 11.8 / 2.4 | 3.0 |
| Jun. 2024 | 354.4 | 15.45 | 32.51 | 11.3 / 2.2 | 3.1 |
| Jul. 2024 | 328.8 | 14.98 | 31.50 | 11.2 / 2.1 | 2.8 |
Grinding-media configuration before and after regrading
| Condition | Chamber | Media load by ball size (mm: t) | Total (t) | Mean ball diameter (mm) | Filling rate (%) |
| Before (2023) | Chamber 1 | 60: 3.5; 50: 4.0; 40: 3.5; 30: 1.9 | 12.9 | 47.1 | 17.5 |
| Before (2023) | Chamber 2 | 30: 5.5; 25: 7.5; 20: 4.0 | 17.0 | 25.4 | 18.4 |
| After (2024) | Chamber 1 | 60: 1.5; 50: 3.0; 40: 3.5; 30: 1.9 | 9.9 | 44.1 | 13.4 |
| After (2024) | Chamber 2 | 30: 3.5; 25: 6.5; 20: 3.0 | 13.0 | 25.2 | 14.1 |
Uncontrolled air ingress increases the load on major fans, including the kiln induced-draft fan, exhaust fan and raw-mill circulating fan. In the raw-mill circuit, the principal leakage points were the inlet airlock, roller access doors and reject discharge.
At the inlet airlock, the installation height was increased and a material buffer plate was added to reduce direct abrasion and maintain a reasonable sealing clearance. Around the roller doors, steel plates narrowed the moving clearances before flexible connections completed the seal. At the reject outlet, two curtains made from reused steel-cord rubber belt were installed 1.5 m apart inside the chute. After these measures, the raw-mill circulating-fan damper opening fell from 100% to 85%, while oxygen at the kiln exhaust-stack outlet decreased from 8.0-8.5% to approximately 7.5%.
For the kiln system, routine inspections targeted preheater access openings, flap valves, grate-cooler access doors and kiln-hood doors with refractory sealing compound or fiber. A purpose-built double seal combining overlapping metal plates and high-temperature fabric was installed between the burner and kiln door and tightened with counterweights. At the kiln-tail connection between the shell and smoke chamber, an additional double flexible seal reduced leakage while allowing axial kiln movement. Kiln ID-fan speed fell from 1,200 to 1,165 r/min, and oxygen at the C1 preheater outlet decreased from a typical 2.8-3.2% to 1.8%.
Compressed air is easy to overlook in clinker-production energy reviews. The plant introduced quarterly compressor maintenance to preserve air-generation efficiency, fine-tuned dust-collector pulse-cleaning parameters, extended the interval between preheater blockage-clearing air blasts, and separated the air supply for the coal mill and conditioning-tower system. Specific electricity consumption for compressed air fell from 2.25 to 1.48 kWh/t of clinker.
In May 2024, the plant added an electricity demand-side service platform at its main step-down substation. The platform provided power analysis, statistical reports, electricity-bill review, monitoring-point configuration and energy-consumption-unit management. This created a stable data foundation for tracking abnormal loads and sustaining the reduction in clinker-production power consumption.
The combined program reduced average overall specific electricity consumption for clinker production to 54.65 kWh/t from April through July 2024, compared with a 2023 baseline of 57.50 kWh/t. This represents a reduction of 2.85 kWh/t, or approximately 5.0%.
Reported site performance before and after the coordinated improvement program
| Metric | Baseline | Post-improvement | Change / operational effect |
| Overall clinker-production power | 57.50 kWh/t | 54.65 kWh/t | -2.85 kWh/t (-5.0%) |
| Limestone ≤30 mm | 70.1% | 93.9% avg. | +23.8 percentage points |
| VRM wear measurement | 5.0 mm | 1.2 mm avg. | -3.8 mm |
| VRM instantaneous current | 85-88 A | <80 A | Lower load and vibration |
| Raw-mill fan damper opening | 100% | 85% | -15 percentage points |
| Kiln exhaust-stack O₂ | 8.2% | 7.5% avg. | -0.7 percentage points |
| C1 preheater outlet O₂ | 3.0% | 1.8% avg. | -1.2 percentage points |
| Compressed-air power | 2.25 kWh/t | 1.48 kWh/t | -0.77 kWh/t |
At an annual clinker output of 660,000 t, the 2.85 kWh/t reduction corresponds to approximately 1.88 million kWh of electricity saved per year. Using the original project assumption of RMB 0.534/kWh before tax, the estimated annual electricity-cost saving was approximately RMB 1.0 million.
The most important lesson is diagnostic discipline. A larger crusher gap may protect throughput but transfer a size problem to the raw mill. More grinding media may appear to increase capacity but can waste power when drying is the real bottleneck. Worn or mismatched grinding surfaces can increase vibration and current. Small air leaks, unstable feeders and poorly managed compressed-air demand can collectively impose a substantial electrical penalty.
Effective clinker-line optimization therefore requires the crusher, raw mill, coal mill, fans, kiln seals and plant utilities to be assessed as one operating system. Measurements should identify the actual constraint before equipment or process settings are changed.
Share your line capacity, equipment models, feed-size distribution, raw-material moisture, product fineness, motor-load trends and recent kWh/t data with SYM. Our engineering team can help identify whether equipment modification, wear-part optimization or operating adjustments are most likely to deliver a measurable return.
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