Separator Fine-Coarse Recovery Efficiency

 Separator is the most pivotal component of closed-circuit grinding in the cement industry. The basic purpose of a separator in a closed circuit is to avoid over-grinding by removing or separating out the material already ground to product size and returning coarse material for re-grinding. By doing so, a significant slice of energy is saved, which was wasted in an open circuit for over-grinding mill feed to meet the final product fineness specifications. And the mill is made available to receive more fresh feed; therefore, mill capacity is improved for a given L/D, and specific power consumption is reduced in closed circuit grinding compared to open circuit grinding.

Calculation Methodologies

As far as the benefits of closed-circuit grinding are concerned, it depends on the performance and efficiency of the separator. There are two approaches/ways to find the efficiency of your separator in a closed-circuit ball/tube mill.

Fine recovery or Coarse rejection efficiency

And energy-saving efficiency.

In this lesson, the second approach is considered, which in totality is described as under

Energy Saving Approach: The separator should perform to reduce specific energy consumption in closed circuit grinding operation compared to open circuit grinding. In this way, separator efficiency is defined as the percentage of energy saving achieved relative to the maximum energy saving with ideal separation.

FORMULA ON CALCULATOR

Importance for Process Optimization and Energy Saving

  • Reducing Specific Power Consumption (SPC): High-efficiency separators (HES) allow for a narrower particle size distribution (PSD). By increasing Se​, the system avoids the "cushioning effect," where fine particles dampen the impact of grinding media, leading to a 5–10% reduction in total circuit power.
  • Capacity Expansion: Improving separation efficiency can increase mill throughput by up to 30% without requiring additional mill drive power.
  • Managing the "Grace Factor": Optimization involves balancing the mill and separator to ensure the ball charge "half floats" in feed, maximizing impact efficiency.

Industrial Benchmarks and Impact Data

Separation efficiency varies drastically across equipment generations:

Separator Generation

Typical Efficiency (Se​)

Expected Circulating Load

1st Gen (Static/Mechanical)

25% – 40%

200% – 300%

2nd Gen (Whizzer Type)

40% – 60%

200% – 250%

3rd Gen (High Efficiency/HES)

75% – 85%

150% – 200%

Energy Impact Example...

Summary of Important Aspects...

  • The Bypass Penalty...
  • Circulation Link...
  • Quality Lever...
  • Thermal Control...

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