Circuit Dynamics: Mastering Circulating Load (CL%) and Circulation Factor (C)

In closed-circuit ball milling, the relationship between the mill and the separator is defined by how much material is returned for regrinding. Circulating Load (CL%) and the Circulation Factor (C) are the primary metrics used to evaluate the efficiency of this "loop". By returning coarse particles to the mill and removing finished fines, the system prevents overgrinding and optimizes the specific power consumption (SPC).

Definitions and Core Concepts

  • Circulation Factor (C or u): Also known as the recycle ratio, this represents the total number of times a particle passes through the mill before exiting the system. Mathematically, it is the ratio of the total separator feed (A) to the finished product (F).
  • Circulating Load (L or CL%): This is the quantity of separator tailings (rejects) returned to the mill, expressed as a percentage of the original fresh feed.
  • Mass Balance Stability: In a steady-state operation, the tonnage of the fresh feed entering the mill must equal the tonnage of the finished product leaving the separator.
  • Rejects (R): The coarse material that the separator determines is not yet fine enough and returns to the mill inlet.

Calculation Methodologies

There are two primary ways to determine these values, depending on the data available at the plant.

1. Mass Flow Basis (Direct Method) If the plant utilizes weigh feeders for the separator feed or rejects, the calculation is direct:

  • Circulation Factor (u): u=A/F.
  • Circulating Load (CL%): CL%=(R/F)​×100.
  • Mill Discharge (A): A=R+F.

2. Sieve Analysis Basis (Indirect Method) When mass flow meters are unavailable, the circulating load is calculated using the fineness of the three circuit streams (Separator Feed, Fines, and Rejects):

CL%=[(fp​−fa)/(fa​−fr​​​)]×100

Where:

  • fp​: % passing a specific sieve in the finished product.
  • fa​: % passing in the separator feed (mill discharge).
  • fr​: % passing in the separator rejects.

Importance and Process Optimization

  • Preventing Overgrinding...
  • Energy Efficiency...
  • Particle Size Distribution (PSD)...
  • Flexibility...

Typical Data and Benchmarks(table)...

Summary Table...

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