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58 E&MJ • MARCH 2017 www.e-mj.com PROCESSING SOLUTIONS Minerals processing plants typically use grinding mills in closed circuit with hy- drocyclones to produce a product with a specifi c particle size distribution for opti- mum downstream process recovery. Exist- ing instrumentation that provides particle size measurement is considered standard in most modern concentrator plants. However, instrumentation availability is often very low, mainly owing to high main- tenance requirements of the analyzer and associated sampling system. A novel and robust technology has been developed that provides a high- ly reliable and low maintenance system for online measurement of the particle size in the overfl ow of individual cy- clones. The system is based around a wetted sensor design with no moving parts and provides a real-time trend of the desired target grind size parameter, such as a percentage retained on screen (e.g., % +100 mesh). The system does not require sampling and associated sample transfer piping that is prone to plugging, thus avoiding high mainten- ance requirements. The CYCLONEtrac Part Size Tracking (PST) system differs from the traditional particle size measurement approach in a number of ways. Table 1 outlines some of the key differences between the available technologies used for particle size mea- surement in comminution circuits. It was developed to bring a particle size measurement solution to comminu- tion circuits. A demonstrated combina- tion of high online availability and fast update rate enable closed loop control of the circuit product. Benefi ts of Controlling Particle Size The particle size of the product stream from the grinding circuit is a critical key performance indicator (KPI) because it is directly linked to the mineral recov- ery, grinding effi ciency and overall plant throughput. There exists a trade-off be- tween the circuit input (i.e., fresh feed or throughput) and the circuit product (i.e., cyclone overfl ow particle size). With the development of PST comes the commercial availability of a robust on- line particle size measurement allowing for the development and optimization of particle size control schemes that can take advantage of this trade-off within the circuit constraints. A large concentrator recently devel- oped a new multivariable control scheme using PST. Grinding effi ciency is main- tained by holding the particle size and ball mill power within a desired range through manipulation of the cyclone feed percent solids. Figure 1 shows an example of the vari- ables under control and their set points/ targets. A recent paper* describes the case study and control in more details. Using a PST-based control scheme, the operation was able to demonstrate: • Up to a 4.5% reduction in particle size at the same throughput. Particle Size Tracking System vs. Traditional Measurement Techniques By Dylan Cirulis Table 1—Particle Size Measurement Technology Comparison Feature CYCLONEtrac PST Traditional Consolidated Laboratory Sieving Cyclone Overfl ow Measurement Systems Using Calipers, Ultrasonics, or Laser Diffraction Update Rate 4 seconds 3-9 minutes Typically 2 hours with 12-24 hours latency Enables Sustainable Yes No, (typically limited by system No Closed Loop Control availability and data latency) Full Stream Analysis Yes No No Sampler Free Yes No Yes Availability >98% Typically low, with exceptions High Number of Particle Sizes The one key particle size Multiple b Multiple b Reported a needed for control. (2 or more possible in future) Calibration Frequency One time Continuous N/A Performance Monitoring of Yes No Possible but not typical Individual Hydrocyclones Notes: a. The majority of control systems today utilize only one particle size as an input. b. Multiple sizes typically include one size reported to the control system, the rest for general reporting and process monitoring.