Advanced fine-particle gravity separation

The RC combines a conventional fluidised bed separator with a set of parallel inclined plates that form lamella channels. The feed slurry enters the RC below the lamella plates via internal feed chambers located in the lamella chamber. As the fluidised bed builds up in the mixing chamber below the feed chambers, material with a higher density than the bed will sink, whereas a material with a lower density than the bed will float.

At the bottom of the mixing chamber, as a higher-density bed of settling solids forms, jets of incoming fluidisation water keeps it in suspension. Two pressure probes in the mixing chamber’s lower/middle section are used to calculate the fluidised bed density. The RC uses the relative density of the fluidised bed between the two probes to determine the discharge rate of the high-density solids via a single central underflow valve. The underflow contains high-density particles, and is generally coarser than the feed. 

At the same time, the coarse and fine low-density particles that may have been trapped in the dense fluidised bed will rise due to their density differential, and eventually migrate to the lamella section of the classifier.

The low-density and fine particles tend to overflow from the RC lamellas in their first pass, along with the majority of the process water and any slimes. Fine heavy particles in suspension below the lamella section form an autogenous dense medium, this medium aids with the separation of the slightly denser and larger particles encountered within the vessel, enabling them to rise and be displaced to overflow. The internal launders at the top of the RC direct the overflow slurry into a single discharge “overflow” collector. The lamella channels enhance the settling rate of any misplaced fine, high-density particles, which slide down the plates and slowly re-circulate back into the autogenous zone of the mixing chamber.

The RC is a volumetric machine, feed and fluidisation volume control are critical for the efficient operation of the machine.   

The newly designed HC series REFLUX Classifiers incorporate the following enhancements: 

• Increased lamella chamber open area which results in increased unit capacity
• Cartridge-style lamella plates, for improved stiffness and maintainability
• Straight lead-in to lamellas for improved slurry distribution
• External feed box, housing oversize protection screens
• Inspection windows and hinged access hatch for easier oversize protection screen removal
• Feed enters below lamellas for improved solids distribution and reduced wear
• Stepped feed pipe for improved feed distribution. Pipe sizing is application specific ensuring optimal feed velocities
• The hydraulics of all unit designs have been thoroughly modelled using global CFD experts 
• Lamella plate spacing from 3 mm to 18 mm to suit specific applications 

Horizontal feed system

The feed slurry enters the classifier below the lamella plates via internal feed pipes. As the fluidised bed builds up below the feed chambers, material with a higher density than the bed will sink, whereas a material with a lower density than the bed will float. 

Pressure probes

Generally two pressure probes measure the density of the mixing chamber’s lower/middle section. Alternately, load cells can be used in specific applications instead of pressure probes. The classifier uses the relative density of the fluidised bed between the two probes to determine the discharge rate of the high-density solids via a single central underflow valve.  

Automated underflow valve

The automated underflow valve is manufactured from highly wear-resistant ceramics and materials that are ideal for reducing wear. The underflow typically will discharge into a collection tundish or launder (supplied by others). Units can also be fitted with pinch valves for specific applications.  

Parallel inclined lamella plates

As the high-hydraulic load carries the smaller/lighter particles in the suspension up into the parallel inclined lamella plates, slower-settling particles, (which are unable to settle in the flow) emerge through the lamella plates and report to the overflow. Faster-settling particles drop out of suspension and onto the plates before sliding back to the zone below.

Internal launders

Internal launders at the top of the classifier direct the overflow slurry, containing most of the process water, the low-density solids and any misplaced slimes in the feed, into a single discharge “overflow” collector.

Safety

We engineered the RC to comply with global standards, using Finite Element Analysis on each section to ensure that our design is within allowable limits. Each section of the machine incorporates Rated Lifting Lugs for lifting each section individually, or to lift the entire machine into the plant.

The pressurised fluidising chamber incorporates a stainless-steel pressure relief valve to ensure the fluidising chamber cannot be over-pressurised. A pressure indicator allows the operator to monitor the fluidising chamber pressure from the control room. An automatic pressure relief system incorporating a knife gate valve is also now installed and can operate to relieve the fluidisation chamber before the maximum pressure is reached. 

All moving components are covered by highly visible guards with ISO-compliant warning labels. All guarding is designed to allow easy removal and installation for maintenance.

Quality

The RC is manufactured from high-quality 316 stainless steel, which provides a superior corrosion protection. The outside of the machine is painted with a high-build epoxy coating to provide additional corrosion protection. All joints are sealed with a high-quality elastic joint sealant to ensure leak-free operation. All RC units are preassembled in our FLSmidth factory and leak tested prior to delivery.

Productivity

The RC will significantly improve your plant productivity through recovery of fine material using new technology never before seen in the mining industry. The smaller installation footprint allows installation of the RC in tight spaces within existing plants. The classifier uses minimal power and water and provides efficient recovery of previously wasted material. All components in the RC are designed to minimise wear and reduce maintenance.