Met Dynamic - Dynamic Example Projects

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Dynamic Grinding Example

Project Location

..\SysCADXXX\ExamplesDynamic\MetDynamics - Grinding Example.spf

Available from Build 139.36389. Updated in Build139.37069.

Features Demonstrated

1. The use of Met Dynamics - Crusher
2. The use of Met Dynamics - Mill
3. The use of Met Dynamics - Screen
4. The use of Met Dynamics - Hydrocyclone
5. The use of Met Dynamics - Pump

Brief Project Description

The project shows the dynamic simulation of a three-stage grinding circuit which consists of:

• Primary grinding with a Semi-Autogenous (SAG) mill, wet vibrating screen, and pebble crusher in closed circuit
• Secondary grinding with a ball mill and hydrocyclones in closed circuit
• Tertiary grinding with a stirred mill and hydrocyclones in closed circuit

Solids in the circuit feed are represented by species designated as HardOre and SoftOre to demonstrate the impacts of ore blending on simulated plant performance. Different hardness properties are applied to each solid species at the mills.

A Profile unit model is used to change the hard-soft ore blend and the overall solids and liquids feed rates as simulated time progresses. This introduces disturbances into the circuit which the unit operations and control system must manage.

The SAG, ball and stirred mill models are configured in dynamic mode, which maintains transient solids and liquids inventories in the mill load. Grinding performance and residence time delays are automatically computed as the composition of the mill load changes.

A load-based screen model recycles SAG mill scats to pebble crushing. The efficiency of separation at the screen is determined by the screen's physical configuration and the feed rate of mill pebbles.

Hydrocyclone models are actuated into on-off states and the resulting pressure drop across a cluster is continuously calculated for the changing feed rate and composition.

Centrifugal slurry pump models are used to determine the volumetric flow rate discharging from sumps based on vendor pump curves, impeller rotational speeds and slurry properties.

Tanks configured in Layered mode are used to simulate transport delays arising from piping systems of variable diameter and length. These delays can impact process control responses.

Transmitter unit models are used to simulate process instrumentation such as level, flow and density meters. First order filters are applied to limit signal noise and smooth controller responses, similarly to operating plants.

A system of PID controllers is used to manage mill load/power, water addition, bin and sump levels, flow rates, and cyclone feed pulp densities by adjusting feeder and pump speeds, mill speeds, and water addition rates. Cascade PID control is applied in some cases.

In particular:

• The Crushed Ore Stockpile reclaim rate is controlled to achieve a SAG mill load set point.
• SAG mill rotational speed is controlled by a combination of targeted mill power draw and media trajectory impact position.
• The pebble crusher is operated in maximum-power mode, whereby the crusher feed bin is completely emptied at full crusher rate, before being refilled while the crusher idles. The on-off pebble crushing introduces a step-change disruption to the SAG mill load, which must be managed by the control system.

Two General Controller unit models perform a number of process control logic and instrumentation tasks:

• The ore reclaim, pebble bin, and process slurry sumps are interlocked and flow shut off if operating levels become critically low. Flow does not resume until some larger level is observed.
• Hydrocyclones are actuated on or off to maintain cluster operating pressure set points. Frequent on-off cycling is prevented by a minimum cycle time counter.
• A Particle Size Analyser process instrument is simulated by sampling the tertiary cyclone overflow P80 at fixed periods.

Trend windows indicate mill load/power/media trajectory, ore reclaim, crusher power, water addition, sump levels, cyclone operation, and recirculating load.

The example project is intentionally configured to demonstrate an intermittently-stable primary grinding circuit, a stable secondary grinding circuit, and an unstable tertiary grinding circuit, all following an initial mill filling period.

Project Configuration

• The Met Dynamics - Mill model in the primary grinding area uses the AG/SAG (Variable Rates) method. The model is configured in Dynamic mode with an optional mill media trajectory computation.
• The Met Dynamics - Screen models use the Vibrating (Metso) method for load-efficiency sensitivity.
• The Met Dynamics - Crusher model in the pebble crushing area uses the Whiten method.
• The Met Dynamics - Mill model in the secondary grinding area uses the Ball (Perfect Mixing) method. The model is configured in Dynamic mode with an overflow-type discharge arrangement.
• The Met Dynamics - Mill model in the tertiary grinding area uses the Stirred (Perfect Mixing) method. The model is configured in Dynamic mode. The Nitta vertimill power calculation option is used to estimate the mill power draw.
• The Met Dynamics - Hydrocyclone models in the secondary and tertiary grinding areas both use the Narasimha-Mainza (2014) method.
• The Met Dynamics - Pump models in the secondary and tertiary grinding areas both use the Flow Rate calculation mode, as pump speed is adjusted by the PID controllers.

Dynamic Flotation Example

Project Location

..\SysCADXXX\ExamplesDynamic\MetDynamics - Flotation Example.spf

Available from Build 139.37030. Updated in Build139.37057.

Features Demonstrated

1. The use of Met Dynamics - Flotation
2. The use of Met Dynamics - Pump
3. The use of Piping System Model

Brief Project Description

This project demonstrates the dynamic simulation of a typical rougher–scavenger flotation circuit, comprising:

• Four rougher mechanical flotation cells
• Two scavenger mechanical flotation cells
• Common concentrate collection launder, pump box, and centrifugal pump.

The important mineral solids are represented by distinct chemical species (Au, FeS₂ and FeAsS) with the rest assigned to a Non-Sulphide Gangue pseudo species (NSG). Floatability classes are assigned using SysCAD's Individual Phase (IPhase) species property.

Feed to the rougher cells originates from an upstream grinding circuit. The scavenger cells receive feed from a combination of rougher tailings and recycled tails from a downstream cleaner-scavenger stage.

A Profile controller continuously varies the grinding circuit and cleaner-scavenger tails flow rates based on data extracted from a plant data historian. The cleaner-scavenger tails grades are also varied by the Profile controller to reflect the changing flow rate (and hence downstream residence time). The Profile controller introduces disturbances into the circuit which the unit operations and control system must manage.

Standard SysCAD tank models are used to simulate the Feed, Mixing and Discharge Boxes. The "WithStaticHead" option is activated to compute the hydrostatic head at the tank feed and discharge heights.

Flotation cells apply the continuous (perfectly mixed) Savassi method, also known in industry as the "P9" model:

• The cells are configured in dynamic mode, which maintains solids and liquids inventories in the cell contents.
• Concentrate production and residence time delays are automatically computed as the composition of the cell contents changes.
• The dynamic Savassi flotation model computes the hydrostatic pressure head (including gas hold-up) at the feed and tailings discharge heights.

The boxes and flotation cells are connected by:

• Flanged tank couplings (orifice-like), or
• Dart valves (control elements).

The tank couplings and dart valves are simulated with the SysCAD Piping System Model:

• Computes flow rate and pressure drop across each connection based on feed and destination static head and interface type (coupling/valve)
• Static head includes instantenous pulp levels plus step height differences between units (Relative Levels)
• A simple linear valve position–Cv relationship is applied for dart valves (but can be customised easily)

Transmitter units simulate process instrumentation such as froth depth and tank level. First order filters limit signal noise and smooth controller responses, similarly to operating plants.

A set of PID controllers maintain the froth depth of cells FC002, FC004 and FC006 by adjusting the cell discharge valve positions, i.e. the discharge flow rates.

Concentrate is collected by a Launder, before flowing under gravity to a Pump Box.

A centrifugal slurry pump model is used to determine the volumetric flow rate discharging from the pump box based on impeller speed and slurry properties. A PID controller adjusts pump speed to maintain the pump box level.

A Trend window displays transient circuit feed flow rates, froth depths, pump box level and final tailings Au grade.

Project Configuration

The Met Dynamics - Flotation models all use Cell (Savassi) method. The model is configured in Dynamic mode with additional parameters for feed/tailings connections and froth transport limits.

The Met Dynamics - Pump model uses the Flow Rate calculation mode, as pump speed is adjusted by the PID controller.

Operator Training

Dynamic SysCAD models configured like this example can be used as Operator Training Simulators.

The SysCAD software includes an industry-standard Open Platform Communications (OPC) interface and can be connected to most commercially-available SCADA/DCS Human Machine Interface (HMI) software.

Operators can be trained on an actual plant's control interface while driving a dynamic SysCAD flowsheet model (a digital twin) rather than a live plant.