Minerals & Metals
5800-PCP-001 Revision Number C
Compañía Minera Suyamarca S.A.C Inmaculada Project Process Control Philosophy 23/02/2012
5800-PCP-001 Rev: C Date: 23/02/2012
Table of Contents 1
Introduction
1
2
Common Control Functions
1
3
Process Control
4
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List of Tables Table 2-1 Sampler Type and Locations.
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List of Appendices Appendix 1 – Automatic Group Start-up Sequence Example
ABBREVIATIONS
PCS
Process Control System
SAG
Semi Autogenous Grinding
PLC
Programmable Logic Controller
OS
Operator Station
CCTV
Closed Circuit Television
MCR
Main Control Room
CCR
Crusher Control Room
LCR
Leach Control Room
ECR
Elution Control Room
RCR
Refinery Control Room
UPS
Uninterruptible Power Supply
PID
Proportional, Integral and Derivative
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Introduction This document is intended to provide an overview of the control philosophy for the Inmaculada Gold Plant. The document should be read in conjunction with t he following document: •
Process control strategy 5800-PCS-001.
The general strategy adopted for the Inmaculada Gold Project is as follows: •
•
•
Integrated control via the PCS for areas where equipment requires sequencing and process interlocking. Hard wired interlocks for personnel safety. Motor controls for starting and stopping of drives at local control stations, via the PCS or hard wired, depending on the drive classification. All drives can be stopped from the local control station at all times. Local and remote starting is dependent on the drive class and control mode.
Monitoring of all relevant operating conditions on the PCS and recording selected information for data logging or trending. •
Use of Independent Control Systems (ICS). These are used on various sections of the plant or pieces of equipment that are supplied as complete packages. These will communicate alarms and status information via a data link to the plant PCS for recording and monitoring purposes. The preference is to minimise the number of such individual ICS’s and to maximise control through the PCS.
Trip and alarm inputs to the PCS are to be failsafe in operation, i.e. the signal reverts to the deenergised state when a fault occurs
2
Common Control Functions
2.1
Current Indication All motor current draw is displayed and recorded on the PCS.
2.2
Conveyors Conveyors in the crushing and grinding areas will be fitted with the following control instrumentation: •
Lock off stop at the motor.
•
Hardwired start-up sirens at the conveyor head and tail end where necessary.
•
Pull wire emergency stops.
•
Belt rip switches (after load points, as required).
•
Belt drift switches.
•
Belt speed detector and under-speed alarm.
•
Blocked chute switches on selected transfer chutes.
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Pull wire “emergency stop” switches will be mounted adjacent to all conveyors, which are accessible to operations personnel. When activated, pull wire switches initiate a hardwired stop of the conveyor and a controlled emergency stop of the appropriate upstream equipment. Activating a pull wire switch generates an alarm on the PCS. Pull wire switches must be reset in the field. Belt drift switches are located outside the line of the conveyor trough idlers. If a belt drift switch is activated for a preset time, the conveyor is tripped. Activating a belt drift switch generates an alarm on the PCS. Each belt drift switch (pair) will alarm on the PCS. Belt speed sensing elements (i.e. proximity switch) generate a conveyor under-speed alarm, via the PCS under the following conditions: •
•
The conveyor speed drops below a set level during normal operation. The conveyor fails to reach full speed within a specified time after receiving a start signal from the PCS.
Transfer chutes containing level switches or blocked chute switches, when activated will stop the feeding conveyor, and activate an alarm on the PCS. Belt rip detectors are located after the load points of a conveyor and at other points where deemed as necessary. If a belt rip switch is activated, the conveyor is tripped. Activating a belt rip switch generates an alarm on the PCS, which must be reset in t he field. The above alarms will trip the conveyor and upstream equipment.
2.3
Pump Hopper Levels A number of the pump hoppers are fitted with level control. This generally includes an ultrasonic level probe mounted over the hopper providing input to a level control loop. The level set point that is entered by the operator into the PID controller is maintained by adjusting the speed of the associated pump when auto mode is selected on the PID controller. Level monitoring includes various alarms including high and l ow level. All variable speed pumps can be controlled at a set output (%) when Manual mode is selected on the PID controller.
2.4
Sump Pump Control Sump pumps will have a LCS located near them with the ability to switch between Remote and Local (maintenance) mode. When selected in Remote, the control for sump pumps will be via a high-level switch. When the switch activates, the pump will start. On deactivation of the switch, the pump will run for a preset amount of time before stopping. A second timer is set up to alert the control room operator by way of PCS alarm, if t he pump runs for longer than a preset time. Some sump pumps in the reagent area will be local start only.
2.5
Pump Start/Stop Sequence All associated valves required in a pump sequence need to be in auto mode before the sequence can be activated by the PCS operator (start/stopped). This includes the suction and discharge valves.
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2.5.1
Start Sequence Pumps that are automated will typically have the following starting sequence based on set timers for each step to be completed: •
Confirmation of gland seal water flow via the flow sheet after the operator has opened the manual valve.
•
Pump suction valve open.
•
Pump start.
•
Pump discharge valve open.
Timers are adjusted for the opening time for the various valves used. All interlocks are present and failure of any valve in the sequence will cause the pump to stop/remain stopped.
2.5.2
Stop Sequence Pumps that are automated will typically have the following stopping sequence based on set timers for each step to be completed: •
Pump discharge valve close.
•
Pump stop.
•
Pump suction valve close.
Timers are adjusted for the opening time for the various valves used. All positive displacement pumps will be interlocked to low-level indications on the pump hopper to prevent the pumps running dry. Positive displacement pump discharge lines are fitted with pressure release valves recycling the discharge to the feed tank to prevent deadheading of the pump.
2.5.3
Gland Seal Water Flow confirmation is required to enable a pump to start. A low gland water flow when the pump is running will alarm on the PCS. A low gland flow will also trip the pump after a pre-set time lapse to prevent frictional damage to the gland seal. A minsup fitting is provided to allow a manual pressure gauge to be installed at each pump to check the delivered pressure. Individual pump gland water lines are equipped with a mechanical pressure control valve (If required) and a Maric type restrictor (included in the slurry pump vendor package and not indicated on the PIDs) to deliver the required pump gland water flow and pressure.
2.6
Mass Flow Measurement For process control and metallurgical accounting purposes, mass flow measurement is provided in required areas of the plant. For dry material on conveyors this is achieved by belt weightometers. All belt weightometers are frame supported with precision balanced idlers installed before and after the weightometer. The belt weightometers have a local display of instantaneous belt loading and integrated wet tonnage flow rate, as well as totalised tons.
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The weightometers are to be installed on straight sections of the belt as close as possible to the feed point. The belt above the weightometer must be free of skirting, and tracking idlers need to be located greater than five idler frames away. Slurry flow mass measurement will utilise magnetic flow meters and nucleonic density meters. The mass flow instrumentation is installed on pipelines as determined by the process requirements. Instantaneous slurry density and volumetric flow are displayed locally and on the PCS. Totaliser flows are displayed on the PCS and the dry mass flow rate calculated on a shift, daily and continuous basis. These instruments are typically installed on a vertical section of pipe ten pipe diameters after and five pipe diameters before any constriction, valve, bend or feature in the pipe that may cause a disturbance in the slurry flow.
2.7
Samplers Slurry samplers are provided at locations identified in Table 2-1. Table 2-1 Sampler Type and Locations.
Sampler
Sampler Type
Location
Leach feed sampler
Double Stage, rotary cross-cut
Located on the concentrate thickener line feeding into the distribution box.
Leach tail sampler
Double Stage, rotary cross-cut
Located at discharge of last leach tank into the CCD feed hopper.
Detoxification discharge sampler
Double Stage cross-cut
Located at overflow of detox tank
Pregnant leach solution sampler
Wire sampler
Located on the feed line to the polishing filters
The double stage cross cut sampler consists of an electric motor driven sample cutter that travels through the process stream. Primary sample is delivered into a surge launder to smooth out the flow. The primary sample is passed through a Vezin type secondary sampler. The sample is collected in a sample collection bucket. The reject sample from the secondary sampler either gravitates into the pump hopper or returns to the circuit via the area spillage pump. Sample frequency can be adjusted by changing the sampler timer settings via the PCS. All samplers are interlocked so they do not operate without process flow. Manually operated valves are provided at certain sample points for spot checks on streams
3
Process Control The following descriptions highlight some of the main control loops that will form part of the treatment plant. Details of each control loop will be contained in the descriptions for each area.
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3.1
Crushing Area
P&IDs 5800-PI-101 & 102
Key processing equipment in this area i ncludes: •
ROM bin vibrating feeder
•
Jaw crusher
•
Overland conveyors to the crushed ore stockpile
Run of Mine (ROM) ore is transported to the primary crusher by truck to the stockpile and loader from the ROM pad and tipped onto the crusher grizzly. The feed rate through the crusher is dependent on the loader cycle time, ROM ore material properties and the crusher gap setting. Crushed ore falls from the crusher through a discharge chute and onto a discharge conveyor which transfers crushed ore to the overland conveyor 1. The control of this area is from the Crushing Area Control Room (CCR). The following sections describe the control and indication of the crushing area.
3.1.1
Crusher Feed Ore can be fed to the crusher if a Green dump light adjacent to the tipping point is illuminated. If the crusher stops, a red dump light is illuminated. A level indicator above the ROM bin activates the red dump light in the event of a high bin level. The green light is illuminated when it is possible to dump, i.e. the level in the ROM bin is low enough to accept the truckload of crushed ore. The operator can select the light control to Manual to display Red or Green at any time. A CCTV camera monitors the material flow through the ROM Bin. Ore is fed to the crusher by a vibrating feeder. The speed of the feeder will typically be controlled at a fixed output in manual. This allows more efficient choke feeding of the crusher. Feedback control of the feeder speed is provided to maintain a set tonnage on the crushed ore conveyor. A high level in the crusher feed chute will cause a non-latching interlock to the vibrating feeder.
3.1.2
Crusher All monitoring, control and sequence functions are performed by the PCS. Jaw Crusher gap is manually checked by lowering a piece of lead into the crusher. The gap is adjusted manually using 10 mm spacing shims. The crusher is equipped with vendor supplied lubrication systems. The systems provide pressurised oil or grease to lubricate bearings and bushes based on a timer set-up.
3.1.3
Conveyors The crushing area conveyors will be fitted with control and interlocks as per Section 2.1.
3.1.4
Stockpile Feed Conveyor Weightometer The overland conveyor 1 (10-01-CV-002) has a weightometer installed for measuring throughput from the crusher. The instantaneous weight passing over the conveyor is displayed locally, and displayed on the PCS.
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The totalised tonnes are displayed locally and tonnes totalised over a previous or current 12 and 24-hour period are also displayed on the PCS. A high-level switch is in place above the coarse ore stockpile. A high level on the crushed ore stockpile causes the red light adjacent to the crusher feed bin to illuminate to prevent further dumping. It also initiates a timer to allow the stockpile feed conveyors to run empty before stopping it.
3.1.5
Dust Suppression Raw water sprays located at the head of the Stockpile Feed Conveyor are activated through the PCS when dust suppression is required.
3.1.6
Services High pressure air is delivered to the crushing area by a dedicated compressor located at the crusher. Raw water is supplied by a pump and tank dedicated to the crushing plant.
3.2
Stockpile Reclaim and Grinding
P&IDs 5800-PI-103,104,105,106
Key processing equipment in this area i ncludes: •
Crushed ore reclaim vibratory feeders.
•
SAG Mill Feed Conveyor.
•
SAG Mill and ancillary equipment.
•
SAG Mill Discharge Screen (Trommel Screen).
•
The Primary Cyclone cluster and associated pumps, hoppers and launders.
•
Ball Mill
The strategy for process control of the grinding circuit is to maximise the feed rate to the grinding circuit whilst producing a leach feed size distribution as close as possible to the nominated target. Achievement of target leach feed particle size P80 will facilitate throughput and recovery. The principal control of this area will be via the PCS stations located in the main plant control room (MCR). The following sections describe the control and indication of the stockpile reclaim and grinding areas.
3.2.1
Conveyors All conveyors in the grinding area are fitted with the same protection devices as described in Section 2.1 All sump pumps in the grinding area are fitted with high-level switches. Control is as per Section 2.4.
3.2.2
SAG Mill Vendor Control and Instrumentation P&ID 5800-PI-105 The SAG mill is supplied as a vendor package including: •
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SAG Mill, feed chute and discharge trommel.
6
•
Variable frequency variable voltage (VVVF) SCIM mill motor.
•
Trunnion bearing lubrication system.
•
Gearbox and ring gear lubrication system.
The PCS displays the status of both the temperature and lubrication systems for the SAG Mill. The PCS starts and stops all the associated SAG Mill systems; except the SAG Mill Inching Drive, which has an independent Local Control Panel. Details of the process control for this equipment must be included in the Vendor’s installation and operation manual.
3.2.3
Mill Power Draw SAG Mill power draw is indicated and recorded within the PCS. A high-high mill power alarm interlocks the reclaim feeders when activated, thereby enforcing a grind-out.
3.2.4
Reclaim Feeder Speed The stockpile reclaim system consists of three variable speed vibrating pan feeders delivering ore onto the SAG Mill Feed Conveyor. The nominal speed (speed control loop output %) of each of the Reclaim Feeders is indicated and recorded in the control room on the PCS system. Each reclaim feeder may operate in fixed speed mode or variable speed mode. The speed of the feeders operating in variable speed mode is controlled by a signal from the stockpile reclaim belt weightometer (via the PCS). Typically, two of the three feeders will operate at any given time with at least one feeder operating in variable speed mode. When more than one feeder is operating in variable speed mode, the speed of the feeders will vary simultaneously to maintain the same proportional feed rate per feeder. Ratio controllers will set the proportion of the total feed from each individual feeder.
3.2.5
Mill Feed Conveyor Weightometer The mill feed conveyor weightometer is located on the SAG mill feed conveyor. The feed rate passing over the conveyor is displayed locally and within the PCS. Totalised tonnes are displayed locally and tonnes totalised over the previous and current 12, and 24-hour periods are displayed on the PCS in the control room.
3.2.6
SAG Mill Weight Measurement SAG mill weight is calculated from hydrostatic bearing oil pressure. The SAG mill weight is recorded on the PCS in the control room. The SAG mill weight is the primary indication used to control the mill speed. If the SAG mill weight exceeds the high-high alarm, the reclaim feeders will stop, thereby enforcing a grind-out.
3.2.7
SAG Mill Speed The SAG mill speed is calculated based on the motor speed and displayed on the PCS as a percentage of critical speed. The speed range available when operating in variable speed mode is 60% to 80% of critical speed. The mill speed is controlled by the SAG mill weight control loop.
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3.2.8
SAG Mill Acoustic Measurement The SAG Mill is fitted with an “electronic ear” system, close to the mill shell that measures the nature and magnitude of noise created by the mill charge. The SAG mill noise is analysed by vendor information outputting a 4-20 mA signal to the plant PCS. This signal is displayed on the PCS SAG mill graphic and can be used to determine the frequency of ball/liner impacts and therefore allow the operator to adjust the mill weight setpoint accordingly. A high-high alarm will notify the operator of potential damage to the SAG mill liners and/or grates.
3.2.9
SAG Mill Feed Water Addition The objective of this control loop is to maintain the SAG Mill discharge density at or close to a target pulp density (manually checked on an intermittent basis at the mill discharge). The controller uses signals from the SAG Mill feed weightometer, and the SAG Mill feed water flow meter and is based on a ratio of water flow to the SAG Mill feedrate. The ratio is selected by the operator and will be entered as a target density (wt% solids value). The SAG Mill feed chute water addition flow rate is recorded and the control valve position and the selected ratio are displayed on the system in the control room.
3.2.10
SAG Mill Feed Rate The SAG mill feed control uses a signal from the mill feed conveyor weightometer to control the speed of the reclaim feeders as outlined in Section 3.2.4. The objective of the control loop is to maintain a steady feed rate to the SAG mill. The set point for feed rate will initiall y be manually set by the control room operator.
3.2.11
Ball Mill Vendor Control and Instrumentation P&ID 5800-PI-105 The ball mill is supplied as a v endor package including: •
Ball Mill, feed chute and discharge trommell.
•
WRIM mill motor with Liquid Resistance Starter (LRS).
•
Trunnion bearing lubrication system.
The PCS displays the status of both the temperature and lubrication systems for the ball mill. The PCS starts and stops all the associated ball mill systems; except the ball mill inching drive, which has an independent Local Control Panel. Details of the process control for this equipment must be included in the vendor installation and operation manual.
3.2.12
Ball Mill Power Draw Ball Mill power draw is indicated and recorded within PCS, and is controlled manually via media addition.
3.2.13
Ball Mill Feed Water Addition Provision is made for a water dilution stream to the ball mill feed if required due to high cyclone underflow density. This flow will be adjusted manually by the operator in the field to achieve the required ball mill feed density.
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3.2.14
Mill Discharge Hopper Water Addition Water addition to the SAG/Ball Mill discharge hopper is automated and adjusted to control the cyclone feed density. The slurry density set point for cyclone feed is entered into the PCS. The cyclone feed hopper water addition is controlled by adjusting the position of an actuated flow control valve to give the required flow measured by a magnetic flow meter.
3.2.15
Cyclone Feed Pump Speed The cyclone feed pumps can be operated in either automatic or cascade mode. In automatic mode, the speed of these pumps is controlled to maintain the level in the pump hopper within a set range, which is manually selected in the system by the operator. The pulp level in the hopper is detected using an ultrasonic level detector, a signal from which is transmitted to the pump speed controller. Hopper level is displayed locally and recorded on the PCS in the control room. The speed and the power draw of the pump is displayed and recorded on the PCS in the control room. If cascade control of the pumps is selected, the pumps speed is controlled to maintain a desired flowrate set point. The level in the pumpbox changes the flowrate set point to maintain the level in the pumpbox. The tonnes are totalised and displayed on the PCS. This includes separate totalised calculation for the previous 12-hour shift.
3.2.16
Cyclone Feed Pressure The pressure in the cyclone feed distributor is measured, displayed and recorded in the control room on the PCS. Four cyclones on the cluster will be fitted with an air actuated knife gate valves that can be opened and closed from the PCS. The mill area operator will also be able to control the number of cyclones in operation and therefore the cyclone inlet pressure.
3.3
Pre-leach Thickener P&ID 5800-PI-107 This area consists of a high rate thickener with duty and stand-by underflow pumps thickening the cyclone overflow. The principal site for monitoring of this plant area is from a PCS station located in the main plant control room. The pre-leach thickener can also be monitored from a control panel on the bridge of the thickener. Rake torque, rake height and bed pressure are displayed at the local control panel and at the PCS. Thickener operations are controlled using process control loops that have proven effective in similar applications. All general alarms associated with the rake drive are displayed on both the local control panel as well as the PCS.
3.3.1
Bed Pressure The mass of settled solids is measured by a pressure transducer on the cone of the thickener and a signal transmitted to the PCS. Thickener bed pressure is controlled in either manual or automatic mode via the PCS. The operator selects the operating bed pressure set point through the pressure controller on the PCS. In automatic mode, the PLC controls the position
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of the underflow flow control valve set point; in manual mode, the operator adjusts underflow flow control valve position at the PCS.
3.3.2
Rake Position and Torque Thickener rake height and rake torque is controlled at the thickener control panel by a PLC. When rake raise/lower control is selected to auto on the local control panel, upon reaching a high rake torque alarm (>50%) the rake mechanism will rise until the torque reaches 45%. Once the torque is at 45%, the rakes will lower at intervals. Whilst lowering the rake torque is monitored. The rakes will stop lowering if the rake torque reaches or exceeds 45%. In manual mode, the operator can raise and lower the rakes at the local control panel. Limit switches located on the rake shaft will indicate either fully raised or rakes fully lowered alarm once activated. The rake level is measured using a vendor supplied ultrasonic level element. The rake position (indicated as a percentage of the rakes fully lowered) and alarms are displayed on both the local control panel and on the PCS. Density and volumetric flow rate of the thickener underflow are displayed at the PCS. The PCS calculates a mass flow with high and low alarming. The alarm status is r ecorded at the PCS.
3.3.3
Pre-Leach Thickener Underflow Density and Mass Flow The mass flow on the pre-leach thickener underflow to the leach area is measured via the philosophy discussed in 2.6. The thickener underflow flow control valves are controlled either by the thickener bed pressure or the leach feed discharge density. The operator selects the control mode on the PCS. The tonnes are totalised and displayed on the PCS. This includes separate totalised calculation for the previous 12-hour shift. The underflow and overflow discharge pumps are automated as per Section 2.5. The pump speed is controlled based on pump hopper level as per Section 2.3
3.4
Leaching P&ID 5800-PI-108 This area consists of seven leach tanks and associated reagent and support services. The principal control of this area will be via the PCS stations located in the main plant control room (MCR). The following sections describe the control and indication of the leaching areas.
3.4.1
pH Control Lime is added to the leach distribution box to control the pH in the leaching circuit. The pH of the slurry in tank 1 and tank 2, is measured with inline pH meters. The operator can select either tank 1 or tank 2 for control to obtain the required pH. The selected output feeds back to a pH controller, which regulates the Lime dose rate to the distribution box by adjusting the pulse output to a control valve. There will be separate manual valves on the lime ring main that can be used to manually dose the tanks from the field. The signals from the two pH probes are compared in the event one probe is out of calibration. If a significant difference in signal is detected, an alarm advises the operator of the discrepancy. Additional provision for manual lime addition is provided in tank 3.
3.4.2
Cyanide Control Cyanide is measured by manual titration. A slurry sample is taken from the first leach tank and titrated in the field for free cyanide. Based on this value the operator adjusts the cyanide flowrate to the leaching circuit, and in automatic mode the flow control valve is adjusted to maintain the set flowrate.
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3.4.3
Oxygen Control Oxygen is added to each leach tank through a sparge at the bottom of the tank. Control over oxygen addition to the leach tanks is achieved by adjusting manual valves located at the tanks. The dissolved oxygen (DO) must be checked on a periodic basis by the operator using a handheld DO meter.
3.4.4
Flow Control Leach tank feed can be diverted to the second leach tank if tank one requires maintenance, by manually moving the dart valves located in the leach distribution box.
3.5
CCD Thickeners P&ID 5800-PI-109 and 110 This area consists of four high rate thickeners with duty and stand-by underflow pumps. Leached ore is introduced to the first thickener and underflow is pumped to the next thickener. Thickener overflow moves counter current to thickened underflow diluting the previous th ickener feed. The principal control of this area will be via the PCS stations located in the main plant control room (MCR). The control of all four CCD thickeners is similar as that discussed in Section 3.3. The differences are detailed in the following section.
3.5.1
pH Control The pH of the individual thickener overflows is measured with an inline pH meter installed above each thickener. The output from the pH transmitter feeds back to a PID controller, which regulates the lime dose rate to the distribution box. The PID controller uses a timer to control the on/off dosing valve. The operator sets the cycle time on the PID faceplate, with the PID controller adjusting the pinch valve open time to achieve the set point pH. The operating pH in each thickener is displayed locally and at the PCS. An alarm with low and low-low set points will activate in the PCS when a pH outside of the safe operating range is measured in any of the CCD thickeners.
3.5.2
Wash Water Control Flowrate of barren solution acting as wash water into the fourth and final CCD thickener distribution box is controlled via a flowmeter and automatic valve. This control loop is operated in automatic based on an operator specified flowrate setpoint.
3.5.3
Underflow Pump Control
A pressure transducer on the cone of the CCD thickener measures the mass of settled solids. The signal is transmitted to the system in the control room and thickener bed pressure controlled via the PCS. The underflow pumps are variable speed pumps. The pressure set point that is entered by the operator into the PID controller is maintained by adjusting the speed of the associated pump when auto mode is selected via the PSC. Pressure monitoring includes various alarms including high and low pressure.
3.6
Pre-Clarification P&ID 5800-PI-111 This area consists of a high rate clarifier thickener and associated reagent and pumping systems.
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Control of the clarifier thickener is in a similar manner to other thickeners on site as described in Section 3.3. The only difference is the bed mass control as described below.
3.6.1
Bed Pressure A pressure transducer on the cone of the clarifier measures the mass of settled solids. The signal is transmitted to the PCS and alarms alert operators to high and high-high states.
3.6.2
Underflow Pump Control The underflow pump is fixed speed and typically operates in recycle mode to increase the solids concentration. When the underflow density reaches the desired concentration the operator manually discharges the underflow slurry to t he leach circuit.
3.7
Polishing Filters and De-aeration P&ID 5800-PI-112 and 113 This area consists of clarifier overflow handling and diatomaceous earth dosing for polishing filter pre-coat and polishing filters.
3.7.1
Polishing Filter Feed Pumps In automatic mode the pumps control to a set flowrate through the de-aeration tower, as measured by a magnetic flowmeter installed on the feed line to the de-aeration tower. The polishing filter feed pumps do not have an automatic start/stop sequence. The manual valves are opened/closed by the operator in the field, and the pump started/stopped on the PCS. If a pressure is not indicated in the feed line to the filters within a preset time, the pumps will interlock.
3.7.2
Diatomaceous Earth Pre-coat Control Diatomaceous earth is used to pre-coat the polishing filter prior to the unpolished solution being fed to the filters. The pre-coating of a filter is a manual process completed by an operator in the field. The operator selects the filter to be pre-coated by adjusting the manual valves. The precoat tank is then manually filled and diatomaceous earth added to provide the required concentration. The pre-coat filter feed duty pump is started and the operator checks the return solution to ensure it is clear.
3.7.3
Polishing Filters Control and Indication The polishing filters are manually controlled and sequenced by an operator in the field (there are no automatic sequences for the filters). The solution feed header pressure and flowrate to each filter is measured and displayed on the PCS. These indications are used to determine when a filter should be taken offline for cleaning.
3.7.4
Diatomaceous Earth Body Feed Control The diatomaceous earth used for the body feed is controlled based on the flowrate of unpolished solution to the polishing filter. The flowrate to the filter is measured by a magnetic flowmeter and this is used to adjust the speed of the body feed positive displacement pump. The operator adjusts the speed of the pump based on the vendor supplied pumps speed to flowrate ratio.
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3.7.5
De-aeration Tower Control This area consists of a de-aeration tower and associated pumping and air extraction equipment. Feed to the de-aeration tower is started from the PCS. There are no start/stop sequences for this circuit The vacuum pump above the de-aeration tower is fixed speed. The sealing liquid for this pump is barren solution.
3.8
Precipitation and Filtration P&ID 5800-PI-113 and 114 De-aerated Merrill Crowe solution from the CCD circuit is treated in the precipitation and filtration circuit. This area consists of one precipitation system and three filters. The principal control of this area will be via the PCS stations located in the main plant control room (MCR). The following sections describe the control and indication of the leaching areas.
3.8.1
Lead Nitrate and Zinc Dust Dosing Lead nitrate and zinc dust dose rates are adjusted via the PCS by changing the speed of the respective feeders. The operator measures the precious metal content in the barren solution exiting the precipitation circuit and adjusts the lead nitrate and zinc addition rate manually.
3.8.2
Diatomaceous Earth Body Feed The diatomaceous earth used for the body feed is controlled based on the flowrate of pregnant solution to the precipitation filters. The flowrate to the filter is measured from a magnetic flowmeter and this is used to adjust the speed of the body feed positive displacement pump. The operator manually set the speed of the pump based on the vendor supplied pumps speed to flowrate ratio.
3.8.3
Precipitator Cone Level Control The precipitator cone is always full to ensure and that no entrained air or oxygen can be introduced into the de-aerated solution stream. The precipitator cone level is maintained by a steady head tank which has a manual float/control valve arrangement. When the level is low, the float drops causing a manual valve to open and allow the barren solution to fill the cone. The valve shuts when the level reaches setpoint and the float rises. Discharge valve control?
3.8.4
Precipitate Filter feed Pumps The precipitate filter feed pumps are submerged in a vendor supplied tank to ensure no air is introduced into the precipitate stream. The level of the seal water tank is controlled via a float/control valve arrangement. The precipitate filter feed pumps do not have an automatic start/stop sequence. The manual valves are opened and closed by the operator in the field, and the pump started/stopped on the PCS. The pumps are variable speed, in automatic mode the speed of the pump is adjusted to control the level in the de-aeration tower.
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3.8.5
Precipitate Filter Control The precipitate filters are manually controlled and sequenced by an operator in the field (there are not automatic sequences for the filters). The solution feed header pressure and flowrate to each filter is measured and displayed on the PCS. These indications are used to determine when a filter should be taken offline for cake removal. The precipitate filters are supplied with an LCP that will allow basic control functions for the hydraulic open/close system to be operated locally.
3.8.6
Diatomaceous Earth Pre-coat Diatomaceous earth is used to pre-coat the precipitate filter prior to the pregnant solution being fed to the filters. The pre-coating of a filter is a manual process completed by an operator in the field. The operator selects the filter to be pre-coated by adjusting the manual valves. The precoat tank is then manually filled and diatomaceous earth added to provide the required concentration. The pre-coat filter feed duty pump is started and the operator checks the return solution to ensure it is clear.
3.9
Refinery P&ID 5800-PI-115 and 116 The refinery area includes the mercury retort kiln, calcine and flux handling system, furnace and vault. The majority of the refinery processes are manually operated with instruments providing advisory functions and monitoring of system states.
3.9.1
Precipitate Retorting The wet precipitate is dropped into retort pans and placed in the mercury retort. The retort is a 22-hour cycle, where a maximum 600 °C temperature and 27 kPa absolute pressure is reached. Residual moisture and mercury if present are removed and collected in the retort condenser. The mercury retort is supplied with an LCP and will be controlled locally.
3.9.2
Flux Dosing/Mixing Fluxes and precipitate are loaded by hand into a weighing hopper to allow the operator to add the required flux. This material is then screw fed into the flux mixer before being screw fed into the furnace. All equipment is started/stopped locally only at the LCS.
3.9.3
Precipitate Smelting The 450 liter diesel reverbatory furnace is supplied as a vendor package with a standalone independent control system (ICS). The flux and precipitate mixture is typically heated to approximately 1400 °C before being poured into doré molds. The furnace is controlled locally at the ICS.
3.10
Detoxification and Tailings Disposal P&ID 5800-PI-117 and 118 This area treats the CCD tailings to reduce the level of cyanide in the slurry going to the TSF to below specified discharge limits. The area consists of a cyanide reduction tank, and associated
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oxygen and reagent addition monitoring and control. Cyanide is detoxified using the air/SO 2 detoxification process. The principal control of this area will be via the PCS stations located in the main plant control room (MCR). The following sections describe the control and indication of the detoxification and tailings disposal areas.
3.10.1
Sodium Metabisulphite (SMBS) Addition The solution volumetric flow is used in a PCS algorithm for reagent dose control to the detox tank feedbox. A slurry sample is taken from the last CCD thickener underflow and titrated in the field for free cyanide. This result becomes the input into the PCS algorithm. The expected ratio of CNfree : CNWAD and SO2 : CNWAD as developed from test work and plant data are put into the algorithm as well as the SMBS mix strength. The PCS calculates the dose rate of SMBS to the detox tank feed box. A flow control loop adjusts the speed of the SMBS dose pump to maintain the calculated flowrate.
3.10.2
Copper Sulphate (CuSO4) Addition The speed of the copper sulphate dosing pump adding solution to the detox tank is ratio controlled based on the volumetric flowrate to the detox tank. The operator inputs the mix strength and copper addition rate set point in grams Cu2+ per cubic meter of solution into the PCS algorithm. A flow control loop adjusts the speed of the CuSO4 dose pump to maintain the calculated flowrate.
3.10.3
Lime Addition Lime addition to the detox tank is automated and controlled as per Section 3.4.1
3.10.4
Oxygen Control Oxygen is added to the tank through sparging at the bottom of the tank, with control via a manual valve located above the detox tank. The dissolved oxygen is checked on a periodic basis by the operator using a handheld DO meter.
3.10.5
Oxidation Reduction Potential (ORP) An ORP probe is located in the detox tank to provide an online millivolt reading displayed both on the PCS and at the field unit. The ORP is an online indication of the cyanide reduction performance.
3.10.6
Slurry Density Control The objective of this control loop is to maintain the detox pulp density at or close to a target pulp density (manually checked on an intermittent basis at the mill discharge). The feed density calculation in the PCS uses signals from the detox tank feed flow and density along with an operator inputted solids S.G and target detox feed density to calculate the required dilution water required. This calculated water requirement is then inputted as the setpoint to the dilution water flow controller. The flow control valve adjusts the flowrate of dilution water to then achieve the desired dilution water flowrate.
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3.10.7
Tailings Thickening Detoxified slurry discharges by gravity into the tailings thickener. The thickener control is similar to that discussed in Section 3.3. The differences are discussed below. The thickener underflow flow control valves are controlled either by the thickener bed pressure or the tailings discharge density. The operator selects the control mode on the PCS. The density option is available due to the requirement to have a relatively stable density for pumping to the tailings storage facility (TSF). The tonnes are totalised and displayed on the PCS. This includes separate totalised calculation for the previous 12-hour shift. The tailings thickener overflow solution gravitates to a pump hopper. The solution is then pumped between the tailings detoxification tank, Copper Arsenic (CuAs) removal circuit and barren solution tank according to the fol lowing control philosophy: •
•
•
3.10.8
Target solution flowrate to the AsCu circuit is set by the operator on the PCS. The flow control valve is then adjusted automatically to achieve this solution flowrate setpoint Solution flowrate to the detoxification circuit is automatically controlled as outlined in Section 3.10.6 The level in the tailings thickener overflow tank is maintained by a bleed line to the barren solution tank. The bleed valve opens when the tank reaches a high level, and closes when the tank reaches a low level. If the tank reaches a low-low level the raw water make-up valve opens to fill the tank back up to the low le vel.
Tailings Disposal Thickener underflow tailing is pumped to the TSF. The tailings discharge pumps are automated as per Section 2.5. The pump speed is controlled based on pump hopper level as per Section 2.3 Water addition to the tailings discharge hopper is automated and adjusted to control the tailings discharge density. The density set point for the tailings is entered into the PCS. The tailings density water addition is controlled by adjusting the position of an actuated flow control valve to give the required flow measured by a magnetic flow meter. The tailings discharge solid mass flow is measured and totalised as per Section 2.6.
3.11
Paste Backfill Plant P&ID 5800-PI-139 The underflow thickener tailings slurry is pumped at 55% solids in intermittent fashion to the paste backfill plant where it is filtered to achieve approximately 72% solids, Cement is metered to give the adequate properties for mine backfill. Reclaimed filtrate water from paste backfill is returned to the barren solution tank. The paste is transported to the mine backfill boreholes either by positive displacement pumps or trucks. The paste backfill plant is a vendor supply package and will be supplied with an ICS. Refer to vendor documentation for the instruments and controls of t his package.
3.12
Reagents P&ID 5800-PI-121 to 125 Control of reagent mixing and distribution is an operator responsibility and are generally controlled locally at the respective activity.
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All tanks in the reagent area are fitted with high and low level alarms. Generally, a low level alarm will warn the operator that a mix is required whilst a low-low alarm will cause the dosing pump to shutdown. The alarms are raised on the PCS in the control room. All positive-displacement dosing pumps are installed with a pressure release valve back into t he feeder tank. This is a safety device to prevent dead heading of the pumps and excess pressure in the piping.
3.12.1
Quick Lime (CaO) Slaking and Storage The detailed vendor supplied control philosophy document should also be referred to for the lime container unloading and slaking systems. Hydrated lime will be produced onsite by slaking quick lime using a dedicated lime slaking mill. The hydrated and ground product will be pumped to a storage tank used to supply the site lime ringmain. The ringmain will supply lime to the Leach, CCD and Detoxification circuits. The Lime Slaking Area consists of a one tonne bag hoist and splitter, quicklime storage silo, silo vibrating feeder, screw conveyor, a ball mill slaker discharging into a hopper and a lime slaker discharge pump. Lime addition rate is controlled through variation of the screw conveyor speed. The speed is either manually entered by the operator into the PCS or automatically adjusted to achieve the lime mill discharge temperature setpoint. In addition, mill water addition will be automatically controlled to a setpoint to maintain consistent feed pulp densities. Alternatively, the mill feed water addition flowrate can be set manually in the PCS. Any build-up of lime in the discharge cone of the Lime Storage bin is dislodged by the lime bin activator. The activator operates on a timer, which will be determined during commissioning. The setpoint can be changed through the PC S. Interlocks and indicators are included to protect personnel and equipment as required. These include: •
•
•
•
•
Slaking temperature: A general high temperature alarm for the mill discharge (the milk of lime temperature is monitored in the mill discharge hopper) will be di splayed on the PCS. Mill feed chute: A blocked chute switch will be located in the mill feed chute to alert operators to a blocked feed chute via the PCS. A high alarm will be interlocked with the Rotary Valve. The valve will not be able to be restarted until the alarm is cleared. Mill Motor Temperature: A temperature probe is installed on the mill motor. Alarms for high temperature alert the operator to unusual motor temperature, the high-high alarm on the temperature probe will stop the mill. The high-high alarm must be inactive before the mill can be restarted. Mill Motor power: Mill motor power draw will be displayed on the PCS. High and low alarms will notify the control room operator of any potential issues. A high-high alarm will cause the motor to trip out. Mill roller bearing lubrication: Grease is pumped manually into the mill roller bearings.
Lime slurry is pumped to the dosing points via a ringmain. The lime ringmain pressure is controlled by manually adjustable diaphragm valves.
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3.12.2
Flocculant, Storage and Mixing The detailed vendor supplied control philosophy document should also be referred to for the flocculant mixing system. Flocculant is supplied in 1 tonne bulk bags. The bags are loaded manually into a storage silo. The mixing system is controlled by a vendor supplied ICS. The mixing system operates automatically via the following steps outlined below: •
•
•
•
•
•
3.12.3
Raw water is added to the mixing tank via an automated valve when a low level alarm is activated on the main storage tank. The mixing tank agitator then starts automatically. A screw feeder and air blower system transfers the flocculant into the mixing tank for a set time. Following a 30 minute conditioning time the mixed flocculant is ready for transfer into the main storage tank. Transfer is carried out automatically by the vendor supplied ICS and will do so only if the storage tank has a low level. The mixing tank agitator stops automatically.
Sodium Cyanide (NaCN) Storage and Mixing The cyanide mixing system is vendor supplied and automatically controlled. The mix is transferred to the holding tank and dosed via a ring main using a duty/standby fixed speed pump. The cyanide holding tank has a level indication interlocked with the cyanide mixing pump to prevent overfilling the holding tank. An interlock will stop the duty dosing pump at low level. Level indication of the holding tank is provided locally at each tank and at the PCS.
3.12.4
Zinc and Lead Nitrate, Storage and Addition Zinc dust is delivered to site in 500 kg bags and loaded into the zinc hoppers using a hoist. Lead Nitrate is delivered to site in 25 kg bags stored on pallets and is loaded into the respective storage hoppers manually by the operator as required.
3.12.5
Antiscalant, Storage and Transfer Antiscalant is dosed directly from an intermediate bulk container into the required stream by dedicated metering pumps. Stop/start of the pumps and dosage rate is controlled locally in the field.
3.12.6
Diatomaceous Earth, Storage and Mixing Diatomaceous earth is mixed on site using a manual process. All tank levels are displayed both on the PCS and locally DE used for precipitate and polishing filter body-feed is pumped from the storage tank to the required dosing point via variable speed pumps.
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The polishing filters and precipitate filters have a designated tank for pre-coat. The pre-coat pump circulates solution to the filters and back to the tank until the solution is clear and the diatomaceous earth remains in the filters.
3.12.7
Copper Sulphate (CuSO4) Storage and Mixing Copper Sulphate is mixed onsite using a manual process. The CuSO4 mixing tank level is displayed both on the PCS and locally. The high and low level alarms are displayed on the PCS. Two metering pumps, one operating and one standby, deliver the solution to the detox tank. A flow meter and a controller vary the speed of the metering pumps to achieve the calculated flowrate requirement for detox.
3.12.8
Sodium Metabisulphite (SMBS) Storage and Mixing SMBS is delivered in 1 tonne bulk bags. The bags are hoisted to the bag splitter and split open to discharge into the mixing tank. SMBS dust generated during bag splitting is extracted by the extraction fan and discharged to the atmosphere. The SMBS mixing tank level is displayed both on the PCS and locally. The high and low level alarms are displayed on the PCS. Two metering pumps, one operating and one standby, deliver the solution to the detox tank. A flow meter and a controller vary the speed of the metering pumps to achieve the calculated flowrate requirement for detox.
3.13
Arsenic and Copper removal circuit P&ID 5800-PI-140 A fraction of tailings thickener overflow is pumped to the Arsenic and Copper (AsCu) removal circuit. Arsenic and copper precipitation occurs in a series of four agitated tanks. Each tank is equipped with an agitator to ensure uniform mixing.
3.13.1
Solution Feed Rate The solution flowrate to the AsCu circuit is measured via a magnetic flowmeter on the pipeline to the first mix tank. This flowrate is used in PCS algorithms to calculate the required ferric sulphate and hydrogen peroxide dosing rates.
3.13.2
Lime Addition Hydrated lime slurry is added to the precipitation tanks (tanks 3 and 4) to control the pH. The pH in the first precipitate tanks is controlled between 9 - 11. The pH probe output then feeds back to the pH controller, which regulates the Lime dose rate by adjusting the output to a flow control valve (pinch valve). A timer is programmed to periodically pulse the lime flow control valve fully open for a short period to remove any scale and build-up on the valve or pipeline.
3.13.3
Hydrogen Peroxide Addition Hydrogen peroxide is dosed to the first mixing tank to promote the dissociation of Arsenic and Copper with Cyanide ions. The dosing rate of hydrogen peroxide is automatically controlled through the PCS based on the required hydrogen peroxide to cyanide ratio. The operator inputs the following into the PCS algorithm: •
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The incoming solution CNwad content
19
•
Hydrogen peroxide concentration
•
Ratio of hydrogen peroxide to CNwad ratio
•
Positive displacement pump flowrate : speed calibration curve
Based on these inputs as well as the measured solution flowrate to the AsCu circuit the hydrogen peroxide pump speed is adjusted to maintain the required hydrogen peroxide to CNwad ratio in solution.
3.13.4
Ferric Sulphate Addition Ferric sulphate is dosed to the second mixing tank to enhance co-precipitation of arsenic. The dosing rate of ferric sulphate is automatically controlled through the PCS based on either the solution ORP or a calculated based on the concentration of arsenic in solution (selection of control mode is made in the PCS). In ORP control mode, the speed of the ferric sulphate dosing pump is automatically adjusted to achieve a set oxidation/reduction potential (ORP) as measured by the inline ORP meter installed in the mixing tank. In ratio control mode, the operator inputs in the PCS algorithm the f ollowing: •
The incoming solution As content
•
Ferric sulphate concentration
•
Ratio of ferric sulphate to As
•
Positive displacement pump flowrate : speed calibration curve
Based on these inputs as well as the measured solution flowrate to the AsCu circuit the ferric sulphate pump speed is adjusted to maintain the required ferric sulphate to As ratio in solution.
3.13.5
Oxygen Addition Oxygen is added to each leach tank through a sparge at the bottom of the tank. Control over oxygen addition to the leach tanks is achieved by adjusting manual valves located at the tanks. The dissolved oxygen (DO) must be checked on a periodic basis by the operator using a handheld DO meter.
3.14
Water P&ID 5800-PI-128 to 130
3.14.1
Fresh Water Fresh water will be pumped from the underground mine to a fresh water dam to service the process plant, and general site buildings. The dam pumps deliver fresh water into a fresh water storage tank at the crushing plant and process plant sites. The fresh water storage tank will supply water for process make-up requirements, gland water, dust suppression, reagent mixing and fire services. Fresh water flow rate pumped into the fresh water tank is monitored on the PCS. Pressure of the same line is indicated locally.
3.14.2
Gland Water P&ID 5800-PI-130 Gland water is supplied by the plant raw water pumps off the fresh water tank.
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A single gland water pressure is supplied to all pumps in the plant. A flow alarm is displayed on the PCS if a low flow is detected. Each gland water addition point at relevant slurry pumps is instrumented and controlled identically. The instrumentation at each pump consists, a low flow switch, a flow control orifice and a non return valve.
3.15
Fire Water P&ID 5800-PI-131 Control of the firewater pumps is incorporated in the vendor package ICS and independent of the PCS, other than the following PCS alarms: •
•
3.16
A common fault alarm from the vendor control panel. An alarm indicating that the diesel firewater pump is running. (This pump must be shut down manually following an auto start. Hence, the operator needs to be aware that it is running.)
Plant Potable Water Supply P&ID 5800-PI-132/133/134 A separate fresh water system will be harvested from two well pumps to service the accommodation camp. The well pumps deliver fresh water to a pre-treatment tank and then to a potable water treatment plant(vendor package). The package will be controlled by a vendor supplied ICS without supervision or monitoring by the PCS. Water discharging the vendor package will be stored in a potable water storage tank. The potable water distribution system for the plant and camp has a duty and standby electric distribution pump
3.16.1
Safety Showers and Eye Wash Stations P&ID 5800-PI-133 Safety showers and eyewash stations are located around the process plant. These are all supplied from a water header. All showers and eyewash basins are activated by local push levers. The potable water pumps operate at fixed speed. The system is designed based on the pumps delivering higher pressure and flow than the maximum required with the system pressure controlled by a manually operated mechanical backpressure-sustaining valve.
3.17
Decant Water P&ID 5800-PI-120 Two submersible pumps will be used to reclaim water from the tailings dam. This unit is vendor supplied and will be fitted with level indication that will be shown on the PCS. Local pressure indication will be provided on the discharge side of the submersible pumps. Two additional booster pumps will deliver the decant water to the barren solution tank.
3.18
Barren Storage and Distribution P&ID 5800-PI-126/127 Barren solution from the precipitation filters is combined with decant from the tailings pond in the barren solution tank. Decant water flowrate is measured and monitored from the PCS. An additional fresh water line fitted with a control valve will supply the barren tank with makeup water as needed. Three centrifugal pumps will deliver the barren solution to a distribution loop through a main line. A pressure indicator provides local monitoring of this line.
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3.19
Compressed Air Cycling and lead/lag arrangement of the operating and standby compressors will be via a vendor supplied Independent Control System (ICS), with local start/stop only however the following information is displayed on the PCS
3.19.1
•
Run status.
•
All general alarms.
•
Critical pressure indications.
Control and Indication Compressed Air Pressure Instrument air and process/service air pressures will be measured and indicated locally and indicated and recorded on the PCS.
3.20
Oxygen Supply The PSA oxygen plant is vendor supplied with an Independent Control System (ICS). The PSA plant is controlled from the ICS only however the following information is displayed on the PCS
3.20.1
•
Run status.
•
All general alarms.
•
Critical pressure indications.
Control and Indication Oxygen Pressure Oxygen supply pressures will be measured and indicated locally and indicated and recorded on the PCS.
3.21
Diesel Storage Diesel will be delivered to site by truck. The diesel will be off-loaded into a number of tanks situated around the Inmaculada site. All tanks contain level indicators with the level displayed both locally and at the PCS.
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Appendix 1 – Automatic Group Start-up Sequence Example The following is a systematic description of a typical group start sequence that can be activated from the PCS Operator Control Stations (OCS). •
The OCS will indicate if the sequence is ready for a start by displaying a coloured text message describing the sequence and stating that it is ready for an auto start.
Sequence ready status indicates that: •
All drives required for the group start are healthy and ready to run.
•
The Remote/Maintenance switch on the LCS is set to Remote.
•
All alarms are reset.
•
The requisite down stream equipment is running.
A display to show the status of all sequence interlocks and devices will be available. The status display will show the control selection of all devices in the sequence. If drives are faulty, the fault will be indicated by the drive icon changing to orange and the fault will be listed on the alarm page and detailed on the drive status page. If a valve in the sequence is selected to “manual”, the sequence cannot be started. If a drive faults or a valve fails during a sequence, the sequence will stop until the fault is rectified. The sequence can then be continued following a sequence ‘restart’ command. If a sequence is ready then the operator can start the sequence by clicking on the start icon. A “please confirm” message will then appear that requires the operator to press the enter key. The icon will then change colour to indicate a start in progress. •
•
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A graphic screen will diagrammatically indicate the progress of the start up sequence so that the operator can monitor the progress and easily see which drive fails. On completion of a successful sequence start, a message indicating that the start is complete will be displayed.
Appendices
AUTOMATIC GROUP SHUT DOWN SEQUENCE EXAMPLES A group shutdown can be initiated by the operator or the sequence logic acting on a process or fault considerations. The following is a systematic description of a typical group stop sequence that can be activated from the OCS. If a group start is underway, it can be terminated by initiating a group stop command. A group stop cannot be terminated by a group start unless otherwise stated. This is due to the possibility that the shutdown may not be a reverse of the start-up sequence. •
•
•
•
The OCS will indicate if the sequence is running or starting by displaying a text message describing the status (see previous section). A shutdown sequence is initiated by the operator clicking on the shutdown icon. A “please confirm” message will then appear that requires the operator to press the enter push button. The icon will then start flashing to indicate a shutdown in progress. A graphic screen will diagrammatically indicate the progress of the shutdown sequence so that the operator can monitor the progress. On completion of a successful sequence shutdown a “Shutdown complete” message will display.
For some shutdown sequences, it will be necessary to change mode selection for some devices to “Auto” to allow the sequence to complete without halting. This will be defined for each sequence.
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Appendices
