Controlling a tailings pipeline to maximise concentration and minimise water consumption

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IRR Conf., November 2013

MaxSolids™

Controlling a Tailings Pipeline to

Maximise Pumping

Concentration and Minimise

Water Consumption and Energy

Allan Thomas Slurry Systems Engineering Pty Ltd

Typical Tailings Pumping System

TAILS RETURN WATER•

TAILING RETURN WATER TO PROCESS

THICKENER

MULTISTAGE CENTRIFUGAL

THICKENER

U/F PUMPS

TAILINGS

SUMP TAILINGS PIPELINE WATER RETURN PIPELINE RETURN WATER PUMPS

DISCHARGE

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Optimum Tailings Pumping Operation • For constant solids throughput, if flow rate is decreased the concentration increases.

• Optimum operating velocity is just above the deposit velocity, whether deposition is due to laminar transition or turbulent deposition.

• By operating just above deposition Maxsolids™ gives maximum concentration, minimum water consumption and minimum pump power.

MaxSolids Control System (Patented) • Based on measurement of pressure drop

over a short length of slightly larger

diameter pipe at start of pipeline. • This pressure drop is combined with flow rate and density from DCS to give the MaxSolids parameter M. • MaxSolids control system progressively decreases flow rate within limits of M to optimise maximum concentration.

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MaxSolids Parameter M For Newtonian homogeneous turbulent flow: ДР/L = (32/17) fp Q2/D5 Approximating f with Blasius friction factor: ДР/L = K pt-n u" Q2-n/D5+n For a particular pipe diameter:

К = ДP/L /(p'-" u" Q2-n) for a Newtonian fluid

Viscosity is related to density so absorb u into p

M =ДР/L /(pa Q°)

for a non-Newtonian fluid

Two Types of Deposition Turbulent or Laminar

Magnetite in 210 ID Pipe 18 16 Actual Laminar deposition, 67.5% at transition velocity 1.63 m/s

12

67.5%

10 Transition Head Loss Gradient (m slurry/km) 14 4 2 6 0.5 Velocity, 60% 0.8 m/s 60% Velocity (m/s) - "Turbulent deposition", 67.5%, 1.03 m/s Turbulent deposition, 60%, 1.07 m/s 1.5 2

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When Deposition is Controlled by Laminar Transition

Pressure Gradient versus Flow Rate, 743 ID Pipe Gold Tails, p80 = 130 microns, High Rheology 100 90

60 -.- Water Laminar flow * Turbulent flow

.....- -56%

- 58% -60% - 62%

1000 2000 3000 4000 Flow Rate (cu.m/h)

When Deposition is Controlled by Laminar Transition

MaxSolids Number versus Flow Rate, 743 ID Pipe Gold Tails, p80 = 130 microns, High Rheology 200

· 160 180

5: 140 Z • 120 --Water

HOM -56% -58% - 60% -62%

1000 2000 3000 4000 Flow Rate (cu.m/h)

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Deposition under Turbulent Flow

Pressure Gradient versus Velocity, 593 ID Pipe Gold Tails, p80 = 150 microns, Low Rheology..-•Water

• 50% -55% - 60%

Pressure Gradient (kPa/km) 100 10 1 Velocity (m/s) 2 2.4 -Vd, 55% - Vd, 60% —Vd, 50% — 65% •Vd, 65%

Deposition under Turbulent Flow MaxSolids Number versus Velocity, 593 ID Pipe Gold Tails, p80 = 150 microns, Low Rheology

---Water -50% - 55% - 60% - 65% -Vd, 50% -Vd, 55% -Vd, 60% •Vd, 65%

0.6 0.8 1.2 1.4 1.6 1.8 2 2.2 2.4 Velocity (m/s)

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Case Study

• 1000 tph dry tails • 500 mm ID pipe • 10 kms pipeline length. Flat route profile • Solids SG 2.8 • Particle size, p80 = 130 microns • Thickener underflow concentration 52% to 60% • Rheology Yield stress 4.5 Pa at 60%, 1.35 Pa at 52% Plastic viscosity 11.8 mPas at 60%, 6.4 mPas at 52%

Energy and Water Savings are Achieved by Operating at Maximum Concentration (60%) Just Above Transition Pump Head versus Velocity 500 mm Pipe, 10 kms -. Water

70 Base Case, Cw=52%

50 MaxSolids control - Head vs Q, 60% Cw=60%, 0.20 kWh/t

Pump Hd, 60%

Pump Head (m of slurry) 10 0.6 0.8 1.0 1.2 1.4 1.6 Velocity in 500 mm Pipe (m/s) Energy=0.36 kWh/t, 1.8 2.0 - Operating Point, -Operating Point, —Head vs Q, 52% 1000 tph, 52% 1000 tph, 60% Pump Hd, 52%

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Case Study

Pressure Gradient Comparison at 60% Concentration 500 mm Pipeline and Larger Diameter Measuring Pipe 100 200

70

80 60 Pressure Gradient, MaxSolids Number, Cw=60% 140 160 120 Number

Main Pipeline - - - 100 Pressure Gradient (Pa/m) 90 30 20 10 40 50 0 700 Pressure Gradient, Measuring Pipe 800 900 Flow Rate (cu.m/h) 1000 1100 1200 L Transition in Measuring Pipe 1300 1400 180 80 20 40 MaxSolids

Case Study, 1000 tph Solids Throughput

Benefits of Operating at 60% c.f. 52%

At 52% At 60% Concentration Concentration MaxSolids Control

Flow rate (cu.m/h) 1,280 1,024 Velocity in 500 ID pipe (m/s) 1.81 1.45 Pump head (m of slurry) 48.3 30.5 Slurry Power at 0.7 efficiency (kW) 361 198 Water Return Power at 0.8 efficiency (kW) 85 22 Annual energy (MWh) (0.9) 3,516 1,734 Annual energy cost saving at 10c/kWh $178,000

(50% saving)

Water in slurrv (cu.m/h) 923 667 There will also be Annual water savings because water not pumped to TSF is not subject to evaporation.

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Advantages of MaxSolids Control - Laminar Deposition • Once the flow is laminar the coarser particles will start to slowly settle. • But with a fine particle tailings slurry, a bed of solids may not form for tens or even hundreds of metres from the pump(s). • MaxSolids detects the onset of laminar flow rather than the presence of a bed. • MaxSolids detects the onset of laminar flow in the measuring pipe while turbulent flow still exists in the main pipeline so there is no chance of bed formation in the main pipeline.

Advantages of MaxSolids Control - Turbulent Deposition • When deposition occurs under turbulent flow, a bed of solids forms immediately, within a few metres of the start of the measuring pipe. • The MaxSolids system reacts to the higher pressure gradient and starts a step increase in the flow rate. • Because the velocity in the main pipeline is slightly higher than in the measuring pipe, deposition has not occurred in the main pipeline.

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Feed to pipeline is either direct from thickener or via a break tank

• When the pipeline is direct coupled to thickener, MaxSolids controls flow rate to a minimum, resulting in higher thickener underflow concentration. (The thickener will need to be capable of safely operating under this condition or the thickener control will need to overide the MaxSolids control)

• When the pipeline is fed from a break tank, the thickener needs to be able to deliver at higher concentration than the pipeline can handle with MaxSolids then controlling dilution water addition

Applicability

• Applicable to almost all thickener underflows.

• MaxSolids not applicable to very

heterogeneous slurries such as gravel or coarse coal rejects where the pressure gradient exhibits a gradual, rather than a sudden deviation from the homogeneous pressure gradient curve. But these slurries are not thickened anyway.

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MaxSolids™

Maximises pumping concentration within the restraints of the thickener and pumping system, so as to minimise the amount of water sent to the TSF and minimise energy consumption.

• UTILIZES CONVENTIONAL, COMMERCIALLY

PROVEN COMPONENTS

• SOFTWARE BASED - PROGRAMMED INTO PLANT

DCS

• READY FOR FULL SCALE DEMONSTRATION

• NO RISK TO OPERATIONS

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