Improving Bucketwheel Reclaimer Performance and Asset Integrity using SCADA Data

Improving BW Reclaimer Performance & Asset Integrity using SCADA Data

Bulk Materials Handling Conference, Perth

Mark BiggsAdam Mayers

Outline


• Introduction / context

• Operating within design envelope of machine – AS4324.1 Complianceo Using SCADA data to compare actual operating loads to design loads. o Operating loads (conveyor live load, digging loads, etc).o Machine balance monitoring.

• Capital Planning – When will the machine reach the end of its life?o Fatigue damage monitoring.

• Improving throughput performance by monitoring SCADAo Fundamentals of Operationo Reducing trips and unexpected downtime.o Alternative control philosophieso Identify opportunities for performance improvements.

Bucketwheel Reclaimers

• Bucketwheel reclaimers are extensively used in materials handling facilities in Australia. Predominately slewing, luffing, long travel machine.

• Large, expensive items of equipment. Many new machines have been constructed in last 5 years.

• Typically high required availability and utilisation.

• Machines typically fitted with SCADA system (Supervisory Control and Data Acquisition).

• Data available to optimise performance within design envelope of machine. Challenge is to turn this Data into useful Information.

• Approach can be applied to different equipment types.


AS4324.1 Design Envelope

• AS4324.1 – 1995 is the Australian Standard relating to ‘Mobile equipment for continuous handling of bulk materials’

• Specifies how machine structures are designed for structural strength and fatigue life.

• New revision to be released in 2015

• Vast majority of new machines in Australia have been designed to this standard.


AS4324.1 Load Combination Table 3.7 – Related to Fatigue and Strength Design Loads, and SCADA Data

Rare loads and accidents – strength designe.g. -Flooded Belt-Collisions-Grounding-Cyclone

Operational loads used for strength design-Dead weight-Conveyor-Digging-Dynamics

Loads used to calculate fatigue life of machine structure-Conveyor-Digging

Abnormal operation strength design-High digging loads-Slew bearing jacking

Many of the loads can be related to drive torque, or production rate which are data logged by the control system (SCADA system)Improving BW Reclaimer Performance & Asset Integrity

using SCADA Data

Using SCADA Data to Compare Real Loads with AS4324.1

Luff cylinder forces:AS4324.1-Dead load balance-Slew brg loads-Combined live loads-Collisions

Belt weigher tonnes/hr:AS4324.1Conveyor live load (F)Flooded belt (FF)

BW drive powerAS4324.1Normal digging (U)Abnormal digging (UU)

Slew drive power and angle:AS4324.1-Lateral digging (S)-Lateral collision (FS)-No. Slew cuts for fatigue

Bucketwheel boom

Counterweight


Example – Conveyor Live Loads

Live Load (F) is the normal operating load for strength design.

The load can be converted to tph using the belt speed (green line)

Flooded Belt Load (FF) is the accidental load used for strength design

Measured conveyor throughput is below strength design envelopes.

Fatigue design to AS4324.1 is based on 0.8 x (F) = 15,113 tph

Conclusion: Conveyor live load is within strength and fatigue design envelopes during this SCADA data sample.


0 20 40 60 80 100 120 140 1600

x 105 BW motor current

BW motor current (A)

Bin

cou

nts

(fre

quen

cy)

0 20 40 60 80 100 120 140 1600

50

100

Cum

ulat

ive

sum

(%

)

Cumulative sumAS 4324.1 fatigue digging CU.U

Motor full load current 108 AAS 4324.1 normal digging U 175 kNAS 4324.1 abnormal digging UU 239 kN

Example – Digging Loads A histogram is useful for large data sets as it gives an idea of the amount of time at each load level.

Green line represents digging load used in fatigue calculations.

Blue line represents Normal Digging Load (U) used in strength design.

Conclusion: Digging load is higher than assumed in the fatigue design which may reduce the life of certain areas of the structure. The loads are generally within the strength design envelope

Magenta line represents the Abnormal Digging Load (UU) used in strength design.


Example – Luff Cylinder Loads

The combined effect of the live loads can be seen in the luff cylinder pressures/loads.

We can also infer information about the dead load balance e.g. counterweight trim compared to design.


Example – Luff Cylinder Loads

Machine is slightly discharge boom heavy compared to design balance (green line)

Peak tensile luff cylinder loads approach the AS4324.1 III/6 Flooded Belt and Blocked Chute Combination but are inside the strength envelope (red dotted line)

Loads exceed the fatigue design assumptions quite often (blue line) Conclusions:

- Strength OK.- May need CW trim- Fatigue life may be shorter than design


Capital Planning – Remaining Fatigue Life

• Machines specifications typically require 20 years of operation or perhaps 100,000 operating hrs. Typically, primarily limitation on life of machine structure is accumulated steel fatigue damage which results in cracking, at which point, machine replacement is often required.

• Fatigue is caused by stress fluctuations at the welds. The magnitude of the stress range and the number of cycles are important.

• For a Bucketwheel Reclaimer, the stress fluctuations and cycles are mainly proportional to the number of slew cuts i.e. the digging and conveyor load cycles, and magnitude of loads. The designer therefore converts the 20 year life requirement to a number of slew cut cycles for the fatigue design calculations. The conversion is based on the annual throughput rate, stockpile shape and digging parameters.

• SCADA data can be analysed to count the number of slew cuts that actually occur per million tonnes reclaimed and estimate the magnitude of loads, to estimate remaining life based on historical throughput data.


Example – Remaining Fatigue Life

0 90 180 270 3600

500

1000

1500

2000

2500

3000

3500

4000

4500

5000Slew passes at slew angle

Slew angle (deg)

Sle

w p

asse

s pe

r m

illio

n to

nnes

rec

laim

ed p

er q

uadr

ant

Statistic can be calculated for number of slew cuts per million tonnes reclaimed e.g. 4,300 slew cuts per Mt


Example – Remaining Fatigue Life

Historical production records converted to accumulated slew cuts e.g. 4,300 x annual production.

Variations in the production rate are captured.

Current point in time

Estimated point in time when the design fatigue life will have been consumed.

Suited to longer term capital planning i.e. approximate machine replacement


Example – More Detailed Fatigue Assessment

SCADA analysis and FEA can be used together to derive stress/cycle distributions as inputs to fatigue life calculations.

More accurate because it includes the load variations and cycles.

Suited to life extension studies and targeting resources for asset integrity inspections.

Finite Element Structural ModelFinite Element Structural Model

LoadsLoads

Stress cyclesStress cycles

Fatigue life calculationFatigue life calculation


Improving Performance - Fundamentals of Operation

Re-positioning Losses at ends of cut

Trips result in production losses

Geometric & Control opportunities


Example – Modifying the Geometry of the Reclaim Process

SCADA data review and subsequent reclaim simulation indicated that a Stacker-Reclaimer was under-performing. One suggested change including moving from 4 bench to 3 bench reclaiming – estimated 10% improvement in average reclaim rate.

Change implemented in early 2015. SCADA review confirmed approx. 10% increase in average rate!


Example – Troubleshooting Trips to Minimise Production Delays using 3D Graphics: Slew Clutch Alarms

Colour scale shows SCADA parameter as a function of 3D boom tip position e.g. BW current, throughput, slew torque

Black dots are logged alarms/trips which represent production delays (lost revenue) Concise way of finding patterns using very large data sets e.g. ~5 million data points in

picture below Easy to see that trips mainly occur at outer edges of lower benches using this technique Not easy to look at these patterns using normal “trend” software

1 month of 1Hz data1 month of 1Hz data


Example – Troubleshooting Trips to Minimise Production Delays using 3D Graphics: Slew Clutch Alarms

Trips occur when slew speed is changing quickly.

Zooming in on individual trips found that the slew brakes were being applied incorrectly.

Brake always applies before trips


Example – Troubleshooting Trips to Minimise Production Delays using 3D Graphics: Luff Cylinder Trips

Machine balance is boom heavy Luff cylinders trip the machine due to

spikes in the digging load Each black dot is a trip which stops the

machine until it is re-set. The average delay is 3 mins

195 alarms in 90 days 195 alarms x 3 mins x 8,500 tph x $60/t

= $5M potential lost revenue per quarter $20M annualised

195 trips

Trip frequency vs duration



Add 2 tonnes to counterweight

Trips reduce from 195 to 69



Add 8 tonnes to counterweight


Example – Identification of Repositioning Losses

12 second delay between weightometer and BW. Consider incl. some BW torque feedback or relocate weightometer.

Significant repositioning losses, particularly at far end of slew cut.


Additional Opportunities

• Throughput measurements typically lag behind reclaim operation → slows control system response. Alternative more direct feedback, such as bucketwheel current or torque arm feedback control can be effective.

• Using SCADA data to benchmark performance against similar machines in fleet. Recent example showed two identical machines were performing differently: Reclaimer 1 average = 2815 TPH, Reclaimer 2 average = 3050 TPH → 8% difference.

• Learn mode algorithms can be implemented to provide predictive feedback based on SCADA data. Control of one slew reclaim cut is influenced by previous slew reclaim cuts (e.g. pile edges, soft / hard sections of stockpile etc).

• Good stacking is very important!


Summary – Benefits of SCADA based Engineering Analysis

Asset Management

• Understand whether operating machines are compliant with AS4324.1

• If not full compliant, risks can be explored

• Targeting structural integrity inspections to fatigue prone areas

• Understanding machine balance via the luff cylinders.

Capital Planning

• Estimate when machine may need to be replaced in the future based on remaining fatigue life.

Production

• Reduce production losses due to overload trips

• Identify under-utilisation within the design envelope and opportunities to increase production rates.

• Benchmark production performance against similar machines in the fleet

• Highly cost effective method of “sweating the assets” for maximum productivity.


Thank you!


Improving Bucketwheel Reclaimer Performance and Asset Integrity using SCADA Data

Engineering

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