wqd2011 – breakthrough process improvement – silver winner – dubal - increase current...

Increase Current Efficiency of Potline 3 (P/L-3)

2

Dubai Aluminium Company Limited (DUBAL)

• Annual Production of > 1 million tonnes of aluminium

• >4000 Employees

• Based in Jebel Ali, Dubai

• 8 Potlines consisting of 1573 aluminium cells

• One of the few smelters in world to produce primary high purity metal for use in electronics and aerospace industries.

Introduction

3

• Smelting converts alumina (ore) into aluminum metal

through electrolysis process

―By using Direct Current (DC)

―Current Efficiency (CE) is the ratio of electrical direct

current that results in actual metal production

• Therefore, improvement in Current Efficiency remains

one of the strategic objectives of any Aluminium

smelter

Project Background

4

Problem Statement:• Potline 3 Current Efficiency is at 92.9% for H1 2009 which is below target

since increase of current amperage to 200 kA,

• resulting in decreased plant hot metal output.

Project Target: Increase average Potline 3 current efficiency to

target of 93.1% for 2010.

1. Define 2. Measure 3. Analyze 4. Improve 5. ControlDefine Phase

5

In Scope:

Potline 3 Process Parametersand Procedures

Out of Scope:

All other Potlines

Unit of measurement: Potline 3 Current Efficiency

Operational Definition: Monthly Average CE from iRPMS (Smelting Database System)

1. Define 2. Measure 3. Analyze 4. Improve 5. Control

Project Scope:

6

Team Charter:

Data collection and implementation of solutions.Act, Manager, Line 3, 7 & 9Devadiga H.R. 7

Data collection and implementation of solutions.Snr. Manager - PC PR &

CLMaryam Al-Jallaf8

Data collection and implementation of solutions.Supt Potroom OperationsTariq Majeed 6

Team Leader.Manager – Projects D18Daniel Whitfield1

Data collection and implementation of solutions.Snr Process Control Engineer – PotroomsAdam Sherrif 9

5

4

3

2

S.No

Data collection and implementation of solutions.Snr ManagerNajeeba Al-Jabri

Data analysis and report making.Snr. Planner – ProdnServicesSaif Mohamed

Data analysis and report making.H.O.D: PC-CLMohamed Tawfik Boraie

Data analysis and report making.Snr Process Control Engineer – PotroomsAndries Louw

Project ResponsibilitiesFunctional RoleName

Data collection and implementation of solutions.Act, Manager, Line 3, 7 & 9Devadiga H.R. 7

Data collection and implementation of solutions.Snr. Manager - PC PR &

CLMaryam Al-Jallaf8

Data collection and implementation of solutions.Supt Potroom OperationsTariq Majeed 6

Team Leader.Manager – Projects D18Daniel Whitfield1

Data collection and implementation of solutions.Snr Process Control Engineer – PotroomsAdam Sherrif 9

5

4

3

2

S.No

Data collection and implementation of solutions.Snr ManagerNajeeba Al-Jabri

Data analysis and report making.Snr. Planner – ProdnServicesSaif Mohamed

Data analysis and report making.H.O.D: PC-CLMohamed Tawfik Boraie

Data analysis and report making.Snr Process Control Engineer – PotroomsAndries Louw

Project ResponsibilitiesFunctional RoleName


7

Stake Holder Model : ARMI Chart

Adam Sheriff

Maryam Al-Jallaf

Devadiga H.R.

Tariq MajeedP/L-3 Process Technician

VP-Power & Desal.Najeeba Al JabriP/L-3 Operators

VP-FinanceSaif MohamedP/L-3 Technicians

VP-MarketingMohamed Tawfik BoraieP/L-3 Superintendent

VP-CasthouseAndries LouwManager D-18VP-Smelter Ops.

Interested PartyMemberResourceApprover


8

Project Schedule


9

2. Measure1. Define 3. Analyze 4. Improve 5. ControlMeasure Phase

• Current efficiency is key measure of process performance, and is regularly reported and monitored

• It is difficult to be measured directly; therefore, inferred from actual metal production as below:

Actual Hot Metal ProductionCurrent Efficiency = --------------------------------------

Theoretical Hot Metal Production

• Three months average taken to ensure reasonable accuracy of the data

10

Measurement System Analysis

• Review of existing plant system for measuring and reporting current efficiency showed no significant concerns over accuracy or precision

2. Measure1. Define 3. Analyze 4. Improve 5. Control

• Actual Metal Production =Total Weight of Metal delivered to Casthouse

Casthouse scales regularly calibrated and checked – Verified Calibration Records and is OK

• Theoretical Metal Production = f (Amperage supplied by Power Plant)

Power Plant amperage supply tested on monthly basis – Found Ok

Measurement System – Found Satisfactory

11

Carbon Dusting

Anode Spike

High Bath Temp /

Low AlF3

Excessive Sludge

Cell Underfeeds

Excessive Anode Effects

Bath Height Too Low

Cell Overfeeds

Low Bath Temp /

High AlF3

Excessive Anode Airburn

BRSP Set too low

Cell ACD Reduced

Al solubility in bath

increases

Al mixes back into

electrolyte

Oxidation of Al to Al2O3

Low Current

Efficiency

Cell Becomes Unstable

Excess heat

generation

Current bypasses electrolyte

Current Efficiency – Back Reaction Flow Chart

Possible causes for low Current Efficiency Bath temperature/AlF3 Age Anode Effects Alumina Feeding Metal and Bath height Base Resistance Set Point (BRSP) Noise/stability Operational problems Anode Problems

3. Analyze1. Define 2. Measure 4. Improve 5. ControlAnalyze Phase

Tool (s) Applied:- Process Flow

Diagram

12

Tool (s) Applied: Multi-Variable Linear Regression

• In multi-variable linear regression, there are several independent variables up to N.

Yi = βo + β1xi + β2xi + … where i = 1, …. N.

Variable P-valueBath Temperature 0.000

AlF3 0.034Age 0.038AEF 0.066

TRSP 0.094UF Duration 0.275

Time Unstable 0.305Dumps 0.451BRSP 0.537

Metal Height 0.554Bath Height 0.583

Average Resistance 0.608Volts 0.736Noise 0.746

• Age refers to life of reduction cell, and hence it is an unassignable cause

3. Analyze1. Define 2. Measure 4. Improve 5. Control

• P-value shows the significance of the correlation (p-value of 0.05 = 95% statistical significance or confidence). As much P-value closer to 0.0 as much as the parameter is statistically significant

• Strongest correlation between bath temperature and AlF3 (interrelated variables)

Needs more investigation

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• Based on accumulative experience, it is proven that increase of 5oC in bath temperature can lead to 1% drop in current efficiency

960

962

964

966

968

970

972

974

976

84 86 88 90 92 94 96 98 100

Current Efficiency (%)

Bath

Tem

pera

ture

(C)


Bath Temperature

Linear regression covers the relationship:

CE = (-0.2259 x bath temperature) + 309.13

(R2= 0.9543)

14

• Relationship between BRSP/ACD and CE well established

84

86

88

90

92

94

96

98

100

13.5 14.0 14.5 15.0 15.5 16.0 16.5

BRSP (micro-ohms)C

urre

nt E

ffici

ency

(%)

• Initial analysis looked BRSP and CE. No big correlation above ~14.75 µ

• Some correlation < 14.75 µ

Base Resistance Set Point (BRSP)


15

Tool (s) Applied: Cumulative chart

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Number of Cell (%)

Loss

of C

urre

nt E

ffici

ency

(%)


~20% of cells represent 47% of total CE loss (Actual CE – Target CE).

Poor Performing Cells

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Root Cause 1: High Bath Temperature

Root Cause 2: Low Base Resistance Set Point (BRSP)


Validated Root Causes/ Parameters

× Age – Life of Cell: Difficult to address this cause

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Improve Phase

Current Efficiency Vs Bath Temp

y = 0.052x + 92R2 = 0.6879

91.0

91.5

92.0

92.5

93.0

93.5

94.0

94.5

95.0

22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 1 3

Week No. (2009 - 2010)

Cur

rent

Effi

cien

cy (%

)

954

956

958

960

962

964

966

968

Bat

h Te

mp

(°C

)

Bath TemperatureCurrent EfficiencyLinear (Current Efficiency)

Root Cause 1: Action plan for high bath temp and low CE pots

4. Improve1. Define 2. Measure 3. Analyze 5. Control

Dec. 2009Daniel Whitfield

Adjust Bath Chemistry to improve Current Efficiency

1

Completion Date

Responsibility

Action PointS. No.

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• Established Control Limits so that BRSP not to be lowered below 14.5 µ without careful monitoring of the current efficiency

• Critical BRSP Limit of 14.75 µ.

• Increased the BRSP in low CE/BRSP cells

• Example of “action plan for implementation” as a result of weekly meetings is given below

Cell CE - 4wks CE - 16wks CE - 52wks Action Person Target Date146 89.3 90.6 92.9 Increase BRSP by 0.1µcheck dumpweight AS/MSW 07/01/2010198 90.3 91 92 Check BFT, Cu tab and dumpweight MSW 10/01/2010271 92.5 91 91.9 Improving in last 28 days, no action 20/01/2010149 89.3 91.1 93 Increase BRSP by 0.05µcheck Cu tab MSW 07/01/2010117 92 91.2 90 Under Fe attack FM NA102 93 91.3 91.5 Increase BRSP by 0.1µ AS 07/01/2010


• Average increase of 0.34 µ in 25 cells, average increase of 1.5% CE

Root Cause 2: Action plan for low Base Resistance Set Point (BRSP)

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Current efficiency after improvement actions

91.5

92.0

92.5

93.0

93.5

94.0

94.5

95.0

95.5

Nov-07

Jun-0

8

Dec-08

Jul-0

9

Jan-1

0

Aug-10

Feb-11

Sep-11

Curr

ent E

ffici

ency

(%)

193

194

195

196

197

198

199

200

201

Ampe

rage

(kA

)

Monthly CE3-month Running AverageTarget CEAmperage

Project Start


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• List of poor performing cells in Potline 3 developed, updated and released on weekly basis for setting up proper action plans.

• Work Instruction was developed to diagnose and action poor performing cells

System established for identifying and improving poor CE cells

9693908784

Summary for L3 CE, June 2009

98969492908886

Summary for L3 CE, Feb 2010

+1.3%

-0.76%

+1.38%

Difference

91.4 %

2.47 %

92.32 %

227

92.7 %1st Quartile

1.71 %STD. Dev.

93.70 %Mean

227Sample size

Distribution of L3 CE, Feb 2010Distribution of L3 CE, June 2009

After the ProjectBefore the project

5. Control1. Define 2. Measure 3. Analyze 4. ImproveControl Phase

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• Potline 3 monitoring on daily basis by Potline Engineers and Technicians through potroom monitoring and reporting system (Smelter Analytics)

• Fine-tuning and changes to pots operating targets

5. Control1. Define 2. Measure 3. Analyze 4. Improve

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Increased average Potline 3 current efficiency

92.292.492.692.8

9393.293.493.693.8

9494.2

2009, 2nd Half 2010, 1st Half 2010, Full year 2011, YTD

Cur

rent

Eff

icie

ncy

(%) Actual CE%

Target CE%

Project yielded re-occurring financial benefits of AED 1.47 millions per annum

Project Success & Benefits

Improved overall Potline performance

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Recognitions:

• All team members received gift and cash award

• Project selected for Share Best Practice Session – to 200+ employees

• Nominated for CII Symposium

Learnings and Roll-over:

• Documentation of the project report

• Use of statistical tools and gained better understanding w.r.t. Smelting Process

• Roll-over of the successful initiatives from projects – to sister Potline 1– Achieved similar increase in current efficiency

Project Closure

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• Achieved one of the best current efficiencies in D-18 type of cell design (at higher Amperage of 200kA)

• Combination of technical as well as statistical methods by using DMAIC approach

• Project experiences rolled-over to Potline of similar cell design and resulted in improvements

• Quantum contribution to company’s process performance

• Environmentally beneficial

Why this Project is an Excellent Improvement Example?

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Thank you

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