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This information is confidential and was prepared by Bain & Company solely for the use of our client; it is not to be relied on by any 3rd party without Bain's prior written consent.
DRAFT
A different approach to teaching Hydrometallurgy
June 2009
2071121-AP4-Meeting with Prince
Presentation…
• Presentation is not overly technical …
• …but describes a portion of a journey we have embarked upon as the Processing Division of Anglo Platinum
• It will focus on the efforts of a team of young engineers participating in the Anglo Graduate Development Program (AGDP)
• AGDP entails a two year program consisting of varied plant experience across process division, supplemented by, discipline specific, examinable course work (UCT) culminating in an operational basedplant survey
• Today it is my privilege to share with you a part of our story…
3071121-AP4-Meeting with Prince
Number of particles in by flow into reactor
Number of particles out by flow from reactor
In by reactionOut by reaction
Num
ber
dist
ribut
ion
Size
Number of particles in by flow into reactor
Number of particles out by flow from reactor
In by reactionOut by reaction
Num
ber
dist
ribut
ion
Size
2009 AGDP Hydromet Plant Survey
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Objectives
• AGDP students increase relevant skills base on a “real working operation”
• Consolidate previous fundamental learnings attained through course work in an applied manner to make “sense” of operational plant “challenges”
• Experience the powerful value associated with a collaborative approach to problem solving
5071121-AP4-Meeting with Prince
Novel approach to learning advanced concepts in hydrometallurgy
• Hypothesis framework – Clearly outline a problem to be solved which adds value to the organization
Contextualize the work – not just an exercise
• No pre-prepared lectures or notes
Test the ability to complement previous learnings with available knowledge bases
6071121-AP4-Meeting with Prince
Novel approach to learning advanced concepts in hydrometallurgy
• Build an a priori model to describe the behavior of the plant or unit operation to be studied
Test the ability to apply knowledge to fundamentally re-create the problem from first principles – acid test for
demonstrating understanding
• No use of commercial modeling or simulation packages to solve the math
Excel would be used to build the model – universal technical language which can also acts as a knowledge repository
7071121-AP4-Meeting with Prince
Novel approach to learning advanced concepts in hydrometallurgy
• Test the hypothesis - validating the model by collecting and comparing it to actual operational data
First hand experience that operational systems do behave according to the laws of physics – dismiss mythology
• Conduct the whole exercise in two and a half weeks
Demonstrate that the only possible way for achieving success in this situation would be that of a collaborative
approach
8071121-AP4-Meeting with Prince
Advantage of using a privileged asset
• From a hydrometallurgical perspective oxidative leaching, on a continuous basis, in a pressure autoclave is one of the most exciting unit operations to study or operate
• Hence it was decided use the BMR’s secondary leach autoclaves as a basis for the survey
• In conjunction with these valuable assets BMR has excellent technical and engineering library facilities
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Problem… Secondary leach is under capacity constrained…why?
CopperRemoval
PrimaryLeach
SecondaryLeach
LeadRemoval
CobaltRemoval
NickelElectrowinning
SulphurRemoval
Sodium Sulphate
NickelCopperMatte
Secondary LeachConcentrate
Nickel Cathode
Selenium Removal
CopperElectrowinning
CopperCathode
Caustic Soda
•Current capacity 21 ktpa Ni equiv. with 3 x 80 m3 autoclaves
•Objective: 21 ktpa Ni equiv with 2 x 80 m3 autoclaves (Hofirek and Nofal 1994)
10071121-AP4-Meeting with Prince
Secondary Leach Autoclave
Vent to cyclone
Discharge to Flash tank
Air Pump
Feed
Enriched Air Enriched Air Enriched Air
Steam
Air
1250Design Pressure (kPag)
13.6m
3.6m
80m3
Dimensions
Length
Shell ID
Volume
160Max Temperature (˚C)
25 mm
6.35 mm
Stebbins
Material of Construction
Mild Steel Shell
Lead lining
Layer of acid bricks
11071121-AP4-Meeting with Prince
Knowledge collation : Actions
• Familiarization with the principles of leaching with respect to the secondary leach
• Collection and collation of mechanical equipment specifications – both current and original Sherritt Gordon
• Review the control philosophy
• Review works instructions and meet plant operating staff -Business Manager-Operations Manager-BMR technical staff-Control room operators etc
• Review and be trained and declared competent in sampling and analytical methodologies
12071121-AP4-Meeting with Prince
Knowledge collation : Major finding
• Since commissioning in 1982 the secondary leach autoclave agitators type have been changed resulting in 3 autoclaves with different agitator configurations:
• Rushton Turbine
• A315
Secondary 3
Original
Secondary 2
Dual
Comp. 4 Comp. 3 Comp. 2Comp. 1
Why?
13071121-AP4-Meeting with Prince
The concept of an “a priori” model
• Entrenches a “back to basics” approach
• For a modelling exercise to be instructive in terms of understanding a system it needs to include all the pertinent fundamental building blocks which may manifest themselves in the day to day, month to month,and year to year operation of the system:
-Day to day : Flowrate or residence time-Month to month: Feed characteristics e.g. PSD-Year to year : Mechanical equipment e.g. agitator types
• Most published work to date (academically rigorous) characterising continuous leaching unit operations are solved and partially or totally fitted to actual operating data
14071121-AP4-Meeting with Prince
So what needs to be considered in the model
• Predominant or rate limiting reaction(s) vs. overall reaction?
• Continuous three phase dispersed kinetic systems
• Gas-liquid phase mass transfer kinetics and interpret it in terms of agitator type and performance
• Batch kinetic data and how to manipulate it into a useful form to model continuous reactors
• What assumptions to make and what numerical methods to use to solve the above systems in Excel
15071121-AP4-Meeting with Prince
Reaction Mechanism
• Sequential reaction mechanism:
Cu2S + H2SO4 + 0.5 O2 → CuS + CuSO4 + H2O
CuS + 2 O2 → CuSO4
• Overall:
Cu2S + H2SO4 + 2.5 O2 → 2 CuSO4 + H2O
Cu2S CuS
MS MS
16071121-AP4-Meeting with Prince
l
l
lld
ntrdnn
outs
outin
−=)(
)()(
_
Attempting to apply the population balance methodology from batch data…
+
=
reactionby shrinkage to due class size of out particles of number Net
class size the of out and reactor of out
particles of Number
class size the into and reactor the into particles of Number
Ltr
)X1(1 s3/1 =−−
san
O rRTEkC =− )exp(2
NB!!!
17071121-AP4-Meeting with Prince
Gas - Liquid Mass Transfer
ρ53DNNP P=
)cc(akrate bsL −=
mass transfer coefficient (m/s)
specific surface area (m2/m3)
Gas bubble
Liquid film
pbps
cb
cs
Interface
Gas film
Liquid film
Bulk LiquidBulk
Gas
P = power applied to impeller (W)
N = impeller speed (1/s)
D = impeller diameter (m)
ρ= fluid density (kg/m3)
NP = impeller power number
βα
= sL u
VPkak
k = 0.002
α = 0.7
β = 0.2
Rushton NP: 5.75
A315 NP: 0.75
Mass Transfer Agitator Performance
Hpc s
sat =
The partial pressure in the gas phase and the concentration in solution at the surface are in equilibrium, described by Henry’s law:
18071121-AP4-Meeting with Prince
• Liquid phase steady state oxygen balance:
but
• Gas phase steady state oxygen balance
• Both of which need to be solved simultaneously together with the population balance
• 3 unknowns : rs , CO2,o and pO2,o
Oxygen Gas and Liquid Phase Heterogeneous Balance
( ) VrVCCakQCQC OiOsOLiOoO 22222 ,,,, +−−=
sO rr25
2=
( )
.,
.
,
,
.
,
.
2
2
22
V
RTnp
VCCaknn
oOoO
isLiOoO
=
−+=
19071121-AP4-Meeting with Prince
How can “normal” people do this in Excel?
• Population balance:
• Simultaneous equations in Excel
0 1
1
No. of Particle Balance:
IN
( ) ( )( )
1
flow rxn flow rxnIN OUT OUT
n l n l l rateln l
ratel
τ
τ
+ = +
+ + ∆ ⋅∆=
+∆
31 1
Converting back to mass population:
( ) ( )m l n l l= ⋅
1
0
0
0
:
1
Conversion
m dl
X
m dl
∞
∞
= −
∫
∫
1 2
Trapesoidal Rule:
2y y
Integral l+ = ⋅∆
Sub Button1 Click()a1 = Falsea2 = FalseWhile a1 = False Or a2 = Falsea1 = Worksheets("Summary").Range("D6").GoalSeek(0.00001,Worksheets("Summary").Range("B6"))a2 = Worksheets("Summary").Range("D7").GoalSeek(0.00001,Worksheets("Summary").Range("B7"))Wend
20071121-AP4-Meeting with Prince
Ok…so what happened?
21071121-AP4-Meeting with Prince
Plant trial
• After preliminary modelling a significant difference was noticed between the performance of an autoclave with Rushton versus A315 impellers particularly in the first compartment hence it was decided to validate Dual versus Sec 2
Secondary 3
Secondary 2
Dual
Comp. 4 Comp. 3 Comp. 2Comp. 1
22071121-AP4-Meeting with Prince
Plant trial results…
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
C 1 C 2 C 3 C 4
Cu
Ext
ract
ion
Actual: Dual Ac tual: S ec2
23071121-AP4-Meeting with Prince
Batch Data
y = 0.2021x + 0.158R2 = 0.9616
y = 0.1546x + 0.3199R2 = 0.9429
y = 0.1046x + 0.541R2 = 0.7046
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Time (Hrs)
1-(1
-X)1
/3
T=150 T=140 T=130 Linear (T=130) Linear (T=140) Linear (T=150)
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Rosin Rammler Bennett
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 20 40 60 80 100 120 140
siz e (mic rons)
%
25071121-AP4-Meeting with Prince
Modelling results vs. plant campaign
• Feed rate equivalent to 19 ktpa Ni in 2 autoclaves
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
120.0%
C 1 C 2 C 3 C 4
Cu
Ext
ract
ion
Model: Dual Actual: Dual Model: S ec2 Actual: S ec2
26071121-AP4-Meeting with Prince
Did we over simplify the reaction mechanism?
Ref: Dixon and Dreisinger
27071121-AP4-Meeting with Prince
Fit sequential rates for Cu2S and CuS to plant data?
• But how does this account for work done by Hofirek and Nofal 1994?
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
C 1 C 2 C 3 C 4
Cu
Ext
ract
ion
Model: Dual Ac tual: Dual
28071121-AP4-Meeting with Prince
PSD: RRB vs. Actual
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 20 40 60 80 100 120 140
size (microns)
%
29071121-AP4-Meeting with Prince
Using actual PSD in population balance
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
C 1 C 2 C 3 C 4
Cu
Ext
ract
ion
Model: Dual A ctual: Dual Model: S ec2 Ac tual: S ec2
30071121-AP4-Meeting with Prince
Pre-1994 PSD
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 20 40 60 80 100 120 140 160 180
Size (micron)
2009-Actual NCM-1986 NCM-1990
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Agitator Configuration: 1994
Secondary 3
Original
Secondary 2
Secondary 1
Comp. 4 Comp. 3 Comp. 2Comp. 1
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Hofirek and Nofal 1994 vs. Model
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
C 1 C 2 C 3 C 4
Cu
Ext
ract
ion
Model A ctual
33071121-AP4-Meeting with Prince
Hofirek and Nofal 1994 vs. Model: Effect of Agitator type
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 1 2 3 4 5
C ompa rtment
Co
nve
rsio
n
R R R R A AA A
34071121-AP4-Meeting with Prince
Outcomes
• Rushton turbines appear to perform better when high gas to liquid mass transfer rates are required under highly gassed conditions – a program has been initiated to return to Rushton turbines in the first two compartments of our secondary leach autoclaves
• PSD can have a significant effect on leach performance –commissioning of a new matte milling section (end 2009) will be monitored with interest especially with respect to our secondary leach performance
• Building “a priori” type models, using a hands on approach, in an operational context is a superior medium for knowledge transfer
35071121-AP4-Meeting with Prince
The Team