ENEM20003 Project: Aluminum Refining Flow Process Design, Term 1, 2020

This project focuses on designing a flow processing system for an aluminum refining plant, covering key aspects of thermofluids engineering. The project begins with an executive summary outlining the Bayer and Hall-Heroult processes for aluminum production. It includes detailed pump system design and calculations, incorporating system schematics, friction loss calculations, and duty point analysis. The design extends to the precipitation tank, addressing scaling and agitation. The project also involves cavitation checks, power cost analysis, and an exploration of alternative transportation systems. The report provides a comprehensive analysis of the flow process, including calculations, design schematics, and literature review. The project aims to understand industrial processes and factors to consider when designing flow processes within the aluminum refining plant.

ENEM20003: Thermofluids Engineering Applications
Term 1, 2020
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School of Engineering and Technology
Central Queensland University
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Executive Summary
It is essentially important to understand the processes of aluminum production from
its ore, Bauxite. This is achieved by two processes, Bayer and Hall-Heroult, developed in the
late ’80s by Josef Bayer and Hall in Austria. The Bayer process involves three processes to
produce alumina oxide. These processes are; digestion, clarification, precipitation, and
calcination. During digestion, the ore is crushed into small powder particles and dissolved in
sodium hydroxide solution at around 175 degrees Celsius. In clarification, the solids settle
and are removed. In the precipitation stage, the alkaline slurry is cooled to around 32 degrees
Celsius where alumina hydroxide precipitates out. This process involves agitation, cooling,
and seeding. In the final stage, calcination, the solution is heated to give off moisture to
produce aluminum oxide powder which is transported to the Hall-Heroult plant or other uses.
Ideally, 2 kgs of bauxite produce at least 1.5 kg of pure aluminum (Parfenov et al 2016). This
process is represented in the flow diagram below.
Figure 1: Bayer process
The alkaline liquor is after this process is transported to a thickening tank from where
excess solids settle. The clarified slurry is transported to the precipitation tank before being
sent to the tertiary tank. The three tanks are spaced as follows; 200m between thickening and
precipitation tank and 800m between precipitation tank to the tertiary tank.

Declaration of Contribution
(Insert the signed document here)

Table of Contents
Executive Summary...................................................................................................................2
Declaration of Contribution.......................................................................................................3
Table of Contents.......................................................................................................................4
List of Figures............................................................................................................................5
List of Tables..............................................................................................................................6
List of Abbreviations and Acronyms.........................................................................................7
PART A: General (10 marks)......................................8
A.1 Introduction, aim, and objectives of the project..............................................................8
A.2 Brief literature review relevant to this project................................................................9
A.3 Brief description of related systems..............................................................................10
A.4 Assumptions and data presentation...............................................................................11
A.5 Academic writing and Referencing...............................................................................11
PART B: Pump system design and calculation (50 marks).......................................12
B.1 Project schematic showing relevant components (front and top use CAD)..................12
B.2 Fittings ∑KL values Tables for the full plant pipeline..................................................13
B.3 Pipe material, diameter (I/O), busting pressure, friction factor (f) for entire system
including precipitation tank C.2...........................................................................................14
B.4 System equation (static head, dynamic head, and head loss) for Thickening Tank pump
P-101....................................................................................................................................15
B.5 Duty point (DP) of the feed pump for Thickening Tank P101......................................16
B.6 Pump characteristics at DP (head, power, efficiency, specific speed, etc.)..................17
B.7 Draw velocity triangles for inlet and outlet of the pump impeller................................18
B.8 Calculate theoretical head (H), power and compare with DP values............................19
B.9 Cavitation check (NPSHA) for feed pump P-101.........................................................20
B.10 Apply similarity laws for Precipitation & Tertiary pumps P102, P103......................21
B.11 Analyse CH, CP vs CQ at a fixed speed for P-102, P-103 separately........................22
B.12 Cavitation check (NPSHA) for all Tank pumps..........................................................23
B.13 Calculate total power cost per day for running all pumps (show in a Table)..............25
PART C: Precipitation tank design (scaling & agitation system) (15 marks)..........26
C.1 Brief literature on scaling and scale mitigation.............................................................26
C.2 Detail design of a simplified agitator system in the precipitation tank.........................27
C.3 Analysis of velocity and power required for scale suppression....................................29

D.1 General description and assumption for rheometer design...........................................30
D.2 Design/schematics and theory.......................................................................................31
D.3 Location of installation and soundness of the operation)..............................................32
PART E: Alternate transportation system design (5 marks).........................................33
E.1 General discussion on the type of transportation...........................................................33
E.2 Schematics and operating principles.............................................................................34
E.3 Justification/comparative assessment with the existing method...................................35
PART F: Others (10 marks).....................................36
F.1 Conclusion and recommendations.................................................................................36
References............................................................................................................................37

List of Figures
Figure 1: Process Flow Schematic...........................................................................................13
Figure 2: K-Factors (Source: Janna, 2014)..............................................................................14
Figure 3: Duty Points (Source, Grundfos.com).......................................................................17
Figure 4:Pump Curves (Source: Grundfos.com)......................................................................18
Figure 5: Velocity Diagram.....................................................................................................19
Figure 6:Pump Curves (Source: Grundfos.com)......................................................................20
Figure 7: Pump Curves (Source: Grundfos.com).....................................................................21
Figure 8: Pump Schematic.......................................................................................................23
Figure 9:Pump Curves (Source: Grundfos.com)......................................................................24
Figure 10:Pump Curves (Source: Grundfos.com)....................................................................25
Figure 11:Swirl agitator...........................................................................................................28
Figure 12:Agitation schematic.................................................................................................28
Figure 13:Rheometer Schematic..............................................................................................32
Figure 14: Alternative schematic.............................................................................................35

List of Tables
Table 1: K-Factors for Various Fittings...................................................................................16

List of Abbreviations and Acronyms
PVC- Poly Vinyl Chloride
NPSH-Net Positive Suction Pressure
V-Velocity
g-Gravity
D-Diameter
H-Head
Q-Flow rate
f-Friction factor

PART A: General (10 marks)
A.1 Introduction, aim, and objectives of the project
In this project, Thermal fluids Engineering Applications are put in place in the study
of Aluminium production. This project aims to develop a flow process for the slurry in the
Aluminium refining plant. The importance of this design is to help understand the industrial
processes as well as factors to consider when designing flow processes. Bayer and Hall-
Heroult processes shall be explored as they are the main modern processes for pure aluminum
metal production.

A.2 Brief literature review relevant to this project
Since ancient times when man discovered mineral ores, processes have been developed since
then to suite different extractions from these ores. The mineral ores are as a result of
processes within the earth interiors that happened millions and billions of years ago. Final
metal products that people interact with daily are the end products of the processes. In this
case, aluminum is the end product under study. According to (Den Hond et al 2016),
Aluminum ore was refined using alkaline acids and thermal methods in the past decades.
However, this extraction method was deemed expensive and did not meet the standard for
pure aluminum. According to (Sun et al), in the middle east, lime and soda were used as
extraction solvents. Since the aluminum ore contains several impurities such as iron oxide
and silica, these extraction processes did not exhaust these impurities and hence the process
turned to be environmentally hazardous.

A.3 Brief description of related systems
The initial stage involves dissolving the aluminum oxide in the ore into a sodium
hydroxide solution as shown below.
In the process, silica is dissolved according to the equation below
In the precipitation process, the following equation applies
In the calcination process, alumina oxide powder is produced by the heating process
and the water vapor is produced in the process as shown in the below equation

A.4 Assumptions and data presentation
It is assumed that the Aluminum ore contains minimal impurities and that the Bayer
and Hall-Heroult processes produce a substantial amount of red mud. The red mud will be put
into ceramics production and the final waste shall be disposed of as per the statutes. It is also
assumed that no red mud dries shall be recycled to produce aluminum since this has proven
environmental hazards in the past. Finally, it is assumed that the end product from the process
is pure aluminum that is ready for further machining processes to produce usable products.
A.5 Academic writing and Referencing
(No need to address because it is on the overall report)

PART B: Pump system design and calculation (50 marks)
B.1 Project schematic showing relevant components (front and top use CAD)
Figure 1: Process Flow Schematic
The process begins by receiving the liquor from the Bayer process which is stored in
the thickening tank. From this tank, it is pumped into the precipitation tank where it
undergoes agitation with the help of agitator. After the process is done, the product is pumped
into the tertiary tank from where it is stored temporarily before being sent to the Hall Heroult
processing.

B.2 Fittings ∑KL values Tables for the full plant pipeline
Figure 2: K-Factors (Source: Janna, 2014)

B.3 Pipe material, diameter (I/O), busting pressure, friction factor (f) for the
entire system including precipitation tank C.2
The recommended pipe material for the entire pipework is stainless steel as this is
strong and also corrosion-resistant. From the calculations below, the pipe diameter is 150mm,
and the bursting pressure is 30% above the calculated value using a friction factor of 0,0075.
Thickening and precipitation tank capacities =350,000 litres (Assumed)
Approximate time to fill the liquor is 4 hours (Assumed)
Thus;
Required flow rate ,Q=350 m3
4
¿ 87.5m3/hr (0.0245 m3/s
Finding pipe diameter;
Q=V X A
Where V=2m/s
A=Q
V = π
4 D2
A=0.0245
2 = π
4 D2
A=0.0122 Sq . m
D=124.63 mm
Available pipes ,OD=155 mm , ID=150 mm

B.4 System equation (static head, dynamic head, and head loss) for Thickening
Tank pump P-101
The maximum liquor height in the tank (Static Head);
=18 m/10 m
¿ 1.8 ¯¿
Friction loss (Dynamic head) in the pipe is calculated from;
Hf = 4 flv ²
2 gD
Where f-Pipe friction factor =0.0075
l-length of pipe = 200m (Approximate)
d-liquor flow speed in the pipe=2 m/s
D-Pipe diameter=150mm
g- gravity=9.81
Hf = 4 × 0.0075× 200 ×2²
2× 9.81 ×0.15
¿ 8.1 m (Approximately 0.9 bar)
Pressure loss due to pipe fittings;
Fitting Qty K Factor Leq/D Head loss
90˚ elbow (Threaded) 5 1.4 30 42
45˚ elbow (Threaded) 5 0.35 16 5.6
T-Joints (Threaded) 3 0.9 20 18
Gate Valve (Fully
Open)
2 0.15 13 1.95
Total Head Loss 67.55m (6.755
Bar)
Table 1: K-Factors for Various Fittings
Total head loss =1.8 ¯+0.9 ¯+6.755 ¯¿ 9.455¯¿

If this pressure is exceeded by at least 30%, the pipework is likely to burst.
B.5 Duty point (DP) of the feed pump for Thickening Tank P101
The pump duty point, therefore, is at 87.5 m3/hr at 10bar from the calculation. With
this calculated duty point, the pump can be selected from manufacturers such as Grundfos
among others. The duty point helps in determining the efficiency as well as other pump
characteristics such as power input.
Figure 3: Duty Points (Source, Grundfos.com)

B.6 Pump characteristics at DP (head, power, efficiency, specific speed, etc.)
Figure 4:Pump Curves (Source: Grundfos.com)
From the Grundfos selection tool, and using the calculated duty point, the above figure shows
the pump parameters for the Grundfos CR95-4 pump set. The head is 100.1m, and the power
consumption is 31.48kw

B.7 Draw velocity triangles for inlet and outlet of the pump impeller
Figure 5: Velocity Diagram

B.8 Calculate theoretical head (H), power and compare with DP values
Figure 6:Pump Curves (Source: Grundfos.com)
The calculated Duty point is 87.5 Cu.m/hr at 10 bars. The theoretical values, however,
vary slightly as they are 87.52 Cu.m/hr at 10.1 bar. The variation is marginal and thus the
sizing is correct. For the power, the theoretical is at 29.38kw while the duty point power is
31.48kw. The difference shows that the pump can operate at several different speeds within
the power rating.

B.9 Cavitation check (NPSHA) for feed pump P-101
Figure 7: Pump Curves (Source: Grundfos.com)
The calculated NPSH head of the pump is 2.71m. This is the difference in pressure
between the suction and the lowest pressure inside the pump. Positive pressure is required in
such that stagnation suction pressure should be greater than the vapor pressure at the inlet
temperature. With this positive available NPSH, cavitation is eliminated.

B.10 Apply similarity laws for Precipitation & Tertiary pumps P102, P103

B.11 Analyse CH, CP vs CQ at a fixed speed for P-102, P-103 separately
Figure 8: Pump Schematic
From these equations, for pump P-102,
CH =0.04 , CP=0.52 ,∧CQ =0.64
For pump P-103,
CH =0.02, CP=0.45 ,∧CQ=0.44

B.12 Cavitation check (NPSHA) for all Tank pumps
Figure 9:Pump Curves (Source: Grundfos.com)
The NPSH for pump P-102 is 2.65m

Figure 10:Pump Curves (Source: Grundfos.com)
The NPSH for pump P-102 is 2.51m

B.13 Calculate total power cost per day for running all pumps (show in a
Table)
Total power=31.48 kw+ 38.19 kw+25.65 kw
Total power=95.32 kw
Per day, the pumps are assumed to run for 12 hours in a day thus;
Total Daily Power=95.32 kw x 12=1143.84 kwh
Assuming each kW of power is 40$ per kWh

Total Daily cost of Power=1143.84 kw x $ 40=$ 45753.6 PART C: Precipitation tank design
(scaling & agitation system) (15 marks)
C.1 Brief literature on scaling and scale mitigation
Scaling is the formation of a layer of materials on surfaces which is an undesirable
occurrence in industrial processes with huge impacts on machinery and equipment downtime
as time is consumed during descaling and cleaning of such surfaces. Bayer slurries contain
quite some considerable amounts of alumina and impurities such as silica and sodium oxalate
that are prone to scaling. This is eminent in the precipitation tank as well as in the pipework.
According to (J. Wu et al 2018), scaling can be significantly reduced in the
precipitation tank by maintaining an agitation speed in the range of 0.5m/s to 2m/s. This is
because, at high flow velocities, the flow erosion effect is high thus limiting scaling on the
surfaces. Also, swirl flow technology for the agitator is recommended as contrary to
conventional tube agitators. With these types of agitators, the velocity within the precipitation
tank is uniformly maintained at recommended values. This has been found to increase plant
life by more than 50% (Davoody et al 2019).

C.2 Detail design of a simplified agitator system in the precipitation tank
The most important part of any agitator system is the impeller. In this proposed
simple design, the impeller is circular with radial fins embedded between the top and bottom
plates that create the swirls. The shaft is made to penetrate only a metre into the liquor and
the swirling is aided by the impeller as shown in the figure below.
Figure 11:Swirl agitator
Figure 12:Agitation schematic

Since the velocity is maintained at the recommended values, the suspended solids and
slurry is mixed creating a tornado-like vortex that interns reduce the spinning power
requirements of the agitator. Also, with a short shaft, there is limited inertia created hence
low power is required to provide the rotary motion.

C.3 Analysis of velocity and power required for scale suppression
The recommended velocity for scale suppression is a maximum of 2m/s. This has
been accounted for in the design. The power for the agitation is estimated as a rule of thumb.
From repeated experimental tests, 2 Kilowatts are required per metre of the liquor height
(Connor et al 2016). In this case, the liquor height is 27m thus the power required is 54
Kilowatts. This is 40% less than what would be required by a conventional agitator hence
power bills are significantly reduced. The motor recommended for the agitator is an induction
motor that works on a 3-phase power source.

PART D: Rheometer design (10marks)
D.1 General description and assumption for rheometer design
A rheometer is a device that determines the viscosity of fluids with the forces applied.
It is mostly used with fluids that have varying viscosity depending on the physical
parameters. The figure below shows a typical Rheometer component. The displacements are
measured by the optical decoder device and the results are digitized for ease of interpretation.
The most common rheometer is the capillary tube type whose working principle depends on
the mode of pressure application, whether gas or air. In other cases, the fluids are forced into
the capillary tubes using a piston tube. Several requirements are required in the design
including a capillary tube that is smooth, a means of pressure applied to be identified. Also,
the means of pressure measurement as well as the flow rate should be clearly defined.
Finally, temperature control is needed.

D.2 Design/schematics and theory
A small diameter tube is mostly used to develop the rheometer. With a long tube, the end
effects are minimized. However, care should be taken as long tubes might lead to an increase
in temperature. The material recommended for the tube is copper or stainless steel. Since the
fluids used are of low viscosity, gravitational forces are enough to cause turbulence thus a
horizontal tube is at times recommended. The tube dimensions are 800mm in length and
1,82mm diameter. The fluid in the test is contained in a PVC container measuring 300mm in
length and 100 mm in diameter. When conduction the measurements, the capillary tube
should be fitted at least 20mm above the base of the container to avoid wall effects that can
cause turbulent flow which is undesirable.
Figure 13:Rheometer Schematic

D.3 Location of installation and soundness of the operation)
The Rheometers shall be located at the inlet and discharge lines of the pumps where
samples shall be drawn. With this configuration, the properties shall be adjusted accordingly
depending on the real-time viscosity. Depending on the particles packing in the slurry, the
pumping rate is adjusted accordingly and at times, a change of pump impellers can be
effective. When the operating temperatures are as specified, there is less likelihood for failure
or scaling formation hence continuous temperature monitoring alongside the rheometer is
recommended.

PART E: Alternate transportation system design (5 marks)
E.1 General discussion on the type of transportation
An alternative recommended transportation is the pneumatic system that employs
compressed air to pump the slurry in the pipes. This process has proved to be efficient in the
construction industry in pumping concrete in high rise buildings without complications of
scaling of the pipework and equipment. The figure below shows the schematic for this
alternative process. Compared to the existing method, the power consumption in pumping the
slurry will be reduced by approximately 30%.

E.2 Schematics and operating principles
Figure 14: Alternative schematic
In the schematic above the pumps are replaced by compressed air pumping stations that use
air compressors to pump the slurry in the pipeline.

E.3 Justification/comparative assessment with the existing method
As compared to the existing method, compressed air systems can reach the desired pumping
pressure as well as flow velocity easily and with minimal power consumption which
translates to low power bills at the end of the operations. Since the slutty does not come into
contact with impellors, there are fewer losses in the head as well as little to no damage to the
system. Compressed air pumping can pump the slurry containing larger particle sizes as
compared to the conventional system. Since the fluid viscosity is low, the rate of delivery
using the pump is dictated on the temperature which has to be maintained throughout. With a
compressed air system, the temperature is not among the factors to worry about.

PART F: Others (10 marks)
F.1 Conclusion and recommendations
Industrial transportation of low viscosity fluids is critical because unlike other fluids,
more power is required by the large pumps. It is important, therefore, to size the transport
system to optimize power consumption while increasing efficiency. Scaling is an undesirable
occurrence in the transport system and thus the system should be sized to limit it at all costs.
It is recommended that the diameter of the pipework be calculated and optimized to reduce
the frictional losses in the head loss. Also, pipe fittings should be limited and finally, the
pumping, as well as agitation velocity, should be maintained at least 2m/s. To sum up,
production and maintenance costs in a plant can be significantly reduced when the
recommended practices are adhered to.

References
Connor, T, Wu, J., Wang, S., Nguyen, B.,., Daniel, M. and Ola, E., 2016. Gain improved tank
slurry agitation via swirl flow technology. Engineering and Mining Journal, 217(4), p.78.
Davoody, M., Graham, L.J., Wu, J., Witt, P.J., Madapusi, S. and Parthasarathy, R., 2019.
Mitigation of scale formation in unbaffled stirred tanks-experimental assessment and
quantification. Chemical Engineering Research and Design, 146, pp.11-21.
Den Hond, R., Hiralal, I. and Rijkeboer, A., 2016. alumina yield in the Bayer process past,
present, and prospects. Essential Readings in Light Metals (pp. 528-533). Springer, Cham.
Janna, W.S., 2014. Design of fluid thermal systems. Cengage Learning.
Parfenov, O.G., Kustov, A.D. and Solovyov, L.A., 2016. A new non-electrolytic aluminum
extraction method. Transactions of Nonferrous Metals Society of China, 26(9), pp.2509-
2517.
Sun, X., Sun, Y. and Yu, J., 2016. Removal of ferric ions from aluminum solutions by
solvent extraction, part I: iron removal. Separation and Purification Technology, 159, pp.18-
22.
Wu, J, Das, P., Khan, M.M.K., Rasul, M.G., and Young, I., 2018. Swirl flow agitation for
scale
suppression, International Journal of Mineral Processing, 112-113 (2012) 19-29.