Practical training: Simulation of crushing station
Simulation of mineral processing
Supervisor: Professor Mehdi Parian
By
Mariana Tavares de Oliveira
Pasindu Raviranga
20th September 2019
TABLE OF CONTENTS
1 Introduction ............................................................................................................... 3
2 Methods .................................................................................................................... 3
2.1 Assumptions .................................................................................................................. 5
1.1 Simulation Procedure .................................................................................................... 5
3 Result and discussion ................................................................................................. 5
3.1 Unit and models used in Simple Simulation ................................................................... 5
3.2 Unit and models used in Advanced Simulation .............................................................. 6
3.3 Simulation using Simple models .................................................................................... 7
3.4 Simulation using Advance models.................................................................................. 9
4 Selection of crushers ................................................................................................ 10
4.1 Crushers in Simple model ............................................................................................ 10
4.2 Crushers in Advanced model........................................................................................ 11
5 Comparison of simulation models ............................................................................ 12
6 Conclusion ............................................................................................................... 14
7 References ............................................................................................................... 15
1 INTRODUCTION
Crushing is the first mechanical stage of a mineral processing plant within the
comminution in which a principal objective is the liberation of the minerals of interest
from the gangue minerals. It consists in an operation where the feed is usually dry,
and can be performed in two or three stages. The determination of product size is
given by the size of the opening at the discharge, which is usually called setting. The
reduction ratio of a crusher is the ration between the feed size and the product size,
often using an 80% passing as a reference, thus as expressed in Equation 1 (Wills &
Finch, 2016). This parameter is important taking into account that all crushers have a
limited reduction ration, and its determination will guide the number of crushing stages
required to provide the requested product size, given a certain feed size (Metso
Corporation, 2015).
.
𝑅𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑖𝑜 = 1/0 ; (1)
/0
Crushing may be performed in open or closed circuit, depending on the requirements
of the particle size distribution. One of the main reasons that implies the use of closed
circuits is the increased flexibility given to the plant as a whole. It is possible to operate
the equipment at a wider setting if necessary, altering the product size distribution,
and by making a selective cut on the screen, allowing the product size to be adjusted
according to the required specification (Wills & Finch, 2016).
The importance of crushing circuits and its optimization for the mineral processing
sector, led to a development of quantitative modelling, using a diverse range of
software packages and models, in order to predict and evaluate this comminution step.
The present assignment consists in building a crusher station using a simulation
software MODSIM (Modular Simulator for Mineral Processing), following the required
modifications of a given flowsheet in combination with further assumptions. After
building the flowsheet, the task comprises performing a simple and advanced
simulation based on the complexity of different functions through related to the
different models. The main purpose is to acquire knowledge and experience on
crushing simulations.
2 METHODS
An existing crushing station flowsheet for gravel and sand production for building
purposes was provided, and it is presented in Figure 1. The flowsheet included three
crushing stages combined with classifying screens to provide the required fractions.
Figure 1: Given crushing station flowsheet for gravel and sand processing.
The assignment required a number of modifications on the given flowsheet, which
included:
- Use a double deck screen replacing the two simple deck screens at steps 1
and 2, in order to separate the coarser fraction to be fed in the jaw crusher;
- Removal of the process streams 10 and 21;
- Process stream 31 directly gives the fraction 0-4 mm
- Replacement of the crushers used, which in this work were chosen to be:
o Primary: Jaw crusher
o Secondary: Cone crusher
o Tertiary: Short head cone crusher
- Adjustment of splitter 8 with a default value of 50%, which should be the same
for the other splitters of the station.
The purpose is to be able to acquire final products in the fractions 0-40, 0-20, 40-70,
10-20, 4-10 and finally, 0-4 mm.
The crusher selection must be done regarding the operational conditions, such as feed
size, capacity, material hardness and so on (Metso Corporation, 2015). According to
Metso minerals processing book, for the type of ore given in the present assignment,
for primary crushing, the options are jaw and gyratory crushers. Since gyratory
crushers are used mostly for high capacities (from 1200 to higher tph), the primary
crusher chosen in the flowsheet was the jaw crusher.
For secondary crusher, the chosen was the cone crusher, since it is pointed out to be
suitable for size reduction and shaping downstream a crushing circuit, since the
equipment allows to change feed and discharge openings during operation (Metso
Corporation, 2015).
Finally, the tertiary crushing, being a stage of special interest, the machinery used was
also a cone crusher.
2.1 Assumptions
Regarding the material, it was assumed for it to have 20 fractions, in which the largest
particle size is 600 mm. The process has a feed flowrate of 300 tph of material
containing 2% moisture. The Rosin-Rambler distribution was selected, and the given
parameters used were: d63.2=150 mm, lambda (n) 1.26.
In addition, the material undertaken as having a composition of one mineral, with a
density of 3.0 t/m3. For the products, since no specific tonnage was required, no
assumptions were made in order to have any proportion between the fractions.
In addition, for the flowsheet design, the middling of the first double deck screen (1)
was chosen to be sent directly to the screen of 70 mm mesh size (4) instead of been
mixed to the course particles and sent to the jaw crusher. This assumption had the
objective to reduce the energy consumption of the Jaw crusher (primary), aiming to
reduce the operation cost of this equipment. The reason for this assumption is the fact
that the operational cost for cone crusher are usually lower (Metso Corporation, 2019).
2.2 Simulation Procedure
Firstly, the flowsheet was designed following the given circuit, presented in Figure 1,
using the assumptions that were required. The “system data” was edited, inputting the
given data about the material. The default values for both, crushers and screens, were
used to run the first simulation. After checking that the simulation was running
appropriately, the modelling started following the instructions to first, simulate the
crushing station using simple models, adjusting the parameters of the equipment, until
the required product fractions were obtained. After each simulation, the particle size
distribution was check, together with the resulting report, to be certain that not only the
size requirements were met, but also, that the screens were not being overloaded and
that crusher capacities were being respected.
The physical properties of the equipment were altered until these conditions were
satisfied. When it was found that the results were acceptable, and the goal was
achieved, the machinery was dimensioned using METSO manual, in order to find the
best suitable machinery according to market availability, to make possible to
dimension the circuit in real scale.
3 RESULT AND DISCUSSION
3.1 Unit and models used in Simple Simulation
The simple model configuration used the respective models for each equipment: for
Jaw crusher “JAW1”; for the double screen was “DSC1”; for screens “SCRN”; and for
Cone Crusher “CRS1”. When using simple models, there are a highly limited number
of parameters to be considered, in comparison to the advanced model. In this case,
the only relevant parameters are open-side set (OSS) of Jaw crusher, closed-side set
(CSS) of cone crushers, and mesh size of all single and double deck screens
according to the particle size distribution requirements. Default screen dimensions
maintained, being below 5𝑚 𝑥6𝑚 as requested in the exercise guide. Table 1 and
Table 2 show the respective unit and all parameters selected or obtained after
simulation, with exception of crushing units that will be discussed in section 4.1.
Table 1: Parameters of Double-deck screen in Simple model.
Table 2:Parameters of Single-deck screen in Simple model.
3.2 Unit and models used in Advanced Simulation
In advanced simulation, the model selected for double screens was “DSC2” (Karra
model), for single screens “SCR2”, for Jaw crusher “CRSH” for Cone Crusher
(Secondary) “CRSH” and Cone Crusher (Tertiary) “SHHD”. These models provide a
higher level of manipulation of the parameters, bringing more realistic results,
compared to simple models. The mesh size and wire diameter of screens were
selected according to tabled values. The combination of the parameters should give
an area utilization factor between 0.90 and 1.1, which indicates that the screens are
working properly. In this simulation, all the screens were found to be working according
to this requirement, and the values are presented in Table 4. To acquire this result,
the screen size had to be adjusted, and the selected dimensions are also presented
in Table 4. The smallest screen size used was LF1030 1 𝑥 3 𝑚, from Sandvik (Sandvik,
2019), and the biggest was VFS 42/18 2d from Mesto, which size is 4.2 𝑥 1.8 𝑚,
(Mesto, 2015). All the parameters inputted/obtained are realistic values and included
in Table 3 and Table 4, except the parameters for crushers, which are presented in
section 4.2. The material was considered as medium heavy when selecting the wire
diameter of the screen.
Table 3:Parameters of Double-deck screen in Advanced model
Table 4:Parameters of Single-deck screen in Advanced model.
3.3 Simulation using Simple models
After simulation of simple model, from the flowsheet in Figure 2 it is possible to
conclude that the models which had been used in this simulation give the satisfactory
amount of required size fractions. However, particle size distribution of final product
fraction must be considered to analyze the overall quality of the simulation flowsheet
in the way it satisfies the initial goal.
Figure 2: Flowsheet of Simple model simulation
The production of the 0-40 mm size range was successful as 95% passing of the
product is under 40 mm. The same success can be seen in the 40-70 mm as 80%
passing of the product is under 70mm and 10 % passing is under 40 mm providing
85% of product within the required range. In contrast, the size distribution obtained
from 0 to 20 did not meet the expected result, with only 70% of product fitting the
desired particle size range. This is justified by the flowsheet itself, where the 50% of
the overflow from the 20 mm screen was sent to the 0-20 mm product. In general, it
can be concluded that Primary Crushing and Screening result is in satisfactory level.
The secondary crushing and screening stage also achieved successful particle size
distribution for the required size range for product. In the 0-4mm, 100% of products
are within the desired size range. In the product 4-10mm, around 80% of products are
within the desired size range. Finally, the product 10-20mm around 83% of products
are within the desired size range. All the particle size distribution curves obtained for
different range of final products are presented in Figure 3.
16 Fraction 10-20mm
20 Fraction 40-70mm 19 Fraction 0-4mm 18 Fraction 4-10mm
1 feed 2 Fractiion 0-40mm 11 Fraction 0-20mm
100
90
80
Cumulative % smaller
70
60
50
40
30
20
10
0
103 104 105 106
Particle size microns
Simple model 1
Figure 3: Particle size distribution of Feed and final products in simple model simulation
3.4 Simulation using Advance models
The flowsheet of Advanced model is presented in Figure 4. Result of this model is also
in satisfactory level with advance parameter selection for each unit as in real industry.
However, in this model also it is essential to analyze particle size distribution to
analyze the overall quality of the flowsheet.
Figure 4:Flowsheet of Advanced simulation
The production of the 0-40 mm size range was successful as 95% passing of the
product is under 40 mm. The same success can be seen in the 40-70 mm as 80%
passing of the product is under 70mm and around 10 % passing is under 40 mm giving
85% of particles within the required range. In contrast to simple model, this simulation
gives around 80% of product of 0-20mm within the range even though 50% of +20mm
were mixed with final product. In general, the Primary Crushing and Screening result
are quite similar to the simple model simulation result.
The secondary crushing and screening stage also achieved successful particle sized
distribution for the required size range for product. In the product 0-4mm, 100% of the
particles are within the desired size range. In the product 4-10mm, 85% of the particles
are within the desired size range. Finally, the product 10-20mm with around 80% of
the particles in the desired size range. Particle size distribution curves obtained for
different range of final products are presented in Figure 5.
27 Fraction 10-20mm
16 Fraction 40-70mm 26 Fraction 0-4mm 28 Fraction 4-10mm
1 feed 4 Fraction 0-40mm 14 Fraction 0-20mm
100
90
80
Cumulative % smaller
70
60
50
40
30
20
10
0
102 103 104 105 106
Particle size microns
advanced model
Figure 5: Particle size distribution of Feed and final products in Advanced model simulation
4 SELECTION OF CRUSHERS
In both models, Jaw crusher was used as a primary crusher and cone crushers were
used as secondary crusher and Tertiary crushers.
4.1 Crushers in Simple model
The Jaw crusher was used as primary crusher in order to achieve output particle size
less than 100mm for downstream treatment. In this model only 2 parameters had been
considered, which are OSS and Impact work index of feed. Default value of
12kWhr/ton of feed material while OSS was decided as 100mm. After successful
simulation, around 66% of the output is bellow 70mm as shown in Figure 6, which is
the aperture of next screen followed by primary crushing stage. This size distribution
of jaw crusher is in satisfactory range. Estimated pawer requirement is 39kW to crush
the estimated flowrate about 257.6 tph with reduction ration is about 3.03.
Two cone crushers were chosen as secondary and tertiary crushers where secondary
crusher was fed with 3 stream which come from oversize fraction of screen size 70mm
(unit 4), oversize fraction of screen size 40mm(unit12) and 50% of product from 20-
40mm size range while tertiary crusher was fed with 50% of oversize product of screen
20mm(unit6). CSS of both were defined as 20mm as the aperture size of next
classification stage is 20mm. However, Figure 6 shows that oversize product
percentage is significantly high. Therefore, crusher performance must be improved in
order to reduce the circulation load to secondary crusher.
24 Jaw crusher output 12 secondary crusher output 13 Tertiary crusher out put
100
90
80
Cumulative % smaller
70
60
50
40
30
20
10
0
103 104 105 106
Particle size microns
Simple model 1
Figure 6: PDS curve for jaw and cone crushers discharge for simple model.
4.2 Crushers in Advanced model
Same flowsheet as simple simulation had been used for this simulation with advance
type of crusher models. Primary crusher model was chosen as “CRSH” and CSS was
chosen at 100mm as it had already given the desire particle size range. Input
parameters and the models of secondary crusher and tertiary crushers are listed in
Table 5 below.
Table 5: Models and Parameters of Cone crushers in Advanced simulation
After simulation, 50% of jaw crusher product are under 70mm which is considerably
within the required size rage for downstream process. In secondary cone crusher, 90%
of product is under 20mm which is the perfect size rage for downstream process while
tertiary crusher product has 100% of product under 20mm as shown in Figure 7
6 Primary crusher output 20 secondqry crusher output 21 Tertiary crusher outpu
100
90
80
Cumulative % smaller
70
60
50
40
30
20
10
0
102 103 104 105 106
Particle size microns
advanced model
Figure 7: PDS curve for jaw and cone crushers discharge for advanced model.
The parameters obtained for crushers after simulation are listed in Table 6 below.
Table 6: Obtained parameters of Crushers in Advanced simulation
Selection of jaw crushers and cone crushers were selected from Mesto crusher
specification (Mesto, 2017) mainly based on CSS, Capacity, Feed top size and
required power of each crushers. In this case, smallest possible crusher was selected
for tertiary crusher as there wasn’t a crusher with required low capacity. All parameters
of selected crushers are included in Table 7 below.
Table 7: Selected crusher type in Advanced simulation and their parameters
5 COMPARISON OF SIMULATION MODELS
Basically, the PSD of final products and the discharge of Primary, Secondary and
Tertiary crushers were compared between simple and advanced models. From Figure
6 and Figure 7, it can be observed that advanced model has around 50% of product
below 70mm which is the size of next classification screen (unit4). It is a less amount
compared to simple model (65%). It can be justified by considering type of opening of
the jaw crushers because both OSS and CSS were chosen as 100mm for simple and
advance model respectively and there is a possibility to have more particle bigger than
CSS rather than OSS. CSS has to be changed according to the required quantity of
size fraction (if more product required for secondary stage, CSS has to be increased
otherwise decreased).
Next parameters to be considered is PSD of secondary and Tertiary crushers. From
Figure 6 and Figure 7, the output of secondary and tertiary crushers in simple model
have 60% and 35% of passing under 20mm which is considerably low value that
leads to higher Circulation load to the secondary crusher. In contrast, output of
secondary and tertiary crushers in advanced model have 94% and 100% of passing
under 20mm that decreases the circulation load to secondary crushers.
The final parameters to compare are the final product of both primary crushing product
and secondary crushing product between each model. From the Figure 3 and Figure
5, it can be observed that primary crushing stage product (0-40mm,0-20mm,40-
70mm) are more similar, except slightly different between product fraction 0-20mm of
simple model (67% passing) and Advanced model (80%) passing. Product 4-10mm of
Advanced simulation has 85% of product within desired size range while simple
simulation has 75% within the range. Product 10-20mm in Advanced simulation has
35% product under 10mm but 100% passing under 20mm whereas Simple model has
10% product under 10mm but 90% product under 20mm giving overall 80% of product
in simple model and 65% of product in Advanced model within desired size range.
These results might be due to low screen efficiency which might have increased
undersize particle in oversize fraction. Generally, it can be observed that Advanced
Model has better performance compare to Simple model. Suggestion to improve these
issues will be discuss in next paragraph.
Overall comparison of different parameters between simple and advanced model is
presented in table Table 8
Table 8: Overall comparison of different parameters
Regarding the reduction ratio of 3 crushing stage, the primary crushing stage of
advanced model has low reduction ratio while secondary and tertiary crusher stage
having higher reduction ration of advanced model. This opposite behavior during the
primary crushing is due to selection of CSS for advanced model since if CSS and OSS
were same size for both models, the model with CSS must have bigger particle
meaning that less reduction ratio.
6 CONCLUSION
The assignment required a number of modifications on the given flowsheet performed
accordingly, and the fraction sizes requirements for the products were respected. The
crushers were selected based on the operations conditions, and were chosen to be a
Jaw crusher (primary), cone crusher (secondary) and a short head cone crusher
(tertiary). It could be observed that, even though the simple model provided coherent
results, the simulation parameters that can be controlled are very limited, which
impacts the right equipment selection.
The results presented show that the simulations, especially regarding the advanced
model, provided satisfactory results, since the six products were obtained within the
high particle size range, using equipment and parameters choice that respected
realistic conditions. The area utilization factor results showed that the screens were
properly working, suggesting a right choice of operational parameters. The particle
size distributions also indicate a successful operational condition for the crushers, that
chosen using equipment manual and analysis of the simulation requirements, in order
to propose a realistic result, that were defined after several trials. It should be
mentioned that, some of the parameters used for the results were default values, thus
not altered during the simulation process.
Comparison of crushing in both models were performed, and the overall, it shown that
the requirements were better achieved using advance model, leading to a conclusion
that, Karra model for screens could be a result of increased screen efficiency. In terms
of reduction ratios, the values for advanced models were higher than the ones found
for simple model, expect for jaw crusher, and a possible justification for this is the
choice of CSS instead of OSS for the jaw crusher, since it was the input required for
the advanced model used.
It can be argued that the achievement of better parameters, improved performance of
operation units, lower consumption of energy could be possible, due the selection of
new values for the default parameters chosen. In addition, a few modifications in
flowsheet could be done, e.g. directing oversize fraction of screen to tertiary (short-
head) cone crusher, reducing the flowrate and energy consumption of secondary
crusher. However, it can be concluded that, in general, the achieved results are
satisfactory for circuit balancing and equipment dimensioning.
7 REFERENCES
Mesto, 2017. Mesto Crushing and Screening solution. [Online]
Available at: https://www.metso.com/globalassets/saleshub/documents---
episerver/metso-crusher-screen-en-2973.pdf
Metso Corporation, 2015. Basics in Minerals Processing. s.l.:s.n.
Metso Corporation, 2019. www.metso.com. [Online]
Available at: https://www.metso.com/products/crushers/
[Accessed 15 September 2019].
Sandvik, 2019. rocktechnology.sandivik.com. [Online]
Available at: https://www.rocktechnology.sandvik/en/products/stationary-crushers-
and-screens/stationary-screens-and-feeders/lf-linear-motion-screens/
[Accessed 16 September 2019].
Wills, B. A. & Finch, J., 2016. Wills’ Mineral Processing Technology. Oxford: Elsevier.
