Exercise 3-5. Three-stage crusher circuit
The folowing elements are included in this exercise:
4.Report file for tertiary crushers.
In this exercise you will add a third stage of crushing to the flowsheet to reduce the size to meet the requirement that the product should have a d80 size of 10 mm. The third stage will be operated in closed circuit, and this will introduce you to the simulation of plants with recycle.
Open the job that you saved as exercise 3-4. Change the job name to Exercise 3-5. Add a screen and a cone crusher and connect the final product as the feed to the screen. (You can draw the screen icon then move it so that it just touches the arrowhead of the product stream. MODSIM will recognize the connection when you refresh the flowsheet.) Direct the screen oversize to the crusher. At this stage it is not advisable to close the circuit, and you should run the simulator in open circuit at least once to make sure that all parameters are properly set up.
Use model SCRN for the screen with a mesh size of 13 mm. Choose the short head model SHHD for the crusher and set the CSS to 13 mm.
Run the simulation and check the report files for the two units that have been added. You should also check the size distributions in the products from the screen and the mill. When you are satisfied that the units are functioning properly, direct the crusher product back to the screen. Remember that the screen icon can accept only one feed stream so that a mixer or sump must be inserted in the flowsheet ahead of the screen to receive the secondary screen undersize, the secondary crusher product, and the tertiary crusher product.
Run the closed-circuit simulation and MODSIM should converge easily. If you are using a slow computer (<66 MHz), you should notice that the calculation does take a little longer because the recirculating load is calculated by iteration. In the unlikely event of some difficult with the iterative calculation, MODSIM will give you some diagnostic information to pinpoint the trouble. By far the most common cause of difficulty with iterative calculations is caused by inappropriate choice of model parameters. Check these thoroughly and you should find your error. If you cannot diagnose the problem, download the exercise job from the course FTP site and investigate any differences that you can find. If you cannot sort out a problem, pack the job and send it by internal course e-mail to the instructor.
When you are comfortable with the simulation, you could try any number of what-if scenarios. Try all or some of the following:
1. Vary the mesh size of the tertiary screen over the range 8 mm to 15 mm and observe how the recirculating load and the size distribution of the final product change.
2. Vary the mesh size and the CSS in the tertiary circuit and seek out an optimal combination that will minimize the size and number of crushers required. Also keep track of the area requirements for the screen.
3. Reverse the order of the tertiary screen and the tertiary crusher so that the entire product from the secondary circuit passes through the crusher which is then screened to close the circuit.
TOP
Unit
number 6 MODSIM model name SHHD
Job name: Exercise 3-5 Three-stage crushing
PARAMETERS:
Fines fraction .2000
Breakage function K(x/y)^0.518 + (1-K)(x/y)^2.475
Classification function parameters .653 2.000 n=2
Tonnage to be processed 1429. tons per hour
Closed side setting 13.00 mms
Size distribution in feed
Size % passing
mms
.101E+04 100.00
713. 100.00
505. 100.00
357. 100.00
252. 100.00
178. 100.00
126. 100.00
89.2 100.00
63.0 100.00
44.6 95.26
31.5 73.86
22.3 56.55
15.8 30.43
11.2 7.65
7.88 5.33
5.58 3.88
3.94 2.98
2.79 2.36
1.97 1.91
1.39 1.56
.985 1.28
.697 1.05
.493 .87
.348 .72
.000 .00
Top size in feed is approximately 53.1 mms
Open side feed opening must be at least 66.4 mms
Size distribution in product
Size % passing
mms
.101E+04 100.00
713. 100.00
505. 100.00
357. 100.00
252. 100.00
178. 100.00
126. 100.00
89.2 100.00
63.0 100.00
44.6 100.00
31.5 100.00
22.3 98.47
15.8 81.90
11.2 50.63
7.88 32.41
5.58 21.98
3.94 16.19
2.79 12.58
1.97 10.10
1.39 8.26
.985 6.82
.697 5.66
.493 4.71
.348 3.92
.000 .00
Select a crusher size and
cavity type to suit the closed side setting and
feed opening requirements.
Crusher selected is......
Capacity in tons per hour? ....
Number of crushers required?....
Impact work index of the
material is 12.00 kWhr/ton
80% passing size in feed is 34.04 mms.
80% passing size in product is 15.39 mms.
Estimated power requirements 453. kW