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PPD710S - Process Plant Design and Economics 315 - 2nd OPP - JUN 2023 |
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nAmlBIA unlVERSITY
OFSCIEnCEAno TECHn OLOGY
FACULTY OF ENGINEERING AND THE BUILT
ENVIRONMENT
DEPARTMENT OF CIVIL, MINING AND PROCESS ENGINEERING
QUALIFICATION : BACHELORS OF ENGINEERING IN METALLURGICAL &
CHEMICAL ENGINEERING
QUALIFICATION CODE: BMET
&BCHEM
LEVEL: 7
COURSE CODE: PPD710S
COURSE NAME: PROCESS PLANT DESIGN &
ECONOMICS 315
SESSION: JUNE 2023
PAPER:THEORY
DURATION: 3 HOURS
MARKS: 100
SECOND OPPORTUNITY EXAMINATION
EXAMINER(S) Prof Vusumuzi Sibanda
MODERATOR: Prof Godfrey Dzinomwa
INSTRUCTIONS
1. Answer all questions.
2. Read all the questions carefully before answering.
3. Marks for each question are indicated at the end of each question.
4. Please ensure that your writing is legible, neat and presentable.
PERMISSIBLE MATERIALS
I. Examination paper.
2. Two Graph Papers
3. Mathematical Instruments
THIS MEMORANDUM PAPER CONSISTS OF 5 PAGES (Including this front page)
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Question 1 [5 marks]
SECTION A [50 MARKS]
Modelling and simulation is now established in process engineering as an invaluable tool of
the trade. What are the main benefits of Modelling in Process Design?
[5 marks]
Question 2 [5 marks]
Process flow diagrams (PFDs) are among the key deliverables of a process design. What key
information can be obtained from a PFD?
[5 marks]
Question 3 [10 marks]
Write a short essay discussing the critical issues that must be given attention when developing
an integrated minerals processing circuit to concentrate an ore with more than one mineral
of value.
[10 marks]
Question 4 [5 marks]
"Reducing particle size of ores in comminution generally increases the degree of liberation".
i. What do you understand by the "degree of liberation" in this context?
[2 marks]
ii. What is the effect of or texture on liberation
[3 marks]
Question 5 [10 marks]
Why do smaller particles
i.
have larger surface area than larger ones per unit volume?
[2 marks]
ii.
require more unit energy for breakage than larger ones?
[3 marks]
iii. Which of the ore breakage mechanism results in a bi-modal distribution of
progeny particles and why?
[5 marks]
Question 6 [10 Marks]
The cyclone shown below was used to classify material produced by a Rod mill prior to a
flotation process at a Cu-Zn concentrator plant. The particle size analysis of a 67g sample
obtained from the Rod mill product is as given in the table below. During the test-work on the
cyclone the solids Feed-Rate was set at 125kg/hr.
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I Cyclone Overflow
(0/FJ
Cyclone Feed (C/F)
- 125 kg/hr solids
flowrate
Cyclone Underflow
(U/F)
Screen Size (µm)
250.0
125.0
62.5
31.3
Pan
Mass retained on screen (g)
4.1
21.6
23.4
12.6
5.2
You are given that classification behavior of the cyclone is given by the equation:
Ru; =1-exp(-(d/dso)l. 2),
where Ru; - is the recovery of each size class to the cyclone underflow (U/F), and
the dsosize is given as 125µm.
Use this information to calculate the following:
(i) Flowrate to the underflow
[7 marks]
(ii) dsoof the cyclone overflow
[4 marks]
(iii) Describe briefly how a cyclone achieves the desired classification
[4 marks]
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SECTION B [50 MARKS]
Question 1 [10 Marks]
Show from ist principles that the total recovery of a component A in a continuously stirred
flotation tank is given by;
1
Rec= l - ( l+kT )
Where
Rec - is the total conversion of component A
K - is the reaction rate constant
T - is the residence time
Question 2 [20 marks]
The copper-zinc ore from the milling circuit discussed in Section A- Question 6 was fed into a
flotation plant at the rate of 250 t/h. The final products were a copper concentrate and a zinc
concentrate and tailings. Analysis of each stream were:
Stream
Feed
Copper Cone.
Zinc Cone.
Tailngs
Assay
% Cu
% Zn
25
3.1
78.2
6.3
2.1
55.4
0.7
0.8
Determine the mass flows in the two concentrate streams and the recovery of metal in each
product stream. [20 marks]
Question 3 [10 marks]
What do you understand by the following in the context of economic evaluation of a mineral
beneficiation project.
a. Contingency [2 marks]
b. Cost of Capital [2 marks]
c. Working capital [2 marks]
d. Return on Investment (ROI) [2 marks]
e. Profitability index [2 marks]
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Question 4 [10 marks]
The Koeberg nuclear power station in South Africa has process design project A and B
which are expected to have the cash flows presented in the table below. The capital cost
of each project is $1 000 000. Answer the following questions:
(a) Calculate the return on investment (ROI) for design project A.
[3 marks]
(b) Determine the internal rate of return (IRR) for design project B by using a graphical
method within a discount rate of 5% to 30%. Use a discount rate interval of every 5%
in your calculations.
[7 marks]
Table 1: Cashflows for two competing projects
Cash Flows $1000
Year
Design
Design
Project A
Project B
0
-1000
-1000
1
150
500
2
250
450
3
350
300
4
400
200
5
400
100
_______________
THE END _____________
_