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PNM720S - Pyrometallurgy of Ferrous Metals 324 - 1st Opp - Nov 2022 |
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nAmI BIA unIVERSITY
OF SCIEnCE Ano TECHnOLOGY
FACULTYOF ENGINEERINGAND SPATIALSCIENCES
DEPARTMENT OF MECHANICAL,MINING AND PROCESSENGINEERING
QUALIFICATION:BACHELOROF ENGINEERINGIN METALLURGY
QUALIFICATIONCODE: 0SBMET LEVEL:7
COURSECODE: PNM 720S
COURSENAME: PYROMETALLURGYOF FERROUSMETALS
SESSION:NOVEMBER 2022
PAPER:THEORY
DURATION: 3 HOURS
MARKS: 100
EXAMINER(S)
MODERATOR:
FIRSTOPPORTUNITYQUESTION PAPER
Prof. Sofya Mitropolskaya
Dr. Silas lthete Hango (University of Namibia)
INSTRUCTIONS
1. Answer all questions.
2. Read all the questions carefully before answering.
3. Marks for each questions are indicated at the end of each question.
4. Please ensure that your writing is legible, neat and presentable.
PERMISSIBLEMATERIALS
1. Examination paper.
THIS QUESTION PAPERCONSISTSOF 5 PAGES(Excluding this front page)
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Question 1 [25 marks]
(a) A blast furnace makes hot metal containing 2.6 wt.% C, 1.1 wt.% Si, 1.3 wt.%Mn, the
remainder being Fe. The ore burden contains 85% Fe2031 the remainder being gangue of
Si02 and Al203. Calculate the weight of ore W(ore) used for the production of 1 ton of hot
metal.
Note: Atomic weights are - Fe= 56, 0 = 16.
[10)
(b) Why do the charge materials descend to the bottom of the blast furnace? Provide five
reasons.
[5]
(c) Below is a simplified Oxygen Potential diagram (Fig. Ql). With the aid of the diagram,
specify, in which parts of a blast furnace (throat, stack, cylinder bosh, bosh or hearth) the
following oxides can be reduced to pure metals: Cao, MgO, A'203, Si02, and MnO. Provide
the relevant reactions.
[10)
·••
""
.... ,soo
·2000
lSCO
Figure Ql. Oxygen Potential diagram.
Question 2 [25 marks]
(a) Discuss the factors that you would consider in order to set up a ferroalloys smelter in a
given location. What measures could be taken for Namibia to be a favorable destination
for such an investment.
[SJ
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(b) Assume your responsibility is to procure necessary equipment for a sponge ironmaking
plant being under construction in Namibia. You have discovered that the following pieces
of equipment are marketed at a reasonable price: (a) a coke oven; (b) Ingot-casting
machine; (c) a methane reforming unit; (d) a 100 t ladle and (e) a slag-granulating
machine. Make up an acquisition list with reference to items (a) to (e). Briefly explain your
choice. Since your budget is limited, select only those items that are needed urgently in
Namibia.
[5]
(c) The World Steel Association recently recommended a number of interventions to mitigate
CO2emission by the global iron making industry. The most ambitious initiative involves the
replacement of carbon with green hydrogen.
(i) With the aid of Fig. Q2, briefly explain environmental benefits of the coke
replacement with hydrogen in ironmaking industry. Provide necessary reactions. [SJ
t JOO
80
i 60
~. .40
"i 20
0
400
600
800 1000 1200
Figure Q2. Equilibrium diagram for H2 (gas), H20 (steam) and iron oxides.
(i) What is green hydrogen? What makes Namibia a promising location for green
hydrogen production in general?
[SJ
(ii) In your opinion, is it possible to substitute coke totally with green hydrogen in blast
furnace ironmaking? Briefly explain.
[SJ
Question 3 [25 marks]
(a) A hypothetical integrated steelmaking plant is processing high-manganese hot metal into
steel. Both types of oxygen steelmaking convertors are available: basic type and acidic
type. Should they use a basic oxygen converter or an acidic oxygen convertor for this job?
Kindly advise and briefly explain your choice by relevant chemical reactions.
[SJ
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(b) How much electric energy is consumed by an average basic oxygen converter? Is it
possible to run a hypothetical basic oxygen converter using the solar energy only? [5]
(c) For obtaining the optimum slag viscosity, the composition of Basic Oxygen Converter slag
at "Tata steel" is to meet the following requirements:
Si02/A'203 =85/15; CaO/Si02=65/35.
Estimate the slag composition in the point of interest with the aid of a ternary diagram
(Fig. Q3c).
[5]
Si0 2
0%
%
Figure Q3c. Ternary diagram for steel making slag.
(d) Overblowing is an excessive oxygen lancing during the final stage of the oxidation period
in oxygen convertor steel making.
(i) With the aid of Fig. Q3d, briefly indicate the negative consequences of overblowing.[5]
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OKidation Reactions
%C, Mn, P, Si
oxidation
100% ,---------y-----------~
Si
Fe oxidation /
kg/t
20
10
Fe
0%c;_ _______________
Time/ min
_, 0
Figure Q3d. Reaction rates for the oxidation reactions in basic oxygen converter (BOC).
(ii) What steps should be practiced to prevent overblowing?
[SJ
Question 4 [25 marks]
(a) Research at a steel making plant has revealed three morphological types of non-metallic
inclusions formed in the cast steel (see Figure Q4a).
Type A
Type B
Type C
Figure Q4a. Scanning electron micrographs of the three types of non-metallic inclusions
in cast steel. Type A: 2000x. Type B: 3000x. Type C: 2000x.
(i) What type(s) of inclusions are acceptable in final steel products?
[SJ
(ii) Briefly explain a relevant method of the liquid steel treatment to insure the formation
of this type of inclusions. Note: morphology means shape and size of particles. [SJ
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(b) Why killed steel is referred to as killed steel? Briefly discuss advantages and limitations of
the killed steel.
[SJ
(c) Stokes law estimates the velocity of elimination of solid globular particles through molten
steel as follows:
In this expression Vis the velocity of particles elimination from the molten steel (m/s); g is
acceleration
due to
gravity
(9,8 m/s 2);
d is diameter
of the
particle
(m);
p
5
is the density
of silica; pf is the density of liquid steel; and µ is the viscosity of liquid steel. With the aid
of Stokes law calculate the velocity of silica globular particles elimination from the molten
steel and the residence time with reference to silica globule of radius 3 mm moving through
2 m of a ladle given that the silica density 2.20x10 3 kg/m3, the density of liquid steel is
7.16x10 3 kg/m 3 and the viscosity of liquid steel is 6.lx10- 3 kg/(m·s).
[10)
Endof ExaminationQuestion Paper
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