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PNM720S - Pyrometallurgy of Ferrous Metals 324 - 2nd Opp - Nov 2022 |
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nAm I BIA UnlVERSITY
OF SCIEnCE Ano TECHnOLOGY
FACULTYOF ENGINEERINGAND SPATIALSCIENCES
DEPARTMENT OF MECHANICAL, MINING AND PROCESSENGINEERING
QUALIFICATION: BACHELOR OF ENGINEERING IN METALLURGY
QUALIFICATION CODE: 08BMET LEVEL: 7
COURSE CODE: PNM 720S
SESSION: NOVEMBER 2022
COURSE NAME: PYROMETALLURGY OF FERROUS METALS
PAPER: THEORY
DURATION: 3 HOURS
MARKS: 100
EXAMINER{S)
MODERATOR:
SECONDOPPORTUNITYQUESTIONPAPER
Prof. Sofya Mitropolskaya
Dr. Silas lthete Hango (University of Namibia)
INSTRUCTIONS
1. Answer all the 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 PAPER CONSISTS OF 4 PAGES (Excluding this front page)
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Question 1 [25 marks]
(a) Figure Qla features a typical 18th century blast furnace in England. What ways can you
suggest to modernize the design in order to improve blast furnace productivity? State and
explain five possible interventions.
[5]
Vale RoyalFurnace_"'=---=--=..--·
.
.
Figure Qla. Layout of a typical 18th century blast furnace in England.
(b) A blast furnace makes hot metal containing 3.6 wt.% C, 1.1 wt.% Si, 1.3 wt.% Mn, the
remainder being Fe. The ore burden contains 80% Fe2O31 the remainder being gangue of
SiO2and Al2O3.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, C= 12, Si= 28 and Mn= 55.
[15]
(c) A junior student prepared the C-O-Fe equilibrium diagram for his presentation on blast
furnace ironmaking (see Fig. Qlc). However, he forgot to specify the chemical reactions
featured by curves (1), (2), and (3). You have noticed that he forgot a very important line
(4) in the bottom of the diagram. Draw the line missing in the diagram and indicate all the
relevant reactions (1), (2), (3), and (4).
[5]
:,0
Fo,O,
300
900
UXX>
1,100
1200
1.3'.X)
Tornporalur(oK)
Figure Qlc. The Fe-O-Cdiagram. One line is missing.
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Question 2 [25 marks]
(a) South Africa is a top global manufacturer offerrochromium. In your opinion, what makes
the country a favorable destination for setting up ferroalloy smelters?
[5]
(b) The World Steel Association recently recommended a number of interventions to
mitigate CO2emission by the global ironmaking industry. The most ambitious initiative
involves the replacement of carbon with green hydrogen. What are the key challenges
hindering the implementation of "hydrogen ironmaking"? State and briefly explain five of
them.
[5]
(c) As an expert in iron making, you are participating in a public discussion on prospects of an
ironmaking plant construction in Namibia. The plant should process local iron ore. Your
opponents promote setting up a Blast Furnace plant in Namibia to produce liquid cast
iron. In contrast, you argue that the construction of alternative iron making plant will be
a better choice for this country. Provide three key technical reasons in favor of the
production of sponge iron in Namibia by utilizing gas-based processes of sponge
ironmaking.
[15]
Question 3 [25 marks]
(a) For obtaining the optimum slag viscosity when producing low alloy steel from the low
manganese pig iron the composition of Basic Oxygen Converter slag at ArcelorMittal is to
meet the following requirements:
Indicate and all the necessary tie lines on the diagram provided (Fig. Q3) and estimate the
slag composition.
[5]
Si0 2
___%
.,
,.___•
Y--¥---4---¥--l~•
.,.,o\\
!;.!!Q '?os\\;?;..,,.,.-¾-,-,...,..,.~,,...,.;~+,.,,~.,.,.,,;,..,.,.;~-¥-.,~..:...:.e\\•
";
Figure Q3. Ternary diagram for steelmaking slag.
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(b) A basic oxygen converter (BOC)treats the following charge components: 284000 kg hot
metal, 4400 kg light scrap; 1000 kg heavy scrap. The post-combustion ratio (PCR) =
= 0.1 Assume that 11350 kg Fe was oxidized during lancing. The chemical
CO+C02
composition of the components is provided in Table Q3.
Table Q3. The chemical composition of charge components.
Charge component Weight charged Chemical composition (wt.%)
(kg)
C
Mn
Fe
Hot metal
284000
4.5
0.5 Balance
Light scrap
4400
0.05
0.12 Balance
Heavy scrap
1000
0.05
0.12 Balance
The target steel chemical composition is given as: 0.16 wt.% C and 1.5 wt.% Mn. The target
steel weight is 275 000 kg.
(i) Make up the oxygen balance and calculate the total volume of oxygen used in the BOC
process. Note: Atomic weights are - Fe= 56, 0 = 16, Si= 28, Mn= 55, C = 12. [15)
(ii) Estimate the time of blowing in case oxygen is lanced at a constant rate of 3 m3 per
ton per min.
[5]
Question 4 [25 marks]
(a) Liquid steel is being deoxidized in ladles by the addition of ferrosilicon. The deoxidation
product is solid globular silica. In Ladle 1 an average diameter of the silica particles is 5
µm, while in Ladle 2 an average diameter is about 50 µm.
(i) In which ladle a cleaner steel will be produced, if other conditions (the time of
treatment, the dimensions of the ladles, etc) are the same? Briefly explain. Assume
the rate of settling obeys Stock's law. According to Stokes law, the velocity of
elimination of solid globular particles through a layer of molten steel is given by:
gdz (ps- Pr)
V=
18µ
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);
dis
diameter
of
the
particle
(m);
p
5
is the density
of silica (2.20x10 3 kg/m 3); pI is the density of liquid steel (7.16x10 3 kg/m 3); and µ is the
viscosity of liquid steel, 6.1x10-3 kg/(m·s).
[10)
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(ii) Explain the practical steps the Plant Metallurgist should take to increase the velocity
of elimination of deoxidation products from the steel and therefore insure faster steel
refinement.
[S]
(b) During the secondary steelmaking processing stirring of a 200 ton ladle of steel is
performed by argon injections through porous plug in the bottom. Indicate five technical
reasons for stirring the steel bath during secondary steel making treatment.
[S]
(c) You are casting the following steel using a continuous casting machine:
Wt.%
C
0.1450
Si
0.2000
Mn
1.4000
p
<0.0250
s
<0.0200
Estimate the required steel temperature before casting. Note that the liquidus temperature
as a function of steel chemical composition is given by:
= Tliq 1537 - 78%C - 7.6%Si - 4.9%Mn - 34.4%P - 38%S [S]
------------------------------------------EofnEd xamination----------------------------------
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