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FFR820S - Fuel Furnaces and Refractories - 1st OPP - JUN 2023 |
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nAmlBIA untVERSITY
OF SCIEnCEAno TECHnOLOGY
FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
DEPARTMENT OF CIVL, MINING AND PROCESSENGINEERING
QUALIFICATION: BACHELORS OF ENGINEERING IN MINING ENGINEERING
QUALIFICATION CODE: 08BMEG
LEVEL: 8
COURSE CODE: FFR820S
COURSE NAME: FUELS FURNACES AND
REFRACTORIES
SESSION: JUNE 2023
PAPER: THEORY
DURATION: 3 HOURS
MARKS: 60
FIRST OPPORTUNITY QUESTIONS
EXAMINER(S) Maweja Kasonde
MODERATOR: Prof. Vusumuzi Sibanda
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
1. Examination paper.
2. Calculator
THIS QUESTIONPAPERCONSISTSOF 4 PAGES(Including this front page)
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Question 1
(max 5)
Considering typical losses from furnaces.
How do you improve the thermal efficiency of high temperature furnaces. Use examples of
a kiln furnace, a reverberatory furnace and a blast furnace.
Why do you limit air excess in high temperatures furnaces operating above 1000°C?
Question 2
(max 5)
Explain the effect of fuel choice on the following operation conditions of a metallurgical
furnace.
a. Heat transfer and performance
b. Furnace atmosphere
c. Refractory life
Question 3
(max 5)
Consider the physics of combustion.
a. Explain the importance of jet recirculation in a furnace heated up by a combustion
flame.
b. How will you design the burner in a furnace where the flame is not restricted by the
walls?
Question4
(max 5)
In a 3-phase electric arc furnace, how do you adjust the voltage drop through the arcs?
How do you protect the power supply system from large surges during the melting step?
Question 5
(max 5)
Explain the working principle and technical advantage of the Outokumpu furnace for matte
smelting copper sulphide concentrates.
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Question 6
(max 5)
During the operation of a reverberatory furnace, the analysis reveals that the flue gas
contain some amount of carbon monoxide CO, which infers an incomplete combustion of
the hydrocarbon liquid fuel used to generate the heating flame.
a. What is the cause of incomplete combustion? How would you proceed to safely
adjust the operation parameters?
b. Describe the safe procedure to avoid an explosion during furnace start-up.
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Question 7
(max 5)
The true way to prevent crack growth due to thermal shock in refractories is described by
the parameter:
How do you implement this behaviour in practice to improve the refractory life?
Question 8
(max 7)
The phase diagrams of two refractory material systems (CaO- SiO2) and (MgO -AliO 3) are
given. Motivate your choice of the bricks for constructing a furnace operating at 1600°(.
JOOO
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R=l.35,
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1200
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Question 9
(max 8)
A new furnace was designed to work with a burner of manufactured Lean Reformer Gas
LRG.The traditional supplier of LRGgas is temporarily unable to meet your order quantities
and schedules. Considering the properties in the table below, would you consider the blast
furnace off-gas, Commercial propane LPGor Coke Oven Gas as substitute in the meantime?
Note: Changing the burner would lead to months long downtime of the furnace.
Property
CH4{%)
C2H6(%)
C3HB(%)
Higher CxHv(%)
CO{%)
H2
N2{%)
CO2(%)
02(%)
Relative density/air
Calorific value CV {MJ/m 3]
Air required [m 3/m 3]
Blast furnace
24
2.5
56
17.5
1.04
3.18
0.631
Coke oven
28
2
7.4
54
5.6
2
0.4
0.38
19.89
4.572
Lean Reformer Gas
22.7
5.0
0.4
2.2
53.7
Commercial Propane
1.5
91
7.5
16.0
0.593
18.92
4.398
1.523
93.87
23.762
Question 10
(max 10)
Fuel oil with the following ultimate composition (w%/w) is burnt with a 10% excess air in a
furnace. Carbon 82%, Hydrogen 18%.
Assuming air composition is 76.7 w% Nitrogen and 23.3 w% Oxygen. Considering complete
combustion, determine:
(i) The mass of air required to burn 1kg fuel oil
(ii) The mass of flue gas formed from the combustion of 1kg fuel oil
(iii) The volume of flue gas formed at (300°C, latm) from 1kg oil