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FFR820S - Fuel Furnaces and Refractories - 2nd OPP - JUN 2023 |
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nAmlBIA UnlVERSITY
OF SCIEnCEAno TECHnOLOGY
FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
DEPARTMENT OF CIVL, MINING AND PROCESSENGINEERING
QUALIFICATION: BACHELORSOF ENGINEERINGIN MINING ENGINEERING
QUALIFICATIONCODE: 08BMEG
LEVEL: 8
COURSECODE: FFR820S
COURSENAME: FUELSFURNACESAND
REFRACTORIES
SESSION:JUNE 2023
PAPER:THEORY
DURATION: 3 HOURS
MARKS: 60
SECOND 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 QUESTION PAPERCONSISTSOF 3 PAGES(Including this front page)
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Question 1
(max 8)
Basic furnace control strategies are based on either the product temperature control or the
fuzzy logic and rule-based systems. Give summary principles of the two control strategies.
Question 2
(max 8)
Consider resistance heating in furnaces.
a) Explain why coiled heating elements, sometime tape form elements are preferred to
straight round wires (or rods) heating elements.
b) Explain the failure of heating elements by "hot spot". What are the other causes of
failure of heat elements?
Question 3
(max 9)
Consider the physics of combustion.
a. What are the stages of the combustion of a fuel with oxygen. Which is the slowest
stage?
b. What would be the consequences of insufficient fuel/air mixing in a diffusion
burner? How do you design the air supply to the furnace to avoid such risks?
c. Explain the occurrence of jet entrainment in furnaces.
Question 4
(max 10)
Refractory bricks rarely fail under compression, however they can fail under strain loading
due to internal forces, such the volume thermal expansion (contraction) due to heating
(cooling). How do you design the refractory construction to avoid this failure mode of the
bricks.
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Question 5
(max 10)
Discuss the effect of the electric courant frequency on the careless and cored designs and
operation conditions of induction furnaces. Fully explain the effect on the heating depth.
p =.2._ cm
2TT
Question 6
(max 6)
Consider the wear of refractories by dissolution (corrosion) and by penetration by liquid
slag. Fill in the table below.
Dissolution
(corrosion)
Penetration by
liquid slag
Rate factors
Control
Worse conditions
Question 7
(max 9)
Good instrumentation is an essential component of furnace control. The most important
parameters are temperature, heat input and excess air. Give short summary of
measurement of these parameters in industrial furnaces.