This set of Basic Civil Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Calcination and Slaking of Lime”.
1. Which of the following methods yields quick, small supplies of Quick Lime?
a) Intermittent kiln
b) Continuous kiln
c) Clamp burning
d) Kankar burning
Explanation: In a kiln, lime is produced in large quantities for commercial purpose. In clamp burning, available quantity of limestone is stacked with fuel and burnt.
2. How is the arrangement in a clamp, if the fuel used is coal?
a) Stacked in alternate layers
b) Placed on a platform
c) Mixed and poured into a basin
Explanation: If fuel used is wood, they are stacked together in alternative layer. In case of coal or charcoal, it is mixed with limestone and placed in heap form.
3. How can one understand the completion of the burning of lime?
a) Blue flame at the top disappears
b) Blue flame appears at the top
c) Smoke is released in huge quantity
d) Red flame appears at the top
Explanation: A blue flame indicates complete combustion, implying no wastage of resources. Hence, we can ensure the proper burning of lime.
4. The term Calcination comes from:
a) Greek word Calcinare
b) Latin word Calcinare
c) Greek word Calcinate
d) Latin word Calcinate
Explanation: Calcinare is a Latin word. It means to burn lime, hence calcination is accorded to as burning of Lime.
5. Which of the following is not an example of Calcination process?
a) Decomposition of Calcium Chlorate
b) Decomposition of volatile matter in petroleum coke
c) Removal of ammonium ions in synthesis of zeolites
d) Decomposition of hydrated minerals
Explanation: All the other process leads to burning or thermal decomposition of lime in some forms. Calcium Chlorate decomposes into calcium chloride and oxygen.
6. The temperature at which standard Gibbs free energy is zero for calcination reaction is called:
a) Absolute temperature
b) Negative temperature
c) Transition temperature
d) Thermal decomposition temperature
Explanation: Transition temperature is for phase transitions. Absolute temperature is measured relative to absolute zero. Negative temperature is the one measured below zero.
7. In which feed type kiln, limestone does not come in contact with fuel?
a) Single feed
b) Isolated feed
c) Separate feed
d) Mixed feed
Explanation: There are only 2 feed types of kiln – namely mixed and separate. In mixed feed type, fuel and limestone are mixed together during burning.
8. Which one of the following is an advantage of Kiln burning over clamp burning?
a) Burning is not complete
b) Requires more fuel
c) No wastage of lime
d) Time effective
Explanation: Clamp burning takes weeks to burn limestone, whereas kiln burning takes only hours. Kiln burning operation involves loading, burning, cooling and unloading. All these lead to wastage of lime in some amount.
9. Slaking of lime refers to:
a) Mixing NaCl in hydraulic lime
b) Mixing water in quick lime
c) Mixing water in limestone
d) Mixing NaCl in quick lime
Explanation: Slaking refers to the process of mixing water in quick lime. Only after this, it can be used in construction works.
10. How many brick lined tanks are used in tank slaking method?
Explanation: Two tanks are used for tank slaking method. One is constructed 45cm deep, at a higher level. Other one adjoining the first one is constructed 60-75cm deep, at lower level.
11. In tank slaking, the second tank (60-75cm deep) is filled with:
Explanation: Lime is gradually added to water present in the first tank and stirred continuously. It results in formation of milk of lime, which is allowed to falls through a sieve into the second tank.
12. The lime-milk can be utilized after and for:
a) 2-3 days for putty
b) 2-3 hours for putty
c) 2-3 days for waste water treatment
d) 2-3 hours for waste water treatment
Explanation: The lime-milk is allowed to stand for the requisite time of 2-3 days. It matures itself and forms lime putty.
13. The quantity of water to be added for hydrating 100kg of lime is:
a) 10 litres
b) 1 litre
c) 15 litres
d) 32 litres
Explanation: Quantity of water to be added depends on composition of lime, method of slaking, form of lime required (dry or putty). Practically water up to 100 litres can also be added for lime putty.
14. Rate of hydration (slaking) does not depend on:
a) Degree of burning of lime
b) Degree of agitation
c) Atmospheric conditions
d) Composition of lime
Explanation: Over and under burned lime is undesirable. Composition of lime (pure, clay) are important to determine slaking. Pure lime slakes vigorously. Slaking is carried in tank in closed conditions. Too little agitation results in uneven mixing and leads to drowning or unhydrated particles of CaO.
15. Why is the middle portion in a continuous kiln widened?
a) To accommodate more fuel
b) To collect lime at bottom
c) To allow the flow of limestone from top
d) To accommodate hot gases of combustion
Explanation: The kiln has two sections – upper one to store limestone and lower one to collect lime. As burning continues, hot gases are releases. These are then accommodated in the middle portion.
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