Power Plant Engineering Multiple Choice Questions on “Draught System”.
1. Which of these terms defines the pressure difference in the furnace?
a) draught
b) duct
c) stack
d) chimney
Answer: a
Clarification: The term ‘draught’ is used to define the static pressure in the furnace, in the various ducts and the stack.
2. The draught or pressure difference for a chimney of height of H metres is given by?
a) Δp = gH(ρa-ρg)
b) Δp = gH(ρg-ρa)
c) Δp = gHρg
d) Δp = gH(ρa+ρg)
Answer: a
Clarification: The draught produced is given by Δp = gH(ρa-ρg).
3. Which of these is not a type of mechanical draft system for a furnace?
a) balanced draft
b) induced draft
c) forced draft
d) actuated draft
Answer: d
Clarification: The three types of mechanical drafts are balanced, induced and forced drafts.
4. Stack heat losses can be minimised by __________
a) using low c.v. fuels
b) controlling the excess air
c) oxygen enrichment of combustion air
d) maintaining proper draft in the furnace
Answer: b
Clarification: Excess amount of air leads to significant losses in energy due to heat loss through flue gases.
5. Which of these accentuates clinkering trouble on furnace grate burning coal?
a) low reactivity of carbonised residue containing high proportions of iron and sulphur
b) low forced draught and low fuel bed temperature
c) thick fire bed and preheated primary air
d) all of the mentioned
Answer: d
Clarification: All these reasons lead to clinkering.
6. Natural draught produced by a chimney depends upon __________
a) density of chimney gases
b) height of chimney
c) both ‘density of chimney gases’ and ‘height of chimney’
d) none of the mentioned
Answer: c
Clarification: Natural draught depends on density of gases in chimney and its height.
7. In a furnace employing forced draught compared to induced draught __________
a) the fan operates hot and hence blades are liable to corrosion and erosion
b) positive pressure exists in the furnace
c) air is sucked in, so air leaks are more and hence furnace efficiency is reduced
d) none of the mentioned
Answer: c
Clarification: A positive pressure exists in the furnace employing forced draught.
8. Which of the following types of the fans has the highest cost?
a) centrifugal fans
b) axial fans
c) primary fans
d) gas recirculation fans
Answer: b
Clarification: Axial fans have the highest cost.
9. Which of these is not a type of drive of variable speed control?
a) variable speed turbine
b) hydraulic coupling
c) multiple speed ac motor
d) electronically adjustable turbine drive
Answer: d
Clarification: Except ‘electronically adjustable turbine drive’, all other are a type of drive in variable speed control.