Boilers MCQ Quiz in தமிழ் - Objective Question with Answer for Boilers - இலவச PDF ஐப் பதிவிறக்கவும்

Concept:

Equivalent Evaporation:

- It is defined as the amount of feed water evaporated per unit of time during the conversion of feed water at 100 ºC into dry and saturated steam at 100 ºC.

Equivalent Evaporation \(m_e = \frac{m_w × (h-h_w)}{m_f × 2257}\)

Where, m_w = mass of water evaporated

h = enthalpy of steam after evaporation

h_w = enthalpy of feed water

m_f = mass of fuel

and 2257 in the denominator indicates heat required in kJ for 1 kg of feed water at 100 ºC and 1 atm pressure to convert into dry and saturated steam at the same pressure and temperature. 

Calculation:

m_w = 13000 kg

m_f = 1250 kg

h = 2570.7 kJ

h_w = C_p × (T-0) = 4.184 × 40 = 167.36 kJ

Here, the heating value of coal is given which is redundant data for this calculation.

\(m_e = \frac{13000 \times (2570.7-167.36)}{1250 \times 2257}\)

Therefore, \(m_e = 11.075\)

Explanation:

Fire Tube Boiler:

• When the flames and hot gases, produced by combustion of fuel, pass through the tubes (called multitube) which are surrounded by water, then the boilers are named as fire tube boilers.

Types of Fire Tube Boilers:

• Simple vertical boiler
• Lancashire boiler
• Cochran boiler
• Cornish boiler
• Locomotive boiler

Water Tube Boiler:

• When water is contained inside the tubes (called water tube) which are surrounded by flames and hot gases from outside, then the boilers are named as water tube boilers.
• They are safe, quick steaming, flexible in construction and operation.
• These boilers are extensively used because they can be built for high pressure and large evaporative capacities.

Types of Water Tube Boilers

• Babcock and Wilcox boiler
• Stirling boiler
• Lamont boiler
• Benson boiler
• Loeffler boiler, etc.

Concept: 

Boiler efficiency: It is defined as the ratio of actual heat utilized in the steam generation to the heat delivered by fuel.

\(\eta_{boiler}=\frac{m_s(h_s-h_f)}{m_fCV}\)

Where,

\(m_s\) = mass flow rate of steam (kg/s)

\(m_f\) = mass flow rate of fuel (kg/s)

\(h_s\) = enthalpy of steam (kJ/kg)

\(h_f\) = enthalpy of feed water (kJ/kg)

\(CV\) = calorific value of fuel (kJ/kg).

Calculation: 

Given:

\(\eta_{boiler}\) = 80%

\(m_s=\frac{10}{9} \) kg/s

\(h_s\) = 3245.5 kJ/kg, \(h_f\) = 209.3 kJ/kg, \(CV\) = 44500 kJ/kg

\(m_f=\frac{m_s(h_s-h_f)}{\eta_{boiler}\times CV}\) = \(\frac{\frac{10}{9}\times(3245.5-209.3)}{0.8\times44500}\times3600\) = 341.15 kg/h.

Thus, option (1) is the correct answer.

Explanation:

Spring loaded safety valve:

• For a spring-loaded safety valve, the pressure required to lift the valve (also known as the cracking pressure) is less than the pressure required to open it fully (also known as the popping pressure).
• This is because the spring exerts a force that opposes the pressure of the fluid acting on the valve. In order to overcome the spring force and lift the valve, the fluid pressure must be slightly higher than the spring force.
• Once the valve is lifted, the fluid pressure can then act on a larger area of the valve, which increases the force on the valve and causes it to open fully.

​Therefore, the pressure required to lift the valve is less than the pressure required to open it fully

Concept:

Fire Tube Boiler: In this boiler, the hot flue gases are present inside the tubes and water surrounds them. They are low-pressure boilers. The operating pressure is about 25 bar.

Example to fire tube boilers:

• Cornish boiler
• Cochran boiler
• Locomotive boiler
• Lancashire boiler
• Scotish marine boiler

Water Tube Boiler: In this boiler, the water is present inside the tubes and the hot flue gases surround them. They are high-pressure boilers. The operating pressure is about 250 bar.

Examples of water tube boilers:

• Stirling boiler
• Babcock and Wilcox boiler
• Yarrow boiler
• La mont boiler
• Loeffler boiler
• Velox boiler

Explanation:

In all modern power plants, high-pressure boilers (> 80 bar) are universally used as they offer the following advantages:

• The efficiency and the capacity of the plant can be increased as a reduced quantity of steam is required for the same power generation if high-pressure steam is used.
• The forced circulation of water through boiler tubes provides freedom in the arrangement of furnace and water walls, in addition to the reduction in the heat exchange area.
• The tendency of scale formation is reduced due to the high velocity of the water.
• The danger of overheating is reduced as all the parts are uniformly heated.
• The differential expansion is reduced due to uniform temperature and thus reduces the possibility of gas and air leakages.
• Fire-tube boilers are low-pressure boilers, while water-tube boilers are high-pressure boilers.

Types of high-pressure boilers

• La-Mont Boiler
• Benson Boiler
• Loeffler Boiler
• Velox Boiler
• Cornish Boiler
• Babcock and Wilcox Boiler

Additional Information

Explanation:

• Fusible plug is fitted to the fire box.
• It is generally made up of brass
• It's object is to put off the fire in the furnace of the boiler when the level of water in the boiler falls to an unsafe limit and avoids the explosion which may takes place due to overheating of the furnace.

Important Points

• The boilers are the part of the boiler and are required for proper functioning. It is essential fitting for the safe working of a boiler.
• Some of the important mountings are: Water level Indicator, Pressure Gauge, Safety Valve, Fusible Plug, Feed Check Valve, and Steam Stop Valve.
• The accessories are mounted on the boiler to increase its efficiency. These units are optional on an efficient boiler.
• The following accessories are normally used on a modern boiler: Economizer, Superheater, Air pre-heater, Feed water pump, Steam injector, Chimney

Explanation:

• Babcock and Wilcox is a water tube boiler used in steam power plants.
• In this, water is circulated inside the tubes and hot gases flow over the tubes.
• Water tubes are placed between the drum and furnace in an inclined position (at an angle of 10 to 15°) to promote water circulation.

Concept:

Overall efficiency = η_g × η_t × η_b× η_c × η_a

Where, η_g = Efficiency of Generator, η_t = Efficiency of turbine, η_b = Efficiency of Boiler

η_c = Efficiency of Thermodynamics cycle , η_a = Efficiency of Auxiliary

Calculation:

Overall efficiency = η_g × η_t × η_b× η_c × η_a

0.33 = 0.97 × 0.95 × 0.92 × 0.42 × η_a

∴ η_a = 0.926

Explanation:

Economizer: 

• It is also known as a feedwater heater.
• It is a device in which the waste heat of the flue gases is utilized for heating the feed water.

Air Preheater: 

• It is used to increase the temperature of the air before it enters the furnace.
• It is generally placed after the economizer; so that the flue gases pass through the economizer and then to the air preheater.

Superheaters: 

• It is used to dry the wet steam and raise the temperature of the steam above its saturation temperature.
• It is generally placed in the path of the furnace gases so as to utilize the heat from the hot flue gases.

Steam trap: 

• A Steam trap is an automatic drain valve that distinguishes between steam and condensate.
• A steam trap holds back steam & discharges condensate under varying pressures or loads.