Steam Power Plants MCQ Quiz in తెలుగు - Objective Question with Answer for Steam Power Plants - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Concept:

• In a thermal power plant, a condenser is installed to condense the exhaust steam coming out of turbine
• After the steam has passed through the turbine, doing work and losing pressure and temperature, it is sent to the condenser.
• The primary function of the condenser is to condense the exhaust steam from the turbine for reuse in the boiler as feed water. The condenser creates a vacuum that maximizes the energy extraction from the steam, leading to increased efficiency.

Additional Information Coal-fired power plant:

• A coal-fired power station or coal power plant is a thermal power station that burns coal to generate electricity.
• A coal-fired power station is a type of fossil fuel power station.
• The coal is usually pulverized and then burned in a pulverized coal-fired boiler.
• The furnace heat converts boiler water to steam, which is then used to spin turbines that turn generators.
• Thus chemical energy stored in coal is converted successively into thermal energy, mechanical energy, and, finally, electrical energy.

Main components of coal-fired power plant:

1.) Conveyor Belt:

Coals from the coal storage area are transported to the plant through a large conveyor belt. The load-carrying capacity of this belt is very high because very large quantities of coal are required every day.

2.) Pulverizing Plant:

Pulverized coal firing ensures complete combustion of coal, thus ensuring higher efficiency of steam generators. The finer the grinding of coal, the more efficient its combustion.

3.) Boiler:

Boilers are used in power plants in order to produce high pressured steam which is used to run the turbine.

4.) Turbine:

High-pressure steam from the boiler is fed to the steam turbine, which converts its pressurized energy into mechanical energy.

5.) Generator:

A generator uses the mechanical energy generated by the turbines to generate electricity at significantly higher voltages.

6.) Condenser:

The steam leaving the turbines is condensed into a condenser, which is pumped back into the boiler. Cold water from a water source (river) or expansion process is used to cool steam into water.

7.) Chimney:

A chimney is the tallest structure in the power plant for venting hot flue gases or smoke from a boiler, stove, furnace, or fireplace to the external atmosphere.

It also ensures that enough air is drawn into the stove for the fire to burn clean.

Concept:

Overall efficiency can be calculated as

\(\% \eta = \frac{{100}}{{{m_f} × CV}}\)

Where,

mf = mass flow rate of fuel or fuel consumption in kg / Joule

CV = calorific value of fuel in Joule/kg

1 cal = 4.18 Joule

Calculation:

mf = 0.215 kg / kWh = \(\frac{{0.215}}{{3600 × {{10}^3}}}\;kg/J\)

CV = 10,000 kcal / kg = 4.18 × 107 J / kg

The correct answer is option 2): 30%

Concept:

The overall efficiency of the steam power plant is given as

\(Overall\;Efficiency\;\; = \frac{{Electrical\;energy\;output}}{{chemical\;energy\;input}}\)

Overall efficiency is also expressed as

\({\eta _0} = \;\frac{{Thermal\;Energy}}{{Chemical\;Energy}} × \frac{{Mechanical\;Energy}}{{Thermal\;Energy}} × \frac{{Electrical\;Energy}}{{Mechanical\;energy}}\)

So, the overall efficiency of the power plant is equal to the multiplication of the efficiencies of the boiler, turbine, and generator.

Overall Efficiency = Boiler efficiency × turbine efficiency × generator efficiency

Boiler efficiency = Thermal efficiency Turbine efficiency × Generator efficiency = Electrical efficiency.

Calculation:

Given

Boiler efficiency = 75%,

Electrical Efficiency = 50%

Turbine efficiency = 80%

Overall Efficiency = Boiler efficiency × turbine efficiency × generator efficiency

= 0.75 × 0.5 × 0.80

= 0.30 

= 30 %

Prime Mover: Prime Mover is a machine that used to convert another form of energy into rotational energy or mechanical energy for driven the shaft of Alternator to create revolving flux or cut the stationary flux for the generation of electrical energy.

Example: Steam turbine, gas turbine, water turbine, etc

The Prime Mover used in various power plant:

In a thermal power plant, feedwater heaters, superheaters, and air preheaters are mainly used to increase the efficiency of the plant.

Additional Information

Thermal (Steam) Power Plant :

A generating station that converts heat energy of coal combustion into electrical energy is known as a Thermal/Steam power station.

Layout of Steam Power Plant:

1. Coal and ash handling plant:
The coal is transported to the power station by road or rail and is stored in the coal storage plant. From the coal storage plant, coal is delivered to the coal handling plant where it is pulverized in order to increase its surface exposure, thus promoting rapid combustion without using a large quantity of excess air. The coal is burnt in the boiler and the ash produced after the complete combustion of coal is removed to the ash handling plant and then delivered to the ash storage plant for disposal.

2. Steam generating plant:
The steam generating plant consists of a boiler, superheater, and economizer for the production of steam and other auxiliary equipment for the utilization of flue gases.

(i) Boiler: The heat of the combustion of coal in the boiler is utilized to convert water into steam at high temperatures and pressure. The flue gases from the boiler make their journey through superheater, economizer, air pre-heater and are finally exhausted to atmosphere through the chimney.

(ii) Superheater: The steam produced in the boiler is wet and is passed through a superheater where it is dried and superheated by the flue gases on their way to the chimney. Superheating provides two principal benefits. Firstly, the overall efficiency is increased. Secondly, too much condensation in the last stages of the turbine is avoided. The superheated steam from the superheater is fed to the steam turbine through the main valve.

(iii) Economiser: An economizer is essentially a feedwater heater and derives heat from the flue gases for this purpose. The feed water is fed to the economizer before supplying to the boiler. The economizer extracts a part of the heat of flue gases to increase the feedwater temperature.

(iv) Air preheater: An air preheater increases the temperature of the air supplied for coal burning by deriving heat from flue gases. Air is drawn from the atmosphere by a forced draught fan and is passed through the air preheater before supplying to the boiler furnace. The air preheater extracts heat from flue gases and increases the temperature of the air used for coal combustion.

3. Steam turbine:
The dry and superheated steam from the superheater is fed to the steam turbine through the main valve. The heat energy of steam when passing over the blades of a turbine is converted into mechanical energy.

4. Alternator:
The steam turbine is coupled to an alternator. The alternator converts the mechanical energy of the turbine into electrical energy.

Exhaust fan:

Exhaust fans are used to pull excess moisture and unwanted odors out of a particular room or area.

Exhaust fans pull odors, fumes, and moisture from an area of the home, venting them outdoors for removal.

Ceiling fan:

It is a device suspended from the ceiling of a room, with hub-mounted rotating blades that circulate the air, thereby producing a loading effect.

Wall bracket fan:

Windy wall bracket fan can be directly mounted on the wall so that it doesn’t occupy floor space, it can manually oscillate when required.

Fan regulator:

A fan regulator is a crucial component that serves to increase or decrease the speed of one’s fan according to one’s needs.

Note:

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.

In economizer, feed water is preheated to improve overall efficiency and only sensible heat transfer is taking place so feed water is heated without converting it into steam. Therefore, the economizer is placed after the superheater and located in the feeding water circuit.

Following are the advantages:

• There is about 15 to 20% of coal saving.
• It increases the steam raising capacity of a boiler because it shortens the time required to convert water into steam.
• It prevents the formation of scale in boiler water tubes.          

The efficiency of Steam Power Station:

• The overall efficiency of a steam power station is low (about 29%) due mainly given reasons.
• Firstly, a huge amount of heat is lost in the condenser.
• Secondly, heat losses occur at various Stages of the plant.
• We cannot avoid the heat lost in the condenser. It is because heat energy cannot be converted into mechanical energy without temperature difference.
• The greater the temperature difference, the greater is the heat energy converted into mechanical energy.
• Therefore we have to keep the steam in the condenser at the lowest temperature. But the greater temperature difference causes a greater amount of heat lost.

\(Thermal\;Efficiency = \frac{{Heat\;equivalent\;of\;mechanical\;energy\;transmitted\;to\;turbine\;shaft}}{{Heat\;of\;combustion\;of\;coal}}\)

Thermal Efficiency: The ratio of heat equivalent of mechanical energy transmitted to the turbine shaft to the heat of combustion of coal is known as thermal efficiency of the steam power station.

The thermal efficiency of a modern steam power station is about 30%.

Overall efficiency: The ratio of heat equivalent of electrical output to the heat of combustion of coal is known as the overall efficiency of the steam power station.

\(Overall\;Efficiency = \frac{{Heat\;equivalent\;of\;electrical\;output}}{{Heat\;of\;combustion\;of\;coal}} \)

The overall efficiency of the Thermal Power Plant is about 29% because there is an approximation of 1% loss in the Alternator.

Concept of Overall Efficiency:

The overall efficiency (η_overall) of a station is the product of its thermal efficiency (η_thermal) and its electrical efficiency (η_electrical).

The formula to calculate the overall efficiency is:

η_overall = η_thermal × η_electrical

Where,

• η_thermal = Thermal efficiency (in decimal form)
• η_electrical = Electrical efficiency (in decimal form)

Given Data:

• Thermal efficiency (η_thermal) = 30% = 0.30
• Electrical efficiency (η_electrical) = 95% = 0.95

Calculation:

Using the formula:

η_overall = η_thermal × η_electrical

Substituting the given values:

η_overall = 0.30 × 0.95

η_overall = 0.285

Converting to percentage:

η_overall = 0.285 × 100%

η_overall = 28.5%

Conclusion:

Hence, the overall efficiency of the station is 28.5%.

Economizer:

• It is also known as feed water heater. It is a device in which the waste heat of the flue gases is utilised for heating the feed water.
• In a steam boiler, it is a heat exchanger device that heats up fluids or recovers residual heat from the combustion product i.e. flue gases in a thermal power plant before being released through the chimney.
• Economiser is situated before air pre-heater in the flue gas path. 
• Economiser increases the efficiency of the power plant.

Important Points:

Air preheater:

• Air preheaters are used in large boilers found in thermal power stations producing electric power.
• An air preheater or air heater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler) with the primary objective of increasing the thermal efficiency of the process.
• The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas.

Superheater:

• A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam
• Superheated steam is used in steam turbines for electricity generation, steam engines, and in processes such as steam reforming
• While the temperature of the steam in the superheater rises, the pressure remains the same as that of the boiler.