Thermal Power Plant

What is Thermal Power Station?

 A generating station that converts heat energy (coal combustion) into electrical energy which is called a thermal power plant. The thermal power plant consists of a lot of essential components and the power plant provides a reliable electrical power supply. For this reason, thermal power station or steam power plant is widely used. Basically, thermal power plant and coal power plants operation are the same and coal power plant is sometimes called thermal power plan. 

Types of Turbine in Thermal Power Plant

Basically, most of the power plants is the thermal power plant, such as steam power plants, coal fired power plants, etc. A thermal power plant is the most crucial power plant in the electrical power system. On the other hand, the turbine is a common component of electrical power plants. There are two types of turbine, such as propeller and kinetic turbine.


Those are the propeller turbine that has six blades and the kinetic turbine is a reaction turbine. Basically, a steam turbine is used for the steam power plants instead steam engine. It is because the steam engine has more disadvantages than the steam turbine. Basically, the kinetic turbine is used in hydroelectric power plants to convert the kinetic energy of the water into mechanical energy.

What are the Advantages of Thermal Power Plants?

There are lots of advantages of thermal power plant these are given below

  • Low initial cost compared to the other electrical power plant.
  • The thermal power plant can be installed at any place where coal and water are available.
  • Thermal or steam power plants require a small place than the Hydro power station.
  • Construction cost is low compared to the Nuclear power plant.

It is noted that there are no more disadvantages of a thermal power station due to the above advantages the disadvantages of the power plant are given below

Thermal Power Plant Working Principle

Thermal power plants are the most reputed bulk electrical generating station. We will explain the working of thermal power plant/thermal power plant components and working. The gas power plant works on the thermodynamic cycle but the steam power plant works on the Rankine cycle. Suppose coal is used as fuel for the thermal or steam power plant, the water is heated into the boiler by coal combustion then the steam is produced in the boiler.

The generated steam is expanded to the prime mover or steam turbine. The steam turbine converts steam energy into mechanical energy and the alternator converts the mechanical energy of the steam turbine into electrical energy. It is noted that the steam turbine and alternator are coupled together. After completing one cycle, the exhausted steam is condensed into the condenser to be feed into the boiler again.


Where coal and water are available the coal power plant is very suitable at that location to generate a large amount of electrical energy. It is noted that the thermal power generation process is not the same as the solar thermal plant. It is noted that we already refer above the working of thermal power plant with diagram, you can take a look to remember. We have given here a thermal power plant working diagram that shows the thermal station components and working procedure.

Schematic Arrangement of Thermal Power Plant

Thermal power plants require the large number of equipment to complete (from coal handling arrangement to generating electricity). Every electrical power plant consists of a large number of components the steam power plant depends on coal combustion. For this reason, a thermal generating station requires a large number of components such as

  • Coal handling arrangements   
  • Steam turbine
  • Alternator
  • Condenser
  • Super-heater
  • Water treatment plant
  • Cooling arrangement

Coal and Ash Handling Arrangements   

Steam or thermal power plant requires a huge amount of coal but it needs storage. The coal is transported by road or rail and all of the coal is not possible to use at a time. For this reason, coal is stored in the coal storage plant. The coal is delivered from the coal storage plant to the coal handling plant where coal is crushed into small pieces.

The crushing coal is transferred to the boiler by the conveyer belt the coal is burnt in the boiler and generates steam that is used to produce electricity. On the other hand, smoke and fumes are also produced. After the complete coal combustion, the coal is removed to the ash handling plant and coal is delivered to the smoke or fumes storage plant for disposal. The huge electrical energy is produced by burning huge coal.   

Steam Generating Plant

The steam generating plant is one of the most important parts of the thermal power plant. The steam generating plant consists of some important components such as a boiler, super-heater, air preheater, and economizer. 


The boiler is a very crucial part of the coal or thermal power plant because the boiler is used to contain water and the water of the boiler is heated by coal combustion. The boiler is utilized to convert water into steam energy at very high temperatures and high pressure.

The steam flow at high pressure to the turbine and the turbine converts it into mechanical energy and alternator is coupled with the turbine then the alternator converts mechanical energy into electrical energy. The flue gases come from the boiler through the super-heater, economizer, and air preheater, and the steam is finally exhausted into the atmosphere through the chimney.


The wet steam is produced in the boiler and generated wet steam flows through the super-heater. Super-heater consists of a bunch of tubes of special alloy. The super-heater super-heat the wet steam (steam temperature is increased above the water boiling point). The superheating system provides two major benefits such as

  • The overall efficiency of the thermal power plant is increased
  • The wet steam can be caused for the steam turbine blade corrosion

Air Pre-Heater 

An air preheater is used to increase the temperature of the air which is supplied for coal combustion by driving the heat from the steam or flue gases. The air pre-heater extracts heat from the flue gases and increases the air temperature that is used for coal combustion. The thermal efficiency and steam capacity are increased per square meter of the boiler surface due to the air preheater of the power plant.  


The economizer is one of the most crucial components of the thermal power plant. An economizer is a feedwater heater and is used to drive heat from the flue gases. Before supplying the water into the boiler again the feed water is feed to the economizer.   

Prime Mover

Before discussing steam turbines we have to know about the prime mover. A Prime mover is a mechanical device that converts some other forms of energy into mechanical energy. There are two types of a prime mover such as

  • Steam engine
  • Steam turbine

Steam Turbine

The steam turbine is a mechanical device that converts steam energy into mechanical power. Most of the steam power plant uses steam turbine because steam turbine has high efficiency and high speed, and take a small floor area than the steam engine. For this reason, all the modern coal power plants are using steam turbines. There are two types of steam turbine

  • Impulse turbine
  • Reaction turbine             

The superheated and dry steam from the super-heater is fed to the turbine by the main valve. The heated steam heat the turbine blade and then the turbine starts rotating and mechanical energy is produced. The efficiency of thermal power plant is increased by reducing the exhaust pressure of the turbine.  


 The alternator is an electromechanical device. The alternator and turbine are coupled together the alternator convert the mechanical energy of the turbine into electrical energy. The alternator generates 11KV AC, and the output electrical power of the alternator is delivered to the generation substation where the transformer is connected with the output line of the transformer. The transformer steps up the generation voltage at 132KV/230KV/400KV or more depending on the distance of the transmission line.


A condenser is a device that condenses the exhaust steam of the turbine. Condenser works for two main purposes such as condenser creates very low pressure at the exhaust steam of the steam turbine and condenser steam is used as feed water into the boiler again. There are two types of condensers one is a Jet condenser and another is a surface condenser.

Jet condensers mixed exhausted steam and cooling water but these types of condensers are used for low maintenance cost, low initial cost, small floor area required, and required small cooling water. The surface condenser has no direct contact between exhaust steam and cooling water. The surface condenser consists of a bunch of horizontal tubes and is closed with a cast-iron shell.   

Types of Electrical Equipment

The modern electrical power plant consists of a bunch of electrical components because electrical power generation is not easy and power plant works are divided into different kinds of stages like water fill into the boiler and steam section, cooling section, power generating section, power transmission section. For this reason, electrical power plants required a lot of electrical equipment such as.

  • Alternator  
  • Turbine  
  • Boiler
  • transformer
  • Auxiliary-transformer
  • Switchgear equipment

Water Treatment Plant

The water treatment plant is one of the most important parts of the thermal power plant. The water treatment plant is used to refine water to feed the boiler. The boiler requires clean and soft water for high efficiency and longer life. The source of the feed water of the boiler is generally a big canal, lake, river, and another large amount of water source.

First of all, water is stored in the water storage tank from the water source (river, canal, lake) the impurities and some other pollutant objects of water are suspended by the chemical treatment in the tank. The water is softened by removing permanent and temporary hardness through the chemical process. If the water becomes pure and soft then the water is provided to the boiler to generate steam.

Cooling Arrangement

To increase the efficiency of the thermal power plant the exhausted steam of the power plant is condensed by the condenser. The water is collected from the lake, river, big canal, and some other huge water sources, and water is circulated through the condenser. The circulating water of the condenser takes up the heat of the exhausted steam and it becomes hot.

The hot water that comes out from the condenser is discharged at a suitable location down the river or lake. The cooling tower is also used as a cooling arrangement. During the scarcity of water in the lake, river, or any water source, hot water from the condenser is passed up to the cooling towers but the cold water from the cooling tower of the thermal power plant is reused in the condenser to reduce the water treatment cost.    

Thermal power plant works on which cycle?

Most of the power plants in the electrical power system are thermal power plants. Basically, the working principle of thermal power plant is almost the same. It means we need to generate steam in the thermal power station to supply the steam turbine to produce mechanical energy. All the thermal power plants work by following the same rule. Basically, a thermal power plant works on Rankine cycles.

What is the Efficiency of a Thermal Power Plant?

The efficiency of a power plant is a crucial part because electricity generation and transmission depend on efficiency and input and output power depend on efficiency. If the efficiency of the plant is high then the energy loss will be low and if the efficiency is low the energy loss will be high. For this reason, the efficiency of a thermal power plant plays an important role. There are two types of efficiency in the power plant such as

  • Overall efficiency
  • Thermal efficiency

  Overall Efficiency

The heat equivalent of electrical output power to the heat of coal combustion is called overall efficiency. The overall efficiency of this power station is at 29% (low) due to two reasons. First of all, a huge amount of heat is lost in the condenser and another one is heat loss occurs at the various stages of the power plant, but the condenser cannot avoid heat loss.

It is because the heat energy of the condenser cannot convert into mechanical energy without temperature difference. If the temperature difference becomes high then more heat energy will be converted into mechanical energy. It is important to note that a greater amount of heat loss occurs due to the greater temperature difference. It is noted that overall efficiency is less than thermal efficiency.

Overall efficiency = Thermal efficiency * Electrical efficiency

Thermal efficiency of a thermal power plant

The ratio of heat equivalent to mechanical power transmitted to the steam turbine shaft o the heat of coal combustion which is called a thermal power plant. The thermal is about 30%. It means that if 100 calories of the heat of the power plant are supplied by the coal combustion the mechanical power equivalent will be available at the steam turbine shaft and the rest is lost.

The condenser is responsible for losing 50% of energy. Another heat loss occurs at the various stages of the thermal or steam power plant. Basically, the thermal efficiency of the steam power station is 35% and 49% because more heat losses occur at the various stages of the thermal station. Visit here to know more about electrical power systems.

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