What are the equipment used in a typical Steam Power Plant?

ElectronElectronics & ElectricalDigital Electronics

A thermal or steam power plant is a generating station which converts heat energy of coal combustion into electrical energy. A modern thermal power plant consists of a number of necessary and auxiliary equipment. In this article, we will take a look at the most important equipment of a thermal power plant.

Boiler

A boiler is a device in which water is converted into steam by utilising the heat energy of coal combustion. There are two types of steam boilers viz −

  • Water Tube Boiler - In a water tube boiler, water flows through the tubes and the hot gases of combustion of coal flow over these tubes.

  • Fire Tube Boilers - In a fire tube boiler, the hot gases of coal combustion pass through the tubes and the tubes are surrounded by the water.

Boiler Furnace

A boiler furnace is a chamber in which coal is burnt to liberate the heat energy. The boiler furnace provides support and enclosure for the combustion equipment. The walls of the boiler furnace are made up of the refractory materials such as fire clay, silica, etc. because these materials have the property to resist change of shape, weight or other physical properties at high temperatures.

Super Heater

A super-heater is a device which superheats the steam, i.e., it increases the temperature of the steam above boiling point of water. The use of super-heated steam increases the overall efficiency of the thermal power plant. A super heater consists of a group of tubes which are made up of special alloy steels. These tubes are heated by the heat of flue gases during their journey from the furnace to the chimney.

Depending upon the system of heat transfer from flue gases to steam, the super-heaters are of two types −

  • Radiant Super-Heater - The radiant super heater is the one which is placed between the water walls and receives heat from the combustion of coal through the radiation process. Sometimes, the radiant super-heater may get overheated due to high furnace temperature. Also, the temperature of the radiant super heater falls with increase in steam output.

  • Convection Super-Heater - The convection super heater is the one which is placed in the tube bank of the boiler and receives heat from flue gases through the convection process. In case of the convection super heater, the temperature of the super heater increases with the increase in the steam output.

Economiser

The economiser is a device which increases the temperature of feed water by driving heat from the flue gases. It consists of a large number of closely spaced parallel steel tubes connected by headers of drums. The feed water flows through these tubes and the flue gases flow outside the tubes. Thus, the heat of flue gases is transferred to the feed water and hence raising its temperature. The use of economiser increases boiler efficiency, saves fuel and reduces stresses in the boiler due to higher temperature of feed water.

Air Preheater

The air preheater is a device which extracts heat from the flue gases and gives it to the air being supplied to the furnace for the combustion of coal. This increases the temperature of the furnace and hence increases the thermal efficiency of the power plant.

The air preheaters are classified into two types according to the system of transfer of the heat from flue gases to air viz −

  • Recuperative Type Air Preheater - It consists of a group of steel tubes. The flue gases are passed through the tubes and the air flows over to the tubes. Hence, the heat of the flue gases is transferred to the air.

  • Regenerative Type Air Preheater - It has slowly moving drum made up corrugated metal plates. The flue gases flow continuously on one side of the drum while air flows on the other side. In this way, the heat of flue gases is transferred to the air being supplied to the furnace for coal combustion.

Condenser

Condenser is a device which condenses the exhausted steam from the turbine. The condenser serves two important functions −

  • It creates a very low pressure at the exhaust of the turbine, hence permitting expansion of steam in the turbine to a very low pressure. This helps in converting the steam energy into the mechanical energy.

  • The condensed steam can be used as the feed water to the boiler.

The condensers are of two types as −

  • Jet Condenser

  • Surface Condenser

Jet Condenser

In a jet condenser, the exhausted steam is mixed with the cooling water. Hence, the temperature of the condensate and cooling water is the same when leaving the condenser. The advantages of the jet condenser are low initial cost, less floor area required, low maintenance cost, etc. But, it also has some disadvantages which are − condensate is wasted and high power is required for pumping the water.

Surface Condenser

In a surface condenser, the cooling water and exhausted steam are not mixed together. The surface condenser consists of a bank of horizontal tubes enclosed in a cast iron shell. The cooling water flows through the tubes while the exhausted steam over the surface of the tubes. In this process, the steam gives up its heat to water and is itself condensed.

The advantages of the surface condensers are condensate can be used as the feed water, less pumping power is required and it create better vacuum at the turbine exhaust, etc. Though, the disadvantages of the surface condensers are: high initial cost, requires large floor area, and high maintenance cost, etc.

Prime Mover

In the context of a thermal power plant, the prime mover is a device which converts the steam energy into mechanical energy. There are two types of steam prime movers viz.: steam engine and steam turbine. In modern thermal power plants, the steam turbines are used as prime mover because of several advantages such as high efficiency, simple construction, higher speed, etc.

Depending upon the action of steam on moving blades, the steam turbines are classified into two types viz −

  • Impulse Turbine - In an impulse turbine, the steam expands completely in the stationary blades and the pressure over the moving blades remain constant. This results in an impulsive force on the moving blades which sets the rotor rotating.

  • Reaction Turbine - In a reaction turbine, the steam is partially expanded in the stationary blades, the remaining expansion takes place during its flow over the moving blades. Consequently, the momentum of steam causes a reaction force on the moving blades which sets the rotor rotating.

Alternator

The alternator is an electrical device which converts the mechanical energy of the turbine into electrical energy. The alternator is connected to the turbine and converts the mechanical energy into electrical energy.

Transformer

A power generating station has different types of transformers for stepping-up or down the voltage levels.

  • Generating transformer - This is the main step-up transformer which step-up the generated voltage for the transmission of the electric power.

  • Station transformer - These transformers are used for general services such as lighting in the power plant.

  • Distribution transformers - These are the step-down transformers which step down the voltage for the distribution of power.

  • Instrument transformers - The instrument transformers are used for measurement and protection applications.

Switchgears

switchgear is the category of the equipment which are used to locate the fault on the system and isolate the faulty section from the healthy section of the system. It contains circuit breakers, relays, switches and other control & switching devices.

raja
Updated on 11-Feb-2022 11:05:05

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