How Does a Thermal Power Plant Work?

Brief introduction of Thermal Power Plant:

HISTORY:

Reciprocating steam engines have been used for mechanical power sources since the 18th Century, with notable improvements being made by James Watt. The very first commercial central electrical generating stations in the Pearl Street Station, New York and the Holborn Viaduct power station, London, in 1882, also used reciprocating steam engines. The development of the steam turbine allowed larger and more efficient central generating stations to be built. By 1892 it was considered as an alternative to reciprocating engines ^[2] Turbines offered higher speeds, more compact machinery, and stable speed regulation allowing for parallel synchronous operation of generators on a common bus. Turbines entirely replaced reciprocating engines in large central stations after about 1905. The largest reciprocating engine-generator sets ever built were completed in 1901 for the Manhattan Elevated Railway. Each of seventeen units weighed about 500 tons and was rated 6000 kilowatts; a contemporary turbine-set of similar rating would have weighed about 20% as much. 

INTRODUCTION:

A thermal power plant is generally  a steam driven power plant in which Water is heated, turns into steam and as the steams are high pressurized it spins a steam turbine which drives an electrical generator and electrical energy being produced. After it passes through the turbine, the steam is condensed in a condenser and recycled to it’s liquid form and returns to the boiler where it was heated. The greatest variation in the design of thermal power plant is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electricity. Some thermal power plants also deliver heat energy for industrial purposes, for district heating, or for desalination of water as well as delivering electrical power.

 

Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as many natural gas power plants are thermal. Natural gas is frequently combusted in gas turbines as well as boilers. The waste heat from a gas turbine can be used to raise steam, in a combined cycle plant that improves overall efficiency. Power plants burning coal, fuel oil, or natural gas are often called fossil-fuel power plants. Some biomass-fueled thermal power plants have appeared also. Non-nuclear thermal power plants, particularly fossil-fueled plants, which do not use co-generation are sometimes referred to as conventional power plants.

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How does a thermal power plant work?

In thermal power plants, fuel is converted into thermal energy to heat water, making steam. The steam rotates turbine, creating mechanical energy to run a generator. Magnets turn inside the generator, producing electric energy.

Coal, oil and gas are used as fuels to make thermal electricity. They all work basically the same way (with a few exceptions: for example, in an oil- or gas-fired plant, fuel is piped to the boiler).

Coal supply :—

This deals mainly with feeding the boiler with coal for combustion purposes. After haulers drop off the coal, a set of crushers and conveyors prepare and deliver the coal to the power plant. When the plant needs coal, coal “hoppers” crush coal to a few inches in size and conveyor belts bring the coal inside. The belts dump coal into a huge bin (pulverizer), which reduces the coal to a fine powder. Hot air from nearby fans blows the powdered coal into huge furnaces (boilers).

 Boiler: —

A boiler or steam generator is a device used to generate steam by applying heat energy to water. The boiler walls are lined with many kilometers of pipe filled with water. As soon as the coal enters the boiler, it instantly catches fire and burns with high intensity (the temperatures inside the furnace may climb to 1,300° C). This heat quickly boils the water inside the pipes, changing it into steam.

 Electrostatic Precipitators and stack: —

As the coal burns, it produces emissions (carbon dioxide, sulphur dioxide and nitrogen oxides) and ash. The gases, together with the lighter ash (fly ash), are vented from the boiler up the stack. Huge air filters called electrostatic precipitators remove nearly all the fly ash before it is released into the atmosphere. The heavier ash (bottom ash) collects in the bottom of the boilers and is removed.

Feed Water & Steam: –

This section deals with supplying of steam generated from the boiler to the turbines and to handle the outgoing steam from the turbine by cooling it to form water in the condenser so that it can be reused in the boiler plus making good any losses due to evaporation etc.

 Turbine and generator: —

Meanwhile, steam moves at high speed to the turbines, massive drums with hundreds of blades turned at an angle, like the blades of a fan. As jets of high-pressure steam emerge from the pipes, they propel the blades, causing the turbine to spin rapidly. A metal shaft connects the turbine to a generator. As the turbine turns, it causes an electro-magnet to turn inside coils of wire in the generator. The spinning magnet puts electrons in motion inside the wires, creating electricity.

Condensers and cooling system: —

A device or unit used to condense vapor into liquid. Next, the steam exits the turbines and passes over cool tubes in the condenser. The condensers capture the used steam and transform it back to water. The cooled water is then pumped back to the boiler to repeat the heating process. At the same time, water is piped from a reservoir or river to keep the condensers constantly cool. This cooling water, now warm from the heat exchange in the condensers, is released from the plant.

Water purification: —

To overcome corrosion, plants purify water for use in the boiler tubes. Wastewater is also treated and pumped out to holding ponds.

 Ash systems: —

Taking care of the ash that is generated during the combustion process and includes equipment and paraphernalia that is used to handle the transfer and storage of ash. Ash is removed from the plant and hauled to disposal sites or ash lagoons. Ash is also sold for use in manufacturing cement.

Transformer and transmission lines :—

Transformers increase the voltage of the electricity generated. transmission lines then carry the electricity at high voltages from the plant to substations in cities and towns.

Typical diagram of a coal-fired thermal power station

1. Cooling tower	10. Steam Control valve	19. Superheater
2. Cooling water pump	11. High pressure steam turbine	20. Forced draught (draft) fan
3. transmission line (3-phase)	12. Deaerator	21. Reheater
4. Step-up transformer (3-phase)	13. Feedwater heater	22. Combustion air intake
5. Electrical generator (3-phase)	14. Coal conveyor	23. Economiser
6. Low pressure steam turbine	15. Coal hopper	24. Air preheater
7. Condensate pump	16. Coal pulverizer	25. Precipitator
8. Surface condenser	17. Boiler steam drum	26. Induced draught (draft) fan
9. Intermediate pressure steam turbine	18. Bottom ash hopper	27. Flue gas stack

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