This article explains the basics of the working of a coal fired thermal power plant.
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More than half of the electricity generated in the world is by using coal as the primary fuel.
The function of the coal fired thermal power plant is to convert the energy available in the coal to Electricity.
Coal power plants work by using several steps to convert stored energy in coal to usable electricity that we find in our home that powers our lights, computers, and sometimes, back into heat for our homes.
image provided by the Tennessee Valley Authority
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How Coal Power Plants Produce Electricity
The conversion from coal to electricity takes place in three stages.
The first conversion of energy takes place in the boiler. Coal is burnt in the boiler furnace to produce heat. Carbon in the coal and Oxygen in the air combine to produce Carbon Dioxide and heat.
The second stage is the thermodynamic process.
The heat from combustion of the coal boils water in the boiler to produce steam. In modern power plant, boilers produce steam at a high pressure and temperature.
The steam is then piped to a turbine.
The high pressure steam impinges and expands across a number of sets of blades in the turbine.
The impulse and the thrust created rotates the turbine.
The steam is then condensed and pumped back into the boiler to repeat the cycle.
In the third stage, rotation of the turbine rotates the generator rotor to produce electricity based of Faraday’s Principle of electromagnetic induction.
In practice to effect these three stages of conversion, many systems and sub systems have to be in service. Also involved are different technologies, like combustion, aerodynamics, heat transfer, thermodynamics, pollution control, and logistics.
As an example consider these facts for typical coal fired power plant of capacity 500 MW.
Around 2 million tons of coal will be required each year to produce the continuous power.
Coal combustion in the boiler requires air. Around 1.6 million cubic meter of air in an hour is delivered by air fans into the furnace.
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The ash produced from this combustion is around 200,000 tons per year.
Electrostatic precipitators capture almost all of this ash without dispersing this to the atmosphere. Pollutants from coal power plants like carbon dioxide, sulphur dioxide, and nitrogen oxide can also affect the environment. Thermal power plants are the biggest producers of Carbon Dioxide.
The boiler for typical 500 MW units produces around 1600 tons per hour of steam at a temperature of 540 to 600 degrees Centigrade. The steam pressures is in the range of 200 bar. The boiler materials are designed to withstand these conditions with special consideration for operational safety.
Heat transfer from the hot combustion gases to the water in the boiler takes place due to Radiation and convection.
The Electrical generators carry very large electric currents that produce heat and are be cooled by Hydrogen and water.
The steam leaving the turbine is condensed and the water is pumped back for reuse in the boiler. To condense all the steam it will require around 50,000 cubic meter per hour of cooling water to be circulated from lakes, rivers or the sea. The water is returned to the source with only an increase of 3 to 4 degrees centigrade to prevent any effect to the environment.
Apart from the cooling water the power plant also requires around 400 cubic meter per day of fresh water for making up the losses in the water steam cycle.
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Details of Generating Electricity from Coal
These are some of the facts to highlight the complexities of the working of a Coal Fired Power Plant generating Electricity.