What is Thermal power plant? (All About thermal power stations)
Thermal power plant definition:
What is thermal power plant?... Thermal power plant or thermal power station is the place where we use the energy of heat to produce electric power, and it’s the most convenient sources of electric power generation, as we burn fuels such as oil, coal or liquefied natural gas to produce high temperature, high-pressure steam then we use this steam to turn a steam turbine which by the way drives an electrical generator which produces the electrical energy.
And we can also call the thermal station a steam power station because we use the steam to run a steam turbine.
Beside using thermal stations to generate the electrical power we can use a central thermal power station to produce heat energy for industrial purposes, district heating and desalination of water.
Of course, we know some of this information from the last article.
we need to understand how thermal plants work,
and that’s what we will do,
But we first should know the history of thermal power station let’s see.
History of thermal power station:
What is Thermal power plant? … To talk about a thermal power plant we should start from the 18th century, when James Watt designed a reciprocating steam engine which used to produce mechanical power, and the first commercial electrical power station powered by reciprocating steam engine was built at the pearl street station in New York and Holborn viaduct power station in London in 1882.
And in 1884 the steam turbine developed to provide larger and more efficient design for central generating stations, then in 1892, the steam turbine becomes alternative which made the turbine offered higher speeds, more compact machinery and also stable speed regulation, and by 1905 the large central power stations entirely the reciprocating engines.
Steam power plant working principle:
What is Thermal power plant?
It’s the time to know that the thermal power plant depends on its work on the principle of Rankine cycle, which is a closed cycle which uses the same fluid repeatedly.
Firstly we fill the water into the boiler until we fill the entire surface area of heat transfer.
And we use hot gases of combustion fuel with air to heat the water in the boiler.
So, the water turned into vapor.
Then we take this produced steam with the needed pressure and temperature to produce the mechanical power in the turbine.
Next, we cool the steam out of the turbine into a condenser using cooling water which turned into water.
And we reused the condensate water as a boiler feed water.
This cycle goes on and repeated many times.
But it doesn’t stop here as we use the rotation of the turbine to turn a generator which is directly coupled to the turbine, and as well as the turbine rotates the generator output terminals generate the electricity.
Take care; although this process is a closed cycle process there would be a reduction of water as the water may decrease due to an intentional or unintentional lake of the water.
Thermal power plant diagram:
What is Thermal power plant? …
Here we will have a look at the layout of the thermal power plant.
which illustrates how coal is converted into electricity, let’s see:
Coal: we started from coal, which transported from coal mines through train, trucks or ships to the generating station to be stored in the bunker house which capable to run a plant for 8-12 Hours.
We usually use bituminous or brown coal after we clean it in a magnetic cleaner to filter it from any iron particles.
Boiler: at this stage, we mix the air with the pulverized coal and then burn them in the combustion zone, which produces a large fireball at the center of the boiler which used to convert water into a high-pressure, high-temperature steam.
The flow gases go out of the boiler to superheater, reheater, economizer, evaporator, air preheater; Then from the chimney to the atmosphere.
Superheater: we hang the superheater tubes at the hottest part of the boiler, and after the steam saturates in the boiler it is superheated in the superheater to about 540ᵒ then this high pressure superheated steam fed to the steam turbine.
Economizer: simply, it’s a feed water heater where we heat the water before we supply it to the boiler.
Air preheater: we use a primary air fan to take air from the atmosphere, then we pass it to the air preheater injected with coal in the boiler to be warmed to help improve the coal combustion.
here we feed the high-pressure superheated steam to cause a rotation of the turbine blades.
So, a mechanical energy produced which makes the steam turbine acts as a prime mover.
That makes the pressure and temperature of the steam fall to a lower value.
And when it passes through the turbine it extends in volume.
Then this extended low-pressure steam exhausted in the condenser.
Condenser: we use means of cold water circulation to condense the low pressure exhausted steam, which starts to lose its pressure and temperature until it is converted back into water which is essential for increasing the efficiency of the cycle.
Alternator: we couple the steam turbine to an alternator so when the turbine rotates the alternator rotates to generate the electrical energy, then we use a transformer to step up this generated electric voltage to be transmitted to where it’s utilized.
Feed water pump: we re-fed the condensed water to the boiler using the feed water pump, and we may use an external water source to supply water lost during this working cycle.
And this layout makes us interested in components of thermal power plants and how we use each component.
Components of a thermal power plant:
What is Thermal power plant? … We mention that we heat the water in the boiler and the steam produced a mechanical energy in the turbine; so we need to know all the components of the thermal power plant which are:
It is an enclosed vessel which provides a means of combustion heat to transfer into the water until it becomes steam, and we use this steam under pressure for transferring the heat to a process, and this boiler contains:
Feed water system: which provides water to the boiler and regulates it to meet the steam demand.
Steam system: which collects and controls the steam produced in the boiler.
Fuel system: which include the equipment used to provide fuel to generate the heat needed.
It’s a rotary engine used to convert the energy of a moving stream of water, steam or gas into mechanical energy and then we transfer this energy through a driven shaft to operate a machine, compressor, electric generator or propeller.
And turbines are classified as hydraulic turbines, water turbines, steam turbines or gas turbines.
It’s a widely used device for the removal of air and dissolved gasses from the feed water to steam generating boilers.
They are equipment which transfers heat from one medium to another, the proper design, operation and maintenance of the heat exchangers will minimize energy losses and make the process energy efficient.
And heat exchangers may classify according to the flow arrangement to:
firstly, In parallel-flow heat exchangers.
In counter-flow heat exchangers.
In cross-flow heat exchanger.
It is a device on a steam engine which used to re-heat the steam generated by the boiler again to increase its thermal energy and decrease the likelihood which condenses inside the engine.
We use the superheater to increase the efficiency of the steam engine as they are widely adopted.
It is a mechanical device which used to reduce energy consumption or perform useful functions like preheating fluids.
and we can simply say that the economizer is a heat exchanger.
The condenser consists of a shell in which the exhaust steam from the low-pressure turbine enters to be cooled and converted to condensate by flowing into the other component of the condenser the tube heat exchanger.
We take care to keep the temperature in the condenser as low as practical to achieve the lowest possible pressure in the condensing steam to have the best efficiency.
- Feed water heater:
It’s the device in through the condensate pump pumps the condensate water.
Then it raises the temperature of the water through by utilizing extraction steam from various stages of the turbine.
We use the feedwater heater to improve the thermodynamic efficiency of the system as it reduces the irreversibilities involved in the steam generation, which by the way reduce plant operating costs and helps to avoid thermal shock to the boiler metal in any case.
It’s an electrical device which converts the mechanical energy into electrical energy using electromagnetic induction.
This generator forces the electric charges to move through an external electrical circuit but doesn’t create electricity.
And it is somewhat analogous to a water pump which creates a flow of water but doesn’t create the water inside.
Location of thermal power plant:
What is Thermal power plant? … The most important factor which affects the economy of the thermal station is the location where we build it and we determine that by graphical methods as:
The ideal location of the plant is the center of gravity of the load as it will make the length of the power transmission network minimum which will reduce the capital cost of the system.
From this equations, we deduce that the best location for the station is the center of gravity of the load.
But it isn’t available all the time to establish the thermal station at the center of gravity.
So, we consider other points to decide the best location of the plant as:
- We must construct the electric power plant at a place where the land cost is quite reasonable.
- The electric power plant would build beside big sources of water such as river because the condensers need a large quantity of cooling water.
- The availability of a large amount of fuel at a reasonable cost.
- The thermal plant would cause smoke, noise steam, water vapors and so on so we shouldn’t build it near to dense locality.
- We should care to have ample scope of development of the future demand.
- There would also be a very near place for ash handling plant.
Types of thermal power generation:
Steam power generation plant:
In this plant we burn fuels as heavy oil, liquefied natural gas, and coal in a boiler to generate a high_temperature, high_pressure steam, then we use this steam to rotate the impeller of the steam turbine, so the power generators connected to the turbine driven to generate the electricity.
And this steam power plant has a thermal efficiency of about 42% to 46% of middle load supply.
Combined cycle power generation plant:
In this method, we incorporate a gas turbine to reuse his waste heat to drive a steam turbine, and we power this gas turbine by high_temperature combustion gas, which produces a sufficient temperature and pressure steam which drives a steam turbine and generate the electricity.
And this combined cycle plant has high thermal efficiency.
and it also has a lower cost than the oil_fiered thermal power.
Gas turbine power generation plant:
It’s a special type of thermal power plant as we burn fuels like liquefied natural gas (LNG) or Kerosene to produce high-temperature combustion gas with sufficient energy to rotate the gas turbine which then produces electricity.
Efficiency of thermal power plant:
What is Thermal power plant? … After we approximately know everything about thermal power plants; we have to know the most important thing which is the efficiency.
efficiency is the ratio of heat equivalent of electrical output to the heat of combustion of coal.
and the overall efficiency of thermal power plant varies from 20% to 26%depends upon the capacity of the plant.
Advantages of thermal power station:
What is Thermal power plant? … The thermal power plant has great advantages as:
- The low initial cost.
- It requires less space land.
- The maintenance is easier than for other stations.
- The fuel cost is economical.
- We can build in any location as transportation is very easy.
Disadvantages of thermal power station:
What is Thermal power plant? … But unfortunately, we may meet some drawbacks as:
- The comparatively high running cost.
- The low overall efficiency which may be 30%.
- It causes a large amount of smoke which populate the atmosphere.
- The heated water produced by the thermal station disturbs the ecology and affect the aquatic life.
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