Boilers/Turbines/Generators
Boilers
The purpose of a boiler is to produce steam.
In the boiler section of our power stations, brown coal is used as the fuel to heat water to produce steam. The chemical energy of the coal is converted into the heat and kinetic energy of the steam.
From the coal storage bunker, coal is conveyed to the power station and dropped down a chute to the crushing mills located in the basement of the boiler building. Hot gases, from the boiler furnace, are fed into the drying shaft and the crushing mills to pre-dry, and raise the temperature of the brown coal. The brown coal is pulverised or ground into a fine powder in the crushing mills.
The hot, dried, powdered coal and heated air are blown into the combustion chamber (or furnace) to burn at very high temperature and pressure.
The walls of the furnace are lined with metal pipes in which pure water flows. The heat energy created as the coal is burnt heats the water in the pipes until it boils into steam to a temperature of approximately 535 Celsius.
The steam passes through superheaters where hot furnace gases are used to raise the temperature of the steam above the temperature at which it is produced.
This high pressure, superheated steam then travels through pipes to the turbines.
Changes in demand for electricity vary the loading requirements of the stations which in turn varies the flow of steam required for the turbines. To provide for these variations a combustion control system controls the flow of fuel (that is the powdered coal), air and water to the boilers.
Turbines/Generators
High pressure superheated steam from the boilers is used to drive the turbines.
A turbine is a machine in which the energy of the steam is converted into the kinetic (movement) energy of the turbine shaft.
A turbine consists of a central shaft, or rotor, set horizontally inside a cylinder.
Set around the rotor are a large number of angled blades, like the blades on a fan.
High pressure superheated steam, from the boiler, is shot into the cylinder through nozzles. The steam first strikes the blades and causes the shaft to rotate (or spin).
Also when the steam enters the cylinder it expands. As the steam expands it is directed over more blades on the turbine shaft and further causes the shaft to rotate.
Generators are machines that transform or change the mechanical energy, produced by the spinning turbine shaft, into electrical energy.
The movement produced by the turbines is used to spin the powerful electromagnets at high speed inside fixed coils of wire wound inside a large cylinder (called the stator). This movement of a magnetic field inside the stator produces an electrical current in the fixed wire. Thus converting mechanical energy to electrical energy.
To produce electricity in commercial quantities, the generator typically runs at a speed of 3000 rpm (revolutions per minute) and produces a current at 50 cycles per second. Basically electricity generation consists of a magnet spinning inside a group of wire coils.xu;
A simple analogy is laying a windmill in a horizontal position and comparing the wind pushing the vanes to steam turning the turbine blades as a power source.Also when the steam enters the cylinder it expands. As the steam expands it is directed over more blades on the turbine shaft and further causes the shaft to rotate.In modern thermal power stations the turbines rotate at speeds of 3000 rpm (revolutions per minute).The turning shaft is connected to the generator, and thus spins the generator rotor.
