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How does a thermal power plant work?

A thermal power plant is a large-sized plant that turns the thermal energy into electric energy, using water as working fluid.
Thanks to their production of electricity we can turn on the lights and make all our household appliances work, so that we can take advantage of many comforts.

The first thermal power plant was built in New York in 1882, during the second industrial revolution, in order to supply the first public lighting network in the world.
From this moment, the commercial production of electrical energy started, and it continues today with the same principles, providing the majority of the world’s demand of electricity.

In this video, we will see how a coal-fired power plant achieves this objective.

Jaes, thanks to its 10 years of expertise in the in the industrial supplies sector, has become the reference partner for some of the main companies involved in the production of electrical energy.

The first step is to increase the water temperature: there are many types of fuel for this purpose, (for example, natural gas, nuclear fission or hard coal), as well as renewable energy sources (such as the terrestrial heat or the solar irradiance).

In this example, we can see that the pulverized coal is burned inside a special type of boiler, called “water-tube boiler”.

Here the water catches energy from the combustion fumes: it initially goes through an economizer, (a heat exchanger that preheats it), to be then sent to the base of the burner. Here, ascending through the coils, the water receives a lot of energy and turns into steam.

This vapour, at high pressure and temperature, is sent from the cylindrical body to the next stage: the steam turbine.

The steam turbine is composed by high, middle and low pressure sections. In fact, pressure and temperature decrease as the steam yields its energy to the blades, so that they can rotate at great speed.

The resulting mechanical energy is then sent to a shaft which is linked to an electricity generator. Thanks to the transformers, the generator can feed this energy into the power grid.

The turbine’s waste steam is sent to a condenser, where its temperature gets decreased by a water flow, coming from a lake, a river or, as in this example, the atmosphere itself (by using the characteristic cooling towers). In this way, the steam returns to its liquid state.

Then a hydraulic pump increases the pressure of the water, so that it can be sent to the boiler again.
This process is called “Rankine cycle” and can be repeated to provide a constant electricity production.

But how can this system be made more efficient?

To increase the efficiency, one employs the Rankine cycle with superheated steam.
With this technique the steam in the boiler gets overheated up to the maximum physical limit of the plant. In fact, according to the second law of the thermodynamics, the higher the temperature of the heat source, the more efficient the cycle.

Another improvement can be achieved by modifying the turbine’s power source. This process is called “Rankine cycle with reheat”.
As we said before, the temperature of the steam decreases as it flows through the turbine. That’s why the vapour is sent to the boiler again when leaving the high pressure section. Here it is overheated again; then, the steam enters the middle pressure section, where its expansion continues. More than one re-heating is possible.

However, the suction action of the turbine and the hydraulic pump causes some infiltration of atmospheric air. This is a problem frequently affecting power plants. In fact, these gases tend to ruin the boiler over time, so a part of the steam exiting from the turbine and all the water coming from the hydraulic pump are sent to a deaerator to remove them.
The water must be heated for this process of gas removal so that when it is sent to the boiler, it is already preheated, which improves even more the efficiency of the thermal power plant.

The biggest issue of the fossil fuel power plants is their negative impact on the environment: in fact, they release carbon dioxide, greenhouse gases, acids and particulates in large quantities.
In order to overcome this problem, the combustion materials are previously processed and the waste gases go through an electrostatic precipitator before being released in the atmosphere.
The ESP uses plates with high tension static electricity to absorb the polluting particles and minimise environmental damage.

For the long term we should abandon fossil fuels in favour of renewable energy sources. If you are interested in the functioning of photovoltaic panels, you may watch our previous video.

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