In this video, we will learn about the operation and construction of a typical power plant boiler.

We will also clarify a popular misconception associated with boiler operation near the end of the video.

The function of the boiler is to convert energy contained in the coal into high temperature steam.

Large power plants typically use a type of boiler called a water tube boiler, where water flows through the tubes and fire surrounds it.

Water tube boilers are ideal for high pressure applications.

There are also fire tube boilers, but they are used for small scale applications.

Burners in the boiler convert chemical energy in the pulverized coal into thermal energy.

The hot gas that is produced travels all over the boiler.

The first heat absorption unit of the boiler is an economizer.

Highly pressurized water supplied by the feed water pump enters here.

The economizer absorbs energy from the flue gas, which raises the temperature of the liquid.

From there, the water flows into a steam drum to the downcomer.

It then passes through a narrow tube section called a water wall.

The phase change of the water happens in the water wall.

The steam that is produced, in addition to some water droplets, enters the steam drum again.

The real function of the steam drum is to separate the water droplets from the steam.

As a result, the steam leaving the steam drum is saturated and pure.

Now, here are some thermodynamics facts.

According to the second law of thermodynamics, the greater the temperature of the heat source, the more efficient the cycle.

Therefore, making the steam temperature very high will result in a highly efficient power plant.

But this temperature increase has certain limitations.

The steam turbine blade material cannot withstand temperatures greater than 600 degrees Celsius.

So, one more heat exchanger is added after the steam drum to superheat the steam, and it is heated to the maximum allowable limit.

Superheating also reduces the moisture content in the steam.

The steam is then supplied to the turbine inlet.

After the first turbine stage, the temperature drops.

A clever idea to increase the power plant efficiency is to bypass the steam completely after the first stage and add more heat.

This process is known as reheating.

A heat exchanger known as a reheater is used for this purpose.

Reheating and superheating also increase the power plant capacity along with the efficiency.

Now, let's discuss an important misconception about boilers.

We know that the temperature rises across the boiler, but what about pressure?

Consider this droplet of water.

Assume it is surrounded by a cover.

If it gets converted to steam, obviously the pressure will rise.

Now consider the same droplet with no cover.

Here, if the liquid gets converted to steam, the pressure will remain the same.

Because the fluid does not have a fixed volume here, it is free to expand.

Water inside the boiler is also like the water droplet, without a cover.

It's an open-flowing system.

The water is free to expand when the liquid is converted into steam, which means that the pressure should remain the same throughout an ideal boiler.

In actual practice, due to friction and other irregularities, a small drop in pressure occurs across the boiler.

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