[Physics Class Notes] on Working of Boiler Pdf for Exam

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What is a Boiler ?

The boiler is commonly defined as a closed vessel into which water is heated to the point it is converted into steam at the imperative pressure. The main function of the boiler is either to produce hot water or steam. The Hot water boiler heats water for the domestic or commercial purpose of heating and hot water supply, whereas Steam boilers generate steam to power turbines for power generation and other various industrial heating applications.

To understand the steam generation effects using a boiler, try thinking about the steam powering a turbine. When steam is made to flow through the turbine blades, the force turns the blades and accelerates the turbine.

Also, Steam has an enormous amount of energy as it consists of the energy given for raising the temperature of the water along with the latent heat of vaporization. So, it makes the turbine quite efficient and based on the fuel used to boil the water, very energy-efficient too. The Boilers work under pressure to heat any liquid types for external use by the combustion of fossil fuels or energy from the sun.

Parts and Accessories of a Boiler

The boiler parts are classified into two divisions, these are:

Boiler Mounting

They are the essential parts that define the boiler’s performance. The main components of boiler mounting include:

• Pressure Gauge: The gauge type is used to measure the pressure inside the boiler, fitted at the boiler’s front.

• Water Level Indicator: This is used to check the inside water level of a boiler, fitted in the front of the boiler having a glass tube and three cocks and 

• Stop Valve: We can control the flow of steam from the boiler to the steam pipe using this.

• Safety Valve: The valve is fitted on the drum, which is used to prevent the boiler explosion due to high pressure, which blows off when the inside pressure exceeds the limit. There are always two of them present to ensure no explosion takes place in the boiler.

• Blow Off Cock: It is used to blow off water and mud, and is used to empty the boiler. It is generally fitted at the bottom of the drum

• Grate: It is the space in the furnace used for fuel-burning

• Feed Check Valve: The valve is used as a Non-Return Valve, and is fitted on the drum slightly below the normal water level. It is useful to regulate the water supply.

These boiler accessories are responsible for boiler efficiency. The main components of the boiler include:

• Super Heater: The heater is used to superheat the steam before it is passed in the turbine as saturated steam that causes corrosion

• Feed Pump:  This is to pump the water into the continuous boiler working. The Steam or electricity or turbine is used for the feed pump running

• Air Preheater: It is also used to increase the boiler’s efficiency by preheating the air

• Economizer: This component is used to increase the boiler’s efficiency as the flue gasses from the boiler is prepared to flow through the economizer before releasing it into the atmosphere

Working Principle of a Boiler

It is simple to understand how the boiler works. To understand it, let us have a look at it.

 

The boiler is a closed vessel, where the water is stored. Hot gasses are formed by burning fuel in the furnace. These glasses are made to come in contact with the water vessel, the point where the heat transfer takes place between the steam and water. Thus, the boiler’s basic principle is to convert water into steam with heat energy. There are various types of boilers available to use for different purposes.

 

Efficiency of Boiler

It is defined as the total percentage of heat exported by the outlet steam to the total supplied fuel.

 

Boiler Efficiency (%) = (Heat Exported by Outlet Steam) / (Heat Supplied by the Fuel) * 100

 

Classification of Boiler

Boiler’s classification is based on the following criteria:

 

According to the Relative Passage of Hot Gasses and Water

• Fire-Tube Boiler: This is the one where the hot combustion gasses are surrounded by the water

• Water-Tube Boiler: In this, the water flows via the tubes, surrounded by hot combustion gasses

 

According to the Arrangement of Water Circulation

• Forced Circulation: The is the circulation that happens by pumping the water present inside the boiler

• Natural Circulation: This circulation happens because of the density difference 

 

According to the Usage

• Locomotive: Used in the railway engines

• Marine Boiler: Used in ships

• Stationary Boiler: Used for power plants

• Portable Boiler: These are used temporarily in sites and are movable

 

According to the Boiler’s Position

 

According to the Pressure Generated by the Steam

• Medium Pressure Boiler: The maximum pressure is of 20-80 bars and is used to generate power

• Sub-Critical Boiler: If the boiler produces steam at a pressure less than the critical pressure it is called sub-critical

• Low-Pressure Boiler: The maximum pressure is of 15-20 bar and is used for the purpos
  e of heating

• High-Pressure Boiler: This boiler has a maximum pressure of more than 80 bars

• Supercritical Boiler: These are used to produce steam at a pressure greater than the critical pressure

 

According to Charge in the Furnace

• Pulverized fuel

• Supercharged fuel