Working of Boiler

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What is a Boiler?

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

To visualize the steam generation effects using a boiler, think about the steam powering a turbine. When the steam flows via the turbine blades, the force turns the blades and accelerates the turbine.

Steam has an enormous amount of energy, and so that it makes the turbine quite efficient and based on the fuel used to boil the water, quite energy-efficient too. Boilers work under pressure to heat any liquid types for external use by the combustion of fossil fuels.


Parts of Boiler

The boiler parts or boiler components are classified into two divisions, which are given below.


Boiler Mounting

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

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

  • Water Level Indicator: This is the one, 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: Using this, we can control the flow of steam from the boiler to the steam pipe

  • Safety Valve: This 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. Always, these are present two in number

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

  • Grate: It is nothing but space in the furnace used for fuel-burning

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


Boiler Accessories

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

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

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

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

  • Economizer: It is used to increase the boiler’s efficiency as the flue gases from the boiler is prepared to flow through the economizer before releasing it to the atmosphere


Working Principle of a Boiler

It is simple to understand the boiler working. To understand it, let us have a look on it.

The boiler is a closed vessel, where the water is stored. Hot gases are formed by burning fuel in the furnace. These gases 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 Gases and Water

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

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


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

  • Inclined

  • Horizontal


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 purpose 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

FAQ (Frequently Asked Questions)

1. Mention the Applications of the Boiler?

Boiler applications are indispensable in many industries. Hot water boilers can be used for hot water supply (like bathing hot water) and heating. It is also used in hotels, urban heating systems, accommodation areas, office buildings, farms, and planting greenhouses.


Steam boilers can be used for cooling, heating, cleaning, humidification, and in production processes and also can be used for power generation. Steam boilers can be used in industries like feed, food processing, textile, paper, building materials, metal smelting, heating engineering, and many more.


The cogeneration boilers application is gradually increasing, and steam boilers are also used for generating power, and auxiliary machines like heat exchangers are used for heating purposes. Now, biomass cogeneration is a new trend.


Some Additional Applications of the Boiler Can Be Given as the Following

  • Refineries and distilleries

  • Thermal power plants

  • Sugar plants

  • FMCG (Fast Moving consumer goods)

  • Health care industries

  • Pharmaceutical industries

2. What is the Difference Between an AFBC and the CFBC boiler?

Boilers are just a way of burning fuel or any liquids.

For example, a Travelling Grate Stoker can burn the fuel in Static Mode such that the fuel rests on the grate. Besides, the Pulverized Fuel firing burns the fuel in the Suspension Mode in the transport condition.

Between these, the two extremes lye on the Fluidized Mode.

According to 3T’s of combustion, there are two types of combustion beds, given as Residence Time, Temperature of Bed, and Turbulence.

  • CFBC (Circulating Fluidized Bed Combustion) - Higher residence time, combustion efficiency, and turbulence

  • AFBC (Atmospheric Fluidized Bed Combustion) - Comparatively lesser residence time, turbulence, lower desulfurization, and lower combustion efficiency.

(Image to be added soon)

We should also make a note that the primary reason to develop this combustion type is to limit the emission of hazardous gases such as SOx and NOx generated at higher bed temperatures.