A Comprehensive Overview of Boilers: Definitions, Types, Applications, Necessities, and Fuels

In this article, we aim to provide a thorough understanding of boilers, encompassing their definitions, diverse types, applications, indispensability, and the array of fuels used in their operation.

A Comprehensive Overview of Boilers: Definitions, Types, Applications, Necessities, and Fuels

1. Boiler Overview

A steam boiler, often referred to as a steam generator, is a sealed container designed to heat water until it transforms into steam at a pressure exceeding atmospheric pressure. This critical apparatus serves as the cornerstone of thermal power plants. According to the Vietnam Boiler Regulation Act of 2008, a steam boiler is defined as a closed vessel with a capacity exceeding 22.75 liters, exclusively used for generating pressurized steam.

2. Essential Boiler Terminology

To grasp the nuances of boilers, it's crucial to acquaint oneself with essential terminology frequently employed in this context. Here, we introduce and elucidate these key terms:

- Boiler Shell: A hollow cylindrical structure constructed from steel plates, either riveted or welded together.
- Furnace: The section of the boiler where fuel undergoes combustion, producing heat that generates steam.
- Grate: A space dedicated to fuel combustion, comprised of cast-iron bars with gaps for airflow and ash disposal, with both circular and rectangular variants.
- Grate Area: The surface area of the grate upon which fuel burns, typically measured in square meters.
- Heating Surface: The area of the boiler exposed to hot gases on one side and water on the other.
- Water Space and Steam Space: The volume occupied by water in the boiler constitutes the water space, while the remaining area stores steam and is termed the steam space.
- Flue Gases: Hot gases stemming from fuel combustion within the furnace, containing a mixture of water vapor (H2O), carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), and products of incomplete fuel combustion.

3. Classifications of Boiler Types

Boilers exhibit a myriad of designs, categorized in six ways:

1. Circulation of Gases:
   - Fire-Tube Boiler: In this type, hot gases pass through tubes immersed in water before being released via the chimney.
   - Water-Tube Boiler: Here, water circulates through tubes while hot gases pass around them en route to the chimney.

Water Tube Boiler Schematic Diagram

Water Tube Boiler Schematic Diagram

2. Circulation of Water:
   - Free Circulation: Heat is transferred via convection as water circulates naturally. Found in Lancashire and Babcock and Wilcox boilers.
   - Forced Circulation: Pumps maintain continuous water flow, ideal for high-pressure, high-capacity water-tube boilers.

3. Nature of Use:
   - Stationary Boilers: Employed for thermal power generation and industrial processes.
   - Locomotive Boilers: Powering locomotive steam engines.
   - Marine Boilers: Installed in steamships.

4. Fuel Type:
   - Fuel-Fired
   - Gas Fired
   - Liquid Fuel Fired
   - Electrically Fired
   - Nuclear Fired (e.g., Babcock and Wilcox boilers utilizing solid or gaseous fuel)

5. Pressure:
   - High-Pressure Boiler: Operates above 80 bar.
   - Medium-Pressure Boiler: Steam pressure ranges from 20 to 80 bar.
   - Low-Pressure Boiler: Generates steam at 15-20 bar, often used for process heating.

6. Boiler Shell Axis:
   - Vertical Boiler: Boiler axis is vertical, exemplified by the Cochran boiler.
   - Horizontal Boiler: Boiler axis is horizontal, typified by the Lancashire boiler.

Fire Tube Boiler Schematic Diagram

Fire Tube Boiler Schematic Diagram

Three Types of Fuels Used in Boilers

Boilers utilize three primary fuel categories:
1. Solid Fuels: Wood, Coal, Briquettes, Pet Coke, Rice Husk.
2. Liquid Fuels: LDO (Light Diesel Oil), Furnace Oil.
3. Gaseous Fuels: LPG (Liquified Petroleum Gas), LNG (Liquified Natural Gas), PNG (Piped Natural Gas).

The Necessity of Boilers

Boilers are integral to:
- Central heating in industrial and residential settings.
- Generating heat via controlled combustion using natural gas from pipelines.
- Efficiently distributing heat through pumps, radiators, and heat exchangers.
- Advancing eco-friendly, cost-efficient, and potent equipment through technological innovations in boiler manufacturing.

Applications of Boilers

Boilers find extensive use in:
- Powering steam engines and turbines.
- Driving reciprocating pumps.
- Facilitating industrial processes, notably in chemical engineering.
- Providing hot water for room heating, especially in cold regions.
- Electricity generation in thermal power stations.
- Process heating in various industries like sugar mills, textile mills, dairy production, and chemical processing.

Diagram of boiler principle in thermal power plant

Diagram of boiler principle in thermal power plant


1. *Definition of a Boiler as per Mechanical Engineering?* In mechanical engineering, a boiler is a sealed vessel designed to generate steam or hot water for industrial, commercial, or residential heating through controlled combustion.

2. *Types of Boilers and Their Applications?* Boilers come in various types, including fire-tube, water-tube, electric, and biomass boilers, each suited to specific applications based on factors like capacity, fuel availability, cost, and environmental impact.

3. *Boiler Safety Precautions?* Safety precautions encompass regular maintenance, inspections, proper installation, ventilation, monitoring boiler parameters (water level, pressure, temperature), and incorporating safety devices like pressure relief valves and flame safeguards.

4. *Applications of Boilers in Everyday Life?* Boilers play a vital role in heating homes, powering engines, and generating electricity in power plants. They are also indispensable in industrial processes, including chemical manufacturing, and provide hot water in various sectors.


In summary, boilers serve as the cornerstone of thermal power plants, producing pressurized steam essential for numerous industrial processes. This comprehensive article elucidated their definitions, types, applications, and the array of fuels vital for their operation. Moreover, it delved into crucial boiler terminology and classification based on several parameters. A firm grasp of boiler types and terminology is pivotal for ensuring their safe and efficient operation.