- Steam Boiler Definition: A steam boiler is defined as a closed vessel in which water is heated to generate steam for various applications.
- Boiler Working Principle: The working principle of a boiler involves burning fuel to produce hot gases, which then heat the water in the boiler to generate steam.
- Types of Boilers: The main types of boilers are fire tube boilers and water tube boilers, each with different designs and uses.
- Fire Tube Boiler Characteristics: Fire tube boilers pass hot gases through tubes surrounded by water, making them compact and cost-effective but limited in pressure capacity.
- Water Tube Boiler Advantages: Water tube boilers heat water inside the tubes with surrounding hot gases, offering high efficiency and the ability to handle high pressures, suitable for large power plants.
What is a Steam Boiler?
A steam boiler is a closed vessel that heats water, usually to steam, for process use or power. In thermal power plants that steam drives the turbine.
Working Principle of Boiler
The working principle of a boiler is heat transfer from furnace gases to water in a closed vessel. Fuel, often coal, is burned in a furnace.
Those hot gases heat the water vessel and steam forms in the boiler.
In a thermal power plant the steam is piped to the turbine. Other types of boiler supply process steam, heating or sterilising.
Steam Boiler Efficiency
Steam boiler efficiency is heat in the steam leaving divided by heat in the fuel, often coal.
That covers thermal, combustion and fuel-to-steam figures. Steam boiler efficiency is often quoted as 80% to 88% for a well-run industrial boiler. This range describes fuel-to-steam boiler efficiency rather than whole-plant thermal efficiency. Size, firing method and heat recovery change the figure.
Incomplete combustion, casing radiation and unused heat in the flue gas all reduce steam boiler efficiency below the heat in the fuel.
Types of Boiler
The two main types of boiler are the water tube boiler and the fire tube boiler.
In a fire-tube boiler, hot gases travel through several tubes that sit in water.
A water-tube boiler is the reverse: water flows inside the tubes and hot gases pass around them.
Those two types of boiler each split into many constructions, listed below.
Fire Tube Boiler
In a fire-tube boiler, hot gases travel through tubes immersed in water inside a closed shell.
The shell holds the water. The hot tubes pass through that water.
Heat from those tubes boils the water. Steam collects in the same shell.
Because water and steam share one shell, a fire tube boiler is not used for very high pressure.
Textbook figures often stop around 17.5 kg/cm2 and about 9 metric tons of steam per hour. Some packaged fire-tube units differ.
Types of Fire Tube Boiler
Fire-tube boilers are built with an external furnace or an internal furnace.
External-furnace types include-
- Horizontal Return Tubular Boiler.
- Short Fire Box Boiler.
- Compact Boiler.
Internal-furnace fire-tube boilers are mainly horizontal tubular or vertical tubular.
Horizontal-return fire-tube boilers appear in small thermal power plants. A horizontal drum holds several water-covered tubes.
Coal is usually burned under that drum. Hot gases go to the rear, then through the fire tubes to the front smoke box.
Heat passes from the gases to the water. Steam bubbles rise and pressure builds in the closed shell.
Advantages of Fire Tube Boiler
Advantages of fire-tube boilers include:
- It is quite compact in construction.
- Fluctuation of steam demand can be met easily.
- It is also quite cheap.
Disadvantages of Fire Tube Boiler
The disadvantages of fire tube boilers include—
- As the water required for operation of the boiler is quite large, it requires long time for rising steam at desired pressure.
- As the water and steam are in same vessel the very high pressure of steam is not possible.
- The steam received from fire tube boiler is not very dry.
What is a Water Tube Boiler?
In a water tube boiler water is heated inside the tubes and hot gases pass around them.
That is the reverse of a fire-tube boiler, where hot gases go through tubes in a water-filled shell.
Types of Water Tube Boilers
Water-tube constructions include
- Horizontal Straight Tube Boiler.
- Bent Tube Boiler.
- Cyclone Fired Boiler.
Horizontal straight-tube boilers split into two kinds,
- Longitudinal Drum Water Tube Boiler.
- Cross Drum Water Tube Boiler.
Bent-tube boilers split into four kinds,
- Two Drum Bent Tube Boiler.
- Three Drum Bent Tube Boiler.
- Low Head Three Drum Bent Tube Boiler.
- Four Drum Bent Tube Boiler.
Advantages of Water Tube Boiler
Advantages of water-tube boilers include:
Those points are why a water tube boiler is used in a large thermal power plant.
- Larger heating surface can be achieved by using more numbers of water tubes.
- Due to convectional flow, movement of water is much faster than that of fire tube boiler, hence rate of heat transfer is high which results into higher efficiency.
- Very high pressure in order of 140 kg/cm2 can be obtained smoothly.
Disadvantages of Water Tube Boiler
The disadvantages of water-tube boilers include:
- The main disadvantage of water tube boiler is that it is not compact in construction.
- Its cost is not cheap.
- Size is a difficulty for transportation and construction.
