A boiler is an closed vessel that produce steam from water utilizing combustion of oil or gases.Hot water or steam circulated inside the pipe and transfer heat in many industrial applications.Classification of boiler are discussed bellow.
Boilers is the most widely used in power generation, food processing industry, textile industry, paper industry and also in chemical industries. In early days it was used in steam engine. The major reason of boiler failure is corrosion and need to monitor continuously to avoid failures.
Boiler heating source
- Coal /wood
- Nuclear energy
Classifications of boiler
According the gas circulation
- Fire tube boiler
- Water tube boiler
In a fire tube boilers hot gas or fires goes inside the tubes and tubes are surrounded with water. Hot gases transfer heat to the water through a couple tubes. Earlier fire is inside the tube so it is naming as fire tube. Cochran boiler and locomotive boiler is an example of fire tube boiler.
Advantages of Fire tube boiler
- Initial cost is low
- Operation simple
In a water tube boiler water goes through the number of tubes and hot gases flow around the tubes. Example: Benson boiler and Babcock Boiler.
Advantages of water tube boiler
- Fast heat transfer
- High efficiency
According to water circulation of boiler
Forced circulation Boiler: In These types of boiler, a feed pump used to circulate the water inside the vessels.
Free circulation of Boiler: In these types of boiler no feed pump used to circulate the water and water circulation is done by natural convection.
According to the Axis of Boiler
Horizontal boiler: Horizontal boiler is installed and operated horizontally.
Vertical boiler: Vertical boiler is installed and operated Vertically.
According to firing system of boiler
Internally fired boiler: The boiler furnace is located inside the shell is called internally fired boiler. Cochran boiler is an example of Internally fired boiler.
Externally fired boiler: The boiler furnace is located outside the shell is called externally fired boiler. Benson boiler is an example of Externally fired boiler.
According to the tube of boiler
According to tube, boilers can be classified as
Single tube boiler: The boiler that consist of one water or fire tube is called single tube boiler. Cornish boiler is an example of single tube boiler.
Multitubuler boiler: The boiler that consist of two or more water tubes is called multitubuler boiler. Locomotive boiler and Babcock boiler is an example of Multitubular boiler.
According to the uses of Boiler
Stationary boiler: Usually stationary boilers are installed permanently and most commonly used in powerplants.
Mobile boiler: Typically, these boilers are portable type boiler and can transport one place to another. Marine and locomotive boiler is an example of Mobile boiler.
Components of boiler
Burner: Burner Is the main component of boiler that produce heat for the boiler by firing. Air and fuel mix through the burner and produce a flame of fire and this firing flame produce heat to make steam from water.
Heat Exchanger: Heat exchanger allows the heat from burner to heating the water.
Return line: When the water or steam is getting cold, return line send the water for Re-heating.
Supply line: The heated steam or water is delivered by the supply line pipes to the distribution point.
Circulation pump: Circulation pump circulates the water inside the boiler shell and enhance the boiler operation.
Firebox: Firebox is unit where flame is created with mixed air and fuel.
Economizer: Economizer is a device that collects waste heat from the boiler and transfer to feed-water to boost steaming and enhance the boiler efficiency.
Super heater: Typically, Super heaters generates the temperature of the steam above its saturation temperature that is done by passing through the steam into a small set of tubes and hot gases over the tubes.
Feed pump: Feed pump supply the required water to the boiler. Duplex pumps are used for medium boilers as a feed water pump. Reciprocating and Rotary pumps are used as a feed water pump.
Air preheater: Air preheater collects the waste hit like economizer from the flue of the chimney gases and used to preheating the supplied air into the combustion chamber.
Injector: Injector uses the steam for feeding the boiler water. It consists of two parts, on parts contains steam cone or water cone that converts pressure into velocity and another part generates kinetic energy to potential energy.
Boiler Mounting and accessories
- Safety valve: Safety valve is used to protect the boiler from blast or damages when the pressure is exceeds than require pressure of steam
- Pressure switch: Pressure switch is a device that operated by external force.
- Blowdown valves: During removing the steam from boiler blowdown is happened when boiler is operating. Blowdown valves are used to remove suspended solids and slugs from steam boiler.
- Fuel oil valves: Fuel oil valve is a safety device for Oil type burner and use to ensure proper shut off for burner when require.
- Boiler sight glass: To determine the boiler water level slight glasses are used and it is very important for equipment safety.
- Gas valves: To control the flue of gas into the pilot light and burner is used the gas valve.
- Pressure gauge (Pressure gauge determine the pressure of steam inside the boiler)
- Ignition and ignition transformers:
- Steam stop valve: stop valves control the steam flow of main steam pipe and also shut off the steam flow when require
- Feed check valve: Feed check valve cut off the flow and also allow the flow of water when it’s required for boiler operation and also the feed check valve prevent the back flow in case of pump failure.
- Boiler pressure control switch: To shut off the heating system down during the pressure exceeds than required pressure.
- Pressure reducing valves: Pressure reducing valve provide the constant pressure to the delivery side.
- Temperature controller: Temperature controller control the high temperature and low temperature for the boiler. When temperature reached low temperature at set point burner calls for heating and when the temperature reached at high temperature at set point the burner turns off.
- Stack: Stack is known as several names like smoke stack, flue-gas stack or chimney. Stack exhausted the flues gases to the Environment.
- Air fans: Air fans are used to supply air for combustion of fuel in the furnace.
- Blow-of cock: Blow-of cock is used to discharge the muds and sediments that stay last bottom of the boiler during boiler is in operation. And also used to drain off water.