A boiler can be defined as a closed vessel in which steam is produced from water by combustion of fuel. A boiler is used in many industries such as in steam power generation, in sugar industries, in textile industries for sizing and bleaching etc. and in many other chemical industries. Earlier it was mainly used in generating power in the steam engine.
A boiler is simply an enclosed vessel which boils water and ultimately turns it into steam which is used for heating of rooms and heavy fuel oils on the ships.
The boilers are fitted with different safeties as the steam pressure is up to 8 bars in most cases. There are normally two kinds of boilers on ships, Auxiliary and Exhaust, some ships have composite boilers.
Boiler are of two type
- STB (Smoke tube Boiler) or donkey boiler
- WTB (Water tube Boiler) or High pressure boiler
On board a vessel, STB or WTB maybe used as per the requirement.
Stages Of Combustion-
Since a boiler operates through fuel combustion, heat transfer and energy release, the stages of combustion are typically described as follows:
- Standby: boiler is ready to meet demand.
- Call For Heat: system pressure or temperature has fallen below a pre-determined set point.
- Safety Check: A series of self-tests are performed to ensure the boiler is safe to operate (water level, gas pressure, electrical status, etc.).
- Pre-purge: a forced draft fan or blower is used to force air through the furnace or combustion chambers to remove any potential unburned fuel that might be present.
- Pilot Ignition: fuel and air are mixed and forced through a small pilot flame tube where a spark is generated to ignite the fuel.
- Pilot Flame Trial: a flame sensor is used to make sure a strong, sustainable flame has been developed.
- Main Igniion: Fuel and air are mixed and forced through a burner nozzle and are ignited by the pilot flame. Main combustion continues at various rates – low to high fire – until the system set point pressure or temperature is met.
- Post Purge – the forced draft fan or blower is run to remove any potential unburned fuel from the furnace or combustion chamber.
- Boiler goes into standby mode until temperature or pressure falls below the set point.
WORKING PRINCIPLE OF BOILER-
The basic working principle of boiler is very very simple and easy to understand. The boiler is essentially a closed vessel inside which water is stored. Fuel (generally coal) is bunt in a furnace and hot gasses are produced. These hot gasses come in contact with water vessel where the heat of these hot gases transfer to the water and consequently steam is produced in the boiler. Then this steam is piped to the turbine of thermal power plant. There are many different types of boiler utilized for different purposes like running a production unit, sanitizing some area, sterilizing equipment, to warm up the surroundings etc.