BOILER

Boiler is a closed vessel in which water is heated & converted into steam at the desired rate at desired pressure & temperature by the combustion of fuels in the furnace.

• In boiler water is considered as a working medium that undergoes a change of phase by heat addition.
• When water is boiled into steam its volume increases about 1600 times at the same pressure.
• Liquid (water) when heated up to the gaseous state this process is called evaporation.
• In the boiler heating surface, separate hot gases of combustion are on one side & water on the other.
• The larger the heating surface a boiler has, the more efficient it becomes.

DEFINITINO OF BOILER AS PER IBR

A close vessel in which steam is generated by circulating of water through the tubes & exposed to heat, having the following criteria

• Closed vessel has a volume more than 22.5 liter.
• Steam is generated under pressure.
• Pressure is greater than 3.5 Kg/cm².
• It has attachments like mounting & fittings.

Boilers are classifies in different types & category. But all types of boilers have same aim to generate steam as per required property.

Boiler is not a single system but it is a combination of different sub-system which assist the combustion & provide heat to water which is converted in to steam.

Water is used as the working fluid to transfer heat to the process because it is not expensive also if it leaks in to the atmosphere not poisonous & hazards.

If phase of water changes in to steam its volume increase several times so it needs most careful handling.

A boiler consist of the following subsystem:-

• Fuel & air system (this is further divided in following system)
  • Fuel system
  • Primary air & secondary air system
• Water & steam system (this is further divided in following system)
  • Feed water system
  • Steam system

Fuel System

• It consist of pulverizers/mills, coal feeders, fuel burners, oil guns, soot blowers etc.
• Fuel system lead to availability of fuels in all conditions to the boiler furnace.
• Amount of fuel demand is controlled according to steam demand by the steam turbine.
• Mill /pulverizer are used for solid fuels firing system while oil pumps are used for liquid fuel firing system.
• Coal feeders are used to regulate the quantity of fuel in to the mills/pulverizer.
• Burners are fired the coal in to the furnace.
• Fuels burners distribute the coal with the help of primary air in to the furnace.
• Soot blowers are used to clean the furnace, super heaters, reheaters, economizers & APH.

Primary & Secondary Air System

• Primary air is first headed in to the APH & then goes to mills/pulverizers.
• Primary air used to dry the coal & transportation of coal from pulverizers to boiler furnace.
• Secondary air also heater in the air heater & then supplied to the furnace with the help of SADC.
• SADC maintain a differential pressure between air and furnace due to which flame is stable at the center of furnace.

Feed Water System

• Feed water system includes Economizers, Feed regulating station or feed control stations, boiler drum, down comers, Ring headers, Boiler circulation pump & associated piping
• High pressure feed water under preheat condition is supplied to the boiler for steam generation.
• Boiler circulation pump lead to high pressure boiler (pressure greater than 180 Kg/cm² ) installed in to the down comer from drum. Its discharge is connected to the bottom ring header of boiler.

Steam System

• It includes boiler from , superheaters, reheaters, desuperheaters, safety valve, MS lines, CRH line, HRH line, startup vents, & ERV.

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