Introduction to Steam Generating Unit ()

A boiler is a closed vessel in which steam is produced from water by combustion of fuel.

How a Boiler works::

 Water is pumped into the boiler at operating pressure  Heat of flue gases vaporizes water to form steam  Steam formed is passed into steam space above the water space

Applications of steam generatorss (Boilerss))

The steam generators or are integral components of steam turbines which are used as prime movers to drive generators to produce electricity in all thermal and nuclear power plants. These are used in the industry for example in heating systems or for cement production, textiles. These are used to produce distilled water for medicines, pharmaceuticals and other usage. The boilers are used in cold countries for heating large buildings, in agriculture as well for soil steaming.

Components of a steam generator (Boiler)

 Boiler drum, tubes, furnace  Boiler mountings  Boiler Accessories

Boiler mountings are devices which are required for proper operation, safety and control of the boiler. Examples ar ee water level indicator (WLI), pressure gauges (PGs), steam stop valve, safety valves, fusible plug, feed-check valve, blow-off cock, manhole and mudhole, etc.

Boiler accessories are devices which are used to increase the efficiency of a boiler. Examples are , economizer , ss, uperheater , feedpump or , baffles, etc..

Boiler classification:

1.1. Tube content: (i) Fire tube boiler and (ii) water tube boiler

2.2. Axis of shell: (i) Horizontal, (ii) vertical, (iii) inclined

3.3. Location of furnace: (i) Externally fired, (ii) internally fired

4.4. Method of circulatlation: (i) Natural, (ii) forced d

5.5. Mobility: (i) Stationary, (ii) portable

6.6. Usage: (i) Packaged, (ii) unpackaged

7.7. Pressure: (i) High, (ii) low

8.8. Tubes: (i) Single-tube, (ii) Multi-tube How a Fire Tube Boiler works:

 Hot flue gases are fed through the tubes.

 Tubes are surrounded by water.

Cochran Boiler (A Fire Tube Boiler):

Fig: Cochran Boiler

 Vertical mulititubular  Low initial cost  Efficiency 70 - 75%  Suitable for fluctuating loads  20 kg/hr to 3000 kg/hr How a Water Tube Boiler works:

 Small parallel tubes contain water connected to drum with the header

 Gases pass outside tubes containing water

Babcock and Wilcox Boiler ( A Water Tube Boiler:

Fig: Babcock and Wilcox Boiler  High pressures and capacity  Higher Efficiency  Suitable for power plant Boiler mountings and accessories:

Fusible Plug Water Level Indicator Bourdon Tube Pressure Gauge

Lever Flue gas before entering chimney Economizer and

Functions of Boiler mountings:

Water level indicator: This is required to indicate the safety level of water inside the boiler shell. Pressure gauge: This is required to indicate the steam pressure inside the boiler shell. Steam Stop Valve: The valve used to regulate the supply of steam to the turbine. Fusible plug: This is required to stop the boiler if the boiler gets dry to prevent damage to the boiler. It is a metallic plug installed in the water pathway. If the boiler temperature exceeds a safe value, it melts and allows shell water to pass through extinguish the furnace fire. Safety valves: These are required to release the internal boiler pressure if the pressure exceeds a predetermined safety level.

Functions of Boiler accessories:

Air preheater: This is usually used to utilize the waste heat of the chimney to preheat the furnace air thus increasing the boiler efficiency.

Economizer: This is usually used to utilize the waste heat of the chimney to preheat the boiler feed water thus increasing the boiler efficiency.

Superheater: This is usually used to utilize the waste heat to dry and/or superheat the steam leaving the boiler on the delivery side, thus increasing the steam quality and boiler efficiency. Baffles: These are built inside the boilers. These baffles significantly increase the efficiency by helping feed water in extracting heat from the flue gas.