Power Plant Engineering

6. Steam Stop Valve. It regulates the flow of steam supply outside. The steam from the boiler
first enters into an ant-priming pipe where most of the water particles associated with steam are re-
moved.
7. Feed Check Valve. The high pressure feed water is supplied to the boiler through this valve.
This valve opens towards the boiler only and feeds the water to the boiler. If the feed water pressure is
less than the boiler steam pressure then this valve remains closed and prevents the back flow of steam
through the valve.

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STEAM GENERATOR
183
Water
Steam
Fire and hot gases
Air in
Ash-pit
Grate
Fire Box
Fire Tubes
Water
Steam
Steam stop
valve
Pressure gauge
Manhole
Feed check
valve
Water in
Water level
indicator
Fusible plug
Combustion
Chamber
Fire brick lining
Blow off cock
Mud and water out
during blow off
Boiler shell
Fire door
Smoke Box
Doors
Chimney
Anti priming
pipe
Dead Weight
Safety Valve
Steam out
Fig. 5.1. Cochran Boiler.
5.4 LANCASHIRE BOILER
It is stationary fire tube, internally fired, horizontal, natural circulation boiler. This is a widely
used boiler because of its good steaming quality and its ability to burn coal of inferior quality. These
boilers have a cylindrical shell 2 m in diameters and its length varies from 8 m to 10 m. It has two large
internal flue tubes having diameter between 80 cm to 100 cm in which the grate is situated. This boiler
is set in brickwork forming external flue so that the external part of the shell forms part of the heating
surface.
The main features of the Lancashire boiler with its brickwork shelling are shown in figure. The
boiler consists of a cylindrical shell and two big furnace tubes pass right through this. The brick setting
forms one bottom flue and two side flues. Both the flue tubes, which carry hot gases, lay below the water
level as shown in the Fig. 5.2.
The grates are provided at the front end of the main flue tubes of the boiler and the coal is fed to
the grates through the fire doors. A low firebrick bridge is provided at the end of the grate, as shown in
the Fig. 5.2, to prevent the flow of coal and ash particles into the interior of the furnace tubes. Otherwise,
the ash and coal particles carried with gases form deposits on the interior of the tubes and prevent the
heat transfer to the water. The firebrick bridge also helps in deflecting the hot gases upward to provide
better heat transfer:

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184
POWER PLANT ENGINEERING
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