Power Plant Engineering

4.6 AUTOMATIC BOILER CONTROL
By means of automatic combustion control it becomes easy to maintain a constant steam pres-
sure and uniform furnace draught and supply of air or fuel can be regulated to meet the changes in

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STEAM POWER PLANT
157
steam demand. The boiler operation becomes more flexible and better efficiency of combustion is
achieved. This saves manual labour also.
Hagan system of automatic combustion control is shown in Fig. 4.19. Master relay R
1
, is sensi-
tive to small vanations in steam pressure and is connected to steam pressure gauge.
Boiler
Combustion
Chamber
Stoker
Draft
Connections
Fan Vanes
Fan
Vanes
Stoker
Motor
Hand Regulator
Air supply
Air supply
Relay
Air supply
Master
Relay
Steam Pressure
Gauge
Hand
Regulator
Secondary
Air Fan
I. D.
Fan
F. D. Fan
R
1
Fig. 4.19. Hagan System of Automatic Combustion Control.
A fall in pressure operates the master relay R
1
which in turn operates the servomotor coupled to
the vanes of the induced draught (LD) fan to open them slightly and simultaneously the secondary air
fan damper gets opened proportionately. By this readjustment of induced draught takes place and stabi-
lized conditions in the combustion chamber get changed. These changes operate relay R
2
to alter the
position of forced draught fan servo-motor to adjust the position of forced draught fan vanes so that
stable conditions in combustion chamber are maintained. This change causes more air to flow through
passage which in turn operates relay R
3
. This causes stoker motor to supply extra fuel into the furnace.
In case of an increase of pressure of steam the above process is reversed. Hand regulators are provided
to servo motors and master relay for manual control of system.