Automatic Boiler Control

By means of automatic combustion control it becomes easy to maintain a constant steam pressure and uniform furnace draught and supply of air or fuel can be regulated to meet the changes in 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. Master relay R1, is sensitive to small vanations in steam pressure and is connected to steam pressure gauge.

Hagan System of Automatic Combustion Control.

A fall in pressure operates the master relay R1 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 stabilized conditions in the combustion chamber get changed. These changes operate relay R2 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 R3. 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.

Water Walls

Larger central station type boilers have water cooled furnaces. The combustion space of a furnace is shielded wholly or partially by small diameter tubes placed side by side. Water from the boiler is made to circulate through these tubes which connect lower and upper headers of boiler.

The provision of water walls is advantageous due to following reasons: (1) These walls provide a protection to the furnace against high temperatures. (2) They avoid the erosion of the refractory material and insulation. (3) The evaporation capacity of the boiler is increased.

Various Water Walls Arrangement.

The tubes are attached with the refractory materials on the inside or partially embedded into it. Fig. shows the various water walls arrangement.