Power Plant Engineering

Fig. 4.31
4.9.1 CYCLONE FIRED BOILERS
In cyclone fired boilers the fur-nace is arranged as a horizontal cylinder. The pulverised fuel is
bed along the periphery of the cylinder. The hot gases travel axially into the water tube section having
a tight helix path. The temperature generated in the combustion zone is quite high and because of this
the tubes are coated with fused ash which goes on collecting the ash particles going in the flue gases.
The out going gases contain particles less than 20 microns.
The cyclone furnaces can successfully burn coals having low ash fusion temperature. The
cyclone furnace is operated under combustion air pressure of 700 to 1000 mm of water gauge.
Cyclone fired boilers have the following advantages : (i) Quick load variations can be easily
handled. (ii) Nearly 55% of ash in coal is burnt in the form of liquid slag. The ash can be removed in the
molten form. (iii) The slag can be used as a building material. (iv) Fly-ash problem is reduced to much
lower limits.
4.10 WATER WALLS
Larger central station type boilers have water cooled furnaces. The combustion space of a fur-
nace 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.

---

STEAM POWER PLANT
167
Insulating Concrete
Expanded Metal Lath
High Temp Plastic
Insulation
Magnesia Block
Casing
Touching tubes
Cast
Refractory Brick
Insulation
Blanket
Insulation
Casing
Half radiant cast refrectory
Tubes
Flat refractory
Tile
High Temperature
Insulating Brick
Magnesia Block
Casing
Tangent tubes-flat files.
 Fig. 4.32. Various Water Walls Arrangement.
The tubes are attached with the refractory materials on the inside or partially embedded into it.
Fig. 4.32 shows the various water walls arrangement.