Steam Boilers, Engines, Nozzles and Turbines
In accelerated circulation type boiler

Water is converted into steam in one pass without any recirculation
Water is supplied in drum and through down comers located in atmospheric condition it passes to the water wall and rises to drum in the form of mixture of water and steam
Feed pump is employed to supplement natural circulation in water wall type furnace
Heating takes place at bottom and the water supplied at bottom gets converted into the mixture of steam bubbles and hot water which rise to drum

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Steam Boilers, Engines, Nozzles and Turbines
Spontaneous combustion is a phenomenon in which

Coal bursts into flame without any external ignition source but by itself due to gradual increase in temperature as a result of heat released by combination of oxygen with coal
Explosion in furnace
All the fuel burns instantaneously producing high energy release
Fuel burns with less air

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