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

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
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
Water is converted into steam in one. Pass without any recirculation
Feed pump is employed to supplement natural circulation in water wall type furnace

ANSWER DOWNLOAD EXAMIANS APP

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

All the fuel burns instantaneously producing high energy release
Fuel burns with less air
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

ANSWER DOWNLOAD EXAMIANS APP