General Requirements for a burner Mixture of fuel with primary air should be within the limits of inflammability Flame stability should be maintained throughout the combustion All factors causing flame extinction and flash back should be avoided
General Requirements for a burner Adequate combustion space should be provided for its completion Complete mixing of oxygen and fuel is desirable( may be obtained by creating turbulence in the combustion space) Flame shape should correspond to the geometry of furnace
Burner Selection Flame Shape Combustion Volume Stability Drive Turndown Ratio: Ratio of maximum to minimum heat input rates within which burner operates satisfactorily Maximum limit depends upon flame blow off. Minimum limit depends upon flame flash back
Burners for Liquid Fuels The purpose of a fuel burning system are to To position flame at areas of useful heat release Initiate and maintain ignition Mix the fuel and air Volatilize the fuel Proportion the fuel to air
Liquid Fuel Burners Oils may be burnt in two ways it is vaporized before ignition so that it burns like a gas (vaporising burners) it is converted into droplets which are injected into hot air so that they evaporate while burning (atomising burners)
Liquid Fuel Burners Atomising burners: On industrial scale, most commonly used burners are atomising burners Oil is heated to low viscosity and atomised (i)Mechanically by means of a rotating disc or cup with a uniform droplet size (50 microns) (ii)By a high pressure ejection from a fine orifice which gives a conical spray
Liquid Fuel Burners by an entrainment in a blast of air or steam air atomisation gives a better theoretical flame temperature as compared to steam steam atomisation is preferred for high viscosity fuels to reduce the viscosity e.g. for residual fuel oils
Liquid Fuel Burners For most of the applications compressed air is the atomising fluid The minimum temperature at which an oil is pumpable in practice depends upon the viscosity of the oil