General Requirements for a burner

1
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

2
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

3
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

4
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

5
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)

6
Liquid Fuel Burners

• Atomising burners On industrial scale, most
  commonly used burners are atomising burners
• Oil is heated to low viscosity and atomised
• Mechanically by means of a rotating disc or cup
  with a uniform droplet size (50 microns)
• By a high pressure ejection from a fine orifice
  which gives a conical spray

7
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

8
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