What is a burner?
A burner is a mechanical device that.
- supplies required amount of fuel and air
- creates condition for rapid mixing of fuel and air
- produces a flame which transfers thermal energy to furnace and charge
In oil burners, oil is atomized into a fine spray by a spray nozzle and air is supplied for combustion in the spray chamber.Industrially these types of burners are not in use. Alternatively oil may be atomized by high speed air to produce a fine dispersion of droplets into air.These atomised burners are in use for industrial heating.
There are liquid fuel and gaseous fuel burners. In liquid fuel burner, oil is heated and atomised either mechanically or by high speed gaseous jet.In mechanical methods oil is atomised by means of a rotating disc or cup or by swirler as shown in the figure 27.1a and b
| Figure27.1: |
(a) Rotary cup burner and (b) Swirling nozzle |
Mechanical atomization produces wider spray of oil and wide flame area with uniform droplet size.
In atomization, compressed air or steam is the atomizing fluid. Air atomization produces higher flame temperature than steam atomization. Steam atomization is preferred for viscous oil. Some ways of air atomization are shown in the figure 27.2
| Figure 27.2: |
(a) Convergent-Divergent burner or venturi burner (b) Air atomized burner |
For further details, see the references given at the end of the lecture.
A gaseous fuel burner could either be of premixed type or diffusion type. In a pre-mixed type, gas and air are mixed prior to passing through the nozzle. In diffusion type fuel and some amount of air is mixed and the mixture is passed through the burner. Rest air for combustion is supplied in the furnace chamber. Combustion of fuel is controlled by the rate of mixing of air and fuel. In these burners small portion of air is mixed with fuel as primary air and the rest amount, known as secondary air is supplied in the furnace.
Industrial burners for gaseous fuel are diffusive type.
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