The main type of combustion process is called the suspended flame. The flame front remains in the same position relative to the burner and quarl. The fuel particles pass through the flame completing their combustion process and exiting at the same rate as the fuel entering.
- The primary flame is essential to good combustion.
- By design the primary flame exists where it receives maximum reflected heat from the shape of the quarl. The size of the primary flame just fills the quarl space
- Here the heavier fractions are burnt. The velocity of the air and fuel must be matched to the required flame propogation rate.
Combustion in furnace space
- For proper combustion of fuel in the furnace and adequate supply of air must be supplied and intimately mixed with a supply of combustible material which has been presented in the correct condition.
- Air- it is the purpose of the register, swirler vanes and (vortice) plates, and quarl to supply the correct quantity of air for efficient combustion suitably agitated to allow proper mixing.
- The air is generally heated on larger plant to;
– improve the combustion process
– improve plant efficiency (bled steam and regenerative)
- Fuel: It is the purpose of the burner to present the fuel in suitable condition for proper combustion. Generally this means atomising the fuel and giving it some axial (for penetration) and angular (for mixing) velocity.
- For effective atomisation the viscosity of the fuel is critical, for fuels heavier than gas or diesel oils some degree of heating is required.
- The smaller the droplet size the greater the surface areas/volume ratio is, this increases evaporation, heating and combustion rate