Flames &

Burners

Fuel Preparation

Fuel properties for kiln firing have to fulfill certain requirements in order to: Produce similar combustion characteristics with different fuel qualities .Avoid incomplete combustion, e.g. CO at kiln inlet or local reducing conditions due to secondary combustion of oversized particles in the clinker bed .

The ideal flame is:

Stable over entire length of flame, i.e.

• Continuous (controlled) combustion along the whole length

•No local temperature peaks

•No reducing atmosphere over clinker bed

•Complete burn-out at end of flame

Prerequisites for ideal flame

The ideal flame is stable over its entire length , i.e.

• by continuous mixing with hot secondary air, combustion is constant along the whole flame zone

• no local temperature peaks are produced .• no zones of reducing atmosphere are formed over the clinker

bed .• burn-out is completed at end of flame .• adequate fuel preparation ( oil droplet size, coal fineness ) .• regular furl feed • presence of Oxygen for complete combustion .

Prerequisites for ideal flame

Completeness of combustion within available time (burning zone depends on three main factor:

• Fuel preparation(oil droplet size, coal fineness)• Fuel feed to burner(accurate and constant feed and transport )

• Availability of oxygen for complete combustion (excess air factor)

Firing Systems

Coal versus oil versus gas firing

Provided complete combustion there is theoretically no significant difference between oil and coal firing, whereas with natural gas firing a slightly higher energy consumption (approx.+5 %) is attributed to the higher stoichiometric exhaust gas quantity.

Burners

Oil nozzles

1 tangential oil flow

2 axial oil flow

3 tangential slots

4 swirl chamber

5 orifice plate

Pillard atomizer

Burners

Oil nozzles

1 tangential oil flow

2 axial oil flow

3 tangential slots

4 swirl chamber

5 orifice plateUnitherm atomizer

Gas burners

8 ignition burner.

11 radial gas.

12 axial gas

13 cooling airPillard Gas

Burner

81112

13

Gas burners

Kloeckner-Humboldt-Deutz Gas Burner

FLAME ADJUSTMENT.

Combustion air

FLAME ADJUSTMENT.For low energy consumption

Primary air :low

Secondary air : low

FLAME ADJUSTMENT.For low energy consumption

Secondary air : high

FLAME ADJUSTMENT.For low energy consumption

Excess air :

low

Flame Shape

• Type of fuel (fuel oil: medium, gas: long)• Fuel characteristic (coal fineness, volatiles, ash,

moisture, fuel oil viscosity)• Fuel oil atomizing pressure• Gas pressure and velocity• Burner nozzle geometry• Secondary air temperature• Angle of burner with kiln axis• Dust circulation in burning zone• Thickness of coating/pressure of ring• Material bed temperature

Flame ShapeParameters that influence the flame shape and length as well:

•In most cases combustion in gas/air mixture instead of pure air•Combustion in very dusty atmosphere

Secondary Firing / PrecalcinerThe burning conditions for a secondary firing or precalciner burner are quite different from the kiln firing:

•Temperature range of 1000°C instead of 2000°C

•higher gas temperature at bottom cyclone outlet than at precalciner outlet

•moderate drop of gas temperature over the two lowermost cyclone stages

Secondary Firing / Precalciner

Combustion indicators