High Momentum Design for Alternative Fuels

Adriano Greco

Ricardo de Paula Costa

Alternative Fuels Benefits

• Cement plant point of view • Cheaper kiln fuel resource

• Lower NOx emission

• Wastes elimination point of view (comparing to other elimination methods) • Utilize its heat capacity

• Full destruction of the material

• Do not have ashes (incorporated to the clinker)

Worldwide trend

3

Austria: >70% Germany: >60% 2015

Alternative Fuels – Latin America

Latin America: < 20%

Alternative Fuels used at Cement Industry

• Animal Meal

• Shreaded Plastics

• Wood chips

• Saw dust

• Biomass – husks

• Tires chips

• Fluff – municipal waste

• Chicken feathers

• Glycerin

• Textiles

• Solvents

• Sewage sludge

• Oil Sludge

• Cellulose, paper, board

Firing Alternatives Fuels

• Modern Kilns • Start using calciner for AF firing

• Bigger particles sizes of AF

• High Substitution – Main Burner

• Old Kilns – No calciners • Main burner

• Mid kiln tires firing

• Small portion in the kiln back

Alternative Fuels Selection

To be considered when firing AF: - AF preparation - Constant feed / conveying - Chemical analysis - C, H, O, N, S, Cl - Moisture, Volatiles - Flame adiabatic temperature - Refractory infiltration - Sulfur balance - Cl balance - Presence of heavy metals P, Hg, Ti ... - Lower clinker production (O2 and H2O) - Maximum and Minimum particle dimension - Shape of the particle

Picture: Courtesy of Aixergee

Videos: Courtesy of LEAT Bochum / Aixergee

3D plastic 2D plastic

Slow ignition Fast ignition Super fast ignition

Low volatile High volatile High volatile

Long time burn out Fast burn out Very fast burn out

Keeps shape Becomes a sphere Forms droplets

High ash content Low ash content Low ash content

sphericityparticlerealofarea

volumesamethewithsphereofarea

Importance of particle shape:

COMBUSTION:

• Particles with lower sphericity have more surface area for the same volume, i.e. they tend to present better heat and mass tranfer

• Particles with lower sphericity have lower terminal velocity, thus they have higher “flying” time

C (mm)

L (mm)

A (mm)

Superficial area (mm2)

Particle volume (mm3)

Equivalent sphere area

(mm2)

I 1.0 5.0 10.0 130.0 50.0 65.6 0.50

II 3.0 3.0 5.5 84.0 49.5 65.2 0.78

Combustion of Solid Wastes Overview

• Unstable flame

• Wrong kiln thermal profile

• Higher kiln inlet temperatures

• Fuel falling onto clinker bed

• Reduction zone near clinker

• Excessive Sulphur recirculation

• Rings formation

• CO emissions

• Clinker quality

• Cement Strength

• Operational problems

• Environmental problems

When higher substitution rates are attempted with inadequate technology:

Firing Alternatives Fuels

Burners development

One or more pipes above the burner

• High oxygen zone

• Low control

• Low mixing

• Low oxygen zone

• High control

• High mixing

One or more pipes inside the burner

Old Concept New Concept

High Momentum Burner

11

Advantages of High flame momentum : • Kiln operations becomes more stable & improved

fuel efficiency for hard to burn fuels • Improved clinker reactivity and shorter sintering

zone • Lowered volatility and recirculation of sulfur in kiln

gases (control of surfur into the clinker) • Tendency for ring formation is lower • Clinker granulometry more uniform Requirement: • Quick mixing of secondary air to the flame, to allow

the complete combustion which is iniciated by primary air.

• Primary air jets need to accellerate the secondary air.

• Internal recirculations are controlling the ignition distance of the fuel

Combustion SECONDARY AIR

• High oxygen availability: 95-100% of required amount

• Low control and mixing • Low velocity

PRIMARY AIR • Low oxygen availability: 8-12% of

required amount • High control and mixing • Ignition fuel zone • Flame stability

Combustion

Secondary Air

Secondary Air

Primary Air

Recirculated

Gases

Lofting

Air

supply

RDF Pipe – easily

removable

Axial Air

Swirl Air

Coal / Petcoke

Igniter

Flame Scanner

Natural Gas

Alternative Fuels

Alternative Fuels

With Lofting Air

Burner Concept

• Primary air pressure – 250 up to 650 mbar(g) • Minimum coal/petcoke transport air - up to 5,0 kg/kg of air • 8 to 12% of stoichiometric combustion air • AF (solids) – with Lofting air • Easy to burn AF – up to 4,0 kg/kg of air • Hard to burn AF – up to 2,5 kg/kg of air

Axial Air

• Injection of solid alternative fuel through a ring channel

• Ring channel wide enough to avoid blockages

• Even fuel and air distribution

• Wear protection

• High momentum

• High flame control

• Up to 100% solid alternative fuel

New concept for solid

alternative fuels injection:

Through the burner:

HIGH CONTROL

Near secondary air:

HIGH OXYGEN

Mixing of the fuel and air occurs primarily as a result of jet entrainment

A free jet can entrain as much of the surrounding air until it’s velocity is the same as its surroundings and thus is able to expand unimpeded

U

Um

Uo

r

do

Nozzle

Potential

Core

Mixing

Region

Transition

Region

Axial Air

Air Assisted Dispersion of RDF and other similar fuels

Lofting

Air

supply

RDF Pipe – easily

removable

Lofting air

solid

dispersion

pattern

Lofting Air

Effect of lofting air on volatiles burnout - RDF

Lofting air OFF

Lofting air ON

RDF volatiles mass fraction (coloured regions show RDF concentration)

Burner tip

Lofting air OFF

Lofting air ON

Flame temperature

The effect of lofting air on flame temperature map

Lofting Air

Lofting Air

Conclusion

• High Alternative Fuels Substitution requires a burner with high momentum and good design in order to provide:

• Better mixture between secondary air and fuel;

• Better control of the flame envelope;

• Fast interation between the AF and O2;

• Good thermal flux.

Thank You