High Momentum Design for Alternative Fuels Adriano Greco Ricardo de Paula Costa
Cement plant point of view Cheaper kiln fuel resource Lower NOx emission Alternative Fuels Benefits 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 Austria: >70% Germany: >60% 2015 3
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
Combustion of Solid Wastes Overview Importance of particle shape: COMBUSTION: area of sphere with the same volume area of real particle sphericity C (mm) L (mm) A (mm) Superficial area (mm 2 ) Particle volume (mm 3 ) Equivalent sphere area (mm 2 ) 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 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
Firing Alternatives Fuels When higher substitution rates are attempted with inadequate technology: 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
Burners development Old Concept New Concept One or more pipes above the burner High oxygen zone Low control Low mixing One or more pipes inside the burner Low oxygen zone High control High mixing
Advantages of High flame momentum : High Momentum Burner 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
SECONDARY AIR High oxygen availability: 95-100% of required amount Low control and mixing Low velocity Combustion Secondary Air Primary Air Secondary Air PRIMARY AIR Low oxygen availability: 8-12% of required amount High control and mixing Ignition fuel zone Flame stability Recirculated Combustion Gases
Burner Concept Axial Air Coal / Petcoke Swirl Air Flame Scanner Igniter Lofting Air supply Alternative Fuels Natural Gas RDF Pipe easily removable Alternative Fuels With Lofting Air 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 Mixing of the fuel and air occurs primarily as a result of jet entrainment Nozzle Uo r U Um do Potential Core Mixing Region Transition Region 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
Axial Air
Lofting Air Air Assisted Dispersion of RDF and other similar fuels Lofting Air supply Lofting air solid dispersion pattern RDF Pipe easily removable
Lofting Air Effect of lofting air on volatiles burnout - RDF The effect of lofting air on flame temperature map RDF volatiles mass fraction (coloured regions show RDF concentration) Flame temperature Lofting air OFF Lofting air OFF Burner tip Lofting air ON Lofting air ON
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