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Por: Miguel Leocádio João Meyer

MEASURES TO REDUCE NO x EMISSIONS. Por: Miguel Leocádio João Meyer. PRIMARY MEASURES Modification of the Combustion Process. NO x formation strongly depends on:. Flame Temperature (above~1600ºC) Presence of O 2 (Slightly lean mixtures). PRIMARY MEASURES. Low Excess Air .

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Por: Miguel Leocádio João Meyer

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  1. MEASURES TO REDUCE NOx EMISSIONS Por: Miguel Leocádio João Meyer

  2. PRIMARY MEASURES Modification of the Combustion Process NOx formation strongly depends on: • Flame Temperature (above~1600ºC) • Presence of O2 (Slightly lean mixtures)

  3. PRIMARY MEASURES • Low Excess Air • Reduce the air inlet into combustion chamber • Simple to implement • Inflammability problems • Possible formation of unburned fuel & CO • Efficiency: 10 - 44% Main features:

  4. PRIMARY MEASURES • Air Staging 10-65% Efficiency • Divide combustion into 2 separate zones • Lack of Oxygen Zone • Excess of Oxygen zone • Biased Burner Firing (BBF) • Lower burners: Oxygen; Upper Burners: Oxygen • Burners Out Of Service (BOOS) • Lower Burners Oxygen; Upper Burners not in use • Over Fire Air (OFA) • Air ports (15-30%) installed in addition to existing burners

  5. PRIMARY MEASURES • Flue Gas Recirculation • 20-50% Efficiency • Introduction of Flue gas (20-30%) into chamber • Gas Should be cleaned • Reduction of available oxygen in chamber • Decrease of flame temperature (dilution effect) • Difficult adaptation • Increase fan work • Flame instability Main features:

  6. PRIMARY MEASURES • Reduced Air Preheat • 20-30% Efficiency • Inlet Air temperature • Lower flame temperature For the same fuel amount • Reduction of Thermal efficiency (Carnot) • Increase of fuel consumption or bigger heat exangers for maintaining energy output Disavantages:

  7. PRIMARY MEASURES • Fuel Staging (Reburning) • 50-60% Efficiency • Staged injection of fuel and air • Slightly lean primary zone • Rich reburning zone • Reburning zone temp.~1200ºC • Increased residence time • Conditioned to site specifications Main Features: 85-90%

  8. PRIMARY MEASURES • Low NOx Burner • Traditionally: • - Air and fuel introduced at the same time • - Hot oxidizing primary zone + colder secondary zone at flame end • Now: Air Staged LNOx BurnerFlue Gas LNOx BurnerFuel Staged • LNOx Burner

  9. PRIMARY MEASURES • Air Staged Low NOx Burner • 25-30% Efficiency Disavantages: • Flame instability • Incomplete Burn Out

  10. PRIMARY MEASURES • Flue Gas Recirculation Low NOx Burner • up to 20% Efficiency • Zones separated with flue gas • High N content fuels

  11. PRIMARY MEASURES • Fuel Staged Low NOx Burner • 50-60% Efficiency • Very Lean Primary zone (low temperatures) • Rich Secondary zone Reduction of already formed NOx. • Burnout zone

  12. SECONDARY MEASURES Concept: End-of-Pipe techniques to reduce the NOx already formed (Independently or in combination with primary measures) Injection of Ammonia or Urea in the flue gas to reduce NOx to molecular Nitrogen How: • Selective Catalytic Reduction (SCR) • Selective Non Catalytic Reduction (SNCR) Forms:

  13. SECONDARY MEASURES • Selective Catalytic Reduction (SCR) • The reducing agent is injected into the flue gas upstream of the catalyst • NOx conversion takes place on the catalyst surface at a temperature • between 300 and 450ºC Materials: Heavy metal oxides, zeolites, iron oxides and activated carbon

  14. SECONDARY MEASURES • Selective Catalytic Reduction (SCR) with ammonia as a reduction agent: 4 NO + 4 NH3 + O2 4 N2 + 6 H2O 6 NO2 + 8 NH3 7 N2 + 12 H2O with urea as a reduction agent: 4 NO + 2 (NH2)2CO + 2 H2O + O2 4 N2 + 6 H2O + 2 CO2 6 NO2 + 4 (NH2)2CO + 4 H2O 7 N2 + 12 H2O + 4 CO2

  15. SECONDARY MEASURES • Selective Catalytic Reduction (SCR) Homogeneous mixing of ammonia with the flue gas Injection through a system of nozzles and addictionally the placement of static mixer in the exhaust gas channel Main features: Homogeneous NH3 / NOx ratio in the exhaust gas NOx removal efficiency vs. NH3 slip

  16. SECONDARY MEASURES • Selective Catalytic Reduction (SCR) Existing configuration of abatement technologies

  17. SECONDARY MEASURES • Selective Catalytic Reduction (SCR)

  18. SECONDARY MEASURES • Selective Non Catalytic Reduction (SCR) • It is operated without a catalyst at a temperature between • 850 and 1100ºC • The temperature window is strongly dependent on the reagent used • (ammonia, urea or caustic ammonia) Using ammonia as a reagent: 4 NH3 + 5 O2 4 NO + 6 H2O 4 NO + 4 NH3 + 5 O2 4 N2 + 6 H2O

  19. SECONDARY MEASURES • Selective Non Catalytic Reduction (SCR)

  20. SECONDARY MEASURES • Selective Non Catalytic Reduction (SCR) Additive and NOx must undergo sufficient mixing Main features: The size of additive drops reduced NOx abatement rate vs. NH3slip NH3 / NOx ratio must be ammonia-rich rather than stoichiometric Optimization of the NH3 / NOx molar ratio (1.5 - 2.5)

  21. SECONDARY MEASURES • Selective Non Catalytic Reduction (SCR) Ammonia, caustic ammonia or urea • Criteria: • formation of N2O (nitrous oxide) • corrosion problems Choice of the additive:

  22. General performance of secondary measures to reduce NOX emissons

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