MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

Por:Miguel Leocádio

João Meyer

MEASURES TO REDUCE NOMEASURES TO REDUCE NOxx EMISSIONS EMISSIONS

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Flame Temperature (above~1600ºC)

• Presence of O2 (Slightly lean mixtures)

PRIMARY MEASURESPRIMARY MEASURESModification of the Combustion Process

NOx formation strongly depends on:

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

PRIMARY MEASURESPRIMARY MEASURES

• Low Excess Air • Reduce the air inlet into combustion chamber

Main fe

atures

: •Simple to implement

•Inflammability problems

•Possible formation of unburned fuel & CO

•Efficiency: 10 - 44%

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Air Staging • Divide combustion into 2 separate zones

1. Lack of Oxygen Zone2. 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

10-65% Efficiency

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Flue Gas Recirculation

• Reduction of available oxygen in chamber• Decrease of flame temperature (dilution effect)

• Difficult adaptation• Increase fan work• Flame instability

Main fe

atures

:

Introduction of Flue gas (20-30%) into chamberGas Should be cleaned

20-50% Efficiency

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Reduced Air Preheat

Disavan

tages:

Inlet Air temperature For the same fuel

amount

Lower flame temperature

20-30% Efficiency

• Reduction of Thermal efficiency (Carnot)• Increase of fuel consumption or bigger heat

exangers for maintaining energy output

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Fuel Staging (Reburning)

Main Fea

tures:

Staged injection of fuel and air

50-60% Efficiency

• Slightly lean primary zone• Rich reburning zone• Reburning zone temp.~1200ºC• Increased residence time• Conditioned to site specifications

85-90%

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• 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 Burner Flue Gas LNOx Burner Fuel Staged LNOx Burner

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Air Staged Low NOx Burner

• Flame instability• Incomplete Burn Out

25-30% Efficiency

Disavan

tages:

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Flue Gas Recirculation Low NOx Burner

• Zones separated with flue gas

• High N content fuels

up to 20% Efficiency

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Fuel Staged Low NOx Burner

• Very Lean Primary zone (low temperatures)

• Rich Secondary zone Reduction of already formed NOx.

• Burnout zone

50-60% Efficiency

PRIMARY MEASURESPRIMARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

End-of-Pipe techniques to reduce the NOx already formed

Injection of Ammonia or Urea in the flue gas to reduce

NOx to molecular Nitrogen

(Independently or in combination with primary measures)

• Selective Catalytic Reduction (SCR)

• Selective Non Catalytic Reduction (SNCR)

Concep

t:

How:

Forms:

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• The reducing agent is injected into the flue gas upstream of the catalyst

• Selective Catalytic Reduction (SCR)

• 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

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

4 NO + 4 NH3 + O2 4 N2 + 6 H2O

6 NO2 + 8 NH3 7 N2 + 12 H2O

4 NO + 2 (NH2)2CO + 2 H2O + O2 4 N2 + 6 H2O + 2 CO2

with urea as a reduction agent:

with ammonia as a reduction agent:

6 NO2 + 4 (NH2)2CO + 4 H2O 7 N2 + 12 H2O + 4 CO2

• Selective Catalytic Reduction (SCR)

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

4 NO + 4 NH3 + O2 4 N2 + 6 H2O

6 NO2 + 8 NH3 7 N2 + 12 H2O

with ammonia as a reduction agent:

Homogeneous mixing of ammonia with the flue gasInjection through a system of nozzles and addictionally the

placement of static mixer in the exhaust gas channel

Homogeneous NH3 / NOx ratio in the exhaust gasNOx removal efficiency vs. NH3 slip

Main fe

atures

:

• Selective Catalytic Reduction (SCR)

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

Existing configuration of abatement technologies

• Selective Catalytic Reduction (SCR)

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• Selective Catalytic Reduction (SCR)SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

• 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)

• Selective Non Catalytic Reduction (SCR)

4 NH3 + 5 O2 4 NO + 6 H2O

4 NO + 4 NH3 + 5 O2 4 N2 + 6 H2O

Using ammonia as a reagent:

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

SECONDARY MEASURESSECONDARY MEASURES

• Selective Non Catalytic Reduction (SCR)

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

Additive and NOx must undergo sufficient mixing

Main fe

atures

:

4 NH3 + 5 O2 4 NO + 6 H2O

4 NO + 4 NH3 + 5 O2 4 N2 + 6 H2O

Using ammonia as a reagent:

The size of additive drops

reduced NOx abatement rate vs. NH3 slip

NH3 / NOx ratio must be ammonia-rich rather thanstoichiometric

Optimization of the NH3 / NOx molar ratio (1.5 - 2.5)

• Selective Non Catalytic Reduction (SCR)

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

Ammonia, caustic ammonia or urea

Criteria:

• formation of N2O (nitrous oxide)

• corrosion problems

Choice

of th

e add

itive:

• Selective Non Catalytic Reduction (SCR)

SECONDARY MEASURESSECONDARY MEASURES

MEASURES TO REDUCE NOx EMISSIONS

M. Sc. Engineering Policy and Technology Management Energy Management and Policy

General performance of secondary measures to reduce NOX emissonsGeneral performance of secondary measures to reduce NOX emissons