Control of NO x

Control of NOx

• Two distinct reduction methods1. Control over the reaction that produces the

pollutant. (3T)2. Removal of the pollutant after its formation

Combustion control methods for NOx from Stationary Sources

1. Effect of excess air2. Effect of combustion air temperature3. Effect of combustion-zone cooling4. Effect of furnace-burner configuration5. Flue gas recirculation6. Two-stage or Off-stochiometric combustion7. Status of combustion modification

techniques

Effect of Excess Air

Effect of Combustion Air Temperature

• Waste heat is avaliable to help preheat air entering a combustion process. The added gas increases the flame temperature. Thus, NOx emissions increase.

• Significant formation occurs from 200 0C to 300 0C pre-heat (as 3-fold)

Effect of Combustion-Zone Cooling

Effect of Furnace-Burner Configuration

Flue-Gas Recirculation

• A portion of cooled flue gas is injected back into the combustion zone.

• Overall combustion temperature is reduced.• Additionally O2 amount is reduced.• Gives the operator an additional element of

control• In amounts of up to 25 %, the recirculated gas

negligible effect on flame development.

Two-Stage of Off-Stochiometric Combustion

• Fuel and air are burnt near stochiometric conditions.

• First fuel-rich feed• Second fuel-lean feed

Status of Combustion Modification Techniques

Flue-Gas Control Methods for NOx

Selective Catalitic Reduction•Optimum reduction occurred 300 to 400 0C•Platinum (Pt) or Palladium (Pd) optimum operation temperature 175-290 0C•VnO5 or TiO2 optimum operation temperature 260-450 0C•75 to 90 % removal efficiency is possible

• Selective Non-Catalitic Reduction

•Urea or ammonia based chemical are injected•900 to 1100 0C is needed for reaction•Catalyst is eliminated•20 to 60 % reduction is possible

Example : 50 ppm NO is going to be reduced to 10 ppm. Determine the NH3 amount needed for a plant having flowrate of 10 Nm3/sec