Nitrogen oxides from waste incineration: control by selective non-catalytic reduction

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Combustion Science

Background:

• Hospital waste incineration generates significant nitrogen oxides (NOx) emissions.
• Effective NOx control technologies are crucial for regulatory compliance and environmental protection.

Purpose of the Study:

• To evaluate the NOx removal efficiency of the Selective Non-Catalytic Reduction (SNCR) process.
• To establish the ammonia (NH3) mass balance in a full-scale SNCR system.
• To determine the impact of the ammonia-to-nitrogen oxide molar ratio on NOx reduction and ammonia slip.

Main Methods:

• Experimental testing of a full-scale SNCR system in a hospital waste incinerator.
• Injection of anhydrous ammonia (NH3) at the boiler entrance for NOx reduction.
• Analysis of ammonia after each flue gas treatment stage to determine mass balance and monitor stack gas ammonia slip.

Main Results:

• NOx reduction efficiencies ranging from 46.7% to 76.7% were achieved with ammonia-to-nitrogen oxide molar ratios between 0.9 and 1.5.
• The fraction of ammonia effectively utilized for NOx reduction decreased as the molar ratio increased.
• Ammonia slip in the stack gas was consistently low, remaining below permitted limits, even at higher ammonia dosages.

Conclusions:

• The SNCR process is effective for NOx reduction in hospital waste incineration.
• Low ammonia slip is attributed to the conversion of residual ammonia into ammonium salts and its dissolution in the scrubbing liquor.
• Optimizing the ammonia-to-nitrogen oxide molar ratio is key to balancing NOx reduction efficiency and minimizing ammonia slip.