Nitrogen oxides emission control options for coal-fired electric utility boilers

Area of Science:

• Environmental Engineering
• Combustion Science
• Air Pollution Control

Background:

• Regulatory mandates necessitate significant reductions in nitrogen oxides (NOx) emissions from electric utility boilers.
• Effective NOx control technologies are essential for coal-fired utility boilers to achieve compliance.
• This review focuses on established and emerging NOx abatement strategies for utility-scale combustion.

Purpose of the Study:

• To comprehensively review available NOx control technologies for coal-fired utility boilers.
• To assess the performance and effectiveness of current primary and secondary NOx control methods.
• To examine recent advancements and future directions in NOx emission reduction.

Main Methods:

• Review of established commercial primary NOx control technologies (low-NOx burners, overfire air).
• Analysis of secondary NOx control technologies: reburning, selective noncatalytic reduction (SNCR), and selective catalytic reduction (SCR).
• Evaluation of reported emission reduction data from operational U.S. utility boilers.

Main Results:

• Primary controls (low-NOx burners, overfire air) achieved 35%–63% NOx reduction from 1995 levels.
• SNCR applications on 36 boilers yielded NOx reductions of 15%–66%.
• SCR systems on over 150 boilers demonstrated low NOx rates (0.04–0.07 lb/10(6) Btu) in 2003.

Conclusions:

• Primary and secondary NOx control technologies are effective in reducing emissions from coal-fired utility boilers.
• Continuous improvement and effective implementation of these technologies are vital for regulatory compliance.
• Selective Catalytic Reduction (SCR) shows significant promise for achieving very low NOx emission rates.