A Comprehensive Approach to NOx Reduction Without Low NOx Burners

Abstract

The traditional approach to reduce NOx has been to retrofit and install commercially available “plug-in” Low NOx burners. Typically, these use a combination of internal staging and are often used in conjunction with over-fire air to create off-stochiometric or staged combustion. That is, the complete combustion of the fuel occurs in several stages. Often, well designed Low NOx burners are installed without a comprehensive systems approach. The typical challenges associated with staged combustion are related to the fact that burner performance must be nearly perfect to complete combustion within the available residence time of the furnace. Specifically, attention to airflow measurement and control by use of reliable & repeatable venturis and with pulverizer performance optimization. To maintain or improve this unit’s excellent reliability, a focus on optimizing the inputs and completing the combustion prior to the furnace exit was implemented. The goals of this project were as follows: 1. NOx Reduction from .78lb/mmBtu(full load) – 1.0#/mmBtu(low load) to less than 0.36 lb/mmBtu; 2. Flyash Carbon Content less than 10%; 3. Combustion Optimization; 4. Minimal slagging; 5. Maintain the same as baseline FEGT or reduce FEGT; 6. Maximum Load Capability; 7. Maximum Fuel Flexibility; 8. Complete the project at the lowest cost per kW possible (with the best results). All of the goals were accomplished. The technical success of this project is the results of applying a systematic and comprehensive approach beginning with raw coal feed to the pulverizers. The benefits of this total combustion optimization project is that later when additional NOx reductions are required, they can be added as a complimentary change to the present system. For example, if this unit is later equipped with SNCR or SCR, reduced rates of ammonia will be required, there will be reduced “popcorn ash” production, and less SCR catalyst wear and overall unit improved performance and reliability.