NO reduction performance of pyrolyzed biomass char: Effects of dechlorination removal pretreatments

Abstract

In the current era of renewable energy prominence, the wide operational capacity of coal-fired boilers has emerged as crucial for ensuring the sustainability of power plants. However, attaining ultra-low nitrogen oxides (NOx) emissions during periods of low-load operations presents a significant and persistent challenge for coal power enterprises. While techniques such as biomass re-burning and advanced re-burning have shown promise in enhancing NO reduction efficiency above 800 °C, their elevated levels of chlorine (Cl) and alkali metals pose potential risks to boiler equipment integrity. Therefore, this study proposes the utilization of biomass char derived from pyrolysis as a dual-purpose solution to enhance NO reduction efficiency while safeguarding boiler integrity during low-load operations. Findings indicate that pyrolysis treatment effectively reduces the Cl and alkali metal content of biomass. Specifically, it was determined that biomass char produced through deeply pyrolysis at 300 °C achieves the highest NO reduction efficiency while minimizing the presence of harmful components. At a reduction temperature of 700 °C, both re-burning and advanced re-burning techniques exhibit NO reduction efficiencies of 55.90% and 62.22%, which is already an ideal deficiency at low temperatures. The addition of water vapor at 700–800 °C obviously avoids the oxidation of ammonia to NO in advanced re-burning. Upon further analysis, denitrification efficiency in biomass char re-burning and advanced re-burning is influenced not only by volatile content but also by physicochemical properties such as porosity and surface functional group distribution under certain reaction conditions. This study provides a theoretical framework for the industrial implementation of biomass char for NO control in coal-fired power plants, offering insights into optimizing NO reduction efficiency while mitigating potential risks to boiler equipment.