Study on Pollutant Emission Characteristics of Oxy-Fuel Combustion Under Deep Oxy-Staged Combustion

Oxy-fuel combustion, as a clean coal combustion technology that combines carbon capture potential with low NOX emissions, is considered a key pathway for achieving low-carbon retrofits in coal-fired power plants. Previous researchers have conducted various pulverized coal oxy-fuel combustion experiments to understand NOX formation mechanisms and guide low-NOX clean operation in industrial boilers; however, there has been no comprehensive study on NOX formation patterns under the combined influence of multiple parameters. To investigate the NOX formation characteristics in actual entrained-flow oxy-fuel coal combustion, this study conducted both air combustion and oxy-fuel combustion experiments on a down-fired furnace setup designed and constructed in-house. First, the reliability of the furnace was verified through air-staging experiments, which reproduced the classic experimental phenomena observed in air-staged combustion experiments and validated the classic conclusions regarding air-staged combustion. Subsequently, one-dimensional oxy-fuel combustion experiments were conducted in the down-fired furnace experimental system. The effects of furnace wall temperature, oxygen concentration, oxy-staged ratio and oxy-staged position on NO emission characteristic were studied. Experimental results show that whether the oxy-staged technology was adopted has a huge impact on the NO emission characteristic at different furnace wall temperature. With the increasing of furnace wall temperature, the NO emission rises without oxy-staged technology. However, the increasing furnace wall temperature reduces the NO emission when the oxy-staged technology was adopted. Under the optimal conditions of 20%–30% OFA ratio at 1100–1300°C, the NO concentration at the furnace exit was reduced by approximately 60%–80% compared to non-staged combustion, while maintaining a burnout rate exceeding 97%. This work summarizes the variation trends of NOX emissions and qualitatively discusses relevant transformation pathways, providing data support for the optimization and validation of chemical mechanism models for oxy-fuel combustion, as well as direct experimental evidence for optimizing NOX emission reduction technologies in down-fired furnaces.