A review of NOx control by MILD-oxy combustion

Abstract

MILD combustion technology possesses several advantageous characteristics, including its ability to accommodate a wide range of fuels, achieve high fuel utilization, and effectively reduce NOx emissions. Meanwhile, oxy-fuel combustion technology is one of the most promising solutions for carbon capture, utilization and storage (CCUS). The study of the combination of MILD and oxy-fuel combustion (MILD-Oxy) technologies is of great significance in realizing the efficient utilization of fuels and ultra-low NOx emissions. This study focuses on the application of MILD-Oxy combustion to control NOx emissions, providing a comprehensive review of the combustion of methane and coal.Firstly, the basic principles of MILD and MILD-Oxy combustion technologies will be introduced, and the advantages of MILD-Oxy combustion technology in controlling NOx emissions will be analyzed. Meanwhile, papers over the last 10 years on MILD-oxy combustion of methane and coal have been reviewed and summarized. Secondly, the analysis of the basic pathways and principles of controlling methane and coal NOx emissions are also involved. CO2 in MILD-Oxy combustion of methane mainly reduces thermal-NO route production through reducing atmosphere and lowering combustion temperatures. H2O changes the free radical pool for combustion, especially the generation of OH radicals, controlling the choice of the N-element reaction path. The diffusion/kinetic determined Char-O2 (char + O2→CO) reaction and the kinetically controlled Char-CO2 (char + CO2→CO) and Char-H2O (char + H2O→CO + H2) reactions in MILD-Oxy combustion of coal strongly influence the generation of Fuel-NO. Enhancing the gasification reaction by controlling the ratio of H2O, CO2, and O2 in the secondary stream may achieve ultra-low NOx emissions. However, some issues remain unresolved. More research is needed in this type of quantitative analysis of the control of combustion emissions by inlet conditions such as oxygen concentration, jet velocity, and burner construction.