Abstract: In practical operations, the carbon monoxide (CO) distribution in an opposite-wall-firing furnace (OWFF) is characterized by a high concentration near the side walls and a low concentration in the center, accompanied by a series of combustion-related issues. To find the reasons for the CO distribution, a numerical study was conducted on a 660 MWe OWFF. The CO concentration profiles, distribution coefficients of coal and air, mixing coefficients, and the aerodynamic characteristics were extracted for analysis. The CO distribution within the furnace greatly depends on the mixing of coal and air. A mismatch between the aerodynamic behaviors of coal and air causes the non-uniform distribution of CO. Taking into consideration that distinctive flow patterns exist within the different regions, the formation mechanisms of the CO distribution can be divided into two components: (1) In the burner region, the collision of opposite flows leads to the migration of gas and particles toward the side wall which, together with the vortexes formed at furnace corners, is responsible for unburned particles concentrated and oxygenized from the furnace center to the side wall. Thus, high CO concentrations appear in these areas. (2) As the over-fire air (OFA) jet is injected into the furnace, it occupies the central region of furnace and pushes the gas from the burner region outward to the side wall, which is disadvantageous for the mixing effect in the side wall region. As a consequence, a U-shaped distribution of CO concentration is formed. Our results contribute to a theoretical basis for facilitating the control of variation in CO concentration within the furnace.

Key words: Opposite-wall-firing furnace (OWFF); Carbon monoxide (CO) distribution; Distributions of coal and air; Gas/particle flow; Corner vortex; Over-fire air (OFA)

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