Synergistic activation of reburned char for ultra-low NOx emissions using flue gas recirculation and natural gas in a 10 kW furnace

The technology of powdered coal injection with recirculating flue gas and natural gas conditioning for reburning represents an advanced and innovative approach to enhancing the efficiency of coal powder reburning. By consuming excess oxygen in the recirculated flue gas, natural gas fosters an environment enriched with reducing agents, which stimulates the reactivity of reburning coal powder and augments its effectiveness in reducing nitrogen oxides (NO). This technology has been comprehensively investigated through experiments conducted in a segmented multi-reactor flow system, simulating conditions akin to those in industrial boilers. To achieve a high level of NO abatement, complete combustion of coal powder, and operational cost-effectiveness, a series of optimal operating parameters has been identified: the temperature in the reburning zone (T₁) should be controlled at approximately 1573 K; the reburning fuel ratio (R_f) should be maintained around 20%; the excess air coefficient (λ_fuel) in the reburning zone should be approximately 0.228; the residence time in the reburning zone (t₂) should be 0.6 s, and the burnout zone residence time (t₃) should also be 0.6 s; finally, the oxygen concentration in the recirculating flue gas should be regulated to around 10%. This configuration ensures that reactive intermediates such as CO∗, OH∗, H, and CH_i generated through natural gas modification enhance the physicochemical structure of coal char, thus amplifying the coal char's capacity for the chemical reduction of NO. Precise control of these parameters is expected to facilitate ultra-low NO emissions, while minimizing the consumption of costly active gases and ensuring the economic efficiency of the system.