Industrial Experimental and Numerical Simulation Study on the Combustion and NOx Formation Characteristics in a 600MWe Utility Boiler with a Novel Swirl Burner Burning Bituminous Coal

Abstract

To minimize the NOx formation, a novel low-NOx swirl pulverized-coal combustion technology characterized by the annulus recirculation was proposed by the Harbin Boiler Company Limited. By employing the industrial experiments to study the combustion and NOx formation characteristics in a 600MWe utility boiler burning the bituminous coal, and simultaneously using the Reynolds Stress turbulence model and the Realizable k-ε model to reveal the in-burner flow characteristics and the full-scale combustion characteristics in the 600MWe utility boiler. The numerical results were in good consistent with the experimental results. The results show that an obvious annular recirculation zone is generated in the axial direction at the burner outlet zone. The recirculation zone brings the high-temperature flue gas back to the near burner zone and heats the primary coal/air flow, which promotes the pulverized coal ignition and maintains the flame stability. Additaionaly, the recirculating high temperature gas has the lowest oxygen content, is thus beneficial to the NOx reduction. On reducing the blade angles of the inner and outer secondary air from 65° to 30°. The size of the recirculation zone is gradually reduced, the entraining capacity of the flue gas weakens, the coal ignition is simultaneously delayed. The oxygen contents in the main combustion zone increase, associated with the gradually weakened reducing atmosphere. The NOx content is increased by 8.5%, while the CO content and carbon in fly ash are slightly reduced. While the blade angles becomes larger, the outlet flow field of the burner is easy to fly, and the water wall is prone to coking、high temperature corrosion, etc. It is recommended that the blade angle of the inner and outer secondary air is set to 45° in the actual boiler operation. The numerical results show that due to the combined combustion effect of the secondary air and the pulverized coal, the combustion performance fluctuates. As the newly injected overfire air in the burnout zone, under the combined effects of the oxygen concentration and the high-temperature flue gas, the combustion performance under each case varies less, and the influence degree of adjusting the inner secondary air blade angle is greater than that of the outer secondary air.KeywordsBurnerIndustrial experimentNmerical simulationRecirculation zonePulverized coal combustionAngle of inner/outer-secondary-air bladeNOx