Computational fluid dynamics (CFD) investigations have been carried out to understand the combustion and NO x emission characteristics in a 1000 MW pulverized-coal boiler, which is equipped with a dual-circular tangential-firing system in a single furnace. One group of separated over fire air (SOFA) nozzles has been widely studied and used in controlling the NO x emissions in a pulverized-coal boiler. In this work, a multi-group of SOFA nozzle arrangement is investigated for the NO x control and reduction. The predicted results agree well with the measured information from the full-scale boiler. The flow field, temperature distribution, species concentration, and char burnout are discussed. The relationship between the NO x formation and the SOFA arrangement are analyzed. The numerical results show that the multi-group of SOFA nozzle arrangement is an efficient method to control the NO x emissions in the pulverized-coal boiler, with few unfavorable effects on the coal burnout. The arrangement of the two-group of SOFA nozzles being in service presents better ability than the one-group arrangement in reducing the NO x emissions. The distance between the two groups of the SOFA nozzles should be longer for a better result of NO x reduction. The technology of air-staging combustion presented in this work is good to enhance the understanding of the NO x formation characteristics and useful for the NO x control and reduction in pulverized-coal boilers.

A novel tiny-oil ignition cyclone burner is presented in this paper. Such a burner is an improvement and modification of the cyclone burner of the Foster Wheeler (FW) Company. In order to reduce the oil consumption during the start up and low load operation of the W-shaped flame pulverized coal-fired utility boiler, tiny-oil technology is introduced to the cyclone burner based on the design concept of staged ignition. This burner is employed in down-fired boiler, with the advantages of burning low volatile coal more efficiently and reducing the oil consumption. Experiments are carried out to investigate the aerodynamic characteristics and the coal particle separation efficiency of the novel tiny-oil ignition cyclone burner. The influence of the vent air damper opening on the performance of the cyclone is studied. The modifications and improvements on the novel tiny-oil ignition cyclone burner produce no unfavorable influence on performance of vent air ratio and the separating efficiency. This burner has been employed for a 300-MW down-fired pulverized coal utility boiler in China, and the oil consumption reduces by 70% compared with the technology of FW Company. 

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