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Show 4 temperature profiles of the furnace. In addition, the results of A R D E M U S calculations were compared to other boilers with similar burners, which were also calculated by A R D E M U S and on which the operational data were available. 3.3 Simulation results Flow fields Computed flow fields of Naantali Unit No. 3 indicated that the burner jets were rapidly bending to the furnace walls instead of penetrating more to the centre of the furnace (Appendix 1). This is mainly derived from the structure of the comers, where the burners are situated. Figure 2 presents two different kinds of comer structures. Structure A is similar to the structure of Naantali boilers and structure B is similar to another boiler. The comer structure has a remarkable influence on the penetration of the burner jets. This can also be seen in Appendix 1, where the flow fields of Naantali boiler are compared with other two tangentially fired boilers equipped with the same kind of burners and over fire air system, but the comer structure is B. When comparing the results of simulations and the operational experience, it was found that there was a flame impingement to the furnace wall in Naantali Unit N o . 3, but, in the other two boilers, no flame impingement occurred. Structure A Structure B Figure 2. Different kind of comer structures of tangentially fired boilers Particle trajectories Computed trajectories of coal particles in Naantali Unit No. 3 boiler as well as in the other two tangentially fired boilers (Boiler I and Boiler H) showed that a great amount of coal particles had accumulated near the furnace walls. This is a c o m m o n phenomenon in tangentially fired boilers, where the centrifugal forces caused by the centre fireball are influencing the coal particles and driving them toward the walls. Big particles, especially, are heading near the walls. |