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Show have shown a supenor heating performance of the system'4'. Relatively uniform flames generated by the FDI combustion has shown an improved heat transfer profile to the steel billets. A strong circulation of combustion products around billets induced by the regenerative burner system helped generate uniform heat transfer profile as well. For the present muffle type cylindncal furnaces, therefore, all the burner arrangements shown in Fig.8 are intended to create strong circulation around the muffle. Combustion products ejected from burners are designed to circulate in identical rotation during one of the two firing modes of the regenerative burner system. In C a s e 1 in Fig.8, burners are installed in-line along the furnace side wall. In C a s e s 2 and 3, burners are installed along the opposite sides of the furnace wall. The difference between C a s e s 2 and 3 is the relative height of the burners. In C a s e 2, a burner is located height-wise in the center of the two burners on the opposite side. N o two burners are located at the same height in C a s e 2. In C a s e 3, pairs of two burners are located at the same height. C a s e 3 is the same burner arrangement as the conventional burner system shown in Fig.3. In the regenerative burner system, all burners are equipped with regenerators and a set of two burners operate in acyclic manner. One burner is in firing m o d e while the other behaves as a flue with a regenerator storing the heat of the flue gas. The firing mode switches typically every 15-20 seconds. While the furnace is, in practice, thermally transient with a cyclic manner, the numerical simulation assumes a steady state. One burner is continuously in firing mode with preheated air of constant temperature while the other is in flue mode. In C a s e 1, burners in firing mode and in flue mode are next to each other. In C a s e s 2 and 3, burners along one side of the furnace are simultaneously in firing m o d e while other burners along the opposite side are assumed to behave as a flue. N o other auxiliary flue is considered. In the calculation, the top and bottom ends of the calculation domain are treated as symmetrical planes. The temperature of the muffle is assumed to be constant so that the heat transfer inside the muffle, i.e., the reducing zone is neglected. The heat flux distnbution onto the muffle surface is calculated and compared to determine the optimum design of FDI regenerative burner system that produces the most uniform profile of heat transfer to the muffle. 5.2 Results and Discussion 5.2.1 Flue gas temperature Table 1 compares the predicted flue gas temperature, which is used to evaluate the thermal efficiency or degree of heat transfer of the furnace. C a s e 1 shows the lowest flue gas temperature among the three cases. The flue gas temperature in C a s e s 2 and 3 is almost the same and higher than that in C a s e 1. In terms of thermal efficiency. Case 1 shows the best performance. 6 |