Five-zone reheat furnaces

Fig. 6.25. Five-zone reheat furnace temperature control for best productivity, lowest fuel use. This control scheme allows quick recovery from production delays. PV = process variable SP = setpoint T/s = temperature sensor.

Fig. 1.3. Five-zone steel reheat furnace. Many short zones are better for recovery from effects of mill delays. Using end-fired burners upstream (gas-flow-wise), as shown here, might disrupt flame coverage of side or roof burners. End firing, or longitudinal firing, is most common in one-zone (smaller) furnaces, but can be accomplished with sawtooth roof and bottom zones, as shown. 

Fig. 4.18. Continuous steel reheat furnace, longitudinally fired in all five zones. Unless a recuperator will be above the furnace, flues at the far right bottom zone would be better than the up-flue shown (a) to minimize cold air inflow around the charge entrance and (6) for better circulation in the bottom right end of the furnace.

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