Sawtooth roof furnaces

The sawtoothed roof furnaces sometimes had several zones practically im-fired, but they at least had some firing even with reversed gas flow. Furnaces side fired, or roof fired with flat-flame (type E) burners had burners all along the walls or roof. Sawtoothed roof furnaces may have cost less, but with large loads and one fixed baffle, control was difficult. Regardless, a move to sawtooth roofs proceeded because of less cost. 

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. 1.8. Rotary hearth furnace, donut type, sectioned plan view. (Disk type has no hole in the middle.) Short-flame burners fire from its outer periphery. Burners also are sometimes fired from the inner wall outward. Long-flame burners are sometimes fired through a sawtooth roof, but not through the sidewalls because they tend to overheat the opposite wall and ends of load pieces. R, regenerative burner E, enhanced heating high-velocity burner. (See also fig. 6.7.)...

Rotary furnaces cannot be end fired, but they can be roof fired with type E flat flame burners or with a sawtooth roof. They may be side fired on the outside only, or inside and outside with a donut design. 

Longitudinal firing of steel reheat furnaces in top and bottom heat and soak zones, including sawtooth-roof rotary furnaces, is used to reduce the number of burners and to develop a uniform temperature across the hearth. Otherwise, most of these furnaces would be side fired to hold the heat transfer temperature higher and longer (many times for as long as 40 ft, perhaps 25 ft, for longitudinally fired zones). 

If three baffles had been used, with a moveable baffle between the charge and discharge vestibules, the sawtooth roof rotary furnace would have delivered at least... 

The next method was called the sawtooth roof system, wherein each fired zone had one tooth of the sawtooth roof with burners firing through the vertical wall of the tooth toward the charge door, firing counter to the direction of product movement. This system was less expensive for larger diameter products and furnaces because it required fewer burners and less piping, especially if preheated combustion air was used. 

S.4. Continuous Reheat Furnaces. Continuous reheat furnaces may be rotary or linear. Either can be side fired or top fired. Top firing may be done with conventional type A, F, or G forward thmst flames (fig 6.2) in a sawtooth roof or with type E flat flames in a flat roof. End firing alone can be used only in small linear reheat furnaces, but it is sometimes used in combination with roof- or side-firing in all sizes. (See also sec. 3.8.5.) For donut rotary hearth furnaces, much detail is discussed in section 6.4.1. 

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