Rotary hearth reheat furnaces

Little difference exists in the fuel economy of end-fired, side-fired, and rotary continuous furnaces operated above 2200 F (1204 C) and properly designed and operated, and using a fuel of high calorific value (not blast furnace gas or producer gas). 

For metallurgical reasons, some rotary hearth furnaces are divided into sections by radial baffles. Rotary furnaces designed to heat rounds for seamless tube mills have some very special problems (1) furnace pressure control, (2) air/fuel ratio 

Firing Fluing Firing Fluing Firing —Top heat zones------- Top preheat zone 1 

Bottom heat zone 4-4 Bottom preheat zone sj 

Continuous steel pusher reheat furnace side fired with regenerative burners in the top and bottom heat and preheat zones, and root tired in the soak zone. Preheat zones often have been designed as unfired preheat zones, which are good for fuel economy. However, also firing the preheat zones with regenerative burners would add capacity while retaining high fuel efficiency. (For a discussion of controls for this furnace, see sec. 6.11.1.) 

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The so-called accordion effect upsets the supposedly steady pattern of temperature progression as load pieces move through the zones of multizone reheat furnaces, whether rotary, pusher, walking beam, or walking hearth. (See chap. 6.)... 

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). 

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. 

Case 1 Hearths In rotary-hearth steel-reheat furnaces, where load pieces are positioned directly on the hearth, the weight of the loads will cause depressions in the hearth after perhaps 6 mo. of operation. The cure for this problem is to build the hearth with stainless-steel rails built into the refractory hearth so that the ball of each rail protrudes above the top of the refractory surface 2 to 3 in. (5.8 to 7.6 cm). With this arrangement, loads are supported from deep in the hearth refractories where materials are cooler, and therefore stronger and not attacked by the furnace gases. 

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