Multizone furnace

The canister is placed in a multizone furnace and coupled directly to the output of the calciner as shown in Fig. 11.11. The canister is heated to 1050 C and calcine and frit, which are metered continuously at a rate proportional to the calcine generation rate, are fed to the canister. Once the calcine-frit mixture in a zone has melted to a glass, heating is stopped and cooling is initiated to prevent excessive exposure of the canister to high temperatures. After the canister is full, feed is diverted to another canister in a parallel furnace. 

Fuel economy calculations are more complex for multizone furnaces, including rotary furnaces—side fired, roof fired, or longitudinally fired—with or without baffles between zones. (See sec. 2.6, 3.4, 3.5.) With thick loads, load placement is more critical. (See sec. 3.5, 6.9, 6.10.)... 

Figure 12.6 Schematic diagrams of (a) the hot wall and (b) the cold wall reactor designs. Hot wall reactors have high termal mass multizone furnaces that provide heating of the entire reactor tube and its contents. Note that in this design one can have many substrates standing upright in the flow inserted using a rod that holds them off of the tube surface. In the cold wall design only the susceptor and substrate get hot due to induction current resulting from the rf field due to the coil.

Figure 5-23 has been used to correlate furnace performance data for a multitude of industrial furnaces and combustors. Typical operational domains for a variety of fuel-fired industrial furnaces are summarized in Table 5-7. The WSCC approach (or speckled furnace model) is a classic contribution to furnace design methodology which was first due to Hottel [op. cit.]. The WSCC model provides a simple furnace design template which leads to a host of more complex furnace models. These models include an obvious extension to a tanks-in-series model as well as multizone models utilizing empirical cold-flow velocity patterns. For more information on practical furnace design models, reference is made to Hottel and Sarofim (op. cit., Chap. 14). Qualitative aspects of process equipment have been treated in some detail elsewhere (Baukal, C. E., ed., The JohnZink Combustion Handbook, CRC Press, Boca Raton, Fla., 2001). 

Temperature uniformity within the reactor is one of the key parameters to be precisely controlled for CVD processes. For thin film deposition on the surface of silicon wafers, multizone (up to five zones) resistively heated furnaces are designed to enable a uniform temperature field for the deposition of the thin film, as shown in Figure 3.21. Several kinds of thermocouples (Types B, K, R and S) are available for CVD systems to measure temperatures. The features of these thermocouples are hsted in Table 3.5. Because the CVD processing atmosphere... 

Fig. 1.6. Roller hearth furnace, top- and bottom-fired, multizone. Roller hearth furnaces fit In well with assembly lines, but a Y In the roller line at exit and entrance Is advised for flexibility, and to accommodate parking the loads outside the furnace In case of a production line delay. For lower temperature heat treating processes, and with Indirect (radiant tube) heating, plug fans through the furnace celling can provide added circulation for faster, more even heat transfer. Courtesy of Hal Roach Construction, Inc.

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.)... 

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