Continuous Furnaces for

In comparison, continuous furnaces for the sintering of P/M parts are more complicated because of the needs for a more differentiated temperature profile (Fig. 9.15) as well as for controlled gas environments (see Section 9.2.1). The latter requires some sort of separation of the atmospheres in different sections along the kiln, either by oscillating doors or by gas curtains. 

Fig. 9.15 Typical temperature profile of a continuous furnace for the sintering of powder metallurgical parts [B.25].

The determination of the need for either a batch or continuous furnace is dependent on production rate and the physical size and weight of the work to be processed. 

At temperatures above 1150°C, alloys used for the hearth or material handling systems in low and medium temperature furnaces lose strength rapidly (2) and temperatures are reached where ceramic refractories are required to support the work. This results in less use of roUer-hearth and belt-type hearths and greater use of pushers or walking-beam designs for continuous furnaces. 

Over 25 years ago the coking factor of the radiant coil was empirically correlated to operating conditions (48). It has been assumed that the mass transfer of coke precursors from the bulk of the gas to the walls was controlling the rate of deposition (39). Kinetic models (24,49,50) were developed based on the chemical reaction at the wall as a controlling step. Bench-scale data (51—53) appear to indicate that a chemical reaction controls. However, flow regimes of bench-scale reactors are so different from the commercial furnaces that scale-up of bench-scale results caimot be confidently appHed to commercial furnaces. For example. Figure 3 shows the coke deposited on a controlled cylindrical specimen in a continuous stirred tank reactor (CSTR) and the rate of coke deposition. The deposition rate decreases with time and attains a pseudo steady value. Though this is achieved in a matter of rninutes in bench-scale reactors, it takes a few days in a commercial furnace. 

Continuous Furnaces Continuous furnaces are employed for the same general duties cited for batch furnaces. Units are gas, oil, or electrically heated and utihze direct circulation of combustion gases or muffles for heat transfer. Continuous furnaces frequently have an extension added for cooling the charge before exposure to atmospheric air. 

Figure 4.5 Worcra furnace for the continuous production of copper.

The environmental problem of sulfur dioxide emission, as has been pointed out, is very much associated with sulfidic sources of metals, among which a peer example is copper production. In this context, it would be beneficial to describe the past and present approaches to copper smelting. In the past, copper metallurgy was dominated by reverberatory furnaces for smelting sulfidic copper concentrate to matte, followed by the use of Pierce-Smith converters to convert the matte into blister copper. The sulfur dioxide stream from the reverberatory furnaces is continuous but not rich in sulfur dioxide (about 1%) because it contains carbon dioxide and water vapor (products of fuel combustion), nitrogen from the air (used in the combustion of that fuel), and excess air. The gas is quite dilute and unworthy of economical conversion of its sulfur content into sulfuric acid. In the past, the course chosen was to construct stacks to disperse the gas into the atmosphere in order to minimize its adverse effects on the immediate surroundings. However, this is not an en-... 

Continuous furnaces, 12 289-290, 598 Continuous heat processing equipment, for food processing, 12 81... 

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