Furnace shell

Most furnace shells are short vertical cylinders but may also be triangular, elliptical, or rectangular in plan view. Single-phase furnaces may have one or two movable electrodes. Three-phase furnaces usually have three movable electrodes, but some have six (three paks, two electrodes for each phase). 

A typical large three-phase ferroalloy furnace using prebaked carbon electrodes is shown in Eigure 4. The hearth and lower walls where molten materials come in contact with refractories are usually composed of carbon blocks backed by safety courses of brick. In the upper section, where the refractories are not exposed to the higher temperatures, superduty or regular firebrick may be used. The walls of the shell also may be water-cooled for extended life. Usually, the furnace shell is elevated and supported on beams or on concrete piers to allow ventilation of the bottom. When normal ventilation is insufficient, blowers are added to remove the heat more rapidly. The shell also may rest on a turntable so that it can be oscillated slightly more than 120° at a speed equivalent to 0.25—1 revolution per day in order to equalize refractory erosion or bottom buildup. 

The furnace is constmcted with a steel shell lined with high temperature refractory (see Refractories). Refractory type and thickness are deterrnined by the particular need. Where combustion products include corrosive gases such as sulfur dioxide or hydrogen chloride, furnace shell temperatures are maintained above about 150—180°C to prevent condensation and corrosion on the inside carbon steel surfaces. Where corrosive gases are not present, insulation is sized to maintain a shell temperature below 60°C to protect personnel. 

AH the reduction reactions are endothermic, regardless of the reductant used. The heat for these reactions, along with the requirements for the sensible heats of the hot metal and slag, and heat losses through the furnace shell, is provided by the heat generated from equation 1 plus the sensible heat of the hot blast. 

Top-Blown Basic Oxygen Process. The top-blown basic oxygen process is conducted ia a cylindrical furnace somewhat similar to a Bessemer converter. This furnace has a dished bottom without holes and a tmncated cone-shaped top section ia which the mouth of the vessel is located. The furnace shell is made of steel plates ca 50-mm thick it is lined with refractory 600—1200-mm thick (11). 

Fig. 8. Blackbody and furnace A, furnace shell B, furnace tube C, thermal insulation D, heater winding E, outer wall of graphite cmcible F, pure metal...

Metallurgical coke gives rise to ferrosiHcon, which in the Hquid phase is more dense than calcium carbide and tends to setde and penetrate the bottom of the furnace. After a lengthy operating period it may extend 30 cm or more below the taphole, eventually reaching the furnace shell where it causes hot spots requiring repair and replacement of the furnace refractory. 

Furnaces Shell and tube Air-cooled Vertical Horizontal ... 

Hemd, . shirt chemise (of a blast furnace) shell. 

Steam blanketing results in a departure from nucleate boiling (DNB) and typically dryout (localized total evaporation) conditions. It also may result in the formation of secondary (silicate-based) deposits that cannot be rinsed or resolublized, overheating problems, and eventual boiler tube or furnace shell rupture. 

Choose a tube length between 30 and 60 ft or so, so as to make the box dimensions roughly comparable. The exposed length of the tube, and the inside length of the furnace shell, is 1.5 ft shorter than the actual length... 

Fig. 3.4-1. Electric-arc furnace for ferrosilicon manufacture, a) furnace shell with lining (rotatable) b) electrodes c) transformers d) secondary energy supply e) raw material bunker f) feeding tube g) raking machine h) tapping unit i) receiving pan...

In order to demonstrate the ease of scaling this process to fabricate much larger work pieces Besmann et al. [36] developed a large F-CVI system at the Oak Ridge National Laboratory, USA, as shown in Figure 5.20. The furnace shell and lid are water-cooled. The top lid needs to be raised by pneumatic lifters. There are two... 

In another small fired heater, castable refractory was originally installed for a design refractory face temperature of 1,600° F and a furnace shell temperature of 220° F. After several years of operation, the original castable spalled and cracked resulting in a shell temperature of 300° F. A four-inch ceramic refractory blanket was installed that dropped the furnace shell temperature to less than 200° F and reduced heat losses 55 percent. 

At present, the coke/air-gas cupola furnace finds limited implementation in Europe. This may be attributed to the difficulty in controlling the process and the increased complication of the furnace shell. 

The technique may be applied on both cold blast and hot blast cupolas in both new and existing installations. The advantages drawn from the application (increased flexibility, economical benefit, reduced flue-gas volume, increased capacity) will depend on the specific melting conditions of the installation under consideration. The technique has been reported to cause difficulties for controlling the process and also increases the complication of the furnace shell required. 

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