Wall refractory lining

The corrosion situation in a thin-wall refractory lining is illustrated in Figure 2. Here the refractory corrosion reactions occur primarily at the immediate hot face, and there is little or no slag penetration. Microscopic examinations usually show... 

The empirical model of Endell, Fehling, and Kley for thick-wall refractory linings provides the following information ... 

In wetted-wall units, the walls of a tall circular, slightly tapered combustion chamber are protected by a high volume curtain of cooled acid flowing down inside the wall. Phosphoms is atomized by compressed air or steam into the top of the chamber and burned in additional combustion air suppHed by a forced or induced draft fan. Wetted-waU. plants use 25—50% excess combustion air to reduce the tail-gas volume, resulting in flame temperatures in excess of 2000°C. The combustion chamber maybe refractory lined or made of stainless steel. Acid sprays at the bottom of the chamber or in a subsequent, separate spraying chamber complete the hydration of phosphoms pentoxide. The sprays also cool the gas stream to below 100°C, thereby minimising corrosion to the mist-collecting equipment (typically type 316 stainless steel). 

Refractory lining life was at one time an important maintenance cost, but developments using a nitrogen lance to splash slag over the walls have increased lining life by a factor of -- 10 (2000 to 20,000 heats). 

Furnace Design. Modem carbide furnaces have capacities ranging from 45,000 t/yr (20 MW) to 180,000 t/yr (70 MW). A cross-section of a 40 MW furnace, constmcted in 1981, having a 300 t/d capacity is shown in Figure 2. The shell consists of reinforced steel side walls and bottom. Shell diameter is about 9 m and the height to diameter ratio is shallow at 0.25 1.0. The walls have a refractory lining of 0.7 m and the bottom has a 1-m layer of brick topped by a 1.5-m layer of prebaked carbon blocks. The steel shell is supported on concrete piers and cooling air is blown across the shell bottom. A taphole to withdraw the Hquid carbide is located at the top of the carbon blocks. 

In tunnel equipment, the solids are usually heated by direc t contact with hot gases. In high-temperature operations, radiation from walls and refractory lining may be significant also. The air in a direc t-heat unit may be heated directly or indirectly by combustion or, at temperature below 475 K, by finned steam cods. 

Stripper shell Carbon steel, cold wall with 4 in. (10 cm) medium weight refractory lining... 

Current designs for venturi scrubbers generally use the vertical downflow of gas through the venturi contactor and incorporate three features (1) a wet-approach or flooded-wall entry section, to avoid dust buildup at a wet-dry junction (2) an adjustable throat for the venturi (or orifice), to provide for adjustment of the pressure drop and (3) a flooded elbow located below the venturi and ahead of uie entrainment separator, to reduce wear by abrasive particles. The venturi throat is sometimes fitted with a refractory lining to resist abrasion by dust particles. The entrainment separator is commonly, but not invariably, of the cyclone type. An example of the standard form of venturi scrubber is shown in Fig. 17-48. The wet-approach... 

Natural gas is reacted with steam on an Ni-based catalyst in a primary reformer to produce syngas at a residence time of several seconds, with an H2 CO ratio of 3 according to reaction (9.1). Reformed gas is obtained at about 930 °C and pressures of 15-30 bar. The CH4 conversion is typically 90-92% and the composition of the primary reformer outlet stream approaches that predicted by thermodynamic equilibrium for a CH4 H20 = 1 3 feed. A secondary autothermal reformer is placed just at the exit of the primary reformer in which the unconverted CH4 is reacted with O2 at the top of a refractory lined tube. The mixture is then equilibrated on an Ni catalyst located below the oxidation zone [21]. The main limit of the SR reaction is thermodynamics, which determines very high conversions only at temperatures above 900 °C. The catalyst activity is important but not decisive, with the heat transfer coefficient of the internal tube wall being the rate-limiting parameter [19, 20]. 

Refractory Linings. The refractory linings (2,3) for the hearth and lower walls of furnaces designed for melting ferrous materials may be acidic, basic, or neutral (see Refractories). Silica has been widely used in the past, and is still being used in a number of iron and steel foundries. Alumina, a neutral refractory, is normally used for furnace roofs and in the walls for iron foundries, but basic brick can also be used in roofs (4). 

In practice, the catalyst system is in the form of a soaromatic hydrocarbons, and which contains 25 to 30 weight per cent of promoted aiuminum chloride, combined with 45 to 50 per cent of benzene/ethyU benzene and about 25 per cent of higher mtdecular weight hydrocarbon compounds. Because it is heavier the catalyst settles at the bottom of the reactor. Since the complex is also corrosive, the reactor must be provided with a refractory lining or the reactor walls vitrified. 

The reactor containment is another choice that requires consideration. Some means of protecting the pressure shell from the reaction temperature is required. The alternatives are a) refractory lining, b) a water-cooled membrane wall between the reaction space and the pressure shell, or c) a water jacket integral to the pressure shell. Although most processes have settled for one system or another. Future Energy offers a choice between all three according to application. 

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