Steel shells

The steel shell that encloses the refractory is exposed to significant forces from the expansion of the refractory as well as the load from the refractory and the charge within the furnace. Similarly, the stmctures that support the furnace and the foundations must be designed to assure safe operation. A failure of any component can have serious consequences. 

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. 

For commodities that soHdify at temperatures commonly encountered during shipping, tank cars are equipped with internal or external heating coils. In some cases, cars are insulated with both sides of the insulation protected by thin steel shells. Approximately 15% of the tank cars in the United States are constmcted for the transportation of pressuri2ed commodities, such as anhydrous ammonia and propane. 

Structural Considerations. Sdos, bins, and hoppers fail, in one way or another, each year. The causes of silo failures are many and varied (9). Such failures can range from a complete and dramatic stmctural coUapse, to cracking in a concrete wall, or denting of a steel shell. This last is often a danger signal indicating that corrective measures are required. 

Fig. 2. Downs cell A, the steel shell, contains the fused bath B is the fire-brick lining C, four cylindrical graphite anodes project upward from the base of the cell, each surrounded by D, a diaphragm of iron gau2e, and E, a steel cathode. The four cathode cylinders are joined to form a single unit supported on cathode arms projecting through the cell walls and connected to F, the cathode bus bar. The diaphragms are suspended from G, the collector assembly, which is supported from steel beams spanning the cell top. For descriptions of H—M, see text.

A conventional circular-wedge roaster consists of a brick-lined steel shell with hearths arched gendy upward from the periphery to a central shaft. The brick hearths may number from 8 to 16 and are ca 1 m apart. The central steel shaft (ca 1.2 m in diameter) revolves at 1 rpm or less carrying two rabble arms per hearth. These rabbles, cooled with air or water, plow the ore from the outside to the center of the hearth where it is dropped to the next hearth for plowing in the opposite direction. The calcine thus proceeds to the bottom where it is dropped into a conveyor. The sulfide sulfur at this point is ca 3.5% (22). 

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 duidized-bed roasters (19), the concentrate is suspended in an upward-moving air stream. The vessel is a refractory-lined steel shell with air entering through holes in a refractory-lined plate at the base. The sulfur dioxide concentration of the exit gas is 10—15%. 

When alloy construction for one of the two fJiiids is required, a carbon steel shell combined with alloy tube-side parts is less expensive than alloy in contact with the shell-side fluid combined with carbon steel headers. 

Clad Tube Sheets Usually tube sheets and other exchanger parts are of a solid metal. Clad or bimetallic tube sheets are usecito reduce costs or because no single metal is satisfactory for the corrosive conditions. The alloy material (e.g., stainless steel, Monel) is generally bonded or clad to a carbon steel backing material. In fixed-tube-sheet construction a copper-alloy-clad tube sheet can be welded to a steel shell, while most copper-alloy tube sheets cannot be welded to steel in a manner acceptable to ASME Code authorities. 

Joy Denver Equipment Div Manufactures a variety of grinding mills. Designs incorporate cast steel heads, hea y rolled steel shell, replaceable cast steel trunnions, hydraiilic starting lubricator, inter-... 

Because of the high operating temperatures, the unit must be constructed of metals capable of withstanding this condition. Combustion devices are usually constructed with an outer steel shell that is lined with refractory material. Refraclory-waU thickness is usually in the... 

In a third process, a loose liner is fastened to a carbon steel shell by welds spaced so as to prevent collapse of the hner. A fourth method is weld overlay, which involves depositing multiple layers of alloy weld metal to cover the steel surface. 

Heat exchangers that utilize copper coils are potential candidates for galvanic corrosion due to dissolved copper salts interacting with the galvanized steel shell. This problem can be avoided by nickel plating the coils. The coils then can be separated from direct contact with the vessel via insulation. Also, it is preferable to conduct the water on the tube side of heat exchangers. 

Insulation - The steel shell of the stack is lined for its entire length with monolithic type castable refractory. 

Control of low-pressure injection during an anticipated transient without scram (ATV i Dry well steel shell to prevent melt-through in a Mark 1 containment... 

Stahl-blech, n. steel plate, sheet steel, -block, m. (Metal.) steel ingot, -bombe, /, steel cylinder steel bomb, steel shell, -brunnen, m. chalybeate spring, -draht, m. steel wire, -eisen, n, steely iron, steel pig, stShlen, v.t. steel, harden convert into steel. stShlern, a. of steel, steel. 

Figure 10-8. Single-pass shell and tube Teflon tube heat exchanger, countercurrent flow. Tube bundles are flexible tube Teflon joined in integral honeycomb tubesheets. Shell-side baffles are provided for cross-flow. Standard shell construction is carbon steel shell plain or Teflon (LT) lined. Heads are lined with Teflon . Tube diameters range from 0.125-0.375 in. O.D. the temperature range is 80-400°F pressures range from 40-150 psig. (Used by permission AMETEK, Inc., Chemical Products Div., Product Bulletin Heat Exchangers of Teflon . )...

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