Shell diameter

Determination of Sheii and Tube Heat Exchanger Sheii Diameter 

Draw the equilateral triangle connecting three adjacent tube centers. Any side of the triangle is the tube pitch (recall 1.25 Do is minimum). 

Triangle area is V2bh where b is the base and h is the height. 

Calculate shell diameter to contain this area. 

Add one tube diameter all the way around (two tube diameters added to the diameter calculated above). 

Determination of Shell and Tube Heat Exchanger Shell Diameter 

---

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. 

External-pressure failure of shells can result from overstress at one extreme or n om elastic instability at the other or at some intermediate loading. The code provides the solution for most shells by using a number of charts. One chart is used for cylinders where the shell diameter-to-thickness ratio and the length-to-diameter ratio are the variables. The rest of the charts depic t curves relating the geometry of cyhnders and spheres to allowable stress by cui ves which are determined from the modulus of elasticity, tangent modulus, and yield strength at temperatures for various materials or classes of materials. The text of this subsection explains how the allowable stress is determined from the charts for cylinders, spheres, and hemispherical, ellipsoidal, torispherical, and conical heads. 

Some judgment is required in the use of these correlations because of construction features of the condenser. The tubes must be supported by baffles, usually with maximum cut (45 percent of the shell diameter) and maximum spacing to minimize pressure drop. The flow of the condensate is interruptea by the baffles, which may draw off or redistribute the liqmd and which will also cause some splashing of free-falling drops onto the tubes. 

Diameter. The nominal diameter shall he the inside diameter of the shell in inches, rounded off to the nearest integer. For kettle rehoders the nominal diameter shall he the port diameter followed hy the shell diameter, each rounded off to the nearest integer. 

The outer tube limit approaches the inside of the sldrt but is farther removed from the inside of the shell than for any of the previously discussed constructions. Clearances between shell diameter and bundle OTL are 22 mm (% in) for small-diameter pipe shells, 44 mm (1% in) for large-diameter pipe shells, and 58 mm (2M6 in) for moderate-diameter plate shells. 

Minimum baffle spacing is generally one-fifth of the shell diameter and not less than 50.8 mm (2 in). Maximum baffle spacing is hm-ited by the requirement to provide adequate support for the tubes. The maximum unsupported tube span in inches equals 74 dP (where d is the outside tube diameter in inches). The unsupported tube span is reduced by about 12 percent for aluminum, copper, and their alloys. 

When points for 20-ft-long tubes do not appear in Fig. 11-41, use 0.95 times the cost of the equivalent 16-ft-Iong exchanger. Length variation of steel heat exchangers affects costs by approximately 1 per square foot. Shell diameters for a given surface are approximately equal for U-tube and floating-head construc tion. 

Special designs of direct rotaiy dryers, such as the Renneburg DehydrO-Mat (Edward Renneburg Sons Co.), are constructed especially to provide lower retention during the falling-rate diy-ing period for the escape of internal moisture from the solids. The DehydrO-Mat is a cocurrent diyer employing a smaU-diameter shell at the feed end, where rapid evaporation of surface moisture in the stream of initially hot gas is accomplished with low holdup. At the solids- and gas-exit end, the shell diameter is increased to reduce gas velocities and provide increased holdup for the solids while they are exposed to the partially cooled gas stream. 

The result is minimum shell diameter. There is no firm standard for shell diameter increments. Use 2-inch increments for initial planning. 

If there are space limitations for the boiler (L or shell dia. may be limited in some cases) we can use the chart to obtain a different shell diameter given by... 

If exchanger shell diameter is in doubt, see Chapter 2, Heat Exchangers, the Shell Diameter section. In addition, this book provides a rough rating method for air-cooled heat exchangers. 

In addition to the type description code there is also a shorthand that is used for classifying heat exchangers. The first element of the shorthand is the nominal diameter, which is the inside diameter of the shell in inches, rounded off to the nearest integer. For kettle reboilers and chillers ii emember the kettle has a narrow end and a fat end), the nominal diame-tci is the port diameter (the narrow end) followed by the shell diameter, each rounded off to the nearest integer. 

A pull-through, floating head, kettle-type reboiler having stationary head integral with the tubesheet, 23-in. port diameter and 37-in. inside shell diameter with tubes 16 ft long is denoted as SIZE 23/37-192 TYPE CKT,... 

From Table 3-4 it is then possible to pick a shell diameter that can accommodate the number of tubes required. Please note that Equation 3-2 calculates the total number of tubes required and not the number of tubes per pass. Similarly, Table 3-4 lists the total number of tubes and not the number per pass. There are fewer total tubes in the same diameter exchanger for more passes of the tube fluid because of the need for partition plates. There are fewer tubes for floating head than fixai head designs because the heads and seals restrict the use of space. U-tubes have the lowest number of tubes because of the space required for the tightest radius bend in the U-tube bundle. 

Once the total number of passes is known, the coil can be laid out geometrically assuming that the center-line minimum radius of bends is 1 times nominal pipe size. The required shell diameter is then determined. 

Fire uihe area required and heater size (shell diameter, shell length, fire luhe rating, coil length and number of passes). 

RGB—Includes all classes of construction/design and are identical shell diameter (inside) not exceeding 60 in., and maximum design pressure of 3,000 psi. 

Nominal Shell Diameter Tie Rod Diameter Minimum Nmnber of Tie Rods... 

---