Dished heads

The volumes of heads must be calculated separately and added to the volume of the cylindrical portion of the tank. The four types of heads most frequently used are the standard dished head, torispherical or ASME head, ellipsoidal head, and hemispherical head. Dimensions and volumes for all four of these types are given in Luken.s Spun Heads, Lnkens Inc., Coatesville, Pennsylvania. Approximate volumes can also be calculated by the formulas in Table 10-65. Consistent units must be used in these formulas. 

The standard dished head does not comply with the ASME Pressure Vessel Code. 

The floating-head cover is usually a circular disk. With an odd number of tube-side passes, an axial nozzle can be installed in such a floating-head cover. If a side nozzle is required, the circular disk is replaced by either a dished head or a channel barrel (similar to Fig. 11-36/) bolted between floating-head cover and floating-tube-sheet sldrt. 

The heatable areas of the diyer are the vessel wall and the screw. The diyer makes maximum use of the product-heated areas—the filling volume of the vessel (up to the knuckle of the dished head) is the usable product loading. The top cover of the vessel is easily heated by either a half-pipe coil or heat tracing, which ensures that no vapor condensation will occur in the process area. In addition to the conical vessel heated area, heating the screw effectively increases the heat exchange area by 15-30 percent. This is accomphshed via rotary joints at the base of the screw. The screw can be neated with the same... 

Evaporators, Horizontal-Tube Type - The basic horizontal-tube evaporator is illustrated in Figure 12. The body of this evaporator is the liquor compartment and is in the form of a vertical cylinder. It is closed, top and bottom, with dished heads, although the bottom may be conical. The lower body ring is provided on opposite sides with steam compartments, closed on the outside by cover plates and on the inside by tube sheets. Between these tube sheets are fastened a number of horizontal tubes. The two steam chests with their connecting mbes form the steam compartment, and the tube wall heating surface. Steam is introduced into one steam chest and as it flows through the tubes it washes non-condensed gases and condensate ahead of it, so that these are withdrawn from the opposite steam chest. 

Faetor for determining the eapaeity (gal) for the bottom head = 0.606 for ASME Standard flanged and dished heads Total heat transfer surfaee area, ft ... 

Note that if 28-inch O.D. X -inch wall pipe is available this could be used with weld cap ends, or dished heads. The percent design velocity would be = 71.8%. 

Referring to the wetted surface, A , the surface areas of ASME flanged and dished head, ASME elliptical heads, hemispherical heads, etc., are often the end assemblies on... 

Tank Capacities, Horizontal Cylindrical-Contents of Standard Dished Heads When Filled to Various Depths... 

Tank Cqiadties, Horizontal Cyiindrical— Contents of Standard Dish Heads When Filled to Various Dq ths... 

Heads May be of Channel Design to Allow Podding of Tubes in Place. AP is Higher than the Dished Head Shown., . , . . . ... 

The ends of the drums should be elliptical or dished heads and never flat. 

Using ASME flanged and dished heads (F D) from Appendix Tables of Blanks, the circle size is 152 in. for a 12-ft diameter tank. Then add 3-in. straight flange which becomes 158 in. which is 158/12 = 13.166 ft diameter. Area of this diameter for surface area of head = 136.14 sq ft equivalent surface area of one head. For a horizontal vessel there are two heads possibly exposed to fire. 

One rule of thumb is to make the floor-to-floor heights 8-10 ft (approximately 3m) higher than the sides of a dished-head vertical tank.6... 

Reactors Assembled cost is 5/lb. Dished bottoms, open tops, height equal to diameter, bottom surface equals 1.5 times the surface of a flat plate of the same diameter. Tanks of over 1500 gal capacity are of 1/4" plate, smaller ones of 3/16" plate. Freeboard equals volume of the dished head. 

Since the the volumes of freeboard and dished head are equal, the volume of the vessel equals that of the straight side. 

The volume constraint is also different from the one previously used because of the dished heads ... 

Together with the depth of liquid in the dished head, the total depth will be close to the 10 ft specified as the maximum. From Figure 18.5, a free board of 5.5 ft is adequate in the absence of a deentraining pad. Accordingly, the vessel will have a diameter of 12.5 ft, a straight side of 14.5 ft, and dished heads designed for full vacuum. The sketch is to scale. 

Although spherical vessels have a limited process application, the majority of pressure vessels are made with cylindrical shells. The heads may be flat if they are suitably buttressed, but preferably they are some curved shape. The more common types of heads are illustrated on Figure 18.16. Formulas for wall thicknesses are in Table 18.3. Other data relating to heads and shells are collected in Table 18.5. Included are the full volume V0 and surface S as well as the volume fraction V/V0 corresponding to a fractional depth H/D in a horizontal vessel. Figure 18.17 graphs this last relationship. For ellipsoidal and dished heads the formulas for V/V0 are not exact but are within 2% over the whole range. 

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