Vessels, process heads, types

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. 

Process pressure vessel cost. Process pressure vessels are always designed in accordance with the current ASME code. These major equipment items are always cylindrical metal shells capped with two elliptical heads, one on each end. Installation can be either vertical or horizontal. Vertical is generally a fractionation-type column with internal trays or packing, although the smaller-height vertical vessels (less than 15 ft) are mostly two-phase scrubber separators. The horizontal vessel is generally a two- or three-phase separation vessel. 

The regenerated extraction gas leaves the second regeneration column at its head and is cooled down in (WT3) to a temperature of approximately 20°C. Depending on the type of extraction solvent the buffer vessel (KP) contains liquid phase in equilibrium state with gas or merely gas of high density. In the last case a pressure controlled pneumatic pump feeds fresh solvent into the circular process. If a gas/liquid equilibrium is achieved in the buffer vessel the gas pressure remains constant until a minimal amount of liquid remains there. For this purpose two optical sensors are introduced into the buffer vessel registrating the minimum and maximum extraction liquid level If the level falls below minimum, fresh liquid extraction solvent is refilled. 

U he real ntwl for the use of formed clt)sures on cylindrical vessels artwe with the development of the power steam b< iler early in the nineteenth century. As a result of the frequent occurrence of boiler explosions, the British House of Commons in 1817 made the recommendation that the heads of cylindrical boilers be hemispherical (12). Since then a wide variety of formed closures termed heads have been developed, standardised, and extensively used in the fabrication of prowss pressure ve sls. The develppment of the thermal cracking process in the petroleum industry during the period from 1915 to 1930 resulted in the construction of thousands of prewure vessels with formed heads operating in the range of from 100 to 400 psi. The heads of t he rly vessels usually were of the torispherical-dish type with a small knuckle radius. 

Fig. 9.1. Nonrotation type of intestinal malrotation. CECT at the level of the pancreatic head shows right-sided contrast-filled small bowel loops, left-sided colon, and absence of the horizontal duodenum. Note an abnormal relationship of the superior mesenteric vessels and aplasia of the uncinate process of the pancreas...

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