Bottom head arrangement

The liquid outlet is located on the bottom head of die tower. If the tower is supported by a skin, the nozzle is routed outside the sldrt. As with the vapor outlet, more than one nozzle may be specified. The elevation of the nozzle is dictated by the constraints discussed previously in this chapter. The orientation can be at any angle, but generally it is dictated by pump suction piping flexibility. Exhibit 10-33 shows a typical bottom head arrangement. 

From these nine basic quantities, numerous other SI units may be derived. Table B.2 lists a number of these derived units, particularly those relevant to colloid and surface chemistry. The table is arranged alphabetically according to the name of the physical quantity involved. Note that instructions for the use of the conversion factors —depending on the direction of the conversion —are given in the top and bottom headings of the columns. Table B.2 is by no means an exhaustive list of the various derived SI units Hopkins (1973) reports on many additional conversions, as do most handbooks and numerous other references. 

Figure 3.14 Hickman still head and air condenser with 5-mL round-bottom flask, arranged for microbumer heating.

A skirt is die most frequently used and most satis-faaory means of suppon for vertical vessels. It is attached by continuous welding to the bottom head of the vessel and is furnished with a base ring, which is secured to a concrete foundation or structural frame by means of anchor bolts. In most cases, the skirt is straight, but on tali, small-diameter towers, the skin could be flared. Access openings are required in vessel skirts for inspection and, when possible, should be oriented toward the main access way. Eidiibit 10-18 shows a typical skin arrangement. 

If specified, reboiler connections are usually located at the bcMtom section of the tower. For the horizontally mounted thermosiphon reboiler, the drawoff nozzle is located just below the bottom tray. For the vertically mounted recirculating thermosiphon reboiler, the draw-off nozzle is located at the bottom head. For both systems, the return nozzles are located just above the liquid level. Exhibit 10-31 shows both of these arrangements. 

Figure 7 shows nozzle locations and support arrangements for a typical horizontal vessel (7). The saddles used for support are sustained by concrete pedestals or steel stmctures. Sufficient clearance between the bottom nozzles and the support saddles needs to be provided for access to the nozzle flange bolts. The manway can be located on the end head of the vessel, the topside of the vessel, or the side of the vessel. The preference is for an end manway wherever possible for accessibiHty, except when it is limited by the level gauges and controls that are commonly mounted off the heads. 

Bucket Elevators. In a bucket elevator, a series of buckets attached to an endless belt or chain are filled with material and lifted vertically to a head pulley or sprocket, where the material is dumped. The buckets are then returned back down to a tail pulley or sprocket at the bottom. Bucket elevators are not self-feeding. They must be fed at a controlled rate to avoid overfilling the buckets and damagiag the machinery. In the usual arrangement of a bucket elevator, the chain or belt path is vertical or steeply inclined ia a single plane. Special chain supported bucket systems that can travel ia two and three planes have been developed. 

Figure 11. Antijunctions and mesojunctions. (a) A 949 knot drawn in a DNA context. Each of the nodes of this knot is shown to be formed from a half-turn of double helical DNA. The polarity of the knot is indicated by the arrowheads passing along it. Various enclosed areas contain symbols indicating the condensation of nodes to form figures. The curved double-headed arrow indicates the condensation of two half-turns into a full turn, the solid triangle indicates a three-arm branched junction, the empty square indicates a 4-strand antijunction, and the shaded square is a four-strand mesojunction. (b) Schematic drawings of 3-strand and 4-strand junctions, antijunctions, and mesojunctions shown as the helical arrangements that can flank a triangle or a square. Each polygon is formed from strands of DNA that extend beyond the vertices in each direction. The arrowheads indicate the 3 ends of the strands. The vertices correspond to the nodes formed by a half-turn of double helical DNA. Base pairs are represented by lines between antiparallel strands. Thin double-headed arrows perpendicular to the base pairs represent the axis of each helical half-turn. The lines perpendicular to the helix axes terminating in ellipses represent the central dyad axes of the helical half-turns. The complexes 33 and 44 correspond to conventional branched junctions. The complex 40 is a 4-strand antijunction. The complexes on the bottom row are mesojunctions, which contain a mix of the two orientations of helix axes.

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