Column hold-down plates

Adsorbers, distillation colunuis, and packed lowers are more complicated vessels and as a result, the potential exists for more serious hazards. These vessels are subject to tlie same potential haz. uds discussed previously in relation to leaks, corrosion, and stress. However, llicse separation columns contain a wide variety of internals or separation devices. Adsorbers or strippers usually contain packing, packing supports, liquid distributors, hold-down plates, and weirs. Depending on tlie physical and chemical properties of the fluids being passed tlirough tlie tower, potential liazards may result if incompatible materials are used for llie internals. Reactivity with llie metals used may cause undesirable reactions, which may lead to elevated temperatures and pressures and, ullinialely, to vessel rupture. Distillation columns may contain internals such as sieve trays, bubble caps, and valve plates, wliicli are also in conlacl with tlie... 

Figure 9-15B. Typical metal hold-down plate for use with ceramic or carbon packing. Note It rests directly on top of the packing bed-limiters are similar in design in metal or plastic, bolted to column wall above packing. Used by permission Norton Chemical Process Products Corp., Bull. TA-80.

Figure 1335. Packed column and internals, (a) Example packed column with a variety of internals [Chen, Chem. Eng. 40, (5 Mar. 1984)]. (b) Packing support and redistributor assembly, (c) Trough-type liquid distributor, (d) Perforated pipe distributor, (e) Rosette redistributor for small towers. (0 Hold-down plate, particularly for low density packing.

Hold-down plates are not used with metal and plastic packings to avoid crushing the metal or compressing the plastic. To prevent fluidization with these random packings, bed limiters (Fig. 8.7c,cf) are used. Bed limiters do not rest on the packing instead, they are fastened to the column wall by means of a support ring or bolting clips. Alternatively, they can be suspended on tie-rods from the liquid distributor. 

Packed columns, 316 s/s column with 316 s/s Pall rings including support trays, hold-down plates, distributor and redistributor trays including column with some nozzles but no access holes. FOB cost 1 425 000 at the product of (column... 

The multiple phase contact inside the column is promoted by internal mass transfer equipment. Three groups of mass transfer equipment are commonly differentiated, which are separation trays, random packings and structured packings. Besides mass transfer equipment, further column internals are required in rectification to ensure the proper operation of the mass transfer equipment. Such internals may include support and hold-down plates, liquid distributors and redistributors, vapour distributor devices, gas-liquid phase separators and liquid collectors that usually do not participate on mass transfer. 

Both bed limiters and hold-down plates should be of sectional construction to permit entry into the column through a manhole. These plates must fit closely to the column wall to prevent passage of individual packing pieces. The free space through these plates must be high enough not to restrict the capacity of the tower packing. 

In some cases of accidentol flooding or motion due to pressure surges in the column, it is possible that a part of the packing, usually of the random one, is swept aw by the flow of the vapour. In order to pievmt such accidents special hold-down plates mounted over the packing, manufictured in metal and plastic are used. L er some constnictions of these types will be considered. 

The hold-down plates type HP-P [1] are used in combination with structured packings, lie on top of teem and are stayed at tee column wall. They are intended to prevent movement in tee packed bed. The liquid distributor used together with packing is supported on tee metal HP-P Hold-down plates by adjustable bolts, thus making a support ring structure unnecessary. 

The hold-down plate Raschig Grid type RG [1] presented in Figs. 21 and 22 is also offered for column diameters 500 to 3000 mm. 

The separation operation called distillation utihzes vapor and hquid phases at essentially the same temperature and pressure for the coexisting zones. Various lands of devices such as r andom or sti uctui ed packings and plates or tr ays are used to bring the two phases into intimate contact. Trays are stacked one above the other and enclosed in a cyhndrical shell to form a column. Pacldngs are also generally contained in a cyhndrical shell between hold-down and support plates. A typical tray-type distillation column plus major external accessories is shown schematically in Fig. 13-1. 

The typical packed column has one or more beds, each consisting of packing, a support plate, a hold-down support plate, and a liquid distributor. 

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