Packed tower internals

Norton Company, "Packed Tower Internals, Bulletin TA-80R, 1974. 

Tower Internals and Equipment Modification. Tower capacity expansion can be achieved through the use of random or stmctured packing, or through the use of higher capacity trays such as the UOP multiple downcomer tray. Packing has been used in the gasoline fractionator, water quench tower, caustic and amine towers, demethanizer, the upper zone of the deethanizer, debutanizer, and condensate strippers. Packing reduces the pressure drop and increases the capacity. 

When the solute has a large heat of solution or when the feed gas contains high percentages of the solute, one should consider the use of internal coohng coils or intermediate external heat exchangers in a plate-type tower to remove the heat of absorption. In a packed tower, one could consider the use of multiple packed sections with intermediate hquid-withdrawal points so that me hquid coiild be cooled by external heat exchange. 

However, in certain cases, the impingement plate design is preferred over packed-tower columns when either internal cooling is desired, or where low liquid flow rates would inadequately wet the packing. 

UK. = Light key component in volatile mixture L/V = Internal reflux ratio L/D = Actual external reflux ratio (L/D) ,in = Minimum external reflux ratio M = Molecular weight of compound Mg = Total mols steam required m = Number of sidestreams above feed, n N = Number of theoretical trays in distillation tower (not including reboiler) at operating finite reflux. For partial condenser system N includes condenser or number theoretical trays or transfer units for a packed tower (VOC calculations) Nb = Number of trays from tray, m, to bottom tray, but not including still or reboiler Nrain = Minimum number of theoretical trays in distillation tower (not including reboiler) at total or infinite reflux. For partial condenser system,... 

Figure 9-1B. Typical packed tower with internals for improved distillation. Used by permission of Jaeger Products Inc., Bull. 1100.

Deviations from optimal design of trays, packings and other tower internals, e.g., distributors and baffles. 

TOWER INTERNAL SPECIFICATIONS SPRAY OR PACKED TYPE COLUMNS... 

Figure 9-74B. Tower internal specifications, Spray or Packed Columns.

Revamp the tower internals with high-capacity trays or packing. 

The very first continuous distillation column was the patent still used to produce Scotch whiskey in the 1830s. It had 12 bubble-cap trays with weirs, downcomers, tray decks, and bubble caps with internal risers. Current trayed towers are quite similar. As most distillation towers have always been trayed rather than packed, one would have to conclude that trayed towers must have some sort of inherent advantage over packed towers. And this is indeed true, in a practical sense even though, in theory, a packed tower has greater capacity and superior separation efficiency than a trayed column. 

In any type of packed tower, the liquid or internal reflux drips through the packing, and forms a thin film of liquid on the surface of the packing. Vapor percolates up through the packing, and exchanges heat and molecules with the thin film of liquid on the surface of the packing. 

The various kinds of internals of packed towers are represented in Figure 13.35 whose individual parts may be described one-by-one ... 

An extractor column is generally a tall, vertical packed tower that has two or more bed sections. Each packed bed section is typically limited to no more than 8 ft tall, making the overall tower height about 40 to 80 ft. Tower diameter depends fully upon liquid rates, but is usually in the range of 2 to 6 ft. Liquid-liquid extractors may also have tray-type column internals, usually composed of sieve-type trays without downcomers. These tray-type columns are similar to duoflow-type vapor-liquid separation, but here serve as contact surface area for two separate liquid phases. The packed-type internals are more common by far and are the type of extractor medium considered the standard. Any deviation from packed-type columns is compared to packing. 

The purchased cost for plate and packed towers can be divided into the following components (1) cost for shell, including heads, skirts, manholes, and nozzles (2) cost for internals, including trays and accessories, packing, supports, and distributor plates and (3) cost for auxiliaries, such as platforms, ladders, handrails, and insulation. 

Adsorbers, distillation colunms, and packed towers are more complicated vessels and as a result, the potential e. ists for more serious liazards. These vessels are subject to tlie same potential hazards discussed previously in relation to leaks, corrosion, and stress. However, tiicse separation columns contain a wide variety of internals or separation devices. Adsorbers or strippers usually contain packing, packing supports, liquid disuibutors, hold-down plates, and weirs. Depending on tlie physical and chemical properties of tlie fluids being passed tluougli tlie tower, potential liazards may result if incompatible materials are used for tlie internals. Reactivity with tlie metals used may cause undesirable reactions, which may lead to elevated temperatures and pressures and, ultimately, to vessel rupture. Distillation colunms may contain internals such as sieve trays, bubble caps, and valve plates, wliich are also in contact with tlie... 

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