Packed columns liquid distributors

As indicated above, packed column internals include liquid distributors, packing support plates, redistributors (as needed), and holddown plates (to prevent movement of packing under flow conditions). Costs of these internals for columns with random packing are given in Fig. 14-81, based on early 1976 prices, and a Marshall and Swift cost index of 460. 

Packed columns must be provided with good initial distribution of liquid across the column cross section and redistribution of liquid at various height intei vals that decrease with increasing column diameter. A wide variety of distributors and redistributors are available. Packed columns should be considered when ... 

FIG. 14-80 Cost of internal devices for columns containing dumped packings, a) Holddown plates and support plates, (h) Redistributors, (c) Liquid distributors. [Pikulik and Diaz, Cbem. Eng., 84(21), 106 (Oct. 10, 1977).]... 

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... 

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. 

The liquid distributor is the most important internal structure of a packed column. The distributor strongly influences packing efficiency. It must spread the liquid uniformly, resist plugging/fouling, provide free space for gas flow, and allow operating flexibility. 

Select and design the column internal features packing support, liquid distributor, redistributors. 

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.

Many studies on the flow distribution in random packed beds have been reported in the literature. Mercandelli et al. [8] published a short review of the flow distribution work in random packed trickle bed, which includes the list of various techniques used to determine and quantify the flow distribution. Conventional methods include, for example, collecting liquid at the bottom of the column from different zones while advanced methods include tomographic techniques. Mercandelli et al. [8] used several techniques to quantify liquid distribution in columns of diameters up to 30 cm with three different distributor designs. They used global pressure drop measurements, global residence time distribution (RTD) of the liquid, local heat transfer probes, capacitance tomography and a collector at the bottom of the column. 

Pilot-plant experiments have been carried out at real process conditions in the coke plant August Thyssen (Duisburg, Germany). The DN 100 pilot column (Fig. 9.11) was made from stainless steel and equipped with about 4 m of structured packing (Sulzer MELLAPAK 350Y), three liquid distributors, and a digital control system. Several steady-state experiments have been compared with the simulation results and supported the design optimization of the coke gas purification process [91]. 

Wad flow (66,67,140,141-149). The tendency of liquid to flow toward the walls of packed columns is a fundamental phenomenon associated with packed-column hydraulics. The development of wall flow is illustrated in Fig. 9.4 using typical measurements by Hoek (140) in a pilot-scale column. The column diameter was 20 in, and the outer distributor nozzle was located about 1.5 in from the wall. In these experiments, wall flow was defined as the flow in the outer ring of the column (with an area of 16 percent of the column cross section). 

In a packed column the liquid comes in at the top, or near the top, and enters the column via a series of nozzles or through a distributor plat. The gas enters below the packing and passes upward. Packing placed in the column is held in place by support plates. 

End Effects Analysis of the mass-transfer efficiency of a packed column should take into account that transfer which takes place outside the bed, i.e., at the ends of the packed sections. Inlet gas may very well contact exit liquid below the bottom support plate, and exit gas can contact liquid from some types of distributors (e.g., spray nozzles). The bottom of the column is the more likely place for transfer, and Sil-vey and Keller [Chem. Eng. Prog., 62(1), 68 (1966)] found that the... 

---