Distillation columns random packing

Bravo and Fair s Correlation for Randomly Packed Columns Bravo and Fair (1982) developed a method of estimating the mass transfer characteristics for distillation in randomly packed columns. Their method is based on Onda s Eqs. 12.3.26 and 12.3.29 for the vapor-and liquid-phase mass transfer coefficients, but uses an alternative correlation for the interfacial area density... 

As in distillation columns, a packed column contains small packing elements dumped into the column in a random fashion, and these elements can provide the needed intimate contacting of the descending liquid and the rising gas or vapor. Packings of an ordered, or structured, form are rarely if ever used for absorption or stripping. 

The situation is very much poorer for stmctured rather than random packings, in that hardly any data on Hq and have been pubHshed. Based on a mechanistic model for mass transfer, a way to estimate HETP values for stmctured packings in distillation columns has been proposed (91), yet there is a clear need for more experimental data in this area. 

Fig. 21. Random packing elements for distillation columns (a), Raschig ring (metal) (b). Bed saddle (ceramic) (c), Intalox saddle (ceramic) (d), PaH ring...

Distillation Applications Packings are now routinely considered for distillation columns with diameters up to 10 m or more. The pressure drop advantages of the modern, through-flow random pack-... 

Random packings are also used they are the same as those used in packed distillation and absorption columns. The properties of random packings are given in Table 11.3. Proprietary structured packing are also used. 

The separation operation called distillation utilizes vapor and liquid phases at essentially the same temperature and pressure for the coexisting zones. Various kinds of devices such as random or structured packings and plates or trays are used to bring the two phases into intimate contact. Trays are stacked one above the other and enclosed in a cylindrical shell to form a column. Packings are also generally contained in a cylindrical shell between hold-down and support plates. The column may be operated continuously or in batch mode depending on a number of factors such as scale and flexibility of operations and solids content of feed. A typical tray-type continuous distillation column plus major external accessories is shown schematically in Fig. 13-1. 

Yin et al. (2000) developed a computational model to simulate flow and mass transfer in randomly packed distillation columns. It is necessary to develop appropriate models for interphase drag and dispersion coefficients. The general approach is to represent the overall pressure drop for gas-liquid flows in a packed column in two parts, namely wet and dry ... 

Distillation columns can be broadly classified into two types, plate columns and packed columns. In plate columns, there is repeated contact between two phases, as in a bubble-cap column. Plate columns are generally used for primary enrichment. Random packings are used for small-diameter columns, whereas ordered packings are used in large-diameter towers. Packed columns are used for the final enrichment. 

Packings for distillation columns come in many types, shapes, and sizes. So-called random packings (or dumped packings ) are relatively small pieces, or elements, that are placed in the column (usually by pouring) in a random arrangement to produce a packed bed. The counterparts... 

Orts, P. 1995. Petformance and Scale-up of a Laboratory-Scale Distillation Column Containing Random Packing, diploma thesis, Universite de Liege, May. 

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