**9. References**

36 Mass Transfer in Chemical Engineering Processes

Helpful discussions with Prof. S. H. Amirshahi of Amirkabir University of Technology and

Dr. N. Taheri of Tehran University are gratefully acknowledged.

**7. Acknowledgment** 

**8. List of symbols**  *A* absorption *a* activity *a* absorptivity

*c* concentration

*D* diffusion coefficient *D* self-diffusion coefficient *DT* thermodynamic diffusion

*De* Deborah number *dp* depth of penetration *G* Gibbs free energy

*N* Avogadro's number *n* number of mole

*R* gas constant *r* radius of filament *S* diffusivity coefficient

*Tg* glass transition *T* temperature *t* film thickness *x* mole fraction

*S* Entropy

*J* flux

*e* 

*P* permeability coefficient

characteristic time of polymer

geometrical impedance factor

immobilization factor

*FV* fractional free volume

interaction parameter

volume fraction

molar volume

density

*H* Enthalpy *l* film thickness intrinsic mobility *M* mass uptake

*b* pathlenght of the component

*C* incremental change in heat capacity at *Tg*


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**3** 

*Brazil*

**HETP Evaluation of Structured and** 

*Chemical Engineering Department, Technology Institute,* 

*Universidade Federal Rural do Rio de Janeiro* 

Marisa Fernandes Mendes

**Randomic Packing Distillation Column** 

Packed columns are equipment commonly found in absorption, distillation, stripping, heat exchangers and other operations, like removal of dust, mist and odors and for other purposes. Mass transfer between phases is promoted by their intimate contact through all the extent of the packed bed. The main factors involving the design of packed columns are mechanics and equipment efficiency. Among the mechanical factors one could mention liquid distributors, supports, pressure drop and capacity of the column. The factors related to column efficiency are liquid distribution and redistribution, in order to obtain the

These columns are useful devices in the mass transfer and are available in various construction materials such as metal, plastic, porcelain, ceramic and so on. They also have good efficiency and capacity, moreover, are usually cheaper than other devices of mass

The main desirable requirements for the packing of distillation columns are: to promote a uniform distribution of gas and liquid, have large surface area (for greater contact between the liquid and vapor phase) and have an open structure, providing a low resistance to the gas flow. Packed columns are manufactured so they are able to gather, leaving small gaps without covering each other. Many types and shapes of packing can satisfactorily meet these

The packing are divided in random – randomly distributed in the interior of the column – and structured – distributed in a regular geometry. There are some rules which should be

a. The column should operate in the loading region (40 to 80% flooding), which will

c. The packing bed is limited to 6D (Raschig rings or sells) or 12D for Pall rings. It is not

d. Liquid initial distribution and its redistribution at the top of each section are very

followed when designing a packed column (Caldas and Lacerda, 1988):

important to correct liquid migration to the column walls.

assure the best surface area for the maximum mass transfer efficiency; b. The packing size (random) should not be greater than 1/8 the column diameter;

A preliminary design of a packed column involves the following steps:

maximum area possible for liquid and vapor contact (Caldas and Lacerda, 1988).

**1. Introduction** 

transfer (Eckert, 1975).

requirements (Henley and Seader, 1981).

1. Choice of packing;

2. Column diameter estimation;

recommended bed sections grater than 10m;

