Packed tower components

If a waste contains a mixture of volatile components that have similar vapor pressures, it is more difficult to separate these components and continuous fractional distillation is required. In this type of distillation unit (Fig. 4), a packed tower or tray column is used. Steam is introduced at the bottom of the column while the waste stream is introduced above and flows downward, countercurrent to the steam. As the steam vaporizes the volatile components and rises, it passes through a rectification section above the waste feed. In this section, vapors that have been condensed from the process are refluxed to the column, contacting the rising vapors and enriching them with the more volatile components. The vapors are then collected and condensed. Organics in the condensate may be separated from the aqueous stream after which the aqueous stream can be recycled to the stripper. 

The other major type is gas absorption of inorganic components in aqueous solutions. For this type design one uses mass transfer coefficients. Packed towers are used so often for this type that its discussion is often included under sections on packed towers. However, in this book it is included here. 

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,... 

Va = molecular volume for component A, diffusing gas Vg = molecular volume for component B, diffused gas (See chapter on Packed Towers, Volume 2, 3rd Ed. for further discussion.) Compute from atomic volumes kj = diffusivity, fL/hr p/ = total pressure, atm Tg = absolute temperature, ° Kelvin Ma and Mg = molecular weights of the gases... 

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. 

A countercurrent packed-tower air stripper has two major components (Fig. 1) ... 

Absorption is a mass transfer operation that is commonly used to recover valuable gaseous components or to remove undesirable components of a gas stream. It is one of the main methods of separation in the chemical process industries. Absorption can take place in packed towers or in plate towers. Perry and Green (9) compare the advantages of packed and plate towers. ... 

This chapter considers the vapor-liquid equilibrium of mixtures, conditions for bubble and dew points of gaseous mixtures, isothermal equilibrium flash calculations, the design of distillation towers with valve trays, packed tower design. Smoker s equation for estimating the number of plates in a binary mixture, and finally, the computation of multi-component recovery and minimum trays in distillation columns. 

The development of the design equation for a countercurrent packed tower absorber or stripper begins with a differential mass balance of component A in the gas phase, in a manner similar to that of Example 2.12. However, this time we do not restrict the analysis to dilute solutions or to constant molar velocity. If only component A is transferred (4 G = VA[ = 1.0), considering the fact that the gas-phase molar velocity will change along the column, and that F-type mass-transfer coefficients are required for concentrated solutions, the mass balance is... 

These processes are carried out in a variety of equipment ranging from a bubbling absorber to a packed tower or plate column. The design of the adsorber itself requires models characterizing the operation of the process equipment and this is discussed in Chapter 14. The present chapter is concerned only with the rate of reaction between a component of a gas and a component of a liquid—it considers only a point in the reactor where the partial pressure of the reactant A in the gas phase is and the concentration of A in the liquid is C, that of B, Cg. Setting up rate equations for such a heterogeneous reaction will again require consideration of mass and eventually heat transfer rates in addition to the true chemical kinetics. Therefore we first discuss models for transport from a gas to a liquid phase. 

In general, pressure drop per unit height is least for towers with structured packings and greatest with tray towers, with randomly packed towers in between. For sieve trays, the components of the pressure drop are (1) pressure drop through the holes in the tray, which depends... 

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