Mixtures adiabatic columns

A useful method for a binary mixture employs an analysis based on the McCabe-Thiele graphical method. In addition to the usual assumptions of adiabatic column and equimolal overflow on the trays, the following procedure assumes neghgible holdup of hquid on the trays, in the column, and in the condenser. 

Figure 7 The vapour flow (mol s) and heat exchanger load (kW) in an optimised diabatic column and an adiabatic column. Both columns separate an equirrwlar mixture of toluene and benzene...

G2. Pressure can have a large effect on the equilibrium data for nonideal systems. Your cortpany plans to process a mixture of acetone, methyl ethyl ketone, and methyl isobutyl ketone in an ordinary, single-feed distillation column with a total condenser and a partial reboiler. Feed flow rate is 200 kmol/h feed mole fractions acetone = 0.25 methyl ethyl ketone = 0.45 and methyl isobutyl ketone = 0.3. Feed can be made available at any desired pressure. Feed tenperature is 75°C, D = 50 kmol/h, and adiabatic column. The purpose is to produce pure acetone. 

The analysis of the reversible distillation of ideal mixtures has led to important practical results. The use of flowsheets of the same type as those shown in Fig. 4.4 but consisting of real adiabatic columns (i.e., columns with finite numbers of separation stages), without intermediate input of heat and cold and with product columns joined into one complex column (Petlyuk, Platonov, Slavinskii, 1965), allows energy consumption for separation to be reduced by thirty to forty percent. 

Therefore, an infinitesimal amount of heat should be drawn off in each cross-section of the top section and should be brought in in each cross-section of the bottom section. For azeotropic mixtures, the phase equilibrium coefficients field is of complicated character, which leads to nonmonotony of the Liquid and vapor flow rates changing along the sections trajectories (i.e., to the necessity of input or output of heat in various cross-sections of the section). Such character of the flow rates changing at reversible distiUation influences on the conditions of minimum reflux mode in adiabatic columns, which results in a number of cases in the phenomenon of tangential pinch (see Chapter 5). 

The location of trajectory bundles and possible product composition segments at reversible distillation of three-component mixtures determines the location of trajectory bundles, and of possible product composition regions of multicomponent mixtures and the locations of trajectory bundles of real adiabatic columns. 

Necessary and Sufficient Conditions of Separability of Mixtures 5.7.1. Adiabatic Columns... 

Columns under consideration are columns of nonadiabatic distillation (that can also be used in simple two-section columns, in complex columns, and in distillation complexes). The application of simple nonadiabatic columns for separation of azeotropic mixtures was examined in Chapter 5, Section 5.7, when separation in adiabatic columns is unfeasible. 

Later, these columns were independently rediscovered (Petlyuk, Platonov, Slavinskii, 1965 Platonov, Petlyuk, Zhvanetskiy, 1970) on the basis of theoretical analysis of thermodynamically reversible distillation because this distillation complex by its configuration coincides with the sequence of thermodynamically reversible distillation of three-component mixture (see Chapter 4), but in contrast to this sequence it contains regular adiabatic columns. The peculiarities of Petlyuk columns for multicomponent mixtures are (1) total number of sections is n(n - 1) instead of 2(n - 1) in regular separation sequences (2) it is sufficient to have one reboiler and one condenser (3) the lightest and the heaviest components are the key components in each two-section constituent of the complex and (4) n components of a set purity are products. 

The proposed process uses two parallel columns containing beds of solid particles. The air-acetone stream, which contains acetone and oxygen in stoichiometric proportion, enters one of the beds at 1500 mm Hg absolute at a rate of 1410 standard cubic meters per minute. The particles in the bed have been preheated and transfer heat to the gas. The mixture ignites when its temperature reaches 562°C, and combustion takes place rapidly and adiabatically. The combustion products then pass through and heal the particles in the second bed. cooling down to 350°C in the process. Periodically the flow is switched so that the heated outlet bed becomes the feed gas preheater/combustion reactor and vice versa. 

It should be pointed out that the equations required to describe the adiabatic flash are of precisely the same form as those required to describe the separation process which occurs on the plate of a distillation column in the process of separating a multicomponent mixture. 

A mixture of ethanol and water vapor is being rectified in an adiabatic distillation column. The alcohol is vaporized and transferred from the liquid to the vapor phase. Water vapor condenses—enough to supply the latent heat of vaporization needed by the alcohol being evaporated—and is transferred from the vapor to the liquid phase. Both components diffuse through a gas film 0.1 mm thick. The temperature is 368 K and the pressure is 1 atm. The mole fraction of ethanol is 0.8 on one side of the film and 0.2 on the other side of the film. Calculate the rate of diffusion of ethanol and of water, in kg/m2-s. The latent heat of vaporization of the alcohol and water at 368 K can be estimated by the Pitzer acentric factor correlation (Reid et al., 1987)... 

A packed-bed distillation column is used to adiabatically separate a mixture of methanol and water at a total pressure of 1 atm. Methanol—the more volatile of the two components—diffuses from the liquid phase toward the vapor phase, while water diffuses in the opposite direction. Assuming that the molar latent heat of vaporization is similar for the two components, this process is usually modeled as one of equimolar counterdiffusion. At a point in the column, the mass-transfer coefficient is estimated as 1.62 x 10-5 kmol/m2-s-kPa. The gas-phase methanol mole fraction at the interface is 0.707, while at the bulk of the gas it is 0.656. Estimate the methanol flux at that point. 

A mixture of benzene and dichloroethane is used to test the efficiency of a packed column that contains 10 ft of packing and operates adiabatically at atmospheric pressure. The liquid is charged to the reboiler, and the column is operated at total reflux until equilibrium is established. At equilibrium, liquid samples from the distillate D and reboiler B, as analyzed by refractive index, give the following compositions for benzene Xo = 0.653, Xg = 0.298. 

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