Column distillation design problems

For specific final performance sizing of a distillation column using Norton s Intalox structured packing the designer is referred to the manufacturer s technical representatives, and should not assume the preliminary results obtained from any manufacturer s bulletin included here will necessarily serve as a final design. As a preliminary examination of a design problem (used by permission of Norton Chemical Process Products) ... 

This will be possible for only a few practical design problems. The technique is illustrated in Example 1.1, and in the derivation of the formula for optimum pipe diameter in Chapter 5. The determination of the economic reflux ratio for a distillation column, which is discussed in Volume 2, Chapter 11, is an example of the use of a graphical procedure to find the optimum value. 

All the obstacles in the path of distillation progress, however, were not equipment fabrication and design problems. It was discovered very early in the running of sour crudes that the shell still corroded severely at the vapor-liquid interface line and in that portion of the shell in contact with vapors. At the same time severe corrosion in pipe stills and tube stills, along with overheating and coking, resulted in expensive equipment failures. These problems started metallurgists on a chain of developments which produced the corrosion- and heat-resistant alloys used in modern oil heaters and the alloy liners used in distillation columns. 

Part 3 of this book presents a number of major developments and applications of MINLP approaches in the area of Process Synthesis. The illustrative examples for MINLP applications, presented next in this section, will focus on different aspects than those described in Part 3. In particular, we will consider the binary distillation design of a single column, the retrofit design of multiproduct batch plants, and the multicommodity facility location/allocation problem. 

Van Dongen, D. B., and Doherty, M. F. Design and Synthesis of Homogeneous Azeotropic Distillations. 1. Problem Formulation for a Single Column, Ind. Eng. Chem. Fundam. 24, 454-463 (1985). 

The distillation column described in Problem 6.2 is to be designed with the provision that the hot process stream will supply only... 

A distillation column was designed to separate a 1000 kmol/h binary mixture of 50% mole component 1 to produce a distillate of 95% mole component 1 and to recover in this product 90% of component 1 in the feed. The column was constructed to handle a liquid traf-flc of 2500 kmol/h. Due to upstream process changes, the column feed composition dropped to 40% mole component 1 at the same total rate of 1000 kmol/h. While maintaining the required 95% distillate composition and operating at optimum performance, what recovery of component 1 is achievable, and can the column handle the required liquid traffic The column operates with a partial condenser at 100 kPa. The feed is a saturated liquid at feed tray conditions. Thermodynamic data given in Problem 6.1 may be used in this problem. 

A distillation column is designed to separate a 70-30 mole percent mixture to produce a distillate product with 97.5% mole component 1 and a bottoms product with 20% mole component 1. The column has a partial condenser and reboiler and operates at 1 atm pressure. Determine the required number of theoretical trays and the optimum feed location at a reflux ratio of 1.5. Calculate the recovery of component 1 in the distillate. Calculate the recovery at the same distillate purity and reflux ratio if the feed is introduced three trays below the optimum feed tray. Use thermodynamic data from Problem 6.1. 

Many of the distillations of industry involve more than two components. While the principles established for binary solutions generally apply to such distillations, new problems of design are introduced which require special consideration. An important principle to be emphasized is that a single fractionator cannot separate more than one component in reasonably pure form from a multicomponent solution, and that a total of C - 1 fractionators will be required for complete separation of a system of C components. Consider, for example, the continuous separation of a ternary solution consisting of components A, B, and C, whose relative volatilities are in that order (A most volatile). In order to obtain the three substances in substantially pure form, the following two-column scheme can be used. The first column is used to separate C as a residue from the rest of the solution. This residue is necessarily contaminated with a small amount of B and an even smaller amount of A. The distillate, which is necessarily contaminated with a small amount of C, is then fractionated in the second column to give nearly pure A and B. 

Van Dongen, D.B. and M.F. Doherty, Design and synthesis of homogeneous azeotropic distillations. 1. Problem formulation for a single column. Industrial Engineering Chemistry, Fundamentals, 1985, 24(4) 454 463. 

The combination of effluent clean-up and solvent distillation should be considered in the design of a stream stripper. For water-miscible solvents that do not form water azeotropes, such as methanol and acetone, the conversion of the stripping column into a fractionating column presents few problems (Fig. 3.4). Similarly, the solvents that are sparingly water miscible can be passed through a decanter and the water phase returned to the stripper feed. 

The distillation column smdied is based on a system that presents challenging design problems because of the severe nonlinearity of the phase equUibrium. The ternary system is water, acetic acid, and formic acid. The physical property package UNIQ-HOC is used in the Aspen simulations, which accounts for the dimerization of acetic acid in the vapor phase. 

In design problems, the desired separation is set, and a column is designed that will achieve this separation. For binary distillation we would usually specify the mole fraction of the more volatile component in the distillate and bottoms products. In addition, the external reflux ratio, L D in Figure 4-6. 

To illustrate, consider a typical design problem for a binary distillation column such as the one illustrated in Figure 3-8. We will assume that equilibrium data are available at the operating pressure of the column. These data are plotted as shown in Figure 4-4. At the top of the column is a total condenser. As noted in Chapter 3 in Eq. (3=7), this means that yi = = Xq. The vapor leaving the first stage is in equilibrium... 

For very complex mixtures, the entire distillation design can be done using the Older-shaw column by changing the number of trays and the reflux rate until a combination that does the job is found. Since the commercial column will have an overall efficiency equal to or greater than that of the Oldershaw column, this combination will also work in the commercial column. This approach eliminates the need to determine vapor-liquid equilibrium (VLE) data (which maybe quite costly), and it also eliminates the need for complex calculations. The Oldershaw column also allows one to observe foaming problems TKister. 19901. 

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