Distillation example design

The optimal robust controller designed with one of the new synthesis techniques is generally not of a form that can be readily implemented. The main benefit of the new synthesis procedure is that it allows the designer to establish performance bounds that can be reached under ideal conditions. In practice, a decentralized (multiloop) control structure is preferred for ease of start-up, bumpless automatic to manual transfer, and fault tolerance in the event of actuator or sensor failures. Indeed, a practical design does not start with controller synthesis but with the selection of the variables that are to be manipulated and measured. It is well known that this choice can have more profound effects on the achievable control performance than the design of the controller itself. This was demonstrated in a distillation example [17, 18] in which a switch from reflux to distillate flow as the manipulated variable removes all robustness problems and makes the controller design trivial. 

Determine the efficiency in the upper portion of the DCB distillation column designed in the preceding example. Relative volatility for the system is 3.6. 

For example, destructive distiiiation of wood oives methanol (wood alcohol ), wood tar or pitch and charcoal. Destructive distillation of bituminous coal gives coal gas, coal tar, coal tar pitch and coke. These products are described in Vol 3 of Encycl, pC379 Molecular distillation is designed for separating compounds of extremely high mole-... 

Example 14.3.3 Ethylbenzene-Styrene Distillation Column Design... 

Since few liquid mixtures are ideal, vapor-liquid equilibrium calculations are somewhat more complicated than for the cases in the previous section, and the phase diagrams for nonideal systems can be more structured than Figs. 10.1-1 to 10.1-6. These complications arise from the (nonlinear) composition dependence of the species activity coefficients. For example, as a result of the composition dependence of yt, the vapor-liquid equilibrium pressure in a fixed-temperature experiment will no longer be a linear function of mole fraction, so that no.nideal solutions exhibit deviations from Raoult s law. However, all the calculational methods discussed in the previous section for ideal mixtures, including distillation column design, can be used for nonideal mix-, tures, as long as the composition dependence of the activity coefficients is taken into account. 

EXAMPLE DESIGN OE HYBRID SYSTEMS USING DISTILLATION MEMBRANE PROCESSES 315... 

Figure 7.36b. The total feed to column 1, F, operating at the lower pressure, P, is the sum of the fresh feed, F, whose composition is richer in A than the azeotrope, and the distillate, D2, whose composition is close to that of the azeotrope at P2, and which is recycled from column 2 to column 1. The compositions of D2, and consequently, F[, are richer in A than the azeotropic composition at P,. Hence, the bottoms product, B], that leaves column 1 is nearly pure A. Since the distillate, Dj, which is slightly richer in A than the azeotropic composition, is less rich in A than the azeotropic composition at P2, when it is fed to column 2, the bottoms product, B2, is nearly pure B. Yet another example is provided by Robinson and Gilliland (1950) for the dehydration of ethanol, where the fresh-feed composition is less rich in ethanol than the azeotrope. In this case, ethanol and water are removed as bottoms products also, but nearly pure B (water) is recovered from the first column and A (ethanol) is recovered from the second. Similar pressure-swing distillations are designed to separate maximum-boiling, binary azeotropes, which are less common.

Formulation of process and control design optimization for the binary Distillation Example... 

Progress of the Iterations for the multiperiod MIDO design problem in the Distillation Example... 

These types of reactors are becoming increasingly common in chemical process industries. They are used to drive away one of the products that inhibit the progress of the reaction via an equilibrium limitation imposed by the Le Chatelier principle. Once the product is removed, the equilibrium shifts to the right and 100% conversions at low temperatures are possible. The key requirement is that there should be sufficient boiling point difference between the products and the reactants such that one of the products can be selectively removed by distillation. The design principles and selected examples are presented in Chapter 14. 

As an example let us consider a binary distillation column designed to separate water from nitric acid. Top composition is controlled by mampulating reflux (see Figure 20.1) while the base composition is controlled by adjusting steam flow. The following transfer functions were derived via the stepping technique ... 

In the next six Examples we use Raoult s law in some typical VLE problems including applications to distillation column design. 

We proceed now to use bubble and dew point calculations in the following Examples that represent typical applications of vapor-liquid equilibrium to distillation column design. 

One distinguishes preparatory distillations that are designed to separate the fractions for subsequent analysis from non-preparatory analytical distillations that are performed to characterize the feed itself. For example, the distillation curve that gives the recovered volume or weight as a function of the distillation temperature characterizes the volatility of the sample. 

Reflux Distillation Unit. The apparatus shown in Fig. 38 is a specially designed distillation-unit that can be used for boiling liquids under reflux, followed by distillation. The unit consists of a vertical water-condenser A, the top of which is fused to the side-arm condenser B. The flask C is attached by a cork to A. This apparatus is particularly suitable for the hydrolysis of esters (p. 99) and anilides (p. 109), on a small scale. For example an ester is heated under reflux with sodium hydroxide solution while water is passed through the vertical condenser water is then run out of the vertical condenser and passed through the inclined condenser. The rate of heating is increased and any volatile product will then distil over. 

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