Binary flash distillation

Figure 1.8. Information flow, binary flash distillation calculation (a) Information recycle (b) Information flow...

To use Eq. (2-2) in the design of binary flash distillation systems, we must take a short tangent and first discuss binary vapor-liquid equilibrium (VLE). 

Figure 2-8. McCabe-Thiele diagram for binary flash distillation illustrated for Exanyle 2-1...

For binary flash distillation, the simultaneous procedure can be conveniently carried out on an enthalpy-composition diagram First calculate the feed enthalpy, hp, from Eq. t2-81 or Eq. (2=9b) then plot the feed point as shown on Figure 2-9 (see Problem 2-All. In the flash drum the feed separates into liquid and vapor in equilibrium Thus the isotherm through the feed point, which must be the T nun isotherm, gives the correct values for x and y. The flow rates, L and V, can be determined from the mass balances, Eqs. f2-51 and 2-61. or from a graphical mass balance. 

Derive and plot the operating equation for a binary flash distillation on a y-x diagram solve both sequential and simultaneous binary flash distillation problems... 

Bl. Think of all the ways a binary flash distillation problem can be specified. For example, we have usually specified F, z, T,jj.ynj, Pdrum- What other combinations of variables can be used (I have over 20.) Then consider how you would solve the resulting problems. 

C8. Show how to use a temperature conposition diagram to solve a binary flash distillation problem when the drum tenperature, feed mole fraction, drum pressure, and feed rate are specified. Show how to determine x, y, L, and V. 

In this section we look at a program for binary flash distillation to help make these statements concrete. First, since VBA is a macro, you must enable macros. 

F. Generalize. This procedure is similar to the one we used for binary flash distillation in Figure 2-9. Thus, there is an analogy between distillation calculations on enthalpy-conposition diagrams (Ponchon-Savarit diagrams) and extraction calculations on triangular diagrams. 

In the previous section we saw that the RT curve took the place of the equilibrium curve in binary flash distillation. For multiconponent flash distillation the y-x equilibrium curve is replaced by equilibrium expressions of the form y = K X and the combination of the operating equations and equilibrium are summed using Hxj = 1, Sy = 1, or Zy - ZX = 0. Since the operating equations for well-mixed permeators are similar to the operating equations for flash distillation fHoffman. 20031. if we can write the rate expression in the form y = Xj, then the mathematics to solve the permeation problem will be very... 

Integral condensation in which the liquid remains in equilibrium with the uncondensed vapour. The condensation curve can be determined using procedures similar to those for multicomponent flash distillation given in Chapter 11. This will be a relatively simple calculation for a binary mixture, but complex and tedious for mixtures of more than two components. 

As stated earlier, distillation is a widely used separation technique for liquid mixtures or solutions. The formation of these mixtures is straightforward, and is usually spontaneous, but the separation of a mixture into its separate constituents requires energy. One of the simplest distillation operations is flash distillation. In this process, part of the feed stream vaporizes in a flash chamber, and the vapor-liquid mixture, which is at equilibrium, is separated. The vapor is rich in the more volatile component, but complete separation is usually not achieved. A simple schematic showing the necessary equipment for flash distillation is given in Figure 10.3. We will illustrate the concepts by using a simple case of the flash distillation of a binary mixture. 

In this study, the phase equilibrium in the binary mixtures that are expected to be found in the flash distillation was modeled with the Predictive Soave-Redlich-Kwong (PSRK) equation of state [4], using modified molecular parameters r and q. Five binary ethanol + congener mixtures were considered for new yield values for parameters r and q. The congeners considered were acetic acid, acetaldehyde, furfural, methanol, and 1-pentanol. Subsequently, the model was validated with the water + ethanol binary system, and the 1 -pentanol + ethanol + water, 1-propanol + ethanol + water, and furfural + ethanol + water ternary systems. 

This work proposed the use of the Predictive Soave-Redlich-Kwong (PSRK) model to describe the phase equilibria in the flash distillation, using modified molecular parameters r and q for ethanol. In this way, the PSRK equation of state becomes more empirical, but keeps the predictive capabilities of the model. Furthermore, the introduction of new molecular parameters r and in the UNIFAC model gives more accurate predictions for the concentration of the congener in the gas phase for binary and ternary systems. 

This chapter discussed VLE and the calculation procedures for binary and multiconponent flash distillation. At this point you should be able to satisfy the following objectives ... 

D2. Two flash distillation chambers are hooked together as shown in the diagram. Both are at 1 atm pressure. The feed to the first drum is a binary mixture of methanol and water that is 55 mol% methanol. Feed flow rate is 10,000 kmol/h. The second flash drum operates with (V/F)2 = 0.7 and the liquid product composition is 25 mol% methanol. Equilibrium data are given in Table 2-7. 

Steam Distillation—Continuous Flash, Multicomponent or Binary... 

Batch with Constant Reflux Ratio, 48 Batch with Variable Reflux Rate Rectification, 50 Example 8-14 Batch Distillation, Constant Reflux Following the Procedure of Block, 51 Example 8-15 Vapor Boil-up Rate for Fixed Trays, 53 Example 8-16 Binary Batch Differential Distillation, 54 Example 8-17 Multicomponent Batch Distillation, 55 Steam Distillation, 57 Example 8-18 Multicomponent Steam Flash, 59 Example 8-18 Continuous Steam Flash Separation Process — Separation of Non-Volatile Component from Organics, 61 Example 8-20 Open Steam Stripping of Heavy Absorber Rich Oil of Light Hydrocarbon Content, 62 Distillation with Heat Balance,... 

Direct contact heat transfer, 185 Dispersion model, 560-562 first order reactions, 561 second order reactions, 562 Distillation, 371-457 batch, 390 binary, 379 column assembly, 371 flash, 375... 

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