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    Copyright
    Preface
    Acknowledgments
    About the Author
    Nomenclature
    Ch. 1. Introduction to Separation Process Engineering
    Ch. 2. Flash Distillation
    Basic Method of Flash Distillation
    Form and Sources of Equilibrium Data
    Graphical Representation of Binary VLE
    Binary Flash Distillation
    Multicomponent VLE
    Multicomponent Flash Distillation
    Simultaneous Multicomponent Convergence
    Three-Phase Flash Calculations
    Size Calculation
    Using Existing Flash Drums
    Summary—Objectives
    References
    Homework
    Chapter 2 Appendix A. Computer Simulation of Flash Distillation
    Assignment to Hand In
    Chapter 2 Appendix B. Spreadsheets for Flash Distillation
    Ch. 3. Introduction to Column Distillation
    Ch. 4. Binary Column Distillation: Internal Stage-by-Stage Balances
    Ch. 5. Introduction to Multicomponent Distillation
    Ch. 6. Exact Calculation Procedures for Multicomponent Distillation
    Ch. 7. Approximate Shortcut Methods for Multicomponent Distillation
    Ch. 8. Introduction to Complex Distillation Methods
    Ch. 9. Batch Distillation
    Ch. 10. Staged and Packed Column Design
    Ch. 11. Economics and Energy Conservation in Distillation
    Ch. 12. Absorption and Stripping
    Ch. 13. Liquid-Liquid Extraction
    Ch. 14. Washing, Leaching, and Supercritical Extraction
    Ch. 15. Introduction to Diffusion and Mass Transfer
    Ch. 16. Mass Transfer Analysis for Distillation, Absorption, Stripping, and Extraction
    Ch. 17. Introduction to Membrane Separation Processes
    Ch. 18. Introduction to Adsorption, Chromatography, and Ion Exchange
    Appx. A. Aspen Plus Troubleshooting Guide for Separations
    Appx. B. Instructions for Fitting VLE and LLE Data with Aspen Plus
    Appx. C. Unit Conversions and Physical Constants
    Appx. D. Data Locations
    Answers to Selected Problems
    Index
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    Homework

    A. Discussion Problems

    A1.In Figure 2-9 the feed plots as a two-phase mixture, whereas it is a liquid before introduction to the flash chamber. Explain why. Why can’t the feed location be plotted directly from known values of TF and z? In other words, why does hF have to be calculated separately from an equation such as Eq. (2-9b)?
    A2.Can weight units be used in the flash calculations instead of molar units?
    A3.Explain why a sequential solution procedure cannot be used when Tfeed is specified for a flash drum.
    A4.In the flash distillation of salt water, the salt is totally nonvolatile (this is the equilibrium statement). Show a McCabe-Thiele diagram for a feed water containing 3.5 wt % salt. Be sure to plot weight fraction of more volatile component.
    A5.Develop your own key relations chart for this chapter. That is, on one page summarize everything you would want to know to solve problems in flash distillation. Include sketches, equations, and key words.
    A6.In a flash drum separating a multicomponent mixture, raising the pressure will:

    1. increase the drum diameter and increase the relative volatilities.

    2. increase the drum diameter and cause no change to the relative volatilities.

    3. increase the drum diameter and decrease the relative volatilities.

    4. not change the drum diameter but increase the relative volatilities.

    5. not change the drum diameter and not change the relative volatilities.

    6. not change the drum diameter but decrease the relative volatilities.

    7. decrease the drum diameter and increase the relative volatilities.

    8. decrease the drum diameter and not change to the relative volatilities.

    9. decrease the drum diameter and decrease the relative volatilities.

    A7.

    1. What would Figure 2-2 look like if we plotted y2 vs. x2 (i.e., plot less volatile component mole fractions)?

    2. What would Figure 2-3 look like if we plotted T vs. x2 or y2 (less volatile component)?

    3. What would Figure 2-4 look like if we plotted H or h vs. y2 or x2 (less volatile component)?

    A8.For a typical straight-chain hydrocarbon, does:

    1. K increase, decrease, or stay the same when temperature is increased?

    2. K increase, decrease, or stay the same when pressure is increased?

    3. K increase, decrease, or stay the same when mole fraction in the liquid phase is increased?

    4. K increase, decrease, or stay the same when the molecular weight of the hydrocarbon is increased within a homologous series?

    Note: It will help to visualize the DePreister chart in answering this question.

    A9.In the vapor-liquid equilibrium data for methanol-water, if the methanol vapor mole fraction is 0.60, what is the methanol liquid mole fraction?
    A10.Is there an azeotrope in the methanol-water system at a pressure of 1.0 atmospheres?
    A11.The equilibrium K value is usually defined as

    1. K = y/x, where y and x are weight fractions of the component in the vapor and liquid phases, respectively.

    2. K = x/y, where x and y are weight fractions of the component in the liquid and vapor phases, respectively.

    3. K = y/x, where y and x are mole fractions of the component in the vapor and liquid phases, respectively.

    4. K = x/y, where x and y are mole fractions of the component in the liquid and vapor phases, respectively.

    A12.In a sequential solution procedure for flash distillation,

    1. the mass balances, equilibrium relationships, and energy balances are solved simultaneously.

    2. the mass balances and equilibrium relationships are solved first, and then the energy balance is solved.

    3. the energy balance is solved first, and then the mass balances and equilibrium relationship are solved.

    A13.Calculations are simpler for multicomponent flash distillation if the feed flow rate and mole fractions of the feed are specified plus

    1. the drum pressure and feed temperature.

    2. the drum temperature and feed temperature.

    3. the drum temperature and the drum pressure.

    4. the feed temperature and feed pressure.

    5. all of the above; they are all equally difficult.

    A14.The Rachford-Rice equation,

    1. has excellent convergence properties for flash distillation.

    2. was derived from the mass balances, equilibrium relationships, and energy balances.

    3. is only useful for binary flash distillation.

    4. all of the above.

    5. none of the above.

    A15.Use the DePriester chart:

    1. What is the K value of propane at 240 kPa and 25°C?

    2. What is the normal boiling point of n-pentane?

    A16.Flash distillation is usually operated adiabatically. Where does the energy to vaporize part of the feed come from?

    B. Generation of Alternatives

    B1.Think of all the ways a binary flash distillation problem can be specified. For example, we have usually specified F, z, Tdrum, pdrum. What other combinations of variables can be used? (I have over 20.) Then consider how you would solve the resulting problems.
    B2.An existing flash drum is available. The vertical drum has a demister and is 4 ft in diameter and 12 ft tall. The feed is 30 mol% methanol and 70 mol% water. A vapor product that is 58 mol% methanol is desired. We have a feed rate of 25,000 lbmol/h. Operation is at 1 atm pressure. Since this feed rate is too high for the existing drum, what can be done to produce a vapor of the desired composition? Design the new equipment for your new scheme. You should devise at least three alternatives. Data are given in Problem 2.D1.
    B3.In principle, measuring VLE data is straightforward. In practice, actual measurement may be very difficult. Think of how you might do this. How would you take samples without perturbing the system? How would you analyze for the concentrations? What could go wrong? Look in your thermodynamics textbook for ideas.


      

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