Sol_HW7_v6__Oct_21_7_PM_KS - Chemical Engineering 150B-...

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Chemical Engineering 150B- Fall 2005 Problem Set #7 Solutions Problem 1. (15 Points) Consider an adiabatic equilibrium flash with a high pressure liquid feed that is separated into liquid and vapor streams at lower pressure. The variables are all as indicated in the following figure: There are C components in equilibrium, and thus all of your answers to the below questions will have C as part of the expression. (a) Both extensive and intensive variables are listed in the figure. Express the total number of variables in terms of C. (b) Write all the independent equations that relate the variables. You may simply write your answer as "one energy balance, three vapor-liquid equilibrium equations, etc." (c) Express the total number of equations in terms of C. (d) Determine the number of degrees of freedom in terms of C. (e) What variables in (a) would you think to be most likely as being fixed by the process for which you are designing the flash unit?
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Note to the Graders: There are multiple ways to solve this problem. However, at the end of the problem, they should most likely have to specify the feed rate, the feed T, the feed P, C – 1 feed mole fractions, the exit pressure, and possibly the heating rate depending upon how they included the energy balance in the above analysis. Problem 2. (20 Points) Saturated liquid feed, of F= 40 mol/h, containing 50 mol% A in B is supplied continuously to the apparatus shown below: The condensate from the condenser is split so that half of it is returned to the still pot. The still pot can be assumed to be an equilibrium stage. (a) If heat is supplied at such a rate that W = 30 mol/h and α = 2, as subsequently defined below, what will be the composition of the overhead and bottom product? 2 pt 7 pt 2 pt 2 pt 2 pt
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(b) If the operation is changes so that no condensate is returned to the still pot and W = 3D as before, what will be the composition of the products? Problem 3. (30 Points) The relative volatility, α , of benzene to toluene at 1 atm is 2.5. Using this fact, construct an x-y diagram for this system at 1 atm. Repeat the construction using the vapor pressure data for both benzene and toluene from the tables below. You may find Raoult’s and Dalton’s law useful. Also, construct a T-x-y diagram. You may also find the following version of Antoine equation useful for fitting your vapor pressure data so you can determine the value at various temperatures: 2 1 3 exp s i k Pk kT =− + , 5 pt 5 pt 3 pt 3 pt 4 pt
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where s i P is the vapor pressure of component i at temperature T ( o C) and the k’s are positive constants of the following values: Toluene (B) Benzene (A) k 1 17.27406 k 1 15.56451 k 2 3896.3 k 2 2602.34 k 3 255.67 k 3 211.271 (a) Verify that the Antoine equation adequately fits the experimental data using the k’s given in the above table, i.e., make a plot of the vapor pressure versus temperature and plot the Antoine equation as well. Note that for the rest of the problem, you will use the Antoine equation for calculations instead of the experimental data.
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This homework help was uploaded on 04/02/2008 for the course CHEM 150b taught by Professor Bell during the Spring '08 term at University of California, Berkeley.

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Sol_HW7_v6__Oct_21_7_PM_KS - Chemical Engineering 150B-...

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