Page 117 - Separation process engineering

are the two runs for part a essentially identical, but runs d and e give very different results?
9. Switch to a Ternary Problem

Remove any leftover dialog boxes or screens. Go to Data in the menu and click on components. Use
Edit to delete the two rows. You may need to click on the row to obtain the Delete Row command in
edit. Then add propane, n-butane, and n-pentane as the three components. Using the menu, go to Data
Properties and change the choice of VLE model. Peng-Robinson is a good choice for hydrocarbons. Use
the Next button and input the mole fractions (propane 0.2, n-butane 0.3 and n-pentane 0.5). Keep
fraction vaporized at 0.4 and pressure of 1.0 bar for now. Click on the Next button and do the run when
ready. Record your results (component flow rates, T, y and x) or print out the report. If you have time,

try different fraction vaporized, different feed compositions, and different temperatures.
10. What Does It All Mean?
Reflect on the meaning of your results for both the binary and the ternary flash systems.

a. Binary: How are the compositions of the vapor and liquid streams from the flash system related?
What is the role of the fraction vaporized? How can you do the calculation by hand?

b. Ternary: How are the compositions of the vapor and liquid streams from the flash system related?
What is the role of the fraction vaporized? How can you do the calculation by hand?
Note that the calculation methods used for hand calculations will be different for the binary and ternary
systems since the equilibrium data are available in different forms (graphically for the binary and
DePriester chart for the ternary).

11. Finish. Exit Aspen Plus and log out. There is no formal lab report for this lab.

Lab 2. Find Equilibrium Data before Lab
For part 1a, use Flash2 with the Peng-Robinson VLE correlation. For part 1b, use Flash3 and find a
VLE correlation that fits the data. For part 1c, use NRTL and Flash3. Use F = 1.0 kmol/h for all cases.
Compare the predictions of Analysis with equilibrium data from the literature.

Part 1. Simulations
a. The feed is 45 mol% n-butane and 55 mol% n-hexane at 1.0 atm. The feed is a saturated liquid
(vapor fraction = 0.0). The drum pressure is 0.8 atm. Do for V/F in the drum = 0.2, 0.4, 0.6, and
0.8 (four runs). Report feed temperature, Q, drum T, y, x, V, L.

b. The feed is 55 mol% benzene and 45 mol% water at 5.0 atm and is a saturated liquid. Drum
temperature is 120°C. Do for V/F in the drum = 0.2, 0.4, 0.6, and 0.8 (four runs). Note: Delete
the block for Flash2, redraw with Flash3, and then reconnect streams and add another liquid
product. Be sure to list valid phases as Vapor-liquid-liquid in both SETUP and ANALYSIS.
Use the y-x diagram to explain your results. Report VLE correlation used, feed temperature,
drum pressure, Q, and compositions of all three phases for each V/F.

c. Feed is initially 60 mol% furfural (a cyclic alcohol) and 40 mol% water at 1.0 atm and 50°C.
The drum operates at 105°C and V/F = 0.4. Use NRTL, Flash3, and list valid phases as Vapor-
liquid-liquid. With 40 mol% water, the two liquid phases should be identical, which means
there is only one liquid phase. Try 60, 70, 90, and 99 mol% water in the feed. Generate a y-x
diagram with ANALYSIS, and use it to explain your results. Report the drum pressure, Q, and
the compositions of all three phases for each feed composition.

Part 2. Design.
Before starting, delete Flash 3 and the second liquid product, add Flash2, and connect streams. List
valid phases as Vapor-liquid in SETUP. Feed is 100 kmol/h that is 3 mol% methane, 25 mol% n-