Page 263 - Separation process engineering

c. Mole fractions have a major impact on K values only for systems with complex equilibrium
behavior.
d. All of the above.

2. The temperature loop is done before the flow rate loop because,

a. Temperatures cannot be constant in distillation.
b. Flow rates are often very close to constant in each section of the column.

c. A very good guess of flow rates can be made.
d. All of the above.

3. A good initial guess of the flow rates is to
a. Assume CMO.

b. Assume liquid and vapor flow rates are constant throughout the column.
c. Use a bubble-point calculation at the top and bottom of the column.

4. For a good initial guess of temperatures,
a. Assume CMO.

b. Use any arbitrary temperature.
c. Use a bubble-point calculation at the top and bottom of the column.

5. The mass balances are solved by developing a matrix that is then inverted. The matrix allows
one to have feed at,
a. Only one location in the column.

b. Two locations in the column.
c. Any stage within the column, but not the condenser and not the reboiler.

d. Any stage in the column, plus the reboiler and the condenser.
A5. The method described in this chapter is a simulation method because the number of stages and the
feed and withdrawal locations must all be specified. How do you determine if you have enough

stages for a design problem?

C. Derivations
C1. Suppose there is a liquid side stream of composition x and flow rate S removed from stage j in
j
j
Figure 6-3.

a. Derive the mass balance Eqs. (6-4) to (6-6) for this modified column.
b. Develop new energy balance equations. Derive new coefficients for Eq. (6-29b).
C2. Derive the mass balance expression for the matrix approach if there is a partial condenser instead

of a total condenser. Replace Eqs. (6-7) to (6-9).
C3. Show that the sum from i = 1 to C of the x in Eq. (6-17) = 1.0.
i,j

D. Problems
*Answers to problems with an asterisk are at the back of the book.

D1. For the first trial of Example 6-1 determine the component matrix for n-pentane and then use the
Thomas algorithm to find the n-pentane liquid flow rates leaving each stage. Compare your n-
pentane flow rates with the values reported in Example 6-1.

D2. We are separating a mixture of ethane, propane, n-butane and n-pentane in a distillation column