Page 269 - Distillation theory

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0521820928c07 CB644-Petlyuk-v1 June 11, 2004 20:18

7.4 Design Calculation of Extractive Distillation Columns 243

Table 7.3. Comparison of the algorithms of design and simulation

Item Design Simulation
1 N r and N s should not be set. N r and N s should be set.
2 Possibility of the chosen split for Possibility of the chosen split is not
azeotropic mixtures is determined determined.
preliminarily during the process of
calculation.
3 N r and N s are determined during the Possibility of obtaining of products of a
process of calculation. set purity at set N r and N s is not
determined.
4 The solution of the task is always The solution of the task can be
achieved. unachieved, even if the chosen split
and the set purity of products are
feasible, for the reason of absence of
convergence of iteration process.
5 Interference of the user in the A change in the estimated profiles of
process of calculation is not temperatures, compositions, and flow
required. rates and other user-defined
parameters of calculation process can
be required to solve the task.
6 Minimum input information is Large amounts of input information can
required to solve the task. be required to solve the task.
7 Designed separation process is It is necessary to carry out a big volume
optimal in expenditures. of calculations to design the
separation process optimal in
expenditures.
8 See item 4. No information about the reasons why
the task was not solved is available.
9 The user can obtain the entire The entire information about the
information (part of it visual) peculiarities of projected separation
about the peculiarities of designed process is not available.
separation process.
10 No participation of qualified users is Participation of qualified users is
required to perform calculations. required to carry out calculations.
11 Conceptual designing is short. Conceptual designing is long.

7.3.5. Advantages of New Design Algorithms
The described new algorithms of design calculation for different splits have great
advantages compared with the known simulation algorithms. These advantages
are listed in Table 7.3.

7.4. Design Calculation of Extractive Distillation Columns

The general approach to design calculation of extractive distillation columns is
similar to the approach applied for two-section columns. We use our notions about
the structure of intermediate section trajectory bundles (see Sections 6.4 ÷ 6.6),
about possible compositions at the trays adjacent to the feed cross-section from
above and below (see Section 7.2), and about possible directions of calculation