Page 280 - Distillation theory

P1: JPJ/FFX P2: JMT/FFX QC: FCH/FFX T1: FCH
0521820928c07 CB644-Petlyuk-v1 June 11, 2004 20:18

254 Trajectories of the Finite Columns and Their Design Calculation

LN
W

r 4

s 4
r 3
HN

s 3
r 2
steam LD
s 2

r 1
crude steam HD
s 1

steam residue
Figure 7.16. Calculation of crude oil column with side strip-
pings using pinch analysis. LN, light naphtha; HN, heavy
naphtha; LD, light diesel; HD, heavy diesel.

steam stripping, and a mixed variant is determined from economic considerations
by means of construction of “temperature-enthalpy” curves for heat sources and
heat sinks (pinch method).
The choice between the absence and availability of liquid flow from one two-
section column into the other and the determination of optimal flow rate are
performed using the same method. Such optimization simultaneously concerns
the distillation column and the system of heat exchangers. As a result of such
optimization in different two-section columns entering into the column with side
strippings,itturnsouttobeprofitabletousethedifferentmodification(reboilersor
steam stripping, availability or absence of liquid flow between columns) (Fig. 7.16).
Special requirements to the refining property make necessary a preliminary
step to the design procedure: the determination of the set of pseudocomponents
specified by their normal bubble temperatures (at 1 atmosphere) in each product,
and the determination of admissible concentration of impurity components in
each product.
The general algorithm of design calculation of the column with side strippings
includes the following stages (the algorithm for columns with side rectifiers in-
cludes similar stages):

1. Determination of the sets of product pseudocomponents and of admissible
concentrations of impurity pseudocomponents in each product.
2. Calculation of the mode of minimum reflux in the first two-section
column.