Page 284 - Distillation theory

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

258 Trajectories of the Finite Columns and Their Design Calculation

2
1
1
2
+
separatrix sharp split regions Reg sh,R (S − S − N ) and Reg sh,R (S − S − N ).
+
s
s
s
sep,s
r
r
sep,r
r
At reflux bigger than minimum and at quasisharp separation with distributed com-
ponent at the set distribution of this component among the products, there is the
only one composition at the first tray above the feed cross-section expressed by
1
2
point x f −1 in the vicinity of separatrix sharp split region Reg sh,R (S − S − N )
+
sep,r
r
r
r
and the only one composition at the first tray below the feed cross-section
expressed by point x f in the vicinity of separatrix sharp split region Reg sh,R
sep,s
1
2
(S − S − N ). The less sharp is separation the farther from separatrix sharp
+
s s s
split trajectory bundles of the sections the composition points in the feed cross-
section are located.
Possible compositions at the trays adjacent to the feed cross-section from above
and below for any splits at the assumption about the linearity of separatrix trajec-
sh
sh
tory bundles and about sharp separation [x f −1 ] , [x f ] sh or (x f −1 ) , (x f ) sh can
lin lin lin lin
be determined from purely geometric considerations by means of solution of cor-
responding systems of linear equations.
At calculation by method “tray by tray” from the ends of the column for qua-
sisharp separation, the calculation section trajectories are “attracted” to separatrix
2
1
line S –S . At direct and indirect splits, calculation “tray by tray” should be carried
out in the upward or downward direction correspondingly.
At intermediate splits and splits with distributed component calculation, “tray
by tray” calculation should be carried out from the ends of the column. Design
calculation of necessary trays number in each section is carried out for the set of
imp imp
values of the summary concentrations of the impurity components x , x at the
f −1 f
first trays above and below the feed cross-section inside possible composition seg-
sh
sh
ments [x f −1 ] , [x f ] . The distribution of the impurity components in separation
lin lin
products is determined for each value from this set from the condition of join-
ing of section trajectories in the feed cross-section by means of systematic search
and execution of trial calculations from the ends of the column. The algorithm of
systematic search ensures guaranteed solution of the task. The mentioned set of
the values of the summary concentrations of the impurity components is limited
sh
) . That value from this
by the values in points (x ∞ ) , (x min sh ∞ sh min sh
) , (x ) , (x
f −1 lin f −1 lin f lin f lin
set, at which calculation tray numbers in the column (N r + N s ) are minimum, is
optimal.
Design calculation of three-section column of extractive multicomponent dis-
(1) (1)
tillation at one-component top product x and entrainer x can be carried out
D E
by method “tray by tray” upward with optimization by flow rates of entrainer and
reflux and by distribution of trays among sections. The general design calculation
of three-section column of extractive multicomponent distillation includes in the
same main stages as at the calculation of two-section column.
Design calculation of “Petlyuk columns” is carried out on the basis of the
algorithm of design calculation of two-section columns with optimization by dis-
tribution coefficient of pseudoproduct flow rates of the prefractionator, by excess
factors of reflux and by distribution of trays among sections in each two-section
column.
Design calculation of columns with side strippings is carried out on the basis
of the algorithm of design calculation of two-section columns and on the basis