Page 216 - Separation process principles 2

5.7 Degrees of Freedom and Specifications for Countercurrent Cascades 181

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Table 5.4 Typical Variable Specifications for Design Cases
Variable Specificationa
- --- - -
-
Case I, Case 11,
Component Number of
Recoveries Equilibrium
Unit Operation ND Specified Stages Specified
(a) Absorption 2N+2C+5 1. Recovery of 1. Number of
(two inlet one key stages
streams) component

(b) Distillation 2N+C+9 1. Condensate at 1. Condensate at
(one inlet saturation saturation
stream, total temperature temperature
condenser, 2. Recovery of 2. Number of
partial light key stages above
reboiler) component feed stage
3. Recovery of 3. Number of
heavy key stages below
component feed stage
4. Reflux ratio 4. Reflux ratio
(> minimum) 5. Distillate flow
5. Optimal feed rate
stageb
(c) Distillation (2N + C +6) 1. Recovery of 1. Number of
(one inlet light key stages above
stream, component feed stage
partial 2. Recovery of 2. Number of
condenser, heavy key stages below
partial component feed stage
reboiler, 3. Reflux ratio 3. Reflux ratio
vapor (> minimum) 4. Distillate flow
distillate 4. Optimal feed rate
only) stageb
Ch

(4 Liquid-liquid 2N +3C+8 1. Recovery of key 1. Number of
extraction component 1 stages above
with two 2. Recovery of key feed
solvents component 2 2. Number of
(three inlet stages below
streams) feed

(e) Reboiled 2N +2C $6 1. Recovery of 1. Number of
absorption light key stages above
(two inlet component feed
streams) 2. Recovery of 2. Number of
heavy key stages below
component feed
3. Optimal 3. Bottoms flow
feed stageb rate

(continued)