Distillation Column Design & Operation: Graphical Analysis and Diagrams
Understand the design and operation of a distillation column using graphical analysis, PFD, McCabe-Thiele diagram, x-y diagram, and temp-comp diagram for a process converting E to M. Learn about stages, feed stage location, L/V in stripping and rectifying sections, and temperature in the cooler with detailed diagrams and explanations.
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Calculation Session 12 Exercise 4.72 Created by: Gina Johnson ( 14) Edited by: Katrina Curtiss ( 15), McKenzie Hubert ( 16), Amy Penick ( 17), Natalie Goh ( 17), Doris Chen ( 18), Olivia Young ( 19), Emily Spiek ( 21), Ailen Lao ( 23), Austin Kwan ( 24), and Ashlyn Dumaw ( 25)
Goal: Describe the design and operation of a distillation column using graphical analysis PFD for a process that converts E to M McCabe-Thiele diagram for the distillation column x-y and temp-comp diagram for the mixture Info: Where to start: Understand the given process Utilize different diagrams for different purposes!
Process Converting E to M condenser 98% M 50.% E 50.% M E 52 mol/min reactor E M cooler 98% E purge (0.001%) 98% E boiler
A) # of Stages & Feed Stage Location 1 12 11 0.9 Always use the equilibrium line to count stages! 10 0.8 9 8 0.7 11 stages 7 0.6 yM 6 0.5 Slope of the operating line changes at the feed stage 5 0.4 0.3 4 Stage 5 0.2 3 0.1 2 0 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
B) L/V in the Stripping Section 1 0.9 Locate the stripping section Find specific endpoints 0.8 0.7 (0.02, 0.02) (0.44, 0.56) 0.6 yM 0.5 (0.44, 0.56) 0.4 Calculate slope 0.3 0.2 0.1 (0.02, 0.02) 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
B) L/V in the Rectifying Section (0.98, 0.98) 1 0.9 Locate the rectifying section Find specific endpoints 0.8 0.7 (0.44, 0.56) (0.98, 0.98) 0.6 yM 0.5 (0.44, 0.56) 0.4 Calculate slope 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
B) Temperature in the Cooler 1 0.9 Composition of cooler? Feed stage at equilibrium 0.8 0.7 A x = 0.37 y = 0.60 B 0.6 yM 0.5 C 0.4 Temperature Temp-comp diagram! 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
B) Temperature in the Cooler 90 Composition of cooler? Feed stage at equilibrium 85 temperature ( C) x = 0.37 y = 0.60 80 79 C Temperature Temp-comp diagram! 75 79 C 70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM, yM
C) Flow Rate of the Product Stream condenser 98% M 50.% E 50.% M E 52 mol/min rate in = rate out reactor E M 1 mol of E 1 mol of M 52 mol/min cooler 98% E purge (0.001%) 98% E boiler
D) Flow Rate of Vapor to the Condenser condenser 98% M 50.% E 50.% M E 52 mol/min reactor E M cooler 98% E purge (0.001%) 98% E boiler
D) Flow Rate of Vapor to the Condenser Mass balance V = L + 52 condenser Relationship between L and V? V 98% M (from Part B: rectifying section) 52 mol/min L 50.% E 50.% M E 52 mol/min V = 0.78V + 52 reactor E M cooler V = 240 mol/min 98% E purge (0.001%) 98% E boiler
E) Distillation Operation with 40% Feed 1 Reactor output: 40% (feed to distillation column) 0.9 0.8 0.7 Feed stage is within constraints! 5 0.6 yM 0.5 Will this operating temperature still work? 0.4 0.20 xM 0.40 0.40 yM 0.62 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
E) Distillation Operation with 40% Feed 90 Reactor output: 40% (feed to distillation column) 85 Feed stage is within constraints! temperature ( C) 80 Will this operating temperature still work? 79 C 75 No change in operation! 70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM, yM
F) Distillation Operation with 30% Feed 1 Reactor output: 30% (feed to distillation column) 0.9 0.8 0.7 Feed stage is not within constraints 5 0.6 yM 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
F) Distillation Operation with 30% Feed 90 Reactor output: 30% (feed to distillation column) 85 Feed stage is not within constraints temperature ( C) 80 Operating temperature no longer works 79 C 75 70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM, yM
F) Distillation Operation with 30% Feed Constraints: Feed enters at stage 5 Feed is 30% M Feed is liquid and vapor xM = 0.3 could be a fulcrum Bottoms is 2% M Distillate is 98% M Must have 11 stages Technique: Guess & Check
F) Distillation Operation with 30% Feed 5 11 1 Locate feed constraint region Locate targets for bottoms/distillate 0.9 0.8 Draw operating lines, intersecting near feed constraint region 0.7 L/V Ratios: 0.6 yM 5 Stripping: 1.52 Rectifying: 0.82 Count off stages Total stages: 11 0.5 0.4 Feed M Composition: Calculate L/V ratios for stripping and rectifying sections 0.3 x = 0.26 y = 0.47 0.2 0.1 Locate feed stage, find composition Feed stage: stage 5 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
F) Distillation Operation with 30% Feed 90 Locate equilibrium from feed on temp-comp diagram 85 Locate 30% feed temperature ( C) 81 C Find operating temperature 80 L/V Ratios: 81 C 75 Stripping: 1.52 Rectifying: 0.82 70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM, yM
F) Minimum M Reactor Output 11 1 10 9 L/V = 1 Total reflux operation! Operating line = x-y line 0.9 8 0.8 0.7 7 0.6 Count backwards to feed stage 5 yM L/V = 1 0.5 Locate equilibrium concentration 6 0.4 Feed: 0.3 5 x = 0.07 y = 0.18 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM
F) Minimum M Reactor Output 90 Locate equilibrium concentrations on temp-comp diagram 85 C 85 Operating temperature: 85 C temperature ( C) 80 Fulcrum at the minimum of the lever (limiting condition) 75 7 mol% M Feed composition: 7 mol% M 70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 xM, yM (x = 0.07, y = 0.18)
Key Takeaways Count stages on the equilibrium line Find liquid/vapor flow rates from the slope of the stripping and rectifying lines (L/V ratio) Don t neglect mass balances! Use temperature-composition diagrams to evaluate changes in feed composition Guess & check is another method of analysis
