Distillation HW 4 Terry A Ring Chemical Engineering

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Distillation HW 4 Terry A. Ring Chemical Engineering University of Utah

Distillation HW 4 Terry A. Ring Chemical Engineering University of Utah

Feed αLK/HK=(y. LK/x. LK)/(y. HK/x. HK)

Feed αLK/HK=(y. LK/x. LK)/(y. HK/x. HK)

Difficulty of Separation when α↓ α↑

Difficulty of Separation when α↓ α↑

Problem Statement • Using distillation heuristics 3 (H 3 - remove greatest molar flows

Problem Statement • Using distillation heuristics 3 (H 3 - remove greatest molar flows early in sequence) and 4 (H 4 - sequence in order of decreasing relative volatilities) determine the most economical sequence in terms of the annual cost of the distillation sequence for this stream assuming a ≥ 98% overall recovery of each component with a mole percentage composition of ≥ 98%.

All Distillation Heuristics • 1 -Remove thermally unstable, corrosive, or chemically reactive components early

All Distillation Heuristics • 1 -Remove thermally unstable, corrosive, or chemically reactive components early in the sequence. • 2 -Remove final products one by one as distillates (implies direct Sequence) • 3 -Sequence separation points to remove, early in the sequence, those components with greatest molar % in the feed. • 4 -Sequence separation points in the order of decreasing relative volatility so that the most difficult splits are made in the absence of the other components • 5 -Sequence separation points to leave to last those separations that give the highest-purity products • 6 -Sequence separation points that favor near equimolar amounts of distillate and bottoms in each column.

Column Sequences • No. of Columns • Nc=P-1 P=5, Nc=4 • P= No. of

Column Sequences • No. of Columns • Nc=P-1 P=5, Nc=4 • P= No. of Products • No. of Possible Column Sequences • Ns=[2(P-1)]!/[P!(P-1)!] • • • P= No. of Products P=3, Nc=2, Ns=2 P=4, Nc=3, Ns=5 P=5, Nc=4, Ns=14 P=6, Nc=5, Ns=42 P=7, Nc=6, Ns=132 No. of Possible Column Sequences Blows up!

P = 4, Nc=3, Ns=5 Example • A/BCD, B/CD, C/D Direct • A/BCD, BC/D,

P = 4, Nc=3, Ns=5 Example • A/BCD, B/CD, C/D Direct • A/BCD, BC/D, B/C • AB/CD, A/B , C/D • ABC/D, A/BC, B/C • ABC/D, AB/C, A/B Indirect

Possible Distillation Sequences • How do I determine which sequence is the most cost

Possible Distillation Sequences • How do I determine which sequence is the most cost effective? ? ?

Marginal Vapor Rate • Marginal Annualized Cost~ Marginal Vapor Rate • Marginal Annualized Cost

Marginal Vapor Rate • Marginal Annualized Cost~ Marginal Vapor Rate • Marginal Annualized Cost proportional to • • • Reboiler Duty (Operating Cost) Reboiler Area (Capital Cost) Condenser Duty (Operating Cost) Condenser Area (Capital Cost) Diameter of Column (Capital Cost) • Vapor Rate is proportional to all of the above

Selecting Multiple Column Separation Trains • Minimum Cost for Separation Train will occur when

Selecting Multiple Column Separation Trains • Minimum Cost for Separation Train will occur when you have a Minimum of Total Vapor Flow Rate for all columns • Ri = 1. 2 Rmin • Vi=Di(Ri+1) • Vi= Vapor Flow Rate in a column • Di= Distillate Flow Rate • Ri =Recycle Ratio • Vtot=∑Vi • We may identify D as the desired distillate flow rate from the feed • Where do we get R or Rmin? ?

Rmin or R from Aspen/DSTWU

Rmin or R from Aspen/DSTWU

Feed αLK/HK=(y. LK/x. LK)/(y. HK/x. HK) (H 3 - remove greatest molar flows early

Feed αLK/HK=(y. LK/x. LK)/(y. HK/x. HK) (H 3 - remove greatest molar flows early in sequence) and (H 4 - sequence in order of decreasing relative volatilities) H-4 1 -A/BCDE 2 -BC/DE 3 -B/C 4 -D/E H-3 1 -ABCD/E 2 -ABC/D 3 -AB/C 4 -A/B INDIRECT H-3 1 -ABCD/E 2 -AB/CD 3 -A/B 4 -C/D H-3 1 -AB/CDE 2 -C/DE 3 -A/B 4 -D/E

Feed αLK/HK=(y. LK/x. LK)/(y. HK/x. HK) (H 3 - remove greatest molar flows early

Feed αLK/HK=(y. LK/x. LK)/(y. HK/x. HK) (H 3 - remove greatest molar flows early in sequence) and (H 4 - sequence in order of decreasing relative volatilities) H-4 1 -A/BCDE 2 -BC/DE 3 -B/C 4 -D/E H-3 1 -ABCD/E 2 -ABC/D 3 -AB/C 4 -A/B INDIRECT H-3 1 -ABCD/E 2 -AB/CD 3 -A/B 4 -C/D H-3 1 -AB/CDE 2 -C/DE 3 -A/B 4 -D/E

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