Evaluation of Heat‐integrated Distillation Schemes

Mansour EmtirLibyan Petroleum Institute, P.O. Box 6431 Tripoli, Libya

EMINENT2 Workshop, 5 - 6 May 2008, Veszprem, Hungary

Outlines

• Background

• Objectives

• Studied distillation schemes

• Case study

• Optimization procedure

• Results & discussion

• Conclusions

2

Background

Distillation is used for (~90%) of all fluid separation in the chemical industry

Distillation is an energy consuming process, it consumes ~13% of the energy needed by the whole chemical industry

Tighter environmental regulations, higher energy costs and growing competition have increased the demand for more efficient distillation system

3

Objectives

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Examine different heat integration modes for the separation of ternary mixture

Comparison based on shortcut method, pinch analysis and rigorous simulation

Evaluate the effect of feed conditions on heat integration

Studied distillation schemes

Direct sequence (D) base case

Indirect sequence (I)

5

Studied distillation schemes (Cont.)

P1 > P2 P2 > P1 

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Forward heat integration,direct sequence (DQF)

Backward heat integration,direct sequence (DQB)

Studied distillation schemes (Cont.)

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Col.1 Col.2ABC

A

B

C

V21

L21

L 12

S

Q

B

L D

V

R=L/ D

SR

BR=V/ B

V12

Petlyuk column (SP)

Studied distillation schemes (Cont.)

P1 > P2 P2 > P1 

8

Sloppy sequence, forward heat integration (SQF)

Sloppy sequence, backward heat integration (SQB)

Case study

The feed is ternary mixture of (Benzene, Toluene, m‐ xylene)

Feed Composition     (0.25/0.50/0.25)        Feed Pressure          = 101.33 KpaFeed flow rate         = 100 kmol/hFeed conditions:

Liquid at 20 °CSaturated liquid Saturated vapor

Products Purity =  99.9 mol % 

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Optimization procedure

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Pressure

Numberof trays

Feedlocation

Checkopti‐malityandspecs

Pressure

Numberof trays

Drawlocation

Feedlocation

Recyclesflow

Column (1) Column (2)

Checkopti‐

malityand

specs

TAC

Design

TAC

Comparingscenarios

HYSYS EXCEL

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Case Study 

Rigorous Simulation Shortcut Analysis

FORTRAN Program 

Shortcut Results (Rmin, Nmin )

Pinch Analysis 

Shortcut Equations (FUG) 

HYSYS Simulation  CPI Software (Sprint)

Composite Curve Analysis 

Pinch Analysis Results 

Simulation Results 

Energy & TAC Saving 

Optimal solution  DataData

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HYSYS PFD for DQB distillation scheme

Results and discussion

13

4445

4647

484928 29 30 31 32

1.090

1.092

1.094

1.096

1.098

1.100

1.102

1.104

1.107

1.109

1.111

1.113

1.115

1.117

1.119

Total annual cost (MM$/year)

Trays of Column 1

Trays of Column 2

3D‐ view for optimization of DQB scheme

Composite curve of  base case (D)

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Composite curve of DQB scheme

15

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Energy & TAC saving compared to base case (D), liquid state

Energy & TAC saving % of DQB, different feed conditions

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Energy & TAC saving % of Petlyuk column, different feed conditions

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Heat‐integrated distillation schemes offers an alternative toconventional distillation schemes, with the possibility of savings inboth energy and capital costs

The state of feed conditions plays important role on the optimizationranking of distillation schemes

DQB & SQD schemes are showing higher energy saving for feedentering at liquid state, this due to the recycling of the energy utilizedto change the phase of the feed inside the integrated system

Petlyuk column is more effecient when supplying the feed atsaturated liquid phase

Conclusions

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THANK YOU ALL