Practical Approach to DWC Design & Optimization Plant Basic Engineering Team

Transcription

1 Practical Approach to DWC Design & Optimization Plant Basic Engineering Team Sang-il Park Oct / 15

2 CONTENTS 1. Introduction to DWC - Benefits - Application. DWC simulation. B-Split - Comparison of Design Variables (conventional vs. DWC) - Vapor & liquid split - Definition - An optimal B-Split (case study) - An optimal B-Split (Theoretical) 4. Design procedure - steps - Case Study Result / 15

3 1. Introduction To DWC Dividing Wall Column (DWC) Fractionation Column that executes two different separations in one column Graphics from Montz Catalogue <Montz Dividing Wall Column> / 15

4 1. Introduction To DWC Benefits of DWC 1. Low Capital Investment (0~0%). Low Operation Cost (0~0%) - Remove Re-mixing Graphics from CEP Journal Reduce Costs with Dividing Wall Column, by Michael A. Schultz (UOP) 4 / 15

5 1. Introduction To DWC Application of DWC product Separation 1. High purity is required for middle boiling point component. Middle product is in excess and lights and heavies are in fairly equal. Separation of A/B is as difficult as B/C TREATED NAPHTHA 15 bar Stabilizer (DeC4) 1.5 bar Naphtha Splitter Isomerization FEED C4- C4- Isomerization Benzene CCR Reformer Other Applications CCR Reformer 1. Extractive Distillation (BASF BD process, Ude Morphylane). Absorption + Distillation (GTC LPG Max) 5 / 15

6 . DWC simulation Design Variables in Conventional Column 1.No. of stages.feed Location.Draw Location 1. No of Stages Duty Feed location. Side Draw location No. Stages 6 / 15

7 . DWC simulation Design Variables in DWC- DWC structure 1.No. of stages in main column.no. of stages in prefractionator.feed location of prefractionator 4.Side draw location 5.Feed location of main column vapor in 6.Feed location of main column liquid in 7.Main column vapor out rate 8.Main column liquid out rate. Prefractionator Tray No. 8. Main Lout (Liquid split ratio) 1. Main column Tray No. 5. Main Vin 4. Side Draw location. Feed location 7. Main Vout (Vapor split ratio) 6. Main Lin 7 / 15

8 . DWC simulation Vapor & Liquid Split in DWC Optimal operating regions at a certain vapor & Liquid Split Duty Liquid out Vapor out The range and stable optimal regions depend on the feed composition and DWC structure Graphics from Chem. Eng. Study of structural characteristics of a dividing wall column using the sloppy distillation arrangement by Moonyong LEE (Yongnam Univ.) 8 / 15

9 . DWC simulation Design Variables in DWC Interaction No. of trays at each section Condenser Duty Liquid split Reboiler Duty Vapor Split An easy and powerful design procedure of DWC is required 9 / 15

10 . B-Split B Split (β) ; Definition The fraction of component B that goes to the top of pre-fractionator out of total B flow B top B btm feed After pre-fractionator Trying to find an optimal B-Split Final Product 10 / 15

11 . B-Split An optimal B-Split (case study) Simulation Result of C4/C5/C6 Separation at a fixed DWC Structure Reboiler duty(a:b:c=1::1) 8 Reboiler duty (A:B:C=1:1:) 1 Reboiler duty (A:B:C=:1:1) B-split B-split B-split There is an optimum B-Split for DWC Design 11 / 15

12 . B-Split An optimal B-Split (Theoretical) Halverson 1) verified optimal B-Split is between Preferred Split and Balanced Split 1) Ivar J. Halverson Minimum Energy Requirement in complex Distillation Arrangements, thesis for Dr.Ing., Norwegian University of Science and Technology d a c b a b c d b: Preferred Split c: Balanced Split 1 / 15

13 . B-Split An optimal B-Split (Theoretical) The graph of Preferred / Balanced Split vs. ESI (ease of separability index, α AB /α BC ) B-split 1 1 Preferred split Balanced split Initial split A:B:C=1::1 A:B:C=:1:1 A:B:C=1:1: ESI B/C cut hard ESI increase More B/C to bottom Preferred Split dec. Large duty for Main-frac Blanced Split inc. 1 / 15

14 4. Design Procedure - Steps column simulation column simulation DWC simulation Design Each column with; 1) A/C nearly perfect cut ) Use Initial B-Split ) Optimization of each column Objective Determine tray No. for I/II/III/IV Design Each column with; 1) No touch on pre-fractionator ) Stage elimination ) Determine Draw location Objective Determine tray No. for I/II/III/IV for DWC Design DWC with; 1) No touch on the tray No. ) Determine feed location ) Total No. of tray optimization Objective Determine final DWC design with total No. of trays & V/L split 14 / 15

15 4. Design Procedure Case Study (BTX separation) Conventional Design DWC Design Main DWC Design Parameters B split (top / total) mole 0.51 L split (main / total) mole 0.64 V split (main / total) mole 0.40 Comparison between Conventional and DWC Column name Benzene Toluene DWC Saving % No. of Actual Stage % Colum ID mm 4,000 4,400 4,800 Column Height m Column Weight kg 69,165 86,698 15,114 1% Condenser Gcal/hr % Reboiler Gcal/hr % 15 / 15

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