Integrated Process Design

1. Integrated Process Design • Distillation Sequencing • Simple Columns • - Practical constrains • - Heuristic rules • - Minimum vapor flow • - Components flow • Complex columns • - Columns with more than two products • - Prefractionator • - Thermal coupling

2. D F W Simple columns • One feed, distillate and bottoms (F  D + W). • Key components adjacent in volatility. • One reboiler and one condenser.

3. A A AB ABC ABC B B BC C D The problem... Alternative separation sequencing in a ternary mixture. DIRECT SEQUENCE INDIRECT SEQUENCE

4. Alternative separation sequencing in a multicomponent mixtures.

5. Problem complexity: • High number of alternatives. • Optimization: capital + operation costing. • Heat integration.

6. Simple Columns • Practical constrains • Remove from the sequence as early as possible: • Hazardous components. • Reactive and heat-sensitive components. • Corrosive components. • Finished products must be taken from column distillates (degradation, polymerization, additives, salts,...). • Light components are normally removed from the top of the first column to minimize the use of refrigeration and high pressures.

7. Simple Columns • Heuristic rules RULE 1 Do the most difficult separation last. RULE 2 Favor the direct sequence. RULE 3 Large fraction components should be removed first. RULE 4 Favor equimolar sequences.

8. EXAMPLE RULE 1 Do the most difficult separation last. ---------------- RULE 2 DIRECT Favor the direct sequence. RULE 3 DIRECT Large fraction components should be removed first. RULE 4 Favor equimolar sequences. DIRECT

9. Simple Columns • Minimum vapor flow Influence on column costs and energy demand: • Capital costs • Diameter • Condenser • Reboiler • Operating costs and energy demand • Reboiler duty • Condenser duty

10. V L D F W • Minimum vapor flow calculation: • Underwood method • Porter & Momoh method

11. EXAMPLE DIRECT DIRECT INDIRECT

12. A B A AB ABCD BC B ABCD C C BCD CD D D • Simple Columns • Components flow Compare two possible separation sequences ....

13. Effect of non-key components flow on column operation: • Larger liquid and vapor flows (capital & operating costs, energy consumption). • Lower condenser temperature • Higher boiler temperature

14. EXAMPLE DIRECT DIRECT S. INDIRECTA

15. Non-Integrated Costs Integrated Alternatives Selection methods of simple columns sequences: • A reduced group of candidate sequences is selected, not a single optimal sequence. • Selection of the optimal by design and costing criteria. • Additional considerations: • Safety, • controllability, • start-up, ... • Costing alteration: heat integration.

16. A B LIQUID ABC C Complex Columns • Complex Columns • Columns with more than two products Requirements: xB > 50% xA < 5% αAB >> 1

17. A ABC B VAPOR C • Complex Columns • Columns with more than two products Requirements: xB > 50% xC < 5% αBC >> 1

18. A Condenser xA ABC B Feed BC xB C xC Reboiler xi • Complex Columns • Prefractionator Inefficient Remixing !!

19. A Condenser AB (vapor) Prefractionator B ABC Feed Column BC (liquid) C Reboiler xB Using a prefractionator as an efficient alternative: • Maximums are removed from concentration profiles. • Energy savings: 30%

20. DIRECT SEQUENCE INDIRECT SEQUENCE A A B B C C • Complex Columns • Thermal coupling Heat addition/removal is carried out using material streams.

21. SIDE STRIPPER SIDE RECTIFICATION B A A C C B

22. PREFRACTIONATOR A B C

23. PREFRACCIONATOR DIRECT SEQUENCE A A B B C T C Q