Process Flowsheet Generation & Design Through a Group Contribution Approach

1. Process Flowsheet Generation & Design Through a Group Contribution Approach Loïc d’Anterroches CAPEC Friday Morning Seminar, Spring 2005

2. Introduction ??? Synthesis Problem • Question: How to solve this problem? Raw materials Products Find the best sequence of operations to convert the raw materials into the desired products Process Flowsheet Generation & Design Through a Group Contribution Approach

3. Introduction Current Methods • Industrial approach • Take a master student looking for a 6 month training session Targets Data (input, …) Data 6 months and some thousands simulations later, the problem is solved. Process Flowsheet Generation & Design Through a Group Contribution Approach

4. Introduction Current Methods • More academic approaches • Knowledge based methods • Database of cases and rules built with time from experience. • Problem: Not a lot of alternatives, feasible but with no guaranteed optimality, need to solve the model at each decision step. • Optimization based methods • Setup of a mathematical superstructure in which all the alternatives are represented, setup the optimization to find the best. • Problem: Optimality only within the mathematical superstructure, hard to setup, need to solve the model at each decision step. Process Flowsheet Generation & Design Through a Group Contribution Approach

5. Introduction General Issues • A new method need to address those issues while improving on the drawbacks of the current methods How to avoid using too many different unit operations but keeping the right ones? Definition of the problem Select the needed unit operations How to do an exhaustive analysis of the alternatives with the correct design parameters for each simulation? Setup each alternative and simulate it How to be sure this is the best? Any metrics? Get the best alternative Process Flowsheet Generation & Design Through a Group Contribution Approach

6. Introduction Core Idea and Main Objectives • Core Idea • Apply the group contribution approach for property estimation to the synthesis, design and modelling of a process flowsheet, with process-groups representing units, bonds representing streams, rules for flowsheet feasibility and a function of group contributions predicting the performance of the flowsheet. • Main Objectives • Efficient on a large range of problems • Ability to integrated and reuse knowledge over the time • Computer implementation for ease of use Process Flowsheet Generation & Design Through a Group Contribution Approach

7. Introduction Overview of the Presentation • Introduction & problem presentation • Molecular Group Contribution Approach • Flowsheet Group Contribution Approach • Presentation • Property Model • Overview of the Framework • Synthesis Algorithm • Design of the Process • Implementation • Conclusion & Future Work Process Flowsheet Generation & Design Through a Group Contribution Approach

8. Molecular Group Contribution Approach Property Prediction 1. Given a molecule Ethanol: 2. Represent it as a combination of groups -CH2- -CH3 -OH 3. Evaluate the property as the sum of the contributions Process Flowsheet Generation & Design Through a Group Contribution Approach

9. Molecular Group Contribution Approach : Ethanol, Tm = 159K Computer Aided Molecular Design 1. Given a set target property values 150K < Tm < 170K 2. Select the groups that will compose the molecules -OH; -CH2-; -CH3 3. Combine the groups to form molecules 4. Evaluate the property to find matching molecules Process Flowsheet Generation & Design Through a Group Contribution Approach

10. Flowsheet Group Contribution Approach Presentation • Same as for molecules but with flowsheets • A process-group (PG) represents a unit or a set of unit operations Reaction PG Solvent based separation PG • A process-group is mass-balance independent • Connectivity is component, P and T dependent Process Flowsheet Generation & Design Through a Group Contribution Approach

11. Flowsheet Group Contribution Approach Presentation • A flowsheet is represented as a combination of process-groups (PGs) Process Flowsheet Generation & Design Through a Group Contribution Approach

12. Flowsheet Group Contribution Approach Overview of the Framework Process Flowsheet Generation & Design Through a Group Contribution Approach

13. Flowsheet Group Contribution Approach Property Model • Energy index for distillation column process-group • pk : Topology factor • ak : Regressed contribution of PG k • dijk : Driving force between the 2 key components • A : Regressed constant • Energy index for solvent based separation • R : Solvent reflux of solvent • dijk : Solvent free force between the 2 components Process Flowsheet Generation & Design Through a Group Contribution Approach

14. Flowsheet Group Contribution Approach Synthesis Algorithm Generation of new process alternatives • Given a set of inlets and outlets, and, property targets • Select the matching PGs (Knowledge based) • Generate all the feasible alternatives starting from the inlets • Evaluate the target properties • Rank the alternatives • No mass-balance is performed during the generation of the alternatives. • Very fast (still depends on the computer implementation) • Combinatorial explosion limited by the constraints Process Flowsheet Generation & Design Through a Group Contribution Approach

15. Flowsheet Group Contribution Approach Synthesis Algorithm Retrofit of existing processes • Represent the existing process as a combination of PGs • Select the PGs with their connections that will be kept as starting structure together with the inlets and outlets. (Several starting structures are possible) • Select the matching PGs (Knowledge based) • Generate all the feasible alternatives from the starting structures • Evaluate the target properties • Rank the alternatives • Retrofit and synthesis of new alternatives are possible within the same framework. Process Flowsheet Generation & Design Through a Group Contribution Approach

16. Flowsheet Group Contribution Approach Design of the Process • Reverse approach • From the process-groups to the process flowsheet. • Define the topology of the unit operations within the PG (Optional). • Define the unit operation design parameters (all the parameters to fully describe the process, i.e. being able to run a rigorous simulation). Process Flowsheet Generation & Design Through a Group Contribution Approach

17. Flowsheet Group Contribution Approach Design of the Process • Reverse approach for a reaction group • Fully based on the Attainable Region concept Maximize the selectivity to C Process Flowsheet Generation & Design Through a Group Contribution Approach

18. Distillation 1 Distillation 2 Flowsheet Group Contribution Approach Number of stages 35 30 Feed location 20 12 Top product specifications Acetone 0.965 Chloroform 0.965 Bottom product specifications Acetone 0.05 Chloroform 0.05 Design of the Process • Reverse approach for a solvent based separation • A solvent fraction of 0.7 is selected to match the 0.25 driving force target • Ex = 0.138 • Use of Bek-Pedersen reverse algorithm to get the full column description Process Flowsheet Generation & Design Through a Group Contribution Approach

19. Flowsheet Group Contribution Approach Implementation • Software implementation Process Flowsheet Generation & Design Through a Group Contribution Approach

20. Flowsheet Group Contribution Approach Implementation • Software implementation Process Flowsheet Generation & Design Through a Group Contribution Approach

21. Conclusion & Future Work What with Respect to the Objectives? • Efficient on a large range of problems • Current PGs: • Simple distillation, pressure swing, solvent based, kinetic reaction, fixed conversion reaction • Theoretically computationally efficient1 • Ability to integrated and reuse knowledge over the time • Yes, if an efficient sequence is found, a translation as a PG is possible  ease of use • Computer implementation for ease of use • Going on. 1. in practice the current implementation of the underlining graph theory could be improved Process Flowsheet Generation & Design Through a Group Contribution Approach

22. Conclusion & Future Work Limitations • Do not take into account interaction between PGs • Snowball effect, controllability of a reaction-separation system • The only way is to create a PG including both reaction and separation • Steady State • Need to go batch • Precision of a group contribution method • Database of PGs • Need to be built with the time Process Flowsheet Generation & Design Through a Group Contribution Approach

23. Conclusion & Future Work Future Work • Single stage separation • Flash, crystallization (Work already done) • Try on a full scale complex process • Multiple reaction/separation blocks with complex units and recycles between the reaction/separation blocks Process Flowsheet Generation & Design Through a Group Contribution Approach