Process Flowsheet Generation & Design Through a Group Contribution Approach Lo ï c d ’ Anterroches CAPEC Friday Morning Seminar, Spring 2005

Process Flowsheet Generation & Design Through a Group Contribution Approach2 Introduction Question: How to solve this problem? Synthesis 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 Approach3 Introduction Industrial approach – Take a master student looking for a 6 month training session Current Methods Targets Data (input, …) 6 months and some thousands simulations later, the problem is solved.

Process Flowsheet Generation & Design Through a Group Contribution Approach4 Introduction 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. Current Methods

Process Flowsheet Generation & Design Through a Group Contribution Approach5 Introduction A new method need to address those issues while improving on the drawbacks of the current methods General Issues Select the needed unit operations Setup each alternative and simulate it Get the best alternative Definition of the problem How to avoid using too many different unit operations but keeping the right ones? How to do an exhaustive analysis of the alternatives with the correct design parameters for each simulation? How to be sure this is the best? Any metrics?

Process Flowsheet Generation & Design Through a Group Contribution Approach6 Introduction 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 Core Idea and Main Objectives

Process Flowsheet Generation & Design Through a Group Contribution Approach7 Introduction 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 Overview of the Presentation

Process Flowsheet Generation & Design Through a Group Contribution Approach8 Molecular Group Contribution Approach 1. Given a molecule Property Prediction Ethanol: 2. Represent it as a combination of groups 3. Evaluate the property as the sum of the contributions -OH -CH 2 - -CH 3

Process Flowsheet Generation & Design Through a Group Contribution Approach9 Molecular Group Contribution Approach 1. Given a set target property values Computer Aided Molecular Design 2. Select the groups that will compose the molecules 3. Combine the groups to form molecules -OH; -CH 2 -; -CH 3 150K < T m < 170K 4. Evaluate the property to find matching molecules : Ethanol, T m = 159K

Process Flowsheet Generation & Design Through a Group Contribution Approach10 Flowsheet Group Contribution Approach Same as for molecules but with flowsheets – A process-group (PG) represents a unit or a set of unit operations Presentation Reaction PGSolvent 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 Approach11 Flowsheet Group Contribution Approach A flowsheet is represented as a combination of process- groups (PGs) Presentation

Process Flowsheet Generation & Design Through a Group Contribution Approach12 Flowsheet Group Contribution Approach Overview of the Framework

Process Flowsheet Generation & Design Through a Group Contribution Approach13 Flowsheet Group Contribution Approach Energy index for distillation column process-group Property Model Energy index for solvent based separation – p k : Topology factor – a k : Regressed contribution of PG k – d ij k : Driving force between the 2 key components – A : Regressed constant – R : Solvent reflux of solvent – d ij k : Solvent free force between the 2 components

Process Flowsheet Generation & Design Through a Group Contribution Approach14 Flowsheet Group Contribution Approach Generation of new process alternatives 1. Given a set of inlets and outlets, and, property targets 2. Select the matching PGs (Knowledge based) 3. Generate all the feasible alternatives starting from the inlets 4. Evaluate the target properties 5. 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 Synthesis Algorithm

Process Flowsheet Generation & Design Through a Group Contribution Approach15 Flowsheet Group Contribution Approach Retrofit of existing processes 1. Represent the existing process as a combination of PGs 2. Select the PGs with their connections that will be kept as starting structure together with the inlets and outlets. (Several starting structures are possible) 3. Select the matching PGs (Knowledge based) 4. Generate all the feasible alternatives from the starting structures 5. Evaluate the target properties 6. Rank the alternatives Retrofit and synthesis of new alternatives are possible within the same framework. Synthesis Algorithm

Process Flowsheet Generation & Design Through a Group Contribution Approach16 Flowsheet Group Contribution Approach 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). Design of the Process

Process Flowsheet Generation & Design Through a Group Contribution Approach17 Flowsheet Group Contribution Approach Reverse approach for a reaction group – Fully based on the Attainable Region concept Design of the Process Maximize the selectivity to C

Process Flowsheet Generation & Design Through a Group Contribution Approach18 Flowsheet Group Contribution Approach Reverse approach for a solvent based separation Design of the Process Distillation 1Distillation 2 Number of stages3530 Feed location2012 Top product specificationsAcetone Chloroform Bottom product specificationsAcetone 0.05Chloroform 0.05 A solvent fraction of 0.7 is selected to match the 0.25 driving force target E x = Use of Bek-Pedersen reverse algorithm to get the full column description

Process Flowsheet Generation & Design Through a Group Contribution Approach19 Flowsheet Group Contribution Approach Software implementation Implementation

Process Flowsheet Generation & Design Through a Group Contribution Approach20 Flowsheet Group Contribution Approach Software implementation Implementation

Process Flowsheet Generation & Design Through a Group Contribution Approach21 Conclusion & Future Work Efficient on a large range of problems – Current PGs: Simple distillation, pressure swing, solvent based, kinetic reaction, fixed conversion reaction – Theoretically computationally efficient 1 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 What with Respect to the Objectives?

Process Flowsheet Generation & Design Through a Group Contribution Approach22 Conclusion & Future Work 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 Limitations

Process Flowsheet Generation & Design Through a Group Contribution Approach23 Conclusion & 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 Future Work