A Framework for Process Synthesis Integrated With Sustainability and Process Intensification

A Framework for Process Synthesis integrated with Sustainability and Process Intensification

 

Deenesh K. Babi¹, Johannes Holtbruegge², Philip Lutze², John M. Woodley¹, Andrzej Górak², Rafiqul Gani¹

 

dkbabi@kt.dtu.dk, johannes.holtbruegge@bci.tu-dortmund.de, philip.lutze@bci.tu-dortmund.de, jw@kt.dtu.dk, andrzej.gorak@bci.tu-dortmund.de, rag@kt.dtu.dk

 

¹Department of Chemical and Biochemical Engineering, Technical University of Denmark (DTU), DK-2800 Kongens Lyngby, Denmark

²Department of Chemical and Biochemical Engineering, Technical University of Dortmund (TU Dortmund), D-44227 Emil-Figge-Str. 70 Dortmund

 

The objective of process synthesis is to find the best flowsheet, among numerous alternatives for converting specific raw materials to specific desired products subject to predefined performance criteria. The unit operations concept is the one most used for process synthesis because it allows to associate the operational tasks with the processing route to be followed. This concept has been sufficient until now, however, due to increasing demands on the chemical industry, such as the design of sustainable/new processes, an extension of the current concepts by considering lower levels of aggregation than the unit operations level as well as sustainability is necessary. That is, when applying the unit operations concept one automatically connects the unit operations with their function and therefore this mode of thinking restricts the solution space to the limited number of ‘'well defined'' unit operations [1]. However, by incorporating a sustainability analysis within process synthesis bottlenecks can be identified and ordered in terms of those having the highest impact for improvement of the process with respect to the environment. But within the solution space, intensified and integrated unit operations must also be included in order to achieve a targeted improvement. Therefore, by incorporating different levels of aggregation at the flowsheet, the unit operations, the task and the phenomena levels, the opportunity to innovate is provided.

Different methods have been developed which perform process synthesis incorporating process intensification at the different levels [2, 3]. This work focuses on the inclusion of a sustainability analysis as a means by which process bottlenecks can be identified and the inclusion of the phenomena level [4] as a lower level of aggregation in process synthesis. It should be noted that the degree of complexity as well as the search space increases as one operates at the lower levels of aggregation. For example, the considered process phenomena need to be combined to perform the identified tasks and these combinations are then translated into unit operations, which define the final process flowsheet. Therefore, operating at the phenomena level allows one to include known as well as new intensified unit operations as part of process synthesis.

The computer-aided framework for process synthesis has been developed and it consists of 10 hierarchical steps exclusive of the intensification method. Steps 1-6 consist of the problem and objective function definition, the investigation of whether a base-case design exist or not. If no, flowsheet alternatives are generated and screened using the means-ends analysis [2] and thermodynamic insights [5]. If yes, then this design is considered as a reference for further improvement/intensification. Steps 7-8 consist of performing a sustainability analysis using data obtained from rigorous simulation of the base case design, to identify process bottlenecks. Having this information the phenomena-based synthesis (PBS) intensification sub-method is entered. Steps 9-10 consist of equipment sizing and economic evaluation followed by a further environmental and sustainability analysis for comparison to the base case design.

The PBS sub-method consists of 7 hierarchical steps. Steps 1-2 consists of metric definition and translation which provide the system constraints related to structural, logical and operational and process analysis where the system is decomposed from the flowsheet level to the phenomena level. The thermodynamic properties of the system [4] are also investigated in order to identify further process bottlenecks. Steps 3-4 consists of identifying tasks and phenomena for overcoming the process bottlenecks based on the thermodynamic insights gained from the process analysis. The means-ends analysis together with the identified phenomena which are connected, are used for generating the flowsheet alternatives based on tasks and phenomena. These connected phenomena referred to as operations are then translated to unit operations which fulfil process requirements, whether traditional, existing or innovative PI equipment. In translating the connected phenomena to unit operations a concept known as S-Files, similar to SMILES for representing molecular information, is used in order to store and easily retrieve from a knowledge-base the unit operations that built the flowsheet. In case a unit operation cannot be found from a set of connected phenomena then a design is proposed for a new unit operation. Steps 5-7 consist of stepwise screening the alternatives with respect to the constraints set previously in Step 2 and optimizing for identifying the most promising flowsheet.

In the proposed presentation the computer-aided framework will be presented along with the tools and data needed for its application, which will be highlighted through two case studies: the production of methyl-acetate for verification of the framework and the production of di-methyl-carbonate as an industrial example.

 

References

[1] H. Freund, K. Sundmacher. Ullmann's Encyclopedia of Industrial Chemistry, Process Intensification, 2. Fundamentals and Molecular Level. Wiley-VCH Verlag GmbH & Co. KGaA, 2000

[2] Jeffrey J. Siirola. Strategic process synthesis: Advances in the hierarchical approach. Comput. Chem. Eng. 1996, Supplement 2 (20) S1637-S1643

[3] Lutze, A. Román-Martinez, J. M. Woodley & R. Gani. A systematic synthesis and design methodology to achieve process intensification in (bio) chemical processes. Comput. Chem. Eng. 2012 (36) 189– 207

[4] P. Lutze, D. K. Babi, J. M. Woodley, and R. Gani. Phenomena Based Methodology for Process Synthesis Incorporating Process Intensification. Ind. Eng. Chem. Res. 2013 Special Issue PSE-2012

[5] C. Jaksland, R. Gani, K. M. Lien. Separation process design and synthesis based on thermodynamic insights. Chem Eng Sci, 1995 (50) 511-530