(421f) ProCAFD: A Computer-Aided Tool for Sustainable Process Synthesis, Design, Analysis and Improvement

The chemical process industry is always looking for innovative designs, which are both efficient and sustainable. To generate a truly optimal process flowsheet a systematic method to identify the types of tasks-operations that need to be performed, the corresponding design of the operation-equipment, their configuration, mass-energy flows, environmental impacts, etc., need to be employed. That is, the synthesis problem (processing route generation), the design problem (design of the individual operations), the analysis problem (simulation and evaluation of alternatives) and the innovation-intensification problem (more sustainable designs) need to be considered within the same method. In this case, development and use of a computer aided tool that combines the best features of knowledge-based and optimization-based approaches into one method is an attractive option.

This work focuses on the development of a computer aided software tool, capable of enumerating all the feasible alternatives within the entire search space defined by a process synthesis problem to determine the most sustainable process using a hybrid approach. In the synthesis problem a superstructure of all feasible alternatives is created using a technique similar to computer aided molecular design (CAMD) for molecular design. According to this technique [1], chemical process flowsheets are synthesized in the same way as atoms or groups of atoms are combined to form molecules in CAMD techniques. The building blocks in the process flowsheet synthesis problem are called process-groups, which represent a single or set of unit operations that are selected by employing a thermodynamic insights-based method. These building blocks are then combined using connectivity rules to generate a superstructure of feasible process flowsheet alternatives, from which the optimal process configuration is determined in two ways: a) Group contribution based flowsheet property models that enumerates and evaluates all possible alternatives (generate and test approach); and b) Superstructure based optimization (direct solution approach) In the first approach, flowsheets are generated and tested by estimating performance indicators of the generated flowsheets through the contributions of the associated process-groups and flowsheet property models (energy consumption, carbon foot-print, , product recovery, product purity etc). In this way, the entire list of feasible process flowsheets are quickly generated, screened and selected. In the second approach, a superstructure based optimization problem is solved by first formulating the synthesis problem as a mixed integer linear or nonlinear programming problem and solved through a suitable solver (GAMS) [2, 3]. Here, the software interface, Super-O helps to set up the optimization problem by creating an input file for GAMS, which is then solved to find the optimal processing route. In design and analysis problems, additional design details not covered by the synthesis problem are added to the process tasks-operations so that simulations with rigorous process models can be performed. The simulation results serve as input for equipment sizing and utilities requirement calculations, which in turn serve as input for process analysis (economic, sustainability factors, safety, LCA factors, etc.). The analysis problem also includes hazards analysis through PHASuite [4], which involves identification, assessment and mitigation of process hazards. This comprehensive process analysis identifies process hotspots, where the corresponding task-operation within an analyzed process could be improved, that is, helps to define targets for improvement. Through the solution of the innovation-intensification problem, any processing route that has been analyzed and targets for improvement defined, is furthered improved by applying various synthesis-intensification methods [5] to determine process alternatives that match the targets for improvement. Any match of the design targets therefore corresponds to a more sustainable process alternative.

The developed methods and associated computer-aided tools have been integrated into ProCAFD – a tool for process synthesis, design, analysis and intensification. ProCAFD has been tested on various case studies involving new as well as retrofit chemical and biochemical process synthesis-design-intensification. The paper will present results from a selection of the developed case studies.

References:

[1] Tula, A.K., Eden, M. R., and Gani, R. (2015). Process synthesis, design and analysis using a process-group contribution method. Computers and Chemical Engineering, 81, 245-259.

[2] Quaglia, A., Sarup, B., Sin, G., and Gani, R. (2012). Integrated Business and Engineering Framework for Synthesis and Design of Enterprise-Wide Processing Networks. Computers and Chemical Engineering, 38, 213-223.

[3] Bertran, M-O., Frauzem, R., Sanchez-Arcilla, A. S., Zhang, L., Woodley, J., and Gani, R. (2017). A generic methodology for processing route synthesis and design based on superstructure optimization. Computers and Chemical Engineering. 106, 892-910

[4] Zhao, C., Venkatasubramanian, V. (2005). Learning in intelligent systems for process safety analysis. Computer Aided Chemical Engineering, 20, 1123-1128.

[5] Babi, D. K., Holtbruegge, J., Lutze, P., Gorak, A., Woodley, J. M., Gani, R. (2015), Sustainable process synthesis–intensification, Computers and Chemical Engineering, 81, 218-244