New Superstructure-Based Optimization for Process Intensification

Process intensification enables “multi-tasking” by combining reaction, separation and other operations in a single unit, and leads to a substantially smaller, cleaner, safer, and more energy-efficient technology [1-3]. However, there is a lack of a systematic method for the identification of intensification opportunities and the optimal synthesis of intensified processes at the flowsheet level. Traditional process synthesis and integration methods have focused on classical unit operations, where units are integrated but they are not merged to perform multiple operations in situ. Though research on process intensification has brought about many promising technologies including reactive distillation, divided wall columns, membrane reactors and task integrated columns, current methods are often suboptimal and consider only a few of all plausible alternatives. While recent phenomena-based design methods [4-6] incorporate process intensification, they are difficult to solve and are based on heuristics and/or decomposition approaches leading to suboptimal solution. Instead of considering classical unit-operation based superstructure representation of a flowsheet, we propose a new flowsheet based on building blocks in which each block represents a unit use of materials performing a specific function (reaction, separation, storage, etc.). An assembly of blocks of the same material would obtain a classical unit operation, while blocks with different materials or functionalities would result in intensified unit operation. This allows a systematic identification, representation and generation of intensification alternatives at the flowsheet level without exhaustive enumeration. We pose the optimal process intensification problem as a mixed-integer nonlinear optimization (MINLP) problem which aims to synthesize a process with intensified units by minimizing or maximizing a process metric given the feed and product specifications, feed and product prices, material properties and bounds on flow rates. In this talk, we will present the overall process intensification method with specific applications.

References

[1] Reay, D.; Ramshaw, C.; Harvey, A. Process intensification: engineering for efficiency, sustainability and flexibility. Waltham, MA: Butterworth-Heinemann, 2013.

[2] Stankiwicz, A.I. , Moulijn, J.A.,. Process intensification: transforming chemical engineering. Chem. Eng. Process, January, 2000, 22-34.

[3] Baldea, M. From process integration to process intensification. Computers & Chemical Engineering 2015, Doi.10.1016/j.compchemeng.2015.03.011.

[4] Arizmendi-Sanchez, J. A., and Sharratt, P. Phenomena-based modularisation of chemical process models to approach intensive options. Chemical Engineering Journal 2008,135, 83-94.

[5] Lutze P, Babi DK, Woodley JM, Gani R. Phenomena based methodology forprocess synthesis incorporating process intensification. Ind Eng Chem Res 2013, 52(22):7127–44.

[6] Babi, D. K., Holtbruegge, J., Lutze, P., G_orak, A., Woodley, J. M., and Gani, R. Sustainable process Synthesis–intensification. Comput. Chem. Eng. 2015, .doi:10.1016/j. compchemeng.2015.04.030.