A Novel and Systematic Method for Process Intensification

Process intensification combines multiple operations in a single unit, and leads to substantially smaller, cleaner, safer, and more energy-efficient technologies [1]. It has been shown that intensification represents a limit case of tight integration through significant material recycling [2]. Although there are established methods for process synthesis and integration, few methods exist for the systematic identification and selection of intensification opportunities. Current superstructure-based process synthesis relies on pre-specified equipment configurations and is unable to automatically construct novel equipment configurations for intensification. Phenomena based process intensification [3-5] allows a bottom-up approach for the identification, screening and incorporation of intensification opportunities, but this approach often requires sequential or decomposition based solution strategies to solve large models, which can lead to suboptimal solutions.

In this work, we propose a unified process synthesis and intensification approach that leverages on an original representation of the flowsheet superstructure. Unlike a classical flowsheet superstructure which encompasses all feasible sequences of unit operations (e.g., reactors, separators, movers, etc.), our proposed superstructure is an ensemble of building blocks, where each block represents a unit use of a material and nexus between the blocks are achieved by intra-block mass and energy transfer. An intensified unit is realized by selecting and assembling multiple neighboring blocks with different functionalities. While reaction, mixing, heating and cooling are achieved within the block, separation related phenomena (e.g., phase separation, phase-contact, etc.,) are achieved via the boundaries between two neighboring blocks. This enables to include many intensification alternatives, including divided wall column distillation, reactive distillation, reactive absorption and membrane reactor, within the same superstructure without any a priori postulation.

The overall process intensification model is formulated as a single mixed-integer nonlinear optimization (MINLP) problem and is solved to optimality. Through a range of applications, we demonstrate that the proposed intensification method is capable of generating innovative and intensified configurations and obtaining optimal process conditions for given feed and product specifications.

References:

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

[2] Baldea, M. From process integration to process intensification. Computers & Chemical Engineering2015, 81:104–114.

[3] Arizmendi-Sanchez, J. A., and Sharratt, P. Phenomena-based modularisation of chemical process models to approach intensive options. Chemical Engineering Journal 2008, 135(1):83-94.

[4] Lutze P, Babi DK, Woodley JM, Gani R. Phenomena based methodology for process synthesis incorporating process intensification. Industrial & Engineering Chemistry Research 2013, 52(22):7127–44.

[5] Babi, D. K., Holtbruegge, J., Lutze, P., Gorak, A., Woodley, J. M., and Gani, R. Sustainable process synthesis–intensification. Computers & Chemical Engineering 2015, doi:10.1016/j. compchemeng.2015.04.030.