(422e) Process Integration Using Block Superstructure

Process integration enables the design of integrated production systems ranging from individual processes to total sites to reduce fresh resource consumption or harmful emissions [1-4]. A classic process integration problem consists of sinks with demand for certain properties, and sources to satisfy the demands of these sinks. These properties exchanged within the system can be materials/contaminants in water networks [5], mass exchange networks [6], etc. The properties can also be exchanged as energy, e.g., heat in heat exchanger networks [7], power in work exchange networks [8]. Capturing these recurring features helps to construct a unified superstructure representation for different integration problems. Besides, there is a symbiotic relation among process integration, synthesis and intensification [9-11], which necessitates the advancement of process integration techniques. Recently, the building block superstructure has been proposed for systematic process intensification by dissecting unit operations into fundamental phenomena building blocks [9]. Later on, this approach is applied for general process synthesis problems without postulating case-specific process superstructures [10].

In this work, we extend the block representation to incorporate various process integration problems by considering their common features. Process units, including regenerators/interceptors, are embedded in blocks. The feed flow and product flow in each block represent sources and sinks, respectively. Adjacent blocks interact with each other through direct connecting streams equipped with heaters/coolers for adjusting the temperature. Besides, we also introduce 'jump flow' among all blocks to avoid more intermediate blocks connecting nonadjacent blocks while maintaining or increasing the number of process alternatives. The block superstructure size is dependent on the number of layers with mixing operations, process units, product streams and heat integration stages. We formulate the general process integration problem as a mixed-integer nonlinear optimization (MINLP) problem to minimize the total annual cost. With the proposed MINLP model, we investigate various process integration problems involving mass integration, heat integration, simultaneous mass and heat integration, and property integration. These case studies showed that the same reported optimal integration networks and/or better network designs can be generated using the proposed block representation approach.

References:

[1] Li J., Demirel S.E., Hasan M.M.F. Process Integration using Block Superstructure. Industrial & Engineering Chemistry Research, 2018, 57: 4377–4398.

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[10] Li, J., Demirel, S.E., Hasan, M.M.F. Process Synthesis using Block Superstructure with Automated Flowsheet Generation and Optimization. AIChE Journal, 2018, under review.

[11] Baldea, M. From process integration to process intensification. Computers & Chemical Engineering, 2015, 81:104–114.