(586c) Novel Module-Based Design and Optimization Approach for Intensified Membrane Reactor Systems

In recent years, manufacturing of smaller modular and intensified chemical plants as opposed to large refineries has been motivated by the potential increased efficiency of smaller process units and the cost savings through mass production of these units. However, there is a tradeoff when intensifying these processes. As their sizes are reduced and unit operations are combined, there is a loss in the degrees of freedom for controlling the process. Thus, although the intensified unit may be more efficient than the traditional unit operations approach at the designed nominal conditions, it is more difficult to reject disturbances, scale the process up or down, or handle different feedstocks. This work aims to address the design and control challenges caused by the integration of phenomena and the loss of degrees of freedom (DOF) that occur in the intensification of membrane reactor units.

The challenge of reduced DOF in intensified processes is one that has been identified in literature as early as 2003 [1] and has continued to be studied and discussed to this day [2]–[6]. To understand this body of research, it is important to categorize the DOF into two main categories. The first are the design DOF that include all the equipment design parameters such as length, diameter, membrane thickness, mass of catalyst, etc. The others are the operational DOF which encompass the operating conditions and manipulated variables used to control the process. If on one end of the design spectrum, there are modular, highly efficient, but potentially poorly controlled units and on the other end of the spectrum there are large, less efficient, but easier to control processes, then intuition suggests that a hybrid design approach considering both cases may provide the desired balance between efficiency and controllability.

First, a novel approach to designing membrane reactor units is proposed. This approach consists of designing smaller modules based on specific phenomena such as heat exchange, reactions, and mass transport and combining them in series to produce the final modular membrane-based unit. A membrane model is developed using the AVEVA Process Simulation platform that allows for the modeling of this novel hybrid design approach for membrane reactor systems [7]. This approach to designing membrane reactors is then assessed using a process operability analysis [8]–[10] to maximize the operability index, as a way of quantifying the operational performance of intensified processes. This is done by converting the mixed-integer programming problem posed that considers phenomena placing and optimization of separate blocks to a gradient-based, non-linear programming problem with only continuous variables that connect the individual blocks. An optimization algorithm developed in Python is then used to optimize the modular membrane reactor system to find the best arrangement of modules to maximize the operability index, subject to both design and economic constraints.

Previous work [6] has demonstrated that the operability index can be improved as much as 37% using this novel design approach for membrane reactor systems, translating to an improvement in achievability for a potential control structure implementation. Through the development of this novel design and optimization approach and by applying economic and design constraints for the first time, this work will identify the upper limit for operability improvement of modular and intensified membrane reactor systems.

References

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