Dynamic Intensification of Chemical Processes

Description
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Executive Summary

This project looks to use modeling and optimization to define PI opportunities in existing hardware. In particular, it takes a general look at dynamically controlled processes to see when this mode of operation can deliver significant improvements in performance. The goal of the project is to provide a general theoretical framework for dynamic intensification, as well as using divided wall column operation as a test case to practice dynamic intensification at the pilot scale.

The project team will develop an analysis framework for screening candidate processes for dynamic intensification. The expectation is to express the suitability of a process in terms of one (or a few) dimensionless numbers, such that the values of the dimensionless numbers correspond to different economically optimal regimes (e.g., if the dimensionless number of a process is larger than a threshold value, periodic operation is economically more advantageous than operating at steady state). The team will begin with defining a prototype intensified system, whose model will incorporate two or more rate-based phenomena. On this basis, the team will utilize the Pi-criterion or other dynamic analysis tools to determine the operating envelopes (e.g., in terms of transport rates, transfer rates) that favor periodic process intensification.

The conceptual results will then be extended and applied to the dynamic model of a dividing wall distillation column (DWC), with the expected outcome being the identification of feasible periodic operation patterns that minimize total energy use in the column reboiler and condenser.

Technical Challenge

A significant portion of bulk chemicals and petrochemicals are manufactured in large facilities that operate mostly at steady state. In many ways, the traditional chemical industry has reached a plateau in terms of productivity and energy efficiency. Improvements based on existing technologies and unit operations are mostly incremental and unable to address fundamental transport limitations that drive process efficiency. Process intensification, largely based on reducing transport and transfer limitations by carrying out multiple conventional “unit operations” in the same physical device, has the potential to take bulk and specialty chemical production to new levels of economic efficiency. In this project, we propose to extend the benefits of process intensification by operating intensified systems in a dynamic/transient regime, focusing on processes that have historically been designed and operated at steady state. The opportunity afforded by this bold concept lies in further (and potentially considerably) reducing transport limitations such that intensified processes are operated much closer to their thermodynamic/kinetic limits, and the average performance of the process over time is much higher than that of the steady-state counterpart.

Potential Impact

Our technology focus will be on dividing wall columns. Recent developments have shown that periodic operation of single distillation systems can lead to up to 30% increased energy productivity compared to conventional processes, and a capital cost reduction (in terms of number of stages) by a factor of 2.6. This suggests that even more substantial savings are within reach when operating already intensified processes (i.e., the dividing wall column) in a transient, periodic regime. These energy efficiency improvement goals are consistent with DOE goals. These predictions are supported by earlier, complementary research carried out on the periodic operation of chemical reactors has suggested that imposing such periodic operation regimes can lead to improvements in product yield of over 7%. Together with the above, this supports our expectation and long-term goal that periodic operation of many (if not all) intensified processes considered by the RAPID Institute research teams can lead to economic and energy efficiency improvements, and, further, that these gains can be considerable. The proposed research thus has broad impacts on the entire activity of the Institute and represents a foundational task in support of the research to be carried out by other teams.

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