(204d) Modular Process Design and Electrification for Grid-Synchronized Plant Operations

Electrifying process heat with Power-to-Heat (PtH) technology presents an opportunity to reimagine the operation and control of chemical manufacturing plants by enhancing process efficiency and achieving industrial decarbonization [1]. Clean electricity for heat generation is needed to accomplish this. The generation rates of renewable sources (wind, solar photovoltaics) of electricity present daily and seasonal variability, thus posing additional challenges in balancing electricity supply and demand. A possible solution is demand-side management, where electricity users (in particular large ones, such as electrified chemical plants) coordinate their operation with the electricity grid to address power availability and/or cost constraints. In this approach, the plant must modulate its electricity demand (and hence its heat load, and ultimately production rate) over a useful time span (typically hourly or shorter). This requires substantial flexibility. However, in integrated processes, the interactions between process units and the resulting slow plant-wide dynamics may inhibit shifting process throughput at the rate required to participate in demand-side management [2].

Material recycling and heat integration techniques implemented in modern chemical processes give rise to feedback effects, and are an important contributor to process interactions [2,3]. The use of electric heating alters process design and process dynamics. It was shown [4] that electrifying process heating has a "de-integration'' effect. Using electricity -- an exogenous energy input, rather than an internal heat source -- to meet process heating needs, provides additional degrees of freedom for control while at the same time removing some feedback connections between process units.

In this work, we explore the process flexibility implications of electrifying process heat, and specifically in enabling fast transitions between substantially different points in the plant operating space. We posit electrified process heating allows for such transitions to be approached in a distributed fashion by charting the fastest path between operating points individually for each unit. Focusing specifically on reactor/separation/recycle processes, we show that this concept can be implemented as a constrained trajectory optimization with two stages. In the first stage, the units are decoupled by restricting or stopping material flow between them, and a trajectory to a state that is closest (based on the process constraints) to the final state is computed. Then, material flow between units is restored, and the transition is completed at the plant level. Since the first stage can be carried out in parallel for all units, it leads to substantial savings in overall transition time.

Our findings are validated through a simulation case study for a prototype dimethyl ether (DME) production plant with electric heating, which features a modular distillation column, an equilibrium-limited chemical reactor, and a recycle stream that adds the overhead product to the feed. We demonstrate that our proposed transition approach increases process flexibility, as measured in terms of savings derived from engaging in demand-side response relative to a conventional DME plant.

References:

[1] J. Cresko, E. Rightor, A. Carpenter, K. Peretti, N. Elliott, S. Nimbalkar et al. U.S. Department of Energy’s Industrial Decarbonization Roadmap; U.S. Department of Energy Office of Energy Efficiency and Renewable Energy (EERE), 2022.

[2] M. Baldea, P. Daoutidis. Dynamics and Control of Integrated Process Systems. Cambridge University Press, 2012.

[3] S.S. Jogwar, M. Baldea, P. Daoutidis. Dynamics and control of process networks with large energy recycle. Ind. Eng. Chem. Res., 48:6087–6097, 2009.

[4] J.H. Rho, M. Baldea, E. Endler, M. Heredia, V. Bojovic, P. Pajand. Probing the impact of electric heating on the design, dynamics, and operation of integrated chemical processes. Ind. Eng. Chem. Res., 64:6043-6059, 2025.