(518h) Implications of Process Heat Electrification on the Design, Control and Operation of Integrated Chemical Processes

Electrification of manufacturing processes using electricity generated by renewable sources is a candidate pathway for decarbonizing the industrial sector, which accounts for a significant portion of the overall carbon emissions in the United States.[1] Electrification may involve a change of the core process technology (e.g., by replacing conventional processes with electrochemical reactions) or modifying and upgrading existing technology. The focus of this work is on the latter, specifically on the electrification of process heating (Power-to-Heat), whereby existing combustion-based process heating is replaced with electric heating technologies, such as resistive heating, inductive heating, electric boilers, and heat pumps.

Process heat electrification can in principle eliminate CO₂ emissions from process heating when the electricity source is renewable (i.e., there are no scope 1 or 2 emissions). It also has potential co-benefits such as more precise/localized heating, faster response, higher heating efficiency, and providing additional degrees of freedom for operation and control.[2] However, several challenges regarding process design and dynamics are expected to arise from electric heating. From a design perspective, electrifying the process heating may disrupt process integration in cases when waste fuel streams (“tail gas” or “fuel gas”) generated within the process are combusted to generate heat, and affect the plantwide dynamics of the process.[3] From an operation and control perspective, the intermittency and the availability of renewable electricity may impact process operations.

Motivated by these challenges, we provide a rigorous analysis of the design and control implications of process heat electrification in the context of integrated process systems. A prototype integrated process structure with reaction, separation, and recycle involving combustion of waste fuel stream as the main heat source is defined. An equivalent process structure that relies on electric heating is constructed and contrasted with the integrated process model. An asymptotic analysis is utilized to investigate and compare the dynamic responses of the two structures. It demonstrates that the dynamic behavior of the two processes exhibits two time scales, with the faster dynamics corresponding to the evolution of the temperatures of the units with high thermal energy throughput, and the slow time scale dynamics capturing the process variables related to the material balance. Furthermore, our analysis reveals structural dynamic differences between the two processes, with the conventional process presenting significant dynamic interactions due to the impact of the downstream units (in the forms of composition/heating value of the waste fuel gas) on the behavior of the upstream units. On the other hand, the upstream section of the process with electric heating is no longer affected by the downstream units, providing extra degrees of freedom for control and operation.

The theoretical findings are validated using a simplified model of a cracking plant using ethane feedstock to produce ethylene in a high-temperature cracking furnace. The dynamic response of the conventional process, which primarily relies on by-product waste fuels for combustion, and that of the electric heating process are compared. The simulation results validate the theoretical predictions.

[1] Ali Hasanbeigi, Lauren A. Kirshbaum, Benjamin Collison, and Don Gardiner. Electrifying U.S. industry: Technology and process-based approach to decarbonization. Technical report, 2021

[2] Electric Power Research Institute (EPRI). Program on technology innovation: Industrial electrotechnology development opportunities. Technical Report 1019416, EPRI, Palo Alto, CA, 2009

[3] Michael Baldea and Prodromos Daoutidis. Dynamics and Control of Integrated Process Systems. Cambridge University Press, 2012.