(737f) Assessment of Frequency Regulation Capacity of Chemical Process Industries

Reliable operation of the electric grid, which requires matching electricity demand and supply, is a tier-one security concern and has received increased attention in recent years. This is a challenging task as both electricity demand and supply are affected by variability and uncertainty; the volatility on the supply end originates in the increased integration of renewable energy in the power generation portfolio, while on the demand side the use of power is inherently variable.

Of particular importance for the operation of the grid is matching of supply and demand on very short (of the order of seconds) time scales, an activity termed frequency regulation. Frequency regulation requires fast modulation of power consumption and/or generation to restore nominal grid system conditions, and is based on a feedback mechanism involving measurements of the frequency of alternative current. Power-intensive chemical processes are desirable participants in grid management, as they consume large amounts of electricity and generally generate products that are easier and cheaper to store compared to electricity. However, chemical processes present several potential disadvantages when considering their engagement in frequency regulation. First, their time constants may be relatively long compared to the relevant time scale. Second, the dynamic behavior of chemical process is generally highly nonlinear and cannot be sufficiently well-described using relatively simple static models (as is the case, e.g, for batteries). These specific features make it relatively difficult to create appropriate dispatch signals for chemical processes, which can both benefit grid operations, and ensure that the process operates safely and without violating production constraints.

In this paper, we address these challenges, we propose a new method for frequency regulation suitable for chemical processes. Specifically, we propose that a process can provide frequency regulation based on a locally-generated production schedule (rather than grid-generated dispatch signal). To generate the aforementioned production schedule, we define new frequency-sensitive electricity price as a correction to day-ahead hourly electricity prices. The schedule is then generated via a dynamic optimization calculation that explicitly accounting for the plant dynamics. The proposed approach had the merit of providing frequency regulation service while ensuring that all operational and safety constraints of the process are met. The developed methodology is illustrated using the model of an industrial process – chlor-alkali production, and the results show that minute-to-minute frequency regulation can be continuously provided with minimum disruption to the process operation. Additionally, the overall change in energy consumption is minimized.