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The flexibility of energy systems in industrial plants will play an important role in helping bulk energy systems to deal with the various challenges brought by the net-zero carbon transition. The emerging digital twins, which have attracted rapidly increasing interests with some industrial applications, have the potential to facilitate the flexibility service provision from industrial energy systems. This potential is identified in this paper by matching the key features of digital twins and key issues and needs of providing flexibility services from industrial energy systems. The study presented in this paper preliminarily frames this new research area, with potential aspects and directions identified for future research.

A heat exchanger is an essential component in district heating and cooling networks as it transfers thermal energy from energy centers to substations or customers. Thermal loads are typically supplied by regulating the temperature output of one stream of the heat exchanger and by modifying the mass flow rate of the other one. The availability of dynamic models suitable for control design can aid this process to be performed in an efficient way. In this paper, thermal dynamic models of counter-flow heat exchangers are developed. The models encapsulate key heat exchanger characteristics and consider the dynamic calculation of heat transfer coefficients—which includes the hydraulic behavior of the streams. Although heat exchangers are non-linear systems, linearized models are obtained to design simple yet effective and robust controllers in the frequency domain. These are validated in an advanced process simulation software. It is shown that a good temperature control performance in heat exchangers can be achieved for a wide range of operating conditions with a simple PI controller.

Electricity systems and heating systems are more coupled than before. Interactions between systems become stronger and influence the performance of integrated energy systems greatly, especially when security is the concern. Steady state analysis methods were usually used in recent research of integrated electricity and heating systems, which are not able to accurately evaluate the interactions due to the slow dynamics of heating systems. This paper studies quasi-dynamic interactions between electricity systems and heating systems in normal operation. Interaction mechanism is analyzed, and transport delay is emphasized as an important feature of quasi-dynamic analysis in time dimension. The transport delay comes from the temperature propagation in heating networks and has significant influences on the quasi-dynamic interactions. The transport delay is quantified by quasi-dynamic models. Electricity systems and heating systems can influence each other when disturbances or actions occur. Control strategies also have great effects on the interactions.

Heat exchangers have a predominant role in heat transfer and constitute a key component of integrated energy systems. For instance, heating and cooling of fluids are the cornerstone of district heating systems. Thus, it is fundamental to understand the heat exchanger's dynamic behavior to design controllers which are robust to temperature variations. Following this line, this paper presents a dynamic model of a plate type heat exchanger. The model is obtained from first principles of energy transfer and fluid mechanics and describes the thermal behavior of fluids involved in the heat transfer process. Although the system is non-linear, system linearization is performed to obtain a frequency domain model suitable for control system design. The linear model is implemented in MATLAB to design a controller that regulates the cold stream outlet temperature. To assess its effectiveness, the controller is discretized, programmed in Python and implemented in Apros — an advanced process commercial simulation software. Simulation results show that the controller is capable of tracking reference temperatures while ensuring a good performance of the heat exchanger system.