Dynamic programming model for a thermal energy storage-based heat recovery system in a process industry plant

Abstract

Heat recovery systems (HRS) exist in conceptual configurations which encompass a set of energy-using processes installed on a particular site, a set of waste heat recovery technologies and all potential recirculation of material and energy streams with the overall aim to generate an overall benefit related to improvement in energy efficiency. A specific example of HRS are those that contain thermal energy storage (TES) components. In the context of the development of computational models, this type of HRS is modelled according to a dynamic simulation and optimisation perspective, owing to the transient state-based nature of these systems. This work presents the development and further analysis of an optimisation model developed according to the dynamic programming (DP) methodology for an HRS set to be implemented in a process industry plant. Such model was developed with the Modelica language, being an integral part of the ThermWatt simulation and optimisation tool. The developed model proved to be useful for the proposed objective of analysing transient state-based heat recovery systems, allowing an accurate modelling of the physical phenomena occurring during the time of operation of these systems. A relative reduction of 20.80% energy-related operational costs has been assessed for the system’s optimal configuration, which corresponds to a 0.51 M€/year absolute reduction (from 2.38 M€/year to 1.87 M€/year). This work is set to compensate for a knowledge gap related to the inexistence of studies approaching the use of mathematical programming methods for the dynamic (transient state-oriented) optimisation of thermal energy storage-based heat integration systems.