Total site heat and power integration for locally integrated energy sectors

Abstract

Maximising energy efficiency is essential for an energy system based on renewable or non-renewable energy sources to minimise fuel demand. Process Integration methodologies for specific energy types (thermal and power) have been well developed in recent years for enhancing energy efficiency. However, the interaction between different types of energy (thermal and power) within a single system could be more deeply studied to achieve the ultimate goal of maximising energy and exergy efficiency. This research work extends the previously developed Locally Integrated Energy Sector (LIES) concept, which integrates the energy systems (thermal and power) of industrial, commercial and residential buildings with thermal energy storage and batteries. The LIES concept aims to reduce overall energy consumption and to enhance overall energy efficiency and power cogeneration. In the present paper, a comprehensive targeting framework is introduced for designing and optimising a combined energy system using a Process Integration (i.e. Pinch Analysis) approach. Steam turbines connect the thermal and power systems, which, in this case, the turbines generate power from waste heat. The on-grid and off-grid power supply options are also considered in this framework. The case study concludes that the lowest energy cost system requires a heat storage systems with let-down in between, power cogeneration from waste heat (i.e. surplus heat below the TS Pinch), Power Pinch Analysis, battery storage and on-grid power supply. The results for the case study show that the overall energy cost of the optimised system is 52% lower than the base case without integration. In this energy system, however, it has been found that the increment of energy efficiency for the steam (thermal energy) system might lead to lower overall energy efficiency and higher total operating cost. This situation happens when there is a lower amount of waste heat available.