Systematic integration of high temperature heat pumps in industrial multi-energy systems

The industrial multi-energy system (MES) introduces electrification of process heat and waste heat recovery to overcome the traditional concept of fossil fuel reliance and waste heat disposal. High temperature heat pumps (HTHPs) are efficient technology for generation of industrial process heat and recovery of waste heat. However, there is a lack of approaches that comprehensively address the challenges of delivered temperature, efficiency, renewable electricity and waste heat availability, and grid reliability. In this paper, a novel component-through-to-system design process is presented to integrate multi-temperature HTHPs in industrial MESs. Based on developed thermodynamic models, a concise map of achievable COP and temperature lift of different HTHP configurations (single stage, two stage, cascade, Joule-Brayton, mechanical vapor re/compression) is proposed as a framework for HTHP selection. A HTHP dynamic model is developed to study the interdependencies between sizing and operation of MES. The advantage of the use of a dynamic model is that it can simulate the HTHP performance in significant load variations caused by time variability of multi-temperature heat demands, waste heat, and renewable electricity availability. Moreover, flexible grid interactive operation strategies are proposed along with performance metrics that can quantify the grid stress. The dairy industry is used as an illustrative example to show (i) a novel HTHP configuration comprising a cascade R717/R718 system topped with a mechanical vapor compression for steam generation, (ii) an original HTHP-integrated MES with thermal energy storage, photovoltaics, and electrical energy storage, and (iii) the dynamic performance characteristics of the industrial MES under two operation strategies. The first strategy aims to achieve a flat electricity consumption profile for HTHP thermal capacity equal to the average heat demand. The second strategy adjusts electricity consumption to renewable generation but at the expense of higher HTHP installed capacity. A parametric analysis shows the compromise between the design capacities of the MES components and the daily electrical energy deficit, the daily excess electrical energy, and the Euclidean norm of the total power profile. The results indicate that the integrated HTHP is a significant distributed source of efficiency improvement and operational flexibility.