Energy efficiency in the industry: A study of the methods, potentials and interactions with the energy system

Abstract

The industry sector has an important role in decarbonising the energy system, as recognised by the European Commission in their 2050 roadmap to a low carbon economy. It has a high share in the final energy use of the European Union, which in 2016 relied heavily on fossil fuels. A shift to a more sustainable energy use is thus needed, requiring both an increased share of renewable energy and a reduction in energy use. In this thesis the manufacturing industry was analysed to show its potential to improve energy use on an energy system and process level. For this purpose the inefficiencies of the industry sector of Denmark were taken as an example and quantified using energy and exergy methods. The developed models were used to quantify the amount of industrial excess heat. Based on these mappings, the potential for recovering and exploiting excess heat was analysed, which required the development of new methods to locate potentials. The methods included spatial, temporal and economic elements to have a realistic assessment of national potentials. This was complemented with multiple case studies, for which the model input uncertainties were taken into account. The second part of the thesis considered specific production processes and methods for assessing them. For the case study of a milk powder production system, different engineering and advanced thermodynamic methods were used for the analysis. The different methods, which include pinch and exergy analyses, located and quantified different optimisation potentials, which were compared against each other. At last, specific optimisation opportunities were identified and evaluated. These consisted of a retrofit heat exchanger network and the integration of heat pumps and solar thermal energy. The results show that the energy efficiency of the Danish manufacturing industry was 80 % and only 72 % when taking the utility system into account. The losses are often in the form of recoverable excess heat. It was found that 1.5 TWh of excess heat could be cost-effectively used for district heating. The tool developed for the case studies enables to overcome some of the barriers for the utilisation of excess heat. It assesses heat sources and possible uses considering the uncertainties and determining important model parameters. The analysis of the dairy factory resulted in potentials for improvement and highlighted merits and drawbacks of the applied methods. The advanced methods allowed for a thorough analysis of components and interactions amongst each other, the engineering approach is quick to indicate possible improvement but requires experience. The specific improvement suggestions show that it is technically and economically possible to reduce energy use by means of heat integration and to partly replace the hot and cold utilities with more sustainable ones.