The final energy use of process heat (without hot water and process cooling) in Germany amounted in total 1 960 PJ in the year 2013 which is equivalent to 21 % of the total final energy demand. The highest amount results with 1 701 PJ respectively 87 % of the industrial process heat (BMWi 2015). Depending on the process, a mostly significant proportion of the used heat is wasted or sometimes has to be dissipated with additional cooling efforts. As a potential source of waste heat, furnaces, heat emissions of production plants and machines, waste water of washing, dyeing and cooling processes, refrigerator systems, cooling of server rooms, motors as well as the exhaust air of the production halls can be worth considering. It is estimated that, despite of great efforts for the heat integration in Germany, almost 500 PJ waste heat are emitted into the environment per year (Enova 2009; Pehnt et al. 2010). This shows the great potential of the savings of primary energy sources as well as of the reduction of CO2 emissions. The theoretically useable waste heat potentials are only partially internally or externally (through third parties) used so far and are in their totality neither spatial nor potential related systematically recorded.
In the course of the development of the climate protection plan of North Rhine-Westphalia (NRW) and downstream stakeholder processes, several industry representatives expressed their interests in a systematic preparation of industrial waste heat potentials. Research needs are seen for example in the question, how heating networks transcending branches and companies in NRW can be realised. Further suggestions of the industry concern pilot projects of combined heat systems, the determination of potentials for the conversion of waste heat into electricity, respectively for the use of electricity in order to raise the temperature level of waste heat or the further development of innovative technologies for the power supply with waste heat, such as organic Rankine cycle (ORC) or the thermoelectric generators (TEG).
Regarding this background, the Wuppertal Institute together with the DLR Stuttgart developed a brief study on behalf of the Ministry for Climate Protection, Environment, Agriculture, Conservation and Consumer Protection of the State of North Rhine-Westphalia (MKULNV). In this study following components were worked out:
In the first part, regional hotspots with high industrial energy consumption were identified on the basis of the fuel and electricity input. High energy consumptions are a necessary but not a sufficient criterion for potentially relevant waste heat potentials. As a result, a map for the energy demand, broken down to different branches, for NRW is available in which the energy consumptions of all industry companies above 200 TJ/a (fuels), respectively 500 TJ/a (electricity), are listed. Additionally, a detailed map for the area Oberhausen/Duisburg was worked out.
In the second part, basic contents like characteristics of waste heat, utilisation strategies, technologies of different maturity levels and energy politic boundary conditions for the use of waste heat were given in an overview. Furthermore, the range of already used technologies and realised projects is presented through thirteen good-practice examples.
Based on ten expert interviews with stakeholders of associations and companies of energy intensive branches as well as of state institutions, research and power supply companies, primarily barriers and factors of success for the use of industrial (and municipal) waste heat are identified in part three. In these interviews, additional questions, for instance concerning the relevance of this topic in companies, concerning suitable approaches for a source-sink matching or regarding research and development demands, particularly for innovative technologies, were considered and the related answers were analysed.
In the fourth part, the concept of the "Heat Network Plans" as a possible methodology for the linking of waste heat sources to waste heat sinks as well as for the assessment of identified source-sink relations (source-sink matching) is outlined. This involves an evaluation method for the analysis and the comparison of waste heat utilisation concepts in consideration of technical, economic and ecological aspects (energy efficiency, energy and resource consumption) as well as the liability law.
In conclusion, the knowledge gained out of the interviews and literature analyses is used in part five in order to derive recommendations for action for the policy. There, the analysis of the expert interviews plays a central role. The recommendations for action are intended to help to eliminate the identified barriers for the use of industrial waste heat on the one hand, and to strengthen the factors of success and driving forces/actors on the other hand. The worked out suggestions are structured in technical, economic, organisational-structural as well as legal action fields. They address the general waste heat use as well as the topics of the feed-in into (external) heat grids, low-temperature heat and innovative technologies.
The analysis shows that high waste heat potentials and a fundamental interest to the utilisation of waste heat are existing on the one hand, however that on the other hand numerous barriers oppose the economic utilisation. The brief study provides information about approaches which help to overcome these barriers. Therefore, the research in the field of waste heat utilisation as well as the practical implementation have to be pushed further. Based on the results of this short study, it would be possible to implement a practical project in the future together with interested companies in order to identify concrete implementation potentials for waste heat while using the system of the source-sink matching (Heat Network Plans) which are worked out within the project.