Fraunhofer Institute for Silicate Research ISC, Center HTL, Bayreuth

In September 2012, the EnerTHERM project was launched at Fraunhofer-Center for High Temperature Materials and Design (HTL). The abbreviation EnerTHERM stands for energy-efficient thermal processes. The project develops methods that can significantly increase the energy efficiency of industrial heat treatment without affecting the product quality. The project is supported by the Bavarian Ministry of Economic Affairs with a total of 9.5 million Euros. EnerTHERM is structured in eight subprojects.

In manufacturing sector alone, approximately 1800 petajoules are used each year for process heating. This corresponds to about 20% of the total energy consumption in Germany. Half of the process heat is used for high-temperature processes with temperatures over 1000 ° C. With the increase in energy efficiency for industrial heat treatment targeted in the EnerTHERM project, the total energy consumption can be significantly reduced. This will be an important contribution to global climate protection goals. Many heat treatments are carried out by gas heating, so that an efficiency increase is also directly converted into lower CO₂ emissions. But an improvement of the energy efficiency of electrical furnaces will have positive effects on the climate as well, since the share of fossil fuels in the German electricity mix is still more than 50%. In addition, the saved energy does not require expensive storage or transmission lines.

In previous projects, HTL has already shown that the energy efficiency of the sintering of technical ceramics can be increased by up to 40% without impairing the quality of the ceramics^[1]. In the EnerTHERM project, this objective extends to the heat treatment of other materials. HTL is pursuing a holistic approach:

• Together with material manufacturers, HTL develops parameters for heat treatments, with which the material can be processed gently, but with the best possible energy efficiency.
• Together with manufacturers of refractory materials and other high-temperature materials, HTL is developing new materials that are used in heat treatment and improve the energy efficiency of the processes.
• Together with furnace manufacturers and suppliers, HTL develops components for furnace use and assessment methods for the energy efficiency of furnace systems.

During heat treatment, numerous parameters have to be optimized. The most important are:

• Arrangement of the heated material in the furnace
• Temperature-time cycle
• Furnace atmosphere

Heat treatment must be optimized both from the furnace perspective and from the perspective of the material. The former essentially determines the energy efficiency and the throughput of the processes, the latter the product quality. It is precisely the worm’s-eye view, that is, the view of the material on the heat treatment process that opens up essential possibilities for improving the understanding of the process. From this, specific measures for optimizing the product properties and minimizing process scattering can be derived. HTL measures the change in the heating material during the heat treatment in situ, derives optimal local heating conditions from it and realizes them in the furnace.

The refractory materials used in heat treatment (furnace coating, forming tools, brackets, capsules, etc.) have to fulfill special requirements. They are frequently subject to severe temporal and spatial temperature changes. While the heat capacity of all periodically heated components has to be minimized, the thermal resistance has to be maximized particularly for furnace coatings. The life expectancy of the refractory components is included in the cost calculation as well as in the CO₂ balance of the overall process. It must be maximized accordingly. HTL develops refractory materials and coatings for specific high-temperature applications. In addition, HTL develops high-temperature test methods for evaluating the properties of refractory materials.

HTL has a mobile furnace measuring system at its disposal, which can be used to determine the energy efficiency and capability of industrial furnaces. Heat losses can be determined quantitatively. The temperature distribution in the furnace and the composition of the furnace atmosphere can be also measured with high accuracy using furnace analysis. In addition, HTL together with furnace suppliers are developing special, particularly stressed components for furnace application, such as hot gas flaps, fans, burner components and heat exchangers. For the composition of complex components from standard parts with simple geometries, high-temperature joining processes for form- and material-fit joints are developed at HTL.

The EnerTHERM project develops methods for characterizing and enhancing the performance of heat treatment processes. They are then tested and put into practice by HTL in cooperation with furnace users, manufacturers and suppliers.

^[1] Raether, F. (Hrsg.): Energieeffizienz bei der Keramikherstellung, ISBN 978-3-8163-0644-3, VDMA-Verlag, Frankfurt, Germany (2013)