By Dr.-Ing. Volker Kienzlen, KEA-BW
Reiner Hagemann, Badische Stahlwerke GmbH (BSW)
Sabine Schimetschek, Calorie-Kehl Strasbourg (CKS)
Badische Stahlwerke has been looking for a way to use this waste heat for decades. In the nearby industrial area of the port and the town of Kehl, three kilometres away, there are no suitable customers for such large quantities of heat. On the other side of the Rhine lies Strasbourg - a city that already op- erates large district heating facilities and would like to expand these even further regarding the climate policy goals. By 2050, at the latest, Strasbourg's heating networks are to be entirely climate-neutral. Therefore, Strasbourg not only plans to extend the district heating system but also intends to lower the net- work's temperature. The first idea to use the enormous amount of excess heat dates back to 2014. In 2018, the KEA-BW, the state energy agency in Baden-Württemberg, initiated another attempt to use the heat that cannot be used within the company. The rising importance of climate protection and the neces- sity to become climate-neutral was a new baseline for the discussion with BSW and the cities of Kehl and Strasbourg. Improved funding conditions were also helpful. In July 2018, the Baden-Württemberg Ministry of the Environment com- missioned a study to the engineering company EGS-Plan, confirming the project's technical and economic feasibility. Since then, the Eurometropolis of Strasbourg, the Badische Stahlwerke, and the city of Kehl have been working with KEA-BW, dena1, ADEME2, and several other stakeholders to push forward the German-French cooperation project. This was followed by further studies to clarify the potential, the heat requirements in Strasbourg and Kehl, as well as the pos- sible layout of the heating grid. Since the district heating network in Strasbourg is rather old, some areas of the network still require flow temperatures of more than 140 °C when the ambient temperature is very cold. For BSW, this means that the outlet temperature in the heat exchangers has to be raised to 160 °C, which increases the operating pressure significantly. The existing system cannot meet the safety requirements, which is why the entire prima- ry cooling system must be rebuilt. This also includes replacing the heat exchangers for the secondary cooling tower circuit, which ensures heat dissipation during low district heating de- mand periods. The part of Strasbourg’s district heating system relevant to the project consists of the two interconnected heating networks, Esplanade and Elsau. Two gas-fired boilers are used to cover the peak load. The base load is generated by a biomass co-
BSW, the Badische Stahlwerke, runs a steel mill in Kehl. In the harbour area north of Kehl, they produce 2 million tons of steel per year, mainly for the construction sector. Two electrical fur- naces use steel scrap to produce reinforcing steel. The main waste heat source is the exhaust gas from the two electric arc furnaces where the steel scrap is melted. There are also other potential sources of excess heat, e.g., the pusher furnaces, where billets are reheated for further processing. In the first step, the waste heat from the electric arc furnace will be used. In the future, however, other waste heat potentials could also be used. The exhaust gases, up to 1,300°C hot, will flow through a water-cooled heat exchanger, which pre-cools the gases to approx. 600°C. The cooling water in the heat ex- changer runs in a closed circuit and has a flow temperature of approx. 70 °C and an outlet temperature of up to 90 °C. Due to the melting process, the water temperature fluctuates greatly since cold scrap is charged at the beginning of the process, and molten steel is tapped at 1,600 °C at the end. In addition, there is a short production downtime in summer and a three- week downtime in winter. On average, a heat flow of 20 mega- watts is cooled to ambient air. Based on the production data of the steel mill, this results in a total available waste heat of 135 gigawatt hours per year.
Direct dedusting of electric arc furnace
to the baghouse
electric arc furnace
dedusting
heat exchanger (160°C)
Badische Stahlwerke GmbH
Schemabild Elektroöfen © Badische Stahlwerke
1 https://www.d-f-plattform.de/fileadmin/dena/Publikationen/PDFs/2022/RZ_dena_Factsheet_U__berarbeitung_Strassburg-Kehl_DE_digital.pdf
2 French environment and Energie management agency - https://www.ademe.fr/en/ademe-the-french-ecological-transition-agency/our-organisation/
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