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Siemens Installs Heat Recovery Pilot Plant at Stahlwerk Thüringen

05/23/2012 - A heat recovery pilot plant installed by Siemens Metals Technologies in the electric steel plant of Stahlwerk Thüringen GmbH in Unterwellenborn, Germany, is now in operation since April 2012. The plant uses molten salt as the heat transfer medium and is connected to the existing exhaust gas system of the EAF.

A heat recovery pilot plant installed by Siemens Metals Technologies in the electric steel plant of Stahlwerk Thüringen GmbH in Unterwellenborn, Germany, is now in operation since April 2012. The plant uses molten salt as the heat transfer medium and is connected to the existing exhaust gas system of the electric arc furnace. The objective of the pilot project, according to Siemens, is to validate possible materials for use under high temperatures, and to investigate the conditions required to achieve the highest possible energy recovery efficiency. The pilot plant is preliminarily set to operate for one year.
 
The heat recovery plant installed by Siemens at Stahlwerk Thüringen uses a molten eutectic ternary salt mixture as the heat transfer medium. About 1,500 kg of molten salt are stored in a buffer vessel at an operating temperature of 430°C. The molten salt can temporarily store and release 65 kWh of energy, which corresponds to a storage capacity of about 90 kWh/m3. The project focuses on investigating a range of materials, especially for the heat exchanger in the hot gas duct, as the materials there are subjected to extreme stresses by the high gas temperatures.
 
Siemens VAI is responsible for the engineering of the heat recovery plant, and for supplying all the components, including the electrical systems and automation, as well as for the installation and commissioning.
 
The new technology is intended to be used in the future to recover energy at a high temperature level, and make it available for high temperature heat consumers or for generating electricity. The knowledge gained from the material investigations is independent of the heat transfer medium, and can therefore also be applied to conventional water/steam systems, according to Siemens.
 
As the stream of hot exhaust gases from an electric arc furnace is not continuous, the recovered energy has to be stored temporarily. Saturated steam is usually used as the heat transfer medium. This requires the installation of pressure vessels and lines, whereas no pressure applies in plants that use molten salt as the transfer medium. Salt also allows media temperatures of over 500°C to be achieved without evaporation starting, Siemens claims.
 
Stahlwerk Thüringen GmbH has been part of the Brazilian corporation CSN (Companhia Siderúrgica Nacional) since February 2012. The company, based in Unterwellenborn, has a range of products that includes beams, profiles, and steel ties. It makes more than 200 different profiles according to various national and international standards. The plant produces general structural steels, fine-grain and weather-resistant structural steels, special steel grades for shipbuilding and low temperature applications, as well as offshore grades.
 
The Siemens Industry Sector (Erlangen, Germany) is a leading supplier with end-to-end automation technology and industrial software, solid vertical-market expertise, and technology-based services. With a global workforce of more than 100,000 employees, the Industry Sector comprises the Divisions Industry Automation, Drive Technologies and Customer Services as well as the Business Unit Metals Technologies.
 
The Metals Technologies Business Unit (Linz, Austria), part of the Siemens Industry Sector, is one of the world’s leading life-cycle partners for the metallurgical industry. The business unit offers a comprehensive technology, modernization, product and service portfolio as well as integrated automation and environmental solutions covering the entire life cycle of plants.