Magnesium is now regarded as the construction material of the 21st century. The light metal is characterized by its lightness, excellent casting properties and ease of machining. In addition, magnesium can be recycledalmost indefinitely compared to other materials. The STIHL company already established a magnesium die casting plant in Weinsheim in 1971. With a casting capacity of approx. 6000 tons per year, the plant is now considered one of the largest and most modern magnesium die casting plants in Europe. More than 20 die casting machines of hot and cold chamber technology with clamping forces of up to 1000 tons are used in the fully automated production. 790 employees create more than 26 million components annually for chainsaws and other power tools of the parent company, but also for external customers.
Focus on Sustainability
The company is committed to environmental protection and energy efficiency at a high level and to their continuous improvement, both in corporate processes and in products. In line with these principles, great emphasis was placed on eco-efficiency when selecting a new exhaust air filtration system. In addition, the climatic conditions were taken into account in the design of the exhaust air technology. In Weinsheim, Rhineland-Palatinate, the thermometer hovers around the zero-degree mark during the winter months. Therefore, when awarding the project, STIHL not only attached importance to reliable exhaust air purification, but at the same time to highly efficient heat recovery. In 2015, KMA Umwelttechnik GmbH installed a unique heat recovery system (Fig. 1) that heats the entire die casting foundry to a constant 18 °C during the winter months without feeding in conventional energy sources such as electricity or gas. The multi-stage heat recovery system is based on two hydraulic circuits in which 45.6 m3 and 22.8 m3 of ethylene glycol flow as a carrier medium every hour.
Multi-Stage Recovery of Valuable Process Waste Heat
Twelve exhaust air filter systems with a total capacity of 236,000 m3/h are installed in a weatherproof housing on the hall roof of the die casting foundry. In addition to the filter elements (Fig. 2), the systems have exhaust air heat exchangers so that the heat contained in the exhaust air can be recovered. The exhaust air from production, which is contaminated with oil smoke, is drawn in under the hall ceiling via fans and first flows through the exhaust air filters. Downstream are the heat exchanger units. Since the exhaust air has a temperature of at least 29 °C even in winter, it has valuable thermal energy that is extracted in the heat exchanger by means of hydraulic carrier medium during the cold season. Each heat exchanger has a capacity of max. 112.5 kW/h. The heat transfer medium circuit leads to the basement below the foundry hall. The central supply air system for supplying fresh air to the foundry is located here. Fans draw in fresh air from outside. Via a first heat exchanger (Fig. 3), the energy recovered from the exhaust air is transferred to the supply air by means of a cycle compound system. In this way, the supply air can be heated to at least 11 °C even on cold winter days. In order to bring the supply air to the required inlet temperature of 18 °C, the system has a second heat exchanger stage (Fig. 4).
Production Independent Heating System
