In 2010, BMW Group commissioned Gammel Engineering to develop a concept for waste heat recovery in the light metal foundry at the BMW plant in Landshut. The planning services included determining the potential, developing the concept, supporting the procurement of funding, system and design planning as well as comparing variants and assessing the economic viability.
Based on the ideas of the Gammel Engineering industrial team, a consortium was commissioned to implement the concept via an energy service contract: Gammel Engineering as an engineering service provider, Siemens, a specialist in electric motors, frequency converters and control technology, and the long-standing BMW Group subcontractor Ulrich Müller GmbH, an expert in plant construction and a specialist company in building services engineering. Combining the expertise of the three professionals ultimately resulted in enormous potential savings in the areas of energy and CO2 for the BMW site in Landshut.After the commissioning of a new melting shop in autumn 2012, it was possible to begin to flesh out the possibilities by continuing the concept with the data from the new melting furnaces. At the Landshut site, the BMW Group uses gas burners to melt solid aluminum material delivered to the plant in a total of six furnaces. On average, three furnaces are in melting mode and three furnaces are in holding mode. The flue gas has a temperature of around 640°C when it exits the melting furnaces. "The most obvious solution at such high temperatures would have been to generate electricity. This is usually the most lucrative option for heat recovery," explains Michael Gammel, Managing Director of Gammel Engineering. "However, this concept using ORC reciprocating engines or ORC turbines and feeding waste heat into the plant's own heating network was not implemented, as a much more efficient option was found for the specific situation." The intensive exchange of ideas between Gammel Engineering, Siemens and Ulrich Müller as experts, the analysis of the energy situation of the entire BMW site in Landshut and the complete energy requirements, resulted in a new, holistic energy concept with significantly higher savings potential.
Cooling is needed for production all year round. Calculations showed that the heat from the melting furnaces is sufficient to provide the necessary cooling. The existing heating network was used to distribute the heat and an absorption chiller was installed wherever cooling was required. Using the light metal foundry as a second feed-in point also increases the capacity of the heating network and reduces the pump energy required - an additional energy saving.
In the heating network, the flow temperature of the water is 130°C and the return temperature is 70°C. This means that the waste heat from the light metal foundry at a level of 640°C can be used in a technically straightforward manner. There are plans to connect two chillers in series in order to further increase efficiency with the help of a lower return temperature. By coupling heating and cooling, the energy that is generated evenly throughout the year in the light metal foundry can always be fully utilized. Calculations suggest that the heat can be fully utilized for over 7200 operating hours per year.
As the heat network is relieved by the heat recovery from the light metal foundry, it no longer matters where an additional CHP unit is installed. In addition to generating electricity, this then provides an additional feed-in point for heat into the heating network.The new energy concept leads to better use of the existing infrastructure, to the utilization of previously unused heat released into the atmosphere, to electricity savings through reduced pump energy in the hot water network and through energy no longer required for the compressor chillers. All this not only saves money, but also protects the environment by reducing CO2 emissions. The concept developed also makes the energy supply more flexible overall, making it easier to react to future developments.
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