German industry releases 200 billion kilowatt-hours of thermal energy a year into the environment as unused waste heat – roughly equivalent to the entire energy consumption of the federal state of Hesse. In a new documentary by VDI ZRE entitled “Stromerzeugung aus industrieller Abwärme” (Generating Electricity from Industrial Waste Heat), two companies demonstrate how they use this valuable energy source to produce electricity, thereby making an important contribution to the conservation of resources.
BILSTEIN GmbH & CO. KG in North Rhine Westphalia processes steel strips for use in the furniture, tool and automotive industries. The strips have to be heated and then re-cooled so that they can later be formed and further processed. The waste heat generated in this recrystallisation process is used to produce electricity, with the aid of an innovative Organic Rankine Cycle (ORC) system. Unlike conventional procedures, ORC can make use of the relatively low temperatures of the waste heat for the generation of electricity. Not only does the company save electricity through the efficient use of waste heat, it can also use the heat for heating buildings and accelerate production thanks to faster cooling times.
The Gebr. Wiesböck & Co. GmbH Portland cement plant in Upper Bavaria produces cement for the construction industry. The required raw materials are heated together with various additional materials in a rotary kiln to produce cement clinker. The 400°C exhaust gases from the rotary kiln contain dust and are used to preheat the raw and additional materials for the firing process. At the same time, they are also fed into a special waste heat boiler to produce steam. The steam then powers a turbine which produces electricity via a generator. In this way the power plant can generate 30% of the electricity it needs, and save the equivalent of 80,000 tonnes of CO2 a year.
These two projects are funded by the Environmental Innovation Programme of the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety.