Anyone who is serious about climate protection prefers to use renewable energies and exploit their potential as far as possible to avoid wasting valuable resources. Stadtwerke Groß-Gerau is one of many examples. For more than ten years, the regional energy supplier has been using a biogas cogeneration plant to generate electricity. Around 8.5 million kilowatt hours of green electricity are generated every year in the biogas plant at the Wallerstädten site. Enough to reliably supply a good 8,500 households with electricity. The green electricity is based on agricultural waste from the region, which is fermented in airtight tanks to produce combustible biogas that is converted directly into electricity on site by combined heat and power (CHP) units.

No more chasing usable energy through the chimney

Burning biogas to generate electricity naturally produces waste heat, which is often released unused into the environment via the chimney. Those responsible at Stadtwerke no longer wanted to put up with this waste of resources, but wanted to make maximum use of the valuable energy contained in the waste heat. The Organic Rankine Cycle (ORC) process quickly emerged as the ideal technology for this. As a result, Dürr Systems AG from Bietigheim-Bissingen was commissioned to integrate a fully automated Cyplan ORC 70 HT CHP into the existing plant concept in order to further optimize renewable power generation.

Additional electricity for around 400 households

Thanks to the now sensible use of exhaust gas heat by means of the installed Cyplan ORC system, Stadtwerke produces an additional 400,000 kilowatt hours of electricity per year and thus covers the needs of another 400 households. The condensation waste heat from the ORC system is decoupled as useful heat at a temperature level of up to 90 degrees Celsius and heats the company's own buildings as well as supplying heat to a neighboring producer initiative for the sustainable drying of spices and medicinal herbs. The higher energy yield therefore generates additional income, on the one hand through the green electricity generated by the ORC system and on the other through the useful heat, and it also reduces operating costs - and all of this is CO2-free.

Robust design and reliable support

The high profitability of the ORC system is also due to its robust design and the comprehensive customer service that Dürr has provided from a single source since the planning and installation. This also includes close cooperation with Ingenia, the operating company responsible on behalf of the municipal utilities. ORC is a tried and tested technology for generating electricity from waste heat. The process is similar to the steam turbine process. However, in decentralized energy generation with a biogas CHP plant, the temperature gradient between the heat source and the heat consumer is too low to drive a turbine with steam. This is why ORC systems use an organic working medium instead of water, which evaporates at low and medium temperatures. It sets the self-contained cycle process in motion and drives a highly efficient single-stage expansion turbine in Dürr's Cyplan ORC systems.

System availability of well over 95 percent

"The Dürr team has reliably supported us for years with extremely short response times and solution-oriented approaches. Over the entire service life to date, we have had a system availability of well over 95 percent. I am convinced that the system will continue to make a reliable contribution to sustainable and CO2-free power generation in the coming years," says Stefan Ruckelshaußen, Managing Director of ingenia Dienstleistung Beratung Management GmbH, with great satisfaction.

The right solution for every application

The Cyplan ORC 70 system used at the Wallerstädten site consists of a prefabricated, TÜV-certified unit. The standard modules cover the entire range from 50 kW to 500 kW electrical output. In addition, Dürr also develops customized solutions for larger or industrial systems, with which the efficient ORC technology converts waste heat into green electricity and clean useful heat for a wide range of applications in an ecologically and economically profitable way.

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