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Increased efficiency thanks to lower temperature level: By connecting its turbine waste heat to a new hot water network instead of to a steam-based district heating system, the new gas and steam turbine plant in southern Munich is able to generate an additional 160 GWh of electricity per year.
Pilot project in Munich
Projektinfo 01/2007
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Converting steam-based district heating systems to hot water

Steam was the first heat transfer medium to be used for distributing heat in district heating systems. This is not surprising, since steam has always played a dominant role in the power station process, so that it was easy to supply customers near power stations with steam. Today, modern power plant technology enables the efficient exploitation of steam when generating valuable electricity. The maximum use of the primary energy is achieved through the co-generation of electricity and thermal heat in the form of hot water, which is why water is advantageous as a transfer medium for supplying district heating.

The increased use of district heating, in particular in the 1960s and 70s, increasingly revealed the disadvantage of steam-based systems: the construction and operation are, taken as a whole, much more expensive than hot water networks. Steam-based networks require a complex condensate system and thus considerable servicing and maintenance work. They have considerably higher operating temperatures, resulting in greater heat losses. Steam requires elaborate pipe and connection systems, which means that it is expensive to connect new customers and the potential for extending district heating systems is limited. The high temperatures also reduce effective cogeneration as well as the inclusion of lower temperature heat from industrial waste heat or renewable energy. Today, most steam networks are in need of refurbishment and their future viability is very much in doubt. At the same time, new impetus for district heating is coming from the gas market, since the charges for using gas grids have considerably reduced and the gas prices are currently anything other than stable.

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The consequence: district heating offers new market potential, and the pressure on the remaining steam network operators to convert is increasing. Steam networks have already been converted in some German cities. Here the heat transfer medium has always been converted in conjunction with the new installation of a hot water distribution network. As part of a BMWi research project, a technical and economic conversion concept was developed and implemented for the Munich steam network – the largest in Germany. A particular feature of the Munich pilot scheme is that this is the first time anywhere in the world that an existing steam and condensate pipe network has continued to be used as hot water supply and return pipes. Therefore, in conjunction with a planned new gas and steam turbine plant, one of the most cutting edge district heating systems in Germany is being created in Munich.

Projektinfo 01/2007:
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Stadtwerke München GmbH