Langzeiteinsatz von Reibungsminderern im Fernwärmenetz Völklingen-Luisenthal

In district heating systems the costs of heat distribution play a decisive rule. Most of the pumping energy is expended on pressure losses in transport pipes. Drag reducing additives offer a new technology which can substantially reduce pressure losses in pipe systems and therefore can lead to a reduction of the transport costs. In 1992 an EU/BMFT (European Union, German Ministry for Research and Technology) demonstration project on the application of drag reducing additives in a real district heating system was started. Therefore, the drag reducing additive Dobon-G in addition with sodiumsalicylate was applied in the distribution system Luisanthal (ca. 10 MW, length of pipeline: 2600 m) of hte Fernwarmeverbund Saar GmbH. The main purpose was the demonstration of the drag reduction under normal operating conditions over a long period. Furthermore, a 1700 m pipe section, a centrifugal pump, a plate heat exchanger and a heat meter with a Woltmann-flow meter have been investigated. A constant drag reduction of 70% in maximum in the 1700 m pipe sectin over a period of nine month was achieved. During this period no problems concerning supply guarantee appeared. The investigation of the centrifugal pump showed that the efficiency could be increased by 5% due to the drag reducing additives. This is caused by the change in the pressure drop characteristic of the system to lower pressure losses. In addition to the drag reducing effect, the heat transfer is reduced due to the damping of radial turbulances. As a result of this heat transfer reduction, the heat output of the investigated plate heat exchanger was reduced by 13% in maximum. This effect was taken into account by designing the heat exchanger with a larger heat transfer area and therefore no problems concerning the supply guarantee occured. Laboratory tests showed that Woltmanflox meters are influenced by the drag reducing effect. The results of the demonstration project confirmed these tests. To compensate for this effect, the influenced heat meters were mounted into the hydraulicly uncoupled side of the consumer stations. The long term demonstration project in Luisenthal showed that the application of drag reducing additives in district heating systems is realizable, the additive is stable and no problems concerning the supply guarantee occur