Das Projekt "Application of drag reducing additives in district heating systems - Phase 2 -" wird vom Umweltbundesamt gefördert und von Fernwärme-Verbund Saar GmbH durchgeführt. Objective: The application of drag reducing hydrous tenside solutions causes a reduction of drag-dependent pressure losses in the case of turbulent pipe flows. The pressure loss reduction achievable can amount to 80-85 per cent when the medium flows through straight pipes. The drag reducing effect can be used in existing district heating systems to save pump current and to raise supply capacity. When planning new district heating networks investment costs are saved by applying drag reducing additives because in this case system elements (pipes, accoutrements, measuring sensors, etc.) of smaller nominal diameters can be installed. General Information: In 1988 and in 1990 two field tests on a transport duct of the 'District Heating System of the Saar region' having a nominal diameter of DN 450 and a duct length of 1,200 m (connection between the power station Fenne and the central station Voelklingen) were carried out (under contract EC./00072/86/DE). In well-aimed tests programmes executed within the framework of the two-large-scale tests, the transfer from laboratory scale to commercial scale (1: 20) as well as individual system elements, such as heat exchangers, pumps, pipe bends and flow meters, were tested. During these tests, volume flow rate, temperature as well as applied concentrations of drag reducing additives were varied in order to find out an optimal application range and an optimal tenside effect. Since January 1993 a long term test is being carried out in a representative district heating system (a partial system of the district heating network of the Saar region, the network Voelklingen-Luisenthal). The above-mentioned network is equipped with a pipeline of a nominal diameter DN 200. The pipe length amounts to 850 m. It is the objective of this 3rd demonstration test to prove the long-term stability of the additive system used and to check the real applicability of drag reducing additives. In particular, two plate heat exchangers specially designed for tenside application are being tested. The drag reducing additives applied are a mixture of dobone-G and sodium salicylate dissolved in district heating water. The applied concentration of the substances is 1,500 wppm of dobone-G and 720 wppm of sodium salicylate. These concentrations proved to be successful with regard to their effect and range of application both in laboratory tests and during the two preceding large-scale tests. The planned test duration is 1.5 years, however, it is to be prolonged when the application of drag reducing additives turns out to be successful. Achievements: During the execution of the measurements in the district heating network Luisenthal the grag reducing effect of the tensides applied could again be proved. A detailed examination of the variation of the pressure loss with the volume flow rate showed that on average a pressure loss reduction of approx. 60 per cent can be achieved in the test network. Especially in the area of high volume flow rates..
Das Projekt "Application of drag reducing additives in district heating systems - Phase 1 -" wird vom Umweltbundesamt gefördert und von Fernwärme-Verbund Saar GmbH durchgeführt. Objective: Preliminary tests on a laboratory scale proved that the drag-depending pressure loss in pipe flows can noticeably be reduced by applying hydrous tenside solutions. The maximum reduction in pressure loss achievable for a turbulent flow in straight pipe sections is about 90 per cent. The drag reducing effect can be used in existing district heating systems for saving pump current or for increasing supply capacity. When planning new district heating systems, investment costs can be saved by the application of drag reducing additives since, in this case, system elements (pipes, fittings, measuring sensors, etc.) of smaller nominal diameters can be installed. General Information: In 1988 and in 1990 two field tests were carried out in a transport pipe of the district heating system of the Saar region. In both large-scale tests, it was checked by specified test programmes whether the laboratory tests could be transferred to real site conditions (scale of approx. 1:20) and individual system elements were tested, such as heat exchangers, pumps, pipe bends and flow meters. Within the framework of these tests, volume flow rates, temperatures and concentrations of drag reducing additives were varied in order to determine the optimum application range and the optimum tenside efficiency. Achievements: In the period from September to October 1988, the drag reducing additive 'dobone' was applied in a 1.2 km long pipe section between the combined heating and power station Fenne and the central station Volklingen. The pipe had a diameter which is typical for transport systems, i.e. DN 450. The applied drag reducing additive showed a marked influence on the pressure loss in the pipeline. However, its drag reducing effect was available exclusively in the temperature range between 90 and 140 deg. C, so that the pressure loss could only be reduced in the flow pipe of the district heating system. A second drag reducing additive, i.e. an additive consisting of the substances dobone G and sodium salicylate, has been developed in cooperation with HOECHST AG. In laboratory tests this additive has a drag reducing effect within a temperature range of 55-140 deg. C which is relevant for district heating systems. In the period from September to October 1990, this additive was again applied in the pipe section between the combined heating and power station Fenne and the central station Luisenthal. During this test an average pressure loss reduction of 50 per cent was observed; the pressure loss reduction for straight pipe sections even amounted to 75 per cent - 90 per cent. The drag reducing additive was effective both in the flow and in the reflux transport pipe. After the applied concentrations of dobone G and sodium salicylate (NaSal) had been varied, the following concentration values were stipulated for future tenside dosings: dobone G = 1,500 wppm sodium salicylate = 720 wppm Given the above-mentioned concentrations of substances, there will nearly be a...