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% 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.
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% can be achieved in the test network. Especially in the area of high volume flow rates a very significant pressure loss reduction of approx. 65% occurred, so that saving of electric pump work is ensured, above all, in the sector of a maximum pump current demand.
An inspection of the drag reducing effect of the tensides and the measurement of the variation in time of the tenside concentration are carried out at intervals of approx. 4 weeks. The above-mentioned measures serve to prove the long-term stability of drag reducing addtives.
An influence of the drag reducing additives on the feed pump could not be noticed, as it had already been the case in previous tests. Only marginal shifts in pump characteristics were observed.
On the contrary, the tensides showed a marked influence on heat transmission behaviour in the heat exchanger. A heat transmission reduction of 50-60% was noticed on that side of the heat exchanger installed in the district heating network Luisenthal which was impinged with tenside-containing water. This resulted in a heat exchanger transmission capacity lowered by 10%. Inspection of the heat transmission behaviour of tenside-containing district heating water, particularly the influence on the district heat reflux temperature, is being continued.
Moreover, two heat quantity counters the volume flow measuring part of which consists of a sail wheel of Woltmann are being tested within the framework of the demonstration project. In order to do so, heat output of one unit on the tenside side (secondary side) is being compared with heat output on the water side (tertiary side). During the preliminary test phase with water a good compliance of both units was observed. First results with applied tenside are in the order of a reduced counting of roughly 5 to 10%. These deviations are considerably lower than the results determined in laboratory tests. These smaller deviations might be caused by shorter inflow lines in front of the volume flow measuring elements of the heat counters in the real system. During a time period of nearly 1 year no negative influences on the long term stability of tensides could be determined.
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.
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Coordinator
6620 VÖLKLINGEN
Germany
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