For Berliner Wasserbetriebe, we are building a heat exchanger within a wastewater pressure line with a total length of 240 metres, pipe in pipe. The diameters of the two pipes differ by 10 cm. Warm wastewater will flow inside and water used for heating will flow in the space between. After completion, the pipe will be connected to a newly planned residential park with apartment buildings.
Pipe freezing
A sewage pressure pipe GGG DN 350 could not be taken out of service due to several broken gate valves. In order to avoid an emptying of the entire sewage pressure pipe network, it had been decided to freeze the pipe in place. After five hours of cooling with -196°C cold liquid gas, the entire pipeline cross section was cooled down to -30 to -50 °C and frozen. The hazard caused by the permanent outflow of nitrogen was monitored throughout the works by using gas detectors, so that there was always enough oxygen available at the workplaces. After about three hours of installation, the defrosting process could be started. After several hours, the pipe cross section was de-iced again, so that the pipeline could be put back into operation after just 24 hours.
