Since 2012, a modernisation programme has been underway to upgrade many of the of the prime movers at the compressor stations along the TENP pipeline system. At Stolberg, Mittelbrunn, Schwarzach and Hügelheim a total of nine gas turbines are being replaced by new “Frame 3” units complete with all ancillary systems. The last upgraded compressor unit is scheduled to be restarted in December 2016.
The upgrade is aimed at significantly reducing exhaust gas emissions and complying with the emission limits specified by clean air legislation (13th BImSchV). The new gas turbines have a so-called Dry Low NOx (DLN) combustion system which allows nitrogen oxide to be reduced by as much as 90 per cent.
The biggest challenge of this major asset project has been to fully maintain gas transmission along the TENP pipeline system throughout the five years of work. This was achieved thanks to a specially devised “roll-over” concept, which has allowed three compressor units (i.e. one unit per station) to be modified every year without interrupting station operation. A total of nine gas engines have been replaced or modified.
However, this resource-saving approach has also required much more upfront planning.
Apart from the prime mover replacements, the units’ ancillary systems have also been either rebuilt or replaced. The main focus here was on incorporating additional heat exchangers (recuperators) for the exhaust gas system. A total of seven of these recuperators were installed. They will increase process efficiency by using the turbine’s exhaust gases to preheat the combustion air. Recuperators require large surfaces to ensure proper heat transfer between the exhaust gas and the combustion air, which is why they are equipped with tube bundles. The large heat exchangers weigh approximately 90 tonnes.
The Trans Europa Naturgas Pipeline (TENP) ships Norwegian natural gas from the Dutch-German border over a distance of some 500 km to Switzerland and Italy. The pipeline was built in the early 1970s. Today it is the most important North-South route of the integrated European natural gas transmission system. The operator of the pipeline is Trans Europa Naturgas Pipeline GmbH & Co. KG , a joint subsidiary of the two transmission system operators Open Grid Europe GmbH and Fluxys TENP GmbH.