The gas pressure regulating and metering station (GPRMS) Dillenburg operated by EAM Netz GmbH supplies part of the Lahn-Dill district in Hesse (Germany) with natural gas. At the station, the pressure of the incoming natural gas is reduced from 44 bar to 4.5 bar. Due to the throttling the gas cools down. In order to avoid effects such as condensation of air moisture or ice formation, which could lead to technical faults at the station, the natural gas is preheated by around 20 K before throttling. The energy requirement for preheating at the GPRMS Dillenburg amounted to approx. 220 MWh/a prior to modernisation of the plant in 2019.
Originally, heat was supplied exclusively by two gas boilers, one boiler being kept in reserve as redundancy to ensure operational safety. An innovative heat supply concept was implemented as part of the modernisation of the GPRMS. The concept consists in the combination of three new different heat generators and a dew point control. The dew point control enables the gas outlet temperature to be adjusted to the air moisture of the room. On the one hand, this enables a reduction of the gas outlet temperature in winter (energy saving), on the other hand, it prevents air moisture condensation on the gas pipeline and hydraulic components in summer, a common effect for GPRMS, resulting in lower maintenance costs.
The dew point control of a GPRMS in conjunction with a solar thermal system is a perfect combination, since the increased gas outlet temperature required to prevent condensation on the components is largely covered by the solar thermal system during the summer months. Thus, a high solar fraction is achieved, and the primary energy demand of the station is significantly reduced. In the GPRMS described above, the preheating requirement was reduced from approx. 220 MWh/a to 150 MWh/a.
The main part of the heat required for preheating is provided by a 30 kWth combined heat and power unit (CHP) and a solar thermal system with 58 m² of flat plate collectors installed on the roof of the station. In summer and during the transition seasons, the two gas boilers can be left completely out of operation and thus only serve to cover peak loads in winter and to provide redundancy. In addition to the CHP unit and the solar system, a heating rod is installed as a power-to-heat (PtH) system. The heating rod is operated within the framework of the research project C/sells, and is to be used to increase the flexibility of the local power grid. A 6 m³ buffer heat storage tank is installed to ensure continuous operation of the three new heat generators. The solar process heat plant has a planned annual yield of around 480 kWh/m² and thus achieves a solar fraction of 17 %. This saves approx. 35 MWh/a of natural gas and 10 t of CO2 per year. In total, all measures reduce the net primary energy demand of the station by 61 %.
The combination of the heat supply system with the solar process heat system allows the CHP to be switched-off for long periods of time in summer. In this way, the preheating of the natural gas can be ensured during periods of lower heat demand, without the CHP unit having to cycle frequently or operate in partial load, which reduces its efficiency, thus increasing the yearly utilisation ratio of the unit.
The modernisation of the plant was carried out within the framework of the BMWi-funded research project “EffGas – Primärenergetische Optimierung bestehender Gas-Druckregelanlagen und Maßnahmenentwicklung für den deutschen Anlagenbestand”. For this reason, several measurement equipment is installed at the station for a detailed monitoring and evaluation of its energetic performances.