It is not only renewable sources that contribute to the energy transition, but also those that exploit barely utilised potential. The recovery of energy during the expansion of natural gas is one such approach. However, the widespread use of gas expansion turbines (GET) has so far been hampered by the high technical effort involved, as the natural gas has to be preheated in order to absorb the temperature changes that occur when the pressure is reduced (Joule-Thomson effect) and to prevent icing. If the required heat is generated by burning natural gas, additional CO2 emissions are produced.
A patented gas expander developed by TU Dortmund University together with W2-Armaturen and RMGS avoids these problems using a special process: Only part of the pressure potential of the gas is expanded in the turbine and the rest in a conventional gas pressure regulator.
This means that no preheating of the natural gas is required and the GET can be used with considerably less effort. The technology can be used universally, including in hydrogen plants in addition to natural gas.
The basic principle of the expander is a nozzle-loaded single-stage constant pressure turbine. The axial turbine stage sits directly on the shaft of the generator, which is cooled inside the housing by the gas flow. The turbine wheel is designed in such a way that a long operating time without maintenance is guaranteed at low speeds.
In addition to the electricity price, the decisive factor for the economic efficiency analysis is whether the gas volume flow is achieved as often and as constantly as possible. As the volume flow decreases, the speed in the nozzles decreases and the efficiency of the expander drops. For operators, the security of supply of electrical energy directly within the system is possible as a supplement or replacement for the emergency power supply.
GETs are particularly economical if the electricity is consumed by the users themselves and valued accordingly. the annual yield is calculated using an organised annual hydrograph.
With an output of 30 kWh and 6,000 full-load hours per year, this results in an annual yield of 180,000 kWh, which leads to CO2 savings of 42 tonnes (2023: electricity generation in Germany 380g CO2 per kWh).
W2-Armaturen and RMGS have now installed seven GETs – series maturity has been achieved.