Pressure-Based Energy Storage in Natural Gas Transmission Networks: Proof-of-Concept Analysis

This paper presents the possibility of energy storage in natural gas transmission networks using two strategies. Proof-of-concept calculations were performed under a steady-state assumption, and the more promising option was additionally modeled in a transient approach. The first strategy is based on a dedicated compressor-expander system installed at two ends of a pipeline. An electric-driven compressor increases the gas pressure in periods of peak electricity generation, while a gas expander allows energy recovery at a later stage. The compressor-expander distance determined by the inlet flow velocity of 5 m/s and a 4-5 h time shift ranges from approx. 75 to 120 km. The system provides a synergy effect, which allows to exceed 100% storage efficiency by reducing transmission losses. Storage efficiency obtained from the simplified model ranges from 70% to 128% for the performed case study. The second option uses existing compressors and pressure letdown stations expanding the gas to the distribution pressure. Here, gas pre-heating required prior to the expansion reduces the storage efficiency to about 30-40%. The dedicated machinery option was also evaluated using a transient model, which reports a lower efficiency if applied to the same assumptions. The system redesigned with the transient model is characterized by a longer storage duration (about 12 h) and a promising efficiency of 103.5%. Further research is needed to find the optimum design system parameters and to solve the detected problem of simultaneous compressor-expander operation which introduces idle work to the designed system.