Integration of Renewable Energy Systems at City Gate Stations to Reduce Pre-Heating Gas Consumption

The Italian Natural Gas distribution network includes thousands of gas metering and pressure reduction stations, called City Gate Stations, for injecting gas into low-pressure networks. These plants are mainly based on the isenthalpic throttling of the gas flow to reduce its pressure, which significantly reduces its temperature by the Joule-Thompson effect. Gas pre-heating systems that avoid excessive cooling are installed upstream of pressure reduction valves and usually exploit conventional gas boilers. The energy consumption and carbon footprint could be reduced by integrating heat pumps and renewable energy sources for natural gas pre-heating to support gas boilers. For this work, an ad-hoc thermodynamic model for estimating the thermal energy demand for pre-heating is developed, exploiting experimental data from a real plant and simplified models of heat pumps and renewable systems. This work aims to assess energy savings' technical and economic feasibility through these technologies. Results show the validated model to be sufficiently accurate to estimate the need for gas pre-heating for these applications. For the considered case study, up to 38%, 32% or 26% of the total thermal energy can be recovered with a payback time of less than 20 years, 15 and about 13 years, respectively.