Efficient method for simulation of long-distance gas transport networks with large amounts of hydrogen injection
For a transformation of current energy infrastructure towards 100% renewables, pipeline systems for natural gas have to be converted to ones for transporting hydrogen or synthetic gases containing hydrogen; this process needs intense planning and optimization based on simulations. Since known simulation tools were designed for natural gas primarily, they are expected to be not accurate enough for scenarios with hydrogen fractions above 10%. Hence, an efficient method for simulating transport of gases from renewable resources as well as impacts of hydrogen injection into gas networks is developed. This includes a method for setting up scenarios for analysis of impacts to long-distance networks for a country based on state-wise transient estimates for wind excess power. The simulation method employs transient non-isothermal Euler equations with the most recent equation-of-state of the European Gas Research Group (GERG-2008), a gas law allowing for hydrogen fractions up to 100 percent, and an approach for shifting compressor characteristics according to gas composition. In case of hydrogen and realistic scenarios, pressure ratios are between 1.025 and 1.075 only. For testing the overall method, a novel set of realistic long-distance gas transport scenarios with hydrogen injection nodes based on a study of wind power as well as power-to-gas plants installed in the federal states of Germany as well as a simple pipeline model for testing biogas, syngas, natural gas and hydrogen qualities were developed. Both models are analyzed with GERG in comparison with the commonly used alternative, showing that GERG is more accurate; depending on gas composition and scenario, differences between the commonly used detailed gas law and GERG can accumulate up to 2.8% in pressure and 6% in velocity for exemplary gases and a simple pipeline model with 100 km length. Additionally, the simulation process with GERG is at least as fast as with the commonly used gas law. Overall, GERG should be used. Moreover, results for the German transport scenarios indicate that with larger hydrogen injections, considerable flow shifts and locally quite different gas compositions over Germany can be expected, and a pure hydrogen network would need large additional injections, favorably from the northwestern part of Europe.