A coupled transient gas flow calculation with a simultaneous calorific-value

Gas systems can provide considerable flexibility in integrated energy systems to accommodate hydrogen produced from Power-to-Hydrogen units using excess volatile renewable energy generation. To use the flexibility in integrated energy systems while ensuring a secure and reliable system operation, gas system operators need to accurately and easily analyze the effects of varying hydrogen levels on the dynamic gas behavior and vice versa. Existing methods for hydrogen tracking, however, either solve the hydrogen propagation and dynamic gas behavior separately or must cope with a large inaccuracy. Hence, existing methods do not allow an accurate and coupled analysis of gas systems in integrated energy systems considering varying hydrogen levels. This paper proposes a calorific-value-gradient method, which can accurately track the propagation of varying hydrogen levels in a gas system even with large simulation time increments of up to one hour. The new method is joined and simultaneously solved with an implicit finite difference scheme describing the transient gas behavior in a single equation system in a coupled Newton-Raphson gas flow calculation. As larger simulation time increments can be chosen without reducing the accuracy, the computation time can be strongly reduced compared to existing Euler-based methods. With its high accuracy and its coupled approach, this paper provides gas system operators a method to accurately analyze how the propagation of hydrogen affects the entire gas system. With its coupled approach, the presented method can enhance the investigation of integrated energy systems as the transient gas behavior and varying hydrogen propagation of the gas system can be easily included in such analyses.