Comprehensive review of hydrogen-natural gas blending: Global project insights with a focus on implementation and impact in Romanian gas networks

As the global shift towards hydrogen utilization progresses, this review examines the technical feasibility and environmental impact of blending hydrogen with natural gas, focusing on its implementation in Romania's residential and commercial gas networks. It provides a comprehensive analysis of various topics, including the safety, sustainability, and operational behavior of existing infrastructure when using a 23 % hydrogen blend (G222). Also, the paper reviews studies on material compatibility with hydrogen, focusing on the long-term effects on pipeline materials such as polyethylene (PE) and steel, as well as the potential for embrittlement in high-pressure systems. It also discusses the performance of household appliances with hydrogen blends, highlighting reductions in CO2 emissions by 6–7%, improvements in nitrogen oxide (NOx) emissions, and sustained combustion efficiency above 98 %. Furthermore, the paper addresses the challenges of leak detection and safety measures in hydrogen-enriched networks and examines regulatory frameworks required for a large-scale transition to hydrogen. By synthesizing current research and field studies, this review provides insights into the readiness of natural gas networks for hydrogen integration, offering recommendations for future research and development in optimizing hydrogen blend ratios and ensuring safe implementation.