Objective Hydrogen blending in natural gas is a critical transitional pathway for integrating green hydrogen, decarbonizing existing gas pipeline networks, and transforming urban gas systems. Existing research suffers from unclear boundaries for low, medium, and high hydrogen blending ratios; insufficient information on demonstration projects; and inadequate support regarding gas quality interchangeability, end-use compatibility, and standardization frameworks. A systematic review of the current status, key constraints, and development trends of natural gas hydrogen blending can clarify the technical boundaries and directions for promotion in different scenarios.

Methods Using a combination of literature review, engineering case comparisons, and inductive analysis, this study compiles findings from natural gas hydrogen blending demonstration projects in Europe, North America, and China, as well as Power-to-Gas technology and pipeline network adaptation. relevant domestic and international projects were selected, and their launch dates, hydrogen blending ratios, application scenarios, and coverage scales were compared to construct an analytical framework.

Results The engineering feasibility of natural gas hydrogen blending is not determined solely by the hydrogen volume fraction but is jointly influenced by gas source composition, pipeline pressure levels, pipe material condition, end-use equipment, and regulatory conditions. The divergent approaches taken by different demonstration projects essentially reflect variations in safety boundaries, monitoring conditions, and equipment retrofitting capabilities across various scenarios. Low-pressure distribution systems, which directly serve residential and commercial users, should begin with low-ratio, incremental validation. Industrial parks, campuses, islands, and self-contained communities have relatively well-defined boundaries, making them suitable for accumulating long-term operational data and validating electricity-hydrogen-gas synergy. End-use equipment such as industrial boilers, kilns, and gas turbines offers strong control capabilities, making them suitable for validation of medium-to-high hydrogen blending ratios and transitions to pure hydrogen. Hydrogen blending also alters the calorific value, the Hua-Bai index, relative density, and flame propagation speed of the mixture, and affects combustion stability, NOx emissions, energy metering, and material compatibility. Therefore, natural gas hydrogen blending cannot simply replicate experience from other projects; instead, scenario-based evaluations should be conducted in conjunction with specific gas sources, pipeline networks, and end-use conditions.

Conclusion Natural gas hydrogen blending should shift from a sole focus on blending ratios to a focus on system adaptation boundaries and risk control conditions across different application scenarios, thereby establishing a tiered, categorized, and progressively enhanced implementation pathway. In the future, efforts should focus on safety limits, equipment compatibility, operational monitoring, and low-carbon value assessment throughout the entire hydrogen-blending process. A systematic evaluation mechanism should be established—covering everything from gas source connection to end-use, and from engineering operations to regulatory standards—to support the standardized and large-scale application of hydrogen-blended natural gas.