Multi-timescale intelligent scheduling of hydrogen-blended natural gas pipeline networks: From planning optimization to closed-loop control

Existing natural-gas pipelines can transport hydrogen–natural-gas blends only within asset- and route-specific limits on material compatibility, equipment capability, gas quality, energy delivery, metering and safety. Variable renewable-hydrogen supply couples pressure, flow, spatial composition, linepack, compression, storage and delivered energy from seconds to days, making fixed blend fractions and isolated schedules inadequate for operational control. This review synthesizes 141 peer-reviewed studies on scheduling and closed-loop control of hydrogen-blended transmission and distribution networks, distinguishing direct pipeline evidence from natural-gas and component support, adjacent energy-system applications and generic intelligent-control methods. Methods are critically appraised by operating scenario, required physical assumptions, computational profile, validation setting and supported engineering claim. Evidence for planning optimization and model-based scheduling is predominantly from disclosed simulation studies and remains limited for end-to-end closed-loop real-time performance, safe online adaptation, structural transfer and sustained field operation. The analysis is structured by three bounded synthesis tools: a multi-timescale responsibility framework assigning planning, rolling coordination, fast feedback and safety supervision; a five-category transfer framework distinguishing temporal, operating-condition, objective, scale, and topology or action changes; and an E1–E7 evidence ladder linking controller authority to validation exposure. Learning is best supported as candidate-action generation or residual correction within a validated dynamic operating envelope. Priority research needs are composition-aware dynamic models and state estimation, gas-quality and energy-delivery integration, physically constrained surrogates, runtime safety supervision, target-system transfer tests and standardized benchmarks with matched physical assumptions and terminal conditions.