Carbon-priced LNG inventory routing with a single FSRU hub: robust branch-and-price for heterogeneous fleets

Floating storage and regasification units (FSRUs) increasingly serve as operational hubs for regional LNG distribution, yet planning models rarely jointly consider hub throughput and inventory bottlenecks, carbon charges, heterogeneous fleets, and schedule reliability. We study a single-FSRU hub-and-spoke LNG shuttle system and formulate a maritime inventory routing problem that jointly optimises vessel assignment, routing, scheduling, and discrete sailing speed levels, subject to berth capacities, time-step load-out limits, and hub inventory-prefix constraints. Carbon charges are represented by both linear and tiered (piecewise-linear) billing rules, with fleet-pooled tiering as the default scope to align with operator-level schemes; per-vessel tiering is discussed as a sensitivity variant. One-sided overruns in sailing and port operations are handled via a Bertsimas–Sim Γ-budgeted delay model enforced as route-prefix robust time feasibility within each single-vessel plan (at the pricing level). The problem is solved using a branch-and-price algorithm with exact and scalable modes. Computational experiments and out-of-sample Monte Carlo validation show the scalability of the proposed method and quantify how hub bottlenecks and tight time windows shape operating cost and emissions when carbon charges and schedule reliability are accounted for.