CO₂ transport at a supercritical state: Nikiski, Alaska pipeline study and cost analysis

Abstract

CO₂ in the supercritical state is suitable for long-distance transportation because of the denser flowing fluid, almost the same density as liquid CO₂ but has lower viscosity and surface tension. Albeit this well-known principle, it is nontrivial to implement a scheme for single-phase, supercritical CO₂ transportation on a given pipeline. As the pressure and temperature are the major state variables governing the state of the transported CO₂, the state of the fluid is determined by a complex interaction among the key parameters: the inner diameter, insulation material, inlet pressure and temperature, and the boundary conditions (including the ambient temperature and inner pipeline wall roughness) of the pipeline; the mass flow rate and distance of transportation. This paper applies the PIPESIM software, with MATLAB for auxiliary calculations, to illustrate a parametric study of the supercritical CO₂ transportation over a 10.618-mile (17,080 m) long model pipeline connecting from Nikiski to the Osprey platform in the Redoubt oil field in Cook Inlet, Alaska, USA. This study aims to understand the limitations and optimize transportation efficiency while maintaining the supercritical state of transported CO₂ throughout the pipeline. With the geographic location, elevation profile of the pipeline, and the ambient conditions considered in the simulations, we calculate the pressure and temperature profiles, erosion kinetics, and the fluid state in the combinatorial set of various diameters, inlet pressures, and temperatures of the pipeline and the mass flow rates of the transported fluid. The major findings are that a larger pressure loss will be expected in better-insulated pipelines because of the warmer transported CO₂ that flows faster. Turbulent flows will be more likely to occur in transportation through pipelines of smaller diameters and will impact on possible change from the supercritical state to the two-phase state. The parametric modeling results offer a scenario-driven approach to determine the optimal range of mass flow rates, pipeline inner diameters, and inlet pressures. A cost analysis was conducted for the construction and operating expenditures of pipelines over a 20-year lifetime span. We highlight the trade-offs between maintaining supercritical conditions, minimizing heat loss, and increasing financial viability for efficient transportation.