Calculation of economic velocity in supercritical CO₂ transport pipelines

Objective Carbon Capture, Utilization and Storage (CCUS) is widely recognized as a leading solution for reducing greenhouse gas emissions, while pipeline transport is the optimal method for large-scale, long-distance CO₂ transport. During supercritical CO₂ pipeline transport, if the pipeline pressure falls below the critical pressure of 7.38 MPa, CO₂ will undergo a phase transition, leading to pipeline erosion and jeopardizing both the stable transport of CO₂ and the safe operation of the pipeline. The pipeline flow velocity affects the transport pressure of CO₂. A flow velocity that is too low increases pressure drop, potentially dropping it below the critical point, while a flow velocity that is too high leads to greater friction loss and increased energy consumption. Additionally, flow velocity is closely linked to pipe diameter, influencing both construction and operational costs of the pipeline. Thus, it is essential to study the economic velocity for supercritical CO₂ transport pipelines.

Methods Focusing on the combination of “booster station + pipeline”, an optimization model was established to calculate the economic velocity in CO₂ pipelines. The model takes the total annual investment cost of the pipeline as the objective function, subject to constraints based on the single-phase transport of CO₂, including pipeline pressure, strength, and stability constraints. A genetic algorithm was employed to solve the optimization model.

Results By establishing a series of economic parameters, the total annual investment cost and economic velocity ranges for each standard diameter of supercritical CO₂ transport pipeline were determined, considering a transport capacity of 1 000–10 000 t/d and booster station spacing of 50–150 km. When the transport capacity was low, the total annual investment cost of the pipeline increased linearly with the pipe diameter. As transport capacity rose, the cost initially decreased before increasing again. For a constant pipe diameter, a higher transport capacity resulted in a greater total annual investment cost. Additionally, the economic velocity of the pipeline exhibited a fluctuating upward trend with increasing transport capacity. Additionally, the impact of pipe material and electricity price on economic velocity was analyzed.

Conclusion The economic velocity of supercritical CO₂ transport pipelines ranges from 1.1 to 2.35 m/s. While the electricity price significantly influences the economic velocity, the impact of pipe material is minimal. By adjusting the operating parameters of the example, nine operation options were designed. The optimal option was identified through evaluation and optimization using the model, verifying the accuracy of the economic velocity. These findings can serve as a reference for the optimal design of pipelines. (5 Figures, 4 Tables, 22 References)