Calculation of economic velocity in supercritical CO2 transport pipelines

ObjectiveCarbon 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. MethodsFocusing 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. ResultsBy 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. ConclusionThe 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.