Design optimisation of a CO2 pipeline network in Australia under variable flow

Abstract

Carbon Capture and Storage is a promising technique for mitigating greenhouse gas emissions that involves separating CO2 from other emitted gases, transporting and storing it in a geologic formation. Pipeline transport of CO2 is generally the preferred method for long-term onshore transport. However, pipeline operations and related costs are impacted by flow rate variability. Hence, this thesis develops and investigates stochastic pipeline design methods suitable for pipelines operating under variable CO2 flow rates. First, the generation rate of CO2 at power plants with potential for capture is analysed stochastically, and the most suitable probability distribution function for modelling the related CO2 flow rates is identified. This selected probabilistic model is then used for developing an optimal pipeline design method, based on an exhaustive search technique. A shortcut method is then proposed, that approximates the costs of the optimal pipeline design for a variable CO2 flowrate with a typical scaled mean flow. Using the proposed method, analysis of the resulting designs shows that pipelines operating at variable flow rate are always overdesigned relative to steady-state, to accommodate the maximum flow rate. The proposed simplistic models for pre-feasibility assessments of CO2 pipeline design and costs identify the scaled mean flow rate as a key parameter for determining the optimal pipeline diameter and unitised cost (A$/t-km). Sensitivity analyses indicate that under either variable flow or steady-state conditions, the steel price, cost of electricity and booster pump costs are the main drivers for the optimal diameter. Finally, simple adjustment factors for pipeline design and costs for a variable flow pipeline are proposed. These adjustment factors can provide quick estimates of design and costs for a scoping analysis within limited ranges of steel price, cost of electricity and booster pump costs.