The capture of CO2 from power plants, its transportation through pipeline systems and its long term deposition in suitable storage reservoirs both on and offshore appears to be an effective method for preventing CO2 from entering the atmosphere, allowing to mitigate adverse greenhouse gas effects due to anthropogenic activities.
Depending on the process or power plant application, three main approaches to capturing the CO2 generated from a primary fossil fuel (coal, natural gas or oil), bio-mass, or mixtures of these fuels are presently considered: Post-combustion capture systems, Pre-combustion capture systems and Oxyfuel combustion capture systems. The production of SO2 or H2S as unintended and potentially dangerous by-products is also considered.
While existing CO2 pipelines in U.S.A. with predominantly relatively pure CO2 streams are running generally through sparsely populated areas, CO2 pipelines from projected fossil-fuelled power plants containing H2S and SO2 as ‘impurities’ may need to cross densely populated areas, for instance in Western Europe.
The availability of reliable calculation methods for the most relevant CO2 properties (density and viscosity), for the influence estimation of impurity concentrations on phase behavior and calculation methods for determination of the optimum techno-economic pipeline diameter, are therefore a pre-requirement for a safe, environment-friendly and economic pipeline design.
A potential new pipeline route has to be examined within the frame of a risk analysis to identify hypothetical hazard scenarios and to estimate potential consequences with regard to severity and estimated frequency. The examination covers the hypothetical case of leakage, evaluates the time-dependent CO2 leak rate (source term), estimates the CO2 outflow / jet formation in the immediate vicinity of the leak, and estimates the dispersion of cold CO2 clouds depending on atmospheric and topographic conditions like hilly terrain, depressions and big buildings.
The integrated approach which is partially an iterative process starts with the investigation of a suitable route avoiding exposed areas and close proximity to inhabited areas, under consideration of the special CO2 and impurity related properties and local conditions. The study continues with selection of appropriate pipe material, wall thickness (design factor), burial depth and optimized number and locations of valve stations, increased quality control during pipe manufacturing, weld control and supervision during construction works. The study additionally refers to measures for leak detection and fast pipeline shutdown including quick closure of sectionalizing valves, as well as implementation of an integrated leak response plan in order to minimize the potential consequences of a hypothetical CO2 leakage to people, environment, assets and project reputation. These measures will be completed by integrated procedures and training measures for the pipeline operators and by pipeline maintenance measures including running of so-called intelligent pigs.
Nevertheless, there remain some challenging engineering tasks like comparison of dispersion models versus CO2 test release results, definition of measures to avoid / reduce potential rupture propagation, investigations referring to potential influence of H2S and H2 impurities on stress cracking promotion, potential interaction of co-absorbed H2S and SO2 (S2 generation) and investigations (based on reported transportation system failures) to minimize the remaining pipeline risk to a level “as low as reasonably practicable” (ALARP).