The main factors affecting heat transfer along dense phase CO2 pipelines

Carbon capture and storage (CCS) schemes will necessarily involve the transportation of large volumes of carbon dioxide (CO2) from the capture source of the CO2 to the storage or utilisation site. It is likely that the majority of the onshore transportation of CO2 will be through buried pipelines. Although onshore CO2 pipelines have been operational in the United States of America for over 40 years, the design of CO2 pipelines for CCS systems still presents some challenges when compared with the design of natural gas pipelines. The aim of this paper is to investigate the phenomenon of heat transfer from a buried CO2 pipeline to the surrounding soil and to identify the key parameters that influence the resultant soil temperature. It is demonstrated that, unlike natural gas pipelines, the CO2 in the pipeline retains its heat for longer distances resulting in the potential to increase the ambient soil temperature and influence environmental factors such as crop germination and water content. The parameters that have the greatest effect on heat transfer are shown to be the inlet temperature and flow rate, i.e. pipeline design parameters which can be dictated by the capture plant and pipeline's design and operation rather than environmental parameters. Consequently, by carefully controlling the design parameters of the pipeline it is possible to control the heat transfer to the soil and the temperature drop along the pipeline.