Contents lists available at ScienceDirect International Journal of Greenhouse Gas Control journal homepage: www.elsevier.com/locate/ijggc Understanding gas-phase breakout with high H 2 content in CCS pipeline gathering networks Matthew Healey a , Ketan Mistry b , Thomas Jones a , Eduardo Luna-Ortiz a, ⁎ a Pace Flow Assurance, 10 Lower Thames Street, London, EC3R 6EN, UK b National Grid, 35 Homer Rd, Solihull, B91 3QJ, UK ARTICLE INFO Keywords: CO 2 transport CCS Flow assurance Hydrogen production Hydrogen breakout Impure CO 2 ABSTRACT An accurate understanding of the behaviour of impure carbon dioxide (CO 2 ) during pipeline transport stage is required for commercial scale deployment of Carbon Capture and Storage (CCS) networks. Impurities in the CO 2 stream modify phase behaviour and change the thermophysical and transport properties of the stream. CO 2 streams containing hydrogen (H 2 ) are a particular challenge due to the unique physical properties of H 2 . In a CCS gathering network where CO 2 is sourced from processes such as pre-combustion capture or hydrogen production, H 2 with a concentration of 2% mol can be expected to be present in the mixture. This paper describes foreseeable operating scenarios where gas breakout in single-phase CCS gathering networks might occur, leading to pockets of gas with high H 2 concentration. Multiphase flow modelling of a CCS gathering network with impure CO 2 containing H 2 has been performed, demonstrating these operating scenarios and providing a basis for design. The H 2 content of the gas breakout is shown to be > 20% mol when the conditions are close to bubble point. High concentrations of H 2 due to gas breakout must be considered as part of a single-phase CCS gathering network design, whenever H 2 is present. This paper provides practical guidelines for understanding, quantifying and, managing the worst design cases for H 2 exposure due to gas breakout. Specific recommendations for what must be included in the project design basis are presented. Potential mitigating factors and engineering measures that can be taken to manage high H 2 concentration in a CCS system are also discussed. 1. Introduction Carbon Capture and Storage (CCS) involves capturing carbon di- oxide (CO 2 ) emissions from industrial processes, transporting pre- dominantly through pipelines, and storing safely in suitable geological formations deep underground. The four common capture processes are (Metz et al., 2005; Heltand et al., 2014): • Post combustion: CO 2 from fossil fuel combustion is extracted from the exhaust gas using a solvent. The CO 2 is then separated and compressed for transportation while the solvent is recycled. • Pre-combustion: Fossil fuel is combined with oxygen and steam through a series of reforming processes to produce CO 2 and H 2 . The CO 2 is disposed of whilst the H 2 can be used as fuel (“blue hy- drogen”). • Oxyfuel: Fuel is burned in oxygen instead of air to produce a flue gas consisting mostly of CO 2 . • High CO 2 Hydrocarbon Stream: Hydrocarbon streams with pre- existing high CO 2 concentrations are stripped of the CO 2 using sol- vent. Transportation of CO 2 is possible in small quantities by lorry or ship, however over large distances and for large scale continuous operation it is more cost effective to use pipelines. For pipeline transportation it is more efficient for the CO 2 to be compressed and transported as a liquid. Notwithstanding these advantages, CO 2 transportation in pipelines is challenging in particular with respect to flow assurance, integrity management and, health and safety factors (Onyebuchi et al., 2018). The captured CO 2 can be stored either onshore or offshore in geological formations such as depleted hydrocarbon fields (as part of Enhanced Oil Recovery (EOR)) or saline aquifers. The design of a CCS pipeline transportation network must consider all possible sources of CO 2 and the impurities that can be collected from those sources. There are economic advantages to transport impure CO 2 over further CO 2 purification at the capture sites (Kolster et al., 2017). Yan et al. (2008) showed that costs associated to purification of CO 2 https://doi.org/10.1016/j.ijggc.2019.102816 Received 10 April 2019; Received in revised form 2 August 2019; Accepted 19 August 2019 ⁎ Corresponding author. E-mail address: eduardo@paceflowassurance.co.uk (E. Luna-Ortiz). International Journal of Greenhouse Gas Control 90 (2019) 102816 1750-5836/ © 2019 Elsevier Ltd. All rights reserved. T