Transporting the Next Generation of CO2 for Carbon, Capture and Storage: The Impact of Impurities on Supercritical CO2 Pipelines

Abstract

Climate change has been attributed to greenhouse gases with carbon dioxide (CO2) being the major contributor. Most of these CO2 emissions originate from the burning of fossil fuels (e.g. power plants). Governments and industry worldwide are now proposing to capture CO2 from their power plants and either store it in depleted reservoirs or saline aquifers (‘Carbon Capture and Storage’, CCS), or use it for ‘Enhanced Oil Recovery’ (EOR) in depleting oil and gas fields. The capture of this anthropogenic (man made sources of CO2) CO2 will mitigate global warming, and possibly reduce the impact of climate change. The United States has over 30 years experience with the transportation of carbon dioxide by pipeline, mainly from naturally occurring, relatively pure CO2 sources for onshore EOR. CCS projects differ significantly from this past experience as they will be focusing on anthropogenic sources from major polluters such as fossil fuel power plants, and the necessary CO2 transport infrastructure will involve both long distance onshore and offshore pipelines. Also, the fossil fuel power plants will produce CO2 with varying combinations of impurities depending on the capture technology used. CO2 pipelines have never been designed for these differing conditions; therefore, CCS will introduce a new generation of CO2 for transport. Application of current design procedures to the new generation pipelines is likely to yield an over-designed pipeline facility, with excessive investment and operating cost. In particular, the presence of impurities has a significant impact on the physical properties of the transported CO2 which affects: pipeline design; compressor/pump power; repressurisation distance; pipeline capacity. These impurities could also have implications in the fracture control of the pipeline. All these effects have direct implications for both the technical and economic feasibility of developing a carbon dioxide transport infrastructure onshore and offshore. This paper compares and contrasts the current experience of transporting CO2 onshore with the proposed transport onshore and offshore for CCS. It covers studies on the effect of physical and transport properties (hydraulics) on key technical aspects of pipeline transportation, and the implications for designing and operating a pipeline for CO2 containing impurities. The studies reported in the paper have significant implications for future CO2 transportation, and highlight a number of knowledge gaps that will have to be filled to allow for the efficient and economic design of pipelines for this ‘next’ generation of anthropogenic CO2.

Worldwide innovations in the development of carbon capture technologies and the utilization of CO2

“…Typical impurities for the respective CCS technology lines differentiated according to the energy sources are listed in Table 6. 111,112 Whereas the fractions of argon and nitrogen dominate in the Oxyfuel techniques due to air penetration, the contaminants CH 4 and H 2 occurring in the pre-combustion process result from the actual gasification process. Also SO 2 , NO x , CO and O 2 are found in the power-plant flue gases.…”

“…112 The anthropogenic sources deal with the synthesis gas production, which explains the H 2 S-content as well as the fraction of hydrocarbons with a lower molecular mass. Upon comparing the compositions from Tables 6 and 7, the differences in the respective compositions of the impurities are obvious.…”

Case study on CO2 transport pipeline network design for Humber region in the UK

“…Supercritical/dense phase is the best phase for pipeline CO 2 transport due to the high density and low viscosity. 5,[19][20][21][22][23] Pipeline transportation in the liquid phase is also possible. 24 CO 2 liquefies at temperatures below the critical temperature and pressures above 516.7 kPa but less than the critical pressure (Figure 2).…”

“…Changing temperature also affects density of CO 2 . 20 However, temperature changes are not a major problem because the pipelines are buried at depths with fairly stable temperature of the surroundings. CO 2 viscosity behaves similarly with changing temperature and pressure.…”

“…In addition, NO 2 impurity is reported to increase both critical temperature and pressure when present in binary or ternary mixtures with CO 2 . 20 Higher critical temperature and lower critical Figure 3. CO 2 density changes along pipeline at different inlet temperatures.…”