9 Pumping, Compression and Other Appurtenances

If the CO2 stream is being transported in supercritical or dense phase, it is important that the pressure is kept sufficiently high to avoid two-phase flow. As mentioned in the previous chapter, that pressure drops occur in the pipeline due to frictional effects and gravitational (static head) effects related to the pipeline elevation. Furthermore, the fact that the supercritical or dense phase CO2 is as dense as most hydrocarbon liquids (600–900kg/m3) means that the effect of static head on the pressure is significant. This will be important in areas where there are variations in topographic height along the pipeline route. This property of CO2 can be advantageous if the elevation decrease in a pipeline can counteract any frictional losses. For example, in the Sheep Mountain pipeline, once the CO2 leaves the production facility at 9.6 MPa, it is delivered to the oil fields at a pressure of 13.7 MPa with no requirement for intermediate compression. The increase in pressure is achieved purely through elevation changes along the 660 km pipeline route. Elevation changes are also being used to prevent offshore compression in the Snøvhit pipeline. In this pipeline the CO2 is compressed to 15 MPa and the 150 km pipeline drops 300 m to the injection site. For systems that rely on changes in elevation to achieve the required pressure changes, it is important that a static analysis is conducted to take account of a shut in, when pipeline pressures could be increased.

Compressor stations in a CO2 pipeline system can be sub-divided in two classes: the originating stations, which are positioned at the inlet to the pipeline, and the booster stations,which are located along the pipeline to compensate for the pressure decrease due to friction and elevation losses. In principle, the longer the pipeline and the elevation of the terrain crossed, the more compressor horsepower is required to achieve the required delivery pressure at destination. Under a fixed route and flow capacity, the number and size of booster stations depend on the circumstances and design as discussed in the previous chapter. Fewer stations might be easier to operate but the disadvantage is the need of for high inlet pressures, which are likely to require the more expensive use of thicker pipes. The present chapter discusses the various aspects of compression and pumping facility requirements as well as other appurtenances and equipment specifications associated with CO2 transportation.