Compression

Machines for compressing gases are called compressors. There are two basic categories - positive displacement compressors and dynamic compressors. The positive displacement compressors have a variety of designs - pistons or various “progressing cavities” created by eponymous “lobes”, “screws”, “scrolls”, or “vanes”. The dynamic compressors increase gas pressure with high velocity vanes in stages - centrifugally or axially (turbines). Because of relatively low maintenance and high capacity options, gas pipeline operators tend to favor centrifugal compressors (Carbon Capture and Storage (CCS) – Basics – Stellae Energy).

Carbon dioxide triple point is 5.112 atm (75 psi) and 216.6 K (-56.6 C). At pressures below the triple point, carbon dioxide has no liquid phase - it changes directly between solid phase and gas phase. Carbon dioxide critical point is 72.8 atm (1070 psi) and 304.1 K (31 C). The critical point marks the upper limit where a distinction can be made between liquid and gas phases. It is common to transport carbon dioxide compressed above the critical point.

In gas cylinders, carbon dioxide is commonly compressed to approximately 75 atm. Cryogenic storage cylinders (Dewars) maintain liquid CO2 at 200 - 300 psi and can store up to about 300 liters. The density of liquid CO2 at 20C is about 0.780 kg/L