DENSE PHASE TREATING OF NATURAL GAS STREAMS

摘要

It is widely recognized that dense phase (1500 to 3000 psig/103 to 207 barg) high-capacity gas pipeline systems have superior economics in comparison to conventional, low-pressure (1000 psig/69 barg) high capacity pipelines (Cornot-Gandolphe, 2003). In many cases the gas intended for these pipelines is available at high pressure, but contains unacceptable levels of CO2 and H2S. If the gas is available at high pressure, it should be treated at high pressure to avoid pressure letdown and recompression costs. Most commercial amine treating simulation programs are based on low-pressure equilibrium data. The use of these programs for dense phase, high-pressure amine treating applications requires extrapolation of low-pressure data to dense phase conditions. This may lead to design problems in some applications and for some amines unless suitable high-pressure data are used to confirm the simulation. This paper reviews the thermodynamics of the amine treating of dense phase natural gas streams and presents a new method that, based on limited data, appears to be suitable for computer simulation of high-pressure treating applications. The ability of the Peng-Robinson equation of state to model highpressure amine treating applications is reviewed as well as the effect of high-pressure treating on CO2 removal. Some limited high-pressure MDEA-H2O-CO2-CH4 vapor-liquid-equilibrium (VLE) and CH4- CO2 and C2-CO2 pressure-volume-temperature (PVT) data are available. These data are used to assess the accuracy of commercial amine simulation programs and the improved MDEA-H2O-CO2-Natural Gas VLE model discussed in this paper.