Experimental Study of N2 Impurity Effect on the Steady and Unsteady CO2 Pipeline Flow

Abstract

Carbon dioxide capture and storage (CCS) technology is arising as one of the key technology for reducing emission of global warming gas and mitigating climate change. Especially the impurity effect on the CO2 transportation is important, cause with small amount of impurity, specific volume, boiling point and critical temperature of CO2 might possibly change tremendously, and along with that problems such as formation of hydrate and pipe clogging, etc are possible. Moreover the real captured CO2 mixture might contain impurities such as N2, O2, H2O, SOx, H2S. Among them, N2 can affect the CO2 transport process by its low boiling point. In other words, a small amount of nitrogen can make change flow conditions from single phase flow to two-phase flow. And a small amount of water in CO2 stream can trigger the clogging problem due to formation of hydrate. To understand the thermo physical behavior of CO2-N2 mixture, experimental investigations are essential. In this study, we designed and built an experimental apparatus for simulating CO2–N2 mixture pipe-line transportation which consists of 4 parts with high pressure compression module, liquefaction module, mixing module, cooling module and transport test section. The transportation test section consists with 2 parts, one for horizontal pipe-line test section made by a horizontal tube and the other for long-pipe test section which composed of horizontal tubes and bended U-tubes. The steady flow experiment was tested on the horizontal pipeline test section to evaluate pressure drop behavior of CO2-N2 mixture in horizontal flow. Test condition was 70, 85, 100 and 120bar with varying N2 impurity composition. With increasing N2 impurity ratio, pressure drop, fluid phase, pressure, and temperature change was acquired and compared the value with calculated by single phase and two-phase model. The unsteady conditions such as severe variations of temperature, pressure and phases can be encountered during shut in, blow down of CO2 transport and injection systems. So designed at built unsteady flow experimental apparatus and conducted unsteady test with pure CO2.