Modelling and Simulation of Carbon Dioxide Transportation in Pipelines: Effects of Impurities

Abstract

Carbon dioxide capture, transportation, and storage has been identified as the most promising way to reduce anthropogenic carbon dioxide (CO2) released into the atmosphere. Efforts made to achieve this purpose include the Paris (Climate) Accord. This agreement seeks to encourage countries to take the issue of rising global temperatures seriously. With nearly all countries signing this agreement, many CCTS projects are expected. Pipelines are employed in the transportation of CO2. CO2 fluids contain impurities that affect the fluid properties and flow dynamics, but pipelines are mostly designed assuming that the CO2 fluid is pure. CO2 pipeline fluids contain at least 90 % CO2 with the balance made up of impurities. The impurities include nitrogen, methane, oxygen, hydrogen, sulphur dioxide, hydrogen sulphide, carbon monoxide, ammonia, argon, etc. The effects of the impurities are studied using simulation software; Aspen HYSYS, gPROMS and HydraFlash. The results show that all impurities impacted negatively on transportation. At equal concentrations, hydrogen had the greatest effect on fluid properties and hydrogen sulphide the least impact. At the specified allowable concentration, nitrogen had the worst effect on pressure loss (32.1 %) in horizontal pipeline, density, and critical pressure. Carbon monoxide (with only 0.2-mol %) had the smallest effect in pressure drop (0.3 %). Analysis of supercritical and subcritical (or liquid) CO2 fluid transportation shows that subcritical fluids have higher densities (more volume transported) and lower pressure losses than supercritical fluids. Subcritical fluid transportation would therefore have lower pipeline transportation costs than supercritical fluids. Also, soil heat conductivity has greater effect than ambient temperature in buried pipelines. Simple equations that approximate binary CO2 fluid properties from pure CO2 properties were developed and presented.