Analysis of transportation systems for CO₂ sequestration

A complete CO₂ capture and sequestration (CCS) system requires safe, reliable and cost-effective methods of CO₂ transmission from the capturing facility to the permanent storage site. Pipeline transport is the most economical solution when it comes to transporting large quantities of CO₂ over moderate distances. CO₂ compression differs from most fuid compression tasks due to the high molecular weight, highly compressible behavior and the presence of the so called critical point. At the critical point, the difference between the liquid and the gaseous fuid phase disappears. Technically, CO₂ can be transported by pipelines in the form of gas, a supercritical fuid or in the subcooled liquid state. In this work, the CO₂ working area was assumed to be either in the liquid or in the supercritical state and results for these two states were compared. It is most cost-effective if CO₂ is in the dense phase i.e. under the liquid or supercritical regime (Fig. 2.1). This is due to the lower friction drop along the pipeline per unit mass of CO₂ compared to transmitting CO₂ as a gas or as a two-phase gas/liquid combination. The commercially available ASPEN PLUS simulation tool with a pipe model was used to determine the maximum safe pipeline distances to subsequent booster stations as a function of carbon dioxide inlet pressure, ambient temperature and the ground level heat fux parameters under three conditions: isothermal, adiabatic and with heat transfer. In the following discussion, the same power station data will be used as reported in Chap. 3: a 900 MW pulverized coal-fred power plant with 90% CO₂ captured (156.43 kg/s) and the monoethanolamine absorption (MEA) method of CO₂ separation from fue gases. The results show that transporting a subcooled liquid maximizes energy effciency and minimizes the cost of CO₂ transport over long distances under isothermal, adiabatic and heat transfer conditions. After CO₂ is compressed and boosted to above 9 MPa, its temperature is usually higher than ambient but the thermal insulation layer slows down the CO₂ temperature decrease process, increasing the pressure drop in the pipeline. Therefore in Poland, considering the atmospheric conditions, the thermal insulation layer should not be laid on the external surface of the pipeline.