Ship transport of CO2 -: Technical solutions and analysis of costs, energy utilization, exergy efficiency and CO2 emissions

Increased focus on reducing CO2 emissions has created growing interest in CO2 capturing from industrial processes for storage in geologic formations or injection in oil reservoirs for enhanced oil recovery (EOR). Due to the scattered CO2 sources and the uncertainty in the growth of the CO2 market, a cost effective and flexible transport system is required. In this work a ship transport concept is developed as an alternative to pipeline transport. New technical solutions, cost-, energy-, exergy- and CO2 emission analysis for ship-based transport of CO2 are presented. The concept includes all the elements in the transport chain, namely liquefaction, intermediate storage, loading system, semi-pressurized ship and offshore unloading system. Economical large-scale transport Of CO2 by ship could be done in semi-pressurized vessels of around 20 000 m 3 at pressures near triple point (6.5 bara and -52 degrees C) in order to use well established design for commercial construction of LPG carriers and intermediate storage. This condition also gives the highest density in the liquid state, which reduces the transport unit cost. Liquefaction Of CO2 is best achieved in an open cycle, where the refrigeration is partly or fully provided by the feed gas itself. The offshore unloading system will transport the liquid CO2 from the dedicated CO2 ship to the wellhead on the platform at the required temperature and pressure. During the unloading phase the ship is connected to a submerged turret loading (STL) system. The CO2 is pumped to a pressure high enough to avoid phase transition in the transfer lines. A flexible riser, a subsea pipeline and an insulated pipeline in the platform shaft bring the CO2 from the unloading location to the topside of the platform. The CO2 is pumped to injection pressure and heated to avoid operational problems before it is injected into the reservoir for EOR using conventional water injection wells. The total specific energy requirement for the selected transport chain is 142 kWh tonne(-1) CO2, where the liquefaction process accounts for 77%. An exergy analysis of the chain is performed showing that the minimum work required in the chain is 60 kWh tonne(-1) CO2, giving a chain rational efficiency of 42%. The total CO2 emissions are estimated to be approximately 1.4% of the inlet CO2. The total costs of ship-based transport are calculated to be 20-30 USD tonne(-1) for volumes larger than 2 Mt y(-1) and distances limited to the North Sea. Ship transport offers a flexible alternative for bringing CO2 to offshore installations. Dedicated CO2 carriers for transport Of CO2 directly from the source to the oil fields might be a key element in future CO2 infrastructures.