System Plan Considering Spare Capability Allowed for Weather Conditions for CO₂ Marine Transport and Release in Deep Waters

Ocean storage of the captured CO₂ from fossil fuel burning is a possible option for mitigating the increase of CO₂ concentration in the atmosphere. Moving-ship type of CO₂ ocean storage is a concept whereby captured CO₂ is delivered by ship to a site and injected into the deep ocean by means of a pipe suspended beneath a ship as it slowly moves through the water. In case of bad weather conditions, CO₂ marine transport and operation on the sea should be adjourned although CO₂ would be captured at the plant every day. It is, therefore, required that the system would have the buffer storage at the port and the extra shipping ability to recover the delay of schedule. Since the large scale of such spare capability might lead to the increase in cost, it is needed to investigate how to plan the system allowed for weather conditions reasonably. In this study, a time series model of sea state through one year is generated for a hypothetic ocean storage site, based on the wind data observed with satellite remote sensing, and simulations of CO₂ marine transport and operation on the sea are carried out considering the operational limit of sea state. In this approach, the continuing bad weather days or the frequent occurrences of rough sea condition during the specific season are counted. Three kinds of system are applied for the simulations and compared; 1) CO₂ carrier and release ship are used separately and moored tandem for CO₂ shift at the site, 2) CO₂ carrier and release ship are used separately and moored in parallel for CO₂ shift, 3) ship is used as a CO₂ carrier and release ship. The third one would not need mooring and CO₂ shift operations on the sea which are sensitive to the sea state, but would need long- and every-time operation of pipe handling. The results are assessed as capital and running cost per tonne of CO₂.