Climate change is a very vital issue that can be no longer avoided. Korea has been a top-level country in dealing with carbon dioxide emissions since 1960s. Many studies have been conducted to suppress or eliminate carbon dioxide emissions, which account for a large portion of greenhouse gases. Carbon Capture and Storage (CCS), the most practical method of them, plays a significant role. These method has the disadvantage of geographical distribution limits and high possibility of re-emission into the atmosphere. Recently, ocean storage has been studied using Accelerated Weathering of Limestone (AWL), a technique for storing carbon dioxide in the ocean as an alternative to CCS, an underground storage. AWL is a method of converting carbon dioxide into concentrated water in the form of bicarbonate ion and discharging it to the ocean to dilute and store it. It does not cause re-emission to the atmosphere, and the discharged concentrated water increases the alkalinity of the ocean to prevent marine acidification. The objective of this study was to understand the behavior of DIC (Dissolved Inorganic Carbon) including carbon dioxide during the ocean discharge of bicarbonate ion concentrated water in AWL method.
The government decided to apply a discharge plan by a ship for the marine treatment of carbon dioxide, and wanted to confirm the behavior of DICs contained in seawater. The study area was set near Ulleung-do where sufficient water depth and operational efficiency were secured. CORMIX model(Cornell Mixing Zone Expert System) was used to calculate the material diffusion by submerged discharge through towed pipe injection from a ship.
Through the CORMIX model, the results were obtained by organizing the discharge numerical model of discharge by offshore and offshore layers and applying the scenario of seawater release rich in the medium carbonate ion pre-set by season for each discharge method. The comparison of the resulting values was made with emphasis on the dilution rate. The environmental sensitivity assessment was based on the time reached of 44.4 mg/L and 221.9 mg/L, which are the criteria for the degree of damage to living organisms in the surrounding waters. The conclusions drawn by analyzing several physical parameters from the simulation results can be summarized as follows.
1) Coastal Surface Discharge : Due to the relative density difference with the surrounding water, the heavy carbonated concentrated water undergoes negative buoyancy motion, which is the same regardless of the season and discharge velocity. It is affected by low-lying and land-based conditions.
2) Outer Sea Surface Discharge : The volume shows a pattern of moving in a low plane with negative buoyancy exercises. This is the same regardless of season and discharge velocity. The surrounding water has a stable layer of density, so the plumes appear to be trapped and move to the lower plane to expand contact with the surrounding water. The faster the discharge speed, the longer the initial mixing area is, the lower the dilution rate. It is a more advantageous method compared to coastal surface discharge.
3) Outgoing Medium Discharge : As with the outer sea surface discharge, the volume shows a pattern of moving in a low plane with negative buoyancy exercise. This is the same regardless of season and discharge velocity. The effects of density differences in ambient water due to medium-layer discharges are greater, resulting in longer initial mixed zones than in winter, and lower dilution rates. This is the most effective manner with a greater dilution rate.
4) Environmental Sensitivity Assessment : As a result of the environmental sensitivity assessment, the seasonal differences are small, as are the dilution rates. It was assessed that the effects on more than 95% of the surrounding sea life in both summer and winter were insufficient, since almost all discharges are diluted in far-off areas.