Study on CO₂ Releasing Nozzle for CO₂ Ocean Storage

Ocean storage of CO₂ is one of greenhouse gas control technologies, where CO₂ captured from flue gas of fossil fuels is injected into deep sea below 3500m depth to be sequestered from the atmosphere. A CO₂ sending method, COSMOS, was proposed as a method of ocean storage, which enables CO₂ drops released in mid-depth water to descend to deep sea floor below the depth of 3500m. Then, the authors have worked for development and evaluation of COSMOS. In the first phase of the COSMOS project, the concept of COSMOS was demonstrated by in situ experiments of small-scale CO₂ releasing at mid-depth water in Monterey Bay, U.S.A. Three models of CO₂ releasing nozzle unit were developed for the experiments. The first model of nozzle unit released liquid CO₂ as one mass; however, it was immediately broken into small droplets and soon turned to ascend. The second and third models were designed to have thermal insulator enough to keep low temperature so that both models successfully released liquid CO₂ with dry ice, which continued descending for a few minutes. Based on these results, COSMOS was improved, where injection of a mixture of liquid CO₂ and dry ice, CO₂ slurry, is expected to enable small CO₂ drops to descend to deep sea floor below 3500m depth. Then, in the second phase of the COSMOS project, the authors started an investigation on the effect of the aspects of releasing nozzle on the behavior of released slurry drops, and obtained a few results from lab experiment of CO₂ slurry releasing from two types of nozzle head.