Dissolution of Direct Ocean Carbon Sequestration Plumes Using an Integral Model Approach

Abstract

We present the results of a double-plume integral model for a positively buoyant multiphase plume of liquid carbon dioxide injected at mid-depths (500–2000m) in the ocean. In addition to the relevant plume physics, the model accounts for dissolution of the carbon dioxide droplets, the effect on dissolution of clathrate hydrate films, and the increase in seawater density due to enrichment by dissolved carbon dioxide. Due to the creation of negative buoyancy in the entrained fluid through dissolution of carbon dioxide, the near-field mixing exhibits a complex set of energetic descending outer plume structures that do not converge to a steady state. The unsteady near field is shown to be inherent in the plume physics, resulting in enhanced distribution of the dissolved carbon dioxide over the plume height and formation of multiple, unsteady intrusion layers. Despite the complex plume near field, we demonstrate that the height of maximum plume rise has a steady solution. A general empirical design equation for the maximum height of plume rise is presented from the model results, dependent on the initial droplet diameter and buoyancy flux, the strength of the ambient stratification, and the linear mass transfer reduction factor due to hydrate formation. A sensitivity analysis of the design equation highlights the droplet diameter as the most important design variable and demonstrates that current uncertainty in the value of the mass transfer reduction factor results in uncertainty of the plume rise height within a factor of three.