Production of a sinking form of CO_2 in the ocean is an attractive option for carbon sequestration because (1) the potential for the CO_2 to re-enter the atmosphere decreases with depth and (2) injection costs may be less if shallower injection depths can be used.An ocean CO_2 injection system has been developed at Oak Ridge National Laboratory (ORNL) over the last several years and has been demonstrated to produce a sinking CO_2 hydrate composite both in the laboratory using the ORNL Seafloor Process Simulator (SPS) as well as in ocean injections.The composite is created by an injection system where seawater and liquid CO_2 are co-injected at pressures and temperatures corresponding to intermediate ocean-depths.Under these conditions,a dense,solid-like composite consisting of liquid CO_2,water,and CO_2 hydrate forms at the interface of the two fluids (Figure 1).CO_2 hydrate is a solid clathrate compound in which water molecules form hydrogen bonded cages that trap CO_2 gas and is denser than seawater.If approximately 25% of the injected CO_2 is converted to hydrate,composite particles will sink in seawater at intermediate ocean depths.Formation of hydrate is beneficial because it will increase the density of the particles and lower their dissolution rate,thus potentially decreasing the environmental impact of high pCO_2 near the injection point.
展开▼
