Yutaka Tabe

Dissolution rate of liquid CO2 in pressurized water flows and the effect of clathrate films

The dissolution rate of liquid in CO2 in seawater, when a CO2 clathrate-hydrate film exists at the interface, is a key factor for estimation of CO2 sequestration in ocean and marine environmental impact assessment. Liquid CO2 dissolution phenomena in CO2 sequestration in the ocean include (i) dissolution and diffusion of liquid CO2 droplets at intermediate sea depths and (ii) CO2 dissolution in undercurrent flows from a liquid CO2 pool at seabeds deeper than 3000 m. For the first case, the present paper presents a data base of clathrate-hydrate covered CO2 droplet surface concentration, which is essential for an analysis of CO2 droplet dissolution behavior. Effects of pressure and temperature are included. A numerical simulation for dissolving liquid CO2 droplets released at an intermediate ocean depth is presented. The effects of released droplet size and ambient CO2 concentration on dissolution behavior are clarified. For the second case, an experiment simulating dissolution of liquid CO2 stored at a seabed into an undercurrent flow was conducted. The pool surface was covered with clathrate and the surface concentration of the clathrate-covered CO2 pool was estimated. Applying the measured surface concentration and mass transfer coefficient obtained from the actual conditions of deep ocean data, the time scale of CO2 dissolution into an undercurrent flow was estimated, which is important for estimation of CO2 disposal in the deep ocean.

MRI Measurement of Hydrate Growth and an Application to Advanced CO2 Sequestration Technology

Abstract: MRI measurements of hydrate thickness growth have been measured and this phenomenon applied to advanced CO2 ocean dissolution technology. CO2 droplets dissolve during the process of sinking from their release point into deep ocean, by forming fine hydrate particles inside CO2 droplets before the droplets are released from a towed pipe on a moving ship. This results in a sufficiently long sequestration period from the atmosphere and further reduces biological impact. The increasing rate of hydrate film thickness in forming hydrate particles was measured by an ultrahigh‐pressure magnetic resonance imaging (MRI) technique.

Measurement of CO2 diffusion coefficient and application of LIF in pressurized water

This paper deals with estimation of the diffusion coefficient in an H2O CO2 system under high pressure and the use of laser-induced fluorescence (LIF) for measuring CO2 dissolution. A liquid CO2 droplet without CO2 clathrate was placed in the flow where the velocity profile is uniform. The diffusion coefficient is estimated by measuring the liquid CO2 droplet-dissolution rate and using the empirical mass transfer coefficient. The measured diffusion coefficient agrees well with the Wilke-Chang equation at pressures of 29.4 and 39.2 MPa. We have used LIF for measurement of the large non-uniform, two-dimensional pH distribution induced by CO2 dissolution. A sheet laser beam was provided by a YAG laser and the two-dimensional LIF intensity was detected by an image-intensified CCD diode-array camera.

CO2 clathrate-hydrate formation and its mechanism by molecular dynamics simulation

Abstract Molecular dynamics simulation has been conducted in order to obtain the fundamental understanding for the formation mechanism of CO 2 clathrate-hydrate that suppresses the dissolution of liquid CO 2 isolated at deep ocean floor. It was demonstrated that the H 2 O molecules formed a characteristic cage structure of type I clathrate around the CO 2 guest molecules after 260 ps from the initial condition of H 2 O molecules at pressurized water state. CO 2 clathrate-hydrate formation kinetics has elucidated that the interactions between the CO 2 guest molecules would form a low potential region, which has an effect to suppress the H 2 O molecules motions in a two-dimensional plane and assist to form cage structures consisted of 5 and 6 membered rings.

Massive CO2 clathrate hydrate growth at a high-polar-energy surface

Abstract Massive hydrate growth, which produced large amounts of hydrate without continual agitation as compared with the thin hydrate film that seals the interface between water and guest phases, was investigated. We found that materials with surface-free energies having large polar components promoted massive hydrate growth in the CO 2 –water system; conversely, materials with small polar components, such as polymers, had only the hydrate film formation.

Numerical simulation for dissolution of liquid CO2 droplets covered with clathrate film in intermediate depth of ocean

Dissolution of liquid CO 2 droplets at intermediate depth of ocean is strongly effected by the release methods of liquid CO 2 and hydrate formation. The present paper presents numerical simulations for the dissolution behavior of C02 droplets released from (1) pipeline outlet which is a fixed point at intermediate ocean depth and (2) pipe of moving ship. Clathrate-hydrate formation on the CO 2 droplet surface was fully included for both cases (1) and (2). External flow conditions around the CO 2 droplets are different between (1) and (2). A rising plume water flow is formed for case (1) and a free stream turbulence induced by the wake behind the pipe is for case (2). It was indicated that, for case (1) the released droplet diameter is required to be controlled to be less than 0.8cm to obtain the complete dissolution for the travel distance less than 1000m. The large travel distance is caused by the rising motion of plume water flow. Even if the CO 2 is released from 16 separated branches, the travel distance is reduced to 30%. In addition, increase of ambient CO 2 concentration drastically decreases the dissolution. On the other hand, for case (2), it was demonstrated that easier released droplet size condition to obtain complete dissolution is acceptable when liquid C02 is released from a pipe of moving ship, which also possesses a high potential that the ambient CO 2 concentration would not increase.

Mass transport phenomena of liquid CO2 with hydrate

Abstract Present paper reports dissolution rate of liquid CO 2 with hydrate film into water which is essential for estimation of CO 2 sequestration in ocean and marine environmental impact assessment. Effect of hydrate film was fully included in the simulations. Droplet diameter released from pipeline introduced from power-plant is required to be less than 0.8 cm to obtain the complete dissolution for the travel distance less than 1000 m. On the other hand, it was demonstrated that easier released droplet size condition to obtain complete dissolution is acceptable when liquid CO 2 is released from a pipe of moving ship. For CO 2 isolation at seabeds deeper than 3000 m, an experiment simulating dissolution of liquid CO 2 stored at a seabed into an undercurrent flow was conducted. Applying the measured surface concentration and mass transfer coefficient obtained from the actual conditions of deep ocean, the time scale of CO 2 dissolution into an undercurrent flow was estimated to be around 240 years for a complete dissolution of the CO 2 pool created by a 1 GW power plant in 10 years.