Sanai Kosugi

Coupling between mass transfer from dissolving bubbles and formation of bubble-surface wave

The dynamic process of gas dissolution from a single CO 2 -containing bubble into a liquid is studied for bubbles with surface oscillations. Both experimental and theoretical analyses are conducted. In the experiment, the bubble behavior is continuously monitored by holding the bubble in the liquid flowing downward. For detailed observation of the bubble-surface motion, high-speed imaging is applied. The fluctuating surface, often associated with bubble deformation, is viewed as a surface with propagating waves. The dissolution rate, claimed to be largely influenced by the liquid-phase contamination level, is found to depend more inherently on the extent of wave motion. The persisting wave propagation is only observable for large bubbles with distinctive rim. The lower critical diameter is roughly 4 mm. The theoretical analysis lays its basis on modeling the dissolution process of a single bubble comprising two components of different solubility. The model demonstrates good predictive capability for the time variations in bubble diameter and gas-phase composition, the latter being measured via gas chromatography by sampling the gas from the suspended bubble. For pure CO 2 bubbles in the liquid pressurized using N 2 , in particular, the complete dissolution process is characterized by little change in the CO 2 mole fraction near unity followed by a transitory decrease down to zero.

Mass transfer and structure of bubbly flows in a system of CO2 disposal into the ocean by a gas-lift column

A new method for ocean sequestration of low-purity CO 2 gas emitted from fired power plant is developed. This is a gas-lift pump system, named progressive gas lift advanced dissolution (P-GLAD) system, to dissolve only CO 2 gas of combustion gas in seawater at shallow waters and to transport CO 2 -rich seawater to great depths. The system is an inverse-J pipeline set at the ocean at a depth between 200 and 3000 m and a releasing system of indissoluble gas. To improve the efficiency of the P-GLAD, one should elucidate bubbly flows accompanying gas phase dissolution formed in the gas-lift column of the system. In the present paper, first, the authors discuss mass transfer in bubbly flows of pure CO 2 gas and filtrated tap water along the pipe axis in laboratory-scale P-GLAD of 25 mm in diameter and 7.69 m in height. Second, mass transfer in bubbly flows of mixed gas (95% volume of CO 2 and 5% volume of pure air) and filtrated tap water in the same setup is discussed. The mass transfer coefficient of CO 2 in the later system has the values of 0.00031-0.000085. It is shown that the mass transfer coefficient is a function of the distance from the gas injection. Finally, the performance of the system is elucidated on the basis of the experimental and numerical investigations. The laboratory-scale P-GLAD dissolved over 98.5% of CO 2 injected in the liquid phase.

GLAD: A gas-lift method for CO2 disposal into the ocean

To mitigate global warming, we have proposed the GLAD (Gas-Lift Advanced Dissolution) system for CO2 release into deep seawater. It is an inverse-J pipeline set in the sea at a depth of 200–400m. CO2 bubbles injected into the pipe form a buoyant plume and dissolve into the seawater as they rise. This dense solution is released from the other side of the pipe. The feasibility of our method has been examined by the numerical simulation of gas-liquid, two-phase flow with a CO2 dissolution model. In the present paper, the performance and cost of the GLAD system are discussed based on a model plant.

Design factors in gas-lift advanced dissolution (GLAD) system for CO2 sequestration into the ocean

A new method for ocean sequestration of low purity CO 2 gas emitted from thermal power plants has been developed. The method utilizes a gas-lift pump system, named gas lift advanced dissolution (GLAD) system, that dissolves the CO 2 (which has been separated from combustion gas) into seawater at a relatively shallow depth of 200-300 m and then transports CO 2 -rich seawater to a depth greater than 1000 m. The CO 2 concentration of seawater after sequestration shall be limited to a certain value (e.g. 3 mol/m 3 ) so as to minimize the impact on marine life. This paper describes the numerical simulation model of GLADs two-phase flow with a CO 2 dissolution that was used to determine the optimal specification of the system. This numerical simulation resulted in the following conclusions: (1) The required length for full dissolution in the dissolution pipes is proportional to the diameter of the injection bubble, and increases linearly with the decrease in the purity of CO 2 gas. (2) The allowable injection rate of CO 2 gas, for a marine life, is proportional to the sectional area of dissolution pipe and increases with the increase in impurity (=1-purity) of the CO 2 gas and the diameter of the injection bubble. (3) Analysis of correlations among these factors will enable system optimization on the total cost basis including the costs for CO 2 separation from exhaust gas, transportation of CO 2 gas to the GLAD site and CO 2 sequestration.

Pneumatic capsule pipelines in Japan and future developments

This chapter presents a review of development in the pneumatic capsule pipeline (PCP) system and its potential future developments. Two commercial PCP systems have been installed in Japan. One is to transport 2 million tons of limestone annually from the mine to the cement works. It has been in operation since 1983 without environmental pollution, with its availability being as high as 94 - 98 %. The other was commissioned for tunneling of Japans bullet train from 1991 to 1994. This application is an epoch-making tunneling project with cleanliness and safety. Sumitomo Metal Industries, Ltd. (SMI) is also studying the application of the PCP system to municipal solid wastes, parcels, etc. It is anticipated that the 21st century will see widespread uses of the PCP system by virtue of its effectiveness without environmental impacts. The PCP system has a long history from the point of feasibility study and engineering design, since its invention in the 19th century; however its use for commercial operations is very limited. Recent industrial concerns and trends such as environmental issues have enhanced the attention of the PCP system because of its environmental friendliness and its effectively diversified applications. This chapter firstly traces SMIs experiences and operational scheme, as well as SMIs recent potential application, and then explains the future technological developments in Japan.

Effect of traveling resistance factor on pneumatic capsule pipeline system

The efficiency of a pneumatic capsule pipeline (PCP) system can be defined by the leak factor and the traveling resistance factor (TRF). The former factor is defined only by size of disks at each end of a capsule which does not change with surrounding condition. On the other hand, the latter factor TRF is defined by characteristics of rubber tyre which change with temperature. This paper describes the effect of TRF on the energy consumption of PCP system. Firstly, it was found that TRF changes with ambient temperature as its measurements were carried out in different seasons. Secondly, the energy consumption is estimated by using the numerical analysis program based on the following formulas: (1) motion formula of air flow in pipeline; (2) continuity formula of air flow in pipeline; (3) formula of air flow between capsule and pipe wall; (4) motion formula of capsules. This estimation shows good agreement with measured data in a commercial PCP system. Seasonal changes in the energy consumption are examined by using data in Canada where the minimum ambient temperature is quite low. The result suggests that TRF data in winter should be used in determining the specifications of blowers and motors.

APPLICABILITY OF PNEUMATIC CAPSULE PIPELINE TO RADIOACTIVE WASTE DISPOSAL FACILITY

Various transport systems have been studied for the transportation of waste packages and buffer materials from the ground surface to the underground radioactive waste disposal facility, such as a lift (vertical shaft type) and a vehicle (inclined tunnel type)(1). This paper introduces pneumatic capsule pipeline system as a new method for the transportation. The system is designed to transport pneumatically waste packages and buffer materials between the surface and the underground as shown in Fig. 1. The system is also used to transport excavated debris, equipment and materials during construction. It is economical to utilize the system for air ventilation in addition to be used for transportation. The capsule moving in the shaft can be controlled at appropriate speed by adjusting the air pressure in the shaft. This paper discusses the applicability of the system to the geological disposal based on analytical simulation and experimental study.