JP2896399B1 - Free sedimentation type liquid carbon dioxide shallow water injection system - Google Patents

Abstract

Abstract: [Purpose] The deep-sea storage method of carbon dioxide is a promising global warming countermeasure technology that can expect that the isolation period of carbon dioxide from the atmosphere will be over 2000 years of the vertical circulation cycle of seawater. The fact that liquid carbon dioxide must be pumped as deep as possible to 3500 m has been considered a disadvantage compared to the dissolution method in which carbon dioxide is released into the middle layer. The present invention focuses on the fact that low-temperature liquid carbon dioxide is heavier than seawater even in shallow seas, and allows free-fall to the storage depth by releasing low-temperature carbon dioxide as large liquid bubbles into the shallow sea,
The aim is to realize deep-sea storage at a cost similar to or less than the melting method. [Constitution] Low temperature carbon dioxide below -26 ° C 0.7m in diameter
When released into the shallow sea at a depth of 500 to 750 m as the above large liquid bubbles, the large liquid bubbles covered by the ice layer having a thickness of 5 cm or more are:
The temperature rises due to the heat received from seawater along with the sedimentation, but at a depth of 275 where carbon dioxide has the same density as seawater in thermal equilibrium.
Until it reaches 0 m, it can maintain a low temperature to maintain the sedimentation force, and eventually settles freely to the storage depth.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

A marine treatment method for carbon dioxide, which has been attracting attention as a promising technology for countermeasures against global warming, has a depth of 1,000 to 20.
"Melting method" to dissolve and diffuse into the middle sea area of 00m and 35
The “storage method” in which the water is stored in deep-sea depressions deeper than 00 m is considered. When the present invention is applied to the storage method in which the marine sequestration period of carbon dioxide is expected to be 2,000 years or more, which is much longer than the 50 to 200 years of the dissolution method, the economic effect is sufficiently exhibited.

[0002]

2. Description of the Related Art Liquid carbon dioxide has a coefficient of thermal expansion and a compressibility as large as 10 times or more that of seawater. Therefore, in a thermal equilibrium state (at the same temperature as seawater), it is lighter than seawater at a depth of less than 2750 m and heavier at a deeper depth. Therefore, it has been considered that it is necessary to pipe liquid carbon dioxide to a depth of at least 2750 m in order to send liquid carbon dioxide to a depth of 3500 m or less, which is an application depth of the storage method in which liquid carbon dioxide is required to be heavier than carbon dioxide saturated dissolved seawater. .

On the other hand, carbon dioxide is generated in seawater at a depth of 45 degrees.
It reacts with seawater at depths of 0 to 900 m or less (differences in depth are caused by several degrees of seawater temperature depending on the sea area) to generate hydrates. Conventional hydrate research has focused on natural gas hydrates, which are difficult to dissolve.Therefore, there is a strong expectation that carbon dioxide hydrate will not dissolve, and there were times when carbon dioxide hydrate was considered an ace of carbon dioxide fixation. there were. However, applicants' experiments showed that carbon dioxide, which can be dissolved well in water, can be well dissolved in seawater even when hydrated. In addition, since hydrate is generated as a film having a thickness of several microns at the interface between liquid carbon dioxide and seawater, it is not easy to produce carbon dioxide hydrate as a lump. From the above, deep-sea storage of carbon dioxide by hydration is not an option.

[0004] Since solid carbon dioxide (dry ice) is heavier than seawater at all depths, when a lump of dry ice is thrown from the sea, part of the dry ice is sublimated or melted, but the rest sinks to the deep sea floor and eventually the seawater. It becomes liquid by the heat from. Although a charging method using this method is conceivable, there is a problem that a large heat loss occurs during the production of dry ice.

[0005]

SUMMARY OF THE INVENTION The conventional deep sea storage method of feeding liquid carbon dioxide through a pipe lowered from a carbon dioxide tanker to a depth of 2750 m or less is not economical due to the long feed pipe. The technical problems of developing long feed pipes have been pointed out.

Accordingly, an object of the present invention is to simultaneously solve the economical and technical problems of the conventional carbon dioxide deep sea feeding method.

[0007]

When low-temperature liquid carbon dioxide, which is heavier than seawater, is released into the shallow water as liquid bubbles, the liquid bubbles settle down in the sea, but the average temperature continues to rise due to heat supply from the surrounding seawater, and eventually the seawater Get lighter and turn up.
However, since the increase in the average temperature of the liquid bubbles due to heat supply from seawater becomes smaller for larger liquid bubbles, even if low-temperature carbon dioxide liquid bubbles with a certain diameter or more are released to the shallow sea,
It can safely pass through 2700 m at an equal density depth and reach a storage depth of 3500 m or less.

Since the low-temperature carbon dioxide liquid bubbles below the freezing point are covered by the ice layer, the buoyancy effect of the ice layer is considered in the analysis of the liquid bubble settling process shown in the following examples.

At the interface between the ice layer and the low-temperature carbon dioxide liquid bubbles, a hydrate film heavier than seawater is formed, but since the thickness is extremely thin, several microns, the density effect on the entire liquid bubbles can be ignored.

[0010] There is a concern that large liquid bubbles may break off during settling. However, the ice layer that covers the liquid bubbles is based on the existing heat transfer method (by Yoshiro Kato: General introduction of heat transfer [Yokendo 1966], p. 153). 5cm when the release temperature is -26 ° C and the liquid bubble diameter is 0.7m
And has a strength not to cause division.

[0011]

FIG. 1 shows that a large liquid bubble of low-temperature carbon dioxide has a depth of 7 cm.
This shows that the water is settled freely when released into a shallow sea of about 50 m. The carbon dioxide transported by the carbon dioxide tanker is-
It is kept at 40 ° C. and 1 MPa. Since liquid carbon dioxide at −40 ° C. is sufficiently heavier than seawater, it sinks without power in the carbon dioxide feed pipe and reaches a discharge depth of 750 m. Large liquid bubbles of low-temperature carbon dioxide formed at the discharge nozzle (part A) settle down freely in the sea as shown.

FIG. 2 shows an example of a discharge nozzle. The low-temperature liquid carbon dioxide sent from the carbon dioxide tanker grows into large bubbles on the inner surface of the hood of the discharge nozzle, and the carbon dioxide liquid bubbles that have reached the required size repeat free sedimentation one after another.

[0013]

EXAMPLE An example of calculation of the diameter of a carbon dioxide liquid bubble which freely settles to a depth of 2750 m will be described. FIG. 3 shows the depth 750
The density difference ratio [Δρ / ρ _SEA = (carbon dioxide density / seawater density) −1] at m is 0.1 (−38 ° C.) to 0.05
In the case of (−26 ° C.), the graph shows how the density difference ratio of the settling liquid bubbles changes using the liquid bubble diameter d as a parameter. The horizontal axis represents temperature, and the vertical axis represents depth and a gauge corresponding thereto. Pressure is shown and many oblique lines in the figure represent _isopycnic ratio lines ρ _co2 / ρ _SEA of carbon dioxide and seawater. Below the saturation line, the carbon dioxide becomes liquid.
C. P. Is the critical point of carbon dioxide (31.06 ° C, 7.3
83 MPa). The dashed line indicates the seawater density ratio taking into account the vertical temperature distribution between the North Pacific Ocean and the North Atlantic Ocean (there is a temperature difference of several degrees between the two seas, but there is almost no difference in the density ratio). Accordingly, the density difference ratio of the liquid bubbles is 2750 m in depth.
If it is on the left side of the chain line, even if it reaches a temperature equilibrium with seawater at a depth of 2750 m or less, the sedimentation will continue to the deep sea floor.

When the low-temperature carbon dioxide liquid bubble sinks in the sea, the surface of the liquid bubble is immediately covered with ice, and the heat of the ice increases due to the supply of cold heat from the liquid bubble. The sedimentation velocity is determined from the balance between the sedimentation force obtained by subtracting the buoyancy effect of the ice layer from the density difference between the liquid foam and seawater determined from the average temperature and the depth of the liquid foam, and the drag associated with the sedimentation. The ice layer thickness is calculated based on the heat transfer coefficient determined from the sedimentation velocity and the liquid bubble diameter. The density ratio of the carbon dioxide liquid bubbles in FIG. 3 is a value calculated under such an assumption.

From FIG. 3, the density ratio of carbon dioxide released at a depth of 750 m is 0.05, that is, the release temperature is -2.
At 6 ° C, if the liquid bubble diameter is 0.7m or more, the critical depth 2
It can be seen that a thermal non-equilibrium sufficient to continue free sedimentation up to 750 m can be secured.

As a matter of course, the larger the carbon dioxide density ratio at the time of release, the smaller the critical liquid bubble diameter. Therefore, when carbon dioxide is released at -40 ° C when transported by land on a tank truck, the critical diameter is 0.7 m.
Smaller.

[Brief description of the drawings]

FIG. 1 is a view showing the concept of low-temperature carbon dioxide large liquid bubble shallow sea discharge.

[Explanation of symbols] Carbon dioxide tanker Carbon dioxide feed pipe Release depth (750m) Large liquid bubbles of low-temperature carbon dioxide that settle freely

FIG. 2 is a view showing the operation of a discharge nozzle for producing a large liquid bubble of carbon dioxide.

[Explanation of symbols] Discharge nozzle hood Growing low-temperature carbon dioxide liquid bubbles

FIG. 3 is a diagram showing a calculation example of a density ratio during sedimentation of low-temperature carbon dioxide liquid bubbles discharged in shallow water.

[Explanation of symbols] Δρ Density difference = carbon dioxide density-seawater density ρ _SEA depth (pressure) and seawater density considering seawater temperature ρ _Freshwater density in _H20 standard state P. Critical point of carbon dioxide (31.06 ° C, 7.38
3MPa)

Claims (1)

(57) [Claims] 1. A low-temperature carbon dioxide of -26 ° C. or less is converted into a large liquid foam having a diameter of at least 0.7 m and a depth of 500 to 750.
m to a depth of 2750 m, where the liquid carbon dioxide passes through a depth of 2750 m, which is in equilibrium with seawater in a thermal equilibrium state, allowing the captured carbon dioxide to be stored in the deep sea by maintaining the thermal non-equilibrium of the carbon dioxide liquid foam CO2 shallow water input system to settle freely to a depth of 3500m or less