Carbon dioxide emission tower, carbon dioxide emission method

Abstract

The objective is to provide a safe carbon dioxide emission tower and carbon dioxide emission method that can prevent deposition on the ground surface by blowing carbon dioxide gas, which has a higher specific gravity than air, upward at a sufficient flow velocity even when the emission flow rate is small. [Solution] The carbon dioxide emission tower 1 according to the present invention is installed at the inlet, outlet, or in the middle of a pipeline 3 that transports carbon dioxide, and emits carbon dioxide from the pipeline 3. It has two or more emission pipes 5 erected in parallel, emission lines 7 connecting the pipeline 3 and each emission pipe 5, and emission valves 9 provided on each emission line 7. The diameter and number of emission pipes are configured so that even if the emission flow rate fluctuates within a predetermined range, the flow velocity inside the emission pipes 5 will be in the range of Mach 0.4 to 0.85.

Description

Technical Field

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[0001] The present invention relates to a carbon dioxide (CO2) emission tower and a carbon dioxide emission method.

Background Art

[0002] In gas pipelines such as natural gas pipelines and city gas pipelines, in order to maintain and manage the pipelines and to cope with unexpected situations such as disasters caused by earthquakes, the gas in the pipelines may have to be discharged. Therefore, a gas emission tower for emitting the gas in the pipeline into the atmosphere is installed in parallel with a shut-off station installed at the inlet, outlet of the pipeline or at predetermined intervals of the pipeline.

[0003] Generally, the gas emission tower is about 15 to 70 m high and has a structure in which a cylindrical pipe, that is, an emission pipe, stands vertically independently or is supported by a framework. Conventional general gas emission towers are shown in FIGS. 7 to 9. In FIGS. 7 to 9, 21 is an emission pipe, 7 is an emission line connecting the pipeline and the emission pipe, 9 is an emission valve, 17 is a flow meter, and 15 is an original valve.

[0004] The higher the height of the emission pipe, the more the atmospheric diffusion effect of the emission gas is expected, but there are restrictions from the viewpoints of construction cost and landscape. Therefore, in the "telescopic gas emission tower" of Patent Document 1 and the "gas emission tower" of Patent Document 2, a gas emission tower having a structure in which the emission pipe extends only during gas emission has been devised.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, carbon dioxide emission reduction projects known as CCS (Carbon Capture and Storage), which involve separating and capturing carbon dioxide from exhaust gases and storing it underground, have attracted attention as a measure against global warming. Pipelines are often planned as a means of transporting carbon dioxide from emission sources to storage locations. The phase state of carbon dioxide within a pipeline is gaseous at pressures below approximately 3 MPaG, and liquid / supercritical at pressures above approximately 8 MPaG. Similar to natural gas pipelines mentioned above, venting facilities are also necessary for carbon dioxide pipelines. When liquid / supercritical carbon dioxide is released into the atmosphere, it may transiently turn into dry ice, but ultimately it will gaseous and diffuse and mix into the atmosphere.

[0007] Because carbon dioxide is denser than air, it tends to accumulate on the ground surface when released in large quantities. Furthermore, it is generally believed that carbon dioxide concentrations exceeding a few percent in the air can cause serious health problems for humans. Therefore, careful equipment design and operational planning are necessary, based on numerical simulations of atmospheric diffusion, to prevent carbon dioxide released vertically upward from release facilities from settling on the ground surface at concentrations exceeding permissible limits.

[0008] The rated discharge flow rate of a discharge tower is set based on emergency discharge, which releases gas from the pipeline in a short time during disasters, etc., and the diameter of the discharge pipe is generally selected so that the flow velocity at the rated discharge flow rate is around Mach 0.8. From the standpoint of diffusion effect, a faster discharge velocity is preferable, but if the transonic velocity exceeds Mach 0.8, noise and shock are likely to occur, and stable gas discharge may become difficult.

[0009] On the other hand, in planned discharges where gas in a pipeline is discharged over a relatively long period of time for maintenance or other purposes, the flow rate is often set to a fraction of the rated discharge flow rate. Therefore, the flow velocity inside the discharge pipe during planned discharge will be at most about Mach 0.3. In the case of gases with low specific gravity, such as natural gas, even at low flow velocities, the gas released upward into the atmosphere is expected to diffuse upward.

[0010] However, heavy gases like carbon dioxide, when released at low flow rates, can lose their inertia and settle due to gravity, potentially accumulating at high concentrations on the Earth's surface. Furthermore, even if sufficient flow rate is maintained in the initial stages of discharge, the discharge flow rate gradually decreases as the pressure inside the pipeline decreases with the progress of discharge. At this time, the opening of the discharge valve is gradually increased to maintain the discharge flow rate, but even with the discharge valve fully open, a decrease in the discharge flow rate is unavoidable in the final stages of discharge.

[0011] The present invention was made to solve the above problems, and aims to provide a safe carbon dioxide emission tower and carbon dioxide emission method that, regarding the emission of heavy gases such as carbon dioxide, can blow upward at a sufficient flow velocity even when the emission flow rate is small, and can effectively dilute by diffusing into the surrounding atmosphere, thereby preventing deposition on the ground surface. [Means for solving the problem]

[0012] (1) The carbon dioxide emission tower according to the present invention is an emission tower installed at the inlet, outlet, or in the middle of a pipeline that transports carbon dioxide, and which emits carbon dioxide from the pipeline, It comprises two or more parallel-erected discharge pipes, a discharge line connecting the pipeline and each discharge pipe, and a discharge valve provided in each discharge line. The diameter and number of discharge pipes are configured such that, in relation to the fluctuation range of the discharge flow rate, the flow velocity inside the discharge pipes is within the range of Mach 0.4 to 0.85.

[0013] (2) Further, the invention according to (1) above is characterized in that it further comprises a control device for adjusting the opening / closing state and the opening degree of each diffusion valve according to the diffusion gas flow rate.

[0014] (3) Further, the invention according to (1) or (2) above is characterized in that the top outlets of each diffusion pipe are inclined in different directions from each other.

[0015] (4) Further, the invention according to any one of (1) to (3) above is characterized in that the top outlets of each diffusion pipe have an elliptical or star-shaped cross-sectional shape.

[0016] (5) Further, the invention according to any one of (1) to (4) above is characterized in that the top outlets of each diffusion pipe have a shape that smoothly expands in diameter toward the tip.

[0017] (6) The carbon dioxide diffusion method according to the present invention is the carbon dioxide diffusion method in the carbon dioxide diffusion tower according to any one of (1) to (5) above, and is characterized in that, for the fluctuation range of the diffusion flow rate, the diffusion pipe to be used is selected and diffused so that the flow velocity in the diffusion pipe is in the range of Mach 0.4 to 0.85.

Advantages of the Invention

[0018] According to the present invention, even when the diffusion flow rate is smaller than the rated diffusion flow rate, the diffusion flow velocity at the diffusion pipe outlet can be maintained above a certain level, and compared with a conventional diffusion tower of the same height, the deposition of carbon dioxide on the ground surface can be reduced.

Brief Description of the Drawings

Mode for Carrying Out the Invention

[0020] The vent tower according to the present invention relates to a vent tower for carbon dioxide having a density greater than that of air. The vent tower 1 according to the present embodiment is provided at the inlet, outlet or in the middle of the pipeline 3 for transporting carbon dioxide, and dissipates the carbon dioxide in the pipeline 3. As shown in FIG. 1, it includes four vent pipes 5 erected in parallel, a vent line 7 connecting the pipeline 3 and each vent pipe 5, a vent valve 9 provided on each vent line 7 connected to each vent pipe 5, and a control device 11 for adjusting the opening / closing state and opening degree of each vent valve 9 according to the vent flow rate.

[0021] <Vent pipe> The vent pipes 5 are erected in parallel and dissipate carbon dioxide upward. The number of vent pipes 5 is shown as four in FIG. 1, but the present invention is not limited to this, and a plurality of vent pipes may be used, specifically, two, three, five or more may be used. The number and diameter of the vent pipes 5 are determined from the fluctuation range and frequency of the vent flow rate and the fluctuation range of the allowable Mach number. As the fluctuation range of the allowable Mach number, empirically, it is preferably from 0.4 to 0.85. If it is less than 0.4, the dissipated carbon dioxide is likely to deposit on the ground surface. If it exceeds 0.85, the flow becomes sonic flow partially, and there is a risk of generating noise and vibration.

[0022] The procedure for selecting the number and diameter of the discharge pipes is as follows: First, the lower and upper limits (rated values) of the discharge flow rate are set. For the lower limit of the discharge flow rate, the diameter of the discharge pipes is set so that when that flow rate is passed through one or two discharge pipes, the flow velocity is Mach 0.4 or higher. Also, for the upper limit (rated value) of the discharge flow rate, the total cross-sectional area of ​​all discharge pipes is determined so that when that flow rate is passed through all discharge pipes, the flow velocity in each pipe is Mach 0.85 or lower. Based on the results of this lower and upper limit examination, the combination of the number and diameter of the discharge pipes is determined.

[0023] For example, let's assume that the carbon dioxide in the pipeline is a gas at room temperature and a pressure of 3 MPaG, and that the emission rate fluctuates within a range of 50 to 200 t / h. In conventional single-pipe diffusers, if the diameter of the diffuser pipe 5 is selected as 400A, the flow velocity inside the diffuser pipe will be Mach 0.2 to 0.8 for a diffuser flow rate of 50 to 200 t / h. In other words, the flow velocity is appropriate for the upper limit of the diffuser flow rate, but it is too low for the lower limit. On the other hand, in the multi-tube gas emission tower 1 according to this embodiment, if a configuration of four 200A emission tubes is used, when the emission flow rate is 50 t / h, a flow velocity of Mach 0.8 can be secured by using only one emission tube. When the emission flow rate is 55 t / h, two emission tubes are used to achieve a flow velocity of Mach 0.44. Furthermore, when the emission flow rate is 200 t / h, four emission tubes are used to achieve a flow velocity of Mach 0.8. Thus, by appropriately adjusting the number of emission tubes used in response to fluctuations in the emission flow rate, emission can always be performed within the desirable Mach number range of 0.4 to 0.85.

[0024] Furthermore, the diameters of the multiple radiation pipes 5 may be the same, or they may each have different diameters. If the four discharge pipes 5 have the same diameter, the configuration should be 25% x 4 pipes relative to the total rated discharge flow rate of 100%. Furthermore, if the diameters of each discharge pipe 5 are different, for example, if the system is composed of four discharge pipes 5 with different diameters such that the individual rated discharge flow rates are 10%, 20%, 30%, and 40%, then even if the discharge flow rate fluctuates within the range of 10% to 100% of the overall rated discharge flow rate, each discharge pipe 5 can be operated at a flow rate close to its respective rated discharge flow rate by appropriately combining the discharge pipes 5 used.

[0025] Furthermore, the upper end of the radiation pipe 5 can take on various forms, which will be explained below. Figure 2 shows an example of the configuration of the upper end of the radiation pipe 5, where Figure 2(a) is a plan view of the four radiation pipes 5 seen from directly above, and Figure 2(b) is a view of the arrow AA in Figure 2(a). As shown in Figure 2, the upper ends of the opposing gas diffusers 5 are bent in opposite directions in a plan view. This bending of the upper ends causes the upper opening surface to be inclined by an angle θ with respect to the axis of the diffuser 5. The angle θ can be determined individually based on the rated diffusion flow rate of the gas diffuser 1 and the average wind speed at the installation site; there are no specific limitations on the value, but a range of 5 to 45° is preferable.

[0026] Figure 3 shows another configuration in which the upper end of the radiation pipe 5 is bent. Figure 3(a) is a plan view of the four radiation pipes 5 seen from directly above, and Figure 3(b) is a view BB as seen by the arrow in Figure 3(a). The configuration shown in Figure 3 is one in which the direction in which each radiation pipe 5 is bent is changed by 90°. Specifically, in Figure 3(a), the radiation pipe 5 located at the top of the figure is bent to the left, the radiation pipe 5 located at the rightmost position is bent upward, the radiation pipe 5 located at the bottom of the figure is bent to the right, and the radiation pipe 5 located at the leftmost position is bent downward.

[0027] Since the diffusion of gas into the atmosphere is promoted by crosswinds, it is more effective for the top of the dispersion tube 5 to be tilted downwind from the crosswind. Therefore, as shown in Figures 2 and 3, by bending the upper end of each radiating pipe 5 so that the orientation of the opening surface of each radiating pipe 5 is different, the radiating pipe 5 can be selected according to the wind direction, allowing for radiation downwind, and promoting the mixing and diffusion of the radiating gas jet with the atmosphere. Specifically, when there are four diffusers 5, the tops of each diffuser 5 are tilted to the east, west, south, and north directions, respectively. For example, when the wind is blowing from the southeast, diffusers are released from the two diffusers 5 facing north and west. This promotes atmospheric diffusion and minimizes deposition on the ground surface. Furthermore, because the opening surface of each vent pipe 5 is inclined, the direction of the gas emitted from each vent pipe 5 can be tilted from the vertical, which is expected to promote the mixing and diffusion of the emitted gas jet with the atmosphere, especially when there is a crosswind.

[0028] Figure 4 shows a plan view of the discharge pipe 5 seen from directly above. In the configuration shown in Figure 4, the shape of the outlet of the discharge pipe 5 is different from a perfect circle. Figure 4(a) shows an example where the cross-section of the top of the discharge tube outlet is elliptical. Figure 4(b) shows an example where the cross-section of the top of each discharge tube outlet is petal-shaped (star-shaped). By shaping the top of the outlet of the radiating pipe in this way, compared to a circular cross-section, it is possible to promote the accompanying mixing of ambient air with the jet, increase the contact surface between the radiating gas jet and the ambient air, and increase the lateral surface area of ​​the jet that is exposed to crosswinds. As a result, improved diffusion and noise reduction effects can be expected.

[0029] Furthermore, the configuration shown in Figure 4 may be used in combination with the configurations shown in Figures 2 and 3. In other words, the upper end of each radiation pipe 5 may be bent, and the cross-section of the top of the radiation pipe outlet may be made elliptical or petal-shaped (star-shaped).

[0030] Figure 5 is a side view of the discharge pipe 5, and the configuration shown in Figure 5 has a shape in which the discharge pipe outlet smoothly widens in diameter towards the tip. By shaping the outlet of the discharge tube in this way, the discharged gas flows along the outwardly curved inner surface due to the Coanda effect, forming a jet with a wider angle of spread compared to the approximately 25° of a jet flowing out of a normal circular pipe. This promotes dilution and mixing through the entrainment of surrounding air. The spreading angle δ can be set individually according to conditions such as the rated discharge flow rate of the discharge pipe 5, and there is no particular limit to its value. However, if the angle δ is too large, it may excessively reduce the velocity of the jet and decrease the inertial force of the upward flow, so an angle of around 5 to 15 degrees is preferable.

[0031] <pipeline> Pipeline 3 is a pipeline for transporting carbon dioxide from the emission source to the storage area, and gas emission towers 1 are installed at the inlet, outlet, or along the route of pipeline 3.

[0032] <Emission line> Discharge line 7 is the line connecting pipeline 3 to each discharge pipe 5. In this embodiment, a main pipe 13 is connected to the pipeline 3, four emission lines 7 are connected to the main pipe 13, and each emission line 7 is connected to an emission pipe 5. A main valve 15 is installed in the main pipe 13, and each discharge line 7 is equipped with a discharge valve 9 and a flow meter 17.

[0033] <Dispersion valve> Each of the discharge valves 9 is provided in the discharge line 7 connected to each discharge pipe 5, and the open / closed state and degree of opening are adjusted by the control device 11 according to the discharge gas flow rate. For the discharge valve 9, a full-bore ball valve is usually used. While it is preferable for the discharge valve 9 to be operated automatically by an electric motor or pneumatic pressure using a program-based control device 11, in extreme cases, it may also be operated manually according to a pre-prepared operation manual.

[0034] <Control device> The control device 11 adjusts the open / closed state and opening degree of each discharge valve 9 according to the discharge gas flow rate. Specifically, the control device 11 takes in the measured values ​​from multiple flow meters 17, calculates the optimal flow distribution, and remotely controls the open / closed state and opening degree of each discharge valve 9.

[0035] The operation of the gas emission tower 1, configured as described above, will be explained. Here, as mentioned earlier, we will explain using the example of carbon dioxide being a gas at room temperature and a pressure of 3 MPaG, with a rated release flow rate of 200 t / h during emergency release and a release pipe configuration of 4 x 200A pipes.

[0036] When performing discharge, the discharge pipe should be selected and used so that the flow velocity inside the discharge pipe is in the range of Mach 0.4 to 0.85, relative to the fluctuation range of the discharge flow rate. Specifically, the main valve 15 is first opened to introduce the gas from pipeline 3 into the main pipe 13 of the discharge line. To discharge at the rated discharge flow rate, the four discharge valves 9 are opened sequentially. Automatic operation of the valves by electric motor or pneumatic pressure is preferable, but manual operation is also acceptable. When performing planned discharge at approximately one-quarter of the rated discharge flow rate, only one of the four discharge valves 9 is opened. This ensures that even when the discharge flow rate is reduced to one-quarter, the gas flow velocity released from the discharge pipe 5 remains almost the same as during rated discharge. [Examples]

[0037] Next, we will explain the effects of the present invention as confirmed by computational fluid dynamics analysis. Figure 6 shows the region where the concentration of carbon dioxide emitted from the emission tube exceeds 5000 ppm. Figure 6(a) shows a case where carbon dioxide is continuously released at a flow rate of 200 t / h from a conventional diffusion pipe 21 of a diffusion tower, with a diameter of 400A and a height of 30m. The outflow velocity was Mach 0.81. At this time, a crosswind of 1 m / s was assumed to be blowing from the left side of the radiation pipe 21 in the diagram. The numerical fluid analysis was performed in three dimensions, and the region 19 (CO2 plume) where the atmospheric carbon dioxide concentration exceeds 5000 ppm is illustrated on a two-dimensional cross-section. As is clear from this diagram, the carbon dioxide concentration at the ground surface does not exceed 5000 ppm, and even if there were people nearby, there would be no safety concerns.

[0038] Figure 6(b) shows the results for the same case as in Figure 6(a), using the same vent pipe 21 and wind speed, but with a vent flow rate of 50 t / h. The outflow velocity was Mach number 0.20. It can be seen that the upward inertial force is insufficient, and the CO2 plume is sinking towards the ground surface due to gravity caused by the density difference with the atmosphere. As a result, the carbon dioxide concentration at the ground surface exceeds 5000 ppm, which raises concerns about potential harm to humans and animals in a real-world setting.

[0039] Figure 6(c) shows a scenario where the same emission flow rate is discharged from a single 200A diameter emission pipe, assuming the emission pipe 5 of an embodiment of the present invention. The discharge velocity is Mach number 0.81, and the upward-blowing CO2 plume does not sink to the ground surface.

[0040] From the comparative calculations above, it was confirmed that a multi-pipe configuration, in this example consisting of four 200A pipes, is preferable to the conventional single 400A pipe configuration, and that by switching the number of pipes used according to the discharge flow rate, safe discharge can be carried out over a wide range of flow rates.

[0041] Furthermore, even in the case of Figure 6(b), it is possible to suppress the accumulation of CO2 plumes on the ground surface by further increasing the height of the dissipation pipes 5. In contrast, in the case of Figure 6(c), it is not necessary to increase the height of the dissipation pipes 5, as only the number of small-diameter dissipation pipes 5 needs to be increased, so it is clear that construction costs can be reduced.

[0042] As described above, according to the present invention, even when the emission flow rate is less than the rated emission flow rate, the emission gas flow velocity at the outlet of the emission pipe can be maintained at a constant level or higher, and the effect of entrainment of ambient air and diffusion due to crosswinds can be maximized, so that the deposition of carbon dioxide gas, which has a specific gravity greater than air, onto the ground surface can be reduced compared to a conventional emission tower of the same height. This allows for a lower height for the radiation pipes, which not only reduces construction costs but also avoids spoiling the landscape of the area where the pipes are installed and reduces the sense of intimidation they may cause to surrounding residents.

[0043] Although the above explanation uses gaseous carbon dioxide as an example, the present invention is not limited to this and can also be applied to diffusion towers installed in pipelines transporting liquid / supercritical carbon dioxide. [Explanation of Symbols]

[0044] 1. Gas emission tower 3 pipelines 5. Discharge pipe 7. Emission Line 9. Dispersion valve 11 Control device 13 Main pipe 15 Former Lawyer 17 Flow meter 19. CO2 plume region (concentration of 5000 ppm or higher) 21. Discharge pipe (conventional example)

Claims

1. A carbon dioxide transport pipeline is installed at the inlet, outlet, or in the middle of the pipeline to release carbon dioxide from the pipeline, It comprises two or more parallel-erected discharge pipes, a discharge line connecting the pipeline and each discharge pipe, and a discharge valve provided in each discharge line. A carbon dioxide evaporation tower characterized by having a configuration of evaporation tube diameters and numbers such that the flow velocity inside the evaporation tubes is within the range of Mach 0.4 to 0.85, corresponding to the fluctuation range of the evaporation flow rate.

2. The carbon dioxide emission tower according to claim 1, further comprising a control device that adjusts the opening and closing state and degree of opening of each emission valve according to the emission gas flow rate.

3. The carbon dioxide emission tower according to claim 1 or 2, characterized in that the top outlets of each emission tube are inclined in different directions from each other.

4. The carbon dioxide emission tower according to claim 1 or 2, characterized in that the top outlet of each emission tube has an elliptical or star-shaped cross-section.

5. The carbon dioxide emission tower according to claim 1 or 2, characterized in that the top outlet of each emission tube is shaped to smoothly widen towards the tip.

6. A method for emitting carbon dioxide in a carbon dioxide emission tower according to any one of claims 1 to 5, characterized in that the emission pipe to be used is selected and emission is performed such that the flow velocity in the emission pipe is in the range of Mach 0.4 to 0.85 with respect to the fluctuation range of the emission flow rate.

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