Carbon dioxide emission reduction plant and carbon dioxide emission reduction method

Abstract

[Problem] To provide a carbon dioxide emission reduction plant and a carbon dioxide emission reduction method capable of reducing the emission of carbon dioxide (CO2) without using fossil fuel and contributing to the suppression of global warming. [Solution] A carbon dioxide emission reduction plant 1 according to the present invention comprises: a sunlight condensing apparatus that takes in sunlight and condenses the taken-in sunlight by means of a parabolic reflection device 2; and a reaction apparatus 10 to which the light condensed by the condensing apparatus is emitted and which is heated by the emitted light, to cause a chemical reaction to occur between carbon dioxide and methane. As a result, by carrying out the reaction by using solar energy which is renewable energy, the carbon dioxide emission reduction plant reduces the emission of carbon dioxide without consuming fossil fuel, and contributes to the suppression of global warming.

Description

Carbon dioxide emission reduction plant and carbon dioxide emission reduction method

[0001] The present invention relates to a carbon dioxide emission reduction plant and a carbon dioxide emission reduction method.

[0002] Carbon dioxide is a causative substance of global warming, and various technologies for reducing its emissions have been proposed conventionally. For example, a technology using the oxidative dry reforming reaction (dry reforming) of methane is disclosed in Patent Document 1. Patent Document 1 describes that, in a method of reacting methane and carbon dioxide to synthesize hydrogen and carbon monoxide, a catalyst in which a carrier supports a mixture of nickel and one or more rare earth metal oxides and a mixture of one or more platinum group metals is used. And it is described that a smooth reaction progress cannot be ensured unless the reaction temperature is in the range of 400°C to 1000°C (preferably about 700°C).

[0003] Japanese Patent Laid-Open No. 5-270802

[0004] However, Patent Document 1 does not describe anything about the type of thermal energy. If thermal energy using fossil fuel as a raw material is used, there is a problem that it does not contribute to the suppression of global warming and may even reverse in some cases.

[0005] Therefore, an object of the present invention is to provide a carbon dioxide emission reduction plant and a carbon dioxide emission reduction method that contribute to the suppression of global warming.

[0006] The present invention has been made in view of the above problems, and includes a solar light collecting device that takes in sunlight and condenses the taken-in sunlight, and a reaction device that is irradiated with the light condensed by the solar light collecting device and causes a chemical reaction between carbon dioxide and methane by being heated by the irradiated light. It is a carbon dioxide emission reduction plant characterized by the above.

[0007] Another aspect of the present invention is a method for reducing carbon dioxide emissions, characterized by comprising the steps of: capturing sunlight using a solar light concentrator and concentrating the captured sunlight; and irradiating a reaction vessel with the light concentrated by the solar light concentrator, thereby heating the reaction vessel with the irradiated light and causing a chemical reaction between carbon dioxide and methane in the reaction vessel.

[0008] According to the present invention, since the reactor can be heated using solar energy, which is a renewable energy source, carbon dioxide emissions can be reduced without using fossil fuels, thus contributing to the mitigation of global warming.

[0009] The drawings illustrate specific embodiments of the present invention as disclosed herein, including not only essential components of the invention but also selective and preferred embodiments. This embodiment is shown as a schematic diagram of a carbon dioxide emission reduction plant. This embodiment is shown as a schematic diagram of a reactor. This embodiment is shown as a control block diagram of a carbon dioxide emission reduction plant. This embodiment shows a schematic diagram in which (a) the reaction tube is in its initial position and (b) the reaction tube has moved to the front side. This embodiment is shown as a diagram illustrating the injection of gas into the reaction tube and the discharge of gas from the reaction tube.

[0010] The embodiments will be described in detail below with reference to the attached drawings. In these embodiments, publicly known technologies will not be described. Furthermore, the devices and methods described are illustrative examples for realizing the technical idea of ​​the invention, and the technical idea of ​​the present invention is not limited to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims. In particular, it should be noted that the drawings are schematic and may differ from reality.

[0011] (Embodiment) The integrated plant is configured to perform the first chemical equation CO2 + CH4 → 2CO + 2H2, then the second chemical equation CO + 2H2 → CH3OH, and then the third chemical equation CH3OH + CO → CH3COOH. The carbon dioxide emission reduction plant according to the embodiment of the present invention performs the first chemical equation described above. This will be explained below.

[0012] As shown in Figure 1, the carbon dioxide emission reduction plant 1 includes a parabolic reflector 2, which is a solar light concentrator that takes in sunlight and concentrates the captured sunlight; a reaction device 10 that is irradiated with the light concentrated by the parabolic reflector 2 and heated by the irradiated light to cause a chemical reaction between carbon dioxide (CO2) and methane (CH4); and an automatic solar tracking device 20 that automatically tracks the parabolic reflector 2 to face the sun.

[0013] The parabolic reflector 2 comprises a parabolic reflector 3 and a primary reflector 4. The parabolic reflector 3 has a side wall 3a whose inner surface is made of a parabolic surface, and the widened tip of this side wall 3a forms a light entry port 3b. The parabolic reflector 3 reflects sunlight incident from the light entry port 3b along the central axis of the side wall 3a toward the focal position. A light transmission port (not shown) is provided at the rear end of the side wall 3a. The light entry port 3b of the parabolic reflector 3 is circular in shape.

[0014] The parabolic reflector 3 is supported by multiple legs 5. Each leg 5 is equipped with three hydraulic cylinders 23 of the automatic solar tracking device 20. By varying the effective length of each leg 5 using each hydraulic cylinder 23, the orientation of the parabolic reflector 3 can be freely changed.

[0015] One end of a fixing cable 6 is fixed to the side wall 3a of the parabolic reflector 3. The other end of each fixing cable 6 is fixed to the spring fixing part 13 described below. As a result, the parabolic reflector 3 and the spring fixing part 13 are connected via a fixed distance. The distance between the parabolic reflector 3 and the spring fixing part 13 remains unchanged even when the reaction tube 12 moves, as described below.

[0016] The primary reflector 4 is fixed to the parabolic reflector 3 via a support rod 7. The primary reflector 4 is positioned on the central axis of the parabolic reflector 3 and in a position where almost all of the reflected light from the parabolic reflector 3 can be incident on it. The primary reflector 4 has, for example, a semi-circular reflective surface, and the incident light from the parabolic reflector 3 is reflected on this surface. The reflected light reflected by the reflective surface passes through the light transmission opening (not shown) of the parabolic reflector 3 and is irradiated as focused light onto the reaction apparatus 10 described below.

[0017] The parabolic reflector 2 is moved by the automatic solar tracking device 20 as described below, but the fixed cable 6 and the reaction device 10 also move together. As a result, even if the radiation reflector 2 is moved, the focal position of the focused light emitted from the primary reflector 4 remains the same relative to the reaction device 10 as described below.

[0018] As shown in Figure 2, the reaction apparatus 10 includes five tanks 11a to 11e, a reaction tube 12, a piston 14 fixed to a spring fixing part 13, and a spring 15 which is a biasing means. The five tanks 11a to 11e are a carbon dioxide (CO2) supply tank 11a, a methane (CH4) supply tank 11b, a water (H2O) supply tank 11c, a carbon monoxide (CO) recovery tank 11e, and a hydrogen (H2) recovery tank 11d.

[0019] The reaction tube 12 is supplied with carbon dioxide (CO2), methane (CH4), and water (H2O) from a carbon dioxide (CO2) supply tank 11a, a methane (CH4) supply tank 11b, and a water (H2O) supply tank 11c, via the tip surface of the piston 14. The water (H2O) is supplied to prevent caulking, etc.

[0020] The reaction tube 12 has a main section 12a with an open rear end, a plurality of first leaf-like vein sections 12b branching off to one side from the main section 12a, and second leaf-like vein sections 12c branching off to the other side from the main section 12a. The tips of each first leaf-like vein section 12b and each second leaf-like vein section 12c extend close to the front end of the reaction tube 12 and close off near the front end. The front end of the reaction tube 12 is located closest to the parabolic reflector 3, and the rear end of the reaction tube 12 is located furthest from the parabolic reflector 3.

[0021] A hydrogen separation membrane (not shown) is provided between adjacent first foliate vein portions 12b and second foliate vein portions 12c (in this embodiment, the first foliate vein portion 12b). A carbon monoxide separation membrane (not shown) is provided between adjacent first foliate vein portions 12b and the other second foliate vein portion 12c (in this embodiment, the second foliate vein portion 12c).

[0022] The inside of the hydrogen separation membrane (not shown) is connected to the hydrogen (H2) recovery tank 11d. The inside of the carbon monoxide separation membrane is connected to the carbon monoxide (CO) recovery tank 11e. The piston 14 is inserted into the main body 12a from the rear end of the reaction tube 12 and is slidably positioned within the main body 12a. In other words, the insertion position of the piston 14 can be varied. The volume of the reaction space inside the reaction tube 12 is varied depending on the insertion position of the piston 14.

[0023] In other words, the first foliate vein portion 12b and the second foliate vein portion 12c, which are blocked by the piston 14, cease to be reaction spaces because carbon dioxide (CO2), methane (CH4), and water (H2O) are not supplied to them. Only the main trunk 12a, the first foliate vein portion 12b, and the second foliate vein portion 12c, which are not blocked by the piston 14, become reaction spaces. As a result, the volume of the reaction space in the reaction tube 12 decreases as the insertion position of the piston 14 increases, and the volume of the reaction space in the reaction tube 12 increases as the insertion position of the piston 14 decreases.

[0024] The spring 15 biases the reaction tube 12 in a direction away from the parabolic reflector 3. In other words, the spring 15 biases the reaction tube 12 in a direction that reduces the volume of the reaction space within the reaction tube 12 (towards the initial position of the reaction tube 12). The initial position of the reaction tube 12 is the position where the tip of the main section 12a abuts the tip of the piston 14, as shown in Figure 4(a). At the initial position, the volume of the reaction space within the reaction tube 12 is zero. When the supply valve 27 is opened relative to the reaction tube 12 at the initial position, and any gas is pressurized and flows in from the tip of the piston 14, the reaction tube 12 moves in the direction of arrow A in Figure 4(b) against the spring force of the spring 15, and a reaction space of minimum volume can be formed. That is, only a part of the main section 12a, the first lamellar vein section 12b, and the second lamellar vein section 12c on the front end side of the reaction tube 12 becomes the reaction space. At the location of the minimum volume of reaction space, the front end surface of the reaction tube 12 is set to the focal point of the focused light from the primary reflector 4, and the front end surface of the reaction tube 12 receives concentrated thermal energy from sunlight.

[0025] As the internal pressure of the reaction tube 12 increases due to the rise in internal temperature, it moves in a direction closer to the parabolic reflector 3 against the spring force of the spring 15 (in the direction of arrow A in Figure 4(b)), and the amount of movement is proportional to the pressure. In other words, as the internal pressure of the reaction tube 12 increases, the volume of the reaction space inside the reaction tube 12 increases proportionally, and the position on the rear end side of the reaction tube 12, rather than the front end surface, becomes the focal point of the focused light from the primary reflector 4, causing the reaction tube 12 to receive the thermal energy of sunlight in a dispersed manner. In this way, the volume of the reaction space inside the reaction tube 12 and the region of the reaction tube 12 that receives thermal energy are adjusted.

[0026] The spring force (spring constant) of spring 15 is set so that when the reaction tube 12 receives solar energy exceeding the minimum temperature at which a chemical reaction occurs (for example, 750°C) (the internal pressure state corresponding to a temperature exceeding 750°C), the reaction tube 12 moves toward the parabolic reflector 3 (in the direction of arrow A in Figure 4(b)). The purpose of moving the reaction tube 12 in this way is to disperse the solar energy more because the part of the reaction tube 12 that receives solar energy on its front becomes too hot, and also because the temperature inside the reaction tube 12 becomes too hot, or to increase the reaction space and use the excess energy more efficiently.

[0027] The automatic solar tracking device 20 includes a solar position acquisition means 21 that acquires the current position of the sun, and a parabolic reflector 3 driving means 22 that drives the light entry port 3b of the parabolic reflector 3 to a position facing the sun based on the data acquired by the solar position acquisition means 21.

[0028] The solar position acquisition means 21 can be any of the following: For example, it has a detection unit that detects the position of the sun by receiving sunlight, and based on this detection data, it acquires the position of the sun with the position of the parabolic reflector 2 as the reference. Alternatively, it can store solar position data acquired by a GPS (Global Positioning System) sensor, the direction on the celestial sphere that the device is facing, and calculations of celestial motion, along with the date and time data, and then acquire solar position data by outputting this stored data based on the actual date and time data. The data acquired by the solar position acquisition means 21 is output to the control unit 25 described below.

[0029] The driving means 22 has hydraulic cylinders 23 attached to each leg 5 that supports the parabolic reflector 3. Each of these hydraulic cylinders 23 is driven and controlled by the control unit 25 described below to position the light inlet 3b of the parabolic reflector 3 directly facing the sun. In other words, it is driven and controlled so that sunlight enters the light inlet 3b parallel to the central axis of the side wall 3a of the parabolic reflector 3.

[0030] Next, the control block diagram of the carbon dioxide emission reduction plant 1 will be described. As shown in Figure 3, the control unit 25 has an NPU (Neural Network Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory), etc. The NPU is, for example, an AI processor (Artificial Intelligence Processor). The control unit 25 executes the control program stored in the RAM, ROM, etc., using the NPU.

[0031] The control unit 25 is responsible for the overall control of the carbon dioxide emission reduction plant 1. Specifically, the control unit 25 controls the driving of the hydraulic cylinder 23 of the drive means 22 based on the data acquired by the solar position acquisition means 21.

[0032] The control unit 25 controls the heat source calculation unit 26. The heat source calculation unit 26 calculates the focal point, which is the position where the irradiated light, the heat source for heating the reaction tube 12, is collected. The focal point is calculated in conjunction with the sun's position data from the automatic solar tracking device 20. The calculation results are output to the control unit 25.

[0033] The control unit 25 controls the opening and closing of the supply valve 27 and the recovery valve 28, respectively. The supply valve 27 is for supplying the gases in the carbon dioxide (CO2) supply tank 11a and the methane (CH4) supply tank 11b to the reactor 10. The carbon dioxide (CO2) and methane (CH4) are supplied to the reactor 10 under pressurization, as shown in the direction of arrow C in Figure 5.

[0034] The recovery valve 28 is for recovering carbon monoxide (CO) and hydrogen (H2) from the reaction apparatus 10 into the respective recovery tanks 11e and 11d. The carbon monoxide (CO) and hydrogen (H2) are recovered into the respective recovery tanks 11e and 11d by reducing the pressure, as shown in the direction of arrow D in Figure 5. Note that the supply valve 27 and recovery valve 28 are omitted in Figures 2 and 5.

[0035] Next, the operation of the carbon dioxide emission reduction plant 1 will be explained. Before dawn, at least carbon dioxide (CO2) and methane (CH4) are introduced into the reaction tube 12 from the tip of the piston 14 under pressure, forming a reaction space of the minimum volume in the reaction tube 12.

[0036] When dawn breaks, the automatic solar tracking device 20 activates, and the primary reflector 4 of the parabolic reflector 3 is controlled to always face the sun as it moves. The parabolic reflector 2 constantly captures the maximum possible amount of sunlight, and the focused light from the captured sunlight is irradiated onto the reaction tube 12 of the reaction device 10. As a result, the inside of the reaction tube 12 is heated by solar heat, the internal pressure inside the reaction tube 12 increases, and the internal temperature rises proportionally. When the internal temperature exceeds, for example, 750°C, the reaction tube 12 moves in a direction closer to the parabolic reflector 3 (in the direction of arrow A in Figure 4(b)) against the spring force of the spring 15. As a result, the insertion depth of the piston 14 into the reaction tube 12 becomes shallower, the reaction space inside the reaction tube 12 expands, and the thermal energy of the sunlight is dispersed and irradiated over a wide area of ​​the reaction tube 12.

[0037] Furthermore, when the intensity of sunlight decreases and the amount of thermal energy decreases, the reaction tube 12 moves away from the parabolic reflector 3 due to the spring force of the spring 15 (in the direction of arrow B in Figure 4(b)). As a result, the insertion depth of the piston 14 into the reaction tube 12 increases, narrowing the reaction space within the reaction tube 12, and the thermal energy of sunlight is dispersed and irradiated over a narrow area of ​​the reaction tube 12. In this way, the size of the reaction space inside the reaction tube 12 is changed to the optimal size according to the current thermal energy of sunlight, and a chemical reaction that makes the most of the current thermal energy of sunlight takes place inside the reaction tube 12.

[0038] As explained above, the carbon dioxide emission reduction plant 1 comprises a parabolic reflector 2, which is a solar light concentrator that takes in sunlight and concentrates the captured sunlight, and a reaction device 10 that is irradiated with the light concentrated by the parabolic reflector 2 and heated by the irradiated light, causing a chemical reaction between carbon dioxide and methane. Furthermore, the carbon dioxide emission reduction method comprises the steps of taking in sunlight using the parabolic reflector 2, which is a solar light concentrator, and concentrating the captured sunlight, and the steps of irradiating the reaction device 10 with the light concentrated by the parabolic reflector 2 and causing a chemical reaction between carbon dioxide and methane in the reaction device 10 by heating the reaction device 10 with the irradiated light.

[0039] Therefore, in the carbon dioxide emission reduction plant 1 and carbon dioxide emission reduction method described above, the reactor 10 can be heated using solar energy, which is a renewable energy source, thus reducing carbon dioxide (CO2) emissions without using fossil fuels, and thus contributing to the mitigation of global warming. It can also contribute to the reduction of methane (CH4). In other words, in this embodiment, carbon dioxide (CO2) and methane (CH4), which are greenhouse gases, can be reduced. Furthermore, hydrogen (H2) and carbon monoxide (CO) can also be produced.

[0040] The reaction device 10 includes a reaction tube 12 into which carbon dioxide (CO₂) and methane (CH₄) are supplied and which is located in a position close to a parabolic reflector 2 that is a solar concentrator on the front end side, a piston 14 that is inserted into the reaction tube 12 from the rear end side and varies the volume of the reaction space in the reaction tube 12 according to the insertion position, and a spring 15 that is a biasing means for biasing the reaction tube 12 toward a position spaced apart from the parabolic reflector 2. The reaction tube 12 moves in the direction approaching the parabolic reflector 2 against the spring force of the spring 15 according to the magnitude of the pressure in the reaction tube 12, and the volume of the reaction space in the reaction tube 12 and the thermal energy applied to the reaction tube 12 are adjusted.

[0041] Therefore, a chemical reaction can be efficiently performed according to the magnitude of the solar thermal energy irradiated on the reaction tube 12.

[0042] When receiving solar energy exceeding the minimum temperature at which a chemical reaction occurs in the reaction tube 12, the reaction tube 12 moves in a direction approaching the parabolic reflector 2 against the spring force of the spring 15, and the front end position of the reaction tube 12 is located in front of the focal position of the light irradiated from the parabolic reflector 2.

[0043] Therefore, in order to adjust the reaction space according to the pressure in the reaction tube 12, a chemical reaction can be efficiently performed according to the magnitude of the solar thermal energy irradiated on the reaction tube 12.

[0044] The reaction tube 12 has a main trunk portion 12a into which the piston 14 is inserted, and a plurality of first leaf vein portions 12b and second leaf vein portions 12c branched in a direction different from the main trunk portion 12a. The tips of each of the first leaf vein portions 12b and each of the second leaf vein portions 12c extend to the front end side of the reaction device 10. The inner surface of the reaction tube 12 is plated with a nickel alloy (catalyst).

[0045] Therefore, since the piston 14 closes and opens the reaction space in the reaction tube 12 according to the pressure in the reaction tube 12, the reaction space of the reaction tube 12 is automatically adjusted.

[0046] A hydrogen separation membrane (not shown) is provided between any adjacent ones of the first leaf-shaped vein portion 12b and the second leaf-shaped vein portion 12c, and a carbon monoxide separation membrane (not shown) is provided between the other adjacent ones of the first leaf-shaped vein portion 12b and the second leaf-shaped vein portion 12c.

[0047] Therefore, since hydrogen (H₂) and carbon monoxide (CO) can be individually recovered from the reaction apparatus 10, there is no need to separately separate them for each gas type, and the plant configuration is simplified.

[0048] In this embodiment, the solar concentrator includes a parabolic reflector 3 having an inlet arranged facing the sun, and a primary reflector 4 that reflects the reflected light from the parabolic reflector 3 and irradiates it as converging light.

[0049] Therefore, the solar concentrator has a simple configuration by using the parabolic reflector 3 and the primary reflector 4, and can efficiently collect the thermal energy of sunlight even with a small installation space. Also, since the reaction apparatus 10 can be arranged in the rear space behind the rear end of the parabolic reflector 3, the installation space for the reaction apparatus 10 can be surely secured, and the design freedom of the reaction apparatus 1 is also increased,

[0050] The carbon dioxide emission reduction plant 1 includes a solar automatic tracking device 20, and the solar automatic tracking device 20 has a solar position acquisition means 21 for acquiring the current position of the sun, and a driving means 22 for driving the light inlet 3b of the parabolic reflector 2, which is a solar concentrator, to a position directly facing the sun based on the acquisition data of the solar position acquisition means 21.

[0051] Therefore, a chemical reaction can be expected in an optimal situation at all times while the sun is out without the operator of the carbon dioxide emission reduction plant 1 having to operate.

[0052] (Modification of the embodiment) In the above embodiment, the solar concentrator is constituted by the parabolic reflector 2, but any configuration that can take in sunlight and concentrate the taken-in sunlight may be used.

[0053] In the above embodiment, the biasing means is composed of a spring 15, but it may be composed of something other than a spring, as long as it is a means that biases the reaction tube 12 in a direction away from the parabolic reflector 3.

[0054] In the above embodiment, the reaction tube 12 is composed of a main trunk 12a, a first foliate vein portion 12b, and a second foliate vein portion 12c, but any configuration that can change the reaction space in accordance with the thermal energy from the sun is acceptable.

[0055] In the above embodiment, a hydrogen separation membrane (not shown) is provided between adjacent first foliate veins 12b, and a carbon monoxide separation membrane (not shown) is provided between adjacent second foliate veins 12c, but the reverse arrangement is also possible. That is, a carbon monoxide separation membrane (not shown) may be provided between adjacent first foliate veins 12b, and a hydrogen separation membrane (not shown) may be provided between adjacent second foliate veins 12c. In the above embodiment, a water (H2O) tank 11c is provided, and water (H2O) is supplied into the reaction tube 12 together with carbon dioxide (CO2) and methane (CH4), but liquid (room temperature) H2O may be supplied from a tank branched off from a supply tube extending from a carbon dioxide (CO2) tank 11a or a methane (CH4) tank 11b. In the latter case, it is preferable to take measures such as introducing water (H2O) into the reaction tube 12 in a mist form at the same time as introducing carbon dioxide (CO2) or methane (CH4) into the reaction tube 12, so that water (H2O) does not flow back into the carbon dioxide (CO2) tank 11a or the methane (CH4) tank 11b.

[0056] (Measures against coking) Next, we will explain how to suppress coking. (1) It is good to use a promoter together with the catalyst. The catalyst promotes the oxidative dry reforming reaction of methane and also contributes to lowering the reaction temperature. However, catalysts, for example, when used with a nickel (Ni) base, are prone to coking. Therefore, a promoter is also used. The promoter is a substance that ensures the catalyst can properly perform its role as a catalyst. In other words, the inside of the reaction tube 12 is plated with a nickel alloy, but as the reaction progresses, soot (carbon) adheres to its surface. In this reaction, CO and H2 are not directly produced from CO2 and CH4, but carbon (C) is produced as an intermediate product. It is thought that this carbon (C) does not react to become carbon monoxide (CO) until the end, but continues to adhere to the surface of the nickel alloy, causing coking. This coking can be prevented by the promoter. Specifically, in the above embodiment, magnesium oxide (MgO) is used as a promoter with a nickel (Ni) based catalyst. This reduces coking and is expected to improve the long-term stability of the catalyst. In addition, an oxide support material is used. Examples of oxide support materials include ceria, alumina, cerium (Ce), lanthanum (La), or alkali metals. Precious metals (e.g., rhodium (Rh), ruthenium (Ru), platinum (Pt), palladium (Pd)) are used as catalysts. This improves caulking resistance, but it is expensive.

[0057] (2) Ensure proper temperature control. If the temperature is too high, coking may occur, and if the temperature is too low, the CH4 conversion efficiency will decrease. Temperature control depends on the catalyst used. When using a nickel (Ni)-based catalyst as in this embodiment, considering cost-effectiveness, it is assumed that a catalyst prepared by adding alkali metals or precious metals to nickel (Ni) will be used. When magnesium (Mg), potassium (K), zirconium (Zr), titanium (Ti), cerium (Ce), etc. are added to improve coking resistance, stable operation is possible at 700°C to 850°C. The optimal temperature range is 720°C to 760°C. Also, when precious metals (ruthenium (Ru), rhodium (Rh)) are added to improve coking resistance, the reaction can proceed at around 600°C to 750°C, allowing for stable operation. The optimal temperature range is 680°C to 720°C.

[0058] (3) Maintain a balanced ratio of methane (CH4) to carbon dioxide (CO2). If there is an excess of methane (CH4), its decomposition (methane cracking) will progress, increasing the likelihood of coking. A balanced ratio of methane (CH4) to carbon dioxide (CO2) minimizes the formation of carbon (C). Based on the reaction equation, a balanced ratio of methane (CH4) to carbon dioxide (CO2) is basically carbon dioxide (CO2):methane (CH4) = 1:1 (molar ratio), and it is preferable to use a slightly higher amount of carbon dioxide (CO2) depending on the properties of the catalyst and operating conditions. This is because carbon dioxide (CO2) promotes the oxidation of carbon (C), preventing solid carbon (soot) from accumulating on the inner surface of the reaction tube 12, and thus suppressing coking.

[0059] (4) Add steam (H2O). In a combination of dry and steam reforming processes, adding a small amount of steam (H2O) promotes the vaporization reaction of carbon (C) and converts it into carbon monoxide (CO₂) and hydrogen (H2) (C + H2O → CO + H2), thereby suppressing the formation of carbon (C).

[0060] (5) The reaction pressure should be close to atmospheric pressure. Operating at a pressure close to atmospheric pressure reduces coking. In other words, coking (deposit of carbon on the catalyst surface) is affected by multiple factors such as temperature, pressure, and the nature of the reaction. At high pressure, the reaction rate in the carbon production pathway increases, so carbon production becomes more pronounced. However, by operating at a pressure close to atmospheric pressure (i.e., at a relatively low pressure without intentionally operating at high pressure), the rate of carbon (C) production is suppressed, and therefore coking is reduced.

[0061] (6) Reduce the residence time (the time the catalyst is exposed to the gas). Reducing the residence time can suppress coking.

[0062] (7) The reactor regeneration cycle should be performed periodically. This is preferable to extend the life of the catalyst and maintain process efficiency. As for the accumulated carbon (C), if necessary, the reactor should be opened periodically at night or on cloudy or rainy days when sufficient solar energy is not available, and the accumulated carbon (C) should be physically removed by brushing or other means. Of course, if the accumulated carbon (C) can be completely removed by burning it with oxygen or steam, it is more thermally efficient, and the resulting carbon dioxide (CO2) can be reused.

[0063] Although each embodiment has been described in detail above, the invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope described in the claims.

[0064] Furthermore, the present invention may include at least the following embodiments. The embodiments may be adopted separately or in combination with each other. (1) The reaction apparatus comprises a reaction tube into which carbon dioxide and methane are supplied, with its front end positioned close to the solar concentrator; a piston inserted into the reaction tube from the rear end, which varies the volume of the reaction space within the reaction tube depending on the insertion position; and a biasing means that biases the reaction tube toward a position away from the solar concentrator, wherein the reaction tube moves toward the solar concentrator against the biasing means in accordance with the magnitude of the pressure inside the reaction tube, and the volume of the reaction space within the reaction tube and the thermal energy to the reaction tube are adjusted. (2) When the reaction tube receives solar energy exceeding the minimum temperature at which a chemical reaction occurs, the reaction tube moves toward the solar concentrator against the biasing force of the biasing means, and the front end position of the reaction tube is positioned in front of the focal point of the light irradiated from the solar concentrator. (3) The reaction tube has a main section into which the piston is inserted, and a plurality of first and second foliate vein sections branching out from the main section in different directions, with the tips of each first and second foliate vein section extending to the front end of the reaction apparatus. (4) A hydrogen separation membrane is provided between adjacent first and second foliate vein sections, and a carbon monoxide layer separation membrane is provided between adjacent first and second foliate vein sections. (5) The solar light concentrator has a parabolic reflector with an entrance facing the sun, and a primary reflector that reflects the reflected light from the parabolic reflector and irradiates it as focused light. (6) The solar automatic tracking device comprises a solar position acquisition means for acquiring the current position of the sun, and a driving means for driving the light inlet of the solar light concentrator to a position facing the sun based on the data acquired by the solar position acquisition means.

[0065] 1 Carbon dioxide emission reduction plant 2 Parabolic reflector (sunlight concentrator) 3 Parabolic reflector 3b Light entry port 4 Primary reflector 10 Reaction apparatus 12 Reaction tube 12a Main section 12b First foliate vein section 12c Second foliate vein section 14 Piston 15 Spring (biasing means) 20 Automatic solar tracking device 21 Solar position acquisition means 22 Driving means

Claims

1. A carbon dioxide emission reduction plant characterized by comprising: a solar light concentrator that captures and concentrates sunlight; and a reaction device that is irradiated with the light concentrated by the solar light concentrator and causes a chemical reaction between carbon dioxide and methane by heating with the irradiated light.

2. The carbon dioxide emission reduction plant according to claim 1, wherein the reaction apparatus comprises a reaction tube into which carbon dioxide and methane are supplied, the front end of which is positioned close to the solar light concentrator, a piston inserted into the reaction tube from the rear end and which varies the volume of the reaction space inside the reaction tube depending on the insertion position, and a biasing means that biases the reaction tube toward a position away from the solar light concentrator, wherein the reaction tube moves toward the solar light concentrator against the biasing means in accordance with the magnitude of the pressure inside the reaction tube, and the volume of the reaction space inside the reaction tube and the thermal energy supplied to the reaction tube are adjusted.

3. The carbon dioxide emission reduction plant according to claim 2, characterized in that when the reaction tube receives solar energy exceeding the minimum temperature at which a chemical reaction occurs, the reaction tube moves in a direction toward the solar light concentrator against the biasing force of the biasing means, and the front end position of the reaction tube is located in front of the focal point of the light irradiated from the solar light concentrator.

4. The carbon dioxide emission reduction plant according to claim 2, characterized in that the reaction tube has a main section into which the piston is inserted, and a plurality of first and second foliate vein sections branching out from the main section in different directions, and the tips of each of the first and second foliate vein sections extend to the front end of the reaction apparatus.

5. The carbon dioxide emission reduction plant according to claim 4, characterized in that a hydrogen separation membrane is provided between adjacent portions of either the first foliate vein portion or the second foliate vein portion, and a carbon monoxide layer separation membrane is provided between adjacent portions of the other portion of the first foliate vein portion or the second foliate vein portion.

6. The carbon dioxide emission reduction plant according to claim 1, characterized in that the solar light concentrating device comprises a parabolic reflector with an entrance opening positioned toward the sun, and a primary reflector that reflects the reflected light from the parabolic reflector and irradiates it as focused light.

7. The carbon dioxide emission reduction plant according to claim 1, comprising an automatic solar tracking device, wherein the automatic solar tracking device comprises a solar position acquisition means for acquiring the current position of the sun, and a driving means for driving the light inlet of the solar light concentrator to a position facing the sun based on the data acquired by the solar position acquisition means.

8. A method for reducing carbon dioxide emissions, comprising the steps of: taking in sunlight using a solar light concentrator and concentrating the taken-in sunlight; and irradiating a reaction vessel with the light concentrated by the solar light concentrator, thereby heating the reaction vessel with the irradiated light and causing a chemical reaction between carbon dioxide and methane in the reaction vessel.

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