Methanation reactor and reaction method

Abstract

To provide a methanation reactor that can extend the lifespan of the catalyst. [Solution] In a methanation reactor 1 that generates methane-containing gas by contacting a raw material gas containing carbon dioxide and hydrogen with a catalyst, the reactor comprises a container 2, a tubular catalyst layer 3 installed inside the container 2 and filled with a catalyst 4, a heat transfer medium 7 that flows inside the container 2 and cools the catalyst layer 3, and at least two heaters 5a to 5e provided in the longitudinal direction of the catalyst layer 3, surrounding the catalyst layer 3 and capable of independently heating the catalyst layer 3.

Description

Technical Field

[0001] The present invention relates to a methanation reactor and a methanation reaction method.

Background Art

[0002] The methanation of CO₂, in which hydrogen and carbon dioxide are brought into contact with a catalyst to produce methane, was reported by Sabatier in the early 20th century. The reaction formula for the methanation of CO₂ is as follows. CO₂+4H₂→CH₄+2H₂O(ΔH=-165kJ / mol(298K)) (1)

[0003] In recent years, the methanation of CO₂ has attracted attention. This is because the methanation of CO₂ enables reduction of CO₂, which is a greenhouse gas, allows hydrogen produced from surplus power of renewable energy such as solar power generation and wind power generation to be stored in the form of fuel gas, and enables the produced methane to be used as city gas.

[0004] As a reactor for carrying out the methanation of CO₂, Patent Document 1 discloses a methanation reactor in which a tubular catalyst layer is filled with a catalyst, a raw material gas containing hydrogen and carbon dioxide is caused to flow through the catalyst layer, and the raw material gas is brought into contact with the catalyst to synthesize methane. As the catalyst, for example, a catalyst in which metal particles such as nickel are supported on a carrier such as zirconia is used. The catalyst has a role of lowering the activation energy of the reaction and allowing the synthesis of methane to proceed smoothly.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0006] The methanation of CO2, represented by reaction equation 1, is an exothermic reaction. As CO2 methanation proceeds, a rapid temperature increase occurs in the longitudinal direction of the catalyst layer or upstream in the direction of gas flow, and a problem arises in that thermal degradation of the catalyst progresses, especially in the high-temperature region. This is because sintering of the supported metal, such as nickel, progresses in the high-temperature region, reducing the specific surface area of ​​the supported metal and decreasing the activity of the catalyst.

[0007] Catalysts are generally expensive because they often use expensive elements and require complex manufacturing processes. Extending the lifespan of the catalyst is necessary for the practical application of methanation reactors.

[0008] This invention has been made in view of the above problems, and aims to provide a methanation reactor and a methanation reaction method that can extend the lifespan of the catalyst. [Means for solving the problem]

[0009] To solve the above problems, one aspect of the present invention provides a methanation reactor for producing a methane-containing gas by contacting a raw material gas containing carbon dioxide and hydrogen with a catalyst, comprising: a container; a tubular catalyst layer installed inside the container and filled with a catalyst; a heat transfer medium flowing inside the container and cooling the catalyst layer; and at least two heaters provided in the longitudinal direction of the catalyst layer, surrounding the catalyst layer and capable of independently heating the catalyst layer.

[0010] Another aspect of the present invention is a methanation reaction method for producing a methane-containing gas by contacting a raw material gas containing carbon dioxide and hydrogen with a catalyst, wherein a tubular catalyst layer, which is placed in a container and filled with a catalyst, is cooled by a heat transfer medium flowing through the container, and the catalyst layer is independently heated by at least two heaters provided in the longitudinal direction of the catalyst layer and surrounding the catalyst layer. [Effects of the Invention]

[0011] According to the present invention, the heater can heat only the portion of the catalyst layer that requires initial thermal compensation (thermal compensation to ignite the methanation reaction). Since the catalyst layer is cooled overall by the heat transfer medium, the peak temperature of the catalyst layer and the temperature downstream of the peak temperature can be lowered. Therefore, thermal degradation of the catalyst can be suppressed, and the lifespan of the catalyst can be extended. [Brief explanation of the drawing]

[0012] [Figure 1] This is a longitudinal cross-sectional view of an example of a methanation reactor according to an embodiment of the present invention. [Figure 2] This graph shows the relationship between the distance from the inlet end of the catalyst layer, the temperature of the catalyst layer, and the gas composition. [Figure 3] This figure shows the change in temperature distribution of the catalyst layer. [Figure 4] This shows the temperature distribution of the catalyst layer when 10 or more heaters are placed along the longitudinal direction of the catalyst layer. [Modes for carrying out the invention]

[0013] Hereinafter, the methanation reactor and reaction method according to embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the methanation reactor and reaction method of the present invention can be embodied in various forms and are not limited to the embodiments described herein. These embodiments are provided with the intention that those skilled in the art will be able to fully understand the invention by making full disclosures in the specification. (Methanation reactor)

[0014] Figure 1 shows a longitudinal cross-sectional view of an example of a methanation reactor 1 (hereinafter simply referred to as reactor 1) according to an embodiment of the present invention. Reactor 1 is supplied with a raw material gas containing carbon dioxide and hydrogen adjusted to a molar ratio of 1:4.

[0015] Reactor 1 includes a vessel 2 and a plurality of tubular catalyst layers 3 arranged in parallel inside the vessel 2. A raw material gas is supplied from an inlet port 2a to a buffer region at the upper part of the vessel 2, and then flows downward through the plurality of tubular catalyst layers 3.

[0016] Catalyst 4 functions to lower the activation energy of the methanation reaction and allow the CO₂ methanation to proceed smoothly. The catalyst 4 is formed by supporting metal particles such as Ni, Co, Fe, Cu, Ru, and Rh on an oxide carrier such as zirconia, magnesia, alumina, silica, zeolite, or calcium phosphate. The shape of the catalyst 4 is not particularly limited, and may be in the form of powder, pellets, or cylinders. The structure of the catalyst 4 is also not particularly limited, and may be a porous structure or a honeycomb structure.

[0017] Around the catalyst layer 3, at least two heaters 5a to 5e surrounding the catalyst layer 3 are provided along the longitudinal direction of the catalyst layer 3. The heaters 5a to 5e are, for example, band heaters (cylindrical heaters), and have a structure in which a heating element is covered with an insulator. The heaters 5a to 5e can heat the catalyst layer 3 independently, and heat only the portion of the catalyst layer 3 that requires initial thermal compensation (thermal compensation for initiating the methanation reaction).

[0018] The heaters 5a to 5e heat the catalyst layer 3 to, for example, 150°C to 350°C, preferably 275°C to 325°C. At a temperature lower than 150°C, it is difficult to initiate the methanation reaction. At a temperature higher than 350°C, even if the catalyst layer 3 is cooled by a heat medium 7 described later, it becomes difficult to lower the peak temperature of the catalyst layer 3 and the temperature on the downstream side of the peak temperature position.

[0019] The number of the heaters 5a to 5e is preferably at least 3, more preferably at least 5. When the number of the heaters 5a to 5e is large, the portion of the catalyst layer 3 heated by each of the heaters 5a to 5e can be reduced, and the catalyst layer 3 can be efficiently cooled by the heat medium 7.

[0020] When the catalyst layer 3 is heated to a temperature equal to or higher than the ignition temperature of the methanation reaction by the respective heaters 5a to 5e, the raw material gas comes into contact with the catalyst 4, whereby the methanation of CO2 represented by the reaction formula (1) proceeds. CO2+4H2→CH4+2H2O(ΔH=-165kJ / mol(298K)) (1)

[0021] As shown in reaction formula (1), gas containing methane (CH4) and water vapor (H2O) is generated by the methanation of CO2. The generated gas unavoidably contains CO2, H2, CO, and CH3OH. The generated gas passes through the buffer region at the lower part of the vessel 2, and is then discharged from the discharge port 2b of the vessel 2.

[0022] FIG. 2 is a graph showing the relationship between the distance from the inlet-side end of the catalyst layer 3, the temperature of the catalyst layer 3, and the composition of the generated gas. The horizontal axis of FIG. 2 represents the distance from the inlet-side end of the catalyst layer 3. The vertical axis on the right side of FIG. 2 represents temperature. The vertical axis on the left side of FIG. 2 represents the concentrations of CO2, H2, CH4, and H2O.

[0023] As shown in FIG. 3, when the methanation of CO2 proceeds, a rapid temperature rise occurs on the upstream side in the longitudinal direction of the catalyst layer 3, the temperature drops sharply from the position of the peak temperature toward the downstream side, and the temperature becomes substantially constant further toward the downstream side. In the region where the temperature on the upstream side of the catalyst layer 3 is high, thermal degradation of the catalyst 4 proceeds.

[0024] In order to suppress thermal degradation of the catalyst 4, the catalyst layer 3 is cooled by the heat medium 7 supplied into the vessel 2 from the heat medium inlet port 6a. The heat medium 7 is steam, oil, or the like. The heat medium 7 flows upward in the vessel 2 from the bottom, exchanges heat with the catalyst layer 3, and is then discharged from the heat medium outlet port 6b.

[0025] The heat transfer medium 7 cools the catalyst layer 3 so that the entire catalyst layer 3 (the portion of the catalyst layer 3 where the methanation reaction has not yet progressed) is at 100°C to 200°C, preferably 150°C to 200°C. Below 150°C, it becomes difficult for each heater 5a to 5e to ignite the methanation reaction. Above 200°C, it becomes difficult for the heat transfer medium 7 to lower the peak temperature of the catalyst layer 3.

[0026] Within the catalyst layer 3, at least two thermometers 8a to 8e are provided in the longitudinal direction of the catalyst layer 3. The thermometers 8a to 8e are, for example, thermocouples, infrared thermographs, etc., and measure the temperature of the catalyst layer 3. The downstream thermometer 8e detects the temperature near the outlet of the catalyst layer 3. The number of thermometers 8a to 8e is preferably the same as the number of heaters 5a to 5e, but they may be different.

[0027] The temperature data detected by thermometers 8a to 8e is input to the heater control device 9, which controls heaters 5a to 5e. The heater control device 9 is a computer equipped with a CPU, ROM, RAM, storage, etc.

[0028] The heater control device 9 controls heaters 5a to 5e in order from the upstream side to heat the catalyst layer 3, based on the measurement data from thermometers 8a to 8e, by having the CPU execute a program stored in ROM or storage. That is, the upstream heater 5a heats the catalyst layer 3 (at which time the remaining heaters 5b to 5e do not heat the catalyst layer 3), then the second heater 5b heats the catalyst layer 3 (at which time the remaining heaters 5a, 5c to 5e do not heat the catalyst layer 3), then the third heater 5c heats the catalyst layer 3 (at which time the remaining heaters 5a, 5b, 5d, and 5e do not heat the catalyst layer 3), and so on. Heaters 5a to 5e switch (for example, from heater 5a to heater 5b) when the temperature peak shifts from the upstream thermometer (for example, 8a) to the downstream thermometer (for example, 8b), as will be described later.

[0029] The product gas discharged from reactor 1 is condensed by a condenser (not shown) connected to the discharge port 2b, separating it into methane-containing gas and water. The methane-containing gas, from which the water has been separated, is then supplied to the customer after impurities such as CO2 and CO are removed by, for example, a decarboxylation device. Note that two or more reactors 1 may be connected in series to improve the CO2 conversion rate. (Methanation reaction method)

[0030] Figure 3 shows the change in temperature distribution of the catalyst layer 3. Figure 3(a) shows the temperature distribution immediately after the start of operation (initial stage), Figure 3(b) shows the temperature distribution after a predetermined time of operation (mid-stage), and Figure 3(c) shows the temperature distribution of the catalyst layer 3 after a further predetermined time of operation (late stage). Although Figure 3 shows an example in which the raw material gas is flowed horizontally through a tubular catalyst layer 3, in reality the catalyst layer 3 extends vertically and the raw material gas is flowed vertically. However, the tubular catalyst layer 3 may also extend horizontally as shown in Figure 3 and the gas may be flowed horizontally.

[0031] As shown in Figure 3(a), initially, the catalyst layer 3 is heated by the upstream heater 5a, igniting the methanation reaction. As methanation progresses, a rapid temperature increase occurs upstream of the catalyst layer 3. Since the catalyst layer 3 is cooled overall by the heat transfer medium 7, the temperature downstream of the peak temperature can be lowered. Therefore, thermal degradation of the catalyst 4 can be suppressed, and the lifespan of the catalyst 4 can be extended.

[0032] As shown in Figure 3(b), after a predetermined period of operation, the catalyst 4 in the catalyst layer 3 surrounded by heater 5a becomes deactivated (however, the time until this part of the catalyst 4 becomes deactivated is longer than in the conventional method), and the temperature peak shifts to the catalyst layer 3 surrounded by heater 5b. Once the temperature peak shifts, the heater control device 9 stops heating the catalyst layer 3 with heater 5a and starts heating the catalyst layer 3 with heater 5b. Even in the intermediate period shown in Figure 3(b), the catalyst layer 3 is cooled overall by the heat transfer medium 7, so the temperature downstream of the peak temperature can be lowered. Therefore, thermal degradation of the catalyst 4 can be suppressed, and the lifespan of the catalyst 4 can be extended.

[0033] As shown in Figure 3(c), after operation for a predetermined time, the catalyst 4 in the catalyst layer 3 surrounded by the heater 5b becomes deactivated (however, the time until this part of the catalyst 4 becomes deactivated is longer than in the conventional method), and the temperature peak shifts to the catalyst layer 3 surrounded by the heater 5c. Once the temperature peak shifts, the heater control device 9 stops heating the catalyst layer 3 with the heater 5b and starts heating the catalyst layer 3 with the heater 5c. In the later stage shown in Figure 3(c), as in the early and middle stages, thermal degradation of the catalyst 4 can be suppressed, and the lifespan of the catalyst 4 can be extended. (Other examples of methanation reaction methods)

[0034] Figure 4 shows an example in which more than 10 heaters 5a to 5q are installed along the longitudinal direction of the tubular catalyst layer 3. In this example as well, the heaters 5a to 5q can independently heat the catalyst layer 3 and heat only the portion of the catalyst layer 3 that requires initial thermal compensation (thermal compensation to ignite the methanation reaction). The heaters 5a to 5q heat the catalyst layer 3 sequentially from the upstream side.

[0035] As shown in Figure 4(a), initially, the upstream heater 5a heats the catalyst layer 3, driving the methanation reaction. At this time, a temperature peak occurs downstream of the catalyst layer 3 heated by heater 5a. Since the portion of the catalyst layer 3 where the temperature peak occurs is not heated by heater 5b, this portion of the catalyst layer 3 can be efficiently cooled. When the temperature peak moves from the area surrounded by heater 5b to the area surrounded by heater 5c, the heater switching from heater 5a to heater 5b is performed. This process is then repeated.

[0036] In the intermediate stage shown in Figure 4(b), only heater 5e heats the catalyst layer 3. Similarly in the intermediate stage, a temperature peak occurs downstream of the catalyst layer 3 heated by heater 5e. The same is true in the later stage shown in Figure 4(c), where a temperature peak occurs downstream of the catalyst layer 3 heated by heater 5j.

[0037] In this way, by causing the temperature peak to occur downstream of the catalyst layer 3 heated by heaters 5a to 5j, the portion of the catalyst layer 3 where the temperature peak occurs can be cooled more efficiently. [Explanation of Symbols]

[0038] 1…Methanation reactor 2…Container 3...Catalyst layer 4…Catalyst 5a~5e... Heater 5a~5q... Heater 7...Heating medium

Claims

1. In a methanation reactor that produces methane-containing gas by contacting a catalyst with a raw material gas containing carbon dioxide and hydrogen, Container and A tubular catalyst layer, which is placed inside the aforementioned container and filled with catalyst, A heat transfer medium flows inside the container and cools the catalyst layer, A methanation reactor comprising: at least two heaters provided in the longitudinal direction of the catalyst layer, surrounding the catalyst layer and capable of independently heating the catalyst layer.

2. The methanation reactor according to claim 1, characterized in that at least three of the heaters are provided in the longitudinal direction of the catalyst layer.

3. The methanation reactor according to claim 1 or 2, characterized in that at least two of the heaters sequentially heat the catalyst layer from the upstream side.

4. The methanation reactor according to claim 1 or 2, characterized in that the heater heats the catalyst layer to 150°C to 350°C.

5. In a methanation reaction method that generates a methane-containing gas by contacting a raw material gas containing carbon dioxide and hydrogen with a catalyst, A tubular catalyst layer, which is placed inside a container and filled with catalyst, is cooled by a heat transfer medium flowing inside the container. A methanation reaction method comprising heating the catalyst layer independently by heaters, of which at least two heaters are provided in the longitudinal direction of the catalyst layer and surround the catalyst layer.

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