JP6740458B2 - Natural gas processing equipment - Google Patents

Description

The present invention relates to the technical field of methanating carbon dioxide in natural gas with hydrogen.

In addition to methane, which is the main component, natural gas is often produced with carbon dioxide, and carbon dioxide is removed to obtain product gas as a raw material for pipeline gas (city gas) and liquefied natural gas. There is a need to. Carbon dioxide in natural gas is generally separated and removed by AGRU (Acid Gas Removal Unit) using amines and released into the atmosphere, but carbon dioxide has the greatest effect on global warming, which is a greenhouse gas. Therefore, emission reduction is required.

On the other hand, the excellent gas fields with low carbon dioxide content, which have been preferentially developed from the perspective of profitability, are running out, and it is necessary to develop natural gas wells containing higher concentrations of carbon dioxide in the future. Therefore, it is possible to use methanation as one of the effective use of carbon dioxide in natural gas. However, when high-concentration carbon dioxide separated by a carbon dioxide separator such as AGRU is used as a raw material, the heat of methanation reaction Causes a rapid temperature rise in the reactor. In addition, the temperature rise is disadvantageous to the progress of equilibrium reaction methanation.

In order to suppress the temperature rise of the reactor, generally, a method of dividing the reactor and placing a cooler between the reactors, a method of returning the product gas generated by the reaction to the inlet of the reactor (recycle), diluting water vapor A method of adding it to the raw material gas as an agent is adopted. However, these methods have problems that the number of reactors increases, that a large amount of product gas needs to be recycled, or that a large amount of steam needs to be entrained in the raw material gas.

In Patent Document 1, hydrogen obtained by supplying natural gas to a hydrogen separation reactor and carbon dioxide in the natural gas are reacted in the methanation reactor in the presence of a catalyst to generate methane. However, it is described that carbon dioxide in natural gas is reduced.
Further, in Patent Document 2, a raw material gas containing carbon dioxide is mixed with hydrogen from a hydrogen gas supply line, the mixed gas is supplied to a first reactor, and then the mixed gas is mixed with hydrogen from the hydrogen gas supply line. A technique for mixing and supplying the mixed gas to the second reactor, further supplying the mixed gas to the third reactor for adjusting the composition of the produced gas, and changing carbon dioxide in the raw material gas to methane is described. Has been done.

Patent Documents 1 and 2 describe a method of extending the service life of a methanation catalyst by making the allowable content of sulfur contained in natural gas extremely low, and a device for suppressing the amount of methanation catalyst used. It has not been. It should be noted that, from the description in paragraph 0037 of Patent Document 2 on and after the fifth line, the use of hydrogen for pretreatment in the preceding stage of the reactor is excluded.

US Pat. No. 6,419,888 JP, 2013-136538, A

The present invention provides a natural gas treatment apparatus capable of simplifying the equipment for methanating carbon dioxide in natural gas, and extending the life of the methanation catalyst and reducing the amount used. It is in.

The natural gas processing device of the present invention is
A natural gas, which is a raw material gas, and hydrogen are supplied, and a pre-stage reactor for reacting carbon dioxide and hydrogen in the natural gas to generate methane,
A post-reactor for adjusting the hydrogen concentration by reacting hydrogen and carbon dioxide remaining in the product gas discharged from the pre-reactor,
A catalyst layer of a methanation catalyst provided in each of the front-stage reactor and the rear-stage reactor,
A catalyst layer of a hydrogenation catalyst that is provided on the upstream side of the preceding-stage reactor and that has a main hydrogenation catalytic action for hydrogenating organic sulfur in natural gas to hydrogen sulfide and a methanation catalytic action,
And an adsorbent layer of an adsorbent for adsorbing hydrogen sulfide, which is located upstream of the pre-reactor and downstream of the catalyst layer of the hydrogenation catalyst.

In the present invention, when methanating carbon dioxide in natural gas, since natural gas is supplied to the reactor as a raw material gas, components other than carbon dioxide in natural gas can be used as a diluent for the methanation reaction. .. Therefore, the temperature rise of the methanation reaction can be suppressed, so that the equipment can be simplified. Also, on the upstream side of the methanation reactor, organic sulfur in natural gas is changed to hydrogen sulfide and adsorbed and removed by an adsorbent, so that the life of the methanation catalyst can be extended and the hydrogenation catalyst As a result, the methanation proceeds, so that it is possible to reduce the amount of the methanation catalyst used in the subsequent stage.

It is a block diagram which shows 1st Embodiment of the processing apparatus of the natural gas of this invention. It is a block diagram which shows an example of a device structure for aiming at the effective utilization of the waste water obtained in 1st Embodiment. It is a block diagram which shows the other example of an apparatus structure for aiming at the effective utilization of the waste water obtained in 1st Embodiment. It is explanatory drawing which shows the application example of 1st Embodiment. It is a graph which shows the relationship between the density|concentration of the carbon dioxide in natural gas, and the density|concentration of COS (carbonyl sulfide) after a hydrogenation reaction. It is a block diagram which shows 2nd Embodiment of the processing apparatus of the natural gas of this invention. It is a block diagram which shows the modification of 2nd Embodiment of the natural gas processing apparatus of this invention. It is explanatory drawing which shows the aspect of Example 1 corresponding to the 1st Embodiment of this invention. It is explanatory drawing which shows the aspect of Example 2 corresponding to the 2nd Embodiment of this invention. It is explanatory drawing which shows the aspect of Example 3 corresponding to the modification of the 2nd Embodiment of this invention. It is explanatory drawing which shows the aspect of the comparative example 1 for comparing with this invention. It is explanatory drawing which shows the aspect of the comparative example 2 for comparing with this invention.

[First Embodiment]
As shown in FIG. 1, the natural gas treatment apparatus according to the first embodiment of the present invention includes a hydrogenation reactor 1, an adsorptive desulfurization reactor 2 for adsorbing hydrogen sulfide, and a pre-reactor. The 1st methanation reactor 3 and the 2nd methanation reactor 4 which comprise, and the back|latter stage reactor 5 which is a methanation reactor are arrange|positioned from the upstream side in this order. Each reactor 1-5 is configured as an adiabatic reactor. In the following description, for the sake of convenience, the flow path of the natural gas connected to the upstream side of the hydrogenation reactor 1 is referred to as the "raw material gas supply path", and the flow path of the gas from the hydrogenation reactor 1 to the post-stage reactor 5 is The "gas flow path" and the flow path of the gas taken out from the post-reactor 5 will be respectively referred to as "produced gas outflow path".

The raw material gas supply passage 101 is connected to the tower top of the hydrogenation reactor 1 via a heater 102, and a hydrogen supply passage 200 for pretreatment is connected to the upstream side of the heater 102. The AGRU (103) indicated by the dotted line will be described later.
In the arrangement of the reactors 1 to 5, of the two reactors adjacent to each other when the gas flow passage is viewed, the tower bottom portion and the downstream tower top portion of the upstream reactor are respectively gas flow passages. They are connected by 10, 20, 30, 40.

In the hydrogenation reactor 1, a catalyst layer 11 of a hydrogenation catalyst for converting organic sulfur contained in natural gas into hydrogen sulfide is arranged. The hydrogenation catalyst contains, for example, an inorganic oxide carrier containing aluminum, a first metal component selected from molybdenum and tungsten, and a second metal component selected from cobalt, nickel and chromium. Used in a sulphurized state. Further, the hydrogenation catalyst has a main hydrogenation catalytic action for converting organic sulfur in natural gas into hydrogen sulfide by hydrogenation, and a methanation catalytic action.

In the adsorptive desulfurization reactor 2, an adsorbent layer 21 of an adsorbent for adsorbing hydrogen sulfide is arranged. As the adsorbent, for example, zinc oxide particles can be used. The adsorbent may be a carrier made of an inorganic oxide such as alumina or silica, on which a metal such as iron or copper is supported.

A cooler 22 is provided in the gas flow path 20 for supplying the gas flowing out from the adsorptive desulfurization reactor 2 to the first methanation reactor 3. When operating the apparatus under operating conditions in which the inlet temperature of the first methanation reactor 3 is lower than the outlet temperature of the adsorptive desulfurization reactor 2, the cooler 22 is required, but the first methanation reactor is required. When operating the apparatus under operating conditions in which the inlet temperature of 3 is the same as the outlet temperature of the adsorptive desulfurization reactor 2, the cooler 22 is not necessary.
As an example of the operating conditions, the inlet temperature of each of the pre-stage methanation reactor (the first methanation reactor 3, the second methanation reactor 4) and the post-stage methanation reactor 5 is, for example, 200 to 300°C. The temperature in the adsorptive desulfurization reactor 2 is 300 to 350°C. In this example, since the inlet temperature of the first methanation reactor 3 is 250° C. and the temperature in the adsorptive desulfurization reactor 2 is 300° C., the gas flowing out from the adsorptive desulfurization reactor 2 is cooled by the cooler 22. ing.

A first hydrogen supply passage 201 and a steam supply passage 203 are connected between the cooler 22 in the gas passage 20 and the tower top of the first methanation reactor 3. A catalyst layer 31 of a methanation catalyst is arranged in the first methanation reactor 3. As the methanation catalyst, a particulate catalyst containing nickel as a main component (for example, 40 to 60 mass% with respect to the entire catalyst) can be used. As the methanation catalyst, it is also possible to use a catalyst in which ruthenium is supported on an inorganic oxide such as alumina or silica.
Inside each of the second methanation reactor 4 and the post-stage methanation reactor 5, catalyst layers 41 and 51 using the same methanation catalyst are arranged.

A gas flow passage 30 for supplying the gas flowing out from the first methanation reactor 3 to the second methanation reactor 4 is provided with a cooler 32, and a second cooler 32 is provided downstream of the cooler 32. Is connected to the hydrogen supply path 202. Further, a cooler 42 is also provided in the gas passage 40 for supplying the gas flowing out from the second methanation reactor 4 to the post-stage methanation reactor 5. In the first methanation reactor 3 and the second methanation reactor 4, carbon dioxide (carbon dioxide gas) reacts with hydrogen (hydrogen gas) to produce methanation reaction, Since this reaction is an exothermic reaction, each outlet temperature is higher than each inlet temperature of the methanation reactors 3 and 4. Therefore, the gas flowing out from each of the methanation reactors 3 and 4 is cooled by these coolers 32 (42).
The pretreatment hydrogen supply passage 200, the first hydrogen supply passage 201, and the second hydrogen supply passage 202 described above are connected to, for example, a common hydrogen supply source, and the flow rate adjusting valves V0, V1, and V2 are respectively provided. Is provided. Further, the water vapor supply path 203 is provided with a valve V3 for adjusting the flow rate.

The post-stage methanation reactor 5 is provided for reacting excess hydrogen contained in the gas with carbon dioxide so that the hydrogen concentration in the produced gas after the treatment falls within a preset concentration range. One end side of the produced gas outflow passage 50 is connected to the tower bottom of the post-stage methanation reactor 5, and the other end side of the produced gas outflow passage 50 is connected to the gas-liquid separation drum 53 via the cooler 52. .. The gas-liquid separation drum 53 flows out from the post-stage methanation reactor 5 to separate and remove moisture (drainage) from the cooled product gas, and the product gas from which the water has been separated is taken out as, for example, a product gas.

Next, the operation of the first embodiment will be described. First, the natural gas that is a raw material gas is mixed with the hydrogen gas for pretreatment sent from the hydrogen supply passage 200 for pretreatment through the raw material gas supply passage 101, and is heated by the heater 102, for example, 250° C. to 350° C. Is heated to. The heated mixed gas is supplied into the hydrogenation reactor 1, and the hydrogenation reaction mainly occurs. That is, the organic sulfur contained in the natural gas is converted into hydrogen sulfide by the hydrogenation catalyst forming the catalyst layer 11. As described above, the hydrogenation catalyst has a methanation catalytic action in addition to the hydrogenation catalytic action. Therefore, the methanation reaction also progresses in the hydrogenation reactor 1, resulting in the oxidation of natural gas. Part of the carbon reacts with hydrogen to produce methane.

Since the methanation reaction which is an exothermic reaction occurs, the temperature of the gas on the outlet side of the hydrogenation reactor 1 becomes higher than the temperature of the gas on the inlet side by, for example, 10°C to 100°C. The amount of hydrogen supplied to the hydrogenation reactor 1 is at least a sufficient amount for hydrogenating organic sulfur (for example, 1 to 2 mol (mol)%), and is 10 mol% in consideration of the heat resistant temperature of the hydrogenation catalyst. Below. The gas flowing out from the hydrogenation reactor 1 is sent into the adsorptive desulfurization reactor 2, and the adsorbent constituting the adsorbent layer 21 adsorbs hydrogen sulfide in the gas for desulfurization. As a result, the sulfur concentration in the gas flowing out from the adsorptive desulfurization reactor 2 becomes 0.1 ppm or less. The concentration unit “ppm” in the specification of the present application represents mol concentration.
In order to reduce the load of the adsorbent in the adsorptive desulfurization reactor 2, when the sulfur concentration in the natural gas is high, an AGRU (Acid Gas Removal Unit) (103) is provided in the source gas supply path 101 as shown by the dotted line in FIG. ) May be used. The AGRU (103) supplies, for example, natural gas from the bottom side of the amine contact tower to let it flow out from the top of the tower, and supplies the amine liquid from the top side of the amine contact tower to make countercurrent contact with the natural gas. It is configured. By contacting the natural gas with the liquid amine, hydrogen sulfide in the natural gas is removed.

The gas, which has been mainly desulfurized and has undergone secondary methanation, which has been subjected to a so-called pretreatment, is discharged from the adsorptive desulfurization reactor 2 and then cooled by the cooler 22 to, for example, 250° C. And is sent to the first methanation reactor 3. In the first methanation reactor 3, a methanation reaction occurs in which carbon dioxide and hydrogen react with each other in the catalyst layer 31 of the methanation catalyst to produce methane. The flow rate of hydrogen supplied from the first hydrogen supply path 201 is added to hydrogen remaining in the gas flowing out from the adsorptive desulfurization reactor 2 to cause a methanation reaction and a methanation reaction when the methanation reaction occurs. The temperature on the outlet side of the first methanation reactor 3 is adjusted to, for example, 540° C. or lower in consideration of the heat resistant temperature of the equipment.

The water vapor is supplied to prevent activity deterioration due to coking of the methanation catalyst, but also has a role of further suppressing the temperature in each of the methanation reactors 3, 4 and 5. The amount of steam supplied is such that, at the inlet of the first methanation reactor 3, the molar ratio of steam to the total of carbon dioxide and hydrogen is, for example, 0.6 [mol concentration of steam/(mol concentration of carbon dioxide+mol of hydrogen) Density)] is set. The water vapor is not always required to be supplied and may not be used.

The gas flowing out from the first methanation reactor 3 is cooled to, for example, 250° C. by the cooler 32 and sent to the second methanation reactor 4. Then, in the second methanation reactor 4, the hydrogen concentration becomes a value according to the concentration of carbon dioxide remaining in the gas, and the temperature on the outlet side of the second methanation reactor 4 is changed. For example, hydrogen is replenished and supplied from the second hydrogen supply passage 202 to the second methanation reactor 4 via the gas passage 30 so that the temperature becomes 540° C. or lower. Then, a methanation reaction occurs in the catalyst layer 41, and the gas in which the concentration of carbon dioxide is reduced is cooled to, for example, 250° C. by the cooler 42 and sent to the post-reactor 5.

Since the gas whose temperature has been raised in the second methanation reactor 4 is cooled and supplied to the second-stage reactor 5, the methanation reaction proceeds further in the catalyst layer 51 of the methanation catalyst of the second-stage reactor 5. However, carbon dioxide and hydrogen are reduced, and the hydrogen concentration in the product gas is adjusted to an allowable concentration, for example, 3 mol% or less. The produced gas flowing out from the latter-stage reactor 5 is cooled by a cooler 52 to a temperature below the temperature at which water condenses, for example, to 50° C., and then the gas and water are separated by a gas-liquid separation drum 53 which is a gas-liquid separation unit, Product gas is obtained.
In the above, the pressure in each reactor 1 to 5 is set to, for example, 1 MPa to 8 MPa. Further, the number of stages of the former-stage reactor (the first methanation reactor 3 and the second methanation reactor 4 in the above example) is determined according to the concentration of carbon dioxide in the natural gas. If steam is used as described above, the number of front-stage reactors used is one if the concentration of carbon dioxide is 25 mol% or less, two if it is 40 mol% or less, and three if it is 70 mol% or less. To be done.

When using natural gas having a high carbon dioxide concentration, in order to suppress the number of methanation reactors, a part of carbon dioxide in the natural gas is removed upstream of the hydrogenation reactor 1. A unit for this may be provided. Further, when the concentration of carbon dioxide in the natural gas is lower than 3 mol%, it can be used as it is as a pipeline gas. Therefore, the natural gas used as a raw material gas has a carbon dioxide concentration of 3 mol% or more. You can

According to the above-described embodiment, a reactor for performing methanation by using a gas other than carbon dioxide in natural gas as a diluent gas is divided into a plurality of stages, for example, two-stage methanation reactors 3 and 4. Since hydrogen is supplied to each of them, the number of reactors for methanation can be suppressed, and the apparatus can be simplified. Then, on the upstream side of the methanation reactors 3 and 4, the hydrogenation catalyst and the adsorbent for hydrogen sulfide are used to reduce the sulfur concentration in the natural gas to 0.1 ppm or less. The service life can be extended. Further, since the hydrogenation catalyst is used, a methanation reaction also occurs in addition to the hydrogenation reaction here, so that the amount of the methanation catalyst used in the methanation reactors 3 and 4 can be suppressed.

Here, examples of configurations for effectively using energy or gas in the above-described natural gas processing apparatus or a system including the processing apparatus will be listed.
The wastewater separated by the gas-liquid separation drum 53 is used as a cooling medium for the coolers 22, 32, 42, 52 as shown in FIG. 2, and the steam obtained by vaporization by the heat of the methanation reaction, It is supplied to the first methanation reactor 3 from the above-described steam supply passage 203.
Similarly, as shown in FIG. 3, the water vapor obtained by vaporization by the heat of the methanation reaction is provided in the hydrogen supply passage 300 on the upstream side of the confluence of the hydrogen supply passages 200, 201, 202 described above. The booster compressor 301 is supplied to the steam turbine 302.
The wastewater separated by the gas-liquid separation drum 53 is electrolyzed by an electrolyzer, and the obtained hydrogen is supplied into the processing system through the above-mentioned hydrogen supply paths 200, 201, 202.

As shown in FIG. 4, in a system in which an LNG (Liquefied Natural Gas) production facility 400 is arranged in the latter stage of the above-mentioned natural gas treatment device, waste water or other water separated by the gas-liquid separation drum 53 The water supplied from the supply source is vaporized by the heat of the methanation reaction to obtain steam, and this steam is used as the heat source of the stripping tower reboiler of AGRU in the LNG manufacturing facility 400. Further, as shown in FIG. 4, by returning the carbon dioxide recovered from the AGRU in the LNG manufacturing facility 400 to the upstream side of the first methanation reactor 3 and recycling it, the emission of carbon dioxide is suppressed and the product is reduced. Increase gas production.

[Second Embodiment]
When natural gas containing carbon dioxide and sulfur is supplied to the hydrogenation catalyst, carbonyl sulfide is produced as a by-product. Therefore, the natural gas treatment apparatus according to the second embodiment of the present invention uses carbonyl sulfide (COS). ) Has been adopted as a configuration. FIG. 5 is a graph showing the relationship between the carbon dioxide concentration in natural gas and the carbonyl sulfide concentration after the hydrogenation reaction. When sulfur in the natural gas is 1 ppm and the carbon dioxide concentration in the natural gas is 64 mol %, the amount of carbonyl sulfide produced is 0.095 ppm, which is an extremely small amount as indicated by the triangle. On the other hand, when the sulfur content in the natural gas is 10 ppm, the production amount of carbonyl sulfide exceeds 0.1 ppm even if the carbon dioxide concentration in the natural gas is several%, as indicated by Δ. As the carbon concentration increases, it increases almost proportionally, and the service life of the methanation catalyst becomes shorter due to poisoning. Therefore, when natural gas having a high sulfur concentration is used as the raw material gas and the AGRU 103 is not provided on the upstream side of the hydrogenation reactor 1, it can be predicted that the production amount of carbonyl sulfide will be considerably large.

Therefore, in the second embodiment, as shown in FIG. 6, carbonyl sulfide is adsorbed on the upstream side of the first methanation reactor 3, for example, between the adsorptive desulfurization reactor 2 and the first methanation reactor 3. The carbonyl sulfide adsorption reactor 6 which is a carbonyl sulfide removal section in which an adsorption layer 61 made of an adsorbent is disposed. Reference numeral 60 is a gas flow path. As the carbonyl sulfide adsorbent, for example, an adsorbent in which copper is supported on a carrier made of an inorganic oxide such as alumina or silica, or a copper-based adsorbent such as copper oxide granules or molded bodies can be used.

Further, instead of separately providing the adsorption desulfurization reactor 2 and the carbonyl sulfide adsorption reactor 6, as the adsorption desulfurization agent used in the adsorption desulfurization reactor 2, only a copper-based adsorbent is used, and hydrogen sulfide is used. And carbonyl sulfide may be adsorbed on the adsorbent. However, since the cost of the copper-based adsorbent is high, the configuration shown in FIG. 6 is adopted from the viewpoint of cost, and the adsorption-desulfurization reactor 2 has a zinc-based adsorbent, for example, an adsorption made of zinc oxide. It is advantageous to use, for example, a copper-based adsorbent in the carbonyl sulfide adsorption reactor 6 together with the agent, and in this case, the amount of the copper-based adsorbent used can be suppressed. Further, instead of providing the carbonyl sulfide adsorption reactor 6, a zinc-based adsorbent and a copper-based adsorbent may be arranged in this order from the upstream side in the adsorptive desulfurization reactor 2.
Further, instead of the configuration shown in FIG. 6, a carbonyl sulfide adsorbent may be provided above the catalyst layer 31 in the first methanation reactor 3.

FIG. 7 shows a modified example of the second embodiment. In this example, instead of adsorbing carbonyl sulfide with an adsorbent, a hydrolysis reactor for hydrolyzing and removing carbonyl sulfide is shown. 7 is provided on the upstream side of the first methanation reactor 3, for example, between the hydrogenation reactor 1 and the adsorptive desulfurization reactor 2, and steam is supplied to the hydrolysis reactor 7 through the steam supply passage 204. There is. As the catalyst that constitutes the catalyst layer 71 provided in the hydrolysis reactor 7, for example, a carrier in which chromium or the like is supported on a carrier of alumina or titanium oxide can be used. Since the operating temperature of the hydrolysis reactor 7 is lower than the operating temperature of each of the hydrogenation reactor 1 and the adsorptive desulfurization reactor 2, a cooler 72 is provided upstream of the hydrolysis reactor 7 and a heater is provided downstream thereof. 73 is provided. 70 is a gas flow path.
According to the second embodiment, since the carbonyl sulfide by-produced by the hydrogenation catalyst is removed, poisoning of the methanation catalyst can be suppressed.

Hereinafter, examples of processing natural gas by simulation (examples and comparative examples) will be described.
[Example 1]
Example 1 is an example in which a natural gas containing 40 mol% of carbon dioxide and 1 ppm of sulfur is treated by the first embodiment to obtain a product gas having a carbon dioxide concentration of 2 mol%. FIG. 8 is an explanatory diagram showing a mode of processing (concentration of components in gas, temperature, etc.) in Example 1.
Hydrogen was mixed with the raw material natural gas at the inlet of the hydrogenation reactor 1 so as to be 10 mol% hydrogen, heated to 250° C. by the heater 102, and supplied to the hydrogenation reactor 1. Due to the methanation reaction occurring in the hydrogenation reactor 1, the outlet temperature of the hydrogenation reactor 1 rose to 340° C., and the carbon dioxide concentration became 35 mol %.
At the outlet of the hydrogenation reactor 1, sulfur was in the form of hydrogen sulfide and was adsorbed and removed by the adsorptive desulfurization reactor 2, and it was confirmed that the sulfur concentration at the outlet of the adsorptive desulfurization reactor 2 was 0.1 ppm or less. .. This allows the downstream methanation catalyst to be used for 2-4 years.

The gas that passed through the adsorptive desulfurization reactor 2 was cooled so that the inlet temperature of the first methanation reactor 3 was 250° C., and the amount of hydrogen so that the outlet temperature of the first methanation reactor 3 was 540° C. , And steam were mixed and supplied to the first methanation reactor 3. The supply amount (mixing amount) of steam was set to an amount such that the molar ratio of steam to the total of carbon dioxide and hydrogen was 0.6 at the inlet of the first methanation reactor 3.
The gas passed through the first methanation reactor 3 is cooled so that the inlet temperature of the second methanation reactor 4 is 250° C., and hydrogen is mixed in an amount capable of adjusting the carbon dioxide concentration of the product gas to 2 mol %. And supplied to the second methanation reactor 4. The outlet temperature of the second methanation reactor 4 rises to 464° C. due to the methanation reaction, and the gas flowing out from the second methanation reactor 4 has an inlet temperature of the latter stage methanation reactor 5 of 250° C. After cooling in this way, it was supplied to the second stage methanation reactor 5.
In the second-stage methanation reactor 5, the residual hydrogen and carbon dioxide reacted, and the outlet temperature rose to 304°C. After the gas flowing out from the second-stage methanation reactor 5 is cooled to 50° C. by the cooler 502, water is separated by the gas-liquid separation drum 53 to obtain a product gas having a carbon dioxide concentration of 2 mol% and a hydrogen concentration of 3 mol%. did it.

[Example 2]
In Example 2, a natural gas containing 40 mol% of carbon dioxide and 10 ppm of sulfur was treated using the carbonyl sulfide adsorption reactor 6 in the second embodiment to obtain a product gas having a carbon dioxide concentration of 2 mol%. Here is an example. FIG. 9 is an explanatory diagram illustrating a processing mode according to the second embodiment.
Hydrogen was mixed with the raw material natural gas at the inlet of the hydrogenation reactor 1 so as to be 10 mol% hydrogen, heated to 250° C. by the heater 102, and supplied to the hydrogenation reactor 1. Due to the methanation reaction occurring in the hydrogenation reactor 1, the outlet temperature of the hydrogenation reactor 1 rose to 340° C., and the carbon dioxide concentration became 35 mol %. At the outlet of the hydrogenation reactor 1, in addition to the form of hydrogen sulfide, sulfur was contained in the gas as by-produced carbonyl sulfide, and the concentration of carbonyl sulfide in the gas was 0.7 ppm.
Hydrogen sulfide is adsorbed and removed by the adsorptive desulfurization reactor 2, but carbonyl sulfide that has not been adsorbed flows out from the outlet of the adsorptive desulfurization reactor 2. By supplying the gas flowing out from the adsorptive desulfurization reactor 2 to the downstream carbonyl sulfide adsorption reactor 6, the sulfur concentration at the outlet of the carbonyl sulfide adsorption reactor 6 became 0.1 ppm or less.
The processing on the downstream side of the carbonyl sulfide adsorption reactor 6 is the same as in Example 1.

[Example 3]
In Example 3, a natural gas containing 40 mol% of carbon dioxide and 10 ppm of sulfur was treated by using the carbonyl sulfide hydrolysis reactor 7 in the second embodiment to obtain a product gas having a carbon dioxide concentration of 2 mol%. Is an example of obtaining. FIG. 10 is an explanatory diagram illustrating a processing mode according to the second embodiment.
Hydrogen was mixed with the raw material natural gas so that the hydrogen concentration was 10 mol% at the inlet of the hydrogenation reactor 1, heated to 250° C. by the heater 102, and supplied to the hydrogenation reactor 1. Due to the methanation reaction occurring in the hydrogenation reactor 1, the outlet temperature of the hydrogenation reactor 1 rose to 340° C., and the carbon dioxide concentration became 35 mol %.

At the outlet of the hydrogenation reactor 1, in addition to the form of hydrogen sulfide, sulfur was contained in the gas as by-produced carbonyl sulfide, and the concentration of carbonyl sulfide in the gas was 0.7 ppm.
The gas flowing out from the hydrogenation reactor 1 is cooled by the cooler 72 so that the inlet temperature of the hydrolysis reactor 7 becomes 150° C., and then steam is mixed so that the steam concentration becomes 5 mol %, and hydrolysis is performed. It was supplied to the reactor 7. The carbonyl sulfide concentration at the outlet of the hydrolysis reactor 7 became 0.1 ppm or less due to the hydrolysis (conversion to hydrogen sulfide) of carbonyl sulfide.
The gas flowing out from the hydrolysis reactor 7 was heated to 350° C. by the heater 73 and supplied to the adsorptive desulfurization reactor 2. Hydrogen sulfide was adsorbed and removed, and the sulfur concentration at the outlet of the adsorptive desulfurization reactor 2 became 0.1 ppm or less.
The processing on the downstream side of the adsorptive desulfurization reactor 2 is the same as in Example 1.

[Comparative Example 1]
In Comparative Example 1, the same raw material natural gas as in Example 1 containing 40 mol% of carbon dioxide and 1 ppm of sulfur was used, and the carbon dioxide concentration was 2 mol% without applying the hydrogenation reactor 1 and the adsorption desulfurization reactor 2. It is an example of obtaining the product gas of. 11: is explanatory drawing which shows the aspect of the process in the comparative example 1 using the apparatus which removed the hydrogenation reactor 1 and the adsorption desulfurization reactor 2 from the structure shown in FIG.
Since a gas containing carbon dioxide at a high concentration is supplied to the methanation reaction section as compared with Example 1, a large amount of heat is generated by the methanation reaction, and the outlet temperature of the second methanation reactor 4 is 487° C., the latter stage. The outlet temperature of the methanation reactor 5 became 316°C.
The methanation reaction, which is an equilibrium reaction, is hindered by the temperature rise, and it is necessary to supply excessive hydrogen in order to obtain a product gas having a carbon dioxide concentration of 2 mol %, and the hydrogen concentration of the product gas is higher than that in Example 1. It became 4 mol%. To achieve the hydrogen concentration of the product gas of Example 1 it was necessary to add a third methanation reactor.
In addition, since the raw natural gas was not desulfurized, the methanation catalyst was deactivated by sulfur and had to be replaced every few months.

[Comparative example 2]
In Comparative Example 1, an example in which the hydrogen concentration equivalent to that in Example 1 is achieved by diluting the raw material natural gas with steam instead of adding the methanation reactor is Comparative Example 2. FIG. 12 is an explanatory diagram showing a mode of processing in Comparative Example 2.
At the inlet of the first methanation reactor 3, a raw material natural gas was mixed with an amount of water vapor having a molar ratio of water vapor to the total of carbon dioxide and hydrogen of 0.76, which is higher than that in Example 1, and the gas to be treated was diluted. By doing so, a hydrogen concentration of 2.9 mol% in the product gas could be achieved.
Comparative Example 2 required more water vapor than Example 1. In addition, since the raw natural gas was not desulfurized, the methanation catalyst was deactivated by sulfur and had to be replaced every few months.

[Evaluation of Examples and Comparative Examples]
As can be seen from the examples and comparative examples, by using the hydrogenation reactor 1 in which the catalyst layer 11 of the hydrogenation catalyst is arranged on the upstream side of the methanation reactor 3, a natural gas containing a high concentration of carbon dioxide can be obtained. When using as a raw material, compared with the case where the hydrogenation reactor 1 is not used, the number of installed stages of the methanation reactor can be reduced, and the amount of steam used can be suppressed. As described in the section of the background art, it is understood that the present invention is an extremely useful technology because it is necessary to develop a natural gas well containing a high concentration of carbon dioxide in the future. By using the hydrogenation catalyst, a methanation reaction occurs in addition to the hydrogenation reaction, and it can be expected to reduce the amount of the methanation catalyst used in the methanation reactor. Further, since carbonyl sulfide is by-produced by using a hydrogenation catalyst, it is effective to provide a carbonyl sulfide removal section.

Claims (5)

A natural gas, which is a raw material gas, and hydrogen are supplied, and a pre-stage reactor for reacting carbon dioxide and hydrogen in the natural gas to generate methane,
A post-reactor for adjusting the hydrogen concentration by reacting hydrogen and carbon dioxide remaining in the product gas discharged from the pre-reactor,
A catalyst layer of a methanation catalyst provided in each of the front-stage reactor and the rear-stage reactor,
A catalyst layer of a hydrogenation catalyst that is provided on the upstream side of the preceding-stage reactor and that has a main hydrogenation catalytic action for hydrogenating organic sulfur in natural gas to hydrogen sulfide and a methanation catalytic action,
An adsorbent layer of an adsorbent for adsorbing hydrogen sulfide, the adsorbent layer being located upstream of the pre-stage reactor and downstream of the catalyst layer of the hydrogenation catalyst. Gas processing equipment. The pre-stage reactor includes a first methanation reactor and a second methanation reactor provided on the downstream side of the first methanation reactor,
A first hydrogen supply passage for supplying hydrogen to the inlet side of the first methanation reactor; and a second hydrogen supply passage for supplying hydrogen to the inlet side of the second methanation reactor. The natural gas processing apparatus according to claim 1, wherein The catalyst layer and the adsorbent layer of the hydrogenation catalyst are arranged in a pretreatment reactor provided on the upstream side of the pre-stage reactor,
The natural gas treatment apparatus according to claim 1, further comprising a hydrogen supply passage for pretreatment for supplying hydrogen to an inlet side of the reactor for pretreatment. The pretreatment reactor is a hydrogenation reactor in which the catalyst layer of the hydrogenation catalyst is arranged, and an adsorbent desulfurization reactor in which the adsorbent layer is arranged downstream of the hydrogenation reactor. The natural gas processing apparatus according to claim 3 , further comprising:

2. A carbonyl sulfide removing unit for removing carbonyl sulfide by-produced in the catalyst layer of the hydrogenation catalyst is provided upstream of the catalyst layer of the methanation catalyst. Natural gas processing equipment.

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