AU2017404979B2

AU2017404979B2 - Treatment device for natural gas

Info

Publication number: AU2017404979B2
Application number: AU2017404979A
Authority: AU
Inventors: Nobuyasu Chikamatsu; Eri SUGI; Yoshiyuki Watanabe
Original assignee: JGC Corp
Current assignee: JGC Corp
Priority date: 2017-03-22
Filing date: 2017-03-22
Publication date: 2022-05-19
Anticipated expiration: 2037-03-22
Also published as: WO2018173143A1; AU2017404979A1; JPWO2018173143A1; JP6740458B2

Abstract

[Problem] To simplify equipment for converting carbon dioxide contained in natural gas into methane, to prolong the life of a methane formation catalyst, and to reduce the use amount thereof. [Solution] Reactors are installed in the following order from the upstream side: a hydrogenation reactor 1 in which a layer 11 of a hydrogenation catalyst has been disposed; an adsorptive desulfurization reactor 2 in which an adsorbent layer 21 for adsorbing hydrogen sulfide has been disposed; and methane formation reactors 3, 4, and 5 in which methane-formation catalyst layers 31, 41, and 51 have been disposed respectively. Hydrogen gas is mixed with natural gas, and the mixed gas is heated and fed to the hydrogenation reactor 1. Thus, the organic sulfur compounds contained in the natural gas are hydrogenated by means of the hydrogenation catalyst to become hydrogen sulfide, and a methane formation reaction takes place. In the methane formation reactors 3 and 4, hydrogen is fed to the desulfurized natural gas to cause a methane formation reaction. Furthermore, in the succeeding-stage reactor 5, the hydrogen concentration in the gas is regulated. Since hydrogenation and methane formation are conducted as pretreatments, the sulfur concentration can be kept extremely low and the amount of the methane formation catalyst to be used can be reduced.

Description

TREATMENT DEVICE FOR NATURAL GAS TECHNICAL FIELD

[0001] The present invention relates to a technical field for methanating carbon dioxide in a

natural gas through use of hydrogen.

BACKGROUND ART

[0002] A natural gas is produced under a state of containing carbon dioxide in addition to

methane serving as a main component in many cases. In order to obtain a product gas serving

as a raw material for a pipeline gas (utility gas) or a liquefied natural gas, it is required to remove

carbon dioxide. In general, carbon dioxide in the natural gas is separated and removed by an

acid gas removal unit (AGRU) mainly using amine, and is released to the atmosphere.

However, carbon dioxide is a greenhouse gas that has the largest influence on global warming,

and hence there is a demand for reduction in emission amount of carbon dioxide.

[0003] Meanwhile, high-quality gas fields containing less carbon dioxide, which have been

preferentially developed from the viewpoint of profitability, are drying up, and in the future, it

will be required to develop a natural gas well containing carbon dioxide in a higher

concentration. In view of the foregoing, as one of effective uses of carbon dioxide in the

natural gas, it is conceivable to perform methanation. However, when carbon dioxide in a high

concentration, which is separated by a carbon dioxide separation device, for example, the AGRU,

is used as a raw material, an abrupt increase in temperature of a reactor is caused by methanation

reaction heat. In addition, the increase in temperature is disadvantageous to the proceeding of

methanation that is an equilibrium reaction.

[0004] In order to suppress the increase in temperature of the reactor, in general, there are

adopted, for example, a procedure for dividing the reactor into parts and arranging a cooler

between the parts of the divided reactor, a procedure for returning a product gas produced by reaction to an inlet port of the reactor (recycling), and a procedure for adding water vapor to a raw material gas as a diluent. However, in the above-mentioned procedures, there is a problem in that the number of the reactors increases, recycling of a large amount of the product gas is required, or a large amount of water vapor is required to accompany the raw material gas.

[0005] In Patent Literature 1, there is described a method involving causing hydrogen obtained

by supplying a natural gas to a hydrogen separation reactor and carbon dioxide in the natural gas

to react with each other in the presence of a catalyst in a methanation reactor to produce methane,

to thereby reduce carbon dioxide in the natural gas.

In addition, in Patent Literature 2, there is described a technology involving mixing

hydrogen from a hydrogen gas supply line with a raw material gas containing carbon dioxide,

supplying the mixed gas to a first reactor, mixing hydrogen from the hydrogen gas supply line

with the mixed gas, supplying the mixed gas to a second reactor, and further supplying the

mixed gas to a third reactor configured to adjust a composition of a produced gas, to thereby

convert carbon dioxide in the raw material gas into methane.

[0006] In Patent Literature 1 and Patent Literature 2, there is no description of prolonging the

service life of a methanation catalyst by significantly decreasing an allowable content of sulfur

contained in the natural gas, and suppressing the usage amount of the methanation catalyst. In

the description after the fifth line in the paragraph [0037] of Patent Literature 2, the use of

hydrogen for pretreatment in a front stage of the reactor is eliminated.

Citation List

Patent Literature

[0007] Patent Literature 1: US 6,419,888 B2

Patent Literature 2: JP 2013-136538 A

SUMMARY

Technical Problem

[0008] The present invention provides a treatment device for a natural gas in which, in

methanation of carbon dioxide in a natural gas, the life of a methanation catalyst is prolonged

and the usage amount thereof is reduced while a facility is simplified.

Solution to Problem

[0009] According to one embodiment of the present invention, there is provided a treatment

device for a natural gas, including: a front stage reactor, configured to receive a natural gas that

is a raw material gas and a hydrogen and to cause a carbon dioxide in the natural gas and the

hydrogen to react with each other, to thereby produce a methane; a rear stage reactor, configured

to cause the hydrogen and the carbon dioxide, which remain in a produced gas discharged from

the front stage reactor, to react with each other, to thereby adjust a hydrogen concentration; a

catalyst bed of a methanation catalyst, provided in each of the front stage reactor and the rear

stage reactor; a catalyst bed of a hydrogenation catalyst, provided on an upstream side from the

front stage reactor, and has a methanation catalysis together with a main hydrogenation catalysis

of hydrogenating an organic sulfur in the natural gas, so as to convert the organic sulfur into a

hydrogen sulfide; and an adsorbent bed of an adsorbent, positioned on an upstream side from the

front stage reactor and arranged on a downstream side from the catalyst bed of the

hydrogenation catalyst, and is configured to adsorb the hydrogen sulfide.

Advantageous Effects of Invention

[0010] In the present invention, in methanation of carbon dioxide in the natural gas, the natural

gas is supplied to the reactor as a raw material gas, and hence a component other than carbon

dioxide in the natural gas can be used as a diluent for a methanation reaction. Therefore, an

increase in temperature of the methanation reaction is suppressed, and hence a facility can be simplified. In addition, organic sulfur in the natural gas is converted into hydrogen sulfide and removed by adsorption with the adsorbent on the upstream side of the methanation reactor.

Therefore, the service life of the methanation catalyst is prolonged, and methanation is caused to

proceed by the hydrogenation catalyst, with the result that the usage amount of the methanation

catalyst in a rear stage can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 is a configuration diagram for illustrating a treatment device for a natural gas

according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram for illustrating one example of a device configuration

for effectively using discharged water obtained in the first embodiment.

FIG. 3 is a configuration diagram for illustrating another example of the device

configuration for effectively using discharged water obtained in the first embodiment.

FIG. 4 is an explanatory diagram for illustrating an application example of the first

embodiment.

FIG. 5 is a graph for showing a relationship between the concentration of carbon

dioxide in the natural gas and the concentration of carbonyl sulfide (COS) after a hydrogenation

reaction.

FIG. 6 is a configuration diagram for illustrating a treatment device for a natural gas

according to a second embodiment of the present invention.

FIG. 7 is a configuration diagram for illustrating a modification example of the

treatment device for a natural gas according to the second embodiment of the present invention.

FIG. 8 is an explanatory diagram for illustrating a mode of Example 1 corresponding to

the first embodiment of the present invention.

FIG. 9 is an explanatory diagram for illustrating a mode of Example 2 corresponding to

the second embodiment of the present invention.

FIG. 10 is an explanatory diagram for illustrating a mode of Example 3 corresponding

to the modification example of the second embodiment of the present invention.

FIG. 11 is an explanatory diagram for illustrating a mode of Comparative Example 1

for comparison to the present invention.

FIG. 12 is an explanatory diagram for illustrating a mode of Comparative Example 2

for comparison to the present invention.

DESCRIPTION OF EMBODIMENTS

[0012] [First Embodiment]

As illustrated in FIG. 1, in a treatment device for a natural gas according to a first

embodiment of the present invention, a hydrogenation reactor 1, an adsorptive desulfurization

reactor 2, a first methanation reactor 3, a second methanation reactor 4, and a rear stage reactor 5

that is a methanation reactor are arranged in the stated order from an upstream side. The

adsorptive desulfurization reactor 2 is configured to adsorb hydrogen sulfide. The first

methanation reactor 3 and the second methanation reactor 4 each form a front stage reactor.

Each of the reactors 1 to 5 is constructed as an adiabatic reactor. In the following description,

for convenience sake, a flow passage for the natural gas connected to an upstream side of the

hydrogenation reactor 1 is referred to as "raw material gas supply passage", a flow passage for a

gas from the hydrogenation reactor 1 to the rear stage reactor 5 is referred to as "gas flow

passage", and a flow passage for a gas to be taken out from the rear stage reactor 5 is referred to

as "produced gas outflow passage".

[0013] A raw material gas supply passage 101 is connected to a top of column of the

hydrogenation reactor 1 through a heater 102, and a hydrogen supply line 200 for pretreatment is

connected to an upstream side of the heater 102. An AGRU (103) represented by the dotted

line is described later.

Of the two reactors adjacent to each other when viewed based on the flow passage for a gas in the arrangement of each of the reactors 1 to 5, a bottom of column of the reactor on an upstream side and a top of column of the reactor on a downstream side are connected to each other through gas flow passages 10, 20, 30, and 40, respectively.

[0014] In the hydrogenation reactor 1, there is arranged a catalyst bed 11 of a hydrogenation

catalyst configured to convert organic sulfur contained in the natural gas into hydrogen sulfide.

The hydrogenation catalyst contains, for example, an inorganic oxide support containing

aluminum, a first metal component selected from molybdenum and tungsten, and a second metal

component selected from cobalt, nickel, and chromium. In this example, the hydrogenation

catalyst is used under a state in which the metal components are sulfurized. In addition, the

hydrogenation catalyst has a methanation catalysis together with a main hydrogenation catalysis

of hydrogenating an organic sulfur in the natural gas, so as to convert the organic sulfur into

hydrogen sulfide.

[0015] In the adsorptive desulfurization reactor 2, there is arranged an adsorbent bed 21 of an

adsorbent configured to adsorb hydrogen sulfide. As the adsorbent, for example, a granular

body of zinc oxide can be used. In addition, as the adsorbent, a carrier made of an inorganic

oxide such as alumina or silica, on which a metal such as iron or copper is carried, may be used.

[0016] A cooler 22 is provided to the gas flow passage 20 configured to supply a gas having

flowed out from the adsorptive desulfurization reactor 2 to the first methanation reactor 3.

When the device is operated under an operation condition in which an inlet temperature of the

first methanation reactor 3 is lower than an outlet temperature of the adsorptive desulfurization

reactor 2, the cooler 22 is required. However, when the device is operated under an operation

condition in which the inlet temperature of the first methanation reactor 3 is the same as the

outlet temperature of the adsorptive desulfurization reactor 2, the cooler 22 is not required.

As one example of the operation condition, the inlet temperature of each of the front

stage methanation reactor (first methanation reactor 3 and second methanation reactor 4) and the

rear stage methanation reactor 5 is set to, for example, from 200°C to 300°C, and the temperature in the adsorptive desulfurization reactor 2 is set to from 300°C to 350°C. In this example, the inlet temperature of the first methanation reactor 3 is set to 250°C, and the temperature in the adsorptive desulfurization reactor 2 is set to 300°C. Therefore, a gas having flowed out from the adsorptive desulfurization reactor 2 is cooled by the cooler 22.

[0017] A first hydrogen supply line 201 and a water vapor supply passage 203 are connected

between the cooler 22 in the gas flow passage 20 and the top of column of the first methanation

reactor 3. In the first methanation reactor 3, a catalyst bed 31 of a methanation catalyst is

arranged. As the methanation catalyst, a particulate catalyst containing nickel as a main

component (for example, in an amount of from 40 mass% to 60 mass% with respect to the entire

catalyst) can be used. In addition, as the methanation catalyst, a catalyst in which ruthenium is

carried on an inorganic oxide such as alumina or silica can also be used.

In the second methanation reactor 4 and the rear stage methanation reactor 5, catalyst

beds 41 and 51 using the similar methanation catalyst are arranged, respectively.

[0018] A cooler 32 is provided to the gas flow passage 30 configured to supply the gas having

flowed from the first methanation reactor 3 to the second methanation reactor 4, and a second

hydrogen supply line 202 is connected to a downstream side of the cooler 32. In addition, a

cooler 42 is provided also to the gas flow passage 40 configured to supply the gas having flowed

from the second methanation reactor 4 to the rear stage methanation reactor 5. In the first

methanation reactor 3 and the second methanation reactor 4, a methanation reaction occurs. In

the methanation reaction, carbon dioxide (carbon dioxide gas) and hydrogen (hydrogen gas)

react with each other to produce methane. This reaction is an exothermic reaction, and hence

each outlet temperature of the methanation reactors 3 and 4 becomes higher than each inlet

temperature of the methanation reactors 3 and 4. Therefore, the gas having flowed from each

of the methanation reactors 3 and 4 is cooled by the cooler 32(42).

The hydrogen supply line 200 for pretreatment, the first hydrogen supply line 201, and

the second hydrogen supply line 202 are connected to, for example, a common hydrogen supply source, and valves VO, VI, and V2 for flow rate adjustment are provided to the hydrogen supply line 200 for pretreatment, the first hydrogen supply line 201, and the second hydrogen supply line 202, respectively. In addition, a valve V3 for flow rate adjustment is provided to the water vapor supply passage 203.

[0019] The rear stage methanation reactor 5 is provided in order to cause excess hydrogen

contained in the gas to react with carbon dioxide to set a hydrogen concentration in a produced

gas after treatment within a predetermined concentration range. One end side of a produced

gas flow passage 50 is connected to a bottom of column of the rear stage methanation reactor 5,

and another end side of the produced gas flow passage 50 is connected to a gas-liquid separation

drum 53 through a cooler 52. The gas-liquid separation drum 53 is configured to separate and

remove moisture (discharged water) from a produced gas having flowed from the rear stage

methanation reactor 5 and cooled, and the produced gas having moisture separated therefrom is

taken out as, for example, a product gas.

[0020] Next, the action of the first embodiment is described. First, a natural gas that is a raw

material gas passes through the raw material gas supply passage 101 to be mixed with a

hydrogen gas for pretreatment fed from the hydrogen supply line 200 for pretreatment, and is

heated to, for example, from 250°C to 350°C by the heater 102. The heated mixed gas is

supplied into the hydrogenation reactor 1, and a hydrogenation reaction mainly occurs.

Specifically, organic sulfur contained in the natural gas is converted into hydrogen sulfide with a

hydrogenation catalyst forming the catalyst bed 11. The hydrogenation catalyst has the

methanation catalysis in addition to the hydrogenation catalysis as described above. Therefore,

a methanation reaction also proceeds in the hydrogenation reactor 1, and a part of carbon dioxide

in the natural gas reacts with hydrogen to produce methane.

[0021] The methanation reaction that is an exothermic reaction occurs, and hence the

temperature of the gas on an outlet side of the hydrogenation reactor 1 is higher than the

temperature of the gas on an inlet side thereof by, for example, from 10°C to 100°C. The amount of hydrogen to be supplied to the hydrogenation reactor 1 is set to an amount, which is sufficient for hydrogenating organic sulfur, or more (for example, from 1 mol% to 2 mol%), and is set to, for example, 10 mol% or less in consideration of the heat-resistant temperature of the hydrogenation catalyst. The gas having flowed from the hydrogenation reactor 1 is fed into the adsorptive desulfurization reactor 2, and an adsorbent forming the adsorbent bed 21 adsorbs hydrogen sulfide in the gas, with the result that desulfurization is performed. With this, the concentration of sulfur in the gas having flowed from the adsorptive desulfurization reactor 2 reaches 0.1 ppm or less. The concentration unit "ppm" as used herein represents a molar concentration.

In order to decrease a load of the adsorbent in the adsorptive desulfurization reactor 2,

when the concentration of sulfur in the natural gas is high, the acid gas removal unit (AGRU)

(103) may be used in the raw material gas supply passage 101 as represented by the dotted line

in FIG. 1. For example, the AGRU (103) is configured to supply the natural gas from a bottom

of column side of an amine contact column to cause the natural gas to flow from a top of column

thereof, and is configured to supply a liquid of amine from an upper portion side of the amine

contact column to bring the liquid of amine into countercurrent contact with the natural gas.

Through contact of the natural gas with the liquid of amine, hydrogen sulfide in the natural gas

is removed.

[0022] The gas that has been subjected to so-called pretreatment, in which desulfurization

mainly occurs, and methanation additionally proceeds, flows out from the adsorptive

desulfurization reactor 2. After that, the gas is cooled to, for example, 250°C by the cooler 22,

and is mixed with hydrogen and water vapor to be fed to the first methanation reactor 3. In the

first methanation reactor 3, the methanation reaction occurs. In the methanation reaction,

carbon dioxide and hydrogen react with each other to produce methane in the catalyst bed 31 of

a methanation catalyst. The flow rate of hydrogen supplied from the first hydrogen supply line

201 is regulated so that the temperature on an outlet side of thefirst methanation reactor 3 reaches, for example, 540°C or less in consideration of the heat-resistant temperatures of the methanation catalyst and a methanation reactor material, when the hydrogen supplied from the first hydrogen supply line 201 causes the methanation reaction together with hydrogen remaining in the gas having flowed from the adsorptive desulfurization reactor 2.

[0023] Water vapor is supplied in order to prevent deterioration of activity caused by caulking

of the methanation catalyst, but also serves to further suppress the temperature in each of the

methanation reactors 3, 4, and 5. The supply amount of water vapor is set so that the molar

ratio of water vapor with respect to a total of carbon dioxide and hydrogen reaches, for example,

0.6 [molar concentration of water vapor / (molar concentration of carbon dioxide + molar

concentration of hydrogen)] at an inlet of the first methanation reactor 3. Water vapor is not

always required to be supplied and may not be used.

[0024] The gas having flowed from the first methanation reactor 3 is cooled to, for example,

250°C by the cooler 32 and fed to the second methanation reactor 4. Hydrogen is refilled and

supplied into the second methanation reactor 4 through the gas flow passage 30 from the second

hydrogen supply line 202 so that, in the second methanation reactor 4, the hydrogen

concentration reaches a value associated with the concentration of carbon dioxide remaining in

the gas, and so that the temperature on an outlet side of the second methanation reactor 4 reaches,

for example, 540°C or less. Then, the methanation reaction occurs in the catalyst bed 41, and

the gas having the concentration of carbon dioxide reduced is cooled to, for example, 250°C by

the cooler 42 to be fed to the rear stage reactor 5.

[0025] The gas having been increased in temperature in the second methanation reactor 4 is

cooled and supplied to the rear stage reactor 5. Therefore, the methanation reaction further

proceeds in the catalyst bed 51 of a methanation catalyst in the rear stage reactor 5, and carbon

dioxide and hydrogen are reduced, with the result that the hydrogen concentration in a product

gas is adjusted to an allowable concentration, for example, 3 mol% or less. The produced gas

having flowed from the rear stage reactor 5 is cooled to a temperature, at which water is condensed, or less by the cooler 52, for example, 50°C. Then, the produced gas is separated into a gas and water in the gas-liquid separation drum 53 that is a gas-separation unit to obtain a product gas.

In the foregoing, the pressure in each of the reactors 1 to 5 is set to, for example, from 1

MPa to 8 MPa. In addition, the number of stages of the front stage reactor (first methanation

reactor 3 and second methanation reactor 4 in the above-mentioned example) is determined in

accordance with the concentration of carbon dioxide in the natural gas. When it is assumed

that water vapor is used as described above, the number of the front stage reactors is set to one

when the concentration of carbon dioxide is 25 mol% or less, two when the concentration of

carbon dioxide is 40 mol% or less, and three when the concentration of carbon dioxide is 70

mol% or less.

[0026] In order to suppress the number of the methanation reactors in the case of using a

natural gas containing carbon dioxide in a high concentration, it is only required that a unit

configured to remove a part of carbon dioxide in the natural gas be provided on the upstream

side from the hydrogenation reactor 1. In addition, when the concentration of carbon dioxide in

the natural gas is lower than 3 mol%, the natural gas can be directly used as a pipeline gas.

Therefore, it can be considered that the natural gas used as a raw material gas contains carbon

dioxide in a concentration of 3 mol% or more.

[0027] According to the above-mentioned embodiment, methanation is performed through use

of a gas other than carbon dioxide in the natural gas as a diluent gas, and the reactor configured

to perform methanation is divided into a plurality of stages, for example, two stages of the

methanation reactors 3 and 4 so that hydrogen is supplied thereto, respectively. With this, the

number of the reactors configured to perform methanation can be suppressed, and the device can

be simplified. The concentration of sulfur in the natural gas is reduced to 0.1 ppm or less

through use of the hydrogenation catalyst and the adsorbent of hydrogen sulfide on the upstream

side of each of the methanation reactors 3 and 4. Therefore, the service life of the methanation catalyst can be prolonged. In addition, through use of the hydrogenation catalyst, the methanation reaction occurs in addition to the hydrogenation reaction, and hence the usage amount of the methanation catalyst in the methanation reactors 3 and 4 can be suppressed.

[0028] Now, description is given of configuration examples for effectively using energy or a

gas in the above-mentioned treatment device for a natural gas or a system including the

treatment device.

As illustrated in FIG. 2, discharged water separated in the gas-liquid separation drum 53

is used as cooling media of the coolers 22, 32, 42, and 52, and the water vapor obtained by

vaporization with heat in the methanation reaction is supplied from the water vapor supply

passage 203 to the first methanation reactor 3.

Similarly, as illustrated in FIG. 3, the water vapor obtained by vaporization with heat in

the methanation reaction is supplied to a steam turbine 302 configured to drive a pressure

boosting compressor 301 provided in a hydrogen supply line 300 on an upstream side from a

joining site of each of the hydrogen supply lines 200, 201, and 202.

Discharged water separated in the gas-liquid separation drum 53 is electrolyzed in an

electrolytic device, and hydrogen thus obtained is supplied into a treatment system through each

of the hydrogen supply lines 200, 201, and 202.

[0029] As illustrated in FIG. 4, in a system having a configuration in which a liquefied natural

gas (LNG) production facility 400 is arranged in a rear stage of the treatment device for a natural

gas, discharged water separated in the gas-liquid separation drum 53 or water supplied from

another water supply source is vaporized with heat in the methanation reaction to obtain water

vapor, and the water vapor is used as a heat source for a stripping column reboiler of an AGRU

in the LNG production facility 400. In addition, as illustrated in FIG. 4, carbon dioxide

recovered by the AGRU in the LNG production facility 400 is returned to the upstream side of

the first methanation reactor 3 to be recycled, to thereby suppress the discharge of carbon

dioxide and increase the production amount of a product gas.

[0030] [Second Embodiment]

When a natural gas containing carbon dioxide and sulfur is supplied to a hydrogenation

catalyst, carbonyl sulfide is produced as a by-product. Therefore, a treatment device for a

natural gas according to a second embodiment of the present invention adopts a configuration in

which countermeasures are taken against carbonyl sulfide (COS). FIG. 5 is a graph for

showing a relationship between the concentration of carbon dioxide in the natural gas and the

concentration of carbonyl sulfide after the hydrogenation reaction. When sulfur in the natural

gas is 1 ppm, and the concentration of carbon dioxide in the natural gas is 64 mol%, the

production amount of carbonyl sulfide is significantly small, that is, as small as 0.095 ppm as

represented by the symbol A. Meanwhile, when sulfur in the natural gas is 10 ppm, as

represented by the symbol A, even in the case in which the concentration of carbon dioxide in

the natural gas is several percent, the production amount of carbonyl sulfide exceeds 0.1 ppm

and increases substantially in proportion to an increase in concentration of carbon dioxide, with

the result that the service life of the methanation catalyst is further shortened due to poisoning.

Thus, when a natural gas containing sulfur in a high concentration is used as a 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 significantly increases.

[0031] In view of the foregoing, in the second embodiment, as illustrated in FIG. 6, there is

provided a carbonyl sulfide adsorption reactor 6 on an upstream side of thefirst methanation

reactor 3, for example, between the adsorptive desulfurization reactor 2 and thefirst methanation

reactor 3. The carbonyl sulfide adsorption reactor 6 is a carbonyl sulfide removal unit in which

an adsorption bed 61 made of an adsorbent configured to adsorb carbonyl sulfide is arranged.

There is illustrated a gas flow passage 60. As the adsorbent of carbonyl sulfide, it is possible to

use, for example, an adsorbent in which copper is carried on a carrier made of an inorganic oxide

such as alumina or silica, or a copper-based adsorbent such as a granular body or a molded body

of copper oxide.

[0032] In addition, instead of separately providing the adsorptive desulfurization reactor 2 and

the carbonyl sulfide adsorption reactor 6, only a copper-based adsorbent may be used as an

adsorptive desulfurization agent used in the adsorptive desulfurization reactor 2 so that the

adsorbent is caused to adsorb hydrogen sulfide and carbonyl sulfide. However, the cost of the

copper-based adsorbent is high. Therefore, from the viewpoint of cost, it is advantageous to

adopt the configuration illustrated in FIG. 6, and use a zinc-based adsorbent, for example, an

adsorbent made of zinc oxide in the adsorptive desulfurization reactor 2 and use, for example, a

copper-based adsorbent in the carbonyl sulfide adsorption reactor 6. In this case, the usage

amount of the copper-based adsorbent can be suppressed. In addition, instead of providing the

carbonyl sulfide adsorption reactor 6, the zinc-based adsorbent and the copper-based adsorbent

may be arranged in the stated order from an upstream side in the adsorptive desulfurization

reactor 2.

Further, in place of the configuration illustrated in FIG. 6, the adsorbent of carbonyl

sulfide may be provided in an upper portion of the catalyst bed 31 in thefirst methanation

reactor 3.

[0033] FIG. 7 is a diagram for illustrating a modification example of the second embodiment.

In this example, instead of adsorbing carbonyl sulfide with an adsorbent, a hydrolysis reactor 7

configured to remove carbonyl sulfide by hydrolysis 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 so that water vapor is supplied to the hydrolysis reactor 7 through a

water vapor supply passage 204. As a catalyst configuring a catalyst bed 71 configured in the

hydrolysis reactor 7, for example, a catalyst in which, for example, chromium is carried on a

carrier of alumina or titanium oxide can be used. The operation temperature of the hydrolysis

reactor 7 is lower than each operation temperature of the hydrogenation reactor 1 and the

adsorptive desulfurization reactor 2. Therefore, a cooler 72 is provided on an upstream side of

the hydrolysis reactor 7, and a heater 73 is provided on a downstream side thereof. There is illustrated a gas flow passage 70.

According to the second embodiment, carbonyl sulfide that is produced as a by-product

with the hydrogenation catalyst is removed, and hence poisoning of the methanation catalyst is

suppressed.

EXAMPLE

[0034] Now, examples (Examples and Comparative Examples) in which a natural gas is treated

through simulation are 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 in the first embodiment to obtain a product gas containing carbon

dioxide in a concentration of 2 mol%. FIG. 8 is an explanatory diagram for illustrating a mode

(for example, a concentration and a temperature of each component in a gas) of the treatment in

Example 1.

Hydrogen was mixed with a raw material natural gas so as to obtain 10 mol% of

hydrogen at an inlet of the hydrogenation reactor 1. The mixture was heated to 250°C by the

heater 102 and supplied to the hydrogenation reactor 1. Through occurrence of a methanation

reaction in the hydrogenation reactor 1, an outlet temperature of the hydrogenation reactor 1 was

increased to 340°C, and the concentration of carbon dioxide reached 35 mol%.

Sulfur was in a form of hydrogen sulfide at an outlet of the hydrogenation reactor 1, and

was removed by adsorption in the adsorptive desulfurization reactor 2. It was confirmed that

the concentration of sulfur at an outlet of the adsorptive desulfurization reactor 2 was 0.1 ppm or

less. With this, a downstream methanation catalyst can be used for from two years to four

years.

[0035] The gas having passed through the adsorptive desulfurization reactor 2 was cooled so

that an inlet temperature of the first methanation reactor 3 reached 250°C. Hydrogen and water vapor in such amounts that an outlet temperature of the first methanation reactor 3 reached

540°C were mixed with the cooled gas. The resultant gas was supplied to the first methanation

reactor 3. The supply amount (mixed amount) of the water vapor was set to such an amount

that a molar ratio of the water vapor with respect to a total of carbon dioxide and hydrogen

reached 0.6 at an inlet of the first methanation reactor 3.

The gas having passed through the first methanation reactor 3 was cooled so that an

inlet temperature of the second methanation reactor 4 reached 250°C. Hydrogen in an amount

of being able to adjust the concentration of carbon dioxide in a product gas to 2 mol% was

mixed with the cooled gas. The resultant gas was supplied to the second methanation reactor 4.

An outlet temperature of the second methanation reactor 4 was increased to 464°C by the

methanation reaction, and the gas having flowed from the second methanation reactor 4 was

cooled so that an inlet temperature of the rear stage methanation reactor 5 reached 250°C.

After that, the cooled gas was supplied to the rear stage methanation reactor 5.

In the rear stage methanation reactor 5, remaining hydrogen and carbon dioxide reacted

with each other, and an outlet temperature of the rear stage methanation reactor 5 was increased

to 304°C. The gas having flowed from the rear stage methanation reactor 5 was cooled to 50°C

by the cooler 52. After that, water was separated from the gas in the gas-liquid separation drum

53, and thus a product gas containing 2 mol% of carbon dioxide and 3 mol% of hydrogen was

able to be obtained.

[0036] [Example 2]

Example 2 is an example in which a natural gas containing 40 mol% of carbon dioxide

and 10 ppm of sulfur was treated through use of the carbonyl sulfide adsorption reactor 6 in the

second embodiment to obtain a product gas containing carbon dioxide in a concentration of 2

mol%. FIG. 9 is an explanatory diagram for illustrating a mode of the treatment in Example 2.

Hydrogen was mixed with a raw material natural gas so as to obtain 10 mol% of

hydrogen at an inlet of the hydrogenation reactor 1. The mixture was heated to 250°C by the heater 102 and supplied to the hydrogenation reactor 1. Through occurrence of a methanation reaction in the hydrogenation reactor 1, an outlet temperature of the hydrogenation reactor 1 was increased to 340°C, and the concentration of carbon dioxide reached 35 mol%. At the outlet of the hydrogenation reactor 1, sulfur was contained in the gas as carbonyl sulfide produced as a by-product in addition to the form of hydrogen sulfide. The concentration of carbonyl sulfide in the gas was 0.7 ppm.

Hydrogen sulfide was removed by adsorption in the adsorptive desulfurization reactor 2,

but carbonyl sulfide, which has not been adsorbed, flowed out from the outlet of the adsorptive

desulfurization reactor 2. The gas having flowed out from the adsorptive desulfurization

reactor 2 was supplied to the carbonyl sulfide adsorption reactor 6 on a downstream side, with

the result that the concentration of sulfur at an outlet of the carbonyl sulfide adsorption reactor 6

reached 0.1 ppm or less.

The treatment on the downstream side from the carbonyl sulfide adsorption reactor 6 is

the same as that given in Example 1.

[0037] [Example 3]

Example 3 is an example in which a natural gas containing 40 mol% of carbon dioxide

and 10 ppm of sulfur was treated through use of the carbonyl sulfide hydrolysis reactor 7 in the

mol%. FIG. 10 is an explanatory diagram for illustrating a mode of the treatment in Example 3.

Hydrogen was mixed with a raw material natural gas so as to obtain a hydrogen

concentration of 10 mol% at an inlet of the hydrogenation reactor 1. The mixture was heated to

250°C by the heater 102 and supplied to the hydrogenation reactor 1. Through occurrence of a

methanation reaction in the hydrogenation reactor 1, an outlet temperature of the hydrogenation

reactor 1 was increased to 340°C, and the concentration of carbon dioxide reached 35 mol%.

[0038] At the outlet of the hydrogenation reactor 1, sulfur was contained in the gas as carbonyl

sulfide produced as a by-product in addition to the form of hydrogen sulfide. The concentration of carbonyl sulfide in the gas was 0.7 ppm.

The gas having flowed from the hydrogenation reactor 1 was cooled by the cooler 72 so

that an inlet temperature of the hydrolysis reactor 7 reached 150°C. After that, water vapor was

mixed with the cooled gas so that the concentration of water vapor reached 5 mol%. The

resultant gas was supplied to the hydrolysis reactor 7. Through hydrolysis (conversion into

hydrogen sulfide) of carbonyl sulfide, the concentration of carbonyl sulfide at an outlet of the

hydrolysis reactor 7 reached 0.1 ppm or less.

The gas having flowed 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 removed by

adsorption, and the concentration of sulfur at the outlet of the adsorptive desulfurization reactor

2 reached 0.1 ppm or less.

The treatment on the downstream side from the adsorptive desulfurization reactor 2 is

the same as that given in Example 1.

[0039] [Comparative Example 1]

Comparative Example 1 is an example in which a product gas containing carbon

dioxide in a concentration of 2 mol% is obtained from the same raw material natural gas as that

of Example 1 containing 40 mol% of carbon dioxide and 1 ppm of sulfur without utilizing the

hydrogenation reactor 1 and the adsorptive desulfurization reactor 2. FIG. 11 is an explanatory

diagram for illustrating a mode of the treatment in Comparative Example 1 using a device

having the configuration illustrated in FIG. 1 excluding the hydrogenation reactor 1 and the

adsorptive desulfurization reactor 2.

A gas containing carbon dioxide in a higher concentration as compared to that of

Example 1 was supplied to a methanation reaction unit, and hence the amount of heat generated

by the methanation reaction was large. As a result, the outlet temperature of the second

methanation reactor 4 reached 487°C, and the outlet temperature of the rear stage methanation

reactor 5 reached 316°C.

The methanation reaction being an equilibrium reaction was inhibited by the increase in

temperature, and in order to obtain a product gas containing carbon dioxide in a concentration of

2 mol%, excess hydrogen was required to be supplied, with the result that the hydrogen

concentration of the product gas reached 4 mol% that was higher than that of Example 1. In

order to achieve the hydrogen concentration of the product gas in Example 1, it was required to

add the third methanation reactor.

In addition, the raw material natural gas has not been desulfurized, and hence the

methanation catalyst was deactivated by sulfur, with the result that it was required to replace the

methanation catalyst every several months.

[0040] [Comparative Example 2]

Comparative Example 2 is an example in which the hydrogen concentration equal to

that given in Example 1 is achieved by diluting the raw material natural gas with water vapor

instead of adding the methanation reactor in Comparative Example 1. FIG. 12 is an

explanatory diagram for illustrating a mode of the treatment in Comparative Example 2.

At the inlet of the first methanation reactor 3, water vapor in such an amount that the

molar ratio of the water vapor with respect to a total of carbon dioxide and hydrogen reached

0.76 that was higher than that given in Example 1 was mixed with a raw material natural gas,

and the treated gas was diluted, to thereby achieve the hydrogen concentration of the product gas

of 2.9 mol%.

In Comparative Example 2, water vapor in an amount larger than that in Example 1 was

required. In addition, the raw material natural gas has not been desulfurized, and hence the

methanation catalyst every several months.

[0041] [Evaluation of Examples and Comparative Examples]

As is understood from Examples and Comparative Examples, through use of the

hydrogenation reactor 1, in which the catalyst bed 11 of a hydrogenation catalyst is arranged, on the upstream side of the methanation reactor 3, when a natural gas containing carbon dioxide in a high concentration is used as a raw material, the number of set stages of the methanation reactor can be reduced, and in addition, the usage amount of water vapor can also be suppressed, as compared to the case in which the hydrogenation reactor 1 is not used. As described in the section of the Background Art, it will be required to develop a natural gas well containing carbon dioxide in a high concentration in the future, and hence it is understood that the present invention is a significantly useful technology. Through use of the hydrogenation catalyst, the methanation reaction also occurs in addition to the hydrogenation reaction, and the usage amount of the methanation catalyst in the methanation reactor can be expected to be reduced. In addition, through use of the hydrogenation catalyst, carbonyl sulfide is produced as a by-product, and hence it is effective to provide the carbonyl sulfide removal unit.

Claims

1. A treatment device for a natural gas, comprising:

a front stage reactor, configured to receive a natural gas that is a raw material gas and a

hydrogen and to cause a carbon dioxide in the natural gas and the hydrogen to react with each

other, to thereby produce a methane;

a rear stage reactor, configured to cause the hydrogen and the carbon dioxide, which

remain in a produced gas discharged from the front stage reactor, to react with each other, to

thereby adjust a hydrogen concentration;

a catalyst bed of a methanation catalyst, provided in each of the front stage reactor and

the rear stage reactor;

a catalyst bed of a hydrogenation catalyst, provided on an upstream side from the front

stage reactor, and has a methanation catalysis together with a main hydrogenation catalysis of

hydrogenating an organic sulfur in the natural gas, so as to convert the organic sulfur into a

hydrogen sulfide; and

an adsorbent bed of an adsorbent, positioned on an upstream side from the front stage

reactor and arranged on a downstream side from the catalyst bed of the hydrogenation catalyst,

and is configured to adsorb the hydrogen sulfide.

2. The treatment device for a natural gas according to claim 1, wherein the front stage

reactor comprises:

a first methanation reactor; and

a second methanation reactor, provided on a downstream side of the first methanation

reactor, and

wherein a first hydrogen supply line is provided and configured to supply the hydrogen

on an inlet side of the first methanation reactor, and a second hydrogen supply line is provided and configured to supply the hydrogen on an inlet side of the second methanation reactor.

3. The treatment device for a natural gas according to claim 1, wherein

the catalyst bed of the hydrogenation catalyst and the adsorbent bed are arranged in a

pretreatment reactor provided on the upstream side of the front stage reactor, and

a hydrogen supply line for pretreatment is provided and configured to supply the

hydrogen on an inlet side of the pretreatment reactor.

4. The treatment device for a natural gas according to claim 3, wherein the pretreatment

reactor comprises:

a hydrogenation reactor, in which the catalyst bed of the hydrogenation catalyst is

arranged; and

an adsorptive desulfurization reactor, which is provided on a downstream side of the

hydrogenation reactor, and in which the adsorbent bed is arranged.

5. The treatment device for a natural gas according to claim 1, further comprising:

a carbonyl sulfide removal unit, which is configured to remove a carbonyl sulfide

produced as a by-product in the catalyst bed of the hydrogenation catalyst, provided on an

upstream side from the catalyst bed of the methanation catalyst.