JP2014198789A - Methane-rich gas production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a methane-rich gas production system having, as a whole system, reduced load in terms of equipment cost, energy consumption, and amount of supplied water vapor.SOLUTION: The methane-rich gas production system is constituted so that a raw material gas flows through in order of a carbon monoxide shift reaction apparatus 2, a desulfurization apparatus 3, a methanation reaction apparatus 4, and a carbon dioxide removal apparatus 5. The system comprises water vapor introduction means for introducing water vapor into the raw material gas, and a recycle path 4d for returning a portion of a gas including carbon dioxide which is transmitted from an outlet part of any of methanation reactors 4a constituting the methanation reaction apparatus 4, to an inlet part of the first-stage methanation reactor 4a with components of the gas unchanged. At an inlet part of the recycle path 4d, gas distribution means is disposed so that a gas delivered from any of the methanation reactors 4a can be supplied and the recycle gas can be distributed into the recycle path 4d.

Description

  The present application relates to a carbon monoxide shift reaction facility for adjusting the ratio of hydrogen and carbon monoxide contained in the raw material gas, a desulfurization facility for performing a desulfurization process for removing sulfur from the gas flowing inside, A carbon dioxide removal facility for removing carbon dioxide from the circulating gas and a raw material gas in which the ratio of hydrogen and carbon monoxide is adjusted through the carbon monoxide shift reaction facility and a catalytic reaction A methanation reaction facility for generating methane from the hydrogen and carbon monoxide, the methanation reaction facility is configured to have one or more methanation reactors, and through the methanation reactor The present invention relates to a methane rich gas production system including a recycling path for returning generated methane rich gas to the raw material gas.

  Today, a methanation technique using a catalyst has attracted attention as a technique for producing methane-rich gas from synthesis gas (also called coal gas) obtained by coal gasification.

In such a methanation system, the ratio of carbon monoxide (CO) and hydrogen (H ₂ ) of synthesis gas generated by coal gasification is adjusted to 1: 3 suitable for methanation by a shift reaction, A methanation reaction is generated to obtain a methane rich gas.
The methanation reaction here is an exothermic reaction described by the following formula.

CO + 3H ₂ ＣＨ CH ₄ + H ₂ O + Q (exothermic reaction)

  Usually, since a catalytic reaction is used for the methanation reaction, in order to suppress poisoning of the catalyst, poisoning components are removed from the synthesis gas. Furthermore, in order to obtain methane-rich product gas, carbon dioxide, which is an unnecessary component, is removed before methanation.

In Patent Document 1, as shown in the figure, a coal gasification facility 12, a catalyst poisoning substance removal facility 14, a carbon monoxide shift reaction facility 16, a carbon dioxide removal facility 18, and a methanation reaction facility 20 are arranged in the order of description. A system comprising the above is disclosed.
In this system, a recycle path 27 for returning a part of the methane rich gas obtained from the methanation reaction facility 20 to the inlet of the methanation reaction facility 20 is provided.
In this system, a catalyst poisoning substance removal facility 14 and a carbon dioxide removal facility 18 are provided upstream of the methanation reaction facility 20.

In Patent Document 2, as shown in FIG. 1, a coal gasification facility (provided upstream of the synthesis gas stream 102), a desulfurization facility 104, a carbon monoxide shift reaction facility 112, a methanation reaction facility 120, 160, A system including 170 and carbon dioxide removal equipment 184 in the order of description is disclosed.
This system comprises a shift reaction facility and a plurality of methanation reactors 120, 160, 170 connected in series, and carbon dioxide is produced from methane-rich gas produced through the first-stage methanation reactor 120. After removal by the carbon removal unit 114, recycling paths 142 and 146 for returning to the raw material gas introduced into the first-stage methanation reactor 120 are provided.
In this system, carbon dioxide removal facilities 184 and 114 are provided on the most downstream side in the gas flow direction and on the recycling path, respectively. These carbon dioxide removal facilities are described as “can be removed by cryogenic cooling, by physical absorption, or by chemical solvent extraction methods” (paragraph [0059]).

GB 2018818 A Special table 2012-514039 gazette

The methanation reaction is an equilibrium reaction, and the lower the reaction temperature, the more the methanation proceeds and the equilibrium is shifted in the direction of increasing the amount of methane produced. Therefore, it is preferable to make the reaction temperature of the methanation reaction as low as possible. In order to reduce the reaction temperature (specifically, the gas temperature at the outlet of the methanation reactor), a part of the gas at the outlet of the methanation reactor is recycled to the inlet of the methanation reactor. The raw material components CO and H ₂ are diluted to suppress an increase in temperature due to an exothermic reaction.

  However, in the study by the inventors, as disclosed in Patent Document 1, when a configuration in which carbon dioxide is removed from the raw material gas on the upstream side of the methanation reaction facility, carbon dioxide is already removed from the raw material gas. Since the methanation proceeds too much because the carbon monoxide concentration and hydrogen concentration in the raw material gas become considerably high, it becomes necessary to recycle the gas after the methanation reaction in large quantities, and the equipment cost increases. At the same time, a lot of energy (electric power, etc.) is required for the operation.

  In addition, in order to suppress carbon deposition on the methanation catalyst, it is necessary to mix water vapor with a certain ratio according to the amount of carbon in the gas used for the methanation reaction. As the amount of gas increases, the amount of water vapor to be added increases accordingly. As a result, in the system for removing carbon dioxide upstream of the methanation reaction facility, there is room for improvement in terms of facility cost, energy consumption, and amount of supplied water vapor when viewed as a whole system.

  On the other hand, in the technique disclosed in Patent Document 2, since at least two carbon dioxide removal facilities are required, the facility cost increases. Furthermore, although a recycling path is provided, carbon dioxide is removed from the gas after the methanation reaction extracted from the communication section from the first methanation reactor to the subsequent methanation reactor, and then the first methanation reaction is performed. Because it is configured to be returned to the inlet of the vessel, it is difficult to obtain the effective dilution effect that is originally expected for recycled gas, and adjustment of the equipment cost, energy consumption, and supply water vapor amount when viewed from the whole system. There is room for improvement above.

  An object of the present invention is to obtain a methane-rich gas production system in which the load is reduced in terms of equipment cost, energy consumption, and amount of supplied water vapor when producing the methane-rich gas as a whole.

In order to achieve the above object, a carbon monoxide shift reaction facility for adjusting the ratio of hydrogen and carbon monoxide contained in the raw material gas, and a desulfurization treatment for performing a desulfurization process for removing sulfur from the gas flowing inside A raw material gas in which the ratio of hydrogen and carbon monoxide is adjusted via the carbon monoxide shift reaction equipment, the carbon dioxide removal equipment that performs carbon dioxide removal treatment to remove carbon dioxide from the gas flowing through the equipment And a methanation reaction facility that generates methane from the hydrogen and carbon monoxide by a catalytic reaction, and the methanation reaction facility includes one or more methanation reactors, and The characteristic configuration of the methane rich gas production system having a recycling path for returning the methane rich gas generated through the methanation reactor to the raw material gas is as follows.
[Configuration 1]
In the configuration in which the source gas is circulated in the order of the carbon monoxide shift reaction facility, the desulfurization facility, the methanation reaction facility, and the carbon dioxide removal facility,
Provided with water vapor introduction means for introducing water vapor into the source gas,
The methanation reactor constituting the methanation reaction facility, which is sent from the outlet of any methanation reactor, and a part of the gas containing carbon dioxide is used as it is with respect to the gas components, and the first stage methanation is performed. A recycling path is provided to return to the inlet of the reactor,
The feature of claim 1 of the present invention is that a gas distribution means for distributing a recycle gas to the recycle path is provided at the inlet of the recycle path so as to be able to supply a gas sent out from any of the methanation reactors. There is.

[Operation effect 1]
In the present application, a desulfurization facility is disposed upstream of the methanation reaction facility, and a carbon dioxide removal facility is disposed downstream. Therefore, the gas containing carbon dioxide is supplied to the methanation reaction facility. That is, “as it is with respect to gas components” means that operations such as temperature adjustment and gas-liquid separation may be performed, but carbon dioxide is not removed and remains as it is. In this state, since carbon dioxide is contained, carbon monoxide, which is a reaction component in the gas, and hydrogen have a relatively low concentration, and the amount of gas to be recycled through the recycling path is reduced. The Furthermore, the gas recycled through the recycling path is a gas before removing carbon dioxide in the system of the present application, and contains carbon dioxide to the same extent as the raw material gas. The gas reaction components can be diluted well.

  As a result, since the amount of gas introduced into the methanation reaction facility (the amount of raw material gas and recycle gas) can be reduced, the scale of the methanation reaction facility can be first reduced. Since the amount of gas recycled through the recycling path can be reduced, the driving means for recycling can be reduced in size, and the amount of energy required for the operation can be reduced. Moreover, since the amount of recycle gas can be reduced, the power consumption of the recycle compressor for the methanation reaction facility can be reduced.

  Further, as described above, the amount of gas introduced into the methanation reaction facility is reduced, and as a result, the amount of water vapor that has been conventionally required to suppress carbon deposition can be reduced. In addition, the water vapor supply means can be downsized and the amount of energy required for its operation can be reduced.

  Therefore, in the production of methane rich gas, it was possible to obtain a methane rich gas production system with a reduced load in terms of equipment cost, energy consumption, and amount of supplied water vapor when viewed as a whole system.

  Furthermore, as described in Patent Document 2, in the configuration of the present application, it is not necessary to provide a carbon dioxide removal facility in the recycling path, and the methanation rich gas can be efficiently produced.

[Configuration 2]
The methanation reaction facility is configured to include a plurality of methanation reactors connected in series, and an inlet portion of the recycling path includes a first-stage methanation reactor and a second-stage methanation reactor. Or between the final stage methanation reactor and the carbon dioxide removal facility.

[Operation effect 2]
In this configuration, the recycling path flows through the part from between the first-stage methanation reactor and the second-stage methanation reactor, or between the last-stage methanation reactor and the carbon dioxide removal facility. The gas is returned as it is to the inlet site of the first-stage methanation reactor. In this recycling, carbon dioxide important in the present application is left as it is. By adopting such a configuration, the gas introduced into the first stage methanation reactor, becomes a gas mixture of a total volume of the recycle gas of the raw material gas, when attention is focused on CO and H ₂ component, substantially CO and H ₂ The component can be in a highly diluted state.
Therefore, the operation and effect described in the configuration 1 can be obtained by a methane rich gas production system including a methanation reaction facility including a plurality of methanation reactors connected in series.
Here, when the inlet of the recycling path is provided between the first-stage methanation reactor and the second-stage methanation reactor, the water vapor that has passed through the first-stage methanation reactor can be further utilized. On the other hand, when it is provided between the methanation reactor in the final stage and the carbon dioxide removal facility, the production efficiency of methane can be increased.

[Configuration 3]
In the above configuration, heat utilization means for recovering heat held in the gas transferred from the methanation reaction facility to the carbon dioxide removal facility and adjusting the temperature of the gas introduced from the desulfurization facility to the methanation reaction facility It is preferable to provide.

[Operation effect 3]
As previously indicated, the methanation reaction is an exothermic reaction, and the gas at the outlet of the methanation reaction facility is heated from the inlet gas. On the other hand, when a desulfurization facility that performs desulfurization by physical absorption by a solvent is adopted, the gas temperature at the desulfurization facility outlet may be led to a lower side than the temperature suitable for methanation. Therefore, by providing heat utilization means, heat can be utilized between the inlet and outlet of the methanation reaction facility, and as a result, an energy efficient system can be constructed.

[Configuration 4]
In the configuration described so far, a part of the inflow gas flowing into the methanation reaction facility is led to the first-stage methanation reactor, and the remainder follows the first-stage methanation reactor. It is preferable to provide a bypass introduction means that leads directly to the subsequent methanation reactor.

[Operation effect 4]
As explained earlier, since the methanation process is an exothermic process, it is preferable to keep the outlet temperature of each methanation reactor as low as possible, but all the raw material gas was introduced into the first stage methanation reactor. In this case, the outlet temperature of the first-stage methanation reactor may be excessively increased.
On the other hand, by providing bypass introduction means, the amount of raw material gas introduced into the first stage methanation reactor can be reduced or adjusted, and the remainder is introduced into the subsequent methanation reactor. It becomes possible to keep the temperature of the vessel at a low temperature side at which methanation easily proceeds.
As a result, methane-rich gas can be produced efficiently.

[Configuration 5]
Furthermore, in the above-described configuration in which the bypass introduction unit is provided, it is preferable that the water vapor introduction unit introduces the water vapor into part of the methanation reaction facility inflow gas led to the first-stage methanation reactor. .

[Operation effect 5]
In this configuration, by-pass introduction means is provided, and the amount of gas introduced into the first-stage methanation reactor is limited by reducing or adjusting the amount of raw material gas introduced into the first-stage methanation reactor. . However, basically, in a plurality of methanation reactors, it is inevitable in operation that the reactor having the highest possibility of carbon deposition is the first-stage methanation reactor. However, as described so far, in the present application, the carbon dioxide removal facility is disposed primarily downstream from the methanation reaction facility, and further, by providing a bypass introduction means, secondarily, the first stage. As a result, the water vapor introduction means is supplied to the methanation reaction facility inflow gas led to the first-stage methanation reactor. By introducing the water vapor into a part of the water vapor, the amount of water vapor can be further reduced.

[Configuration 6]
In the configuration described so far, the raw material gas is a synthesis gas obtained by gasifying coal with a coal gasification facility, and preferably contains 30% by volume or more of carbon dioxide.
[Operation effect 6]
Generally, synthesis gas produced by coal gasification contains a relatively large amount of carbon dioxide, and carbon dioxide may be produced even in a carbon monoxide shift reaction.
Thus, methane-rich gas can be produced by using a system with good energy efficiency, using a synthesis gas containing a relatively large amount of carbon dioxide as a raw material gas.

The figure which shows the structure of the methane rich gas manufacturing system which concerns on this application Schematic diagram (a) showing a schematic configuration of the present system having a desulfurization facility upstream of the methanation reaction facility and a carbon dioxide removal facility downstream, and a desulfurization facility and carbon dioxide removal upstream of the methanation reaction facility Schematic diagram showing the schematic configuration of a conventional system equipped with facilities (b) Chart showing the results of examination of the system shown in Fig. 2 (a) Chart showing the results of examination of the conventional system shown in Fig. 2 (b)

The structure of the methane rich gas production system 100 according to the present application will be described with reference to FIG.
The methane rich gas production system 100 uses a configuration in which gas flows in the order of a coal gasification facility 1, a carbon monoxide shift reaction facility 2, a desulfurization facility 3, a methanation reaction facility 4, and a carbon dioxide removal facility 5. .
This methane rich gas production system 100 uses a synthetic gas containing hydrogen, methane, carbon monoxide, carbon dioxide, nitrogen, etc. generated from the coal gasification facility 1 as a raw material gas, and increases its methane content to produce methane rich gas. To manufacture. In this production, water vapor v is used for the reaction at least in the carbon monoxide shift reaction facility 2 and the methanation reaction facility 4.

[Coal gasification equipment]
The coal gasification facility 1 employed in the present embodiment pulverizes coal c, which is a carbonaceous feed, and supplies the gas c into the gasification furnace 1a, and oxygen-containing gas which is an oxidant under high pressure (for example, air air) Alternatively, it is a facility for obtaining a high-temperature synthesis gas instantly by partial oxidation with O ₂ ).
Here, coal, such as lignite, bituminous coal, subbituminous coal, anthracite, is used as the carbonaceous feed. Air, oxygen-enriched air, oxygen, carbon dioxide (in the reaction producing carbon monoxide) or a mixture thereof is used as the oxidant. As the carbonaceous feed, a liquid material mainly composed of carbon such as petroleum can be used.
The synthesis gas produced in this way (the raw material gas in the present application) contains 30% by volume or more of carbon dioxide.

[Carbon monoxide shift reaction equipment]
The carbon monoxide shift reaction facility 2 employed in the present embodiment reacts carbon monoxide with water vapor v by a catalytic reaction to convert it into hydrogen and carbon dioxide. As the catalyst, Cu—Zn-based and Pt-based catalysts are used. This reaction occurs in a high temperature range (350 ° C to 420 ° C).
This shift reaction is an exothermic reaction represented by the following formula.

CO + H ₂ O⇔H ₂ + CO ₂ + Q (exothermic reaction)

  The system of the present application performs the methanation reaction by supplying carbon monoxide and hydrogen mainly at a predetermined ratio in the subsequent methanation reaction equipment 4, so that carbon monoxide in the raw material gas supplied from the coal gasification equipment 1 is used. The amount of hydrogen is detected, and the amount of hydrogen is adjusted so that the molar ratio is 1: 3. Basically, when the amount of hydrogen is supplied in a deficient state, the shift reaction is promoted so that a predetermined molar ratio is satisfied.

[Desulfurization equipment]
The desulfurization facility 3 employed in the present embodiment is configured as a hydrogen sulfide absorber that removes sulfur contained in the raw material gas. At the time of removal, hydrogen sulfide contained in the source gas or sulfur contained in the source gas is hydrogenated (not shown), and the hydrogen sulfide is absorbed in a physically absorbable solvent to remove the sulfur. Here, specific examples of the solvent include polyethylene glycol.
Examples of the solvent include polyethylene glycol alone, N-methylpyrrolidone, polyethylene glycol dialkyl ether, tributyl phosphate, tetramethylene sulfone, propylene carbonate, methanol, alkanol pyridine, and tetrahydrothiophene-1,1-dioxide, Polypropylene glycol dimethyl ether can also be used.

  In the present application, as shown in FIG. 1, a configuration is adopted in which the solvent circulates between a desulfurization facility 3 to which a raw material gas is supplied and a carbon dioxide absorber 5 a provided in the carbon dioxide removal facility 5. In this circulation path, a sulfur regenerator 52 is provided between the desulfurization facility 3 and the carbon dioxide absorber 5a. In this device 52, hydrogen sulfide (sulfur content) can be removed from the circulating solvent.

  The solvent circulation path related to desulfurization will be described. The solvent with a high hydrogen sulfide concentration taken out from the lower part of the desulfurization equipment 3 is sent to the sulfur regeneration device 52 via the concentrated solution feed path 51 and is regenerated by the device 52. The carbon dioxide absorbing device 5a is fed into the inside thereof. The carbon dioxide concentration rises, and a part of the solvent taken out from the bottom of the apparatus is sent to the diversion pump 63 via the branch path 62 and returned to the head of the desulfurization facility 3 via the return path 64.

[Methanation reactor]
The methanation reaction facility 4 employed in the present embodiment reacts carbon monoxide and hydrogen by a catalytic reaction to convert it into methane and water. As the catalyst, Ni-based or Ru-based catalysts are used. This reaction is a strongly exothermic reaction (200 ° C. to 400 ° C.).
This methanation reaction is an exothermic reaction represented by the following formula.

CO + 3H ₂ ＣＨ CH ₄ + H ₂ O + Q (exothermic reaction)

  As is well known, since the methanation reaction is a strongly exothermic reaction, in the present application, the methanation reactor 4a has three stages, and a cooler 4b is provided at each reactor outlet. In this way, the methanation reactor inlet temperature is lowered so that the methanation proceeds as much as possible. Furthermore, in this application, since the synthesis gas is used as the raw material gas, the concentration of carbon dioxide in the gas is high. Therefore, steam v is added to the gas introduced into the methanation reaction facility 4 for the purpose of preventing carbon deposition. The number of moles of water vapor added to the methanation process is suitably 0.8 to 4.5 times the number of moles of carbon supplied to the methanation process. For this purpose, there is provided a water vapor introducing means 40 for introducing water vapor v into a synthesis gas as a raw material gas to be inserted into the methanation reaction facility 4 (particularly the first-stage methanation reactor 4a).

  Regarding the methanation reactors 4a provided in a plurality of three stages, the gas is sent from the final stage (third stage) methanation reactor 4a3, cooled through the cooler 4b, and branched at the branch part 4c. A recycling path 4d is provided for returning a part of the gas containing carbon dioxide to the inlet portion of the first stage (first stage) methanation reactor 4a1 as it is with respect to the gas components. Thus, in this application, it returns to raw material gas as it is, without removing the carbon dioxide contained in gas. Since this configuration is adopted, the gas supplied to the first-stage methanation reactor 4a1 is diluted with respect to the carbon content, and the amount of water vapor to be supplied to the first-stage methanation reactor 4a1 can be suppressed.

  The inlet of the recycling path 4d is provided between the final-stage methanation reactor 4a3 and the carbon dioxide removal equipment 5, and a recycling compressor 4e is provided as a gas distribution means for circulating the recycled gas through the recycling path 4d. ing.

  Further, in the methanation reaction facility 4 shown in this embodiment, a part of the inflow gas of the methanation reaction facility that is the inflowing raw material gas is led to the first-stage (first-stage) methanation reactor 4a1, and the remainder is the first-stage gas. Bypass introduction means 4g that leads directly to the subsequent methanation reactor 4a2 (second stage in the illustrated example) following the methanation reactor 4a1 is provided. The bypass introduction means 4g is composed of a bypass passage 4g1 for bypassing the first-stage methanation reactor 4a1 and a flow control valve 4g2 for controlling the flow rate of the gas flowing through the bypass passage 4g1, and the flow control valve 4g2 is opened. The amount of bypass can be adjusted by adjusting the degree. The purpose of providing such bypass introduction means is to prevent the outlet temperature of the first-stage methanation reactor 4a1 from rising excessively. In addition, although not shown in figure, it is good also as a structure further equipped with another flow control valve in the entrance part of the methanation reactor 4a1. With this configuration, the flow control can be adjusted over a wider range.

  In the present application, the introduction of the water vapor v by the water vapor introducing means 40 is performed only after the branch of the bypass passage 4g1, that is, only to the gas flowing into the first stage methanation reactor 4a. . As a result, the amount of water vapor is also reduced from this configuration. Of course, it is also possible to supply water vapor to the entire source gas before branching the bypass passage 4g1.

  As shown in FIG. 1, in the system shown in the present embodiment, gas cooling is performed between the respective methanation reactors 4a and in the subsequent stage of the last methanation reactor 4a.

  On the other hand, the gas introduced into the methanation reaction facility 4 from the desulfurization facility 3 and the remaining gas that has undergone methanation treatment in the methanation reaction facility 4 and branched at the branch portion 4c (residual gas that has not been recycled). Heat exchange is also performed. That is, in the present application, as shown in FIG. 1, at least the heat held by the gas transferred from the methanation reaction facility 4 to the carbon dioxide removal facility 5 is recovered, and the desulfurization facility 3 transfers to the methanation reaction facility 4. The heat utilization means 30 is provided to bring the temperature of the introduced gas to a temperature suitable for the reaction. As a result, in the system configuration in which the desulfurization facility 3 and the carbon dioxide removal facility 5 are arranged across the methanation reaction facility 4 as in the present application, it is possible to achieve a useful use of energy.

[CO2 removal equipment]
The carbon dioxide removal equipment 5 employed in the present embodiment employs a configuration in which hydrogen sulfide and carbon dioxide are absorbed in a solvent and removed individually as described in the desulfurization equipment 3.
Hereinafter, a description will be given based on FIG.
The raw material gas that has passed through the shift reaction facility 2 enters the vicinity of the bottom of the desulfurization facility 3, which is a hydrogen sulfide absorption device in which the solvent is dispersed and flowed, via the raw material gas / product gas heat exchanger 99. To absorb and remove hydrogen sulfide and other sulfur compounds. The solvent is taken out from the bottom of the desulfurization facility 3 and sent to the sulfur regenerator 52 through the concentrated solvent feed path 51 to remove hydrogen sulfide. The solvent after the removal is returned to the vicinity of the head of the carbon dioxide removing device 5 a via the return path 54 and the solution pump 53. On the other hand, the gas delivered from the head of the desulfurization facility 3 is at a low temperature (for example, 0 ° C.), and is heated through the heat exchanger, which is the heat utilization means 30 described above. Is sent to.

Part of the heat held by the gas that has undergone methanation treatment at the methanation reaction facility 4 and has reached a high temperature (for example, 300 ° C.) is used for steam generation, and partly at the branch part 4c. It is supplied to a unique recycling path 4d. The remainder is recovered by the heat utilization means 30 and sent to the static mixer 56. The static mixer 56 mixes with the solvent taken out from the bottom of the carbon dioxide absorber 5a by the circulation pump 57, and then the mixed flow is returned to the bottom of the carbon dioxide absorber 5a via the return path 58. The solvent that has absorbed carbon dioxide exits from the bottom of the carbon dioxide absorbing device 5 a and is separated into a flow path 61 following the series of flash drums (70, 80, 90) and a branch flow path 62 leading to the diversion pump 63. . The solvent flowing on the flow path 61 side proceeds to the high-pressure flash CO 2 flash drum 70, and carbon dioxide is released from the head discharge path 71. The solvent further reaches an intermediate pressure flash CO 2 flash drum 80 and a low pressure flash CO 2 flash drum 90, and carbon dioxide is sequentially released through the head delivery paths 81 and 91. The dilute solvent whose absorption capacity has been increased by releasing carbon dioxide is returned to the intermediate portion of the carbon dioxide absorber 5a via the flow path 95, the circulation pump 96, and the flow path 97. The solvent flowing on the branch path 62 side is returned to the head of the desulfurization facility 3 via the diversion pump 63 and the return path 64.
The purified product gas leaves the head of the carbon dioxide absorption device 5a, proceeds to the raw material gas / product gas heat exchanger 99, and after heat exchange, is sent to the subsequent process as a product.

[Another embodiment]
(1) In the above-described embodiment, an example is shown in which a part of the first stage methanation reactor 4a is guided to bypass the remainder and bypass is provided. The total amount of the raw material gas may be introduced into the first-stage methanation reactor 4a1 to produce methane-rich gas.

〔Consideration〕
The above is the description of the methane-rich gas production system according to the present application. Hereinafter, the results of the studies conducted by the inventors in connection with the present application will be described.
In this examination, the subject system shown in FIG. 2A and the conventional system shown in FIG.

In the present system, a desulfurization facility 3 is provided upstream of the methanation reaction facility 4, a carbon dioxide removal facility 5 is provided downstream of the methanation reaction facility 4, and the above-described example is provided in the methanation reaction facility 4. Similarly, the methane rich gas is recycled from the outflow side of the final methanation reactor 4a3 to the inlet 4a1 of the first methanation reactor. In this example, the methanation reaction facility 4 does not include the bypass introduction means 4g described above, and receives the entire amount of the raw material gas (including hydrogen, carbon monoxide and carbon dioxide) in the first-stage methanation reactor 4a1, The entire amount was sequentially methanated in the methanation reactors 4a2, 4a3.
Therefore, the methanation reaction facility 4 is adjusted in the quantity ratio of hydrogen and carbon monoxide, is subjected only to desulfurization treatment, and is supplied with a gas containing carbon dioxide, so that the three-stage methanation reactors 4a1, 4a2, 4a3 are supplied. After being methanated, a part of it is recycled while containing carbon dioxide.

In the conventional system, a desulfurization facility 3 and a carbon dioxide removal facility 5 are provided on the upstream side of the methanation reaction facility 4, and the first-stage methanation reaction is performed in the methanation reaction facility 4 from the downstream side of the final-stage methanation reactor 4a3. The methane rich gas is recycled to the inlet of the vessel 4a1. This methanation reaction facility 4 also does not include the bypass introduction means 4g described above, and accepts the entire amount of the raw material gas (hydrogen, carbon monoxide and carbon dioxide removed) into the first-stage methanation reactor 4a1, The whole amount is sequentially processed in the methanation reactors 4a2, 4a3.
Therefore, the methanation reaction equipment 4 is adjusted in the quantity ratio between hydrogen and carbon monoxide, subjected to desulfurization treatment and carbon dioxide removal treatment, and supplied with the gas from which carbon dioxide has been removed. After methanation in the reactor, some of it is recycled.

In these examinations, the examination criteria were the same amount of methane-rich gas (approximately 100% methane) produced (0.37 Nm ³ / h as can be seen from FIGS. 3 and 4).

In the system of the present application, as shown in FIG. 3, the recycling amount of the methanation reaction equipment = 0.9 Nm ³ / h (55% reduction from the conventional system), the recycling compressor power consumption = 3.1 W (58% reduction from the conventional system) The amount of water vapor required for the methanation reaction was 1.2 kg / h (30% reduction from the conventional system). As a result, the facility through which the recycle gas of the methanation reaction facility passes could be reduced by about 55% compared to the conventional system.

On the other hand, in the conventional system, as shown in FIG. 4, the recycle amount of the methanation reaction equipment = 1.9 Nm ³ / h, the recycle compressor power consumption = 7.4 W, the water vapor amount necessary for the methanation reaction = 1.7 kg / h h.

  In producing methane-rich gas, we were able to obtain a methane-rich gas production system with reduced load in terms of equipment cost, energy consumption, and amount of water vapor supply when viewed as a whole system.

1: Coal gasification facility 2: Carbon monoxide shift reaction facility 3: Desulfurization facility 4: Methanation reaction facility 4a: Methanation reactor 4b: Cooler 4d: Recycle path 4e: Recycle compressor 5: Carbon dioxide removal facility

Claims (6)

A carbon monoxide shift reaction facility for adjusting the ratio of hydrogen and carbon monoxide contained in the raw material gas, a desulfurization facility for performing a desulfurization process for removing sulfur from the gas flowing inside, and a gas flowing inside Carbon dioxide removal equipment for removing carbon dioxide from the carbon dioxide removal equipment and the carbon monoxide shift reaction equipment through which the raw material gas in which the ratio of hydrogen and carbon monoxide is adjusted is received, and the hydrogen is produced by catalytic reaction. And a methanation reaction facility for producing methane from carbon monoxide, the methanation reaction facility is configured to have one or a plurality of methanation reactors, and is generated through the methanation reactor. A methane rich gas production system including a recycling path for returning the methane rich gas to the raw material gas,
In the configuration in which the source gas is circulated in the order of the carbon monoxide shift reaction facility, the desulfurization facility, the methanation reaction facility, and the carbon dioxide removal facility,
Provided with water vapor introduction means for introducing water vapor into the source gas,
The methanation reactor constituting the methanation reaction facility, which is sent from the outlet of any methanation reactor, and a part of the gas containing carbon dioxide is used as it is with respect to the gas components, and the first stage methanation is performed. A recycling path is provided to return to the inlet of the reactor,
A methane rich gas production system in which an inlet portion of the recycle path is provided so as to be able to supply a gas sent out from any of the methanation reactors, and a gas distribution means for circulating the recycle gas through the recycle path is provided.   The methanation reaction facility is configured to include a plurality of methanation reactors connected in series, and an inlet portion of the recycling path includes a first-stage methanation reactor and a second-stage methanation reactor. Or a methane-rich gas production system according to claim 1, wherein the methane-rich gas production system is provided between the first stage methanation reactor and the carbon dioxide removal facility.   The heat utilization means which collect | recovers the heat | fever which the gas which flows from the said methanation reaction equipment to the said carbon dioxide removal equipment hold | maintains, and adjusts the temperature of the introductory gas from the said desulfurization equipment to a methanation reaction equipment is provided. Or the methane rich gas manufacturing system of 2.   A part of the inflow gas flowing into the methanation reaction facility is led to the first-stage methanation reactor, and the remainder is passed to the subsequent-stage methanation reactor following the first-stage methanation reactor. The methane-rich gas production system according to any one of claims 1 to 3, further comprising bypass introduction means for direct guidance.   5. The methane rich gas production system according to claim 4, wherein the water vapor introducing means introduces the water vapor into a part of the inflow gas of the methanation reaction facility led to the first-stage methanation reactor.   The methane-rich gas production system according to any one of claims 1 to 5, wherein the raw material gas is a coal gasification gas obtained by gasifying coal with a coal gasification facility and contains 30% by volume or more of carbon dioxide.

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