Method for producing high calorific value fuel gas and production facility for high calorific value fuel gas

Abstract

To provide a production method for a high calorific value fuel gas that can be used as a city gas from hydrogen and carbon oxides, and contains methane as a main component and at least one of ethane, propane and butane.SOLUTION: A production method for a high calorific value fuel gas comprises: a methanol synthesis step of synthesizing methanol from a gas containing hydrogen and carbon oxides; a methanol separation step of cooling the gas obtained in an above step to separate methanol; a methanation step of passing the gas containing hydrogen and carbon oxides separated from methanol in the methanol separation step through a methanation catalyst to synthesize methane; an olefin synthesis step of passing methanol separated in the methanol separation step through an olefin synthesis catalyst to obtain the gas containing at least one component of ethylene, propylene and butylene; and a hydrogenation step of mixing a methane main component gas obtained in the methanation step and the gas obtained in the olefin synthesis step to pass through a hydrogenation catalyst, and converting olefinic hydrocarbons to paraffinic hydrocarbons by a reaction with hydrogen.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and equipment for producing a high calorific value fuel gas, which is mainly composed of methane and further contains at least one of ethane, propane and butane, from hydrogen and carbon oxides and can be used as city gas. [Background technology]

[0002] In recent years, from the perspective of global warming countermeasures, attention has been focused on carbon-neutral fuels, which do not substantially increase the carbon dioxide concentration in the atmosphere even when burned.

[0003] Methane can be obtained by capturing carbon dioxide from exhaust gases generated in industrial processes and thermal power plants, and reacting it with hydrogen obtained by electrolysis using electricity generated by renewable energy sources such as solar power and wind power. Methane obtained by this method can be considered a carbon-neutral fuel that does not contribute to global warming, as no additional carbon dioxide is produced when it is burned.

[0004] The methanation reaction (formula 1) in which carbon dioxide and hydrogen are reacted to obtain methane is known. CO 2 +4H 2 → CH 4 +2H 2 O (Formula 1)

[0005] In Patent Document 1, CO and H 2 A methanation reactor having a Cu-Zn-based low-temperature shift catalyst arranged upstream and a methanation catalyst arranged downstream is used for methanation of a gas containing CO and H. 2 This paper discloses a method for methanating a gas containing CO. In the upstream low-temperature shift reactor, the CO shift reaction (formula 2) proceeds, so most of the carbon monoxide contained in the raw gas reacts with water vapor and is converted to carbon dioxide, and it is believed that the methanation reaction of carbon dioxide proceeds on the downstream methanation catalyst. CO+H 2 O → CO2 +H 2 (Formula 2)

[0006] The methanation reaction has long been used for the purpose of removing carbon monoxide and carbon dioxide from hydrogen for ammonia synthesis, and it is known that catalysts supporting Ni, Ru, etc. exhibit high activity (Non-Patent Documents 1 and 2).

[0007] The methanation reaction of reacting carbon oxides (carbon monoxide and carbon dioxide) with hydrogen to obtain methane is an industrially established technology (for example, Non-Patent Document 3), but there are still problems in obtaining a fuel gas of a quality that can be used as a town gas raw material.

[0008] What is generally used as a town gas raw material is natural gas, which mainly consists of methane and contains small amounts of ethane, propane, and butane. Natural gas usually does not contain hydrogen and carbon monoxide, and carbon dioxide is removed in the purification process of natural gas. In particular, in the case of town gas produced from liquefied natural gas as a raw material, hydrogen, carbon monoxide, and carbon dioxide are almost completely removed in the liquefaction purification process and are substantially not contained.

[0009] Since the concentrations of hydrocarbons other than methane (ethane, propane, and butane) contained in natural gas vary depending on the production area and purification method of natural gas, when producing town gas, usually propane or butane is added so that its calorific value is within a certain range (for example, 44.2~46.0MJ / m 3 ) and after adjusting, an odorant is added for safety assurance and then sent to consumers through the town gas pipeline.

[0010] If hydrogen, carbon monoxide, and carbon dioxide are contained in town gas, it may cause the following problems.

[0011] First, since carbon monoxide is highly toxic, there is a risk of poisoning accidents if the gas leaks. Its allowable concentration is set at 200 ppm. From a safety perspective, it is desirable that the concentration in the fuel gas be below this level, and even considering dilution with air, it is necessary to keep it below 1000 ppm.

[0012] Next, carbon dioxide is not only non-combustible but also has the function of suppressing combustion. Therefore, when it is mixed into the fuel gas at a high concentration, it not only reduces the efficiency of gas transportation in the conduit due to the decrease in the calorific value of the fuel gas but also may cause a decrease in the efficiency of the combustion equipment.

[0013] Finally, although hydrogen is a fuel gas, its calorific value per unit volume is only about one-third that of methane, which is the main component of town gas. Therefore, when hydrogen is mixed into the fuel gas mainly composed of methane, the calorific value per unit volume decreases. Furthermore, since hydrogen has a high combustion rate, it is also known to have a great impact on combustion equipment.

[0014] As described above, when hydrogen, carbon monoxide, and carbon dioxide are mixed into town gas, they have various effects at each stage of gas supply and consumption. Therefore, in the quality standards of the gas accepted into the town gas pipeline network, it is common to impose restrictions on the concentrations of hydrogen, carbon monoxide, and carbon dioxide.

[0015] In the pipeline network where there is a fueling station for natural gas vehicles, there is an example where the upper limit of the hydrogen concentration is set at 2% on a volume basis (Non-Patent Document 4). There are also examples where the hydrogen concentration is specified to be 4% or less on a volume basis, the carbon dioxide concentration is 0.5% or less on a volume basis, and the carbon monoxide concentration is 0.05% or less on a volume basis (Non-Patent Document 5), as well as an example where the total concentration of methane and ethane is specified to be 93% or more on a volume basis and the total concentration of components other than hydrocarbons is 4% or less on a volume basis (Non-Patent Document 6).

[0016] Several methods are known for reducing the hydrogen concentration in the fuel gas obtained by the methanation reaction. For example, when the methanation reaction is carried out under conditions where the hydrogen is less than the stoichiometric ratio and the excess carbon dioxide is removed by decarburization treatment, both the hydrogen content and the carbon dioxide content can be reduced (Patent Document 4). There is an example where this method has been adopted in the methanation of coke oven gas (Non-Patent Document 3). However, decarburization equipment generally has high equipment costs and also consumes a large amount of energy during operation, so there is a problem that the economic efficiency is impaired.

[0017] As another method, a method is also known in which the methanation reaction is carried out in multiple stages, and the gas generated in the middle stage is cooled to condense and separate water (Non-Patent Document 4, Patent Documents 2 and 3). By removing the generated water, the methanation reaction can be further advanced to the production side, and the conversion rate of carbon dioxide to methane can be improved. However, in this method, heat exchange equipment is required, which increases the equipment cost. Also, if the generated water is removed excessively, the composition will enter the region where carbon deposition occurs in an equilibrium manner, so there is also a problem that the control of the process for separating water becomes complicated.

[0018] Furthermore, for both the method of carrying out the methanation reaction under conditions where the hydrogen is less than the stoichiometric ratio and removing the excess carbon dioxide by decarburization treatment, and the method of carrying out the methanation reaction in multiple stages and cooling the gas generated in the middle stage to condense and separate water, since it becomes a condition where carbon monoxide is likely to be generated in an equilibrium manner, there is also a problem that the carbon monoxide concentration in the produced fuel gas becomes high.

[0019] City gas is produced mainly from natural gas. As described above, propane or butane is added and adjusted to a certain calorific value range before being supplied so that it can be stably used in combustion equipment. In the methanation reaction of carbon oxides, unless special catalysts or reaction conditions are adopted, only methane is produced. The calorific value of methane is 39.9 MJ / m 3 and the calorific value of general city gas (for example, 44.2 - 46.0 MJ / m 3) is slightly lower compared to that. Therefore, when using the gas obtained from the methanation reaction as a town gas raw material, in order to ensure the same calorific value and combustibility as general town gas, a relatively large amount of propane (101 MJ / m 3 ) or butane (134 MJ / m 3 ) corresponding to 15 - 20% on a calorific value basis needs to be added to the methane obtained from the methanation reaction. Although propane or butane that can be regarded as carbon-neutral has extremely limited availability, when using fossil fuel-derived propane or butane as the propane or butane used for calorific value adjustment, the carbon neutrality of the produced gas will be impaired.

[0020] In addition, if a large amount of hydrogen, carbon monoxide, and carbon dioxide are mixed in the gas produced by the methanation reaction, since their calorific value per unit volume is lower compared to methane, it becomes necessary to mix an even larger amount of propane and butane required for calorific value adjustment, which also causes a problem of further impairing the carbon neutrality of the produced gas.

[0021] As described above, the reality is that a method for producing a high-calorific fuel gas mainly composed of methane and further containing at least one component of ethane, propane, and butane, which can be used as town gas from hydrogen and carbon oxides, has not yet been established.

Prior Art Documents

Patent Documents

[0022]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0023]

Non-Patent Document 1

[0024] The problem to be solved by the present invention is to provide a method for producing a high-calorific fuel gas mainly composed of methane and further containing at least one component of ethane, propane and butane, which can be used as city gas from hydrogen and carbon oxides. [Means for Solving the Problems]

[0025] The characteristic configuration of the method for producing a high-calorific fuel gas according to the present invention is a method for producing a high-calorific fuel gas mainly composed of methane and further containing at least one component of ethane, propane and butane from hydrogen and carbon oxides, a methanol synthesis step of synthesizing methanol by passing a gas containing hydrogen and carbon oxides through a methanol synthesis catalyst, a methanol separation step of cooling the gas obtained in the methanol synthesis step to separate methanol, a methanation step of synthesizing methane by passing the gas containing hydrogen and carbon oxides obtained by separating methanol in the methanol separation step through a methanation catalyst An olefin synthesis step of passing the methanol obtained in the methanol separation step through an olefin synthesis catalyst to obtain an olefin hydrocarbon-containing gas containing at least one component of ethylene, propylene, and butylene; A hydrogenation step of mixing the methane-based gas obtained in the methanation step and the olefin hydrocarbon-containing gas obtained in the olefin synthesis step, passing the mixture through a hydrogenation catalyst, and converting the olefin hydrocarbon into a paraffin hydrocarbon by reaction with hydrogen.

[0026] According to this characteristic configuration, since the hydrogen in the gas containing methane as the main component and containing hydrogen obtained in the methanation step is reduced by reaction with the olefin hydrocarbon, the concentration of hydrogen remaining in the fuel gas can be kept low. In addition, since the fuel gas contains at least one component of ethane, propane, and butane generated by the reaction of the olefin hydrocarbon and hydrogen, the generated fuel gas becomes a gas with a higher calorific value than methane, and can be used as a city gas raw material as it is or with only a slight calorific value adjustment.

[0027] A further characteristic configuration of the method for producing a high-calorific value fuel gas according to the present invention is The carbon oxide is carbon dioxide. Prior to the implementation of the methanol synthesis step, a reverse shift step is performed in which a mixed gas of hydrogen and carbon dioxide is passed through a reverse shift catalyst to convert at least a part of the carbon dioxide into carbon monoxide, and the gas obtained in the reverse shift step is cooled to separate at least a part of the water contained in the gas obtained in the reverse shift reaction, and then the gas is fed to the methanol synthesis step.

[0028] The methanol synthesis reaction by hydrogenation of carbon dioxide has a lower equilibrium conversion rate compared to the methanol synthesis reaction by hydrogenation of carbon monoxide. Therefore, when the carbon oxide is mainly carbon dioxide, the amount of methanol produced in the methanol synthesis step is less than that when a large amount of carbon monoxide is contained as the carbon oxide. When the amount of methanol produced is small, the amounts of ethane, propane, and butane contained in the produced fuel gas also decrease, so it may be difficult to sufficiently increase the calorific value of the produced fuel gas. As a method for increasing the amount of methanol produced, there is a method of increasing the reaction pressure in the methanol synthesis step, but this leads to an increase in equipment costs and is not economically advantageous. According to this characteristic configuration, even when the carbon oxide is mainly carbon dioxide, the proportion of carbon monoxide in the carbon oxide can be increased by the reverse shift reaction, so the amount of methanol produced increases, and it is easy to increase the calorific value of the produced fuel gas.

[0029] A further characteristic configuration of the method for producing a high-calorific-value fuel gas according to the present invention is that the reaction heat obtained in the methanation step or the olefin synthesis step is used as the heat source for the reverse shift reaction.

[0030] Since the reverse shift reaction is an endothermic reaction, heat needs to be supplied to proceed the reaction. Since the methanation reaction and the olefin synthesis reaction usually proceed at a higher temperature than the reverse shift reaction, the heat generated in these reactions can be used as the heat source for the reverse shift reaction. According to this characteristic configuration, since the reaction heat of the methanation reaction or the olefin synthesis reaction is used as the heat source for the reverse shift reaction, the efficiency of fuel gas production can be increased.

[0031] A characteristic configuration of the production equipment for a high-calorific-value fuel gas according to the present invention is a methanol synthesis section that synthesizes methanol by passing a gas containing hydrogen and a carbon oxide through a methanol synthesis catalyst, a methanol separation section that cools the gas sent from the methanol synthesis section and separates methanol, A methanation reaction section that synthesizes methane by passing a raw material gas containing hydrogen and carbon oxides, separated from methanol in a methanol separation section, through a methanation catalyst; An olefin synthesis section that passes the methanol separated in the methanol separation section through an olefin synthesis catalyst to obtain an olefin hydrocarbon-containing gas containing at least one component of ethylene, propylene, and butylene; It is characterized in that it includes a hydrogenation reaction section that mixes the methane main component gas obtained in the methanation reaction section and the olefin hydrocarbon-containing gas obtained in the olefin synthesis section, and passes it through a hydrogenation catalyst to convert olefin hydrocarbons into paraffin hydrocarbons by reaction with hydrogen.

[0032] According to this characteristic configuration, since the hydrogen in the gas mainly composed of methane and containing hydrogen obtained in the methanation reaction section is reduced by reaction with olefin hydrocarbons, the concentration of hydrogen remaining in the fuel gas can be kept low. In addition, since the fuel gas contains at least one component of ethane, propane, and butane generated by the reaction of olefin hydrocarbons and hydrogen, the produced fuel gas becomes a gas with a higher calorific value than methane, and can be used as a city gas raw material as it is or with only a slight calorific value adjustment.

[0033] A further characteristic configuration of the production facility for high-calorific fuel gas according to the present invention is It further includes a reverse shift reaction section and a water separation section, and performs a reverse shift process in which a mixed gas of hydrogen and carbon dioxide is passed through a reverse shift catalyst in the reverse shift reaction section to convert at least a part of the carbon dioxide into carbon monoxide, and in the water separation section, the gas containing hydrogen, carbon monoxide, carbon dioxide, and steam obtained in the reverse shift process is cooled to separate at least a part of the steam, and then fed into the methanol synthesis section.

[0034] According to this characteristic configuration, even when the carbon oxide is mainly carbon dioxide, the proportion of carbon monoxide in the carbon oxide can be increased by the reverse shift reaction, so the amount of methanol produced increases, and the calorific value of the produced fuel gas is likely to increase.

[0035] A further characteristic configuration of the manufacturing equipment for high calorific value fuel gas according to the present invention is that it is configured to use the reaction heat obtained from the methanation reaction in the methanation reaction section or the olefin synthesis reaction in the olefin synthesis section as the heat source for the reverse shift reaction.

[0036] According to this characteristic configuration, since the reaction heat of the methanation reaction or the olefin synthesis reaction is used as the heat source for the reverse shift reaction, the efficiency of fuel gas generation can be increased.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0038] 〔Embodiment〕 Hereinafter, embodiments of the method for manufacturing high calorific value fuel gas and the manufacturing equipment will be described. FIG. 1 is a block flow diagram showing the method for manufacturing high calorific value fuel gas and the manufacturing equipment of the present invention.

[0039] The method for producing high calorific value fuel gas according to this embodiment includes a step of synthesizing methanol by passing a gas containing hydrogen and carbon oxides through a methanol synthesis catalyst (methanol synthesis step), a step of cooling the gas obtained in the methanol synthesis step to separate methanol (methanol separation step), a step of synthesizing methane by passing the gas containing hydrogen and carbon oxides after separating methanol in the methanol separation step through a methanation catalyst (methanation step), a step of obtaining an olefin hydrocarbon-containing gas containing at least one component of ethylene, propylene, and butylene by passing the methanol obtained in the methanol separation step through an olefin synthesis catalyst (olefin synthesis step), and a step of mixing the methane main component gas obtained in the methanation step and the olefin hydrocarbon-containing gas obtained in the olefin synthesis step, and passing the mixture through a hydrogenation catalyst to convert olefin hydrocarbons into paraffin hydrocarbons by reaction with hydrogen (hydrogenation step).

[0040] Hydrogen and carbon oxides (carbon monoxide and carbon dioxide) used as raw materials may be produced by any method as long as they have a purity and properties that do not interfere with the implementation of the methanol synthesis step. Hydrogen may be, for example, electrolytic hydrogen obtained by electrolyzing water. Carbon dioxide may be recovered from combustion exhaust gas by a known carbon dioxide recovery method such as the amine absorption method, or may be carbon dioxide recovered from biogas obtained by methane fermentation of organic matter. A mixed gas of hydrogen, carbon monoxide, and carbon dioxide obtained by electrolyzing a mixed gas of carbon dioxide and steam at a high temperature contains both carbon monoxide and carbon dioxide as carbon oxides, and is particularly preferable as a raw material gas because the equilibrium conversion rate of the methanol synthesis reaction is increased.

[0041] When the raw material gas (hydrogen, carbon monoxide, carbon dioxide, or a mixture thereof) contains sulfur components, halogen compounds, siloxane compounds, heavy hydrocarbons, etc., these may cause deterioration of the methanol synthesis catalyst, so it is preferable to remove them before subjecting them to the reaction as necessary.

[0042] In the methanol synthesis process (methanol synthesis unit 1), a gas containing hydrogen and carbon oxides is brought into contact with a methanol synthesis catalyst to produce methanol.

[0043] As the methanol synthesis catalyst, known copper-zinc catalysts, chromium-zinc catalysts, copper-chromium-zinc catalysts, etc. can be used.

[0044] The temperature at which the gas is brought into contact with the methanol synthesis catalyst is preferably 200°C or higher and 350°C or lower, more preferably 220°C or higher and 280°C or lower. When within the above range, a sufficient reaction rate and a conversion rate to methanol can be ensured, so that the production amount of methanol can be ensured without using an excessive amount of catalyst.

[0045] Since the methanol synthesis reaction is accompanied by a certain amount of heat generation, as the methanol synthesis reactor, it is preferable to use a heat exchange type reactor that allows the reaction to proceed while removing the generated heat.

[0046] In the methanol separation process (methanol separation unit 2), the gas containing methanol, unreacted hydrogen, carbon monoxide, and carbon dioxide obtained in the above methanol synthesis process is cooled to separate and recover methanol as a liquid. Since the gas after the methanol synthesis process is at a sufficiently high temperature, its sensible heat can be recovered and, for example, heat-exchanged with the gas to be used for methanol synthesis and used for its preheating.

[0047] Since methanol has a certain vapor pressure even at normal temperature, in addition to cooling by heat exchange, water cooling or air cooling, cooling to below normal temperature using a refrigerator and a heat exchanger can increase the recovery amount of methanol. Preferably, it is cooled to 20°C or lower, more preferably 10°C or lower, to separate methanol.

[0048] In the methanation process (methanation reaction unit 3), the gas containing unreacted hydrogen, carbon monoxide, and carbon dioxide after the separation of the above methanol is brought into contact with a methanation catalyst to produce methane.

[0049] As the methanation catalyst used in the methanation process, known methanation catalysts containing Ni, Ru, etc. can be used.

[0050] The inlet temperature when contacting the methanation catalyst is preferably 200°C or higher and 350°C or lower, more preferably 225°C or higher and 275°C or lower. When within the above range, it is easy to obtain a sufficient reaction rate, so it becomes easy to proceed with the methanation reaction without using an excessive amount of catalyst, and since the outlet temperature of the methanation reaction does not rise too much, it becomes easy to ensure the durability of the catalyst.

[0051] Since the methanation reaction is accompanied by relatively large heat generation, as the reaction proceeds, the temperature of the gas rises, and accordingly the equilibrium conversion rate decreases. Therefore, it is usually difficult to obtain a desired conversion rate in a single-stage reaction. On the other hand, when adopting a heat exchange type reactor, it becomes difficult to extract high-temperature heat. Therefore, it is preferable to use an adiabatic type reactor on the inlet side and adopt a multi-stage process in which the outlet gas whose temperature has risen due to the reaction heat is cooled and then introduced into the next-stage reactor. The adiabatic type reactors may be connected in multiple stages via a heat exchanger for cooling, or at least one adiabatic type reactor on the inlet side and at least one heat exchange type reactor on the outlet side may be connected and used via a heat exchanger for cooling.

[0052] Since the methanation reaction is accompanied by relatively large heat generation, thermal degradation of the catalyst may be a problem in some cases. The gas on the outlet side of the reactor can also be returned to the inlet side of the reactor to dilute the gas to be supplied to the reaction. When using this reactor configuration, the temperature rise can be suppressed due to the dilution effect, so the durability of the catalyst is improved. In addition, since the equilibrium conversion rate increases due to the decrease in the reactor outlet temperature, the number of reactor stages may be reduced compared to the configuration of a simple multi-stage reactor.

[0053] In the olefin synthesis process (olefin synthesis unit 4), an olefin hydrocarbon-containing gas is obtained by bringing the methanol obtained in the methanol separation process into contact with a catalyst. Specifically, the olefin synthesis reaction is a known reaction sometimes called the MTO (Methanol-to-Olefin) reaction, which is carried out by bringing the methanol obtained in the methanol separation process into contact with a zeolite catalyst at 300°C to 500°C. The methanol obtained in the methanol separation process is in the form of a mixed solution with water, but if necessary, water may be separated by means such as distillation and then used for the olefin synthesis reaction. Alternatively, if necessary, at least a part of the methanol may be passed through a solid acid catalyst to be converted into dimethyl ether by a dehydration reaction and then passed through a zeolite catalyst. As the zeolite catalyst, in addition to aluminosilicates such as ZSM-5 type, silicoaluminophosphates such as SAPO-34 can also be used.

[0054] The olefin synthesis reaction may be carried out in a fixed-bed reactor or a fluidized-bed reactor. However, since the reaction is accompanied by relatively large heat generation, carrying out the reaction in a fluidized-bed reactor is advantageous as it is easy to avoid the generation of local high-temperature parts. Also, if the raw material is fed into the reactor at a temperature lower than the above reaction temperature, it can also serve as cooling for the reactor, which is efficient.

[0055] When the product of the olefin synthesis reaction is propylene, the reaction proceeds as follows. 3CH 3 OH → C 3 H 6 + 3H 2 O (Formula 3)

[0056] In the olefin synthesis reaction, mainly propylene is produced, but ethylene, butylene, etc. are also produced depending on the reaction conditions. Since these are converted into ethane and butane respectively by the subsequent hydrogenation reaction, there is no problem unless they are produced extremely in large amounts. In the olefin synthesis reaction, paraffin hydrocarbons such as ethane, propane, and butane may also be produced, but these do not inhibit the hydrogenation reaction process and are also components of town gas, so there is no problem unless they are produced extremely in large amounts.

[0057] In the olefin synthesis reaction, in addition to these, hydrocarbons having 5 or more carbon atoms, carbon monoxide, carbon dioxide, and hydrogen may be generated. Since hydrocarbons having 5 or more carbon atoms may condense in the city gas pipeline, it is not preferable that they be contained in a high concentration in the fuel gas. Since carbon monoxide, carbon dioxide, and hydrogen also need to be below a predetermined concentration for use as city gas, it is not preferable that they be contained in a high concentration in the fuel gas.

[0058] Hydrocarbons having 5 or more carbon atoms can be condensed and separated by pressurizing or cooling the produced olefin hydrocarbons. When the produced olefin hydrocarbons are further pressurized or cooled, propylene and butylene condense, but carbon monoxide, carbon dioxide, and hydrogen are hardly contained in the condensate, so carbon monoxide, carbon dioxide, and hydrogen can be removed from the olefin hydrocarbons.

[0059] In the hydrogenation step (hydrogenation reaction section 5), the olefin hydrocarbons are converted into paraffin hydrocarbons by reaction with hydrogen. The reaction temperature in the hydrogenation step is preferably 200°C or higher and 400°C or lower. Since the hydrogenation catalyst generally exhibits good activity under conditions of 200°C or higher, when the reaction temperature is 200°C or higher, the reaction between the olefin hydrocarbons and hydrogen easily proceeds. Also, when the reaction temperature is 400°C or lower, it is easy to suppress the steam reforming reaction of methane, paraffin hydrocarbons having 2 to 4 carbon atoms, and olefin hydrocarbons having 2 to 4 carbon atoms. The reaction temperature is more preferably 200°C or higher and 300°C or lower.

[0060] The hydrogenation catalyst used in the hydrogenation step has activity for the hydrogenation reaction of olefin hydrocarbons having 2 to 4 carbon atoms (formulas 4 to 6), and preferably shows substantially no activity for the steam reforming reaction of methane, paraffin hydrocarbons having 2 to 4 carbon atoms, and olefin hydrocarbons having 2 to 4 carbon atoms. When a catalyst showing activity for the steam reforming reaction is used, even if hydrogen decreases in the hydrogenation reaction of olefin hydrocarbons having 2 to 4 carbon atoms, new hydrogen is generated by the steam reforming reaction of hydrocarbons, so that the hydrogen concentration in the fuel gas may not be able to be reduced. Examples of such a catalyst showing reaction selectivity include a catalyst in which at least one of palladium or platinum is supported on an inorganic oxide carrier. C 2 H 4 + H 2 → C 2 H 6 (Formula 4) C 3 H 6 + H 2 → C 3 H 8 (Formula 5) C 4 H 8 + H 2 → C 4 H 10 (Formula 6)

[0061] The form of the hydrogenation reactor used in the hydrogenation reaction step is not particularly limited, and for example, it can be a fixed bed adiabatic reactor, a fixed bed adiabatic reactor having a recycle line, a heat exchange type reactor, and the like.

[0062] When the ratio of olefin hydrocarbons to hydrogen remaining in the methanation reaction is low, a large amount of hydrogen will remain in the fuel gas. On the other hand, when the ratio of olefin hydrocarbons is high, the hydrogen concentration will be extremely low, so that the hydrogenation reaction of olefin hydrocarbons will not proceed sufficiently, and olefin hydrocarbons may remain in the fuel gas. In addition, since the olefin hydrocarbon concentration is high during the reaction, polymerization of olefin hydrocarbons on the catalyst may cause problems such as deterioration due to carbon deposition on the catalyst. Therefore, the ratio of olefin hydrocarbons to hydrogen remaining in the methanation reaction is preferably 0.5 or more and 0.9 or less.

[0063] By increasing the ratio of hydrogen to carbon oxides supplied to the methanol synthesis catalyst, the hydrogen remaining in the methanation reaction will increase. Therefore, it is preferable to control the ratio of hydrogen to carbon oxides supplied to the methanol synthesis catalyst so that the ratio of olefin hydrocarbons to hydrogen remaining in the methanation reaction falls within the above range.

[0064] In the methanol synthesis reaction, the higher the pressure, the higher the equilibrium conversion rate. For example, at a pressure lower than 1 MPa (absolute pressure, the same below), in the temperature range where the methanol synthesis catalyst usually shows activity, the equilibrium conversion rate is low, and almost no methanol can be obtained. On the other hand, for example, to carry out the reaction at an extremely high pressure such as 5 MPa or more, equipment that can withstand high pressure is required, which is not economically advantageous. Therefore, the reaction pressure of the methanol synthesis reaction is preferably 1 MPa or more and 5 MPa or less, and more preferably 2.5 MPa or more and 4 MPa or less. When the reaction pressure of the methanol synthesis reaction is within this range, the equipment cost can be suppressed, and a fuel gas with a high calorific value can be obtained economically.

[0065] In the methanation reaction, the higher the pressure, the higher the equilibrium conversion rate. Compared with the methanol synthesis reaction, a sufficient equilibrium conversion rate can be obtained even at a relatively low pressure. However, since there is no need to change the pressure between the methanol synthesis reaction and the subsequent methanol separation process, it is usually carried out at a pressure reduced by only the pressure loss in the path through which the reaction gas flows from the reaction pressure of the methanol synthesis reaction. The same applies to the hydrogenation reaction.

[0066] Since a relatively high equilibrium conversion rate can be obtained even at low pressure in the olefin synthesis reaction, it is not necessarily advantageous to carry out the reaction at high pressure. The reaction pressure is preferably 0.1 MPa or more and 2 MPa or less, and more preferably 0.2 MPa or more and 0.6 MPa or less.

[0067] Figure 2 is a block flow diagram showing a method and equipment for producing a high calorific value fuel gas according to another aspect of the present invention. The method and equipment for producing a high calorific value fuel gas according to this embodiment also include a methanol synthesis step (methanol synthesis unit 1), a methanol separation step (methanol separation unit 2), a methanation step (methanation reaction unit 3), an olefin synthesis step (olefin synthesis unit 4), and a hydrogenation step (hydrogenation reaction unit 5). However, different from the embodiment shown in FIG. 1, the mixed gas of hydrogen and carbon dioxide as a raw material is first fed into a reverse shift reaction step (reverse shift reaction unit 6), and a part of the carbon dioxide reacts with hydrogen to be converted into carbon monoxide and water. After water is separated in the subsequent water separation step (water separation unit 7), it is fed into the methanol synthesis step (methanol synthesis unit 1).

[0068] The equilibrium conversion rate of methanol synthesis from carbon dioxide and hydrogen is lower than that of methanol synthesis from carbon monoxide and hydrogen. Therefore, when a raw material gas composed of carbon dioxide and hydrogen is directly fed into the methanol synthesis unit, a sufficient amount of methanol production cannot be obtained, and as a result, the calorific value of the fuel gas to be produced may not increase. In order to obtain a sufficient amount of methanol production, there is a method of increasing the reaction pressure in the methanol synthesis step, but the equipment cost becomes high, and it is not economically advantageous.

[0069] In the method of this embodiment, since the raw material gas composed of carbon dioxide and hydrogen can be converted into a mixed gas composed of carbon monoxide, carbon dioxide and hydrogen by the reverse shift reaction, a sufficient amount of methanol can be produced without increasing the reaction pressure in the methanol synthesis step.

[0070] Since the reverse shift reaction is an endothermic reaction, input of thermal energy is required. However, since both the methanation reaction and the olefin synthesis reaction are accompanied by relatively large heat generation, if the heat of these reactions is used for the endotherm of the reverse shift reaction, the efficiency of fuel gas production will be increased. As a means of heat exchange, direct heat exchange may be performed using a heat exchanger between the gas after the methanation reaction or the gas after the olefin synthesis reaction and the raw material gas composed of carbon dioxide and hydrogen supplied to the reverse shift reaction. Alternatively, high-pressure steam may be generated by heat exchange with the gas after the methanation reaction or the gas after the olefin synthesis reaction, and the raw material gas composed of carbon dioxide and hydrogen supplied to the reverse shift reaction may be heated by heat exchange with this high-pressure steam.

[0071] As the reverse shift catalyst, known CO shift catalysts such as copper-zinc catalysts and iron-chromium catalysts can be used.

[0072] Due to the constraints of heat exchange, the temperature of the reverse shift reaction is lower than the outlet temperature of the methanation reaction and the olefin synthesis reaction, and is usually 200°C or higher and 500°C or lower, preferably 250°C or higher and 300°C or lower. Within this range, the conversion rate of carbon dioxide to carbon monoxide is ensured, and heat exchange via high-pressure steam is also easy.

[0073] Since the reverse shift reaction is an endothermic reaction, if it is carried out adiabatically, the temperature of the catalyst layer may decrease and the reverse shift reaction may stop progressing. When the reaction is carried out while heating with high-pressure steam using a heat exchange type reactor, the reaction can proceed stably and easily.

[0074] The equilibrium conversion rate of the reverse shift reaction hardly depends on the reaction pressure. On the other hand, side reactions occurring on the reverse shift catalyst (for example, hydrocarbon formation) generally tend to proceed more readily as the reaction pressure is higher. Therefore, when side reactions on the reverse shift catalyst are a concern, it is preferable to carry out the reverse shift reaction at a relatively low pressure, increase the pressure after water separation, and then feed it into the methanol synthesis section.

[0075] The reaction pressure of the reverse shift reaction is 0.2 MPa or more and 4 MPa or less, more preferably 0.3 MPa or more and 1 MPa or less.

[0076] 〔Examples and Comparative Examples〕 The following shows trial calculation examples based on process calculations. The pressure is 0.5 MPa in the olefin synthesis section and 3 MPa in all other parts, and pressure losses and heat radiation losses in each device and piping are not considered. Also, in the olefin synthesis reaction, in addition to propylene, ethylene, butylene, etc. are also produced, but here it is assumed that all produce propylene.

[0077] 〔Example 1〕 As an aspect of the method for producing a high calorific value fuel gas and the production equipment of the present invention, the trial calculation results of an example for producing a high calorific value fuel gas based on the process flow diagram of FIG. 3 are shown. The raw material gas is introduced into the methanol synthesis section 1 at a temperature of 25°C and a flow rate of 1 mol / s of carbon dioxide and 3.895 mol / s of hydrogen. In the methanol synthesis section 1, in the heat exchanger 11, the raw material gas is heated to 210°C by heat exchange with medium pressure steam (MPS, 220°C) and then introduced into the methanol synthesis reactor 12. The methanol synthesis reactor 12 is a heat exchange type reactor, and the reaction proceeds while maintaining approximately 230°C while removing the heat generated by the methanol synthesis reaction, and the methanol synthesis reaction proceeds to the equilibrium composition at 230°C (methanol synthesis step). The heat is recovered as medium pressure steam. The gas after the methanol synthesis reaction recovers heat as low pressure steam (LPS, 150°C) in the heat exchanger 13, is cooled to 160°C, and is sent to the methanol separation section 2.

[0078] In the methanol separation section 2, the gas after the methanol synthesis reaction is cooled to 40°C using cooling water (CW) in the heat exchanger 21, and further cooled to below room temperature using a refrigerator and a heat exchanger (not shown). In the gas-liquid separation drum 22, the produced methanol is separated (methanol separation step).

[0079] In the methanation reaction section 3, the total amount of the synthesis gas from which methanol has been separated in the methanol separation section 2 is heated to 140°C by heat exchange with low-pressure steam in the heat exchanger 31. Further, the gas branched from the outlet of the heat exchanger 33 described later is mixed via the recycle compressor 34 and fed into the methanation reactor 32 at 245°C, where the methanation reaction of the synthesis gas takes place (methanation step). The methanation reactor 32 is an adiabatic reactor. As the methanation progresses, the temperature rises, and the methanation reaction proceeds to the equilibrium composition at 544°C. The gas after the methanation reaction is cooled to 290°C while recovering heat as high-pressure steam (HPS, 280°C) in the heat exchanger 33. The cooled gas branches from the gas sent to the recycle compressor 34, and the remainder is cooled to 230°C while recovering heat as medium-pressure steam in the heat exchanger 35 and fed into the methanation reactor 36. The methanation reactor 36 is also an adiabatic reactor. As the methanation progresses, the temperature rises, and the methanation reaction proceeds to the equilibrium composition at 365°C.

[0080] The gas at the outlet of the methanation reactor 36 is cooled to 230°C while recovering heat as medium-pressure steam in the heat exchanger 37 and fed into the methanation reactor 38, where the methanation reaction further proceeds.

[0081] The mixed solution of methanol and water separated in the methanol separation section 2 is fed into the olefin synthesis section 4. The mixed solution is depressurized to 0.5 MPa at the throttle valve 41, heated to 140 °C with low-pressure steam, and vaporized. The obtained mixed gas of methanol and steam is fed into the olefin synthesis reactor 43. The olefin synthesis reactor 43 is a fluidized bed reactor, and with a slightly large heat release, it generates a gas mainly composed of propylene from methanol. The outlet gas of the olefin synthesis reactor 43 is cooled to 160 °C while recovering heat as low-pressure steam in the heat exchanger 44, further cooled to 40 °C using cooling water in the heat exchanger 45, and in the gas-liquid separation drum 46, the condensed water is separated to obtain a gas mainly composed of propylene, which is then pressurized to 3.0 MPa by the compressor 47 and fed into the hydrogenation reaction section 5.

[0082] In the hydrogenation reaction section, the outlet gas of the methanation reactor 38 and the outlet gas of the compressor 47 are mixed and fed into the hydrogenation reactor 51 at 238 °C. In the hydrogenation reactor 51, the hydrogenation reaction of olefin hydrocarbons proceeds adiabatically, and with a slight temperature increase, the olefin hydrocarbons are almost completely converted to paraffin hydrocarbons. The outlet gas of the hydrogenation reactor 51 is cooled to 160 °C while recovering low-pressure steam in the heat exchanger 52, further cooled to 40 °C using cooling water in the heat exchanger 53, and further cooled to below room temperature using a refrigerator and a heat exchanger (not shown), and in the gas-liquid separation drum 54, the condensed water is separated to obtain fuel gas.

[0083] Table 1 shows the temperature and flow rate at the main parts of the process.

[0084]

Table 1

[0085] The composition of the generated fuel gas (volume basis after dehydration) is 90.8% methane, 7.0% propane, and 2.2% hydrogen, and the content of carbon monoxide, carbon dioxide, and propylene is all 0.01% or less. Also, the calorific value of the generated fuel gas is 43.3 MJ / m3 As a result, by simply adding a small amount of propane or butane, the calorific value can be adjusted to that suitable for use as city gas.

[0086] The ratio of the calorific value of the produced fuel gas to the calorific value of the hydrogen used as the raw material is 77.9%. When the methanation reaction of hydrogen and carbon dioxide proceeds as per the reaction formula, the ratio of the calorific value of the produced methane to the calorific value of the raw material hydrogen is 77.9%. According to the method of the present invention, it can be seen that a fuel gas with a high calorific value can be produced without a significant decrease in efficiency as compared with the case of producing only methane.

[0087] 〔Example 2〕 As one aspect of the method and production equipment for producing a high-calorific-value fuel gas of the present invention, the estimated results of a production example of a high-calorific-value fuel gas based on the process flow diagram of FIG. 4 are shown. The raw material gas is supplied to the reverse shift reaction section 6 at a temperature of 25°C and a flow rate of 1 mol / s of carbon dioxide and 3.850 mol / s of hydrogen. The raw material gas is heated to 270°C by heat exchange with high-pressure steam in the heat exchanger 61 and then fed into the reverse shift reactor 62. The reverse shift reactor 62 is a heat exchange type reactor. The fed raw material gas is heated by high-pressure steam and maintains approximately 270°C for the reverse shift reaction to proceed, and flows out of the reactor at the equilibrium composition of 270°C. The outlet gas of the reverse shift reactor 62 is cooled to 160°C in the heat exchanger 63 while recovering low-pressure steam and sent to the water separation section 7.

[0088] In the water separation section 7, the gas after the reverse shift reaction is further cooled to 40°C using cooling water in the heat exchanger 71. The water condensed by the cooling is separated from the synthesis gas in the gas-liquid separation drum 72 (water separation process). The following steps are the same as those in Example 1.

[0089] The temperatures and flow rates at the main points of the process are shown in Table 2.

[0090]

Table 2

[0091] The composition of the produced fuel gas (by volume after dehydration) is 87.8% methane, 10.0% propane, 2.3% hydrogen, and carbon monoxide, carbon dioxide, and propylene are all 0.01% or less. Also, the calorific value of the produced fuel gas is 45.0 MJ / m 3 and it has a calorific value that can be used as town gas without heat adjustment. Compared with Example 1, the increase in calorific value is due to the implementation of the reverse shift process, which increased the proportion of carbon monoxide in the carbon oxides fed into the methanol synthesis process and thus increased the methanol yield.

[0092] The ratio of the calorific value of the produced fuel gas to the calorific value of the hydrogen used as a raw material is 77.9%, and a high-calorific-value fuel gas can be produced without a significant decrease in efficiency compared to the case of producing only methane.

[0093] 〔Comparative Example〕 As an example of a method and manufacturing facility for producing a high-calorific-value fuel gas not according to the method of the present invention, the estimated results of producing a high-calorific-value fuel gas based on the process flow diagram of FIG. 5 are shown.

[0094] In this example, unlike Example 1, the hydrogenation reaction step is carried out before mixing with the product gas of the methanation step.

[0095] The raw material gas is supplied to the high-calorific-value fuel gas production facility at a temperature of 25°C and a flow rate of 1 mol / s of carbon dioxide and 3.895 mol / s of hydrogen, the same as in Example 1. Among them, 1 mol / s of carbon dioxide and 3.805 mol / s of hydrogen are introduced into the methanol synthesis section 1, and the remaining 0.090 mol / s of hydrogen is mixed with the gas at the outlet of the compressor 47 in the olefin synthesis section and subjected to the hydrogenation reaction step.

[0096] Table 3 shows the temperature and flow rate at the main points of the process.

[0097]

Table 3

[0098] The composition of the produced fuel gas (on a volume basis after dehydration) is 85.9% methane, 6.7% hydrogen, 5.2% propane, 1.3% propylene, 0.9% carbon dioxide, and 0.01% or less carbon monoxide. Also, the calorific value of the produced fuel gas is 41.3 MJ / m 3 It was as follows.

[0099] The ratio of the calorific value of the produced fuel gas to the calorific value of the hydrogen used as a raw material was 78.3%, which was higher than that of the examples. This is presumably because the hydrogen, carbon dioxide concentration, and propylene concentration in the produced fuel gas were high, and thus the methanation reaction, which is an exothermic reaction, and the hydrogenation reaction of propylene were not completed.

[0100] In this comparative example, unlike the fuel gas production method of the present invention, it is not configured to obtain propane by the reaction of hydrogen remaining after the methanation reaction with propylene. For this reason, since the hydrogen remaining after the methanation reaction remains in the fuel gas as it is, the hydrogen concentration in the fuel gas increases. Also, since the hydrogenation reaction of propylene is carried out without being diluted by the gas obtained in the methanation reaction, the temperature rise due to the heat generation of the hydrogenation reaction becomes large, and the hydrogenation reaction does not reach equilibrium. Even though a sufficiently excessive amount of hydrogen exists with respect to propylene, propylene remains at a high concentration. In addition, since the hydrogenation catalyst comes into contact with olefin hydrocarbons at a high temperature, there is also concern about deterioration of the hydrogenation catalyst due to heat and deterioration due to coking.

[0101] 〔Alternative Embodiment〕 〔1〕In the above embodiment, an example in which the pressures in the methanol synthesis step, methanation step, and hydrogenation reaction step were all the same (3 MPa) was particularly described. However, in the methanol synthesis step, methanation step, and hydrogenation step according to the present invention, the pressures may be the same or different. Usually, since a pressure loss occurs in the reactor and heat exchanger, the reaction pressure decreases to some extent in the order of the methanol synthesis step, methanation step, and hydrogenation reaction step unless special pressure increasing means are taken, but this is not a problem.

[0102] 〔2〕In the above embodiment, when the reverse shift process is carried out, the case where the reaction pressure is the same (3 MPa) as the pressures in the methanol synthesis process, the methanation process and the hydrogenation reaction process has been particularly described. However, in the reverse shift process, methanol synthesis process, methanation process and hydrogenation process according to the present invention, the pressures may be the same or different. In addition, when the reverse shift catalyst shows activity for hydrocarbon or methanol synthesis under high pressure conditions, it is conceivable that the reverse shift process is carried out at low pressure and the pressure is increased after the water separation process.

[0103] 〔3〕In the above embodiment, the case where the olefin synthesis catalyst produces only propylene has been described. In the olefin synthesis catalyst, in addition to propylene, ethylene and butylene (1-butene, 2-butene, 2-methylpropene) also usually occur. These are also hydrogenated under the same conditions as propylene to produce ethane or butane. Ethane and butane, like propane, also have the effect of increasing the calorific value of the fuel gas. Therefore, the production of ethylene and butylene does not pose a problem. On the olefin synthesis catalyst, a small amount of paraffinic hydrocarbons (ethane, propane and butane) also occur, but these also have the effect of increasing the calorific value of the fuel gas like propane, so it does not pose a problem.

[0104] The configurations disclosed in the above embodiments (including other embodiments) can be applied in combination with the configurations disclosed in other embodiments as long as there is no contradiction, and the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope not departing from the object of the present invention.

Industrial Applicability

[0105] The present invention can be used as a method and equipment for producing a high calorific value fuel gas mainly composed of methane and further containing at least one component of ethane, propane and butane, which can be used as city gas from hydrogen and carbon oxides.

Description of Symbols

[0106] 1 Methanol synthesis section 2 Methanol separation section 3 Methanation reaction section 4 Olefin synthesis section 5 Hydrogenation reaction section 6 Reverse shift reaction section 7 Water separation section 12 Methanol synthesis reactor 32, 36, 38 Methanation reactors 43 Olefin synthesis reactor 51 Hydrogenation reactor 62 Reverse shift reactor

Claims

1. A method for producing a high calorific value fuel gas mainly composed of methane and further containing at least one component of ethane, propane, and butane from hydrogen and carbon oxides, comprising: a methanol synthesis step of synthesizing methanol by passing a gas containing hydrogen and carbon oxides through a methanol synthesis catalyst; a methanol separation step of cooling the gas obtained in the methanol synthesis step to separate methanol; a methanation step of synthesizing methane by passing the gas containing hydrogen and carbon oxides obtained by separating methanol in the methanol separation step through a methanation catalyst; an olefin synthesis step of obtaining an olefin hydrocarbon-containing gas containing at least one component of ethylene, propylene, and butylene by passing the methanol obtained in the methanol separation step through an olefin synthesis catalyst; a hydrogenation step of mixing the methane main component gas obtained in the methanation step and the olefin hydrocarbon-containing gas obtained in the olefin synthesis step, and passing the mixture through a hydrogenation catalyst to convert the olefin hydrocarbon into a paraffin hydrocarbon by reaction with hydrogen. A method for producing a high calorific value fuel gas.

2. The carbon oxide is carbon dioxide. Prior to the implementation of the methanol synthesis step, a reverse shift step is performed in which a mixed gas of hydrogen and carbon dioxide is passed through a reverse shift catalyst to convert at least a part of the carbon dioxide into carbon monoxide. The gas obtained in the reverse shift step is cooled, and at least a part of the water contained in the gas obtained by the reverse shift reaction is separated, and then the gas is fed to the methanol synthesis step. The method for producing a high calorific value fuel gas according to Claim 1.

3. The method for producing a high calorific value fuel gas according to Claim 2, wherein the reaction heat obtained in the methanation step or the olefin synthesis step is used as a heat source for the reverse shift reaction.

4. Equipment for producing a high calorific value fuel gas mainly composed of methane and further containing at least one component of ethane, propane, and butane from hydrogen and carbon oxides, comprising: a methanol synthesis section for synthesizing methanol by passing a gas containing hydrogen and carbon oxides through a methanol synthesis catalyst; a methanol separation section for cooling the gas sent from the methanol synthesis section to separate methanol; a methanation reaction section for synthesizing methane by passing the raw material gas containing hydrogen and carbon oxides separated from methanol in the methanol separation section through a methanation catalyst; An olefin synthesis section that passes the methanol separated in the methanol separation section through an olefin synthesis catalyst to obtain an olefin hydrocarbon-containing gas containing at least one component of ethylene, propylene, and butylene, A manufacturing facility for high calorific value fuel gas, comprising a hydrogenation reaction section that mixes the methane main component gas obtained in the methanation reaction section and the olefin hydrocarbon-containing gas obtained in the olefin synthesis section, and passes the mixture through a hydrogenation catalyst to convert olefin hydrocarbons into paraffin hydrocarbons by reaction with hydrogen.

5.

6. The manufacturing facility for high calorific value fuel gas according to claim 4, further comprising a reverse shift reaction section and a water separation section, wherein a mixed gas of hydrogen and carbon dioxide is passed through a reverse shift catalyst in the reverse shift reaction section to perform a reverse shift step of converting at least a part of the carbon dioxide into carbon monoxide, and the gas containing hydrogen, carbon monoxide, carbon dioxide, and steam obtained in the reverse shift step is cooled in the water separation section to separate at least a part of the steam, and then fed into the methanol synthesis section. The manufacturing facility for high calorific value fuel gas according to claim 5, configured to use the reaction heat obtained in the methanation reaction in the methanation reaction section or the olefin synthesis reaction in the olefin synthesis section as the heat source for the reverse shift reaction.

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