JP2023025483A - Production method for high calorific value fuel gas and production facility for high calorific value fuel gas - Google Patents

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

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

In recent years, from the viewpoint of global warming countermeasures, carbon-neutral fuels, which do not substantially increase the concentration of carbon dioxide in the atmosphere even when used for combustion, have attracted attention.

Methane can be obtained by collecting carbon dioxide from exhaust gases generated by industrial processes and thermal power generation, and reacting it with hydrogen obtained by electrolysis using renewable energy such as solar power and wind power generation. be done. The methane obtained by this method does not generate additional carbon dioxide even if it is used for combustion, so it can be considered as a carbon-neutral fuel that does not affect global warming.

The methanation reaction (equation 1) in which carbon dioxide and hydrogen are reacted to give methane is known.
_CO2 + _4H2- > _CH4 + _2H2O (formula 1)

In Patent Document 1, when a gas containing CO and H ₂ is methanated, a methanation reactor in which a Cu—Zn-based low temperature shift catalyst is arranged on the upstream side and a methanation catalyst is arranged on the downstream side is used. A method for the methanation of gases containing CO and H ₂ is disclosed, characterized by: Since the CO shift reaction (Equation 2) proceeds in the upstream low temperature shift reactor, most of the carbon monoxide contained in the raw material gas reacts with water vapor and is converted to carbon dioxide, and is deposited on the downstream methanation catalyst. It is thought that the methanation reaction of carbon dioxide is progressing.
CO+ _H2O → _CO2 + _H2 (formula 2)

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 References 1, 2).

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 it can be used as a raw material for city gas. Obtaining quality fuel gas is still a challenge.

The most commonly used source of town gas is natural gas, which is mainly composed of methane and contains minor amounts of ethane, propane, and butane. Natural gas does not normally contain hydrogen and carbon monoxide, and carbon dioxide is removed during the refining process of natural gas. In particular, in the case of city gas produced from liquefied natural gas as a raw material, hydrogen, carbon monoxide and carbon dioxide are almost completely removed in the process of liquefaction refining, so that they are substantially not contained.

The concentration of hydrocarbons (ethane, propane, and butane) other than methane contained in natural gas varies depending on the production area and refining method of natural gas. is added, and the calorific value is adjusted to a certain range (for example, 44.2 to 46.0 MJ/m ³ ). sent to the consumer.

If hydrogen, carbon monoxide and carbon dioxide are contained in city gas, the following problems may occur.

First, since carbon monoxide is highly toxic, there is a risk of poisoning when the gas leaks. The permissible concentration is set at 200 ppm, and from a safety point of view, the concentration in the fuel gas is desirably less than this, and even considering dilution with air, it is necessary to keep it at 1000 ppm or less.

Secondly, carbon dioxide is not only nonflammable, but also works to suppress combustion. Therefore, if it is mixed in 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.

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 city gas. Therefore, when hydrogen is mixed in the fuel gas, which is mainly composed of methane, the calorific value per unit volume is lowered. Furthermore, hydrogen is known to have a large impact on combustion equipment because of its high combustion speed.

As described above, when hydrogen, carbon monoxide and carbon dioxide are mixed with city gas, they have various effects on each stage of gas supply and consumption. , hydrogen, carbon monoxide and carbon dioxide concentrations are generally set.

An example is known in which the upper limit of the hydrogen concentration is set to 2% by volume in a pipeline network in which fuel filling stations for natural gas vehicles exist (Non-Patent Document 4). In addition, an example in which the hydrogen concentration is 4% or less by volume, the carbon dioxide concentration is 0.5% or less by volume, and the carbon monoxide concentration is 0.05% or less by volume (Non-Patent Document 5). , and an example in which the total concentration of methane and ethane is defined as 93% or more by volume and the total concentration of components other than hydrocarbons is defined as 4% or less by volume (Non-Patent Document 6).

Several methods are known for reducing the hydrogen concentration in the fuel gas obtained by the methanation reaction. For example, if the methanation reaction is carried out under conditions with less hydrogen than the stoichiometric ratio and excess carbon dioxide is removed by decarboxylation, both the hydrogen content and the carbon dioxide content can be reduced (Patent Document 4). ). This method has been adopted in the methanation of coke oven gas (Non-Patent Document 3). However, decarboxylation equipment generally has a high equipment cost and consumes a large amount of energy for operation, so there is a problem that economic efficiency is impaired.

As another method, a method is also known in which the methanation reaction is performed in multiple stages, the gas generated in the intermediate stages is cooled, and water is condensed and separated (Non-Patent Document 4, Patent Documents 2 and 3). By removing the produced 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 equipment costs. There is also a problem that the control of the separation process becomes complicated.

Furthermore, a method in which the methanation reaction is performed under conditions with less hydrogen than the stoichiometric ratio and excess carbon dioxide is removed by decarboxylation, and a method in which the methanation reaction is performed in multiple stages and the gas generated in the middle is removed. Both methods of cooling and condensing and separating water have the problem of increasing the carbon monoxide concentration in the produced fuel gas because the conditions are such that carbon monoxide is likely to be produced in equilibrium.

City gas is produced using natural gas as its main raw material, but as mentioned above, it is supplied after adding propane or butane to adjust the calorific value to a certain range so that it can be used stably in combustion equipment. ing. The methanation reaction of carbon oxides only produces methane unless a special catalyst or reaction conditions are employed. The calorific value of methane is 39.9 MJ/m ³ , which is slightly lower than the calorific value of general city gas (for example, 44.2-46.0 MJ/m ³ ). Therefore, when the gas obtained by the methanation reaction is used as a raw material for city gas, in order to ensure the same calorific value and combustibility as general city gas, the methane obtained by the methanation reaction must be It is necessary to add a relatively large amount of propane (101 MJ/m ³ ) or butane (134 MJ/m ³ ) corresponding to 15-20%. The availability of propane or butane, which can be regarded as carbon-neutral, is extremely limited, but when propane or butane derived from fossil fuels are used for calorific value adjustment, the carbon-neutrality of the produced gas will be impaired. Become.

In addition, if the gas generated by the methanation reaction contains a large amount of hydrogen, carbon monoxide and carbon dioxide, these have a lower calorific value per unit volume than methane, so propane and There is also a problem of further impairing the carbon neutrality of the produced gas because it becomes necessary to mix a larger amount of butane or the like.

As described above, a method of producing fuel gas with a high calorific value, which can be used as city gas from hydrogen and carbon oxides and which is mainly composed of methane and further contains at least one of ethane, propane and butane, has not yet been established. The reality is that they are not.

JP-A-60-235893 JP 2015-124217 A JP 2018-135283 A JP 2019-26595 A

Edited by the Japan Society of Chemical Engineers, Chemical Process Collection, 1970, p.153 Catalysis Society of Japan, Catalysis Handbook, 2008, p.535 Kawagoe, Matsuda, Matsushima and Uematsu, Hitachi Hyoron, Vol.68, No.10, 1986, p.73 E.I.Koytsoumpa and S.Karellas, Renewable and Sustainable Energy Reviews, Vol.94, 2018, p.536 Biogas Purchasing Guidelines, Osaka Gas Co., Ltd., 2008 Biogas Purchasing Guidelines, Tokyo Gas Co., Ltd., 2008

The problem to be solved by the present invention is a method for producing a fuel gas with a high calorific value, which can be used as city gas from hydrogen and carbon oxides, and which is mainly composed of methane and further contains at least one component of ethane, propane and butane. is to provide

The characteristic configuration of the method for producing a high calorific value fuel gas according to the present invention is as follows:
A method for producing a high calorific value fuel gas containing methane as a main component and at least one 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 passing a gas containing hydrogen and carbon oxides obtained by separating methanol in the methanol separation step through a methanation catalyst to synthesize methane;
an olefin synthesis step of passing 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;
The methane main component gas obtained in the methanation step and the olefinic hydrocarbon-containing gas obtained in the olefin synthesis step are mixed, passed through a hydrogenation catalyst, and the olefinic hydrocarbons are converted to paraffinic hydrocarbons by reaction with hydrogen. and a hydrogenation step.

According to this characteristic configuration, the hydrogen in the gas containing hydrogen, which is mainly composed of methane and obtained in the methanation step, is reduced by the reaction with the olefin hydrocarbon, so that the hydrogen remaining in the fuel gas is reduced. Concentration can be kept low. In addition, since the fuel gas contains at least one of ethane, propane, and butane produced by the reaction of the olefinic hydrocarbon and hydrogen, the produced fuel gas has a higher calorific value than methane. It can be used as a raw material for city gas as it is or after slight adjustment of the calorific value.

A further characteristic configuration of the method for producing high calorific value fuel gas according to the present invention is as follows:
The carbon oxide is carbon dioxide, and prior to the methanol synthesis step, a reverse shift step of passing a mixed gas of hydrogen and carbon dioxide through a reverse shift catalyst to convert at least a portion of the carbon dioxide to carbon monoxide. In addition, the gas obtained in the reverse shift reaction is cooled to separate at least part of the water contained in the gas obtained in the reverse shift reaction, and then supplied to the methanol synthesis step.

A methanol synthesis reaction by hydrogenation of carbon dioxide has a lower equilibrium conversion rate than a 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 smaller than when the carbon oxide contains a large amount of carbon monoxide. If the amount of methanol produced is small, the amounts of ethane, propane, and butane contained in the produced fuel gas will also decrease, so it may be difficult to sufficiently increase the calorific value of the produced fuel gas.
As a method of 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 facility costs and is not economically advantageous.
According to this characteristic configuration, even if the carbon oxide is mainly carbon dioxide, the reverse shift reaction can increase the ratio of carbon monoxide in the carbon oxide, so that the amount of methanol produced increases and the produced fuel It is easy to increase the calorific value of the gas.

A further characteristic configuration of the method for producing high calorific value fuel gas according to the present invention is as follows:
The point is that the reaction heat obtained in the methanation process or the olefin synthesis process is used as the heat source for the reverse shift reaction.

Since the reverse shift reaction is an endothermic reaction, heat must be supplied for the reaction to proceed. Since the methanation reaction and the olefin synthesis reaction usually proceed at higher temperatures than the reverse shift reaction, the heat generated in these reactions can be used as a heat source for the reverse shift reaction.
According to this characteristic configuration, the reaction heat of the methanation reaction or the olefin synthesis reaction is used as the heat source of the reverse shift reaction, so the efficiency of fuel gas generation can be enhanced.

The characteristic configuration of the high calorific value fuel gas production facility according to the present invention is as follows:
a methanol synthesis section for synthesizing methanol by passing a gas containing hydrogen and carbon oxides through a methanol synthesis catalyst;
a methanol separation unit that separates methanol by cooling the gas sent from the methanol synthesis unit;
a methanation reaction section for synthesizing methane by passing a raw material gas containing hydrogen and carbon oxides separated from methanol in the methanol separation section through a methanation catalyst;
an olefin synthesis section for passing 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;
The methane main component gas obtained in the methanation reaction section and the olefinic hydrocarbon-containing gas obtained in the olefin synthesis section are mixed, passed through a hydrogenation catalyst, and the olefinic hydrocarbons are reacted with hydrogen to produce paraffinic hydrocarbons. is provided with a hydrogenation reaction part that converts to

According to this characteristic configuration, the hydrogen in the gas containing hydrogen, which is mainly composed of methane, obtained in the methanation reaction section is reduced by the reaction with the olefinic hydrocarbon, so that the hydrogen remaining in the fuel gas concentration can be kept low. In addition, since the fuel gas contains at least one of ethane, propane, and butane produced by the reaction of the olefinic hydrocarbon and hydrogen, the produced fuel gas has a higher calorific value than methane. Therefore, it can be used as a raw material for city gas as it is or after slight calorie adjustment.

A further characteristic configuration of the high calorific value fuel gas production facility according to the present invention is as follows:
A reverse shift step further comprising a reverse shift reaction section and a water separation section, wherein the mixed gas of hydrogen and carbon dioxide is passed through a reverse shift catalyst in the reverse shift reaction section to convert at least part of the carbon dioxide into carbon monoxide. and cooling the gas containing hydrogen, carbon monoxide, carbon dioxide and water vapor obtained in the reverse shift step in the water separation section, separating at least part of the water vapor, and then feeding it to the methanol synthesis section. The point is that it is configured to

According to this characteristic configuration, even when the carbon oxide is mainly carbon dioxide, the reverse shift reaction can increase the ratio of carbon monoxide in the carbon oxide, so that the amount of methanol produced increases and the methanol is produced. The calorific value of the fuel gas tends to increase.

A further characteristic configuration of the high calorific value fuel gas production facility according to the present invention is as follows:
It is characterized in that the reaction heat obtained by the methanation reaction in the methanation reaction section or the olefin synthesis reaction in the olefin synthesis section is used as the heat source for the reverse shift reaction.

According to this characteristic configuration, the reaction heat of the methanation reaction or the olefin synthesis reaction is used as the heat source of the reverse shift reaction, so the efficiency of fuel gas generation can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block flow diagram showing one aspect of the high calorific value fuel gas production method and production equipment of the present invention. FIG. 4 is a block flow diagram showing another aspect of the high calorific value fuel gas production method and production equipment of the present invention. 1 is a process flow diagram showing one aspect of the method and equipment for producing a high calorific value fuel gas of the present invention. FIG. FIG. 4 is a process flow chart showing another aspect of the method and equipment for producing a high calorific value fuel gas of the present invention. 1 is a process flow diagram showing an example of a method and equipment for producing a high calorific value fuel gas without using the method of the present invention; FIG.

[Embodiment]
Embodiments of the high calorific value fuel gas production method and production equipment will be described below. FIG. 1 is a block flow diagram showing the method and equipment for producing a high calorific value fuel gas according to the present invention.

The method for producing a high calorific value fuel gas according to the present embodiment includes a step of passing a gas containing hydrogen and carbon oxides through a methanol synthesis catalyst to synthesize methanol (methanol synthesis step), and is cooled to separate methanol (methanol separation step), and a step of passing the gas containing hydrogen and carbon oxides after separating methanol in the methanol separation step through a methanation catalyst to synthesize methane (methanation a step of passing 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 (olefin synthesis step); A step of mixing the methane main component gas obtained in the olefin synthesis step with the olefin hydrocarbon-containing gas obtained in the olefin synthesis step, passing it through a hydrogenation catalyst, and converting the olefin hydrocarbons into paraffin hydrocarbons by reaction with hydrogen (hydrogenation step ).

Hydrogen and carbon oxides (carbon monoxide and carbon dioxide) used as raw materials may be produced by any method as long as the purity and properties do not interfere with the implementation of the methanol synthesis process. do not have. Hydrogen may be electrolytic hydrogen obtained, for example, by electrolyzing water. Carbon dioxide may be recovered from combustion exhaust gas by a known carbon dioxide recovery method such as an 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 water vapor at high temperature contains both carbon monoxide and carbon dioxide as carbon oxides, and the equilibrium conversion rate of the methanol synthesis reaction is is particularly preferable as a raw material gas.

If the raw material gas (hydrogen, carbon monoxide, carbon dioxide, or a mixture thereof) contains sulfur, halogen compounds, siloxane compounds, heavy hydrocarbons, etc., these may cause deterioration of the methanol synthesis catalyst. It is preferable to remove these before subjecting them to the reaction, if necessary.

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

As the methanol synthesis catalyst, a known copper-zinc catalyst, chromium-zinc catalyst, copper-chromium-zinc catalyst, or the like can be used.

The temperature of 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. Within the above range, a sufficient reaction rate and a conversion rate to methanol can be ensured, so that the production of methanol can be ensured without using an excessive amount of catalyst.

Since the methanol synthesis reaction is accompanied by constant heat generation, it is preferable to use a heat exchange reactor in which the reaction proceeds while removing the generated heat as the methanol synthesis reactor.

In the methanol separation step (methanol separation section 2), the gas containing methanol and unreacted hydrogen, carbon monoxide, and carbon dioxide obtained in the methanol synthesis step is cooled to separate and recover methanol as a liquid. Since the gas after the methanol synthesis step is at a sufficiently high temperature, its sensible heat may be recovered and used for preheating, for example, by exchanging heat with the gas to be used for methanol synthesis.

Methanol has a certain vapor pressure even at room temperature, so in addition to cooling by heat exchange, water cooling, or air cooling, using a refrigerator and heat exchanger to cool below room temperature increases the amount of methanol recovered. be able to. It is preferably cooled to 20° C. or lower, more preferably 10° C. or lower to separate methanol.

In the methanation step (methanation reaction section 3), the gas containing unreacted hydrogen, carbon monoxide and carbon dioxide after separation of the methanol is brought into contact with a methanation catalyst to generate methane.

As the methanation catalyst used in the methanation step, a known methanation catalyst containing Ni, Ru, or the like can be used.

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. Within the above range, a sufficient reaction rate is likely to be obtained, making it easier to proceed with the methanation reaction without using an excessive amount of catalyst, and the outlet temperature of the methanation reaction does not rise too high. Therefore, it becomes easy to ensure the durability of the catalyst.

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

Since the methanation reaction is accompanied by relatively large heat generation, thermal deterioration of the catalyst may be a problem. The gas on the reactor outlet side can also be returned to the reactor inlet side to dilute the gas to be subjected to the reaction. Using this reactor configuration improves the durability of the catalyst because the dilution effect reduces the temperature rise. In addition, since the effect of increasing the equilibrium conversion rate is produced by lowering the reactor outlet temperature, it may be possible to reduce the number of reactor stages compared to a simple multi-stage reactor configuration.

In the olefin synthesis step (olefin synthesis section 4), an olefin hydrocarbon-containing gas is obtained by bringing the methanol obtained in the methanol separation step into contact with a catalyst. Specifically, the olefin synthesis reaction is a known reaction sometimes called MTO (Methanol-to-Olefin) reaction. conduct. The methanol obtained in the methanol separation step is a mixed solution with water, but if necessary, the water may be separated by means such as distillation before being subjected to the olefin synthesis reaction. Alternatively, at least part of the methanol may optionally be passed through a solid acid catalyst, converted to dimethyl ether by a dehydration reaction, and then passed through a zeolite catalyst. Zeolite catalysts that can be used include aluminosilicates such as ZSM-5 type, as well as silicoaluminophosphates such as SAPO-34.

The olefin synthesis reaction may be carried out in a fixed bed reactor or a fluidized bed reactor. This is advantageous because it is easy to avoid the occurrence of Also, if the raw material is fed into the reactor at a temperature lower than the reaction temperature, the reactor can also be cooled, which is efficient.

The olefin synthesis reaction proceeds as follows when the product is propylene.
_3CH3OH → _C3H6 + _3H2O ( _equation 3)

In the olefin synthesis reaction, propylene is mainly produced, but ethylene, butylene, etc. are also produced depending on the reaction conditions. These produce ethane and butane, respectively, in the latter hydrogenation reaction, so there is no problem as long as they are not produced in extremely large amounts. Paraffinic hydrocarbons such as ethane, propane, and butane are sometimes produced in olefin synthesis reactions, but they do not interfere with the hydrogenation reaction process and are also components of city gas, so unless they are produced in extremely large amounts. No problem.

In the olefin synthesis reaction, in addition to these, hydrocarbons having 5 or more carbon atoms, carbon monoxide, carbon dioxide, and hydrogen may be produced. Hydrocarbons with 5 or more carbon atoms may condense in the pipes of city gas, so it is not preferable for them to be contained in the fuel gas at a high concentration. Carbon monoxide, carbon dioxide, and hydrogen also need to be contained at a predetermined concentration or less in order to be used as city gas, so it is not preferable for them to be contained in the fuel gas at high concentrations.

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

In the hydrogenation step (hydrogenation reaction unit 5), olefinic hydrocarbons are converted to paraffinic 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, the reaction temperature of 200° C. or higher facilitates the reaction between the olefinic hydrocarbon and hydrogen. When the reaction temperature is 400° C. or lower, the steam reforming reaction of methane, paraffin hydrocarbons having 2 to 4 carbon atoms and olefinic hydrocarbons having 2 to 4 carbon atoms is easily suppressed. More preferably, the reaction temperature is 200° C. or higher and 300° C. or lower.

The hydrogenation catalyst used in the hydrogenation step has activity in the hydrogenation reaction of olefin hydrocarbons having 2 to 4 carbon atoms (formulas 4 to 6), and is also active for methane, paraffin hydrocarbons having 2 to 4 carbon atoms, and carbon It is preferable that it shows substantially no activity for the steam reforming reaction of olefinic hydrocarbons having a number of 2 or more and 4 or less. If a catalyst that exhibits activity for steam reforming reaction is used, even if hydrogen decreases in the hydrogenation reaction of olefinic hydrocarbons with 2 to 4 carbon atoms, new hydrogen is generated by the steam reforming reaction of hydrocarbons. Therefore, it may not be possible to reduce the hydrogen concentration in the fuel gas. Examples of catalysts exhibiting such reaction selectivity include catalysts in which at least one of palladium and platinum is supported on an inorganic oxide carrier.
_C2H4 + _H2 → _C2H6 (equation _{4 )
C3H6 + H2} → _C3H8 (equation ₅ )
_C4H8 + _H2 → _C4H10 (equation _{6 )}

The type of hydrogenation reactor used in the hydrogenation reaction step is not particularly limited, and may be, for example, a fixed bed adiabatic reactor, a fixed bed adiabatic reactor having a recycle line, a heat exchange reactor, or the like.

If the ratio of olefinic hydrocarbons to hydrogen remaining in the methanation reaction is small, a large amount of hydrogen will remain in the fuel gas. On the other hand, when the ratio of olefinic hydrocarbons is high, the hydrogen concentration becomes extremely low, and the hydrogenation reaction of olefinic hydrocarbons does not proceed sufficiently, and olefinic hydrocarbons may remain in the fuel gas. Since the concentration of olefinic hydrocarbons during the reaction is high, the olefinic hydrocarbons may polymerize on the catalyst, and deterioration of the catalyst due to carbon deposition may become a problem. Therefore, the ratio of olefinic hydrocarbons to hydrogen remaining in the methanation reaction is preferably 0.5 or more and 0.9 or less.

By increasing the ratio of hydrogen to carbon oxides supplied to the methanol synthesis catalyst, the amount of hydrogen remaining in the methanation reaction is increased. It is preferable to control the ratio of hydrogen to carbon oxides to be supplied to the methanol synthesis catalyst.

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, hereinafter the same), the equilibrium conversion rate becomes low in the temperature range where the methanol synthesis catalyst normally exhibits activity, and almost no methanol can be obtained. On the other hand, in order to carry out the reaction at an extremely high pressure such as 5 MPa or higher, 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, 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, it is possible to suppress equipment costs and economically obtain fuel gas with a high calorific value.

The higher the pressure, the higher the equilibrium conversion of the methanation reaction. Compared to the methanol synthesis reaction, a sufficient equilibrium conversion rate can be obtained even at a relatively low pressure. , at a pressure lower by the pressure loss in the path through which the reaction gas flows. The same applies to the hydrogenation reaction.

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

FIG. 2 is a block flow diagram showing a method and equipment for producing a high calorific value fuel gas according to another embodiment of the present invention. The method and equipment for producing high calorific value fuel gas according to the present embodiment also include a methanol synthesis process (methanol synthesis section 1), a methanol separation process (methanol separation section 2), a methanation process (methanation reaction section 3), an olefin It has a synthesis step (olefin synthesis section 4) and a hydrogenation step (hydrogenation reaction section 5). However, unlike the embodiment shown in FIG. 1, the raw material mixed gas of hydrogen and carbon dioxide is first sent to the reverse shift reaction step (reverse shift reaction section 6), and part of the carbon dioxide reacts with hydrogen. After the water is separated in the subsequent water separation step (water separation section 7), it is sent to the methanol synthesis step (methanol synthesis section 1).

The equilibrium conversion of methanol synthesis from carbon dioxide and hydrogen is low compared to that of methanol synthesis from carbon monoxide and hydrogen. Therefore, when the raw material gas composed of carbon dioxide and hydrogen is directly sent to the methanol synthesizing section, a sufficient amount of methanol cannot be produced, and as a result, the calorific value of the produced fuel gas may not increase. In order to obtain a sufficient amount of methanol produced, there is a method of increasing the reaction pressure in the methanol synthesis step, but this method is economically unadvantageous due to high facility costs.

In the method of this aspect, the raw material gas consisting of carbon dioxide and hydrogen can be converted into a mixed gas consisting of carbon monoxide, carbon dioxide and hydrogen by the reverse shift reaction, so the reaction pressure in the methanol synthesis step can be increased. It is possible to obtain a sufficient amount of methanol production without

Since the reverse shift reaction is an endothermic reaction, it is necessary to input thermal energy. Endothermic use increases the efficiency of fuel gas production. As a means of heat exchange, a heat exchanger is used to directly exchange heat between the gas after the methanation reaction or the gas after olefin synthesis and the raw material gas consisting of carbon dioxide and hydrogen supplied to the reverse shift reaction. Also, high-pressure steam is generated by heat exchange with the gas after the methanation reaction or the gas after the olefin synthesis, and the raw material gas consisting of carbon dioxide and hydrogen to be supplied to the reverse shift reaction is generated by heat exchange with this high-pressure steam. A method of heating may also be used.

As the reverse shift catalyst, a known CO shift catalyst such as a copper-zinc catalyst or an iron-chromium catalyst can be used.

The temperature of the reverse shift reaction is lower than the outlet temperature of the methanation reaction and the olefin synthesis reaction due to heat exchange restrictions, 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 easy.

Since the reverse shift reaction is an endothermic reaction, if it is carried out adiabatically, the temperature of the catalyst layer may drop and the reverse shift reaction may not proceed. If the reaction proceeds while heating with high-pressure steam using a heat exchange reactor, the reaction tends to proceed stably.

The equilibrium conversion of the reverse shift reaction is almost independent of the reaction pressure. On the other hand, the higher the reaction pressure, the more easily the side reactions (eg, the production of hydrocarbons) that occur on the reverse shift catalyst generally proceed. Therefore, when there is a concern about side reactions in the reverse shift catalyst, it is preferable to carry out the reverse shift reaction at a relatively low pressure, raise the pressure after water separation, and feed the mixture into the methanol synthesis section.

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.

[Examples and Comparative Examples]
An example of trial calculation based on process calculation is shown below. The pressure is 0.5 MPa in the olefin synthesis section and 3 MPa in all other sections, and the pressure loss and heat loss in each device and piping are not considered. Also, in the olefin synthesis reaction, ethylene, butylene, etc. are produced in addition to propylene, but here it is assumed that all of them produce propylene.

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

In the methanol separation unit 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 room temperature or below using a refrigerator and a heat exchanger (not shown). and the generated methanol is separated in the gas-liquid separation drum 22 (methanol separation step).

In the methanation reaction section 3, the total amount of the synthesis gas from which methanol is separated in the methanol separation section 2 is heated to 140° C. by heat exchange with low-pressure steam in the heat exchanger 31, and is further heated to 140° C. at the outlet of the heat exchanger 33, which will be described later. The gas branched from is mixed through the recycle compressor 34 and sent to the methanation reactor 32 at 245° C., where the synthesis gas is methanated (methanation step). The methanation reactor 32 is an adiabatic reactor, and as the methanation progresses, the temperature rises, and the methanation reaction progresses to an equilibrium composition of 544°C. The gas after the methanation reaction is cooled to 290° C. in the heat exchanger 33 while recovering heat as high pressure steam (HPS, 280° C.). After cooling, the gas to be sent to the recycle compressor 34 is branched, and the remainder is cooled to 230° C. in the heat exchanger 35 while recovering heat as medium-pressure steam, and sent to the methanation reactor 36. be done. The methanation reactor 36 is also an adiabatic reactor, and as the methanation progresses, the temperature rises, and the methanation reaction progresses to an equilibrium composition of 365°C.

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

The mixed solution of methanol and water separated in the methanol separation section 2 is sent to the olefin synthesis section 4 . The mixed solution is decompressed to 0.5 MPa by the throttle valve 41, heated to 140° C. by low-pressure steam, and vaporized. The obtained mixed gas of methanol and water vapor is sent to the olefin synthesis reactor 43 . The olefin synthesis reactor 43 is a fluidized bed reactor that produces a propylene-based gas from methanol with a moderately high exotherm. The outlet gas from the olefin synthesis reactor 43 is cooled to 160° C. in the heat exchanger 44 while recovering heat as low-pressure steam, further cooled to 40° C. in the heat exchanger 45 using cooling water, and separated into a gas-liquid separation drum. At 46 , the condensed water is separated into a gas containing propylene as the main component, which is then pressurized to 3.0 MPa by a compressor 47 and sent to the hydrogenation reaction section 5 .

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 olefinic hydrocarbons proceeds adiabatically, and the olefinic hydrocarbons are almost completely converted to paraffinic hydrocarbons with a slight temperature rise. The outlet gas of the hydrogenation reactor 51 is cooled to 160° C. in the heat exchanger 52 while recovering the low-pressure steam, further cooled to 40° C. in the heat exchanger 53 using cooling water, and further cooled by the refrigerator and heat. It is cooled down to room temperature or lower using an exchanger (not shown), and the condensed water is separated in the gas-liquid separation drum 54 to become fuel gas.

Temperatures and flow rates at key points in the process are shown in Table 1.

The composition of the generated fuel gas (based on volume after dehydration) is 90.8% methane, 7.0% propane, 2.2% hydrogen, and carbon monoxide, carbon dioxide, and propylene are all 0.01% or less. becomes. Also, the calorific value of the generated fuel gas is 43.3 MJ/m ³ , which can be adjusted to a calorific value that can be used as city gas simply by adding a small amount of propane or butane.

The ratio of the calorific value of the generated fuel gas to the calorific value of hydrogen used as a raw material is 77.9%. When the methanation reaction between hydrogen and carbon dioxide proceeds according to 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%. It can be seen that according to the method of the present invention, a fuel gas with a high calorific value can be produced without causing a large decrease in efficiency as compared with the case of producing only methane.

[Example 2]
As one aspect of the high calorific value fuel gas production method and production facility of the present invention, trial calculation results of an example of high calorific value fuel gas production 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 sent to the reverse shift reactor 62 . The reverse shift reactor 62 is a heat exchange type reactor, and the supplied raw material gas is heated by high-pressure steam, and the reverse shift reaction proceeds while maintaining a temperature of approximately 270°C. out of the vessel. The outlet gas of the reverse shift reactor 62 is cooled to 160° C. in the heat exchanger 63 while recovering the low-pressure steam, and sent to the water separator 7 .

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

Temperatures and flow rates at key points in the process are shown in Table 2.

The composition of the generated fuel gas (based on 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. becomes. The generated fuel gas has a calorific value of 45.0 MJ/m ³ , which is a calorific value that can be used as city gas without calorie adjustment. The reason why the calorific value increased compared to Example 1 is that the reverse shift process was carried out, which increased the ratio of carbon monoxide in the carbon oxides sent to the methanol synthesis process, and the methanol yield was increased. due to an increase in

The ratio of the calorific value of the generated fuel gas to the calorific value of hydrogen used as a raw material was 77.9%, which is high without causing a large decrease in efficiency compared to the case of producing only methane. Fuel gas with a calorific value can be produced.

[Comparative example]
As an example of a method and equipment for producing a high calorific value fuel gas not according to the method of the present invention, trial calculation results for production of a high calorific value fuel gas based on the process flow diagram of FIG. 5 are shown.

In this example, unlike Example 1, the hydrogenation reaction step is carried out prior to mixing with the product gas of the methanation step.

As in Example 1, the raw material gas is supplied to the high calorific value fuel gas production facility at a temperature of 25° C. at a flow rate of 1 mol/s of carbon dioxide and 3.895 mol/s of hydrogen. is introduced at a flow rate of 1 mol/s of carbon dioxide and 3.805 mol/s of hydrogen, and the remaining 0.090 mol/s of hydrogen is mixed with the gas at the outlet of the compressor 47 of the olefin synthesis section and supplied to the hydrogenation reaction step. be done.

Temperatures and flow rates at key points in the process are shown in Table 3.

The composition of the generated fuel gas (based on volume after dehydration) is 85.9% methane, 6.7% hydrogen, 5.2% propane, 1.3% propylene, 0.9% carbon dioxide, and carbon monoxide 0.01% or less. Also, the calorific value of the generated fuel gas was 41.3 MJ/m ³ .

The ratio of the calorific value of the generated fuel gas to the calorific value of hydrogen used as a raw material was 78.3%, which was higher than in the example, but this is due to the hydrogen, carbon dioxide concentration and This is probably because the exothermic methanation reaction and hydrogenation reaction of propylene did not complete due to the high propylene concentration.

Unlike the fuel gas production method of the present invention, this comparative example is not configured to obtain propane from the reaction between hydrogen remaining after the methanation reaction and propylene. Therefore, the hydrogen remaining after the methanation reaction remains in the fuel gas as it is, so the hydrogen concentration in the fuel gas increases. In addition, since the hydrogenation reaction of propylene is carried out without being diluted with 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 is not completed in equilibrium. Although there is a sufficient excess of hydrogen relative to propylene, a high concentration of propylene remains. In addition, since the hydrogenation catalyst comes into contact with olefinic hydrocarbons at high temperatures, there is concern about thermal deterioration of the hydrogenation catalyst and deterioration due to coking.

[Another embodiment]
[1] In the above embodiment, the example in which the pressure in the methanol synthesis step, the methanation step, and the hydrogenation reaction step is the same (3 MPa) has been particularly described. However, the pressure may be the same or different in the methanol synthesis step, methanation step and hydrogenation step according to the present invention. Since pressure loss usually occurs in reactors and heat exchangers, the reaction pressure decreases to some extent in the order of methanol synthesis, methanation, and hydrogenation, unless special means of increasing pressure are taken, but this is not a problem. should not.

[2] In the above embodiment, when the reverse shift process is carried out, the reaction pressure is set to be the same (3 MPa) in the methanol synthesis process, the methanation process, and the hydrogenation reaction process. bottom. However, the pressure may be the same or different in the reverse shift step, methanol synthesis step, methanation step and hydrogenation step according to the present invention. If the reverse shift catalyst exhibits activity in the synthesis of hydrocarbons and methanol under high pressure conditions, it may be preferable to perform the reverse shift step at a low pressure and increase the pressure after the water separation step.

[3] In the above embodiment, the case where the olefin synthesis catalyst produces only propylene was described. Olefin synthesis catalysts usually produce ethylene and butylene (1-butene, 2-butene, 2-methylpropene) in addition to propylene. These are also hydrogenated under the same conditions as propylene to produce ethane or butane. Ethane and butane also have the effect of increasing the calorific value of fuel gas, like propane. Therefore, production of ethylene and butylene is not a problem.
A small amount of paraffinic hydrocarbons (ethane, propane and butane) are also produced on the olefin synthesis catalyst, but these, like propane, have the effect of increasing the calorific value of the fuel gas, so they are not a problem.

The configurations disclosed in the above embodiments (including other embodiments) can be applied in combination with configurations disclosed in other embodiments unless there is a contradiction. The described embodiment is an example, and the embodiment of the present invention is not limited to this, and can be modified as appropriate without departing from the object of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be used as a method and equipment for producing fuel gas with a high calorific value, which can be used as town gas from hydrogen and carbon oxides, and which is mainly composed of methane and further contains at least one component of ethane, propane and butane. can be done.

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

Claims (6)

A method for producing a high calorific value fuel gas containing methane as a main component and at least one 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 passing a gas containing hydrogen and carbon oxides obtained by separating methanol in the methanol separation step through a methanation catalyst to synthesize methane;
an olefin synthesis step of passing 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;
The methane main component gas obtained in the methanation step and the olefinic hydrocarbon-containing gas obtained in the olefin synthesis step are mixed, passed through a hydrogenation catalyst, and the olefinic hydrocarbons are converted to paraffinic hydrocarbons by reaction with hydrogen. A method for producing a high calorific value fuel gas comprising a hydrogenation step. The carbon oxide is carbon dioxide, and prior to the methanol synthesis step, a reverse shift step of passing a mixed gas of hydrogen and carbon dioxide through a reverse shift catalyst to convert at least a portion of the carbon dioxide to carbon monoxide. The gas obtained in the reverse shift reaction is cooled, and at least part of the water contained in the gas obtained in the reverse shift reaction is separated, and then subjected to the methanol synthesis step. A method for producing a high calorific value fuel gas. 3. The method for producing a high calorific value fuel gas according to claim 2, wherein reaction heat obtained in the methanation step or the olefin synthesis step is used as a heat source for the reverse shift reaction. A facility for producing a high calorific value fuel gas containing methane as a main component and further containing at least one component of ethane, propane and butane from hydrogen and carbon oxides,
a methanol synthesis section for synthesizing methanol by passing a gas containing hydrogen and carbon oxides through a methanol synthesis catalyst;
a methanol separation unit that separates methanol by cooling the gas sent from the methanol synthesis unit;
a methanation reaction section for synthesizing methane by passing a raw material gas containing hydrogen and carbon oxides separated from methanol in the methanol separation section through a methanation catalyst;
an olefin synthesis section for passing 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;
The methane main component gas obtained in the methanation reaction section and the olefinic hydrocarbon-containing gas obtained in the olefin synthesis section are mixed, passed through a hydrogenation catalyst, and the olefinic hydrocarbons are reacted with hydrogen to produce paraffinic hydrocarbons. a high calorific value fuel gas production facility comprising a hydrogenation reaction section for converting to A reverse shift step further comprising a reverse shift reaction section and a water separation section, wherein the mixed gas of hydrogen and carbon dioxide is passed through a reverse shift catalyst in the reverse shift reaction section to convert at least part of the carbon dioxide into carbon monoxide. and cooling the gas containing hydrogen, carbon monoxide, carbon dioxide and water vapor obtained in the reverse shift step in the water separation section, separating at least part of the water vapor, and then feeding it to the methanol synthesis section. 5. A facility for producing a high calorific value fuel gas according to claim 4, configured to: 6. The high calorific value fuel gas according to claim 5, wherein reaction heat obtained from the methanation reaction in the methanation reaction section or the olefin synthesis reaction in the olefin synthesis section is used as a heat source for the reverse shift reaction. production equipment.

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