JP5039426B2 - Hydrogen production and carbon dioxide recovery method - Google Patents

Description

  The present invention relates to a method for producing hydrogen from carbon-containing fuels such as fossil fuels and recovering carbon dioxide.

  Hydrogen is expected as a future energy medium, and active research and development is being carried out in a wide range of technical fields such as production, storage / transport, and utilization. Advantages of using hydrogen as an energy medium include not only high energy utilization efficiency but also only water after combustion.

  Currently, about 80% of primary energy is occupied by fossil fuels such as oil, coal, and natural gas, and even if it gradually decreases due to increased use of renewable energy, the ratio is expected to remain high. Therefore, in the production of hydrogen, it can be said that the importance of the route using fossil fuel as a primary energy source will not be reduced for the time being.

However, when hydrogen is produced using a fuel containing carbon such as fossil fuel, CO ₂ is emitted.

Reduction of CO ₂ emissions is said to be an urgent issue in preventing global warming. Under such circumstances, a technology for separating and recovering CO ₂ produced as a by-product when hydrogen is produced from fossil fuel is important as achieving both CO ₂ emission reduction and early realization of a hydrogen society.

In producing hydrogen using a carbon-containing fuel such as fossil fuel as a raw material, a method for separating CO ₂ has been conventionally known.

Among these methods, the first method is high-purity using a pressure swing adsorption (PSA) device from a mixture of hydrogen, CO, CO ₂ , and methane, which is produced through fossil fuel as a raw material through steam reforming and shift reaction. While obtaining hydrogen, there can be mentioned a method in which CO ₂ is highly purified from offgas containing impurities by a chemical absorption method, and separated and recovered. However, the chemical absorption method using an organic amine solution as an absorbing solution cannot be said to be excellent in terms of energy efficiency of hydrogen production, for example, a great amount of energy is required in the CO ₂ recovery step, that is, the absorbing solution regeneration step.

As a second method, in Patent Document 1, in a process of refining and separating each gas by a two-stage purifier, a CO ₂ concentrator is arranged in the first stage and a gas flow mainly composed of CO ₂ is generated. The high purity hydrogen is obtained by treating the gas with reduced CO ₂ concentration discharged from the CO ₂ concentrator by the PSA arranged in the second stage, and the CO ₂ obtained from each stage is enriched. A method for liquefying and separating CO ₂ from a gas stream is disclosed. However, since CO ₂ is removed from a gas containing a large amount of hydrogen before separating hydrogen, it has to have a very high selectivity as a CO ₂ recovery device and generally has to adopt a method with large energy consumption. Tend to get worse.

As a third method, Patent Documents 2 and 3 disclose a process for producing high-purity hydrogen using a hydrogen purifier such as PSA and recovering CO ₂ after burning off gas containing CO ₂ , hydrogen, and the like. Has been. However, this method burns off the hydrogen purifier off-gas that still contains a large amount of hydrogen, resulting in a decrease in hydrogen yield. In addition, when air is used for combustion, nitrogen is mixed, increasing the load of CO ₂ recovery. To do. On the other hand, pure oxygen can also be used for combustion, but in this case, a great amount of energy is consumed in the production of pure oxygen and the energy efficiency tends to deteriorate.

  As a fourth method, Patent Document 4 discloses a method using a PSA having a serial configuration having a plurality of adsorption towers having different adsorption selectivity. However, this method has a very complicated absorption-regeneration cycle, and it is difficult to suppress an increase in system cost.

As a fifth method, Patent Documents 5 and 6 describe a method of separating hydrogen from a PSA offgas using a membrane and recycling it by recycling it to the PSA inlet. However, in these documents, CO ₂ is only discarded without being recovered, and there is no description about the processing method such as a concentration method.
Special table 2004-519538 gazette JP 2004-292240 A JP 2003-81605 A U.S. Pat. No. 4,913,709 U.S. Pat. No. 4,229,188 U.S. Pat. No. 5,435,836

As described above, there is room for further improvement in the method of co-producing high-purity hydrogen and high-concentration CO ₂ suitable for storage.

  An object of the present invention is to provide a more efficient method that can suppress an increase in system cost when simultaneously performing hydrogen production and carbon dioxide recovery using a carbon-containing fuel as a raw material.

  The present invention provides the following method.

(1) A hydrogen production and carbon dioxide recovery method for producing hydrogen from a carbon-containing fuel and collecting carbon dioxide,
A hydrogen-containing gas production process for reforming a carbon-containing fuel to obtain a hydrogen-containing gas containing hydrogen and carbon dioxide;
An adsorption step in which a component other than hydrogen contained in the hydrogen-containing gas is adsorbed on the adsorbent using a pressure swing adsorption device including an adsorption tower containing the adsorbent to obtain a hydrogen-enriched hydrogen-enriched gas;
A high pressure desorption step of desorbing the component adsorbed on the adsorbent under relatively high pressure;
A low pressure desorption step of desorbing a component adsorbed on the adsorbent at a relatively low pressure; and
Using a carbon dioxide separation membrane, the gas obtained from the low-pressure desorption step is a carbon dioxide-enriched gas that is a gas enriched with carbon dioxide and carbon dioxide that is a gas enriched with components other than carbon dioxide. A hydrogen production and carbon dioxide recovery method comprising a carbon dioxide membrane separation step for separation into a separation membrane off-gas.

  (2) The method according to (1), further comprising a washing step of washing the inside of the adsorption tower after the low-pressure desorption step using the hydrogen-enriched gas obtained from the adsorption step.

  (3) The method according to (1) or (2), further comprising a mixing step in which the gas obtained from the high-pressure desorption step and the gas obtained from the cleaning step are mixed to form a mixed gas.

  (4) The method according to (1) or (2), wherein combustion heat generated by burning the gas obtained from the high-pressure desorption step is used for reforming in the hydrogen-containing gas production step.

  (5) The method according to (2), wherein combustion heat generated by burning the gas obtained from the cleaning step is used for reforming in the hydrogen-containing gas production step.

  (6) The method according to (3), wherein combustion heat generated by burning the mixed gas is used for reforming in the hydrogen-containing gas production process.

  (7) The method according to (1) or (2), further comprising a recycling step of recycling the gas obtained from the high pressure desorption step to the adsorption step.

  (8) The method according to (7), wherein in the recycling step, the gas obtained from the high-pressure desorption step is recycled to the adsorption step after increasing the hydrogen concentration using a hydrogen separation membrane.

  (9) The method according to any one of (1) to (8), wherein the ratio α of the carbon dioxide permeability coefficient to the hydrogen permeability coefficient of the carbon dioxide separation membrane is 5 or more.

  According to the present invention, when hydrogen production and carbon dioxide recovery are simultaneously performed using a carbon-containing fuel as a raw material, an increase in system cost can be suppressed, and a more efficient method is provided.

  Unless otherwise specified, in this specification, pressure means absolute pressure, and% relating to gas composition means mol% calculated excluding water vapor.

[Carbon-containing fuel]
In the present invention, a carbon-containing fuel that is a fuel containing carbon is used as a raw material for hydrogen production. As the carbon-containing fuel, carbon can be appropriately selected from substances that can produce a hydrogen-containing gas by reforming.

  Examples of carbon-containing fuels include fossil fuels. The fossil fuels mean fuels that can be produced using fossil resources such as petroleum, coal, and natural gas as raw materials, and can be in any of gaseous, liquid, and solid forms. Specific examples include hydrocarbons such as methane, ethane, propane, natural gas, liquefied petroleum gas, naphtha, gasoline, kerosene, light oil, and heavy oil. Natural gas, liquefied petroleum gas, naphtha, Kerosene is particularly preferably used. Furthermore, as the carbon-containing fuel, oxygen-containing compounds that can be produced from fossil fuels such as methanol, dimethyl ether, and ethanol and contain oxygen atoms in the molecule can be suitably used. Moreover, it can be used even if it was not necessarily manufactured from fossil resources, such as ethanol obtained from biological resources irrespective of hydrocarbons and oxygenated compounds.

[Hydrogen-containing gas production process]
In the hydrogen-containing gas production process, the carbon-containing fuel is reformed to produce a hydrogen-containing gas containing at least hydrogen and carbon dioxide.

  As a reforming reaction method, a known reforming method such as a steam reforming method, an autothermal reforming method, or a partial oxidation method can be adopted, but a method in which nitrogen in the air is not mixed facilitates the subsequent purification process. Therefore, it is preferable. Therefore, a steam reforming method, or an autothermal reforming method or a partial oxidation method using pure oxygen as an oxidizing agent is preferably employed, and a steam reforming method can be particularly preferably employed.

  First, the case where hydrocarbons such as natural gas, liquefied petroleum gas, naphtha and kerosene are used as the carbon-containing fuel will be described. At this time, in the steam reforming method, the hydrocarbons and water are preferably at a temperature of 300 ° C. to 1000 ° C., more preferably 400 ° C. to 900 ° C., preferably atmospheric pressure to 10 MPa, more preferably 0.2 MPa to 2 MPa. It is made to react at a pressure of 1 to decompose into reformed gas containing hydrogen, carbon monoxide, carbon dioxide and methane. S / C (ratio of the number of moles of water vapor to the number of moles of carbon atoms in the carbon-containing fuel) is preferably set in the range of 2 to 10, more preferably 2.5 to 7. At this time, it is preferable to perform the reforming reaction at a pressure exceeding the pressure necessary for driving the subsequent stage PSA because it is not necessary to pressurize the reformed gas again. The composition of the reformed gas thus obtained depends on temperature, pressure, etc., and is usually 65 to 75% hydrogen, 5 to 20% carbon monoxide, 5 to 20% carbon dioxide, and 0.5 to 10% methane. However, it is preferable to select conditions so that hydrocarbons having a carbon-carbon bond do not remain as much as possible.

  A catalyst is usually used for the steam reforming reaction. As the catalyst, a known steam reforming catalyst can be used. Examples of this catalyst include metals of Group 8, Group 9 and Group 10 such as nickel, ruthenium, rhodium and platinum. It can be determined as appropriate. The autothermal reforming method and the partial oxidation method can be appropriately selected from known catalysts that can be used for these reforming methods.

The hydrogen production apparatus used in the hydrogen production process has a reformer that performs a reforming reaction. Further, in order to further improve the hydrogen yield, a hydrogen production apparatus in which a shift reactor is arranged at the rear stage of the reformer can be used. In the shift reactor, CO and steam in the reformed gas obtained in the reformer are reacted and converted to CO ₂ and hydrogen. If necessary, steam can be added by providing a steam inlet before the shift reactor. As the catalyst used in the shift reactor, known shift reaction catalysts such as iron / chromium, copper / zinc, and noble metals such as platinum can be used. The reaction temperature of the shift reactor is appropriately set in the range of usually 200 ° C to 500 ° C. Although there is no restriction | limiting in particular in the reaction pressure, It is simple and advantageous to implement near the pressure used by the said reforming reaction.

  On the other hand, when using oxygen-containing compounds such as methanol, dimethyl ether and ethanol as the carbon-containing fuel, the same method as described above can be applied. In particular, when methanol or dimethyl ether is used, a shift reactor is obtained by performing a reforming reaction at a low carbon monoxide equilibrium concentration of 400 ° C. or lower, preferably 350 ° C. or lower, using a copper-zinc catalyst as a catalyst. It is also possible to achieve an excellent hydrogen yield without the presence of hydrogen. In this case, when the steam reforming method is applied, the amount of steam is preferably set in the range of S / C of 1.5 to 4, more preferably 1.5 to 2.5.

  From the hydrogen-containing gas production process, for example, a gas containing 65 to 80% hydrogen, 0.2 to 6% carbon monoxide, 10 to 35% carbon dioxide, and 0 to 10% methane can be obtained.

  When the carbon-containing fuel contains a sulfur content, the carbon-containing fuel can be desulfurized and supplied to the reformer in order to prevent catalyst poisoning due to the sulfur content.

[Processing by PSA equipment]
In the adsorption process, the hydrogen-containing gas produced in the hydrogen-containing gas production process is preferably dehydrated and then introduced into a pressure swing adsorption apparatus, that is, a PSA (Pressure Swing Adsorption) apparatus, and components other than hydrogen are provided in the PSA apparatus. A hydrogen-enriched gas enriched with hydrogen is adsorbed on an adsorbent. When the adsorbent is regenerated, a high-pressure desorption step for desorbing the adsorbed component adsorbed on the adsorbent at a relatively high pressure and a low-pressure desorption step for desorbing the adsorbed component at a relatively low pressure are performed (high pressure The pressure in the low pressure desorption process is lower than the pressure in the desorption process). The gas obtained from the high pressure desorption process (high pressure desorption off gas) and the gas obtained from the low pressure desorption process (low pressure desorption off gas) have different compositions.

  In this way, the desorption process is divided into two steps, a high pressure desorption process and a low pressure desorption process, depending on the pressure. However, the desorption process can be performed in three or more stages, the high pressure desorption process can be further divided into two or more by pressure, or the low pressure desorption process can be further divided into two or more by pressure. it can.

  The PSA method is a method for selectively separating a specific gas from a mixed gas. The mixed gas is introduced into an adsorption tower filled with an adsorbent at a high pressure, and a specific component is adsorbed on the adsorbent to thereby adsorb the gas. In this method, the adsorbed component adsorbed on the adsorbent is desorbed by separating the component into a non-adsorbed gas component, then lowering the pressure of the adsorption system, and using a purge gas if necessary. Industrially, a plurality of towers filled with adsorbents are provided, and in each adsorption tower, a series of operations such as pressurization, adsorption, depressurization, and washing are repeated, so that the entire apparatus can be separated and recovered continuously. Things are used.

  As the adsorbent packed in the PSA tower, a known filler capable of separating hydrogen and components other than hydrogen by adsorption, such as activated carbon and zeolite, can be used as appropriate.

  The operating pressure of PSA varies depending on the stage of the cycle, but it is preferably in the range of 0.5 MPa to 10 MPa, more preferably 1 MPa to 5 MPa at the time of adsorption operated at the highest pressure.

  In the PSA method, hydrogen normally corresponds to the non-adsorbed gas component and passes through the PSA tower without being adsorbed by the adsorbent. Accordingly, a hydrogen-enriched gas having a pressure close to the PSA apparatus introduction pressure can be obtained. The hydrogen-enriched gas obtained in the adsorption process can be product hydrogen.

  The hydrogen purity of the hydrogen-enriched gas is preferably 99% or more, more preferably 99.9% or more, and further preferably 99.99% or more. Further, the product hydrogen is preferably hydrogen that can be used in a fuel cell vehicle. In this case, the hydrogen purity is usually preferably 99.99% or more, and the dew point and other requirements for impurities are required to be satisfied. Sometimes. Therefore, the hydrogen-enriched gas can be further subjected to a treatment such as moisture removal as necessary. Further, the product hydrogen can be converted into high-pressure hydrogen or liquid hydrogen, which is in a form suitable for filling in a fuel cell vehicle or transporting and storing in a hydrogen station.

  On the other hand, the regeneration of the adsorption tower consists of a desorption process (depressurization of the adsorption tower and desorption of adsorbed components from the adsorbent. At this time, no gas is supplied to the adsorption tower), a regeneration process consisting of a washing process and a pressurization process. The process can be carried out by the process, whereby the adsorption process can be performed again. The PSA offgas obtained in the regeneration process includes carbon dioxide, methane, carbon monoxide, and the like, which are components adsorbed on the PSA adsorption tower. In the present invention, the PSA offgas is collected in a plurality of portions.

An example of the sequence in PSA operation is shown.
1) A hydrogen-containing gas after dehydration is passed through the regenerated adsorbent to remove components other than hydrogen by adsorbing the adsorbent, and high purity hydrogen (hydrogen-enriched gas) is allowed to pass through (adsorption process).
2) The gas pressure in the adsorption tower is released to obtain off-gas A (high-pressure desorption step).
3) The inside of the adsorption tower is depressurized (pressure less than atmospheric pressure) to obtain off-gas B (low pressure desorption step).
4) The inside of the adsorption tower is washed with high-purity hydrogen to obtain off-gas C (washing step). The inside of the adsorption tower is replaced with high-purity hydrogen. At this time, the remaining adsorbed component may be desorbed.
5) High-purity hydrogen is introduced into the adsorption tower and the pressure is increased (pressure increase step).

  Note that the hydrogen-enriched gas obtained from the adsorption process can be used as the high-purity hydrogen used in the cleaning process and the pressure-increasing process.

  The off-gas carbon dioxide concentration obtained in the above sequence is generally high in off-gas B and low in off-gas A and C. Which of the off-gas A and the off-gas C has a higher carbon dioxide concentration depends on the operating conditions. In addition, additional operations can be inserted into the sequence, and a separate off gas can be generated in each operation. In the present invention, it is possible to perform processing as a single off gas by combining these plural off gases (in the example shown below, the off gases A and C are combined into a hydrogen rich off gas). This is preferable from the viewpoint of simplification of the system.

An example of the PSA sequence will be described in more detail with reference to FIG. FIG. 1 is a conceptual diagram showing a configuration example of a PSA apparatus. Here, the PSA offgas is divided into a hydrogen rich offgas having a relatively high hydrogen concentration (corresponding to the offgas A and C or a mixture thereof) and a CO ₂ rich offgas having a relatively high carbon dioxide concentration (the offgas B is The method of regenerating the adsorption tower while collecting the samples in the same manner will be described. In FIG. 1, v1 to v24 represent stop valves, and v25 represents a pressure reducing valve.

  First, v1 and v5 are opened, and an adsorption process for obtaining high-purity hydrogen is performed by introducing a high-pressure hydrogen-containing gas as a raw material into the adsorption tower A that has been regenerated.

When the adsorption tower A approaches saturation due to impurities in the raw material hydrogen-containing gas, v1 and v5 are closed, while v7 and v11 are opened, and the production of high-purity hydrogen using the adsorption tower B is continued. The adsorption tower A continues to be regenerated. First, v2 is opened to depressurize the inside of the adsorption tower A and perform a depressurization operation i to obtain a first hydrogen rich off gas (high pressure desorption step). The pressure at the end of the depressurization operation i is set lower than the pressure in the adsorption step, and is preferably in the range of atmospheric pressure to 0.5 MPa, more preferably atmospheric pressure to 0.2 MPa. If this is above atmospheric pressure, it is possible to suppress the entry of components other than hydrogen into the first hydrogen-rich off gas. On the other hand, if it is 0.5 MPa or less, it is possible to suppress a large amount of hydrogen from remaining in the adsorption tower. Thus, it is possible to prevent a large amount of hydrogen from being mixed in the CO ₂ rich off gas obtained next.

After depressurization operation i (high pressure desorption step), v2 is closed and v3 is opened, and further desorption is performed under reduced pressure to perform a depressurization operation ii to obtain a CO ₂ rich off gas containing more components other than hydrogen (low pressure desorption step). . Note that the desorption of gas can be promoted by performing desorption under reduced pressure. For this purpose, a vacuum pump P can be used. In order to perform desorption more completely, it is preferable to carry out until the desorption of the gas component from the adsorption tower is eliminated in this step, but the end point is determined in consideration of the time required for the step. The pressure at the end point of the depressurization operation ii is preferably in the range of 0.0001 MPa to 0.05 MPa, more preferably 0.001 MPa to 0.02 MPa when a vacuum pump is used.

  After completion of the desorption operation ii (low pressure desorption step), v3 is closed, v6 is subsequently opened, v2 is opened, the inside of the tower is washed with high-purity hydrogen that has passed through the pressure reducing valve v25, and a second hydrogen rich off gas is obtained. A cleaning process is performed. The pressure at this time is preferably atmospheric pressure to 0.5 MPa, more preferably atmospheric pressure to 0.3 MPa. The first and second hydrogen rich off gases can be taken out as a single gas stream without being distinguished from each other and supplied to an appropriate processing apparatus such as a hydrogen separation membrane or a burner. Further, for example, by mixing a part of the first hydrogen rich off gas and the second hydrogen rich off gas, it is possible to create this mixed gas and the remaining gas of the first hydrogen rich off gas. Alternatively, after the entire amount of the first and second hydrogen rich off gases is mixed, the mixed gas can be divided into two. Thus, if necessary, it can be processed as two or more gas streams through appropriate mixing and division.

  After completion of the washing process, a pressure increasing process is performed in which v6 and v2 are closed, v4 is opened, and the inside of the tower is filled with high-pressure high-purity hydrogen.

By repeating these adsorption process, desorption process (high-pressure desorption process and low-pressure desorption process), washing process and pressurization process in the adsorption towers A to D with different timings, continuous high-purity hydrogen and hydrogen-rich off gas are obtained. And CO ₂ rich off gas can be produced. The composition of these gases depends on the operating conditions of the PSA and the composition of the raw material gas. For example, the composition of the hydrogen rich off gas is 50 to 98% hydrogen, 0 to 10% carbon monoxide, 2 to 30% carbon dioxide, 0 methane. -10%. The composition of the CO ₂ rich off gas is, for example, 2-15% hydrogen, 1-30% carbon monoxide, 40-95% carbon dioxide, and 1-30% methane. The flow ratio (molar basis) of the hydrogen rich off gas to the CO 2 rich off gas is preferably in the range of 1: 5 to 5: 1, more preferably 1: 3 to 3: 1.

[CO2 membrane separation process]
In the present invention, the low-pressure desorption gas obtained from the low-pressure desorption step is separated into a carbon dioxide-enriched gas with a further increased carbon dioxide concentration and a carbon dioxide separation enriched with components other than carbon dioxide using a carbon dioxide separation membrane. Separate into membrane off-gas. Preferably, off-gas obtained when the adsorption tower is depressurized to perform the desorption operation is introduced into the carbon dioxide membrane separation step. In the above sequence example, this is off-gas B.

In the carbon dioxide membrane separation step, carbon dioxide is concentrated using the carbon dioxide separation membrane. As the carbon dioxide separation membrane, a known membrane that can selectively permeate CO ₂ can be appropriately selected and employed. Examples include polymer membranes such as those described in Powel et al., Journal of Membrane Science, 276, 1-49 (2006), FY 2003 carbon dioxide fixation / effective utilization technology countermeasure business, global environment international research, etc. Promotion business, molecular gate function CO ₂ separation membrane basic technology R & D report, dendrimer membrane, amine group-containing membrane, or zeolite membrane as described in WO2006 / 0505051 An inorganic material film etc. can be mentioned.

From the viewpoint of carbon dioxide separation efficiency, the ratio of the carbon dioxide permeability coefficient to the hydrogen permeability coefficient (permeability coefficient ratio) α of the membrane is preferably 5 or more, more preferably 10 or more, and further preferably 20 or more. preferable. When α is 5 or more, the CO ₂ concentration in the carbon dioxide separation membrane permeate gas can be suppressed from being lowered, and when a carbon dioxide liquefaction process is used in the subsequent stage, the energy required for compression increases and the liquefaction yield increases. It can suppress becoming low.

Here, the transmission coefficient ratio α is defined by the following equation.

  However, the permeation coefficient of each component is Q for the gas permeation rate of each component, p1 for the supply side pressure (partial pressure), p2 for the permeation side pressure (partial pressure), A for the membrane area, and L for the film thickness. Is defined by the following equation.

  No matter what material is used, the shape of the separation membrane is not particularly limited, and any shape such as a plate shape, a cylindrical shape, or a hollow fiber shape can be selected.

  The supply-side pressure and permeation-side pressure in the carbon dioxide membrane separation step are appropriately determined according to the gas composition, flow rate, apparatus shape, etc., but the supply-side pressure is preferably 0.2 to 10 MPa, more preferably 0.3. It is -5MPa, More preferably, it is the range of 0.5-2MPa. If the pressure is 0.2 MPa or more, it is easy to improve the permeation rate and suppress the increase in the membrane area. On the other hand, if it is 10 MPa or less, an increase in the strength of the separation membrane to withstand the pressure applied to the separation membrane can be suppressed, and as a result, good permeation performance can be easily obtained. On the other hand, the permeation side pressure is preferably as low as possible for the permeation performance of the membrane, but it is determined by comprehensively considering the power necessary to generate a reduced pressure (pressure less than atmospheric pressure), the pressure strength of the membrane, etc. The range is preferably 0.0001 to 0.5 MPa, more preferably 0.001 to atmospheric pressure.

  The temperature at which the membrane separation is performed is set to a temperature suitable for the membrane material used.

Carbon dioxide can be recovered as a carbon dioxide enriched gas. Although the carbon dioxide-enriched gas can be stored by being injected into the ground as it is, the carbon dioxide-enriched gas can be introduced into the CO ₂ liquefaction step to produce liquefied carbon dioxide. When performing liquefaction, the CO ₂ concentration of the carbon dioxide-enriched gas is preferably increased so as to facilitate the smooth operation of the CO ₂ liquefaction process, and the concentration is preferably 70% or more, more preferably 80% or more, More preferably, it is 90% or more. When the CO ₂ concentration is 70% or more, the energy required for the liquefaction step can be reduced, and the ratio of recovered liquefied CO ₂ can be increased.

As a CO ₂ liquefaction method, a known CO ₂ liquefaction method such as a method using the Joule-Thompson effect or a method of cooling by external cold heat while compressing can be appropriately employed. As the carbon dioxide liquefying apparatus, a known apparatus capable of liquefying carbon dioxide by these known CO ₂ liquefaction methods can be appropriately selected and used. The liquefied CO ₂ obtained in this way can be sequestered in the ground or sea after being transported to a storage location by an appropriate method such as land transport, sea transport or pipeline, or it has a high CO ₂ concentration and is therefore chemically It can also be used as various raw materials such as product synthesis. Since the off-gas (gas that has not been liquefied) obtained in the CO ₂ liquefaction step still contains combustible gases such as hydrogen and methane, it can be sent to the reformer burner and used as fuel.

  On the other hand, carbon dioxide separation membrane off-gas can be sent to the reformer burner and burned to effectively use the amount of heat it holds, and when the content of methane, carbon monoxide, etc. is high, the reformer It can also be introduced at the entrance and reused as a reforming raw material.

[PSA tower cleaning with carbon dioxide]
Before finishing the high pressure desorption process and starting the low pressure desorption process (before entering the pressure reducing operation in the above sequence example), the carbon dioxide concentration is preferably 70% or more, more preferably 80% or more, and further preferably 90% or more. The inside of the tower can be washed with high-purity carbon dioxide. As the carbon dioxide used here, recovered carbon dioxide can be used. Along with this operation, new off-gas (off-gas D) is generated. This cleaning operation with carbon dioxide has the effect of increasing the carbon dioxide concentration in the low-pressure desorption gas (off-gas B in the above sequence example).

Since the off gas D has a relatively high CO ₂ concentration, it can be used as a part of the CO ₂ rich off gas, or can be used as a combustion gas for the burner fuel.

[Use of gas not introduced into carbon dioxide separation membrane]
Of the PSA off-gas obtained in the PSA regeneration process, the gas that is not introduced into the carbon dioxide separation membrane can be used as fuel for a burner provided in the reformer. In particular, at least one of the gas obtained from the high pressure desorption process (off gas A in the above sequence example) and the gas obtained from the cleaning process (off gas C in the above sequence example) (these gases are mixed to form a mixed gas). May be used as fuel for the burner provided in the reformer, and used for reforming in the hydrogen-containing gas production process. The steam reforming reaction is a reaction accompanied by a large endotherm, and heat necessary for the steam reforming reaction can be supplied by using the combustion heat in the burner.

  Alternatively, in order to recover hydrogen from the PSA offgas obtained in the PSA regeneration process that is not introduced into the carbon dioxide separation membrane, at least a part of the gas that is not introduced into the carbon dioxide separation membrane is recycled to the PSA device. It can use for an adsorption process. In particular, at least one of the high-pressure desorption gas obtained from the high-pressure desorption step (off-gas A in the above sequence example) and the gas obtained from the cleaning step (off-gas C in the above-described sequence example) (these gases are mixed together with the mixed gas) Can be recycled to the adsorption step. In recycling, the pressure of the gas can be increased as appropriate.

  Further, the gas to be recycled can be recycled to the adsorption process after increasing the hydrogen concentration using a hydrogen separation membrane. In particular, a hydrogen rich gas such as a high pressure desorption gas, a hydrogen enriched gas (second hydrogen enriched gas) and a gas enriched with components other than hydrogen (hydrogen separation membrane) Off-gas) and the second hydrogen-enriched gas can be recycled to the adsorption step.

  In the above sequence example, off-gas A, off-gas C, or a combination of off-gas A and C can be recycled to the adsorption process, preferably after increasing the hydrogen concentration using a hydrogen separation membrane described below. it can.

  The carbon dioxide concentration of the gas recycled to the adsorption step is preferably 30% or less, more preferably 20% or less, and even more preferably 10% or less, while the hydrogen concentration is preferably 70% or more, more preferably 80% or more, More preferably, it is 90% or more.

  In the present invention, a hydrogen membrane separation step can be provided if necessary as described above. As a hydrogen separation membrane that can be used at this time, a known membrane capable of selectively permeating hydrogen can be appropriately selected and employed. Examples of the hydrogen separation membrane include metal membranes such as palladium, polymer membranes such as polyimide, porous membranes such as porous silica, zeolite, and porous carbon. From the viewpoint of ease of operation and cost, a polymer film is preferably used.

  No matter what material is used, the shape of the separation membrane is not particularly limited, and any shape such as a plate shape, a cylindrical shape, or a hollow fiber shape can be selected.

  The supply side pressure in the hydrogen membrane separation step is in the range of 0.2 to 10 MPa, preferably 0.3 to 5 MPa, and more preferably 0.5 to 2 MPa. When the pressure is 0.2 MPa or more, it is easy to improve the permeation rate and suppress an increase in film area. On the other hand, when it is 10 MPa or less, an increase in the strength of the separation membrane to withstand the pressure applied to the separation membrane can be suppressed, and good permeation performance can be easily obtained. On the other hand, the permeation side pressure is preferably as low as possible for the permeation performance of the membrane, but it is determined by comprehensively considering the power necessary to generate a reduced pressure (pressure less than atmospheric pressure), the pressure strength of the membrane, etc. The range is preferably 0.0001 to 0.5 MPa, more preferably 0.001 to atmospheric pressure.

  The temperature at which the membrane separation is performed is set to a temperature suitable for the membrane material to be used. For example, about 250 to 500 ° C. for a palladium membrane and about room temperature to about 150 ° C. for a polyimide membrane.

  It is possible to increase the hydrogen recovery rate by recycling the hydrogen-enriched gas (second hydrogen-enriched gas) obtained in the hydrogen membrane separation step to the PSA inlet. On the other hand, in the hydrogen membrane separation step, the gas enriched with components other than hydrogen (hydrogen separation membrane off-gas) can be sent to the reformer burner and burned to effectively use the retained heat.

〔process〕
Hereinafter, processes suitable for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  As shown in FIG. 2, the hydrogen production apparatus has a reformer 1-1 and a shift reactor 1-2 connected downstream of the reformer. The reformer is provided with a reforming reaction tube 1-1a and a burner 1-1b for heating it from the outside. Carbon-containing fuel is supplied from a line 100 to a reformer, particularly a reforming reaction tube. Water vapor, oxygen and the like necessary for the reforming reaction are also appropriately supplied to the reformer (not shown). When the carbon-containing fuel is liquid or solid, the carbon-containing fuel can be appropriately vaporized in advance. If necessary, the carbon-containing fuel can be supplied to the reformer after being desulfurized with a desulfurizer (not shown).

The carbon-containing fuel is reformed inside the reforming reaction tube, and the reformed gas is discharged from the reformer (line 101). In the shift reactor, CO and water vapor in the reformed gas are converted into CO ₂ and hydrogen.

The hydrogen-containing gas (line 102) obtained from the hydrogen production apparatus is supplied to the PSA apparatus 2 via the line 103. Specifically, the hydrogen-containing gas is introduced into a PSA tower that is performing an adsorption process, and components other than hydrogen contained in the hydrogen-containing gas are adsorbed by the adsorbent, and a hydrogen-enriched gas (first hydrogen-enriched gas) is obtained. ) Is removed as product hydrogen (line 104). On the other hand, from the PSA tower that is performing the regeneration process, the PSA off-gas is divided into a hydrogen rich off gas (line 112) and a CO ₂ rich off gas (line 106) and discharged.

The CO ₂ rich gas is introduced into the CO ₂ separation membrane 5 through the line 106, the booster 7, and the line 107. Carbon dioxide-enriched gas (line 109) is obtained as gas that has permeated the carbon dioxide separation membrane, and this is pressurized by the booster 9 and supplied to the carbon dioxide liquefier 6 (line 110). The carbon dioxide separation membrane off-gas (line 108) discharged without passing through the carbon dioxide separation membrane is supplied as fuel to the burner 1-1b of the reformer via the line 118.

  Product liquefied carbon dioxide is recovered from the carbon dioxide liquefier (line 111). The non-liquefied gas (line 116) discharged from the carbon dioxide liquefier joins with the hydrogen separation membrane off gas (line 114) (line 117), and further joins with the carbon dioxide separation membrane off gas (line 108). It is supplied from the line 118 to the burner 1-1b.

  The combustible component in the gas supplied from the line 118 is combusted by the burner 1-1b, and the combustion gas is exhausted from the line 124. This combustion heat is used to heat the reforming reaction tube.

  On the other hand, the hydrogen rich off gas (line 112) of the PSA device 2 is supplied to the hydrogen separation membrane 4 through the booster 8 and the line 113. A second hydrogen-enriched gas is obtained as the gas that has permeated through the hydrogen separation membrane, and is recycled to the PSA device (particularly, the adsorption tower performing adsorption) via the line 115, the booster 10, and the line 119. The hydrogen separation membrane off-gas (line 114) discharged without passing through the hydrogen separation membrane is sent to the reformer burner as described above.

  The gas generated by the reforming reaction of the carbon-containing fuel is a mixed gas containing components such as hydrogen and carbon dioxide, and further including components such as methane and carbon monoxide. The PSA method is effective as a method for obtaining high purity hydrogen from this mixed gas. However, it has not been easy to increase the concentration of carbon dioxide in addition to hydrogen using PSA. According to the present invention, high-purity hydrogen can be produced with a simple apparatus and carbon dioxide can be concentrated without imposing an excessive burden on PSA.

  ADVANTAGE OF THE INVENTION According to this invention, when manufacturing carbon dioxide of the form suitable for storage using carbon-containing fuels, such as fossil fuels, as a raw material in parallel with manufacture of high purity hydrogen, energy consumption can be suppressed. In addition, the hydrogen yield can be improved. In addition, hydrogen production and carbon dioxide recovery can be performed with a relatively simple apparatus, and an increase in system cost can be suppressed. Therefore, it contributes to the realization of a hydrogen society and the prevention of global warming.

  According to the present invention, for example, high-purity hydrogen having a purity that can be supplied as fuel for a fuel cell vehicle can be obtained. On the other hand, carbon dioxide can have a concentration suitable for recovery in the form of liquefied carbon dioxide, which is a form suitable for underground storage and ocean storage.

[Example 1]
A thermal mass balance was taken for the process having the configuration shown in FIG. Naphtha 215 kg / h (line 100) and steam 946 kg / h (not shown) are supplied to a reformer 1-1 which is charged with a Ni-based catalyst and performs a steam reforming reaction at an outlet temperature of 830 ° C. and a pressure of 2 MPa, The total flow rate was 54.2 kmol / h, the CO ₂ concentration was 20.5%, the hydrogen concentration was 72 by the shift reactor 1-2 in which the Fe—Cr catalyst was charged and the shift reaction was performed at an inlet temperature of 360 ° C. and an outlet temperature of 425 ° C. A mixed gas (line 102) with a pressure of 4% and a pressure of 2 MPa is obtained. This is dehydrated by a dehydrator (not shown), and an adsorption process is performed by the four-column PSA apparatus 2 to obtain high-purity hydrogen having a purity of 99.99% at a flow rate of 35.9 kmol / h (line 104). The pressure at this time is 2 MPa which is the same as that of the mixed gas (line 102).

In the high pressure desorption process, the pressure in the tower is reduced to atmospheric pressure, and at this time, a first hydrogen rich off gas is obtained. Further, CO ₂ rich off gas (line 106) is obtained by reducing the pressure in the tower in the low pressure desorption process. Subsequently, the inside of the tower is washed with a gas obtained by reducing a part of the product high-purity hydrogen to 0.2 MPa, and a second hydrogen-rich off-gas is obtained as an off-gas at this time. The first and second hydrogen rich off gases are mixed to form a hydrogen rich off gas (line 112) having a CO ₂ concentration of 19%, a hydrogen concentration of 80%, and a flow rate of 7.4 kmol / h. This gas is pressurized to 1 MPa by the compressor 8 and introduced into the hydrogen separation membrane 4 including a polyimide membrane having a CO ₂ / hydrogen permeability coefficient ratio α of 0.11. A gas with a hydrogen concentration of 96% and 0.1 MPa (line 115) is obtained at 3.5 kmol / h on the permeate side of the hydrogen separation membrane, and this is recycled to the upstream of the PSA device 2 via the compressor 10. The non-permeate side gas (line 114) of the hydrogen separation membrane is sent to the reformer burner.

Of the PSA off-gas, the CO ₂ rich off-gas (line 106) having a CO ₂ concentration of 69%, a hydrogen concentration of 5%, and a flow rate of 14.3 kmol / h is boosted to 1 MPa by the booster 7, and the CO ₂ / hydrogen permeability coefficient ratio α Is introduced into the CO2 separation membrane 5 having 30 membranes.

The permeate side gas (line 109) of the CO ₂ separation membrane has a CO ₂ concentration of 95%, which is pressurized to a pressure at which CO ₂ is liquefied by the compressor 9 (about 8 MPa in this embodiment), It is fed into the CO ₂ liquefier 6 to obtain a 9.5 kmol / h liquefied CO ₂ stream (line 111). On the other hand, a gas combining the off gas (non-permeate side gas) (line 108) of the CO ₂ separation membrane, the off gas (non-permeate side gas) of the hydrogen separation membrane (line 114), and the off gas (line 116) of the CO ₂ liquefier. The stream (line 118) is sent to the reformer burner 1-1b and used as fuel.

The energy consumed by the compressor of this process (per 1 kmol of recovered liquefied carbon dioxide) is 10.8 kW / kmol-recovered CO ₂ , based on the amount of CO ₂ contained in the shift reactor outlet gas (line 102). In this case, the carbon dioxide recovery rate as liquefied CO ₂ is 85%.

  Table 1 shows the permeability coefficient ratio α of the carbon dioxide separation membrane, the high-purity hydrogen recovery amount, the carbon dioxide recovery amount, and the energy consumption (total) of the compressor per 1 kmol of the recovered liquefied carbon dioxide. Table 5 shows the thermal mass balance.

[Examples 2 to 4]
The heat and mass balance was taken in the same manner as in Example 1 except that the membrane (permeation coefficient ratio α) used in the CO ₂ separation membrane device 5 was changed. Table 1 shows the permeability coefficient ratio α of the carbon dioxide separation membrane, the amount of high purity hydrogen recovered, the amount of carbon dioxide recovered, and the energy consumption (total) of the compressor.

[Examples 5 to 8]
In Examples 1 to 4, the second hydrogen-enriched gas obtained on the permeation side of the hydrogen separation membrane 4 provided with a polyimide membrane was recycled upstream of the PSA device 2. Here, the hydrogen separation membrane 4 was not used, and the hydrogen rich off-gas in the PSA off-gas was used as the reformer burner fuel as it was. That is, as shown in FIG. 3, the heat and mass balance was taken for the process in which the booster 8 and the hydrogen separation membrane 4 were removed from the process configuration shown in FIG. 1, and the recycle line 119 and the booster 10 were removed. At this time, the permeability coefficient ratio α of the CO ₂ separation membrane was changed as shown in Table 2 to obtain Examples 5 to 8. Table 2 shows the permeability coefficient ratio α of the carbon dioxide separation membrane, the amount of high-purity hydrogen recovered, the amount of carbon dioxide recovered, and the energy consumption (total) of the compressor. Although less energy is consumed in the compressor than in Table 1 where hydrogen is recycled, the amount of recovered high-purity hydrogen and the amount of recovered liquefied CO ₂ are slightly decreased.

  In addition, for Example 7, the thermal mass balance is shown in Table 5.

[Comparative Examples 1-4]
A thermal mass balance was taken for the process shown in FIG. In Examples 1 to 8, the desorption process is divided into a high pressure desorption process and a low pressure desorption process, and PSA offgas (CO ₂ rich offgas) obtained from the low pressure desorption process is treated with a CO ₂ separation membrane, and the high pressure desorption process and the cleaning process. The PSA off-gas (hydrogen-rich off-gas) obtained from is not treated with a CO ₂ separation membrane. In the process hand shown in FIG. 4, without separating the desorption process into a high pressure desorption step and the low pressure desorption step, collectively PSA off-gas obtained in the regeneration step the feed to the CO ₂ separation membrane, CO ₂ separation membrane off-gas (line 108 ) Was supplied to the burner 1-1b as fuel. Others were carried out in the same manner as in Example 5. At this time, the permeability coefficient ratio α of the CO ₂ separation membrane was changed as shown in Table 3 to obtain Comparative Examples 1 to 4. The results are shown in Table 3. Comparative Examples 1 to 4 are similar to Examples 5 to 8 (the hydrogen yield is not obtained but the hydrogen is not recycled, but the PSA off-gas is divided and obtained). The amount of CO ₂ is small. Further, a lot of energy consumed by the compressor is required, and this is particularly remarkable when a CO ₂ separation membrane having a small separation performance of α and not high is used.

  The present invention is suitably used for producing high-purity hydrogen and recovering high-concentration carbon dioxide. The produced hydrogen is suitable as a fuel for a fuel cell or the like, and the recovered carbon dioxide is suitable for storage in the ground or in the sea. In addition, relatively high purity hydrogen can be obtained as a by-product, which can be used for synthesis reactions such as hydrogenation of organic compounds.

It is a conceptual diagram which shows the example of the PSA apparatus which can be used in this invention. It is a flowchart for demonstrating the outline | summary of the example of the apparatus which can implement this invention. It is a flowchart for demonstrating the outline | summary of another example of the apparatus which can implement this invention. It is a flowchart for demonstrating the process in a comparative example.

Explanation of symbols

1: Hydrogen production device 1-1: Reformer 1-1a: Reformation reaction tube 1-1b: Burner 1-2: Shift reactor 2: PSA device 4: Hydrogen separation membrane 5: Carbon dioxide separation membrane 6: Dioxide Carbon liquefaction equipment 7, 8, 9, 10: Booster A, B, C, D: Adsorption tower P: Vacuum pump

Claims (9)

A hydrogen production and carbon dioxide recovery method for producing hydrogen from a carbon-containing fuel and collecting carbon dioxide,
A hydrogen-containing gas production process for reforming a carbon-containing fuel to obtain a hydrogen-containing gas containing hydrogen and carbon dioxide;
An adsorption step in which a component other than hydrogen contained in the hydrogen-containing gas is adsorbed on the adsorbent using a pressure swing adsorption device including an adsorption tower containing the adsorbent to obtain a hydrogen-enriched hydrogen-enriched gas;
A high pressure desorption step of desorbing the component adsorbed on the adsorbent under relatively high pressure;
A low pressure desorption step of desorbing a component adsorbed on the adsorbent at a relatively low pressure; and
Using a carbon dioxide separation membrane, the gas obtained from the low-pressure desorption step is a carbon dioxide-enriched gas that is a gas enriched with carbon dioxide and carbon dioxide that is a gas enriched with components other than carbon dioxide. A hydrogen production and carbon dioxide recovery method comprising a carbon dioxide membrane separation step for separation into a separation membrane off-gas.   The method according to claim 1, further comprising a washing step of washing the inside of the adsorption tower after the low-pressure desorption step using the hydrogen-enriched gas obtained from the adsorption step.   The method according to claim 1, further comprising a mixing step of mixing the gas obtained from the high-pressure desorption step and the gas obtained from the cleaning step into a mixed gas.   The method according to claim 1 or 2, wherein the combustion heat generated by burning the gas obtained from the high-pressure desorption step is used for reforming in the hydrogen-containing gas production step.   The method according to claim 2, wherein combustion heat generated by burning the gas obtained from the cleaning step is used for reforming in the hydrogen-containing gas production step.   The method according to claim 3, wherein combustion heat generated by burning the mixed gas is used for reforming in the hydrogen-containing gas production process.   The method according to claim 1, further comprising a recycling step of recycling the gas obtained from the high-pressure desorption step to the adsorption step.   The method according to claim 7, wherein in the recycling step, the gas obtained from the high pressure desorption step is recycled to the adsorption step after increasing the hydrogen concentration using a hydrogen separation membrane.   The method according to any one of claims 1 to 8, wherein the carbon dioxide separation membrane has a ratio α of a carbon dioxide permeability coefficient to a hydrogen permeability coefficient of 5 or more.

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