JP2023092636A - Purge method and system - Google Patents

Abstract

To provide a method and system for more quickly purging a flammable gas of hydrocarbons adsorbed on an adsorbent in a hydrogen production process that includes a desulfurization step and a steam reforming step.SOLUTION: The present invention provides a method for purging hydrocarbons adsorbed on an adsorbent in a hydrogen production process, the method including (i) a desulfurization step in which sulfur or sulfur compounds, which are impurities, are removed from a feed stream containing sulfur or sulfur compounds and hydrocarbons by using an adsorbent, and (ii) a steam reforming step in which the desulfurized feed stream containing hydrocarbons is subjected to steam reforming with heating by a burner in the presence of a steam reforming catalyst to obtain a mixture of carbon monoxide and hydrogen. In the purge method, a carbon dioxide-containing gas, preferably a carbon dioxide-containing combustion exhaust gas discharged from the burner in the steam reforming step, is used to purge the hydrocarbons adsorbed on the adsorbent.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for efficiently purging hydrocarbons adsorbed on an adsorbent for removing impurities in a hydrogen production process. The present invention also relates to a system for efficiently purging hydrocarbons adsorbed on an adsorbent for removing impurities in a hydrogen production apparatus.

In recent years, new energy technologies have been in the limelight due to environmental problems, and hydrogen utilization systems such as fuel cells have attracted attention as one of these new energy technologies. Petroleum hydrocarbons, such as city gas, natural gas, LPG, naphtha, and kerosene, are known as hydrogen sources used in hydrogen utilization systems. Among these, petroleum-based hydrocarbons such as city gas and LPG are advantageous as hydrogen sources because of the well-developed supply systems. When hydrogen is produced using such hydrocarbons, a steam reforming method or a partial oxidation reforming method is generally used as the reforming process. In the steam reforming method, hydrogen and carbon monoxide are produced by a reforming reaction by heating hydrocarbons and water in the presence of a steam reforming catalyst.

However, petroleum hydrocarbons such as city gas and LPG, which are raw materials for the reforming process, contain sulfur and sulfur compounds such as dimethyl sulfide (DMS), tertiary butyl mercaptan (TBM), and tetrahydrothiophene (THT). It is When the steam reforming method is adopted as the reforming process for hydrogen production, the steam reforming catalyst is poisoned by these sulfur compounds, and the activity declines significantly. It is necessary to perform a desulfurization process for the raw material. As such a desulfurization process, various methods for removing sulfur compounds, such as a normal temperature adsorption desulfurization method and a hydrodesulfurization method, have been proposed.

Zeolite is a typical example of the adsorbent used in the normal temperature adsorption desulfurization method. As a zeolite, for example, an Ag—Y type zeolite in which silver is supported on a Y type zeolite is known (see Patent Document 1).

Patent No. 4026700

When an adsorbent such as zeolite becomes saturated with adsorbed sulfur compounds, it becomes impossible to remove the sulfur compounds in the raw material. Hydrocarbons to be treated, such as petroleum hydrocarbons such as city gas and LPG, are combustible gases. , it is necessary to purge the combustible gas of hydrocarbons adsorbed in the pores of the adsorbent to ensure safety.

In order to purge (desorb/remove) the hydrocarbons such as LPG adsorbed in the pores of the adsorbent such as zeolite, nitrogen gas is supplied at room temperature. However, purging hydrocarbons from an adsorbent such as zeolite by nitrogen gas flow requires a large gas flow rate, increasing the processing cost. Also, it takes a relatively long time to complete the removal of hydrocarbons, resulting in low process efficiency. Thus, the purging of hydrocarbon combustible gases from adsorbents such as zeolite by nitrogen gas flow poses problems such as a decrease in operating efficiency of the entire process and an increase in treatment costs.

Accordingly, an object of the present invention is to improve the operating efficiency of the entire process by efficiently extracting and refilling an adsorbent such as zeolite in a hydrogen production process including a desulfurization process and a steam reforming process. It is an object of the present invention to provide a method and a system therefor for purging combustible gases of hydrocarbons adsorbed on an adsorbent such as zeolite more rapidly in order to improve and reduce processing costs.

As a result of intensive research, the present inventor unexpectedly found that in a hydrogen production process including a desulfurization process and a steam reforming process, a hydrocarbon such as LPG adsorbed on an adsorbent such as zeolite is purged (desorbed/removed). By using a gas containing carbon dioxide (CO ₂ ), that is, a fluid containing carbon dioxide gas, as the purge gas for the The inventors have found that it is possible to purge combustible gases of hydrocarbons from materials, and completed the present invention.

One aspect of the present invention for achieving the above object is as follows.
(i) a desulfurization step of removing sulfur or sulfur compounds from a feed stream containing sulfur or sulfur compounds as impurities and hydrocarbons using an adsorbent; and (ii) said carbonization resulting from said desulfurization step. Hydrogen production comprising a steam reforming step of subjecting a feed stream containing hydrogen to steam reforming with heating by a burner in the presence of a steam reforming catalyst to obtain a mixture of carbon monoxide and hydrogen from said hydrocarbon and water or steam. A method of purging the hydrocarbon adsorbed on the adsorbent in a process, comprising:
A purging method, wherein the hydrocarbon adsorbed on the adsorbent is purged using a gas containing carbon dioxide.

Here, preferably, in the purging method, combustion exhaust gas containing carbon dioxide discharged from the burner in the steam reforming step can be used as the gas containing carbon dioxide.
Further preferably, in the purging method, when the flue gas containing carbon dioxide discharged from the burner in the steam reforming step is used, the flue gas containing carbon dioxide is stored in a buffer tank, and It is also possible to purge the hydrocarbons adsorbed on the adsorbent using the combustion exhaust gas stored in the .

Another aspect of the present invention for achieving the above object is as follows.
(I) A desulfurizer filled with an adsorbent, which receives a feed stream containing sulfur or sulfur compounds as impurities and hydrocarbons and removes sulfur or sulfur compounds from the feed stream using said adsorbent. a desulfurizer and (II) a steam reformer having a burner and filled with a steam reforming catalyst, receiving said hydrocarbon-containing feed stream obtained in said desulfurizer and water or steam; purging the hydrocarbons adsorbed on the adsorbent in a hydrogen production apparatus comprising a steam reformer to subject the hydrocarbon-containing feed stream to steam reforming under heating by the burner to obtain a mixture of carbon monoxide and hydrogen; a system,
It further includes an introduction path for introducing a gas containing carbon dioxide into the desulfurizer, and the hydrocarbon adsorbed on the adsorbent is purged by introducing the gas containing carbon dioxide into the desulfurizer. purge system.

Here, preferably, the purge system further includes an introduction path for introducing combustion exhaust gas containing carbon dioxide discharged from the burner in the steam reforming step into the desulfurizer as the gas containing carbon dioxide, The hydrocarbon adsorbed on the adsorbent may be purged by introducing the combustion exhaust gas containing carbon dioxide into the desulfurizer.
Further preferably, when the purge system further includes an introduction path for introducing combustion exhaust gas containing carbon dioxide discharged from the burner in the steam reforming step into the desulfurizer as the gas containing carbon dioxide. , the introduction route may include a buffer tank for storing the flue gas, and an introduction route for introducing the flue gas stored in the buffer tank to the desulfurizer. The hydrocarbons adsorbed on the adsorbent may be purged by the combustion exhaust gas stored in the exhaust gas.

According to the present invention, in a hydrogen production process including a desulfurization step and a steam reforming step, a common purge gas is used to purge hydrocarbons such as liquefied petroleum gas (LPG) adsorbed on an adsorbent such as zeolite. By using a gas containing carbon dioxide (CO ₂ ) instead of nitrogen gas, the hydrocarbons adsorbed on the adsorbent can be efficiently purged (desorbed / removed) under mild conditions in a shorter time. it becomes possible to In addition, the present invention provides improved operating efficiency and reduced processing costs for the overall process.

According to a preferred embodiment of the present invention, a combustion exhaust gas (including CO ₂ , nitrogen, and water vapor) discharged from a burner in a steam reforming step is used as a gas containing carbon dioxide, and hydrocarbons adsorbed on the adsorbent are By purging, the effective use of exhaust gas containing carbon dioxide within the process flow is promoted without the need for additional equipment and costs for supplying carbon dioxide from outside the process, and as a result, it is more efficient and less expensive. Cost purging and zeolite replacement work become possible, and the operating efficiency of the entire process can be further improved.
Further, according to a preferred additional aspect of the present invention, the combustion exhaust gas containing carbon dioxide discharged from the burner in the steam reforming process is stored in advance in a buffer tank, and when purging hydrocarbons adsorbed on the adsorbent, In addition, by purging with the combustion exhaust gas stored in the buffer tank, it is not necessary to operate the burner using fuel only for the purpose of purging, and it is possible to reduce fuel consumption and burner operating costs. As a result, the operating efficiency of the entire process can be further improved and the cost can be further reduced.

FIG. 1 is an example of a hydrogen production apparatus including a purge system according to one embodiment of the present invention. The figure shows a process flow for the production of hydrogen by desulphurization, steam reforming and CO conversion of a hydrocarbon-containing feed stream with an adsorbent. FIG. 2 shows a process flow of purging hydrocarbons adsorbed on an adsorbent using flue gas from a steam reforming burner in an example of a hydrogen production apparatus including the purge system shown in FIG. be FIG. 3 is an application example of a hydrogen production apparatus including a purge system according to one embodiment of the present invention. This figure shows a purge process flow when a buffer tank for storing combustion exhaust gas from a steam reforming burner is additionally provided to the example of FIG. 1 or 2 . FIG. 4 shows the results when carbon dioxide gas and nitrogen gas are used as gases for purging (desorbing/removing) hydrocarbons (propane) from zeolite as an adsorbent in Example 1 and Comparative Example 1, respectively. 1 is a graph plotting the propane concentration at the exit of a zeolite adsorber against flow time. FIG. 4 also shows an enlarged view (1) of only the initial stage of the flow time of the purge gas, and an enlarged view (2) of only the low-concentration propane portion at the outlet of the zeolite adsorber.

The hydrogen production process to which the purging method according to the present invention is applied includes (i) a desulfurization step of removing sulfur or sulfur compounds from a feed stream containing sulfur or sulfur compounds and hydrocarbons as impurities using an adsorbent; (ii) subjecting said hydrocarbon-containing feed stream obtained in said desulfurization step to steam reforming in the presence of a steam reforming catalyst with heating by means of a burner to convert said hydrocarbons and water to carbon monoxide and hydrogen; including a steam reforming step to obtain a mixture of
Similarly, the hydrogen production apparatus to which the purge system according to the present invention is applied is (I) a desulfurizer filled with an adsorbent, which receives a feed stream containing sulfur or sulfur compounds and hydrocarbons as impurities. , a desulfurizer for removing sulfur or sulfur compounds from the feed stream using said adsorbent; and (II) a steam reformer having a burner and filled with a steam reforming catalyst, said desulfurizer comprising a steam reformer for receiving said hydrocarbon-containing feed stream and water obtained in said step and subjecting said hydrocarbon-containing feed stream to steam reforming under heating by said burner to obtain a mixture of carbon monoxide and hydrogen.

Hydrogen Production Process The hydrogen production process in the specification of the present application generally refers to a process that employs a room temperature adsorption desulfurization method as a desulfurization process and a steam reforming method as a reforming process.
Hydrocarbons contained in the feed stream of the hydrogen production process are not particularly limited, but saturated or unsaturated hydrocarbons having about 1 to 5 carbon atoms, typically liquefied petroleum gas (LPG), and its component propane and/or butane, hydrocarbon mixtures such as natural gas in the production fluids of gas wells, naphtha, olefins, town gas, i.e. liquefied natural gas (LNG) with the addition of LPG as a heating feedstock, other paraffins, etc. is mentioned. The most common examples include city gas, natural gas, and LPG.

Hydrogen production process feed streams contain sulfur or sulfur compounds as impurities along with hydrocarbons. Examples of sulfur compounds as impurities include, but are not limited to, dimethyl sulfide (DMS), mercaptans such as tertiary butyl mercaptan (TBM), and tetrahydrothiophene (THT). LPG (propane, butane) usually contains odorous sulfur-containing compounds such as mercaptans as odorizing components. In addition to sulfur or sulfur compounds, the hydrocarbon-containing feed stream may also contain oxygen-containing compounds having O—H bonds such as methanol or water, nitrogen, carbon dioxide, chlorine compounds, and the like.

Sulfur compounds contained in supply streams such as city gas and LPG are subjected to desulfurization treatment in advance by a desulfurizer filled with an adsorbent such as zeolite in order to prevent the steam reforming catalyst from being poisoned and declining in activity. .
As described above, zeolite is a typical example of the adsorbent used in the normal temperature adsorption desulfurization method. The adsorbent used in the normal temperature adsorption desulfurization method is not limited to zeolite, and other than that, for example, specific activated carbon, specific metal compounds (for example, Japanese Patent Publication No. 5-58768), etc. are known. there is Moreover, it is also possible to use a combination of a plurality of types of these adsorbents.

Zeolite has the ability to adsorb and separate molecules having a molecular diameter smaller than its pore diameter. It should have a pore size larger than the diameter (3.7 Å=0.37 nm) and larger than the molecular diameter of the sulfur or sulfur compound to be removed. Examples of such zeolites are not particularly limited, but Na—X zeolite, Na—Y zeolite, Ag—Y zeolite (see Patent Document 1 above) and the like are known, and among them Ag- Y-type zeolites are preferred.

The desulfurized feed stream containing hydrocarbons obtained in the desulphurization step is subjected to steam reforming in the presence of a steam reforming catalyst with heating by a burner to convert the hydrocarbons and water (steam/steam) into A mixture of carbon oxide and hydrogen (and carbon dioxide) is obtained. The temperature of the steam reforming reaction in the steam reformer is usually about 600°C to 1000°C, typically about 700°C to 900°C. Reactions in this steam reformer include not only reforming reactions (endothermic reactions) but also CO conversion reactions (exothermic reactions), but overall they are endothermic reactions. The operating pressure of the steam reformer is not particularly limited, but may be, for example, 2 MPa or less.

The steam reformer is generally provided with a reforming tube filled with a steam reforming catalyst for reforming the supplied hydrocarbons and a burner for heating the tube. The entire apparatus including a raw material supply pipe, a water (steam) supply pipe, a reforming pipe, a burner, and a waste heat recovery member is sometimes referred to as a steam reforming furnace. As the steam reforming catalyst, a carrier such as alumina impregnated with Ni is generally used, but any known catalyst such as Pt-based or Rh-based catalyst can be used. The burner is supplied with fuel and air, and combustion of the fuel provides the necessary thermal energy for steam reforming. Fuels supplied to the burner include hydrocarbons such as city gas, natural gas, and LPG, and mixed gases (CO ₂ , hydrogen etc.) can be suitably used.

The reformed gas containing a mixture of reformed carbon monoxide and hydrogen (and carbon dioxide) obtained from the steam reformer is cooled, for example, to 150 to 350° C. in a waste heat boiler or the like, and then carbon monoxide (CO) sent to the transformer. Most of the steam generated in this waste heat boiler can be recycled and used as steam for steam reforming, and the rest of the steam can be discharged to the outside.
In the CO conversion step, carbon monoxide in the reformed gas is allowed to react with water (steam) to produce an increased amount of hydrogen (ie, carbon dioxide and hydrogen are produced from CO and water). The CO shift process can employ two methods, high temperature CO shift and low temperature CO shift, depending on the operating temperature. These are related to the reaction equilibrium of CO conversion, with lower operating temperatures increasing the conversion of CO to hydrogen but lowering the reaction rate. For example, when the PSA (pressure swing adsorption) method is used for gas purification, a high degree of purification is possible, so even if the conversion rate of CO to hydrogen is lowered to some extent, it is acceptable, so the operating temperature is high and the reaction A high-temperature CO transformation scheme, which also has a high rate, can be employed. After the high-temperature CO-transformed process gas is cooled, it can be delivered to the gas refining process.

The hydrogen-bearing gas obtained from the CO converter can be subjected to further purification processes before being used as a hydrogen product. Gas purification processes may typically include, but are not limited to, PSA (pressure swing adsorption). After the condensed water is separated, the hydrogen-bearing gas obtained from the CO transformer is sent to a PSA unit where hydrogen gas and other gases (CO, _CO2 , _CH4 , _N2 , _H2O , balance ) can be separated. The hydrogen gas separated by the PSA is used as a hydrogen product in a hydrogen utilization system or the like. The recovery of hydrogen in the PSA (product hydrogen/hydrogen contained in the gas fed to the PSA) can range, for example, from 65 to 95% or more. The hydrogen concentration of the hydrogen product obtained from the PSA may be, for example, 99% or more or 99.9% or more, preferably 99.99% or more, more preferably 99.999% (impurities of 10 ppm or less). . Exhaust gases other than hydrogen products separated from the PSA (including CO, _CO2 , _CH4 , _N2 , _H2O , residual hydrogen, etc.) are reused as fuel supplied to steam reformer burners. can be

The hydrogen product obtained by the hydrogen production apparatus is not particularly limited, but for example, a fuel cell that generates electricity by electrochemically reacting hydrogen and oxygen and converting chemical energy into electrical energy, Haber Bosch A wide range of processes, such as the process of synthesizing ammonia from nitrogen and hydrogen over a catalyst by a method, and the process of synthesizing methanol over a catalyst from synthesis gas containing hydrogen and carbon monoxide and carbon dioxide obtained in a steam reformer. used for purposes. In the methanol synthesis process, attempts have been made to effectively utilize the unreacted gas (including hydrogen) by separating the unreacted gas (including hydrogen) from the synthesis process and circulating it in the synthesis gas supply channel.

Fuel cells include polymer electrolyte membrane (PEFC), phosphoric acid (PAFC), molten carbonate (MCFC), and solid oxide (SOFC). Among them, the PEFC, which uses a polymer membrane, has a low operating temperature of about 70 to 90°C compared to other types of fuel cells that normally operate at 200 to 1000°C. It has advantages such as being short, easy to handle intermittent operation, and having little efficiency loss due to miniaturization, so it is widely used as a power supply for homes and automobiles. Unreacted gas (including hydrogen and the like) discharged from the fuel cell can be suitably used as burner fuel.
In order to promote the application of fuel cells to automobiles, the spread of on-site hydrogen stations has been promoted in recent years. Since high-purity hydrogen fuel for automobiles is required, a hydrogen purifier such as a PSA may be provided between the CO shift converter and the fuel cell to increase the hydrogen purity. As mentioned above, the separated exhaust gases (including CO, _CO2 , _CH4 , _N2 , _H2O , residual hydrogen, etc.) from the PSA are recycled as fuel to the steam reformer burners. can be utilized.

Purging (desorption/removal) of hydrocarbons adsorbed on the adsorbent of the desulfurizer
In the hydrogen production process described above, when the adsorbent, such as zeolite, packed in the desulfurizer becomes saturated with sulfur or sulfur compounds in the feedstock, the adsorbent is unloaded and refilled. Hydrocarbons such as liquefied petroleum gas (LPG) adsorbed in the pores of the adsorbent by circulating gas for purging (desorption/removal) prior to extraction of the adsorbent such as zeolite should be purged and secured.
In the present invention, gas containing carbon dioxide (CO ₂ ) is used as the purging gas instead of nitrogen gas, which is a general purging gas. This allows the hydrocarbons adsorbed on the adsorbent to be purged efficiently in a shorter time under mild conditions, which in turn improves the operating efficiency of the entire process and reduces treatment costs. Purging hydrocarbons by bubbling a gas containing carbon dioxide (CO ₂ ) can significantly reduce gas requirements and purging operation times compared to purging with nitrogen gas, achieving a low cost and highly efficient process. be.

The volume ratio of the gas containing carbon dioxide (CO ₂ ), which is the purge gas in the present invention, may be 5% by volume or more, 8% by volume or more, or 10% by volume or more. well, 20% by volume or more, or 30% by volume or more, or 40% by volume or more, or 50% by volume or more, or 60% by volume or more, or 70% by volume or more, or 80% by volume or more, or 90% by volume or more, and the concentration may be from 99% by volume to 100% by volume (that is, substantially only carbon dioxide gas). The purge gas may contain other inert gas in addition to carbon dioxide gas. Other inert gases include, for example, nitrogen, helium, argon.
As demonstrated in the examples below, the present invention unexpectedly and advantageously provides nitrogen It has been found that the purge operation can be completed in significantly less time than it takes to complete the gas purge operation.

The flow rate of the gas containing carbon dioxide as the purge gas to the desulfurizer is not particularly limited. It can be appropriately determined depending on the type of impurities such as sulfur compounds. For example, the flow rate of a gas containing carbon dioxide (most preferably only carbon dioxide gas) to the desulfurizer may usually be 1 to 100 NL/min per 1 kg of the adsorbent contained, more typically It may be from 5 to 50 NL/min/kg of adsorbent contained. For example, the temperature of the adsorbent may be about 5°C to 40°C, more typically about 10°C to 35°C, when the gas containing carbon dioxide starts to flow. For example, the maximum temperature of the adsorbent during circulation of a gas containing carbon dioxide may be 40°C to 90°C, may be 50°C to 85°C, or may be 60°C to 80°C. . For example, the flow time of the gas containing carbon dioxide to the desulfurizer may normally be about 3 hours, may be 1 hour or less, or may be 50 minutes or less until the removal of adsorbed hydrocarbons is completely completed. may be within 40 minutes.

Carbon dioxide gas (CO ₂ ) can be produced and stored by known methods. For example, carbon dioxide gas is transported and stored from various industrial plants, such as by-product gases from the ammonia synthesis industry, by-product gases from steel mills, and by-product gases from hydrogen plants for heavy oil desulfurization. may be used.

In a preferred embodiment of the present invention, the combustion exhaust gas (including CO ₂ , nitrogen, and steam) discharged from the burner in the steam reforming process is used as the purge gas containing carbon dioxide (CO ₂ ). can be done.
In this way, the combustion exhaust gas discharged from the burner in the steam reforming process is used to purge the hydrocarbons adsorbed on the adsorbent, thereby supplying carbon dioxide from the outside of the hydrogen production process. Effective utilization of exhaust gas containing carbon dioxide within the process flow is promoted without requiring equipment and costs, and thus more efficient and low-cost purging and zeolite replacement operations are possible, and the overall process is improved. Further improvement in operating efficiency is achieved.

In another preferred embodiment of the present invention, the combustion exhaust gas containing carbon dioxide emitted from the burner provided in the steam reformer is discharged from the burner provided in the steam reformer while the hydrogen production apparatus is in operation, without being discharged as waste gas from the buffer tank. can be stored in advance. When purging the hydrocarbons adsorbed by the adsorbent, the combustion exhaust gas stored in the buffer tank can be used for purging without operating the burner for the purpose of purging only.
In this way, by performing the purging operation using the combustion exhaust gas containing carbon dioxide from the burner, which is stored in the buffer tank in advance during the operation of the hydrogen production apparatus, the burner can be operated using the fuel only for the purpose of purging. It is possible to reduce fuel consumption and burner operating costs, thereby further improving the operating efficiency of the entire process and further reducing costs.

As described above, the exhaust gas (including CO, CO ₂ , CH ₄ , N ₂ , H ₂ O, residual hydrogen, etc.) separated from the hydrogen purifier PSA is supplied to the steam reformer burner. In addition, since the exhaust gas from this PSA is rich in carbon dioxide, it can be effectively used for adjusting the concentration of carbon dioxide in the purge gas supplied to the desulfurizer. You can also

In one modified aspect of the present invention, a plurality of desulfurizers filled with an adsorbent such as zeolite are installed in parallel so that the desulfurization operation mode and the operation suspension mode at the time of extracting and refilling the adsorbent can be switched. be able to. With this configuration, for example, when two desulfurizers are installed in parallel, while the first desulfurizer is in desulfurization operation (that is, while continuing the overall hydrogen production), the second desulfurization It is possible to take the desulfurizer out of service for purging hydrocarbons and withdrawing and refilling the adsorbent, and similarly while the second desulfurizer is in desulfurization operation (i.e., continuing overall hydrogen production). However, it is also possible to deactivate the first desulfurizer to serve for hydrocarbon purging and adsorbent draining and recharging. By installing multiple desulfurizers in parallel, it is not necessary to stop the hydrogen production operation when the adsorbent such as zeolite is withdrawn or refilled by switching the operation mode, so the operation efficiency of the process is further improved. Increased.

In one aspect of the invention, a purged hydrocarbon concentration detector may be placed at the outlet of the desulfurizer. Using such a detector, carbon dioxide is released within a predetermined time after the hydrocarbon concentration reaches zero or less than 1/20th of the lower explosive limit (i.e., when the removal of adsorbed hydrocarbons is reliably complete). The treatment program can be set so that the flow of containing gas to the desulfurizer can be automatically stopped. As a result, the supply amount of the gas containing carbon dioxide can be minimized, and the cost can be further reduced.

In one aspect of the present invention, the hydrocarbon gas components purged (desorbed/removed) from the desulfurizer by the flow of the gas containing carbon dioxide, particularly the hydrocarbon gas components purged at the beginning of the flow time, are removed from the desulfurizer. A recycle path may also be formed to combine with the hydrocarbon-containing feed stream prior to introduction into the reactor. Alternatively, the hydrocarbon gas component purged from the desulfurizer, particularly the hydrocarbon gas component purged early in the flow time, may be connected to the delivery path to the steam reformer. The gaseous components of the hydrocarbons purged from the desulfurizer by passage of a gas containing carbon dioxide (e.g., when the carbon dioxide concentration in the gas is about 100% by volume) are the purging gas, dioxide Since it contains little (or no) carbon gas and has high purity, it has high utility value, is suitable for recycling, and contributes to the efficient use of resources.

By purging (desorbing/removing) hydrocarbon gas components from the desulfurizer by circulating the gas containing carbon dioxide, the removal can proceed rapidly at the beginning of the circulating time. In order to perform complete purging, it is desirable to continue the circulation of the gas containing carbon dioxide for a certain amount of time after the initial circulation time. At this time, if approximately 100% by volume carbon dioxide gas is used, substantially pure or 100% by volume carbon dioxide gas may be discharged. Substantially pure carbon dioxide gas thus emitted can be recovered and reused, leading to process efficiencies, cost savings and greenhouse gas emission control.

Description of Embodiments of the Present Invention with Reference to Drawings A more specific embodiment of the present invention will be described with reference to the drawings. These embodiments are illustrative and the invention is not limited thereby. A person skilled in the art can appropriately use only a part of these embodiments, or partially change or modify them, or combine them to implement them within the scope of the present invention.

An embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG.
This embodiment is an example in which the hydrogen production process according to the present invention is applied to a hydrogen utilization system (a non-limiting example is a fuel cell). This hydrogen production process includes a desulfurization step by a normal temperature adsorption desulfurization method, a steam reforming step by a steam reforming method, and a carbon monoxide transformer that transforms carbon monoxide (CO) into carbon dioxide (CO ₂ ) using steam. (hereinafter referred to as the "CO transformer").

FIG. 1 is an example of a process flow for producing hydrogen using a hydrogen producing apparatus including a purge system according to one embodiment of the present invention and using this hydrogen in a hydrogen utilization system.
This process flow includes a desulfurization step in a desulfurizer 1 filled with adsorbent to remove sulfur or sulfur compounds from a feed stream containing sulfur or sulfur compounds as impurities and hydrocarbons, and a steam reforming with a burner 3. steam reforming of the desulfurized feed stream with heating by a burner in a catalyst-filled steam reformer 2 to obtain a mixture of carbon monoxide and hydrogen (and carbon dioxide) from hydrocarbons and water; a CO transformation step in which carbon monoxide in the reformed stream is transformed with water vapor in the CO transformation unit 4 to produce carbon dioxide and hydrogen; 5.

In FIG. 1, when producing hydrogen for use in the hydrogen utilization system 5, the raw material supply valve V10, the desulfurized raw material supply valve V11, the water supply valve V12, the steam reformed gas supply valve V13, The CO-transformed gas supply valve V14, the fuel supply valve V15 and the air supply valve V16 are opened, and the combustion exhaust gas supply valve V17 and the exhaust gas release valve V18 of the steam reformer burner are closed.

A raw material feed stream containing sulfur or sulfur compounds as impurities and hydrocarbons (city gas, natural gas, LPG, etc.) is supplied via a line 10 to a desulfurizer 1 filled with an adsorbent such as zeolite, Here, sulfur or sulfur compounds are adsorbed and removed by the adsorbent. This desulfurized hydrocarbon-containing stream is then fed via line 11 to the steam reformer 2 and simultaneously with water via line 12 . Here, the water supplied to the steam reformer 2 via the line 12 can be replaced with water (liquid) and can be steam. In the steam reformer 2, by heating with the burner 3 in the presence of the steam reforming catalyst, hydrogen and carbon monoxide (CO), which are the products of the reforming reaction, are converted from the desulfurized hydrocarbon and water. A stream containing carbon dioxide (CO ₂ ) is produced. A fuel supply line 15 and an air supply line 16 are connected to the burner 3 to provide thermal energy necessary for steam reforming. As the fuel for the burner from the fuel supply line 15, in addition to hydrocarbons including city gas, natural gas, LPG, etc., the mixed gas (including CO ₂ and hydrogen) discharged from the hydrogen utilization system 5 is also suitable. can be used. A stream containing hydrogen and carbon monoxide (CO) obtained from steam reformer 2 is then fed via line 13 to CO converter 4 . In the CO shift converter 4, hydrogen and carbon dioxide (CO ₂ ) are produced from carbon monoxide (CO) and water vapor in the presence of a shift catalyst. The resulting stream from CO shift converter 4, i.e., a stream containing hydrogen from steam reformer 2 and hydrogen from CO shift converter 4, is then passed via line 14 (and, if desired, After being subjected to a refining process that has not been treated), it is supplied to the hydrogen utilization system 5 (see the bold line in FIG. 1). For example, when the hydrogen utilization system 5 is a fuel cell, power generation using hydrogen is performed here.

FIG. 2 shows an application example of a hydrogen production apparatus including a purge system according to one embodiment of the present invention shown in FIG. 1 is a process flow of purging with exhaust gas;
In this process flow, in hydrogen production shown in FIG. When the need arises, the combustion exhaust gas containing carbon dioxide discharged from the burner 3 provided in the steam reformer 2 is used to adsorb the adsorbent such as zeolite filled in the desulfurizer 1. Including purging hydrocarbons. Such a purging operation is performed to purge the hydrocarbons adsorbed in the pores of the adsorbent, thereby ensuring safety when the adsorbent is extracted and refilled.
In this embodiment, the combustion exhaust gas containing carbon dioxide discharged from the burner 3 provided in the steam reformer 2 is used as the gas containing carbon dioxide, but the purge gas in the present invention is limited to this. Any gas containing carbon dioxide can be used.

In FIG. 2, following the hydrogen production shown in FIG. The raw material supply valve V11, the water supply valve V12, the steam reformed gas supply valve V13, and the CO-transformed gas supply valve V14 are closed (that is, the hydrogen production process is stopped), and the fuel supply valve V15 is closed. , the air supply valve V16, the flue gas supply valve V17 of the steam reformer burner, and the exhaust gas discharge valve V18 are opened.

In the burner 3, using the air supplied from the line 16, the fuel supplied from the line 15 (hydrocarbons including city gas, natural gas, LPG, etc., CO ₂ discharged from the hydrogen utilization system 5, including hydrogen) mixed gas) is burned. The combustion exhaust gas (including CO ₂ , nitrogen, and water vapor) is supplied to the desulfurizer 1 via a line 17 as a purge gas, and is thereby adsorbed by an adsorbent such as zeolite filled in the desulfurizer 1. Hydrocarbons (city gas, natural gas, LPG, etc.), which are the raw materials for hydrogen production, are quickly purged (see the bold line in FIG. 2). The purged hydrocarbons are sent to a flare where they may be combusted (not shown). When the hydrocarbon component is no longer detected in the exhaust gas discharge line 18 from the desulfurizer 1, or when it reaches less than 1/20 of the lower explosive limit, the purge is completed, all the valves are closed, Extraction and exchange work of zeolite is performed.

According to this embodiment, hydrocarbons can be removed under mild conditions in a shorter time by using a gas containing carbon dioxide (CO ₂ ) to purge hydrocarbons adsorbed on an adsorbent such as zeolite. Efficient purging becomes possible, which in turn improves the operational efficiency of the entire process and reduces processing costs. Purging hydrocarbons with a gas containing carbon dioxide (CO ₂ ) can significantly reduce gas requirements and purging operation times compared to purging with nitrogen gas, resulting in a low cost and highly efficient process.
Further, according to the present embodiment, the combustion exhaust gas (including CO ₂ , nitrogen, and water vapor) discharged from the burner of the steam reformer is used as the purging gas for the hydrocarbons, thereby eliminating the carbon dioxide from outside the process. It promotes the effective use of exhaust gas containing carbon dioxide in the process flow without the need for additional equipment and costs of carbon supply, which in turn enables more efficient and low-cost purging and zeolite replacement operations, resulting in improved process efficiency. It is possible to further improve the overall operating efficiency.

FIG. 3 shows a buffer for storing flue gas from a steam reforming burner for an application example of a hydrogen production apparatus including a purge system according to an embodiment of the present invention shown in FIG. 1 or FIG. 1 is a process flow in which a tank is additionally provided and flue gas stored therein is used to purge hydrocarbons adsorbed on the adsorbent.
In the process flow of FIG. 3, in the hydrogen production shown in FIG. 1 (the hydrogen production process itself is also common in FIG. 3), the adsorbent such as zeolite filled in the desulfurizer 1 is When the adsorbent is saturated and it becomes necessary to remove and refill the adsorbent, the operation of the burner 3 provided in the steam reformer 2 is stopped (that is, the fuel to the burner 3 is consumed. without incurring operating costs of the burner 3, and without generating excess greenhouse gas emissions due to combustion of the fuel), the combustion of the burner 3 containing carbon dioxide previously stored in the buffer tank 6 This includes using the exhaust gas to purge hydrocarbons adsorbed on the adsorbent.

In FIG. 3, when the burner 3 provided in the steam reformer 2 is operated during hydrogen production, the combustion exhaust gas containing carbon dioxide emitted from the burner 3 provided in the steam reformer 2 by burning the fuel is preliminarily stored in the buffer tank 6 via the line 19 . During the storage operation of the combustion exhaust gas of the burner 3, the supply valve V19 of the combustion exhaust gas of the steam reformer burner to the buffer tank is opened, and the fuel exhaust gas stored in the buffer tank is supplied to the desulfurizer. Valve V20 is closed.

In FIG. 3, following hydrogen production, when the hydrocarbons adsorbed by the adsorbent are purged using the combustion exhaust gas of the burner 3 containing carbon dioxide stored in advance in the buffer tank 6, the raw material supply valve V10 is closed. , the desulfurized raw material supply valve V11, the water supply valve V12, the steam reformed gas supply valve V13, the CO-transformed gas supply valve V14, the fuel supply valve V15, and the air supply valve V16 are closed (that is, , the entire hydrogen production process including the operation of the burner 3 is stopped), the supply valve V19 for the combustion exhaust gas of the steam reformer burner to the buffer tank is also closed, and the exhaust gas release valve V18 and the buffer tank are closed. The supply valve V20 for supplying the fuel exhaust gas stored in the desulfurizer is opened.

Combustion exhaust gas (including CO ₂ , nitrogen, and water vapor) of the burner 3 containing carbon dioxide stored in advance in the buffer tank 6 is supplied as a purge gas to the desulfurizer 1 via a line 20 and a valve V20. , the hydrocarbons (city gas, natural gas, LPG, etc.) that are the raw materials for hydrogen production adsorbed on the adsorbent such as zeolite packed in the desulfurizer 1 are quickly purged (see the bold line in FIG. 3). ). The purged hydrocarbons are sent to a flare where they may be combusted (not shown). When the hydrocarbon component is no longer detected in the exhaust gas discharge line 18 from the desulfurizer 1, or when it reaches less than 1/20 of the lower explosion limit, the purge is completed, all valves are closed, Extraction and exchange work of zeolite is performed.

According to this embodiment, the combustion exhaust gas of the burner in the steam reforming process stored in the buffer tank is used to purge the hydrocarbons adsorbed on the adsorbent, so the burner is operated only for the purpose of performing the purging operation. It is not necessary, and fuel and power consumption, burner operation and maintenance costs can be greatly reduced. As a result, the operating efficiency of the entire process can be further improved and the cost can be further reduced, and at the same time, resources can be saved and greenhouse gas emissions can be reduced.

EXAMPLES The present invention will be illustrated with reference to examples below, but the present invention is not limited to these examples.

Comparative Experiment of Purge Behavior from Hydrocarbon Adsorbing Zeolite (Example 1 and Comparative Example 1)
2.23 kg of NaX-type zeolite as an adsorbent was accommodated at a height of 200 mm in a zeolite adsorber (including a zeolite accommodating portion) having an inner diameter of 151 mm.
Liquid LPG (propane only) was flowed from the bottom of this zeolite adsorber, and the zeolite was sufficiently immersed in the liquid LPG to achieve a complete adsorption state. After complete adsorption of LPG on the zeolite, the liquid was drained and depressurized (to atmospheric pressure) to obtain a sample of LPG-adsorbed zeolite.

As Example 1 illustrating the purge operation according to the present invention, a zeolite adsorber containing an LPG-adsorbed zeolite sample was charged with carbon dioxide gas (100% by volume CO ₂ ) as a purge (desorption/removal) gas at a linear velocity of 1. Flow rate of 22 NL/min at 0.32 m/min.
The temperature inside the zeolite adsorber (that is, the temperature of the stored zeolite) rapidly rises from about 20°C before the start of the carbon dioxide gas flow to about 60°C immediately after the start of the flow, and then rises to about 70°C at maximum during the flow. °C, it did not rise above that level, and in a short period of time, the temperature dropped sharply, and when the flow was stopped, the temperature dropped again to about 20°C.

On the other hand, as Comparative Example 1, a zeolite adsorber containing an LPG-adsorbed zeolite sample was supplied with nitrogen gas (N ₂ ) as a purge (desorption/removal) gas at a linear velocity of 1.26 m/min and a flow rate of 21 NL/min. circulated in
The temperature inside the zeolite adsorber was constant at about 20° C. from the start to the stop of the flow of nitrogen gas.

Regarding the above example using carbon dioxide gas (100% by volume CO ₂ ) as the purging gas and the above comparative example using nitrogen gas (N ₂ ), the horizontal axis represents the flow time of the purging gas, and the zeolite adsorption FIG. 4 shows a graph in which the vertical axis represents the propane (C ₃ H ₈ ) concentration (% by volume) at the outlet of the reactor. In addition, FIG. 4 shows an enlarged view (1) of only one hour at the beginning of the flow time of the purge gas, and an enlarged view (2) of only the portion where the zeolite adsorber outlet propane has a low concentration of 3% by volume or less. Also shown.

From the graph of FIG. 4, the following matters are grasped.
・When carbon dioxide gas is used as the purge (desorption/removal) gas, the working time for propane purging (when the outlet propane concentration is 0.1% by volume) is shorter than when nitrogen gas is used as the purge gas. time to reach less than 1/20 of the lower explosive limit) was reduced to about 1/50. Thereby, the process efficiency can be enhanced, which in turn can shorten the zeolite extraction work and improve the availability of the equipment.
- When carbon dioxide gas is used as the purging gas, the necessary amount of gas is reduced to about 1/30 of that when nitrogen gas is used as the purging gas. This can significantly reduce the cost of purging gas.
・As shown in the enlarged view (1) of FIG. 4, the decrease profile and decrease rate of the propane concentration at the outlet of the zeolite adsorber at the beginning of the flow time of the purging gas were obtained using carbon dioxide gas as the purging gas. There was a large difference between when nitrogen gas was used and when nitrogen gas was used. That is, when carbon dioxide gas is used as the purging gas, approximately 100% concentration (that is, high purity) propane containing no or little carbon dioxide gas is discharged from the outlet of the zeolite adsorber for the first approximately 10 minutes, The propane concentration then dropped sharply. The gas that is discharged immediately after the purge gas starts to flow can be easily recovered as a product by a simple pressurizing means such as a compressor, making it possible to reduce greenhouse gases by flaring. On the other hand, when nitrogen gas is used as the purging gas, the propane concentration at the outlet of the zeolite adsorber continues to decrease gradually at an almost constant rate immediately after the start of circulation, so low-concentration propane is discharged and recovered as a product. becomes difficult.
・As shown in the enlarged view (2) together with the enlarged view (1) of FIG. 4, when carbon dioxide gas is used as the purge gas, the outlet of the zeolite adsorber is discharged in about 20 minutes from the start of the flow. The propane concentration reached less than 0.1% by volume, ie less than 1/20 of the lower explosive limit. On the other hand, when nitrogen gas was used as the purge gas, it took about 16 hours for the propane concentration at the outlet of the zeolite adsorber to reach less than 0.1% by volume, that is, less than 1/20 of the lower explosion limit. bottom.

Example 2
In the same manner as in Example 1, except that a gas containing carbon dioxide at a concentration of 12.9% by volume was flowed as a purge (desorption/removal) gas at a linear velocity of 1.15 m/min and a flow rate of 19 NL/min. This carbon dioxide-containing gas is passed through the zeolite adsorber containing the LPG-adsorbed zeolite sample, and the relationship between the flow time of the purge gas and the propane (C ₃ H ₈ ) concentration (% by volume) at the outlet of the zeolite adsorber is monitored. bottom.
As a result, surprisingly, even when the carbon dioxide concentration in the purging gas is relatively low at 12.9 vol. , that is, less than 1/20 of the lower explosive limit), which was found to be greatly shortened compared to the time required to complete the purging operation with nitrogen gas, which was about 16 hours.

The purging method and system according to the present invention can efficiently purge hydrocarbons adsorbed on an adsorbent for removing impurities in a hydrogen production process, thereby improving the operating efficiency of the entire process and reducing the treatment cost. Because of the reduction, it can be widely and effectively used for application to various hydrogen utilization systems such as fuel cells, processes for synthesizing ammonia by the Haber-Bosch process, and processes for synthesizing methanol from syngas.

1: Desulfurizer 2: Steam reformer 3: Steam reformer burner 4: CO shift converter 5: Hydrogen utilization system 6: Buffer tank 10: Raw material supply line to desulfurizer 11: Desulfurization treatment from desulfurizer Finished raw material discharge line 12: Water supply line to steam reformer 13: Steam reformed gas discharge line from steam reformer 14: CO converted gas discharge line from CO shift converter 15 : Fuel supply line to steam reformer burner 16: Air supply line to steam reformer burner 17: Steam reformer burner flue gas supply line to desulfurizer 18: Exhaust gas from desulfurizer Release line 19: Supply line for combustion exhaust gas of steam reformer burner to buffer tank 20: Supply line for fuel exhaust gas stored in buffer tank to desulfurizer V10: Raw material supply valve V11: Supply valve for desulfurized raw material V12: Water supply valve V13: Steam-reformed gas supply valve V14: CO-transformed gas supply valve V15: Fuel supply valve V16: Air supply valve V17: Steam reformer burner flue gas supply valve V18 : Exhaust gas release valve V19: Supply valve for combustion exhaust gas of steam reformer burner to buffer tank V20: Supply valve for fuel exhaust gas stored in buffer tank to desulfurizer

Here, preferably, the purge system further includes an introduction path for introducing combustion exhaust gas containing carbon dioxide discharged from the burner in the steam reformer into the desulfurizer as the gas containing carbon dioxide, The hydrocarbon adsorbed on the adsorbent may be purged by introducing the combustion exhaust gas containing carbon dioxide into the desulfurizer.
Further preferably, the purge system further includes an introduction path for introducing combustion exhaust gas containing carbon dioxide discharged from the burner in the steam reformer into the desulfurizer as the gas containing carbon dioxide. , the introduction route may include a buffer tank for storing the flue gas, and an introduction route for introducing the flue gas stored in the buffer tank to the desulfurizer. The hydrocarbons adsorbed on the adsorbent may be purged by the combustion exhaust gas stored in the exhaust gas.

Claims (6)

(i) a desulfurization step of removing sulfur or sulfur compounds from a feed stream containing sulfur or sulfur compounds as impurities and hydrocarbons using an adsorbent; and (ii) said carbonization resulting from said desulfurization step. Hydrogen production comprising a steam reforming step of subjecting a feed stream containing hydrogen to steam reforming with heating by a burner in the presence of a steam reforming catalyst to obtain a mixture of carbon monoxide and hydrogen from said hydrocarbon and water or steam. A method of purging the hydrocarbon adsorbed on the adsorbent in a process, comprising:
A purging method, wherein the hydrocarbon adsorbed on the adsorbent is purged using a gas containing carbon dioxide. 2. The method according to claim 1, wherein the gas containing carbon dioxide is exhaust gas containing carbon dioxide discharged from the burner in the steam reforming step. The flue gas containing carbon dioxide discharged from the burner in the steam reforming step is stored in a buffer tank, and the hydrocarbon adsorbed on the adsorbent is removed using the flue gas stored in the buffer tank. 3. The method of claim 2, purging. (I) A desulfurizer filled with an adsorbent, which receives a feed stream containing sulfur or sulfur compounds as impurities and hydrocarbons and removes sulfur or sulfur compounds from the feed stream using said adsorbent. a desulfurizer and (II) a steam reformer having a burner and filled with a steam reforming catalyst, receiving said hydrocarbon-containing feed stream obtained in said desulfurizer and water or steam; purging the hydrocarbons adsorbed on the adsorbent in a hydrogen production apparatus comprising a steam reformer to subject the hydrocarbon-containing feed stream to steam reforming under heating by the burner to obtain a mixture of carbon monoxide and hydrogen; a system,
It further includes an introduction path for introducing a gas containing carbon dioxide into the desulfurizer, and the hydrocarbon adsorbed on the adsorbent is purged by introducing the gas containing carbon dioxide into the desulfurizer. purge system. Further comprising an introduction path for introducing the flue gas containing carbon dioxide discharged from the burner in the steam reforming step into the desulfurizer as the gas containing carbon dioxide, wherein the flue gas containing carbon dioxide is introduced into the desulfurizer. 5. The system of claim 4, wherein said hydrocarbon adsorbed on said adsorbent is purged by introducing it into a vessel. A buffer tank for storing the combustion exhaust gas, and the combustion stored in the buffer tank, in an introduction path for introducing the combustion exhaust gas containing carbon dioxide discharged from the burner in the steam reforming step into the desulfurizer. 6. The desulfurizer according to claim 5, comprising an introduction path for introducing exhaust gas into said desulfurizer, wherein said hydrocarbon adsorbed on said adsorbent is purged by said combustion exhaust gas stored in said buffer tank. system.

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