JP4932165B2 - Steam reforming system - Google Patents

Description

  The present invention relates to a steam reforming system, and more specifically, an operation method in which combustible gas in the system is purged with steam in an operation method immediately after the operation is stopped, and air is replaced after the catalyst in the system is sufficiently cooled. The present invention relates to a steam reforming system to which is applied.

  Hydrogen, which is the fuel of a fuel cell such as a polymer electrolyte fuel cell (hereinafter referred to as “PEFC” where appropriate), is produced by a steam reforming method or a partial combustion reforming method. Among them, the steam reforming method reforms lower hydrocarbons such as methane, ethane, propane, and butane, city gas containing a plurality of them, petroleum gas, LP gas, or alcohols such as methanol and ethanol with steam. This is a method for generating a hydrogen-rich reformed gas. In the steam reforming method, a steam reformer is used, and these hydrocarbons and alcohols are converted into a hydrogen-rich reformed gas by a catalytic reaction with a steam reforming catalyst.

  The steam reformer is generally composed of a combustion section (heating section) in which a burner or a combustion catalyst is arranged and a reforming section in which a reforming catalyst is arranged. As the reforming catalyst, a Ni-based or Ru-based catalyst is used. In the reforming section, hydrocarbons and alcohols react with water vapor to generate hydrogen-rich reformed gas. Since the catalytic reaction that occurs in the reforming section involves a large endotherm, heat must be supplied from the outside for the progress of the reaction, and a temperature of about 600 ° C. or higher is required.

  For this reason, fuel is burned with air in the combustion section, and the generated combustion heat (ΔH) is supplied to the reforming section. Like the hydrocarbons that are converted into reformed gas in the reforming section, the fuel supplied to the combustion section may also use hydrocarbons such as city gas, etc., in order to distinguish both in this specification and drawings, Hydrocarbons supplied to the combustion section are called fuel, and hydrocarbons (lower hydrocarbons, city gas, petroleum gas, natural gas, etc.) supplied to the reforming section are called raw material gases.

  FIG. 1 is a diagram showing an exemplary embodiment from the raw material gas to PEFC using the steam reformer as described above. Odorants such as mercaptans, sulfides, or thiophenes are added to city gas and LP gas (liquefied petroleum gas). Since the reforming catalyst is poisoned by these sulfur compounds and deteriorates in performance, the reforming catalyst is introduced into the desulfurizer in order to remove those sulfur compounds. Next, steam from a steam generator provided separately is added, mixed and introduced into the reforming section of the reformer, and reforming reaction with city gas or LP gas steam in the reformer reforming section Hydrogen-rich reformed gas is generated.

In the reformed gas produced in the reforming section, unreacted methane, unreacted water vapor, carbon dioxide, carbon monoxide (CO) is by-produced, and the rate is 8 to 15% (volume%, the same applies hereinafter). include. For this reason, the reformed gas is subjected to a CO converter to remove this by-product CO by converting it to carbon dioxide. In the CO converter, a catalyst such as a copper-zinc system or a platinum catalyst is used, but a temperature of about 200 to 250 ° C. is necessary to make the catalyst function. The shift reaction in the CO shifter is indicated by “CO + H ₂ O → CO ₂ + H ₂ ”, and the unreacted residual steam is utilized in the reformer as the steam necessary for this reaction.

  The reformed gas exiting from the CO converter is composed of hydrogen and carbon dioxide gas except for unreacted methane and excess water vapor. Of these, hydrogen is an intended component, but the reformed gas obtained through the CO converter also does not completely remove CO, but contains a trace amount of CO. The CO content in the fuel hydrogen supplied to the PEFC is limited to about 100 ppm (capacity ppm, the same shall apply hereinafter), and if this is exceeded, the battery performance will deteriorate significantly, so the CO component will be removed as much as possible before introduction into the PEFC. It is necessary to keep it.

For this reason, the reformed gas is supplied to the CO remover after the CO concentration is reduced to about 1% or less in the CO shift section. Here, an oxidant gas such as air is added, and CO is reduced to about 100 ppm or less, preferably 50 ppm or less, more preferably 10 ppm or less, by the CO oxidation reaction “CO + 1 / 2O ₂ = CO ₂ ”. For example, a Ru-based metal catalyst is used as the CO removal catalyst. The operating temperature of the CO remover is about 100 to 150 ° C. The purified hydrogen is supplied to the fuel electrode of PEFC.

  By the way, PEFC needs to be started and stopped according to the necessity of power demand. The steam reformer needs to be started and stopped correspondingly, and the CO converter and the CO remover connected to the steam reformer need to be started and stopped. In the present specification and claims, a hydrogen production apparatus including a reformer, a CO converter and a CO remover is appropriately referred to as a “steam reforming system”, “reforming system” or simply “system”. Further, the steam reformer, the CO converter, and the CO remover are appropriately referred to as a reformer, a CO converter, and a CO remover.

  Conventionally, in a PEFC equipped with a steam reforming system, when it stops, no flammable gas remains in the reforming system, and the gas pressure balance on the fuel electrode side and air electrode side of the PEFC is maintained and protected. Therefore, the interior of the reforming system is purged with an inert gas such as nitrogen (see FIG. 1) or steam. On the other hand, at the time of start-up, it is necessary to raise the temperature of the reforming section, the CO conversion section, and the CO removal section to the operating temperature. However, the temperature rise due to air or combustion exhaust gas causes the catalyst to be oxidized and deteriorates performance. Therefore, the temperature is raised using an inert gas such as nitrogen or water vapor as a heat medium, unless an electric heater is additionally provided.

  At the time of stoppage, the raw material gas and the reformed gas are purged by passing water vapor through the reforming section. However, in this method, water vapor is condensed and remains in the reforming section, and at the time of restart, the moisture condensed on the surface of the reforming catalyst or inside the reforming catalyst is vaporized and evaporated, and the reforming catalyst is damaged such as cracking. appear. From this fact, there is no other way but to use an inert gas such as nitrogen for stopping the reformer, but an inert gas cannot be used in PEFC used for general households. That is, in order to use an inert gas, a separate facility is required, and the remaining amount of the inert gas must be managed.

  These problems are mainly caused by the property of the reforming catalyst with respect to oxygen and the phase change (condensation and vaporization) of water vapor. Therefore, the present inventors have assumed that the above-mentioned facts and circumstances when the reforming system is stopped are air, combustion exhaust gas with respect to the reforming catalyst under various temperature conditions from a low temperature range to a high temperature range. We continued experiments and research on the effects of gases such as nitrogen and water vapor. As a result, it has been found that, depending on the temperature conditions, there are cases where the reforming catalyst is affected and whether the gas is affected.

  FIG. 2 shows the temperature change of each catalyst over time in the process from the operation to the stop of the steam reforming system as shown in FIG. At a temperature of 600 ° C. or higher during system operation, the system is in a reduced state due to the reformed gas atmosphere, and this reduced state continues from the time of operation to the time of operation stop. At temperatures exceeding 400 ° C., even if high purity nitrogen is used, the reforming catalyst is oxidized by a small amount of oxygen contained therein. This fact suggests that it is not sufficient to use nitrogen at the time of starting and stopping of the steam reforming system, and that it is necessary to give certain consideration to nitrogen.

  In relation to water vapor, the reforming catalyst is oxidized by water vapor when the temperature exceeds 400 ° C., is not oxidized by water vapor in a short time at 400 to 300 ° C., and is not oxidized by water vapor at 300 ° C. or lower. In any case, when the reforming catalyst is oxidized, the performance deteriorates, and in order to recover the performance, reduction with hydrogen is necessary. It will deteriorate.

  By the way, in the prior art, an operation method is adopted in which the raw material gas in the system is purged with water vapor at the time of stoppage, cooled to 400 to 300 ° C., and then replaced with air (Japanese Patent Laid-Open No. 2002-93447). . However, in order to suppress deterioration due to oxidation of the reforming catalyst, it is necessary to purge and cool with steam to a lower temperature of 200 ° C. or lower, and then to replace air, which is a practical use of the steam reforming system. It became clear from the experiment and research and development. Similarly, it has been found that the CO shift catalyst must be cooled to about 120 ° C. and then replaced with air. As a result, the following issues became apparent.

JP 2002-93447 A

(1) In particular, the temperature of the CO removal catalyst decreases, and the catalyst deteriorates due to the condensation atmosphere.
(2) A vaporizer for producing steam is separately required in order to continuously supply steam to be purged and cooled in the reforming system to the reforming system.
(3) In the process of cooling with steam to a temperature at which each catalyst in the reforming system is not oxidized, steam condenses in some low temperature parts, the reforming system suddenly becomes negative pressure, The catalyst is oxidized by air mixing.

FIG. 3 is a diagram for explaining the above problem based on actually measured values, and shows the temperature of each part during natural temperature drop. In FIG. 3, the horizontal axis represents the elapsed time (temperature drop time) after the stop of the operation of the steam reforming system, and the vertical axis represents the temperature of each part.
(1) During system operation, the reforming catalyst is at a temperature of 600 ° C. or higher, and the system is in a reduced state due to the reforming gas atmosphere, so the catalyst in the system (reforming catalyst, CO shift catalyst, CO removal catalyst) ) Is not oxidized.

  (2) Purge and cool the reforming catalyst with steam from 400 to 200 ° C. from the time of shutdown. As shown in FIG. 3, the temperature of each part from the time when the operation is stopped to the time when almost 4 hours elapse is 100 ° C. or higher, and therefore, condensation of water vapor does not occur in the system. During this time, since the system internal pressure is equal to or higher than the atmospheric pressure, air in the atmosphere does not enter the system.

  (3) After approximately 4 hours have elapsed from the time of shutdown, the CO removal catalyst (= PROX catalyst) outlet side in the system begins to turn off 100 ° C. (ie, starts to drop below 100 ° C.), and when 7 hours have passed, The removal catalyst part has a temperature of 90 ° C. or less, and the CO conversion catalyst part has a temperature of 80 to 120 ° C., and condensation of water vapor occurs in the system. Then, the pressure in the system becomes a negative pressure below the atmospheric pressure. That is, before the temperature of each part in the system decreases, the pressure in the system becomes negative, and air in the atmosphere enters the system.

  The present invention solves the above-mentioned problems associated with each catalyst in the system, particularly the reforming catalyst, and does not leave a flammable gas in the steam reforming system, is safe and does not deteriorate the catalyst. An object of the present invention is to provide a steam reforming system capable of stopping the operation of the system.

The present invention includes a steam reforming section, a CO conversion section, and a CO removal section, and an evaporation mechanism for process water is disposed in the CO removal section, and air purge after steam purge in the steam reforming system as its operation stop means In the raw material gas steam reforming system, a heating means for maintaining the temperature of the CO removal section at 100 ° C. or higher during the steam purge is disposed on the outer periphery of the CO removal section. This is a steam reforming system. Here, it is preferable that the steam generated by the evaporation mechanism of the process water disposed in the CO removing unit is connected to the steam reforming unit in the system.

  According to the present invention, the operation of the steam reforming system can be safely stopped without leaving flammable gas in the steam reforming system and without degrading the catalyst. Therefore, the steam reforming system of the present invention is very useful as an actual steam reforming system attached to, for example, a PEFC that repeatedly starts, operates, and stops.

  The present invention includes a steam reforming section, a CO conversion section, and a CO removal section. A process water evaporation mechanism is disposed in the CO removal section, and a steam purge and an air purge in the steam reforming system are performed as its operation stop means. The present invention is intended for a raw material gas steam reforming system. A heating means, that is, a heating mechanism is arranged on the outer periphery of the CO removing unit.

  When the reforming catalyst is oxidized, the performance deteriorates, and a reduction treatment is required to recover the performance. Since this recovery process is extremely troublesome and requires a lot of work such as requiring hydrogen for reduction, the reforming catalyst needs to avoid oxidation as much as possible. FIG. 4 is a diagram for explaining a steam reforming system targeted in the present invention.

  As shown in FIG. 4, a reforming unit, a CO conversion unit, and a CO removal unit are sequentially provided, and an evaporation mechanism of process water, that is, water for reforming the raw material gas, is arranged on the outer periphery of the CO removal unit, Purge and air purge are performed. For example, in a steam reforming system that supplies hydrogen to PEFC or the like, a plurality of catalysts such as a reforming catalyst, a CO shift catalyst, and a CO removal catalyst are used. As the CO conversion catalyst, a single CO conversion catalyst may be used, or a high temperature CO conversion catalyst and a low temperature CO conversion catalyst may be used in combination.

  The reforming catalyst is not particularly limited as long as it is a catalyst capable of reforming the raw material gas. Ni-based or Ru-based catalysts are used, and examples thereof include a catalyst having Ni supported on alumina, and Ru on alumina. Examples thereof include a supported catalyst. The CO conversion catalyst is not particularly limited as long as it can convert the reformed gas, and a catalyst such as a copper-zinc system or a platinum catalyst is used. The CO removal catalyst is not particularly limited as long as it is a catalyst that can selectively oxidize CO in the reformed gas. For example, a Ru-based metal catalyst is used, and the metal catalyst is, for example, Ru on a carrier such as alumina. The metal catalyst is supported.

  In the steam reforming system of the present invention, as the steam reforming section, the CO conversion section, and the CO removal section, containers filled with these catalysts may be arranged separately, or the containers are arranged in an integrated manner. May be. FIG. 5 shows an example of a mode in which they are integrated and arranged as a longitudinal sectional view (WO02 / 098790A1, Japanese Patent Application No. 2004-1515). The raw material gas steam reforming system targeted in the present invention includes a steam reforming section, a CO conversion section, and a CO removal section, and the process water evaporation mechanism only needs to be arranged in the CO removal section. It is not limited to the steam reforming system as shown.

WO02 / 098790A1 Japanese Patent Application No. 2004-1515

  As shown in FIG. 5, a plurality of cylindrical bodies having the same central axis and having different diameters are arranged in multiple positions at intervals. In FIG. 5, the alternate long and short dash line indicates the central axis, and the arrow indicates the direction, that is, the axial direction. The first cylindrical body 1, the second cylindrical body 2, and the third cylindrical body 3, which are sequentially increased in diameter (diameter, the same applies hereinafter), are arranged at the same center axis and spaced from each other. A fourth cylinder 4 having a diameter larger than that of the third cylinder 3 is disposed on the third cylinder 3. A cylindrical heat transfer partition wall, that is, a radiation cylinder 5 having a smaller diameter than that of the first cylinder 1 is arranged inside the first cylinder 1, and a burner 6 is arranged in the radiation cylinder 5. ing. That is, the burner 6 is disposed at the central shaft portion and is attached to the inside of the radiation tube 5 via the upper lid / burner mounting base 7.

  The radiation cylinder 5 is disposed with a gap between the lower end thereof and the bottom plate 8 of the first cylindrical body 1, and this gap and a gap between the radiation cylinder 5 and the first cylindrical body 1 connected to the clearance are provided. Form an exhaust passage 9 for combustion exhaust gas from the burner 6. The bottom plate 8 is formed in a disc shape with a diameter corresponding to the diameter of the first cylindrical body 1. The exhaust passage 9 is connected to the exhaust port 11 of the combustion exhaust gas through a gap between the upper cover of the exhaust passage 9 (the upper cover and the lower surface of the burner mount 7) and the partition wall 10 (the upper cover of the preheating layer 14 described later) Combustion exhaust gas is discharged from here.

  Reference numeral 12 denotes a raw material gas supply pipe. In the space between the first cylindrical body 1 and the second cylindrical body 2, a preheating layer 14 is provided in the upper part, and a reforming catalyst layer 16 is provided in the lower part. ing. The second cylindrical body 2 is configured such that a portion surrounding the reforming catalyst layer 16 and a portion surrounding the preheating layer 14 are configured separately, and an upper end portion surrounding the reforming catalyst layer 16 and a lower end portion surrounding the preheating layer 14 are formed. Although it joins by the junction part in between, you may comprise integrally, without providing a junction part. Moreover, although the catalyst of the reforming catalyst layer 16 is supported by a porous plate or the like at the lower part, the description thereof is omitted. A single round bar 15 is spirally arranged inside the preheating layer 14, thereby forming one continuous spiral gas passage inside the preheating layer 14.

  The raw material gas is supplied from the supply pipe 12, and water (water vapor) is mixed in the mixing unit 13, and then introduced into the reforming catalyst layer 16 through the preheating layer 14. In the reforming catalyst layer 16, the raw material gas is reformed by water vapor while descending. The reforming reaction in the reforming catalyst layer 16 is an endothermic reaction, and the reaction proceeds by absorbing the combustion heat generated in the burner 6. Specifically, when the combustion exhaust gas from the burner 6 flows through the exhaust passage 9 between the radiation cylinder 5 and the first cylindrical body 1, the heat of the combustion exhaust gas is absorbed by the reforming catalyst layer 16, A reforming reaction is performed. In this embodiment, the portion including the reforming catalyst layer 16 corresponds to the steam reforming portion in the present invention.

  The lower end of the second cylindrical body 2 is spaced from the bottom plate 17 of the third cylindrical body 3, and the flow of the reformed gas is between the second cylindrical body 2 and the third cylindrical body 3. A path 18 is formed. The bottom plate 17 is configured in a disc shape with a diameter corresponding to the diameter of the third cylindrical body 3. The reformed gas is folded between the lower end of the second cylindrical body 2 and the bottom plate 17 of the third cylindrical body 3 and flows through the flow path 18 formed between the second cylindrical body 2 and the third cylindrical body 3. To do. A fourth cylindrical body 4 having a diameter larger than that of the third cylindrical body 3 is disposed on the third cylindrical body 3, and a CO shift catalyst layer 21 is provided between the second cylindrical body 2 and the fourth cylindrical body 4. It has been. A plate 19 (a portion corresponding to the diameter of the third cylinder 3 is occupied by the third cylinder 3 at the upper end of the third cylinder 3 and the lower end of the fourth cylinder 4. ) And a support plate 20 having a plurality of holes for gas circulation at intervals on the plate body 19 (the portion corresponding to the diameter of the second cylinder 2 is occupied by the second cylinder 2). , A donut-shaped support plate) is disposed.

  The CO shift catalyst layer 21 includes a support plate 20 and a support plate 22 having a plurality of holes for gas circulation (the portion corresponding to the diameter of the second cylindrical body 2 is occupied by the second cylindrical body 2, so a donut-shaped support plate And the upper cover of the CO shift catalyst layer 21). The support plates 20 and 22 may be formed of a mesh body made of metal or the like. In this case, the mesh body of the mesh body serves as a gas flow hole. The reformed gas that has flowed through the flow path 18 is supplied to the CO shift catalyst layer 21 through the holes of the support plate 20. In this embodiment, the portion including the CO conversion catalyst layer 21 corresponds to the “CO conversion portion” in the present invention.

  A cylindrical body 24 is disposed on the outer periphery of the fourth cylindrical body 4 with a space therebetween, and a heat insulating material 23 is disposed therebetween. A heat transfer tube 26 connected to a water supply tube 25 is directly wound around the outer periphery of the cylindrical body 24 in a spiral shape. The heat transfer tube 26 functions as a cooling mechanism for indirectly cooling the CO removal catalyst layer 35 and the CO shift catalyst layer 21. The heat insulating material 23 is wound to a thickness that can be uniformly maintained at an appropriate temperature without excessively reducing the temperature of the CO shift catalyst layer 12 by the cooling action of the heat transfer tube 26. Here, the heat transfer pipe 26 has a function as a boiler for the water supplied from the water supply pipe 25 and is a continuous single passage that continues from the water supply pipe 25, so that partial heat generation occurs in a plurality of passages. Stagnation does not occur. In this embodiment, the portion including the heat transfer tube 26 that is directly spirally wound around the CO removal catalyst layer 35 corresponds to the “evaporation mechanism of process water disposed in the CO removal portion” in the present invention.

  A partition plate 27 having one communication hole 28 is provided above the support plate 22 at a predetermined interval, and CO removal air is supplied to the space between both plates through an air supply pipe 29. An annular passage 30 is provided above the partition plate 27. By using one communication hole 28 with a predetermined hole diameter, a predetermined passing speed is obtained when the reformed gas and the CO removal air pass through the communication hole 28, and the reforming gas is modified by turbulent flow during the passage. The quality gas and the air for removing CO can be mixed well. The CO removal catalyst layer 35 is disposed at intervals between the second cylinder 2, the cylinder 36 having a larger diameter, and the lower and upper portions between the second cylinder 2 and the cylinder 36. A support plate 33 having a plurality of holes 34 (a portion corresponding to the diameter of the second cylindrical body 2 is occupied by the second cylindrical body 2), and a plurality of holes for gas circulation 38 and a support plate 37 (a portion corresponding to the diameter of the second cylindrical body 2 is occupied by the second cylindrical body 2), and is provided in a space between the support plate 37 and the support plate 37.

  A plurality of holes 32 that are equally provided in the circumferential direction are provided in the lower portion of the cylindrical body 36. The annular passage 30 is a passage formed by the cylindrical body 24, the partition plate 27, the partition plate 31, and the cylindrical body 36, and the plurality of holes 32 and the support plate 33 through the plurality of holes 34. The reformed gas, which is in communication with the CO removal catalyst layer 35 and mixed with CO removal air, is introduced into the CO removal catalyst layer 35 through the plurality of holes 32 and 34. The CO removal catalyst layer 35 communicates with a reformed gas take-out pipe 39 through a gap between a partition plate 37 having a plurality of holes 38 serving as an upper lid and the partition wall 10. Further, the CO removal catalyst layer 35 is surrounded by a cylindrical body 36, and a heat transfer tube 26 connected to the heat transfer tube 26 on the outer periphery of the cylindrical body 24 is directly spirally wound around the outer periphery of the cylindrical body 36. In this embodiment, the portion including the CO removal catalyst layer 35 corresponds to the “CO removal portion” in the present invention.

  The CO removal catalyst layer 35 is filled with a PROX catalyst (= CO removal catalyst), and an oxidation removal reaction of CO is performed by the PROX catalyst to reduce the CO content in the reformed gas to the ppm unit. The reformed gas from which CO has been removed in the CO removal catalyst layer 35 is discharged from a plurality of holes 38 provided in the partition plate 37 which is the upper lid, and reformed through the gap between the partition plate 37 and the partition wall 10. The gas is extracted from the gas extraction pipe 39. A heat insulating material 40 is disposed on the outer peripheral portion including the third cylindrical body 3, the cylindrical body 24, and the cylindrical body 36 to prevent heat from being dissipated to the outside.

<Aspects of Features of the Present Invention>
The present invention is characterized in that, for example, in the steam reforming system as described above, a heating means is disposed on the outer periphery of the CO removal unit. 6-7 is a figure explaining the aspect. As shown in FIG. 6, the heating means is arranged on the outer periphery of the CO removing unit. This heating means is an important configuration in the present invention, thereby preventing dew condensation on the CO removal catalyst in the reforming system and stopping the reforming system in an oxidizing atmosphere when the reforming system is stopped. And the deterioration of the catalyst can be prevented.

  FIG. 7 is a view showing an example in which the portion including the CO removal catalyst layer 35 in FIG. 5, that is, the CO removal portion is enlarged, and the heating means is arranged on the outer periphery of the CO removal portion. As shown in FIG. 7, heating means, that is, a heating mechanism 41 is arranged on the outer periphery of the cylindrical body 36 surrounding the CO removal catalyst layer 35. FIG. 7B is a view showing the heating means 41 in FIG. 7A taken out. FIG. 7 shows an example in which the heating means 41 is a sheath heater (electric heater). However, the heating means 41 is not limited to this, and a heating means that can achieve the arrangement purpose can be used. Other parts and members in FIG. 7 are the same as those in FIG.

<During operation of steam reforming system>
The operation of the steam reforming system of the present invention configured as shown in FIGS. 6 to 7 is performed as follows. FIG. 8 is a diagram for explaining the course from the operation of the steam reforming system to the stop of operation. During the operation (during operation), each fluid flows as indicated by arrows in FIG. Steam is mixed into the raw material gas and supplied to the reforming section. Process water is evaporated by the evaporation mechanism and mixed into the raw material gas as water vapor. Here, the heating source in the evaporation mechanism is the reaction heat of the CO remover. A reformed gas is generated in the reforming section, and the generated reformed gas is supplied to the CO shift section.

In the CO conversion part, it is converted into carbon dioxide and hydrogen by the CO conversion reaction “CO + H ₂ O → CO ₂ + H ₂ ”. As the steam necessary for the CO shift reaction, unreacted residual steam is used in the reformer. The reformed gas from the CO conversion unit is supplied to the CO removal unit. In the reformed gas, the CO component is further oxidized and removed, and the CO is reduced to about 100 ppm or less, preferably 50 ppm or less, more preferably 10 ppm or less. The operating temperature of the CO remover is about 100 to 150 ° C. In this way, reformed gas (high purity hydrogen) from which CO is removed by oxidation is produced.

<Operation from operation to stop of steam reforming system>
After operating the steam reforming system of the present invention, the operation for stopping the operation is performed as follows. When the system is shut down, the supply of the raw material gas and the CO removal air is stopped. Then, the process water is allowed to flow as indicated by an arrow in FIG. The flow rate of the process water may be small, and the process water is heated by the heating means to become water vapor and flows in the system. Steam flows from the reforming section to the CO conversion section, from the CO conversion section to the CO removal section, purges the combustible gas in the steam reforming section, and cools the system including the steam reforming section.

  At this time, in addition to the role of the steam generation means, the heating means plays a role of keeping the CO removal part of the steam reforming system from becoming a dew condensation atmosphere during purging and cooling with steam. This heat retention is also an important role of the heating means arranged in the present invention. Next, after the catalyst in the steam reforming system, that is, the reforming unit, the CO conversion unit, and the CO removing unit is sufficiently cooled, the system is replaced with air as shown in FIG. Air is supplied through a source gas supply pipe, and is supplied from a source gas supply pipe 12 in the form of FIG.

Thus, according to the present invention, the steam reforming system can be stopped safely without causing flammable gas to remain in the system and without degrading each catalyst, and the following effects (1) to (4) can be obtained.
(1) While the reforming catalyst and the CO shift catalyst are cooled to a desired temperature, it is possible to prevent the CO shift catalyst from becoming a dew condensation atmosphere.
(2) Since water vapor can be continuously produced by the heat of the heating means arranged according to the present invention, there is no need for a separate vaporizer.
(3) Since water vapor can always be circulated in the steam reforming system, air can be prevented from leaking into the system.
(4) Thus, according to the present invention, the interior of the system can be surely prevented from dew condensation or an oxidizing atmosphere, so that catalyst deterioration in the system can be prevented.

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail based on an Example, of course, this invention is not limited to these Examples. In this example, the steam reforming system shown in FIG. 7 was used. A sheath heater (electric heater) is disposed as a heating means. The configuration of the lower part omitted in FIG. 7 is the same as that of FIG. As the reforming catalyst, a catalyst in which Ru is supported on alumina is used. As the CO conversion catalyst, a catalyst in which platinum is supported on alumina is used in the high temperature portion of the CO conversion catalyst layer, and a catalyst in which Cu and Zn are supported on alumina is used in the low temperature portion. As the CO removal catalyst, a catalyst having Ru supported on alumina was used.

Example 1
<Start-up of steam reforming system>
The steam reforming system shown in FIG. 7 was started. Each fluid flows as indicated by arrows in FIGS. Steam was mixed with city gas (desulfurized) as a raw material gas and supplied to the reforming section. Process water is evaporated by the evaporation mechanism and mixed into the raw material gas. Here, the heating source in the evaporation mechanism is the reaction heat of the CO remover. A reformed gas is generated in the reforming section, and the generated reformed gas is supplied to the CO shift section. In the CO conversion part, it is converted into carbon dioxide and hydrogen by the CO conversion reaction. As the steam necessary for this reaction, unreacted residual steam is used in the reforming section.

  The reformed gas from the CO shift section is supplied to the CO removal section. In the reformed gas, the CO component is further oxidized and removed by the CO removal unit, and CO is reduced to 10 ppm or less. The operating temperature of the CO removal section is about 100 to 150 ° C. In the case of FIG. 8, this is the process of FIG.

<Stop of steam reforming system>
After starting and operating the steam reforming system as in <Starting of the steam reforming system>, the operation was stopped. When the operation was stopped, the supply of raw material gas was stopped. Then, process water was flowed as shown by an arrow in FIG. The flow rate of the process water may be small, and the process water was heated by a heating means (electric heater), and the generated steam was continuously supplied to the reforming unit. Steam flowed from the reforming section to the CO conversion section, from the CO conversion section to the CO removal section, purged the combustible gas in the steam reforming system, and cooled the interior of the steam reforming system.

  At this time, in addition to the role of the steam generation means, the heating means plays a role of keeping the CO removal part of the steam reforming system from becoming a dew condensation atmosphere during purging and cooling with steam. Next, after the catalyst in the steam reforming system, that is, the reforming section, the CO conversion section, and the CO removing section was sufficiently cooled, the steam reforming system was replaced with air as shown in FIG.

FIG. 9 is a diagram showing the operation in <stop of steam reforming system> in the present example over time. In FIG. 9, the horizontal axis represents the elapsed time (temperature drop time) after the stop of operation, and the vertical axis represents the temperature of each part.
(1) During operation, the reforming catalyst is at a temperature of 600 ° C. or higher, and the system is in a reduced state due to the reformed gas atmosphere, so the catalyst in the system (reforming catalyst, CO shift catalyst, CO removal catalyst) Not oxidized.

  (2) The reforming catalyst is purged with steam from 400 to 200 ° C. from the time when the operation is stopped, and then cooled. As shown in FIG. 9, the temperature of each part from the time when the operation is stopped to the time when almost 4 hours have passed is 100 ° C. or higher, and therefore no condensation of water vapor occurs in the system. During this time, since the system internal pressure is equal to or higher than the atmospheric pressure, air in the atmosphere does not enter the system. By turning on the heating means when approximately 4 hours have elapsed from the time when the operation was stopped, both the CO conversion section and the CO removal section are maintained at 100 ° C. or higher. For this reason, condensation of water vapor does not occur and the pressure in the system is equal to or higher than atmospheric pressure, so that air in the atmosphere does not enter the system.

  (3) Next, after about 6 hours and 40 minutes had elapsed from the time when the operation was stopped, the operation was switched to purging with air as shown in FIG. At this time, the temperature of the reforming section is about 200 ° C., the temperature of the CO conversion section is about 120 ° C., and the temperature of the CO removal section is 120 ° C. or less. Thus, according to the present invention, it was possible to stop the steam reforming system without leaving flammable gas in the steam reforming system and safely and without degrading the catalyst.

Example 2
The performance of the reforming catalyst of the steam reforming system of the present invention was tested by repeating <starting steam reforming system> and <stopping steam reforming system> as in Example 1. FIG. 10 is a diagram showing the results. In FIG. 10, the horizontal axis represents the number of times of starting and stopping (“starting → running → stop” as a unit, the number of times), and the vertical axis represents the conversion rate (%) of the raw material gas to hydrogen. As shown in FIG. 10, the conversion rate of the raw material gas is decreased little by little, and the conversion rate of about 78% is maintained even if “start-run-stop” is repeated 150 times.

The figure which shows the example of a mode from raw material gas to PEFC using a steam reforming system The figure which shows the temperature change after the time of an operation stop at the time of the operation | movement with a steam reforming system like FIG. The figure explaining the subject of this invention based on an actual measurement value The figure which shows the steam reforming system made into object by this invention The figure which shows the specific structural example of the steam reforming system made into object by this invention The figure explaining the aspect which arrange | positions a heating means to the outer periphery of CO removal part by this invention The figure which shows the example of an aspect which arrange | positions a heating means in the outer periphery of a CO removal part in the steam reforming system like FIG. The figure explaining the operation aspect at the time of the stop of the steam reforming system of this invention The figure which showed operation in <stop of a steam reforming system> in Example 1 over time. The figure which shows the result of Example 2

Explanation of symbols

1 to 4 1st cylinder to 4th cylinder 5 Radiation cylinder 6 Burner 7 Upper lid / burner mounting base 8 Bottom plate 9 Exhaust passage for combustion exhaust gas 10 Partition 11 Exhaust port for combustion exhaust gas 12 Feed gas supply pipe 13 Water (steam) 14 Preheating layer 15 Round bar 16 Reforming catalyst layer 17 Bottom plate of third cylinder 3 18 Reformed gas flow path formed between second cylinder 3 and third cylinder 3 19 Donut shape 20 A support plate having a plurality of holes for gas flow 21 CO conversion catalyst layer 22 A donut-shaped support plate having a plurality of holes for gas flow 23 Insulating material 24 Cylinder 25 Water supply pipe 26 Cylinder 24 Heat transfer tube spirally wound around the outer periphery 27 Partition plate having one communication hole 28 One communication hole 29 Air supply tube 30 Circular passage 31 Partition plate 32 Plural holes 33 Support plate 34 Support plate 33 Multiple of Number of holes 35 CO removal catalyst layer 36 Cylinder 37 Partition plate having a plurality of holes 38 A plurality of holes 39 Reformed gas take-out pipe 40 Heat insulating material 41 Heating means

Claims (2)

It includes a steam reforming section, a CO conversion section, and a CO removal section. A process water evaporation mechanism is arranged in the CO removal section, and an air purge is performed after the steam purge in the steam reforming system as its operation stop means. In the steam reforming system for raw material gas, the steam reforming system is characterized in that heating means for maintaining the temperature of the CO removal section at 100 ° C. or more during the steam purge is disposed on the outer periphery of the CO removal section. system. The steam reforming system according to claim 1, wherein steam generated by an evaporation mechanism of the process water disposed in the CO removing unit is connected to the steam reforming unit in the system. .

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