JPH0328620A - Hydrocarbon modifying device for fuel cell - Google Patents

Abstract

PURPOSE:To reduce starting time and improve operational safety and stability during low load operation by installing a vapor generation pipeline to a combustion gas intake passage comprising a concentric multilayer ring-shaped passage, which is laid out to a reactive cylinder filled with catalyzer. CONSTITUTION:When steady operation is being carried out and especially when a load factor exceeds 50%, a change over valve (f) is shut down, and raw water which enters a pipeline (d) from a water supply pump (c), is fed into a water vapor generator (e). The generated vapor is fed to an intake pipeline 21 where it is mixed with raw gas and the mixed gas is introduced to a modifying device. On the other hand, when the load factor fails to exceeds 50% or when a fuel cell is starting, the change over valve (f) is opened to introduce the raw water to a pipeline (a). The raw water rises in a water vapor generator A which is laid out at the position at which heat arrives most quickly as a cell system, and turns into water vapor. That water vapor enters a separator (h) by way of pipelines (j) and (i), heats the whole system and enters the modifying device. It is, therefore, possible to shorten starting time and stabilize operational stability during low load operation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hydrocarbon reformer for fuel cells that reform hydrocarbons such as methane by steam reforming. This invention relates to a hydrocarbon reformer for fuel cells that can be operated efficiently even when the load is reduced and that can be made more compact. [Prior Art] An example of a device for filling a heating tube with a catalyst and causing a reforming reaction in the heating tube by flowing hydrocarbon and steam is a reforming device such as that shown in Japanese Patent Laid-Open No. 102801/1983. can be mentioned.

This device consists of a triple-tube structure reaction tube with a combustion exhaust gas discharge path in the center, and a fuel supply/combustion path provided on the outer circumferential side of this reaction tube, and the fuel is combusted on the outer circumferential side of the reaction tube. The reactor tube is heated from the inside and outside by adopting a configuration called L that allows the combustion exhaust gas to flow into the center of the tube. Then, the raw material gas is passed from the inner layer passage to the outer layer passage of the triple-pipe structure reaction tube so as to face the combustion gas, and during this time it receives heat and undergoes an endothermic steam reforming reaction. questioned.

In such conventional hydrocarbon reformers, a heat insulating structure is adopted as a means of increasing thermal efficiency by reducing heat radiation to the outside of the system. Since it is located on the surface side, relatively high temperature combustion gas flows outside the reaction tube. Therefore, it became necessary to make the insulation wall provided around the fuel supply/combustion path considerably thicker, which caused the problem of increasing the size of the device. In addition, since the combustion gas, which is a heat supply source, and the raw material gas are configured to flow in opposite directions, the gas temperature along the flow C of the combustion gas changes as shown by BG in Figure 3, and conversely, the raw material gas The gas temperature of the gas or reformed gas changes as shown by MG in the figure. In other words, raw material gas or reformed gas whose temperature has already increased due to heat transfer from the combustion gas on the outlet side in the inner layer passage flows into the catalyst layer in the outer layer passage which is heated by the relatively high temperature combustion gas on the artificial part side. ing. For this reason, the temperature difference between the combustion gas on the inlet portion side and the catalyst layer in the outer layer passage is relatively small, and there is a problem that the heat of the combustion gas in the high temperature section cannot be used effectively.

In addition, since the reformed gas coming out from the outlet of the outer layer passage has a relatively high gas temperature (for example, about 800°C),
It is necessary to lower the temperature of this reformed gas to a specified temperature before taking it out. For this reason, it is necessary to separately provide a heat exchange section between the reformed gas and the raw material gas at the top of the furnace, which is also a factor in increasing the size of the apparatus.

The inventors of the present invention have long been concerned about the above circumstances, and as a result of various studies, we have decided to provide a hydrocarbon reforming device that can increase the thermal efficiency of the entire device and be more compact than conventional ones. Performed precepts and received a special request in 1983-9.
A patent application was filed as No. 4083 (unpublished).

First, the invention related to the above patent application will be explained. According to the device of the present invention, a combustion gas guiding path is formed inscribed in the innermost layer of the reaction tube composed of a multilayer annular passage, and a combustion gas outlet passage communicating with the combustion gas guiding path is formed in the outermost layer of the multilayer annular passage. It is formed by circumscribing the . As a result, the combustion exhaust gas whose temperature has been lowered by supplying heat to the reaction tube side from the innermost layer side passes through the outer circumference of the reaction tube, so the conventional method of reforming in which combustion gas flows from the outer circumference to the center side The insulation structure can be simplified compared to other devices. Moreover, since the raw material gas introduction passage is formed on the outer periphery of the combustion exhaust gas outlet passage, the combustion exhaust gas receives the vapor phase insulation effect from the unpreheated raw material gas, which makes the insulation structure simpler. be able to. On the other hand, the raw material gas is preheated while passing through the raw material gas introduction passage circumscribing the combustion gas outlet passage and introduced into the multilayer passage of the reaction tube, so that a rapid temperature rise of the raw material gas in the reaction tube is avoided and the C precipitation reaction takes place. can be prevented. By the way, when introducing the preheated raw material gas into the reaction tube, there are two methods: one method in which it flows from the inner layer side to the outer layer side of the multilayer passageway (the original gas and the combustion gas flow in parallel), and the other method in which it flows from the outer layer side to the inner layer side of the multilayer passageway. When the latter counterflow method is adopted, the temperature changes along the flow of the raw material gas MG and the combustion gas BG are as shown in Fig. 3 above. becomes. That is, in the case of the counterflow method, the raw material gas MG first rises in temperature while passing through the reaction tube outer layer passage adjacent to the combustion gas guideway, but as described above, the gas temperature in the combustion gas guideway is lower than that in the combustion gas guideway. Since the gas temperature is lower than the gas temperature of , the rise in gas temperature is slow, and it is not until it reaches the inner layer passage of the reaction tube that it comes into contact with the high-temperature combustion gas BG. Therefore, in this case, the temperature difference between the combustion gas and the raw material gas (or reformed gas) in the raw material gas population portion becomes small, and the utilization efficiency of the heat retained in the combustion gas inevitably becomes low. On the other hand, since the outlet of the inner layer passage of the reaction tube comes into contact with relatively high temperature combustion gas, the temperature of the reformed gas coming out from the outlet is quite high. For this reason, a cooling device or a heat exchange device that lowers the temperature of the reformed gas to a predetermined temperature is often provided, which is one of the causes of an increase in the size of the device.

On the other hand, when a parallel flow method is adopted in which the raw material gas MG flows from the outer layer passage to the inner layer passage of the reaction tube, the raw material gas MG
The temperature change along the flow of the combustion gas BG is as shown in FIG. In other words, in the case of parallel flow system, raw material gas M
' Since G is first introduced into the inner layer passage in contact with the high-temperature gas region of the combustion gas guide path, the temperature difference between the raw material gas MG and the combustion gas BG in the raw material gas population area becomes considerably large, compared to the above-mentioned counterflow method. This increases the efficiency of using the heat retained in the combustion gas. Then, the raw material gas (reformed gas) MG that has passed from the inner layer passage to the outer layer passage comes into contact with relatively low temperature combustion gas at the outlet of the combustion gas outlet passage at the outlet where it is led out of the system from the reaction tube. Therefore, the reformed gas temperature can be lowered compared to the counterflow method mentioned above. the result,
It is possible to omit the cooling device and heat exchange device for lowering the temperature of the reformed gas. Fig. 4 is a cross-sectional explanatory diagram showing the parallel flow type of the device invented in the patent application, 1 is a reaction tube, 2 is a raw material 3 is a combustion burner, 4 is a combustion gas guiding path, 5 is a furnace body, and 42 is a combustion gas outlet path.

The reaction tube 1 consists of a triple tube in which an inner tube 11, a middle tube 12, and an outer tube 13 are spaced apart from each other and arranged concentrically, and the inner tube 1! And Chutsutsu! 2, and an annular outer layer passage 15 is formed between the middle cylinder 12 and the outer cylinder 13.

The inner layer passage 14 and the outer layer passage 15 communicate with each other by connecting the inner cylinder 1l and the outer cylinder 13 and cutting off the lower end of the middle cylinder 12. The system is filled with reforming catalyst S. The reaction tube 1 is supported in the furnace body 5 in a suspended state by extending the upper end of the inner cylinder 11 and fixing it to the lid part 51.

Further, the inner wall surface of the furnace body 5 (along which is the annular raw material gas introduction passage 2
is formed, and the lower end of the raw material gas introduction path 2 is
The upper end of the raw material gas introduction path 2 is connected to the inner layer passage 14 of the reaction tube 1 via the conduit 22.
It is connected to the. Further, above the reaction tube 1, a manifold 61 is arranged concentrically with the reaction tube, and branches v62 taken out from a plurality of locations of the outer layer passage I5 of the reaction tube are connected to the manifold 61.
A reformed gas take-off pipe 63 that penetrates the furnace body 5 is pulled out from.

The center side space of the reaction tube 1 constitutes a combustion gas guide path 4, and a combustion burner 3 supported by a lid body 51 is installed downward in the upper part of the center side space, and the tip of the combustion burner 3 is connected to a heat-resistant tile. 31. The annular space between the reaction tube 1 and the raw material gas introduction path 2 functions as a combustion gas derivation path 42, and communicates with the combustion gas guide path 4 at the bottom. A Raschig ring B is filled, thereby extending the residence time of combustion gas and promoting heat transfer. The upper end of the combustion gas outlet path 42 is the lid 5! It communicates with a combustion gas exhaust pipe 43 inserted into the combustion gas exhaust pipe 43 . Incidentally, the furnace body 5 and the lid body 51 are made of a heat insulating material.

In the reformer configured as described above, fuel such as methane and air are supplied to the combustion burner 3 and combusted to generate high-temperature combustion gas. The combustion gas descends through the combustion gas passage 4 in the center, goes around the lower end of the reaction tube 1, turns around, ascends the combustion gas outlet passage 42, and is discharged from the combustion gas discharge pipe 43. On the other hand, a raw material gas consisting of gaseous hydrocarbons such as natural gas, water vapor, etc. is supplied from the raw material gas introduction path 2, and is supplied to the inner layer passage 14 of the reaction tube 1 through the conduit 22. After descending within the inner layer passage 14, it turns back at the lower end and ascends through the outer layer passage 15. While the original gas passes through the catalyst layers of the inner layer passage 14 and the outer layer passage 15, it receives heat from the surroundings and causes a C reforming reaction, changing into a reformed gas mainly consisting of H2 and co. This reformed gas flows through the outer layer passage 15
The manifold 61C is collected from the upper end via the branch pipe 62 and extracted from the reformed gas take-off pipe 63. Note that heat is supplied from the combustion gas guide path 4 and the combustion gas outlet path 42 to the raw material gas by both radiation heat transfer and heat transfer via the filler.

In this embodiment, as can be understood from the above explanation and FIG. 4, the raw material gas and the combustion gas flow in parallel, so as shown in FIG. Utilization efficiency can be obtained. By effectively utilizing the heat of the high-salt combustion gas immediately after combustion, the reactivity of the catalyst layer increases, and the amount of modification per unit volume increases. As a result, the required amount of catalyst can be reduced compared to conventional methods, contributing to the downsizing of the device. For example, in the case of a small to medium-sized reformer with a hydrogen generation rate of several thousand m'/h, it is possible to design a reformer with only one reaction tube as shown in Figure 4, making the device compact. It can be configured as follows.

Further, due to the parallel flow, in the artificial part of the combustion gas, the raw material gas that has not yet received heat from the combustion gas flows through the upper end of the inner layer passage 14, and as a result, the inner cylinder 11
As the wall surface of the reaction tube 1 is cooled, the wall temperature W of the reaction tube 1 changes as shown by the broken line in FIG. That is, the wall temperature W is lower than that of a counter-flow type reformer, and a lower grade material can be used for the reaction tube 1, thereby reducing costs.

Further, the raw material gas in the raw material gas introduction path 2 is preheated by exchanging heat with the combustion gas in the combustion gas outlet path 42,
On the other hand, this heat exchange lowers the combustion gas temperature. In other words, the raw material gas is directly supplied to the reaction tube 1 without passing through the raw material gas introduction path.
Since the combustion gas temperature is lower than that when the combustion gas is introduced into the fuel cell, the temperature of the reformed gas at the outlet of the outer layer passage 15 can be lowered under this influence.

In addition to these effects, the most important feature of the device of the present invention is that the thickness of the heat insulating material P of the furnace body 5 can be reduced. That is, combustion gas whose temperature is lower than that of the combustion gas just released from the burner flows through the combustion gas outlet passage 4 on the outer peripheral side of the reaction tube, and this combustion gas outlet passage 42 is surrounded by the raw material gas introduction passage 2. As a result, the thermal load applied to the furnace body 5 is much smaller than in the past, and the above-mentioned effects can be enjoyed. For safety reasons, the outer surface of the furnace body 5 is
Of course, the thickness of the heat insulating material P required to maintain the temperature below 0°C can be made thinner than in the past, but it is also about 1% thicker than in the case where it is not surrounded by the raw material gas introduction path 2. The thickness of the insulation material can be made as thin as possible, and the equipment can be made more compact. In addition, by changing the amount and type of the filler B in the combustion gas outlet path 4, the retention time of the combustion gas can be changed, and it also functions to adjust the degree of heat exchange. , it is also permissible not to fill with the above-mentioned fillings at all. FIG. 5 is a cross-sectional explanatory view showing another embodiment of the invention of the prior application, and shows a case where raw material gas and combustion gas flow oppositely.

In FIG. 5, the outline of the apparatus is almost the same as the example in FIG. 4, but the upper end of the raw material gas introduction path 2 is
5a by a conduit 22a, and the manifold 61a is connected to the upper end of the inner layer passage 14a by a branch pipe 62a. As a result, the raw material gas supplied from the raw material gas introduction passage is first flowed into the outer layer passage 15a that contacts the combustion gas outlet passage 4, and is turned back at the lower end to form the inner layer passage 15a.
It flows upward through 4a. As a result, the raw material gas or the reformed gas flows opposite to the combustion gas.

Even in such a counterflow system, relatively low-temperature combustion gas flows around the outer periphery of the reaction tube, and the combustion gas is thermally insulated in the vapor phase by the introduced raw material gas flowing around the outer periphery. The thickness of P can be significantly reduced. Note that the reforming apparatus shown in FIGS. 4 and 5 can obtain the same effect even if the entire apparatus is placed horizontally, diagonally, or upside down. Further, in the above example, the raw material gas introduction passage, the reaction tube, and the combustion gas passage were formed in an annular shape, but the shape of the passage is not limited to this, and may be formed in a coil shape or the like. Furthermore, an alkuna-based combustion catalyst may be filled in the combustion gas guiding path on the center side.

[Problems to be solved by the invention] The invention of the prior application improves the thermal efficiency of the entire device, and also
Although this method had the excellent effect of making the device more compact, it was found that the following problems remained when viewed from the perspective of the entire fuel cell system.

(1) In the reformer shown in Fig. 4.5, steam must be supplied from a steam generator independently provided in a separate system both at startup and during steady operation. Therefore, especially at startup, there is a problem in that the fuel cell cannot be started while waiting for water vapor to be generated outside the system. (2) In the above device, when the load on the fuel cell decreases, if the entire amount of fuel J4 (cell waste fuel) that has not reacted in the fuel cell is combusted, the combustion burner 3 shown in Figs.
The amount of combustion heat obtained is a little excessive compared to the amount of heat required for reforming, and the temperature of the wood of the reforming furnace increases. Measures such as introducing air for cooling the breath reforming furnace from the burner 3 are required, and the addition of nine air lines complicates the overall fuel cell system.

(3) Similarly, when the load is reduced, it becomes necessary to increase the (steam)/(natural gas) ratio in the raw material gas in preparation for the next load increase, and the required amount of steam tends to be insufficient for the entire system, resulting in stable operation. Sexuality becomes worse. (4) The combustion exhaust gas flowing through the combustion gas outlet path 42 originally has a small heat transfer coefficient. Therefore, it is standard equipment for reforming furnaces to charge filler B to increase the heat transfer coefficient, but since the heat capacity is quite large, the response to load fluctuations is poor. The present invention was made in view of these circumstances, and
The object of the present invention is to provide a fuel cell reformer that can overcome the above problems.

[Means for Solving the Problems] The reforming device of the present invention that has achieved the above object is different from the device of the prior invention as described above, in that a steam generation pipe is provided in the combustion gas outlet path. The main points are as follows.

[Operations and Embodiments] FIG. 1 shows the device shown in FIG. 4, which has been improved based on the idea of the present invention, in which a steam generating serpentine pipe A is attached to the combustion gas outlet path 42. A raw water introduction pipe a is connected to the lower part of this flexible pipe A, and a raw steam discharge pipe b is connected to the upper part. On the other hand, outside the system, there is a water pump C, a pipe line d, and a dedicated steam generator (for example, one that uses exhaust heat from a fuel cell).
The pipe d branches into the raw water inlet pipe a, and the raw water inlet pipe a is provided with a switching valve f.The generated steam discharge pipe b is connected to a steam separator h via a check valve g. It is branched into a pipe i connected to the inlet pipe 21 and a pipe j connected to the introduction pipe 21. Also, regarding the steam generated by the steam generator e,
It is configured so that it can be fed to the introduction pipe 21 via the pipe h. During steady operation, especially when operating at a load factor of 50% or more, the switching valve f is shut off, and all raw water entering the pipe d from the water supply bomb C is sent to the steam generator e, where it is generated. The steam is sent from pipe k to the introduction pipe 21 and introduced into the reformer in a mixed state with the raw material gas, but when the load factor becomes less than 50% or when starting the fuel cell, the Valve f is opened and raw water in pipe d is introduced into pipe a. This water rises while spiraling inside the corrugated pipe A, but if we think about it now when it is started up, the part where heat enters quickly (combustion gas outlet path 42 in the figure) Since a steam generator (corresponding pipe A in the figure) is provided, steam will be generated quickly. The water vapor is then passed through the pipe to a temperature of ℃. It can also be introduced into the steam separator h through the i outlet and used for heating the entire system, or can be introduced into the reformer as a raw material for reforming through the pipe j outlet. The 50% load factor mentioned in the improvement note is only a rough guideline, and should be set as appropriate, taking into account the scale of the equipment. In addition, the reason why water is not supplied to the corrugated pipe A during high loads is that when considering the heat balance of the entire reformer, if the raw material gas in the raw material gas introduction path 2 is to be sufficiently heated, it is necessary to avoid this heating and steam generation. This is because the total amount of thermal energy must be increased, and commercially available fuel other than battery waste fuel (most of the fuel supplied to the combustion burner 3 is fuel cell waste fuel) must be used. .

Next, when the load on the fuel cell is reduced, in the present invention, even at this point, the flexible pipe At. : Supply water and generate steam. Therefore, when looking at the reformer as a whole, combustion burner 3
The excess amount of heat supplied by the system due to the low load will be used for steam generation, and the heat balance will be balanced. There is also no need to consider introducing air for cooling the reformer as in the past, and it is possible to avoid complication of the fuel electric system and other systems. Another effect is that the steam generated in the snake WA can be supplied as a raw material for reforming through the pipe j as described above, so that it is possible to avoid a shortage of steam in the entire system even if the load is low.

Furthermore, since the corrugated pipe A can also be used as a heat transfer accelerator on the combustion exhaust gas side, even when it is not used as a steam generator, it exerts the effect of increasing the heat transfer coefficient on the combustion exhaust gas side. There will be. Therefore, with the apparatus of this embodiment, there is no need to charge the filler B as shown in Fig. 4.5. Incidentally, a flexible tube A having low fins or high fins outside the tube has even better heat transfer efficiency. However, the present invention does not limit the structure of the steam generator itself as exemplified by the flexible pipe A.

[Effects of the Invention] Since the present invention is configured as described above, in addition to the various effects achieved by the leading invention, the startup time can be shortened, and the heat balance can be maintained even during low-load operation. Therefore, the fuel cell system can be operated safely and stably, and the complexity and size of the fuel cell system can be avoided.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional explanatory diagram showing an embodiment of the present invention, Figs. 2 and 3 are graphs showing temperature change patterns of fuel gas and raw material gas in parallel flow type and counter flow type reformers,
, 5 is a sectional view showing an embodiment according to the invention of the prior application. l... Reaction tube 2... Raw material gas introduction path 3.
... Combustion burner 4 ... Combustion gas guideway 5 ...
Furnace body 1l...inner cylinder l2...middle cylinder
13...Outer cylinder l4...Inner layer passage 15
... Outer layer passage 42 ... Combustion gas derivation furnace S ... Melting medium A ... Serpentine pipe (steam generator) Fig. 1

Claims (1)

[Claims] It consists of a multi-layered annular passage arranged concentrically and communicating with each other at one end, and includes an inlet of a raw material gas for reforming and an outlet of reformed gas, and the passage is filled with a reforming catalyst. a reaction tube, a combustion gas guide path inscribed in the innermost layer of the multilayer passage, a combustion gas outlet path circumscribed to the outermost layer of the multilayer passage and communicated with the combustion gas guide path; A fuel characterized in that it has a reforming raw material gas introduction passage that circumscribes and communicates with the reforming raw material gas inlet portion of the multilayer passage, and a steam generation pipe is provided in the combustion gas outlet passage. Hydrocarbon reformer for batteries.