JP3913624B2 - Evaporator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an evaporator that vaporizes a liquid fuel containing hydrocarbons to generate steam for fuel reforming.
[0002]
[Prior art]
As a method of supplying fuel gas to a fuel cell, liquid raw fuel containing hydrocarbons such as methanol and gasoline is reformed into hydrogen-rich fuel gas (hereinafter abbreviated as hydrogen-rich gas) by a reforming system. In some cases, rich gas is supplied as fuel gas for the fuel cell (Japanese Patent Laid-Open No. 2001-132909, etc.).
In this reforming system, a liquid fuel (raw material) consisting of a mixture of raw fuel and water is evaporated by an evaporator to be a raw fuel gas, which is supplied to the reformer together with reforming air to be a raw fuel gas. Is reformed to hydrogen-rich gas.
[0003]
A conventional evaporator used in this reforming system is disclosed in Japanese Patent Laid-Open No. 2001-135331.
The evaporator includes a catalytic combustor in which an oxidation catalyst (for example, Pt, Pd) is supported on a metal honeycomb carrier, a tube group bent into a substantially U-shape through which combustion gas generated in the catalytic combustor flows, and the tube An evaporation chamber containing a group and surrounded by a shell; a fuel supply device for injecting the liquid fuel into the evaporation chamber; and a take-out port for deriving raw fuel gas generated by vaporization of the liquid fuel. . In this evaporator, off-gas discharged from the anode or cathode of the fuel cell is catalytically combusted by the catalytic combustor, and the obtained combustion gas is introduced into the tube group, and at the same time, the liquid fuel is supplied from the fuel supply device. Is injected toward the surface of the tube group, heat is exchanged between the combustion gas and the liquid fuel, and the liquid fuel is evaporated to obtain a raw fuel gas.
[0004]
[Problems to be solved by the invention]
However, in the conventional evaporator, a part of the liquid fuel supplied from the fuel supply device to the evaporation chamber cannot be completely evaporated while passing through the tube group, and may remain in the bottom of the evaporation chamber as a liquid. . When the liquid fuel pool is generated at the bottom of the evaporation chamber in this way, the amount of steam generated during the transition (raw fuel gas generation amount) cannot follow the output of the fuel cell, resulting in poor response. Arise.
Even if a heating source such as a catalytic combustor is arranged at the bottom of the evaporation chamber to reduce the amount of liquid pool, it is difficult to obtain satisfactory responsiveness. In particular, a fuel reforming system for a fuel cell mounted on a fuel cell vehicle or the like is much more demanding because extremely high transient response is required.
[0005]
Japanese Patent Laid-Open No. 2001-332283 discloses that an evaporation channel through which liquid fuel and fuel vapor circulate and a heating gas channel through which heated gas circulates are alternately installed, and the liquid fuel is disposed above the evaporation channel. The evaporative flow path is lowered by supplying the liquid fuel, and while it is lowered, the liquid fuel is vaporized by heat exchange with the heated gas to generate fuel vapor, and the generated fuel vapor is discharged from below the evaporative flow path. An evaporator is disclosed.
However, in this evaporator, the fuel vapor flows downward in the direction of gravity in the evaporation flow path and is in a parallel flow relationship with the liquid fuel, so that the energy of the fuel vapor can be used effectively. There wasn't.
Therefore, the present invention provides an evaporator that can efficiently vaporize liquid fuel by effectively using energy and has excellent responsiveness.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems, the invention described in claim 1 is an evaporator that vaporizes a liquid fuel containing hydrocarbons to generate fuel vapor for fuel reforming (for example, an evaporator in an embodiment described later). 30), a heating gas passage (for example, a heating gas passage 37 in an embodiment described later) through which the heating gas flows, and the heating gas passage are arranged so as to be able to exchange heat, and are supplied from above in the direction of gravity. The bottomed evaporation channel (for example, an embodiment to be described later) that vaporizes the liquid fuel flowing downward in the direction of gravity and discharges the vaporized fuel vapor upward in the direction of gravity to contact the liquid fuel countercurrently And a fin (for example, a fin 36a in an embodiment described later) provided on the inner surface of the evaporation channel.
With this configuration, the surface area of the heating surface can be increased by the fins, and the liquid fuel can easily spread greatly by adhering the liquid fuel to the surfaces of the fins. In addition, the fin increases the frequency of contact with the liquid fuel and makes the temperature difference from the attached liquid fuel easy to vaporize. Further, since the liquid fuel and the fuel vapor are in countercurrent contact in the evaporation flow path, the liquid fuel droplets to be dripped are miniaturized, and the liquid fuel can be preheated by the fuel vapor. As a result, the evaporator can vaporize the liquid fuel very efficiently and quickly, and is extremely excellent in responsiveness.
[0007]
The invention described in claim 2 is characterized in that, in the invention described in claim 1, the heating gas flow path and the evaporation flow path are alternately arranged.
By comprising in this way, steam production capability can be enlarged although being small.
The invention described in claim 3 is the invention described in claim 1 or 2, wherein at least a part of the heating gas flow path is provided in a direction substantially orthogonal to the evaporation flow path. It is characterized by.
By configuring in this way, the heating gas channel is arranged in the horizontal direction, the arrangement of the entrance and exit of the heating gas channel becomes easy, and the structure of the evaporator can be simplified. Moreover, the pressure loss in the heated gas flow path can be kept low.
According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the fin is provided with a plurality of stages in the direction of gravity, and the fins of adjacent stages are arranged offset. It is characterized by being.
With this configuration, the liquid fuel collides with the fins and is dispersed, and the dispersed liquid fuel further collides with the fins below and is dispersed. By repeating this, the dispersion of the liquid fuel can be promoted. it can. Further, the speed at which the fuel vapor generated in the evaporation channel rises through the evaporation channel is reduced by the presence of the fins provided in a plurality of stages, so that liquid fuel droplets falling through the evaporation channel It is possible to prevent the droplets from being blown up by the fuel vapor, and it is possible to prevent the droplets from being discharged from the upper part of the evaporation channel without being vaporized. Therefore, the frequency of contact of the liquid fuel with the fins can be increased, and the vaporization of the liquid fuel is promoted.
[0008]
The invention described in claim 5 is the invention according to any one of claims 1 to 4, wherein a porous body (for example, a porous body 33 in an embodiment described later) is provided above the bottom of the evaporation flow path. ) And a heating device (for example, a heating chamber 34 in an embodiment to be described later) is provided below the bottom.
With this configuration, liquid fuel that could not be vaporized while descending the evaporation channel can be vaporized in the porous body, and a liquid pool can be prevented from being generated at the bottom of the evaporation channel. Can do.
According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the liquid fuel is a fuel supply pipe disposed above the evaporation channel (for example, an embodiment described later). The fuel supply pipe 60 is dropped from a plurality of supply holes (for example, supply holes 60a in the embodiments described later).
By comprising in this way, liquid fuel can be widely distributed and supplied in an evaporation flow path.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an evaporator according to the present invention will be described below with reference to the drawings of FIGS. In addition, the evaporator in each embodiment described below is an aspect used in a fuel reforming system for a fuel cell, and fuel vapor generated by the evaporator is supplied to the reformer, and hydrogen is generated by the reformer. It is reformed into a fuel gas for a rich fuel cell.
[0010]
[First Embodiment]
First, a first embodiment of the present invention will be described with reference to the drawings of FIGS.
FIG. 1 is a schematic configuration diagram of the evaporator 30. The evaporator 30 includes a rectangular parallelepiped case 31, a porous body 33 is attached to an upper side of a bottom plate (bottom part) 32 of the case 31, and a heating chamber (heating device) 34 is provided below the bottom plate 32.
The case 31 above the porous body 33 is partitioned into a plurality of narrow rooms parallel to each other by partition walls 35, and these rooms are alternately divided into evaporation channels 36 and heating gas channels 37. The outermost chambers are all made into the evaporation channel 36.
[0011]
Each of the evaporation channels 36 is open only at the top, closed at the bottom by a bottom plate 32 having a porous body 33, and closed by a peripheral wall 31 a and a partition wall 35 of the case 31. That is, each evaporation channel 36 has a box shape in which only the upper part is opened. Also, inside each evaporation channel 36, fins 36a having a substantially triangular waveform in cross section are installed with the peaks extending in the vertical direction (the direction of gravity). As shown in FIGS. 2 and 3, the fins 36a are installed in multiple stages in the vertical direction in each evaporation channel 36, and the fins 36a adjacent to each other in the vertical direction are installed with their peak portions offset. . The crests of the fins 36 a are joined to the partition wall 35 that separates from the heated gas flow path 37.
[0012]
On the other hand, each heated gas flow path 37 is closed at the top by a top plate 38, closed at the bottom by a bottom plate 32 having a porous body 33, and closed at both sides by a partition wall 35, and the front side of the case 31. And the back side is configured with a full opening. That is, each heating gas channel 37 has a rectangular tube shape penetrating from the front side to the back side. And in each heating gas flow path 37, the heating gas which flowed in from the opening of the front side is enabled to flow out of the opening of the back side. In addition, fins 37 a having a substantially triangular waveform in cross section are installed inside each heating gas flow path 37, and the peaks of these fins 37 a are connected to the evaporation flow path 36. It is joined to the partition wall 35 separating the two.
[0013]
Further, two fuel supply pipes 60, 60 extending in the axial direction in the direction in which the evaporation flow path 36 and the heating gas flow path 37 are connected are provided above the case 31 in parallel with each other. The tip of each fuel supply pipe 60 is closed, and each fuel supply pipe 60 has a pair of left and right supply holes 60a obliquely downward as shown in FIG. It is open.
The porous body 33 provided on the upper side of the bottom plate 32 is formed of, for example, a nickel-based metal porous body (for example, pore diameter: 0.5 mm, specific surface area: 7500 m ² / m ³ ) having a large specific surface area. 32 is brazed.
A heating medium can flow through the heating chamber 34 provided on the lower side of the bottom plate 32, and heat of the heating medium is transferred to the bottom plate 32 and the porous body 33. In this embodiment, the heating gas discharged from the heating gas channel 37 is introduced into the heating chamber 34 as a heating medium.
[0014]
The operation of the evaporator 30 configured as described above will be described.
The heated gas flows into each heated gas flow path 37 from the opening on the front side of the case 31, travels straight in each heated gas flow path 37 in the horizontal direction, and flows out from the opening on the back side of the case 31. When the heated gas flows through the heated gas channel 37, part of the heat of the heated gas is transferred to the fins 37 a and the partition walls 35, and further transferred to the fins 36 a of the evaporation channel 36.
The heated gas flowing out of the heated gas flow path 37 is supplied to the heating chamber 34, and after flowing through the heating chamber 34, it is discharged out of the system. When the heated gas flows through the heating chamber 34, part of the heat of the heated gas is transferred to the porous body 33 through the bottom plate 32.
[0015]
On the other hand, liquid fuel (mixed liquid of methanol, gasoline, etc. and water) is supplied to each fuel supply pipe 60 and is injected from the supply hole 60 a provided in the fuel supply pipe 60 toward each evaporation flow path 36. The liquid fuel injected from the supply hole 60a becomes droplets and adheres to the fins 36a and flows down along the surfaces of the fins 36a, or drops through the gaps formed between the fins 36a. Most of the liquid fuel dropped in the gaps between the fins 36a collides with the lower fins 36a while descending, and adheres to the surface of the fins 36a. In any case, as shown by the solid line in FIG. 3, the liquid fuel flows in the evaporation channel 36 downward in the direction of gravity. The liquid fuel adhering to the fins 36a is vaporized by heat exchange with the heated gas flowing through the heated gas flow path 37 via the partition walls 35 and the fins 36a, and becomes fuel vapor. Further, the liquid fuel that could not be vaporized while descending in the evaporation flow path 36 penetrates into the fine holes of the porous body 33 before reaching the bottom plate 32, where the heated gas and It exchanges heat and instantly vaporizes into fuel vapor.
[0016]
The fuel vapor generated in this way rises upward in the direction of gravity in the evaporation flow path 36 and flows out from the upper opening of the evaporation flow path 36 as indicated by a broken line in FIG.
Therefore, in this evaporator 30, the liquid fuel or fuel vapor flows downward or upward in the direction of gravity in the evaporation flow path 36, whereas the heating gas flows horizontally in the heating gas flow path 37 as described above. Therefore, the flow directions are orthogonal to each other.
FIG. 5 is a diagram showing the relationship between the distance from the bottom plate 32 and the amount of liquid fuel and generated fuel vapor. The liquid fuel decreases as it approaches the bottom plate 32 and moves away from the bottom plate 32. Therefore, fuel vapor increases.
[0017]
Thus, in the evaporator 30, the evaporation flow paths 36 and the heated gas flow paths 37 are alternately arranged, so that the steam generation capability can be increased while being small.
Further, since the fins 36a are provided in the evaporation flow path 36, the surface area of the heating surface is extremely large, and the liquid fuel is likely to spread greatly. As a result, the vaporization of the liquid fuel is promoted.
Further, when the liquid fuel collides with the fin 36a, it adheres to the colliding part (hereinafter referred to as a colliding portion) and scatters, and the scattered liquid fuel collides with the fin 36a near the colliding portion again. Since the process is repeated, the frequency of contact of the liquid fuel with the surface of the fin 36a which is the heating surface increases, and the vaporization of the liquid fuel is promoted.
In particular, the fins 36a are provided in multiple stages in the vertical direction, and the crests are offset in the upper and lower fins 36a, so that the liquid fuel collides with the fins 36a and is dispersed. The dispersion of the liquid fuel can be promoted by repeating this by colliding with 36a. Further, the speed at which the fuel vapor generated in the evaporation flow path 36 ascends the evaporation flow path 36 is reduced by the presence of the fins 36a provided in multiple stages. The liquid droplets can be prevented from being blown up by the fuel vapor, and the liquid droplets can be prevented from being discharged from the upper opening of the evaporation channel 36 without being vaporized. Therefore, the collision frequency (contact frequency) of the liquid fuel to the fins 36a is further increased, and the vaporization of the liquid fuel is further promoted.
Furthermore, since a temperature gradient is generated in the fin 36a in the direction approaching and separating from the partition wall 35, a portion where the temperature difference between the surface of the fin 36a and the liquid fuel adhering to the surface becomes a nucleate boiling region is created. Heat is easily transmitted and the liquid fuel adhering to the surface of the fin 36a is easily vaporized.
[0018]
Further, since the temperature distribution of the entire fin 36a in the evaporation channel 36 becomes substantially uniform due to the heat conduction of the fin 36a, the entire region of the evaporation channel 36 can be used as a heat exchanging portion, and the liquid fuel is efficiently vaporized. It can be fuel vapor.
Further, since the crests are offset in the upper and lower fins 36a, all the gaps between the fins 36a communicate with each other in one evaporation channel 36. The fuel vapor is diffused and distributed, and the heat load in the entire evaporation channel 36 is equalized. Therefore, the liquid fuel can be efficiently vaporized.
Further, in the evaporation channel 36, the liquid fuel droplets fall from the top to the bottom, and the generated fuel vapor rises, so that the liquid fuel droplets and the fuel vapor come into countercurrent contact with each other. In addition, the preheating and miniaturization of the liquid fuel are promoted, and the thin film formation of the liquid fuel film formed on the surface of the fin 36a is promoted. As a result, the vaporization of the liquid fuel is promoted.
Therefore, the evaporator 30 can vaporize the liquid fuel very efficiently and quickly, and has extremely excellent responsiveness.
[0019]
Further, when the evaporator 30 is mounted on a fuel cell vehicle, it is conceivable that the attitude of the evaporator 30 changes a lot. Even if the attitude changes, the fins 36a function as partition walls in the evaporator 30. As a result, it is possible to prevent the liquid fuel from flowing in a partial area in the evaporation flow path 36, so that the heat load in the evaporation flow path 36 can be kept uniform even when the posture is changed. The evaporation performance can be kept constant.
The fuel vapor flowing out from the upper opening of the evaporation channel 36 is supplied to a reformer (not shown) through a collecting passage (not shown), and reformed into a hydrogen-rich fuel gas in the reformer. And supplied to the fuel cell.
[0020]
[Second Embodiment]
Next, a second embodiment of the evaporator 30 according to the present invention will be described with reference to the drawings of FIGS. The difference between the evaporator 30 of the second embodiment and that of the first embodiment is as follows.
In the evaporator 30 according to the first embodiment, each heating gas flow path 37 is open on the entire front side and back side of the case 31, but in the evaporator 30 according to the second embodiment, On the front side, only the upper part and the lower part of each heating gas channel 37 are open, and on the back side of the case 31, the entire surface of each heating gas channel 37 is closed. An opening 37c provided on the lower side on the front side of the case 31 serves as a heating gas inlet, an opening 37d provided on the upper side serves as a heating gas outlet, and the opening 37c, 37d is closed by a side plate 39. Has been. Further, in each heating gas flow path 37, fins 37b having a substantially triangular waveform in cross section are installed in the height region where the side plate 39 is provided with the peaks extending in the vertical direction (the direction of gravity). . The peaks of the fins 37 b are joined to the partition wall 35 that separates from the evaporation flow path 36. 7 is a cross-sectional view taken along the line II-II in FIG.
[0021]
In the evaporator 30, as shown in FIG. 8, the heating gas flows into the heating gas passages 37 from the lower openings 37 c and travels through the heating gas passages 37 toward the back side of the case 31. The air flows straight into the gaps formed between the fins 37b and rises. When reaching the upper part in the heated gas flow path 37, the direction is changed toward the upper opening 37d and flows out from the opening 37d.
Therefore, in this evaporator 30, all of liquid fuel, fuel vapor, and heating gas will flow along the direction of gravity.
Since other configurations are the same as those of the first embodiment, the same reference numerals are given to the same mode portions and the description thereof is omitted.
The evaporator 30 according to the second embodiment can vaporize the liquid fuel very efficiently and quickly, and has extremely excellent responsiveness.
[0022]
[Other Embodiments]
The present invention is not limited to the embodiment described above.
For example, the shape of the fin 36a provided in the evaporation channel 36 is not limited to a substantially triangular waveform, and various shapes as shown in FIG. 9 can be employed. 9A is a fin having a rectangular cross section, FIG. 9B is a so-called helibone fin, FIG. 9C is a perforated plate fin, and FIG. 9D is a so-called serrated fin. 9 (E) is a so-called louver fin.
Further, in the embodiment described above, the fins 36a are provided in the evaporating flow path 36 in a plurality of stages in the direction of gravity and the adjacent fins 36a are offset, but the fins 36a may not be provided in multiple stages, or The present invention is established without offset.
Further, the heating device provided on the lower side of the bottom of the evaporation channel can be constituted by an electric heater or the like.
[0023]
【The invention's effect】
As described above, according to the invention described in claim 1, the liquid fuel can be vaporized very efficiently and rapidly, and an excellent effect that the responsiveness of the evaporator is extremely improved is achieved.
According to the second aspect of the present invention, it is possible to increase the steam generation capacity while being small.
According to the third aspect of the present invention, the heating gas flow path is arranged in the horizontal direction, the arrangement of the entrance and exit of the heating gas flow path is facilitated, and the structure of the evaporator can be simplified. Moreover, the pressure loss in the heated gas flow path can be kept low.
[0024]
According to the invention described in claim 4, the liquid fuel collides with the fins and is dispersed, and the dispersed liquid fuel further collides with the fins below and is dispersed, and this is repeated to promote the dispersion of the liquid fuel. can do. Further, the speed at which the fuel vapor generated in the evaporation channel rises through the evaporation channel is reduced by the presence of the fins provided in a plurality of stages, so that liquid fuel droplets falling through the evaporation channel It is possible to prevent the droplets from being blown up by the fuel vapor, and it is possible to prevent the droplets from being discharged from the upper part of the evaporation channel without being vaporized. Therefore, the frequency of contact of the liquid fuel with the fins can be increased, and there is an effect that vaporization of the liquid fuel is promoted.
According to the fifth aspect of the present invention, the liquid fuel that could not be vaporized while descending the evaporation channel can be vaporized in the porous body, and a liquid pool is generated at the bottom of the evaporation channel. There is an effect that it can be prevented.
According to the sixth aspect of the invention, there is an effect that the liquid fuel can be widely dispersed and supplied in the evaporation flow path.
[Brief description of the drawings]
FIG. 1 is an external perspective view of an evaporator according to a first embodiment of the present invention.
2 is an external perspective view of fins provided in the evaporation flow path of the evaporator according to the first embodiment. FIG. 3 is a cross-sectional view taken along the line II in FIG.
FIG. 4 is a sectional view of a fuel supply pipe of the evaporator according to the first embodiment.
FIG. 5 is a diagram showing quantitative changes in liquid fuel and fuel vapor in the evaporator according to the first embodiment.
FIG. 6 is an external perspective view of an evaporator according to a second embodiment of the present invention.
7 is a cross-sectional view taken along the line II-II in FIG.
8 is a cross-sectional view taken along the line III-III in FIG.
FIG. 9 is a perspective view showing another embodiment of the fin provided in the evaporation channel.
[Explanation of symbols]
30 Evaporator 32 Bottom plate (bottom)
33 Porous body 34 Heating chamber (heating device)
36 Evaporation channel 36a Fin 37 Heated gas channel 60 Fuel supply pipe 60a Supply hole

Claims (6)

In an evaporator that vaporizes liquid fuel containing hydrocarbons to generate fuel vapor for fuel reforming,
A heated gas flow path through which the heated gas flows;
The liquid fuel is arranged so as to be capable of exchanging heat with the heated gas flow path, vaporizes the liquid fuel supplied from above in the direction of gravity and flowing downward in the direction of gravity, and causes the vaporized fuel vapor to flow upward in the direction of gravity to counter-contact with the liquid fuel and evaporation passages bottomed discharged upward by,
Fins provided on the inner surface of the evaporation channel;
An evaporator, comprising:   The evaporator according to claim 1, wherein the heating gas flow path and the evaporation flow path are alternately arranged.   The evaporator according to claim 1 or 2, wherein at least a part of the heated gas channel is provided in a direction substantially orthogonal to the evaporation channel.   The evaporator according to any one of claims 1 to 3, wherein the fins are provided in a plurality of stages in the direction of gravity, and fins of adjacent stages are offset.   The evaporator according to any one of claims 1 to 4, wherein a porous body is provided above the bottom of the evaporation channel, and a heating device is provided below the bottom.   The evaporator according to any one of claims 1 to 5, wherein the liquid fuel is dropped from a plurality of supply holes of a fuel supply pipe disposed above the evaporation channel.

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