AN EVAPORATOR FOR A FUEL CELL SYSTEM

Abstract

A fuel cell system comprising a fuel cell stack, an evaporator for evaporating a mixture of methanol and water to be forwarded through a catalytic reformer for producing portions of free hydrogen. The fuel cell stack being composed of a number of proton exchange membrane fuel cells each featuring electrodes in form of an anode and a cathode for delivering an electric current. The system provides an enhanced system for evaporating the liquid fuel using a pre-evaporator, which partly evaporates the fuel, followed by a nozzle, which atomizes the fuel into a fine mist, before being passed to the final evaporation zone. This configuration ensures minimal fuel accumulation in the system and fast load transition's.

Claims

1. A fuel cell system, comprising: a fuel cell stack comprising a plurality of proton exchange membrane fuel cells each featuring electrodes in the form of an anode and a cathode for delivering an electric current, wherein a reaction of free hydrogen into ionic form with contact to the anode being proportional to a flow of electric current between the electrodes; a catalytic reformer; an evaporator for evaporating a mixture of methanol and water to be fed through the catalytic reformer for producing portions of free hydrogen, the evaporator including a first section that serves as a pre-evaporator for receiving the liquid fuel; wherein the pre-evaporator facilitates partial evaporation and split-up of the liquid fuel into drops, droplets and mist.

2. The system according to claim 1, wherein the pre-evaporator includes cavity walls that are shaped in such a way that the walls extend vertically and are angled away from a straight vertical line.

3. The system according to claim 2, wherein the cavity walls are further adapted for serving as heating elements.

4. The system according to claim 1, further comprising at least one protruding rod-formed heating elements are element arranged in the pre-evaporator cavity.

5. The systme accoring to claim 4, wherein the rod-formed heating elements are formed with a plurality.

6. The system according to claim 4, wherein the shape of the sides of the rod-formed heating elements can vary from being flat to a curved or concave form.

7. The system according to claim 4, wherein an edge, formed on the rod-formed heating elements or on the walls, form a nose adapted for letting remaining liquid form a drop.

8. The system according to claim 4, wherein the rod-formed heating elements are arranged in a matrix within the pre-evaporator cavity.

9. The system according to claim 8, wherein the rod-formed heating elements are arranged as a grate comprising at least one rod-formed heating element.

10. The system according to claim 8, wherein several rod-formed heating elements are arranged side by side.

11. The system according to claim 9, wherein the grate is formed as a net with several rod-formed heating arranged side by side and at least one rod-formed heating element arranged as a cross member to the side-by-side rod-formed heating elements, the rod-formed heating elements forming joints with each other.

12. The system according to claim 2, wherein the pre-evaporator cavity is separated into a plurality of chambers, each chamber comprising a gap for passing a liquid fuel drop, and a negative angled, substantially vertical portion of a wall followed by a positive angled substantially vertical portion of a wall followed by a gap that leads to a next one of the chambers.

13. The system according to claim 12, wherein each chamber has two mirrored sets of walls and the rod-like heating elements are arranged in-between the walls.

14. The system according to claim 12, wherein a gap between the chambers is adapted for forming a pressure nozzle for two-phase atomization of the liquid fuel into a following lower pressure one of the chambers.

15. The system according to claim 1, wherein a pressure-reducing nozzle for two-phase atomization of the fuel forms the a last outlet of the pre-evaporator cavity.

16. A fuel cell system, comprising: a fuel cell stack comprising a plurality of proton exchange membrane fuel cells, each fuel cell comprising an anode and a cathode to deliver an electric current, wherein a reaction of free hydrogen into ionic form when contacting the anode is proportional to a flow of electric current between the anode and cathode; a catalytic reformer; an evaporator to evaporate a mixture of methanol and water to be fed through the catalytic reformer to produce portions of free hydrogen, the evaporator including a first section that serves as a pre-evaporator to receive liquid fuel, the pre-evaporator facilitating partial evaporation and split-up of the liquid fuel into drops, droplets and mist.

17. The system according to claim 16, wherein the pre-evaporator includes cavity walls that extend vertically and are angled away from a vertical plane.

18. The system according to claim 17, wherein the cavity walls comprise heating elements.

19. The system according to claim 16, further comprising at least one protruding rod-formed heating element arranged in the pre-evaporator cavity.

20. The system according to claim 19, wherein the rod-formed heating elements are formed with a plurality of sides.

Description

DESCRIPTION OF THE DRAWING

[0046] Embodiments of the invention will be described with reference to the accompanying drawing, in which:

[0047] FIG. 1, shows an illustration of a fuel cell system,

[0048] FIG. 2, shows an illustration of an evaporator module for evaporating liquid fuel into gas,

[0049] FIG. 3, shows a detailed part of the evaporator module,

[0050] FIG. 4, shows a detailed part of the inlet for liquid fuel in the evaporator module and

[0051] FIG. 5, shows the outlet nozzle for two-phase transformation of the liquid fuel

[0052] FIG. 1, of the drawing shows a fuel cell system 1 comprising a fuel cell stack 2, a number of supporting modules for supplying the fuel cell stack 2 with a modified fuel enabling the fuel cell stack 2 to produce a steady flow of electrical current. The exceed gas supplied to the fuel cell stack 2 but not being converted into electrical current, is fed to the waste gas burner 3. The exhaust gas is under normal operating conditions in the temperature area of 500 degrees Celsius and the energy content is recycled for preparing the syngas for fueling the fuel cell stack 2. More detailed, the exhaust is forwarded through the heat exchanger module 4, which takes up the heat from the exhaust and transfer the heat to the neighboring module in the stack here being the evaporator module 5.

[0053] The liquid fuel, a mixture of methanol and water, is processed into a syngas consisting of free hydrogen for use in the fuel cell stack 2. In the evaporator module 5, the fuel is atomized and evaporated into the two-phase stage of the liquid fuel. Further, the evaporated gas is forwarded to the catalytic reformer module 6 that reforms the evaporated gas into a syngas consisting largely of free hydrogen. The catalytic reformer module 6 includes a catalyst including copper, which in addition to heat converts the evaporated liquid fuel into the syngas directly usable by the fuel cell stack 2. The exhaust heat of the fuel cell stack 2 and the waste gas burner 3 is led through channels in the evaporator module 5 and catalytic reformer module 6. The temperature demand in the catalytic reformer 6 is highest, so thus the catalytic reformer 6 is arranged directly behind the waste gas burner 3. At a later stage of the exhaust channel the evaporator module 5 takes up the heat from the exhaust in order to evaporate the liquid fuel into gas.

[0054] The evaporator module 5, in shown in FIG. 2 for which a detailed view of the inlet section is shown in FIG. 3 of the drawing and a close up is shown in FIG. 4. The liquid fuel is supplied via the inlet hole 7 of the evaporator module 5. The first part of the evaporator module 5 is formed as a pre-evaporator 8 through which the liquid fuel falls forced by gravity. It has to be observed that the orientation of the evaporator module 5 during operation of the fuel cell system 1 has to be in an upright position. The pre-evaporator 8 is in the present embodiment separated into six chambers 9, which according to specific embodiments could be more or less. When the liquid fuel is supplied via the inlet hole 7, it drops down in the first chamber and is further forwarded to the next chamber via a gap 10. The drop splashes into the next chamber 9 where it will hit a protruding rod. The protruding rod serves partly as a heating element 11, and partly to atomize and evaporate the liquid fuel into droplets and mist. Since the droplets because of gravity fall further down the pre-evaporator 8, more protruding rods are hit and the effect of evaporation is increased. As can be seen from FIG. 4, the walls 12 of the pre-evaporator 8 are vertically angled in order to embrace the protruding rods 11 in such a way that the travel of liquid fuel floating down the walls 12 is prolonged and as most as possible of the liquid fuel is atomized or evaporated. Since the liquid fuel, especially directly after the inlet hole 7, splashes down the pre-evaporator 8, the liquid fuel and the droplets will ricochet from wall 12 to wall 12 and eventually hit the protruding rods 11, the arrangement will help to fully atomize and evaporate the liquid fuel and as such be a fine substitute for a spray injector. It has to be noted that the walls 12 are also heated and forms heating elements for heating and evaporating the liquid fuel. The protruding rods 11, which serves as heating elements, are as well as the walls 12 specially adapted for atomizing the liquid fuel and prolonging the travel of liquid fuel when it floats down the pre-evaporator 8. Experiments have shown that the quadratic shape of the protruding rods 11 have a fine effect on the atomization and evaporation of the liquid fuel. Triangular shapes also works fine. However, more edges support the capture of the drop and thus the time the drop is being subject to heating. Looking at the shapes of the walls and the shape of the rod-like heating elements the edges 15, 16 (FIG. 5) forms noses that enables the fluid fuel to form drops which due to gravity drips further down the evaporator and collide with protruding parts and split into smaller fragments that easier can be atomized into a fine mist.

[0055] The gaps 10 also serve as nozzles, that because of the increased pressure helps the liquid fuel to evaporate and to keep the gas phase through the travel of the channel of the evaporator module 5.

[0056] Looking at FIG. 5, a special pressure nozzle 13 is provided that because of the small passage provides a pressure fall that serves to blow leftovers of atomized liquid fuel further into a vertical channel that is the pathway 14 to the evaporator labyrinth channel 15 in which the atomized and evaporated fuel is further heated into a homogeneous gas mist. Since the pressure through the pressure nozzle 13 is considerable high, the effect is that it serves as a spray injection unit for the evaporator but without the previously mentioned drawbacks since it is a completely integrated feature of the evaporator module 5.

[0057] For the understanding of the system, the system components are build as modules that can be fixed together by conventional screws and bolts. Pathways for e.g. exhaust gas are forwarded from module to module in order to take out as much thermal energy as possible and get a high efficacy of the system. Thus the modules can be joined using gaskets in-between as can be seen in FIG. 1 between the evaporator module 5 and reformer module 6.

[0058] The modules can be made by machining of a bar of material. In the present embodiment, the evaporator module is provided using a bar of aluminum and carving out the channels for the evaporator on a first side of the bar.

[0059] Provided by the invention is an enhanced system for evaporating the liquid fuel using a pre-evaporator, which partly evaporates the fuel, followed by a nozzle which atomizes the fuel into a fine mist, before being passed to the final evaporation zone.