Patent Application
20080044695
In the drawings:
Referring to the drawings in particular, the present invention is explained in detail below with reference to the attached
This mixing chamber 26 is axially limited by a bottom component 28, which has a porous evaporator medium 30 on its side facing away from the mixing chamber 26. A fuel supply line feeds liquid fuel or hydrocarbon into this porous evaporator medium 30. An electrically energizable heating means 34 provided on the back side of the porous evaporator medium, which is carried at a carrier 36 with insulation, heats the porous evaporator medium 30 and thus contributes to the increased evaporation of the hydrocarbon in the direction of the mixing chamber 26. The hydrocarbon vapor thus generated is mixed in the mixing chamber 26 with the mixed material introduced into same and then reaches the area of the reformer arrangement 14. It should be pointed out here that this mixed material flow and also the flow of the mixture formed in the mixing chamber 26 can be generated by a mixed material blower 60 or another feeding arrangement.
In the reformer arrangement 14, the mixed material first flows through a flame retention baffle 38 and then reaches a first catalytic converter arrangement 40. In the direction of flow to the first catalytic converter arrangement 40 follows a second catalytic converter arrangement 42. As an alternative, a catalytic converter may be provided with two catalytic converter zones. A temperature sensor 44 is arranged downstream of the second catalytic converter arrangement 42. Furthermore, an ignition member 46 is assigned to the mixing chamber 26, which ignition member 46 protrudes into this mixing chamber 26 and, as will still be explained below, can ignite the mixture formed in the mixing chamber by means of energizing and can result in combustion.
The flame retention baffle 38, the first catalytic converter arrangement 40 and the second catalytic converter arrangement 42 are carried at the housing 16 via elastic material 48 in order to thus not transmit vibrations occurring during operation to these three components.
Furthermore, it is recognized that the reformer arrangement 14 or the housing 16 in that longitudinal area, in which the second catalytic converter arrangement 42 is arranged, is surrounded radially on the outside by a tubular or housing-like insulation element 50, so that the mixed material entering through the openings 24 in that area, in which the housing 16 is surrounded by the insulation element 50, essentially cannot enter into thermal interaction with the reformer arrangement 14, but rather only in the subsequent longitudinal section, in which essentially the first catalytic converter arrangement 40 is also arranged.
Furthermore, a second ignition member 52 is provided in the area of the mixed material flow space 22, which second ignition member 52 extends into this mixed material flow space 22 and, as explained below, can ignite and bring to combustion the mixed material flowing therein.
By incorporating a reformer system of this type into a fuel cell system with a fuel cell 70, a hydrogen-gas-containing reformate is thus generated by this reformer system 10, which can be used in a fuel cell together with air or atmospheric oxygen in order to generate electrical energy. The residual reformate leaving the fuel cell may, as so-called anode exhaust gas, be fed back to the reformer for better mixture formation by means of a feed unit (blower) 60 and then be thoroughly mixed with air or be introduced into the mixed material flow space 22 together with air via the openings 24, so that this mixture of air and anode exhaust gas essentially provides the previously already mentioned mixed material.
In a start phase of the fuel cell system, i.e., even in a start phase of the reformer system 10, it must, at first, be ensured that various system areas be brought to the suitable operating temperature. This concerns, above all, the two catalytic converter arrangements 40, 42, of which the first catalytic converter arrangement 40 is designed, such that essentially an exothermic catalytic reaction takes place there, while essentially an endothermic catalytic reaction takes place in the second catalytic converter arrangement. It is generally necessary to raise the temperature in the area of the catalytic converter arrangement 14 to an activation temperature of about 330° C. This may take place in the start phase by the mixture of hydrocarbon vapor and mixed material formed in the mixing chamber 26, essentially consisting of air in this case, being ignited and burned. The combustion exhaust gases leave the mixing chamber 26 and flow through the two catalytic converter arrangements 40, 42, whereby these quickly take up heat from the combustion exhaust gases and are brought to the operating temperature. In order to then start the reforming process, the combustion in the mixing chamber 26 is ended, for example, by means of a brief interruption of the fuel stream or of the hydrocarbon stream, so that a mixture of hydrocarbon vapor and air or mixed material is then forwarded into the two catalytic converter arrangements 40, 42 and starts the reforming process there. A reformate with increasingly rising hydrogen gas content then leaves the reformer system 10 and reaches the fuel cell. Above all, when the fuel cell proper is likewise not yet at operating temperature in this phase of operation and provided that the process for generating electrical energy was not yet started, the anode exhaust gas will have essentially the same composition as the reformate that leaves the fuel cell system 10. This residual reformate or anode exhaust gas is fed back or introduced into the mixed material flow space 22 together with air through the openings 24. Since the temperature of the two catalytic converter arrangements 40, 42 is comparatively low in this start phase and still lies distinctly below the optimal process temperature, the second ignition member 52 is electrically energized according to the present invention, so that in the area of the mixed material flow space, conditions are created, under which the mixed material is ignited and burned. The heat forming during this combustion heats the reformer arrangement 14 from outside and prevents the heat forming in the starting reforming process from being increasingly transmitted outwardly to the mixed material flowing in the mixed material flow space 22.
This leads to a distinctly faster increase in the temperature in the area of the reformer arrangement 14 and thus to a distinctly faster reaching of the suitable optimal process temperature.
Moreover, the mixture forming reaction in the mixing chamber experiences the corresponding educt preheating.
Not only to cool off less intensively or to heat even faster by heating the reformer arrangement 14 from the outside, but also to be able to prepare the conditions in the reformer arrangement 14 proper for carrying out a reforming process, it must be ensured that even after burning the mixed material in the mixed material flow space 22, a sufficient amount of air or atmospheric oxygen is still present in order to prepare a mixture suitable for the reforming process in the mixing chamber 26 with the hydrocarbon vapor. This mixture is preferably hypostoichiometric and should have a lambda value of about 0.4. I.e., the combustion in the mixed material flow space 22 is carried out with such an excess of air that a corresponding residual air or residual oxygen quantity can be guaranteed for the introduction into the mixing chamber 26.
After suitable thermal conditions for carrying out a stable reforming process are then created in the reformer arrangement 14 without the risk of generating hazardous components, such as, e.g., soot, the combustion in the mixed material flow space 22 is ended. This may take place, for example, by the air stream being briefly interrupted. Also, the ending of the energizing of the ignition member 52 may lead to the extinguishing of the combustion depending on the external conditions and also depending on the mixing ratio of the components of the mixed material. Subsequently, the comparatively cold or colder mixed material then flows through the mixed material flow space 22 and may in the next operation then remove heat from the area of the reformer arrangement 14, especially from the area of the first catalytic converter arrangement 40 and thus be forwarded into the mixing chamber 26 already preheated. Since in this normal operating phase, the mixed material then reaches the mixing chamber 26 with unchanged mixing ratio from the mixed material flow space 22, the air content or the atmospheric oxygen content can be reduced compared to the combustion phase, so that the hypostoichiometric mixture in the mixing chamber 26 is then again generated in conjunction with the evaporated hydrocarbon quantity.
With the present invention, it is possible in a simple manner to distinctly shorten the start phase of the reforming process in a reformer system. Since a heating of the mixed material is ensured both in the start phase and in the normal operating phase, namely either by combustion of same or by heat uptake by the reformer arrangement 14, the provision of additional heating means for the mixed material to be introduced into the mixing chamber can be eliminated.
It is a matter of course that the ignition or combustion of the mixed material can take place not only in that area of the mixed material flow space 22, in which this surrounds the reformer arrangement 14. Rather, with corresponding structural embodiment, the mixed material could also be ignited and burned already before the introduction to the reformer arrangement in another area, lying upstream, of the mixed material flow space and possibly also still before introduction through the openings 24, so that the heat forming during the combustion can be transmitted to the reformer arrangement 14 in case of further flow through that area of the mixed material flow space 22, which can also be seen in
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 028 699.5 | Jun 2006 | DE | national |
