This application claims the priority of German patent document 197 17 067.6, filed Apr. 23, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a multi-stage reforming reactor system.
Multi-stage reforming reactors are common, for example, for the water vapor reforming of methanol, in which the gas/vapor mixture of methanol and water which is to be reformed (and which can be processed, for example, in a front-connected evaporator) is fed to the inlet-side reactor stage and is converted there (and optionally in one or several adjoining reactor stage(s)) to a high-hydrogen reformate, in an endothermal reforming reaction. Systems of this type are disclosed in U.S. Pat. Nos. 5,248,566 and 5,401,589.
German patent document 196 24 435.8 discloses a three-stage passive reforming reactor in which a heating device is assigned only to the center reactor stage. The inlet-side and the outlet-side reactor stage are in direct or indirect thermal contact, in that the reaction gas flow emerging from the outlet-side reactor stage is guided through a tempering space which is in thermal contact with the inlet-side reactor stage. In this case, the inlet-side reactor stage preferably forms a prereforming stage and the outlet-side reactor stage preferably forms a shift reaction stage, in which carbon monoxide is exothermally converted to carbon dioxide. The inlet-side reactor stage is heated by heat generated in this manner.
German patent document 196 23 998.2 discloses a filter in which a reaction space connection area may be used primarily as a gas outlet area and, as required, may also be used as a gas inlet area. The filter is designed for filtering out fine dust particles of the catalyst pellet bulk used there as the reforming catalyst material. In the reaction space of the reactor, the pellet bulk is carried by a sieve under which a metallic nonwoven is situated. The pellet fragments collected by the metallic nonwoven fall through the sieve, preventing them from reaching adjoining system components via the reaction space connection area.
German patent document DE 27 17 993 A1 discloses a single-stage methanol reforming reactor behind which is connected a combustion device (for example, in the form of a gas motor) in which the high-hydrogen reformate gas delivered by the reforming reactor is burnt. The reactor has a double-tube construction with an interior tube and an exterior tube surrounding the interior tube. The annulus formed between the tubes forms a reaction space which contains a heat-conducting fibrous material in an inlet-side part and a suitable catalyst pellet bulk in the other part. The hot combustion gas generated by the combustion device and returned to the reforming reactor is guided through the interior tube in order to heat the reforming reaction space. Methanol or methanol/water mixture introduced into the reaction space is heated and evaporated during the flow through the spaces between the heat-conducting fibrous material. As an alternative to the fibrous material, a separate evaporator is suggested, which utilizes the combustion gas heat.
Particularly in mobile applications (such as the use of a reforming reactor system in fuel-cell-operated motor vehicles for the purpose of obtaining hydrogen to be fed into the fuel cells), systems are needed which have a compact construction while the volume and weight utilization, the robustness and the durability are high. Also, because such systems are subjected to power demand fluctuations typical with respect to the operation of vehicles, there is the danger that, due to insufficient preceding evaporation, drops can reach the input side of the reforming reactor together with the gas/vapor mixture, with damaging effect.
One object of the invention is to provide a reforming reactor system of the type described above, which is also suitable for mobile applications.
Another object of the invention is to provide such a system which includes measures to ensure a long durability of the catalyst material in the reforming reactor.
These and other objects and advantages are achieved by the reforming reactor system according to the invention, in which a drop catching element is assigned to the inlet side of an inlet-side reactor stage. This element catches drops which may be contained in the gas/vapor mixture fed to the reforming reactor, for example, because of a temporary incomplete evaporation of one or several mixture constituents due to load fluctuations of the system. In a system for the water vapor reforming of methanol, any methanol and water drops which may be formed can be prevented from penetrating into the reforming reactor by the drop catching element. This arrangement thus prevents damage to the reforming catalyst material situated in the reactor, which might otherwise occur if the forming catalyst material comes in contact with such methanol drops or water drops. It also ensures a high durability of the reforming catalyst material.
In the reforming reactor system according to the invention, the drop catching element is warmed by heat generated in a CO shift reaction stage of the reactor, by the exothermal conversion of CO into CO.sub.2. Thus, drops caught from the gas/vapor mixture can then be evaporated again into the gas/vapor mixture without taking the heat required for this purpose from the gas/vapor mixture which is flowing by. The drop evaporation in the drop catching element is therefore largely independent of the momentary condition of the gas/vapor mixture, and therefore of possible load fluctuations of the system.
In one embodiment of the invention, the drop catching element consists of a heat-conductive metallic nonwoven. When the gas/vapor mixture to be introduced into the reactor and to be reformed passes through the metallic nonwoven, any drops contained in the mixture are retained by the metallic nonwoven. In this case, the metallic nonwoven may act virtually as a buffer in that the drops deposit on it and can then evaporate into the gas/vapor mixture flowing by.
In another embodiment, a supplementary active heat source is assigned to the drop catching element. This ensures a sufficient heat supply to the drop catching element whenever the heat generated in the shift reaction stage is insufficient for this purpose.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.