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  Compact reforming reactorThe Patent Description & Claims data below is from USPTO Patent Application 20070000173. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates to an integrated and compact reforming reactor for the production of hydrogen to be used in industrial applications such as in the metallurgical industry, chemical and pharmaceutical industry and fuel cell power plants. In particular the invention relates to a compact reforming reactor for the conversion of hydrocarbon feedstocks to hydrogen where the reformed gas of the reactor is further enriched in hydrogen by passage through a Pressure Adsorption Swing (PSA) unit, a Pd-alloy membrane, water-gas shift unit or by Preferential Oxidation (PROX). More particularly the invention relates to a compact reforming reactor for the conversion of methanol to a hydrogen gas suitable for use in fuel cell plants, especially where the reformed gas of the reactor is further enriched in hydrogen by passage through a PSA unit. The invention further involves a process for reforming the hydrocarbon feedstock into a hydrogen gas using this reactor. BACKGROUND OF THE INVENTION [0002] Fuel cell plants require often the supply of hydrogen as fuel source and accordingly a reforming reactor is normally integrated in fuel cell plants. The reforming reactor converts a suitable hydrocarbon feedstock acting as energy carrier, such as methane, liquid petroleum gas, gasoline, diesel or methanol, into a hydrogen rich gas, which then may be passed through a hydrogen-enrichment unit before entering a fuel cell assembly. Compact fuel cell power plants may today provide about 20 kW of power and even more, for instance up to 50 kW, thereby promoting a wide range of applications. One such application is the use of compact fuel cell plants in the automotive industry. [0003] For widespread application, methanol is still regarded as the best hydrocarbon feedstock for the production of hydrogen-rich gas not only in connection with fuel cell plants but also for application in small plants in other industrial fields. Roughly, methanol is particularly suitable where the demand for hydrogen is the range 50-500 Nm.sup.3/h, which is typical for small plants. For a hydrogen demand of above 500 Nm.sup.3/h a hydrocarbon feedstock such as natural gas is often more expedient. Below 50 Nm.sup.3/h electrolysis or bottled hydrogen is normally more expedient. [0004] Reactors for the reforming of fuel gases, particularly methanol, and which are used in fuel cell plants are known in the art. Dusterwald et al. disclose in Chem. Eng. Technol. 20 (1997) 617-623 a methanol steam reformer consisting of four reactor tubes that are individually balanced. Each reactor tube consists of two stainless tubes arranged concentrically with catalyst filling the inner tube and in which the heat needed for the endothermic reaction of a methanol-water mixture is provided by condensing steam that flows in the gap between the tubes. It is also known from U.S. Pat. No. 4,861,347 to oxidise a raw fuel such as methanol in order to obtain an exothermic reaction, whereby the heat generated by this reaction is used for the endothermic reforming reaction of the hydrocarbon feedstock, which is normally a mixture of methanol and water. The heat is transferred from the combustion section of the reactor to its reforming section by means of heat tubes through which a hot flue gas from the combustion section is passed or as in JP-A-63248702 by means of heat pipes arranged in the reactor. As a result, the heat generated in the combustion system can be evenly distributed to the rest of the reactor, whereby a uniform temperature distribution is obtained. [0005] Often the heat transfer system in the reforming reactor is not rapid enough to achieve the desired operating temperature after changes in process conditions such as after sudden load changes or during start-ups and shut-downs, especially when separate heat pipes are provided in the reforming reactor. Normally a number of more or less sequential steps are required for the start-up of the reforming reactor resulting in a procedure that may be significantly tedious and time-consuming. [0006] In the particular field of fuel cells, the advent of fuel cells with increased power, for instance of up to 20 kW or even more, for instance up to 50 kW has resulted in a need for providing a plurality of catalyst tubes in a single reforming reactor. This in turn imposes more demands in reactor design in terms of i.a. compactness, better temperature distribution and thermal efficiency. In particular, the provision of a uniform temperature distribution by which all catalyst tubes inside the reactor are heated to the same temperature becomes more difficult to achieve when the heating required in reforming has to be provided by means of a single burner in the reactor. [0007] In addition, the catalyst within the catalyst tubes may often be not evenly distributed so that the catalyst may for instance be better packed in some tubes than others. This may create undesired variation in temperature conditions across the catalyst tubes. SUMMARY OF THE INVENTION [0008] It is therefore an object of the invention to provide a reforming reactor with improved temperature distribution across all catalyst tubes. [0009] It is also an object of the invention to provide a reforming reactor which is compact and free for mechanical means for circulating a heat exchanging medium from the high temperature section of the reactor to the reforming section of the reactor. [0010] It is a further object of the invention to provide a reforming reactor which is compact whilst at the same time is able to rapidly and simply achieve or maintain its operating temperature after a change in process conditions, such as a change in hydrocarbon feed flow or temperature or a change in burner conditions or during a start-up operation. [0011] It is another object of the invention to provide a reforming reactor which is less sensitive to divergent catalyst packing across the catalyst tubes. [0012] It is another object of the invention to provide a reforming reactor which is simple in its construction, inexpensive and with lower heat loss than in conventional reforming reactors. [0013] It is yet another object of the invention to provide a reforming reactor which is compact and suitable for use in fuel cell plants, particularly for fuel cell plants capable of producing up to 20 kW of power or even more for instance up to 50 kW. [0014] These and other objects are achieved by the reactor and process of the invention. [0015] In a first aspect of the invention we provide a reforming reactor for the conversion of a process fluid into hydrogen comprising: a reforming section and a boiler section which are both contained within a common volume and a combustion section, in which said reforming section contains one or more catalyst tubes filled with reforming catalyst, said boiler section is provided with one or more tubes carrying flue gas from the combustion section and said combustion section is provided with at least one burner, wherein the heat exchanging medium required for the reforming of said process fluid in the one or more catalyst tubes is a gas-liquid mixture that self-circulates and is encapsulated inside said common volume containing said reforming and boiler sections. [0016] Accordingly, in the invention a gas-liquid mixture circulating outside the catalyst tubes in the reforming section and outside the tubes carrying the flue gas in the boiler section provides for a large heat sink that enables the accumulation and supply of heat for the reforming reaction so that all metal parts within the reactor, particularly the catalyst tubes, maintain or rapidly reach the same temperature, and a robust operation of the reactor is obtained as it becomes i.a. less sensitive to temporary changes in process conditions, such as changes in burner duty. [0017] By the term "self-circulates" it is meant that the gas-liquid mixture acting as heat exchanging medium moves internally in the reactor without the need of any mechanical means. The gas flows to surfaces or catalyst tube walls, where condensation takes place in a movement driven by the slightly lower pressure created by the volume reduction of the gas as it transforms into liquid. Liquid flows then to the boiler section driven by gravity forces. [0018] In the reactor of the invention at least one process feed tube carrying the process fluid to be converted, such as a liquid mixture of methanol and water, may extend inside said common volume of the reactor. Accordingly, the at least one process feed tube may extend into any location inside said common volume containing the reforming and boiler section, for example the at least one process feed tube may extend from a region at the top of the reactor and above the reforming section into this reforming section or even further into the boiler section arranged below. The at least one process feed tube carrying the process fluid to be converted is introduced to the reactor through a conduct in the outer wall of the reactor and may then extend into the reactor from said conduct arranged in the outer wall. Preferably said process feed tube extends substantially co-axially of the reactor wall inside said common volume from the reforming section of the reactor to the boiler section of the reactor. This enables the provision of a compact reactor as the at least one process feed tube, for example a single substantially straight tube or a tube bundle, is advantageously integrated within the reactor whereby the preheating or evaporation of the process fluid can advantageously be effected as the gas in the self-circulating gas-liquid mixture outside the tube condenses. Hence it is possible to integrate the required evaporation stage inside the reactor thus avoiding the inexpedient provision of separate evaporation means outside the reactor. [0019] By the term "extends substantially co-axially" it is meant that a portion of the process feed tube, particularly the inlet portion cooperating with the conduct in the outer wall of the reactor, may extend into the center of the reactor in a direction which is perpendicular to the reactor length axis, thereafter bending 90.degree. and consequently extending vertically into the reforming section or boiler section below. [0020] The at least one process feed tube may extend vertically into a transition compartment from which at least one process tube carrying process gas to be converted extends vertically upwards inside the common volume of the reactor and wherein the at least one process tube carrying the process gas is formed as a coil. Preferably, a single process tube descends from the conduct in the outer wall where the hydrocarbon feed for example a liquid hydrocarbon feed enters the reactor to the transition compartment. The transition compartment is arranged as a box having inlet openings adapted to accommodate the at least one process tube carrying a process fluid present in substantially liquid form and outlet openings adapted to accommodate the at least one process tube carrying a process fluid present in substantially gas form. These tubes extend vertically upwards and are formed as a coil or spiral. This ensures a better heat transfer for the preheating of the process gas prior to reforming and provides at the same time a compact reactor design as the same heat transfer area as for instance a straight tube can be accommodated in a lower height. Furthermore, the use of a coil or spiral imparts a centrifugal effect on the two-phase flow (gas-liquid) thereby enabling backflow of any liquid not yet evaporated and facilitating the upward flow of process gas. [0021] Preferably the at least one process tube extends from a transition compartment in the boiler section of the reactor to the reforming section in order to ensure that the process gas is heated to the proper reaction temperature in the reforming section. Continue reading... Full patent description for Compact reforming reactor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Compact reforming reactor patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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