Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Reexamination Certificate
2000-04-12
2003-11-11
Johnson, Jerry D. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
C422S186220, C422S198000, C422S198000, C422S198000, C422S198000, C422S198000, C422S198000, C422S198000, C422S201000, C422S202000, C422S204000, C422S211000, C422S222000
Reexamination Certificate
active
06645443
ABSTRACT:
The invention relates to a device for reforming educts containing hydrocarbons. The inventive device can be used in particular for industrial, and also smaller, installations for producing hydrogen from fossil energy carriers such as natural gas, liquid gas or naphtha, and thereby operates according to what is known as the “steam reforming method.” The hydrogen-rich synthesis gases obtained in this way are subsequently used for example for the manufacture of ammoniac or alcohol or for the synthesis of methanol, an essential application being the production of high-purity hydrogen, which can also be used in a wide range of fuel cells.
The invention is particularly suited for producing hydrogen from fossil energy carriers in the low-power range, such as for example for membrane fuel cell systems for decentralized stationary production of current, where compact units and structural sizes are particularly important. In such cases of application, a high degree of efficiency must be attained, and in particular the heat losses, which increase proportionally in smaller installations, must be taken into account. The heat emission of the burner unit, taking into account the heat sink formed by the reforming reactor, must here be specifically taken into account and kept efficient.
For this purpose, besides the known large industrial hydrogen production installations, in the course of continuing fuel cell research special reforming systems have been developed that are based on what is called the heat exchanger principle. Using such installations, hydrogen can be produced in a quantity that reaches several hundred kW, in relation to the net calorific value of the hydrogen. The hydrogen produced in this way can then be used in high-temperature fuel cells, such as for example SOFC or MCFC, and also in phosphoric acid fuel cells for decentralized power supply.
In this context, in smaller systems having polymer membrane fuel cells it is known to use methanol as an energy carrier; the steam reforming of methanol already takes place here at temperatures of 200 to 300° C., since the reforming reaction of methanol has a lower reaction enthalpy than that of methane, which can likewise be used. This relatively low temperature range enables a lower installation-related outlay, and heat losses can be caught much more easily than is the case given starting materials (educts) such as for example natural gas. In the reforming of methanol, for example an additional fluid can be used as a heat transfer medium, and the energy losses can be reduced by the use of corresponding insulation.
In the known installations, the reforming reaction takes place with the use of solid catalysts, such as for example Ni/Al
2
O
3
. The standardly used flame burners are generally positioned centrically in the reforming unit, or such a burner is flange-mounted on the reforming unit. The smoke gases that arise during combustion are then led past the reactor walls in gaps, so that the heat required for the reaction can be transferred in convective fashion. In order to achieve good conversions in the reforming, sufficiently large transfer surfaces must be present.
A pre-heating of the educt or educts can be achieved by counter-current flow or same-direction flow of educt gas and process gas, in order to enable partial exploitation of the high enthalpy current of the process gas and reduction of the heating capacity.
However, it is not possible to use simple reduction in size to adapt the known installations to small low-power systems. In particular, problems arise here in the heat transfer, and in smaller installations relatively high heat losses can be compensated, if at all, only at a relatively high expense.
It is thus the object of the invention to propose a device with which educts containing hydrocarbons can be converted into synthesis gases in the low-power range with high efficiency.
According to the invention, this object is achieved by means of the features of patent claim 1. Advantageous specific embodiments and developments of the invention result with the use of the features named in the subordinate claims.
The inventive device can be used for steam reforming of various educts containing hydrocarbons, but can also be used unproblematically in other strongly endothermic processes.
The advantages of the invention are in particular that small power ranges, less than 50 kW, can be covered without a reduction in efficiency due to excessive heat losses.
The inventive device is thereby distinguished in that a radiant burner being used is arranged in connection with a two-part reforming reactor in such a way that the parts of the reforming reactor can be heated by radiation and convection, and the radiation burner thereby surrounds the two parts of the reforming reactor in annular, that is, tubular, fashion, whereby the radiation burner can also be formed from planar elements that form a polygon. The arrangement of the individual elements of the inventive device thereby takes place in such a way that educt gas and smoke gas can be conducted in counter-current flow between the two parts of the reforming reactor.
Preferably, one part of the reforming reactor is fashioned as an annular-gap reactor, and the other part is fashioned as a tube reactor, and the two are arranged in relation to one another in such a way that the annular-gap reactor surrounds the tube reactor in tubular fashion, and smoke gas can be conducted in the intermediate space between the two parts, so that the heat of the smoke gas can be exploited optimally for the reforming.
In a further development of the inventive device, it is particularly advantageous that this device is further fashioned so as to have a heat exchanger that is arranged above the reforming reactor that is made up of the two parts. In this heat exchanger, the heat of the smoke gas can then also be used to pre-heat the educt introduced into the reactor, or also to pre-heat several educts, or to vaporize a liquid educt.
In particular given low powers that are to be produced using an inventive device, this thermal coupling has the result that the heat losses can be minimized.
Coated metal honeycomb bodies, with the aid of which the reforming reaction is carried out catalytically, are housed in the reaction spaces of the tube reactor and the annular-gap reactor. Platinum and nickel, but also copper and zinc, are suitable for use as catalysts with which the metal honeycomb bodies can be coated.
The annular-gap reactor is heated predominantly by the heat radiation of the radiation burner, whereas the tube reactor is heated by convection through the smoke gases conducted past it.
The conducting of the produced synthesis gas advantageously takes place in counter-current to the smoke gas coming from the radiation burner; that is, the first unit is the convectively heated tube reactor, the second unit is the annular-gap reactor, heated via radiation and convection, and the exit of the synthesis gas then takes place via the heat exchanger, which is arranged above the two parts of the reforming reactor.
The radiation burner used in the inventive device can preferably be constructed from ceramic apertured plates, arranged in such a way that, as already stated above, they surround the reforming reactors, and the supplying of the combustion gas to the radiation burner takes place via an annular space that is formed around the individual plates of the radiation burner with a housing wall, and in which the combustion gas can be supplied in pre-mixed form. Moreover, a gas distributor tube, having an aperture structure distributed over the entire height of the radiation burner, can be used for the supplying of the combustion gas, in order to achieve a uniform supplying of combustion gas.
The heat exchanger, which is preferably placed directly on the two parts of the reforming reactor, is essentially made up of a coiled tube through which the educts used for the reforming can flow into the tube reactor. The coiled tube is thereby multiply wound in the shape of a cross, so that before introduction into the tu
Hey Sylvie
Ledjeff-Hey Konstantin
Schuler Alexander
Vogel Bernhard
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
Hey Sylvie
Johnson Jerry D.
Leydig , Voit & Mayer, Ltd.
Ridley Basia
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