DE10143656A1 - Production of energy in fuel cell system comprises introducing hydrocarbon into cracking reactor, endothermically cracking, introducing water vapor, endothermically gasifying the obtained carbon and further treating - Google Patents

Abstract

Production of energy in a fuel cell system comprises introducing a hydrocarbon into the cracking reactor, endothermically cracking with exclusion of oxygen, removing the gas mixture, interrupting the feed and introducing water vapor, endothermically gasifying the obtained carbon with water vapor, introducing gas mixture into fuel cell and oxidizing the hydrogen in the fuel cell to recover heat and electrical energy. Production of energy in a fuel cell system consisting of a cracking reactor and a fuel cell comprises: (a) introducing a hydrocarbon into the cracking reactor having a chamber with exclusion of oxygen; (b) endothermically cracking the hydrocarbon in the reactor with exclusion of oxygen into carbon and a hydrogen-containing gas mixture and removing the gas mixture; (c) interrupting the feed of the hydrocarbon into the reactor; (d) introducing water vapor into the reactor; (e) endothermically gasifying the carbon obtained in the cracking stage with water vapor to form a gas mixture containing carbon monoxide and hydrogen and re-using in the fuel cell system; and (f) introducing the gas mixture obtained formed in the endothermic cracking stage into the fuel cell and oxidizing the hydrogen in the fuel cell to recover heat and electrical energy. An Independent claim is also included for a device for carrying out the process. Preferred Features: The cracking reactor has at least three chambers divided into at least two chamber groups. The hydrogen-containing gas mixture fed to the fuel cell is treated to lower its carbon monoxide content before being introduced into the fuel cell.

Description

The subject of this invention is a method for production of energy in a complete fuel cell system Crack reactor and fuel cell and a device for Execution of the procedure.

There are already a wide variety of processes and Devices for producing fuels, in particular of hydrogen as the most environmentally friendly fuel for Fuel cells for the production of electrical energy and Heat through electrochemical reactions between the Fuel and atmospheric oxygen have been proposed.

• a) "solid oxid fuel cells" (SOFCs),
• b) "molten carbonate fuel cells" (MCFCs),
• c) "phosphoric acid fuel cells" (PAFCs),
• d) "alkaline fuel cells" (AFCs), und
• e) "solid polymer fuel cells" (PEFCs).

A total of five types of fuel cells are known in the prior art:

• a) "solid oxide fuel cells" (SOFCs),
• b) "molten carbonate fuel cells" (MCFCs),
• c) "phosphoric acid fuel cells" (PAFCs),
• d) "alkaline fuel cells" (AFCs), and
• e) "solid polymer fuel cells" (PEFCs).

The use of hydrogen in the low temperature Fuel cells PEFC and AFC as fuel require one very high purity of hydrogen because of the operation of PEFCs by carbon monoxide and that of AFCs by carbon dioxide is affected.

• 1. Dampfreformierung, d. h. die endotherme katalytische Umsetzung mit Wasser,
• 2. Partielle Oxidation, d. h. die teilweise Umsetzung des Brennstoffes mit Sauerstoff und/oder Luft zu einem wasserstoffreichen Gasgemisch,
• 3. Autotherme Reformierung, d. h. eine Kombination aus Dampfreformierung und partieller Oxidation mit gleichzeitiger Zugabe von Wasser/Wasserdampf und Sauerstoff bzw. Luft, und
• 4. Cracken, d. h. endotherme Spaltung von organischen Verbindungen.

Currently, 90% of hydrogen is obtained from all kinds of fossil raw materials. The most preferred hydrogen source for this is natural gas. From the different available hydrogen-containing organic compounds, such as. B. hydrocarbons, z. B. Obtain the required hydrogen using the following four process principles:

• 1. steam reforming, ie the endothermic catalytic reaction with water,
• 2. Partial oxidation, ie the partial conversion of the fuel with oxygen and / or air to a hydrogen-rich gas mixture,
• 3. Autothermal reforming, ie a combination of steam reforming and partial oxidation with simultaneous addition of water / water vapor and oxygen or air, and
• 4. Cracking, ie endothermic cleavage of organic compounds.

Details can be found on pages 302 to 317 of the Monograph Fuel Cells and Their Applications by Karl Kordesch and Günter Simader are taken from the VCH-Verlagsgesellschaft mbH, Weinheim, Germany, 1996 was issued.

It is known that a steam-containing product gas can be produced by steam reforming hydrocarbons, in particular methane as the main constituent of natural gas. Industrial steam reforming technology typically includes a desulfurization unit and a high temperature reactor (800 to 900 ° C) that includes a catalyst. Since, depending on the reaction parameters, pressure, temperature and excess steam, after the reforming stage, concentrations of CO of more than 10% by volume are established, two further reaction stages are often added in order to reduce the carbon monoxide content and to obtain further hydrogen, the so-called shift converters. The conversion takes place after the exothermic homogeneous water gas reaction

CO + H ₂ O → CO ₂ + H ₂ ΔR H 0 = - 41 kJ / mol

in two temperature levels, the high temperature shift (HT shift) on an Fe / Cr catalyst at temperatures between 330 and 500 ° C and the low temperature shift (TT shift) on a CuZn catalyst at 190 to 280 ° C. After that, the hydrogen-rich gas mixture still contains a carbon monoxide content of about 0.5-1%.

As a result of the industrial steam reforming of natural gas a product gas is obtained, which is approximately 75% Hydrogen and 25% carbon dioxide.

Especially for the use of the generated hydrogen The production proves itself in a PEFC fuel cell of hydrogen by steam reforming in that disadvantageous because such a high proportion of carbon monoxide in Product gas for inactivating the catalysts in Fuel cell leads and consequently an expensive one Removal of carbon monoxide from the obtained Product gas is required.

As mentioned, these disadvantages can be seen in the Hydrogen production by thermal or catalytic Cracking of organic compounds containing hydrogen be avoided.

The choice of the catalyst used is particularly important important. To select a suitable catalyst already some studies on the suitability of certain Catalysts carried out. So z. B. made of palladium, Rhodium, nickel, cobalt or aluminum oxide-based iron manufactured catalysts with regard to their activity and Stability for the splitting process and the regeneration step tested. It turned out that all of the above In principle, catalysts are suitable for the production of hydrogen are, however, a long-term activity in need of improvement have.

The product gas from the cracking, which essentially consists of H ₂ and CH ₄ , can still contain traces of CO and CO ₂ , which result from the regeneration of the cracking chamber, after leaving the cracking reactor. The carbon monoxide in the product gas is due to partial oxidation of the catalyst during the regeneration process. Since the partially oxidized catalyst is reduced again immediately at the beginning of the cleavage, carbon monoxide will consequently also be formed at the beginning of a catalytic cleavage with a freshly regenerated catalyst.

In the fuel cell itself, due to the along the Flow path decreasing hydrogen partial pressure in the Hydrogen not completely present in the gas mixture exploited, but only a certain proportion (Fuel utilization factor), which is often around 80% of the offered hydrogen lies.

Although it is already known, that of the fixed bed catalyst deposited carbon by burning it To use heat generation, the heat is generated immediately on Catalyst and consequently cannot be due to the relatively poor thermal conductivity of Catalytic beds directed to another location become.

Furthermore, it is desirable that in the reactor chamber or not during catalytic fission converted methane, or that in the methanization stage created methane also for the production of hydrogen to use for the fuel cell. Because the performance of one Fuel cell directly from the hydrogen portion of the Fuel cell supplied product gas depends, it is also desirable compared to the hydrogen content Product gases, which are known from the prior art Procedures originate to further increase.

There are no solutions to the aforementioned in the prior art Problems known. The object of the invention is therefore in the provision of a method and an apparatus for Generation of electrical energy and heat in one Overall fuel cell system, the resulting Product gas has an increased hydrogen content and the Fuel utilization factor is increased.

• a) Zuführen mindestens eines Eduktes in einen Crackreaktor mit mindestens einer Crack-Kammer;
• b) Endothermes Spalten des Eduktes in dem Crackreaktor unter Ausschluss von Sauerstoff in Kohlenstoff und ein wasserstoffhaltiges Gasgemisch und Abführen des wasserstoffhaltigen Gasgemisches;
• c) Unterbrechen der Zuführung des Eduktes in den Crackreaktor;
• d) Zuführen von Luft oder Wasser bzw. eines Gemisches aus Luft und Wasser in den Crackreaktor;
• e) Endothermes Vergasen, bzw. kombiniertes endothermes Vergasen und exothermes Verbrennen des in Crack- Schritt b. erhaltenen Kohlenstoffs mit Wasserdampf bzw. Wasserdampf/Luft zu einem Kohlenmonoxid und Wasserstoff enthaltenden Gasgemisch und Weiterverwendung des so erhaltenen Gasgemisches in dem Brennstoffzellen-Gesamtsystem;
• f) Zuführen des in Crack-Schritt b. erhaltenen wasserstoffhaltigen Gasgemisches in die Brennstoffzelle und Oxidieren des Wasserstoffes in der Brennstoffzelle unter Gewinnung von Wärme und elektrischer Energie.

The invention therefore relates to a method for generating electrical energy and heat in a complete fuel cell system with a cracking reactor and fuel cell, which comprises the following steps:

• a) feeding at least one starting material into a cracking reactor with at least one cracking chamber;
• b) endothermic cleavage of the starting material in the cracking reactor with the exclusion of oxygen in carbon and a hydrogen-containing gas mixture and removal of the hydrogen-containing gas mixture;
• c) interrupting the feed of the educt into the cracking reactor;
• d) feeding air or water or a mixture of air and water into the cracking reactor;
• e) endothermic gasification, or combined endothermic gasification and exothermic combustion of the cracking step b. carbon obtained with water vapor or water vapor / air to a gas mixture containing carbon monoxide and hydrogen and further use of the gas mixture thus obtained in the overall fuel cell system;
• f) feeding the in cracking step b. obtained hydrogen-containing gas mixture in the fuel cell and oxidizing the hydrogen in the fuel cell to produce heat and electrical energy.

The invention thus relates in particular to a complete fuel cell system in which the hydrogen processor is used for the thermal or additional catalytic cracking of hydrocarbons (e.g. natural gas, methane, propane, butane, LPG, gasoline, heating oil, diesel etc.), alcohols, aldehydes and organic acids (> C ₂ ) based. This enables a product gas with a high hydrogen content to be generated.

The invention preferably relates to two embodiments of the method according to the invention, the hydrogen production process of which is based on thermal or additionally catalytic cracking. The product gas is used in a fuel cell, where electricity and heat are generated. The two exhaust gas streams, the anode exhaust gas (H ₂ , N ₂ , CH ₄ , H ₂ O) and the cathode exhaust gas (air, N ₂ , O ₂ , H ₂ O) are preferably used in-process in the overall system.

In principle, the procedure is for all fuel cell types Except for the direct methanol fuel cell. The In principle, the method is also suitable for a wide range Power range from a few watts to a few hundred kW and for various applications in mobile, portable and stationary area.

An essential peculiarity of the method according to the invention for the entire fuel cell system is the method of generating hydrogen by thermal or catalytic cracking of liquid or gaseous fuels, propane initially serving as an example below. At high temperatures, e.g. B. above 800 ° C, propane is broken down on a catalyst into its components carbon and hydrogen:

C ₃ H ₈ → 3C + 4H ₂ Δ _R H ⁰ = 103.8 kJ / mol.

The gas mixture generated then consists of 90% hydrogen, the rest is almost exclusively methane, an intermediate product of the cracking process, which is the operation a fuel cell practically not affected.

This process-technically simple process can be done without complex and complex gas cleaning processes Hydrogen quality can be shown, even for the Use in a membrane fuel cell (PEFC) is suitable. Hydrogen generation by catalytic cracking can therefore run in a very inexpensive system.

The cracking system is preferably used in batch mode with at least two reactors or in a reactor system driven at least two crack chambers, one of which is or more are in the cracking cycle while the one or more others simultaneously cleaned of the accumulated carbon become.

The chambers can be cleaned in various ways respectively. The easiest way is to do that first exothermic burning of the carbon with atmospheric oxygen, such as in U.S. Patent 3,962,411. However, this leads to high thermal loads on the catalysts.

According to the invention, this is done by endothermic gasification of the solid carbon with water vapor or a combined combustion / gasification with a mixture of water vapor and air. This creates a synthesis gas from CO and H ₂ (possibly also CH ₄ , CO ₂ and N ₂ ), the energy content of which, for. B. can be used in the burner, which heats the reactors to the temperatures required for the cracking or steam gasification of about 800 to 900 ° C.

An important advantage of this process engineering concept is the avoidance of high regeneration temperatures during cleaning, which is very positive for the Lifetime of the catalysts affects.

During the cracking process and steam regeneration the burner provides the required heat of reaction Heat loss and the heat for water evaporation As far as this is not by heat recovery or Heat integration of the process can be delivered.

As an alternative, external electrical heating can also be used be used. When using catalysts on electrically conductive metal honeycombs can also do this directly brought to operating temperature by continuity of current or being held. A combination of the two is also conceivable Heating process in which to start up quickly can be electrically heated, and for further operation a burner is used.

Although the inventive method in a cracking Reactor can be operated with one chamber, whereby in particular one or more buffers used can be in which the discharged from the cracking chamber Gas stored and, if necessary, via a Cleaned gas cleaning stage supplied to the fuel cell a preferred embodiment of the inventive method a method in which a Cracking reactor with at least a first chamber and at least one second chamber is used, whereby to Start of the process in step a. the first chamber with the Educt is continuously filled in the first filled Chamber the endothermic cleavage according to step b. carried out is, the feed of the starting material in the first chamber Step c. is interrupted according to step d. Steam or a water vapor / air mixture in the first chamber is supplied and the gasification step e. in the first Chamber is carried out. At the beginning of step c Feed of the educt from the first chamber to the second Chamber switched. In the second chamber, the Process steps a. till B. performed while in the first chamber the process steps d. and e. to Gasification / combustion of the deposited carbon be performed. After removing the carbon in Steps. in the first chamber the cycle is repeated carried out and it can be the starting material of the first chamber again are supplied, each in step b. formed hydrogen-containing gas mixture to the fuel cell is dissipated.

In this embodiment of the method, a continuous supply of fuel gas to the fuel cell enabled without buffer.

A multi-chamber cracking reactor system is particularly preferred used with at least three chambers, the chambers in at least two chamber groups as previously described are divided and the steps in the chamber groups a. to f. be carried out at different times.

For fuel cells where carbon monoxide is considered Catalyst poison acts, that of the fuel cell supplied hydrogen-containing gas mixture preferably before Feeding into the fuel cell for an intermediate treatment Lowered the carbon monoxide content.

In a variant of the method according to the invention in step e. formed carbon monoxide and hydrogen containing gas mixture for generating the gas in the process, preferably in process steps b. and e. required Heat energy used.

In this embodiment, the content is carbon monoxide already relatively low. Because the carbon dioxide content is very low, therefore that of the fuel cell supplied hydrogen-containing gas mixture before feeding in the fuel cells are subjected to methanation, where the carbon monoxide and carbon dioxide in methane being transformed.

If in a second embodiment of the method in step e. educated, essentially from Carbon monoxide and hydrogen existing gas mixture in the Step b. dissipated hydrogen-containing gas mixture is added to increase its energy content, it will the hydrogen-containing gas mixture supplied to the fuel cell before being fed into the fuel cell of a shift Conversion treatment, and possibly another Fine cleaning to reduce the carbon monoxide content subjected.

In all embodiments of the method, this can be done in Step b. dissipated hydrogen-containing gas mixture one Memory are supplied, from which in turn the hydrogen-containing gas mixture supplied to the fuel cell becomes.

In step a. the procedure used Educt the crack reactor in the gaseous state, preferably fed in an inert gas atmosphere. That in step a. educt used is preferably from lower alkane, alkene and alkyne hydrocarbons, alcohols, aldehydes, ketones and organic acids with up to 30, preferably 20 Carbon atoms or mixtures thereof selected.

High reaction speeds and / or lower Temperatures for cracking can be increased by using Catalysts can be achieved. In recent years in addition studies on the catalytic cracking of light Hydrocarbons, mostly propane, butane, LPG, natural gas and Heating oil has been carried out. The studies showed that Best materials based on Pd, Rh, Ru, N1, Co and Fe are suitable for this application. So far it is in the Literature, however, no life tests to real Catalysts made when cracking hydrocarbons Service. In addition, they also point to the cracking process carbon particles formed a certain catalytic Activity for the cracking process on (autocatalysis). There are to date no commercial catalysts for cracking for the production of hydrogen, since this process for this is not used today. The catalysts are through the cracking process and the subsequent cleaning step considerably thermally and mechanically stressed, so that commercially available catalysts which the above. Contain materials that are not cycle stable. Hence from the inventors a special, stabilized Precious metal catalyst has been developed over several hundred cycles (cracking and regeneration) without measurable Degradation was tested.

In contrast to the prior art according to US Pat. No. 5,899,175 contains the product gas mixture when the The inventive method none at room temperature condensable components. The arrangement of the catalyst, d. H. the empty volume in the area of the catalyst must be Allow carbon to be separated so that there is no build up inadmissibly high back pressure. This can e.g. B. with a catalyst bed, but there are also others Geometries possible, such as B. coated heat exchangers, metallic or coated with catalyst material ceramic supports, e.g. B. honeycomb carrier (honeycomb structures) Etc.

In order to utilize the gas used more energetically, the anode exhaust gas is shown in FIG. 1, preferably mixed with the educt stream fed to the cracking catalyst, or in FIG. 2 to generate the in the process, particularly preferably in process steps b. and e. required heat energy used in the burner.

The endothermic catalytic splitting and the endothermic According to the invention, catalytic gasification is preferred in one Temperature range from 500 to 1000 ° C, preferably from 700 to 1000 ° C and particularly preferably 800 to 900 ° C, while the thermal splitting at significantly higher Temperatures takes place.

The present invention is also applicable to an apparatus for Carrying out the method according to one of the preceding Claims directed.

The method according to the invention is further explained using the following two embodiments. The process shown in Fig. 1 relates to a fuel cell system with cracking and methanation, while the process shown in Fig. 2 relates to a fuel cell system with cracking, shift conversion and CO fine cleaning.

The fuel cell system shown in Fig. 1 is in principle suitable for various applications in the mobile, portable and also stationary area. The fuel is fed to the cracker system and disproportionated in one of the chambers at high temperatures on a catalyst into its components carbon and hydrogen, possibly also CO and CO ₂ (when using oxygen-containing fuels). The catalyst increases the reaction rate or allows the system to operate at lower temperatures, but is in principle not absolutely necessary.

After leaving the cracking reactor, the product gas, which essentially consists of H ₂ and CH ₄ , can still contain traces of CO and CO ₂ which result from the regeneration of the cracking chamber. Both carbon monoxide and carbon dioxide can be converted almost completely with hydrogen to methane in the subsequent methanation step. The carbon monoxide is a strong catalyst poison for a membrane fuel cell (PEFC). Since CO is adsorbed on the anodic precious metal catalyst platinum, it would deactivate it after a short time. PEFC systems therefore require fuel gases with a very low CO content, which can be produced by the cracker with simple methanation alone, without the usual complex CO fine cleaning. The methanation does not require any complex regulation.

The fuel gas then consists almost entirely of hydrogen and methane, which is a harmless inert gas for the fuel cell. The product gas is therefore also ideally suited for use with an alkaline fuel cell (AFC) that is sensitive to CO ₂ . Methanation can be dispensed with for PAFC and SOFC, the PAFC tolerates up to about 1 vol.% CO due to its operating temperature of 200 ° C, for the SOFC carbon monoxide is even a fuel gas.

The product gas (hydrogen and methane) is now converted into electricity in the fuel cell. Electrical energy and heat are generated. However, a fuel cell cannot fully utilize the fuel hydrogen in a gas mixture, but only a certain proportion due to the hydrogen partial pressure decreasing along the flow path, which is indicated by the fuel utilization factor, which is often around 80% of the H ₂ offered.

In this embodiment ( Fig. 1) of the system, the residual hydrogen still present in the exhaust gas is now preferably passed, together with the inert methane (anode exhaust gas), first through a condenser to reduce the water content of the anode exhaust gas and then returned to the cracking reactor. The hydrogen then returns to the fuel cell as part of the product gas, while the methane is split into carbon and hydrogen in the cracking reactor.

In this way, according to the invention, despite the Gas mixtures inevitable fuel efficiency factor a fuel cell by recycling the anode exhaust gas an almost complete conversion of that in the educt Hydrogen reached for power generation.

The likewise moist cathode exhaust gas, consisting of not converted atmospheric oxygen, atmospheric nitrogen and water vapor is initially also preferred via a capacitor directed before it is released into the environment. The water the two capacitors are collected and stand then for the water vapor gasification of the carbon in the Crack reactor and possibly for moistening the Fuel cell gases available.

The carbon accumulated in the reactor during the crack cycle is gasified completely or to a large extent by the water vapor, which is preferably generated from the condensate. However, external water can also be supplied for the regeneration step. This creates a synthesis gas mixture with a high CO and H ₂ content with a significant calorific value, which can be used to supply the burner. The energy content of the synthesis gas is basically sufficient to supply the cracking system.

For the complete regeneration of the reactor chamber, i. H. the complete removal of the accumulated carbon, can it may be necessary to gasify with a Combine combustion of carbon with air.

• - Vollständige Vergasung mit Wasserdampf,
• - Kombinierte Regeneration durchs Vergasung mit Wasserdampf und Verbrennung mit Luftsauerstoff, wobei Wasserdampf und Luft dabei gleichzeitig, nacheinander oder in zyklischer Folge eingebracht werden können,
• - Kombinierte Regeneration durch Vergasung mit Wasserdampf und Verbrennung mit Luftsauerstoff und mit Brennerabgas, wobei Wasserdampf, Luft und Abgas dabei gleichzeitig, nacheinander oder in zyklischer Folge eingebracht werden können.

In this way, according to the invention, the energy content of the deposited carbon can be used for the heat supply of the system via the synthesis gas generation. Alternatively, the deposited carbon can be used as follows:

• - complete gasification with water vapor,
• Combined regeneration by gasification with water vapor and combustion with atmospheric oxygen, water vapor and air being able to be introduced simultaneously, in succession or in a cyclical sequence,
• - Combined regeneration by gasification with water vapor and combustion with atmospheric oxygen and with burner exhaust gas, whereby water vapor, air and exhaust gas can be introduced simultaneously, one after the other or in a cyclical sequence.

Through the regeneration with steam, or the combined Regeneration with water vapor, atmospheric oxygen and / or Burner exhaust will lower the reactor temperature against cleaning by simply burning the Carbon with atmospheric oxygen and thus a protection of the Catalysts reached.

The fuel cell system shown in Fig. 2 with cracking, shift conversion and CO fine cleaning is in principle suitable for various applications in the mobile, portable and also stationary area. The fuel is again fed to the cracker system and in one of the chambers at high temperatures, e.g. B. on a catalyst in its constituents carbon and hydrogen, possibly also CO and CO ₂ (when using oxygen-containing fuels) disproportionated. In contrast to the first system, however, the synthesis gas (CO and H ₂ ) from the other chambers, which is produced simultaneously by gasifying the carbon with water vapor, is mixed after leaving the cracking reactor system and fed to a shift conversion down to about 200 ° C. Here, part of the CO reacts with water vapor to form CO ₂ and additional hydrogen. Then the gas mixture still contains about 0.3 to 1 vol .-% CO, which is then in a gas fine cleaning stage, for. B. a selective oxidation level to the permissible for the membrane fuel cell CO contents of z. B. 20 ppm can be reduced. For PAFC and SOFC or future PEFC developments with a high CO tolerance, there is no need for gas purification, the PAFC tolerates up to about 1 vol .-% CO due to its operating temperature of 200 ° C, for the SOFC carbon monoxide is even a fuel gas.

According to the invention, the product gas corresponds to this Practical procedure in its composition practically that a reformate, d. H. the product gas, which by a Steam reforming of the educt would arise. So can from higher hydrocarbons, such as. B. heating oil or diesel, a reformate gas-like gas mixture with hydrogen contents of 70 to 80% depending on the starting material.

A nitrogen content of almost 50%, as is customary in autothermal reforming or the partial oxidation of hydrocarbons, does not occur in this process. In the case of pure water vapor gasification of the deposited carbon, only the small N ₂ content by the PROX of approx. 5% has to be taken into account. In the case of combined regeneration using gasification and combustion (water vapor, flue gas and air), the nitrogen content can be correspondingly higher.

The product gas (hydrogen and methane) is in turn in the Fuel cell converted to electricity and heat. The rest, unreacted hydrogen is then like in first system, if necessary, first via the Condenser to reduce the water content and then fed to the burner. The water content of the Exhaust air from the cathode is also reduced in the condenser. The Condensate is preferred for the gasification of the separated Carbon used. The resulting Syngas mixture is made with the product gas of the reactors are in the cracking cycle.

• - Das Produktgas weist einen hohen Wasserstoffanteil von ca. 70 bis 80% (je nach verwendetem Brennstoff) auf, was zu einer höheren Leistung der Brennstoffzelle führt.
• - Die Vergasung des abgeschiedenen Kohlenstoffs findet mit geringeren Wassermengen statt (S/C-Verhältnis oder Steam to Carbon ratio ca. 1), zusätzliches Wasser wird für die Shiftkonvertierung benötigt, was zu einem S/C-Verhältnis von etwa 2 für den Gesamtprozess führt. Damit wird deutlich weniger Energie für die Wasserverdampfung benötigt, als dies bei einer konventionellen Dampfreformierung mit üblicherweise S/C = 3 der Fall ist.
• - Üblicherweise werden die Schwefelanteile des Brennstoffs vor der Entschwefelung in einem ZnO-Bett durch die Zugabe eines Wasserstoffstroms zu H₂S umgewandelt. Die Integration der Entschwefelungsstufe in den Verlauf des Gasprozesses ist vorteilhaft, da keine Wasserstoffzugabe zur Erzeugung von H₂S aus den Schwefelkomponenten des Brennstoffs mehr erforderlich ist.
• - Das Anodenabgas der Brennstoffzelle, welches Reste von Methan und Wasserstoff enthält, also brennbare Gase, die nicht in der Brennstoffzelle genutzt werden können, wird zum Brenner zurückgeführt und so energetisch sinnvoll zur Erhöhung des Wirkungsgrades des Gesamtsystems eingesetzt.

This hydrogen production process has the following set of advantages:

• - The product gas has a high hydrogen content of approx. 70 to 80% (depending on the fuel used), which leads to a higher performance of the fuel cell.
• - The gasification of the deposited carbon takes place with smaller amounts of water (S / C ratio or steam to carbon ratio approx. 1), additional water is required for the shift conversion, which leads to an S / C ratio of about 2 for the overall process , This means that significantly less energy is required for water evaporation than is the case with conventional steam reforming with usually S / C = 3.
• - The sulfur content of the fuel is usually converted to H ₂ S in a ZnO bed before the desulfurization. The integration of the desulfurization stage into the course of the gas process is advantageous since it is no longer necessary to add hydrogen to generate H ₂ S from the sulfur components of the fuel.
• - The anode exhaust gas from the fuel cell, which contains residues of methane and hydrogen, i.e. flammable gases that cannot be used in the fuel cell, is returned to the burner and thus used in an energetically sensible manner to increase the efficiency of the overall system.

In Fig. 3, a complete fuel cell system is described according to the circuit of Fig. 1, which consists of a cracker q) and a fuel cell p) and to which natural gas is supplied as fuel. The cracking system q) here consists of the cracking chambers d) and s), the burner i) for providing energy, the heat exchangers e) and f) for using the exhaust gas heat and for using the heat of the gas streams leaving the chambers, the methanation reactor g) for gas cleaning , the fuel cell p) and the valves 1 ) to 10 ) for controlling the gas and water flows.

The two chambers d) and the methanation reactor g) are heated by the burner i) to the temperature necessary for the process. After the temperature has been reached, one of the chambers d) is acted upon by the valve 1 ) with the natural gas stream conveyed by the compressor b), which is desulfurized in the desulfurization stage c). The hydrogen-rich product gas leaving the chamber then transfers heat in the heat exchangers e) and f) to a cooling medium r), e.g. B. water, and is fed via the open valve 5 ) of the methanation reactor g) to remove carbon monoxide.

The hydrogen of the purified product gas is in the Fuel cell p) together with atmospheric oxygen electrical power and heat implemented. Before entering the fuel cell p) is the gas containing oxygen if necessary, in a gas humidifier m).

That which is not fully implemented in the fuel cell p) Product gas as well as that from the regeneration Syngas are mixed and the burner i) Energy supply supplied. Optionally, the performance of the Burner can be increased by adding natural gas.

While gas is cracked in chamber d), the carbon separated in a previous cracking cycle is regenerated in chamber s). For this purpose, the chamber s) is supplied with water via the valve 3 ) and the separated carbon gasified with the water, ie converted into a synthesis gas consisting of H ₂ , CO and CO ₂ . The synthesis gas leaving the reactor s) then transfers heat in the heat exchangers e) and f) to a cooling medium r), e.g. B. water, and is fed via the valves 8 ) and 9 ) to the burner i) for the energy supply of the system. Valves 2 ) and 6 ) are closed during the regeneration cycle. Before starting steam vaporization in reactor d), chamber s) is purged with natural gas. For this purpose valve 4 ) is closed and natural gas is supplied via valve 2 ). The gas produced in the purging cycle is also fed to the burner i) via the valves 8 ) and 9 ) or, in another embodiment, is subjected to a gas cleaning stage for removing carbon monoxide and fed to the fuel cell for use.

It is also possible to get the deposited carbon in a regeneration stage through a water / air mixture gasify, so clean the chamber again and then in the cleaned chamber to start cracking again.

After purging chamber s) with natural gas, chamber d) is subjected to the regeneration phase and a chamber s) produces a hydrogen-rich gas for the fuel cell p). To do this, valve 8 ) is closed and valve 6 ) opened. 3 a pump / compressor for air supply to the burner and the fuel cell.
b Pump / compressor for the fuel gas and the cracking gas
c Desulfurization of the cracked gas
d crack reactor
e Exhaust gas heat exchanger for using the exhaust gas heat in the high temperature range
f Exhaust gas heat exchanger and product gas / regeneration gas heat exchanger. Uses the remaining exhaust gas heat and cools the product gas and the regeneration gas from the reactors.
g methanation
h Pump for condensate / regeneration water
i burner
k combustion chamber to accommodate the reactors and heat exchangers
l Insulation of the combustion chamber
m humidifier for the cathode air of the fuel cell (optional)
o Condensate separator for product water in the fuel cell
p fuel cell
q Cracking system with two reactors
r fluid for heat exchangers e) and f)
s crack reactor
1 valve for cracked gas reactor A
2 valve for cracking gas reactor B
3 valve for air and / or water reactor A
4 valve for air and / or water reactor B
5 valve for methanizing the product gas from reactor A
6 valve for methanizing the product gas from reactor B
7 Regeneration waste gas from reactor A
8 Regeneration waste gas from reactor B
9 Valve for supplying fuel gas
10 Valve for air supply to the burner

Claims (18)

1. A method for generating energy in an overall fuel cell system with a cracking reactor and fuel cell, which comprises the following steps: a) feeding at least one hydrocarbon into a cracking reactor with at least one cracking chamber in the absence of oxygen; b) endothermic splitting of the hydrocarbon in the cracking reactor with the exclusion of oxygen in carbon and a hydrogen-containing gas mixture and removal of the hydrogen-containing gas mixture; c) interrupting the feed of the hydrocarbon into the cracking reactor; d) supplying steam to the cracking reactor; e) Endothermic gasification of the cracking step b. carbon obtained with water vapor to a gas mixture containing carbon monoxide and hydrogen and further use of the gas mixture thus obtained in the overall fuel cell system; f) feeding the in cracking step b. obtained hydrogen-containing gas mixture in the fuel cell and oxidizing the hydrogen in the fuel cell to produce heat and electrical energy. 2. The method according to claim 1, in which a cracking reactor with at least a first chamber and at least a second chamber is used, at the beginning of the method in step a. the first chamber is filled with the hydrocarbon, in the first chamber thus filled the endothermic cleavage according to step b. is carried out, the supply of the hydrocarbon in the first chamber according to step c. is interrupted according to step d. Steam is fed into the first chamber and the evaporation step e. is carried out in the first chamber
where at the beginning of step d. hydrocarbon is fed into the second chamber in the first chamber and process steps b. to e. be performed,
where, after evaporating the carbon in step e. in the first chamber, the first chamber is again supplied with hydrocarbon and the cycle can be carried out again, and
where in step b. formed hydrogen-containing gas mixture is discharged to the fuel cell. 3. The method according to claim 2, in which preferably a Multi-chamber cracking reactor with at least three chambers is used, the chambers in at least two Chamber groups are divided as in claim 2 and in the chamber groups the steps a. to f. chronologically staggered. 4. The method according to any one of the preceding claims, in which the fuel cell supplied hydrogen-containing gas mixture before being fed in the fuel cell an intermediate treatment for Lowered the carbon monoxide content becomes. 5. The method according to any one of claims 1 to 4, wherein the each in step e. formed, carbon monoxide and hydrogen-containing gas mixture for generation in the process, preferably in the Process steps d. and e. required thermal energy is used. 6. The method according to claim 5, wherein the Fuel cell supplied hydrogen-containing Gas mixture before being fed into the fuel cell a methanation treatment to lower the Carbon monoxide content is subjected. 7. The method according to any one of claims 1 to 4, wherein the in step e. formed, carbon monoxide and hydrogen-containing gas mixture that in step b. dissipated hydrogen-containing gas mixture is admixed. 8. The method according to claim 7, wherein the Fuel cell supplied hydrogen-containing Gas mixture before being fed into the fuel cell a shift conversion treatment, and if necessary, a fine cleaning for humiliation the carbon monoxide content is subjected. 9. The method according to any one of the preceding claims, where in step b. dissipated hydrogen-containing Gas mixture is fed to a storage from which the hydrogen-containing gas mixture of the fuel cell is fed. 10. The method according to any one of the preceding claims, where in step a. the hydrocarbon used the crack reactor in the gaseous state, preferably supplied in an inert gas atmosphere becomes. 11. The method according to any one of the preceding claims, where in step a. the hydrocarbon used from lower alkane, alkene and alkyne Hydrocarbons, alcohols, aldehydes, ketones and organic acids with up to 30, preferably 20 Carbon atoms or mixtures thereof selected becomes. 12. The method according to any one of the preceding claims, wherein in step b. the endothermic splitting in Presence of a catalyst, preferably one Metal catalyst is carried out. 13. The method of claim 12, wherein the catalyst is a Pd / gamma alumina catalyst. 14. The method of claim 12, wherein the catalyst is a Palladium, ruthenium, nickel, cobalt and / or Solid phase catalyst is iron. 15. The method according to any one of the preceding claims, the anode exhaust gas for generating the in the process, preferably in process steps d. and e. required thermal energy is used or who Crack catalyst supplied hydrocarbon is admixed. 16. The method according to any one of the preceding claims, the endothermic splitting and the endothermic Gasification in a temperature range of 500-1000 ° C, preferably from 700 to 1000 ° C and particularly preferred 800 to 900 ° C takes place. 17. Device for carrying out the method any of the preceding claims. 18. The apparatus according to claim 17 with a cracking reactor with at least one cracking chamber (d; s), a burner (i) for providing energy, at least one heat exchanger (e; f) for using the exhaust gas heat and for using the heat of the chamber Gas streams, a methanation reactor g) for gas cleaning, a fuel cell p) and connecting lines with valves ( 1 ; 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8 ; 9 ; 10 ) for line and control of the gas and water flows.