WO2010066462A1

WO2010066462A1 - Fuel cell system with a flexible venturi system for selective, controllable operation

Info

Publication number: WO2010066462A1
Application number: PCT/EP2009/008949
Authority: WO
Inventors: Sascha Kuehn
Original assignee: Ezelleron Gmbh
Priority date: 2008-12-12
Filing date: 2009-12-14
Publication date: 2010-06-17
Also published as: DE112009003549T5

Abstract

Fuel cell system whose anode gas supply, especially whose fuel gas supply, and/or whose cathode gas supply is realised via at least one venturi nozzle (3) and/or at least one jet pump, wherein the venturi nozzle (3) and/or the jet pump is/are configured such that with it/them, preferably under the condition that the available static storage pressure of its/their propellant gas(es) and/or its/their propel- lant fluid(s) (1) is constant, the ingested volume per time unit of at least one ingested (2) gas and/or at least one ingested (2) liquid is variable.

Description

Fuel Cell System with a Flexible Venturi System for Selective, Controllable Operation

The present invention relates to fuel cell systems, particularly solid oxide fuel cell (SOFC) systems.

Fuel cells are long-established tertiary galvanic elements. Among the various types of fuel cells, solid oxide fuel cells occupy a prominent position for having the greatest fuel flexibility, as a result of which even hydrocarbons (e.g. propane, butane, methane) and/or alcohols (e.g. methanol, ethanol) can be used directly or after relatively simple treatment. This is particularly important for portable systems, precisely because these fuels have a high volumetric storage density. Many fuel cell systems, especially SOFC systems with their high operating temperatures of several hundred degrees Celsius, often require a variable gas composition for start-up. On the one hand, a variable gas composition facili- tates temperature management and allows better control of reactions which can damage the fuel cells whereby the extent of such reactions varying with the temperature and the gas composition. A major chal- lenge consists inter alia in preventing carbon deposits (soot formation) , when, e.g. hydrocarbons or their reformates are used as fuel. In particular, nickel-based anodes tend to soot formation when hydrocarbons serve as fuel (Handbook of Fuel Cells Fun- damentals, ISBN: 0-471-49926-9) .

For this reason, the use of a reformer for this technology is very often essential in the case of hydrocarbon-rich fuels. In this connection simple reform- ers are needed especially for portable systems. Especially partial oxidation with atmospheric oxygen from air is one favoured technology for small systems. Both the use of a reformer and the case of internal reforming require the production of a suitable mix- ture of oxidising (e.g. air) and reducing medium

(e.g. hydrocarbons) . With existing systems, however, such a mixture or selective variation of the gas composition is possible not at all or only to an unsatisfactory extent, or possible only by using blowers or pumps with a certain energy demand.

The object of this invention therefore is, especially for small mobile and portable systems, to facilitate selective variation of the specific gas composition as a function of the conditions prevailing in the system in an energy- saving manner (that is, under the maximum possible avoidance of pumps and similar systems requiring electrical energy) . Since the thermodynamic window of stable gas compositions is tempera- ture -dependent, it is also an objective of the invention to enable the composition of the supplied fuel mixture to be varied with the temperature . A further objective of the invention is optimised control of the temperature for starting and cooling the fuel cell system by varying the composition of the sup- plied gases (this is possible because such variation enables the energy output of, e.g., burners downstream or reformers upstream of the fuel cells as well as the quantity of supplied heat-absorbing fluid (e.g. cathode air) to be adjusted) .

This object is achieved by a fuel cell system in accordance with claim 1. Further advantageous embodiments of a fuel cell system according to the invention are the subject of the dependent claims.

The basic idea of the invention is to use jet pumps and/or venturi nozzles to produce mixtures of different media. In this connection, the venturi system is designed such that it passively, i.e. without (perma- nent) external energy supply, allows a flexible gas supply for the fuel cell system according to the invention.

The required pressure of the drawing fluid in many cases, such as liquid gas under several bar storage pressure, is provided by the fuel direct.

According to the invention venturi nozzles or jet pumps may or may not be arranged at the exhaust gas outlet of the fuel cell system to dilute the exhaust gas, e.g., with air to reduce the local exhaust gas concentrations and/or to lower the temperature of the exhaust gas. Preferably, a consequential additional cooling effect of the system towards the outside is effected by directing, e.g., cold fresh air, through a channel attached close to the system exterior (e.g. to the outside of thermal insulation) . The quantity of the cooling medium can be variably adjusted with the pumps/nozzles according to the invention, such that the cooling effect too can be designed to be a function of the heat generated by the system (e.g. caused by different operating conditions) . In addition to energy benefits, the use of jet pumps further has the advantage of not having movable, i.e. wearing, parts and thus allows a more compact design relative to other types of pumps.

Possible application areas in the scope of this invention for the combination of variable venturi nozzles and fuel cell systems are the adjustment of dif- ferent compositions of reducing and/or oxidising fluids - especially gases - for supplying cathodes and anodes of fuel cells, especially microtubular solid oxide fuel cells. Furthermore, these nozzles/pumps are also suitable for adjusting gas mixtures that are transformed downstream in reactors (e.g. burners, reformers) . Such an venturi/jet pump according to the invention can also be used for temperature management. Thus, the supply of air for the cathode can be rendered flexible by using such a nozzle/pump to variably draw in the air through the anode exhaust gas such that the desired cooling effect may be achieved.

As already mentioned, oxidising and/or reducing flu- ids (gases and/or liquids, hereinafter also referred to as media) can serve as the ingesting or ingested media. Reducing components can inter alia be hydrocarbons or alcohols - particularly butane, propane, ethanol, methanol, methane, gasoline, diesel - and/or a reformate and/or an anode exhaust gas or mixtures of these media. Preferred oxidising media are air, water, water vapour and oxygen.

If the use of a nozzle according to the invention generates a mixture for a reformer whose exhaust gas is suitable for the operation of fuel cells, especially solid oxide fuel cells, an exemplary mixture for the reformer is an air/propane mixture with an oxygen/propane volume ratio of 1.5/1. The mixture - perhaps pretreated in the reformer - is then suitable for supplying the fuel cell anode. A possible composition of the gas entering the reformer can have a volume ratio of propane/oxygen = 1/1.5. In accordance with the invention, preferably air as oxidising component for supplying the cathode, , can be preferably ingested through the anode exhaust gas exiting the cell and/or air for a reformer can be ingested through preferably pressurised hydrocarbon, such that the mixture exiting the reformer is suitable for supplying the fuel cell anodes . As a further example, water or water vapour, acting as oxidising medium, can be ingested by methane as propellant medium in a molar water vapour/carbon ratio of, e.g., 2/1 to adjust a mixture suitable for the reformer.

One possibility of using the fuel cell systems according to the invention for a start-up procedure is the adjustment of an air/butane mixture with an molar O/C ratio of 1.3 to 3 during the starting phase. This gas is then supplied to a reformer, whose product gas serves to supply the fuel cell anodes. The high proportion of oxygen leads to more extensive full oxidation and thus to increased heat production, a fact which leads to a faster warm-up process. After the operating conditions have been reached, the ratio is preferably adjusted to 1 to 1.3. In the cooling phase, the supply of the ingesting medium is reduced or the supply of air to the cathode is increased. The latter is possible because the exhaust gas from the fuel cell anodes serves as propellant medium in a jet pump system according to the invention and the cathode air is ingested through this medium.

In accordance with the invention, the fuel cell system can be configured such that a gas and/or a liquid can be optionally connected up. This can be achieved with the aid of an additional ingestion channel, whose cross-sectional opening can be varied or closed. The elements of the fuel cell system used for this connection can be configured such that the sta- bility of the fuel cell system is increased, its flexibility increased with respect to temperature management and/or its efficiency increased: Thus, connection of the warm exhaust gas of the fuel cell system enables the heat loss of the entire fuel cell system to be lowered, a fact which can be of crucial importance, especially during the warm-up phase. The blending of the exhaust gas, which can contain inter alia water vapour and/or carbon dioxide and/or oxygen, can give rise to greater reforming activity in reformers upstream of the fuel cell and/or 'in the anodes of the fuel cells themselves whereby the concentration of hydrocarbons (which, especially in nickel- based anodes, can lead to carbon deposition and thus damage to the electrode) can be reduced at the an- odes. Thermodynamically and kinetically stable conditions for preventing the soot formation on the fuel cell anodes are thereby created, as a result of which the service life of the entire system can be increased. One possible embodiment is shown in the fol- lowing Figure 3. Of course, it is also possible to connect up corresponding gases and/or liquids in separate venturi nozzles and/or jet pumps to the system, similar to a system shown in Figure 9.

A special embodiment of the venturi nozzles and/or the jet pumps is characterised by the fact that the venturi nozzles/jet pumps employed to regulate the flow can be used even at several hundred degrees Celsius. To this end, all the materials employed must withstand these high temperatures under the prevailing atmospheres. Among other things, very high- temperature steels or ceramic materials are especially suitable materials for this, while, under reducing conditions, nickel, copper or other oxidisable metals of appropriate high melting points are an alternative solution, too. Of course, combinations of these or other materials can be used, too. For temperatures up to about 250 ⁰C, heat-resistant plastics, e.g., Teflon compounds, are possible too. If the steel will come into contact with the cathode region of the fuel cells at high temperatures, special steels, such as Crofer 22 APU, must be used to prevent chromium poisoning of the cathodes. In a special embodiment, particularly where mixing of the ingest- ing and ingested media leads to ignitable mixtures, the flow channels within the nozzle are designed in such a way that the free flow cross-sections prevent or at least reduce the risk of ignition (e.g. they have flow cross-sections in the range 1-10000 μm) . This can be accomplished for instance by installing a porous foam in the nozzle/pump.

Of course, the jet pumps/venturi systems according to the invention can also be used for single-chamber fuel cells. Moreover, there is also the possibility of using the jet pumps/venturi systems according to the invention permanently or also just temporarily (e.g. in the warm-up and/or cooling phase of the system) to support actively operated (e.g. mechanical and/or electric) pumps/blowers/fans .

In accordance with the invention, at least one of the venturi nozzles and/or jet pumps used for ingesting can contain a desulphurising component, especially zinc oxide, active carbon and/or activated charcoal with additives.

An example of such an arrangement is an adsorbent bed of zinc oxide or active carbon in the inlet zone of a venturi nozzle and/or jet pump upstream of at least one reformer and/or at least one fuel cell, which in the simplest case is placed between two perforated plates. This is especially suitable for the removal of sulphur components, especially hydrogen sulphide in concentrations of 0.1-10000 ppm. Preferably, after desulphurisation, the gas contains less than 1 ppm of these compounds which can damage cells and/or system components .

In accordance with the invention, at least one of the venturi nozzles and/or jet pumps used for ingesting can also contain a reforming component. This is preferably arranged on the outgoing side, i.e. after the mixing of the ingesting and ingested media.

This reforming component can, in the simplest case, be a bed of nickel powder, which, in the simplest case, is placed between two perforated plates. An alternative variant consists in integrating a ceramic carrier (e.g. aluminium oxide) having an applied ac- tive component, such as a noble metal (platinum, rhodium, palladium, ruthenium) . Also, the surface of the venturi/jet pump can be coated with a catalytically active material. The catalytically active coating here is applied preferably by sputtering, dipping, electrochemical deposition, electrophoretic deposi- tion, spraying or other conventional methods. Especially, a ceramic coating, too, can be applied which provides a high specific surface area. This ceramic coating can also be applied by the aforementioned methods or be formed by the material itself through thermal treatment in, e.g., an oxidising atmosphere.

The venturi nozzles and/or jet pumps employed can furthermore have at least one microtubular solid oxide fuel cell by way of extension.

One possible embodiment is afforded by using a ceramic method, especially ceramic injection moulding, to make the body of the venturi nozzle together with the stabilising substrate of a microtubular solid ox- ide fuel cell and, after sintering, providing the fuel cell region with the electrodes and the electrolyte. Thereafter, the region of the venturi nozzle is provided with the appropriate controllers for regulating the flow. Candidate materials here include a mixture of nickel and yttrium- stabilised zirconium oxide or a composite material with a high- temperature steel .

Especially, combinations of the above-described, ad- vantageous embodiments are possible, too.

In accordance with the invention, it is also possible to use at least one parameter measured in the fuel cell system (e.g. temperature and/or pressure) to regulate the volume of gas and/or liquid ingested per time unit by the at least one venturi nozzle and/or jet pump: Thus, simple measurement of the hydrogen concentration in the fuel cell exhaust gas can enable the air supply for the reformer to be increased or decreased appropriately. Alternatively, measurement of the temperature at the fuel cell or in the exhaust gas enables the air ingested for the cathode area to be regulated for the purpose of raising or lowering the temperature of the system through the cooling effect of the ingested air. Alternative control parame- ters are of course possible in accordance with the invention.

Figures 1 to 5, 6a, 6b, 7 to 9 below are used to describe embodiments of the invention.

The individual characteristics of the embodiments described below can, within the context of the present invention, be implemented independently of each other, therefore do not have to be implemented in ex- actly the combinations of characteristics shown in the examples .

Figure 1 :

Figure 1 describes by way of example one possible design in which, in accordance with the invention, the ingested quantity of a medium (2) , which is ingested by means of the so-called venturi effect caused by the ingesting medium (1) entering the venturi nozzle (3) , can be adjusted via the position of the flap (4) arranged in the ingestion tract for the medium (2) . Of course, the supply of the ingesting medium, too, can be varied by, for example, a flap (not shown) arranged in the inlet tract for the ingesting medium (1) . (46) describes the access opening for the ingested medium (2) . (47) describes the inlet channel of the ingesting medium (1) , (48) describes the inlet channel of the ingested medium (2) and (49) describes the outlet channel of the venturi nozzle (3) for the mixture (5) resulting from (1) and (2) .

On account of the setting of flap (4) , the composition of the mixture (5) of medium (1) and medium (2) exiting from the nozzle can be varied. Preferable in this connection is the use of this invention for the purpose of adjusting gas mixtures for a reforming component (perhaps the anodes of the cells themselves) or a burner in accordance with the operating point of the fuel cell system in which this invention is used. Especially, the application preferably takes place within small mobile or portable fuel cell systems in which the use of energy- consuming components is to be specifically avoided; most preferably, these systems are built on the basis of microtubular SOFCs . In accordance with the invention, such a flap can vary the quantity of the ingesting medium (1) , too.

In accordance with the invention, such a system can be used in an environment at several hundred degrees Celsius, too.

Figure 2:

The system here is analogous to that in Figure 1, with the variation in the quantity of ingested medium (2) being effected here not by a flap (4) but instead by a slide valve (30) , by means of which the degree to which the ingestion tract for the ingested medium (2) is opened can be continuously increased and/or reduced.

Figure 3: The system here is analogous to Figure 2, with, in this case, in addition to the medium (2) , a further medium (6) being ingested and the quantity of ingested media (2) and (6) capable of being varied both individually through slide valves (30a) and (30b) arranged in the ingestion tracts of the media (2) and (6) and in their totality by the slide valve (30c) . The overall result is a mixture (7) of the media (1) , (2) and (6) . The ingestion tract for the media (2) and (6) combine to this end to form a common ingestion tract, which leads into the venturi nozzle (3) and in which the slide valve (30c) is arranged. As a preferable - but not exclusive embodiment - anode exhaust gas from the fuel cell unit, water or water va- pour is ingested by way of medium (6) . The branching of the channels (50) and (48) in this regard is preferably designed to offer correspondingly low flow resistance, e.g. is realized by a flat angle of inflow. This supply (6) with portions of the anode or cathode exhaust gas, too, can provide corresponding preheating of the main gases (2) and (1) . The reforming behaviour, too, can be improved by using such an arrangement according to the invention, e.g., through the use of hydrocarbons as fuel (1), air as ingested medium (2) and anode exhaust gas as an additional ingested medium (6) . When these media are used, water vapour and/or carbon dioxide are additionally brought into the fuel. These media can lead to less carbon deposition in the reformer and/or in the cells. This also allows a better temperature management in that endothermic reforming reactions involving, e.g., water vapour as reactant absorb heat from exothermic reactions involving, e.g., oxygen as reactant and/or in that greater efficiencies are achieved because of better fuel efficiency. In addition to the slide valves and flaps shown in Figs. 1 to 3 , all other devices capable of acting as flow regulators are naturally suited: e.g., set screws, squeezable tube connections or pistons and valves .

All these devices can be set electrically, pneumatically or mechanically (manually) .

Flexible setting of the number of ingested media can be achieved in accordance with the present invention by completely closing and at least partially opening flow-regulating apparatuses, such as slide valves or flaps, installed inside the venturi nozzles or jet pumps or generally by valves not integrated in the venturi nozzles/jet pumps. Thus, the flow channel (50) can be completely closed by the slide valve (30a) , and/or the flow channel (48) by the slide valve (30b) . Alternatively, however, valves to regu- late the supply can be integrated outside the venturi nozzle and in the inlet pipes (not shown) to the channels (50) and (48) or to the supply channel of media (1) .

Figure 4:

Figure 4 describes by way of example a fuel cell system according to the invention into which a venturi system of the kind shown in Figs. 1 to 3 is inte- grated. The at least one microtubular SOFC or the at least one stack of microtubular SOFCs (8) is installed in a corresponding heat-exchanger system with air supply (16a) on the cathode side. The electrical contact of the outer cathode (9) of the microtubular SOFC or the stack (8) is provided by contacts (10) , schematically illustrated here, while the power tap of the anode is made by contact (11) , shown schematically. The contacts, for example, can be: steel sheets, which are soldered to the respective electrodes of the cell(s), wire windings and /or other conductive connections with the electrodes. The materials to be used in these cases must be compounds which are stable under the respective operating conditions. At the same time, compatibility with the respective electrodes must be ensured. Thus, the mate- rials chosen, e.g., for the cathode contacts must exhibit little or no chromium evaporation. Located between the anode and cathode of the individual fuel cells is an electrolyte which is used both to (preferably totally) separate the gas spaces between the two electrodes and to prevent direct contact between these electrodes. To prevent electrical short circuits from outside the cell or accidental contact, electrical insulators, which can consist of ceramic films, can be used, e.g. at the point (12) , where contact can occur between contact (10) and the flow channels of the medium (16a) . This prevents an electrical short circuit in case of a contact between the gas inlet pipes of (16a) and the anode contact (11) . The supply of fuel (15) and/or air (16b) at the anode side is controlled, e.g., by simple shut-off valves (13) . Upstream of the cell is a reforming component (17) , in which is provided, for example, a mixture of air or water vapour (16b) and fuel (15) . For adjusting this mixture, a venturi nozzle (21a) according to the invention is provided here on the anode side. To produce heat and reduce the fuel concentration in the exhaust gas, a burner (14) , which is preferably a catalytic porous burner, is used. (21b) here describes a flexibly adjustable jet pump according to the invention having analogous or at least comparable functionality as shown in Figure 1. In other words, in this case, too, changing the flow cross-section of the ingesting medium (22) varies the quantity of ingested medium (16a) .

The further embodiments pertaining to Figs. 5, 6a, 6b, 7 and 8 basically have the same design as those systems or subsystems shown in Figures 1 to 4. Therefore, only the differences are described below.

Figure 5:

Fuel cell system according to Figure 4, in which the heat, which is generated by the afterburner (14) , is used directly to heat the reforming component (17) in the manner that the afterburner (14) encloses the reformer (17), wherein, in this embodiment, there is no gas exchange between (14) and (17) at the point of enclosure, i.e. a gas-tight enclosure is arranged between (14) and (17) . (18) , (19) and (20) describe in this regard a simple system of collecting nozzle, diffusion neck and propellant nozzle. The exhaust gas (22) from the anode passes through the propellant nozzle (20) . As a result, the cathode air (16a) is ingested through the collecting nozzle (18) . Regula- tion of the supply from (16a) can be effected by varying the free flow cross-section of the collecting nozzle (e.g. by pushing the propellant nozzle (20) towards or away from the diffusion neck) . The cathode exhaust gas (23) and the anode exhaust gas (22) then mix inside the diffusion neck (19) . The resulting mixture (28) then passes to the afterburner (14) . To this end, the exhaust gas from the anode and cathode region (22, 23), is transported thermally insulated via the flow channel (27) to the afterburner (14) ar- ranged in the exhaust gas flow channel (27) of the mixture (28) of the cathode exhaust gas and anode ex- haust gas, said afterburner directly enclosing the reformer (17) or being located in its immediate vicinity. As a result, the heat produced during combustion in the afterburner (14) is transferred directly to the reformer (17) . To avoid undesirable oxidation reactions and/or flame propagation, flow channel (27) is preferably equipped with preferably several flow channels with free flow cross-sections of 1 to 10,000 μm.

By means of a (apart from nozzle 21a, see Figure 4) further nozzle (21c) according to the invention, admixed air (16c) to the gas mixture (28) resulting from the anode region (22) and the cathode region (23) can be variably adjusted. Furthermore, also the pressurised fuel (15b) or a different oxidisable gas can be mixed with the mixture (28) via valve (13c) , as a result of which the temperature at the reformer (17) can be adjusted in accordance with the quantity of combusted gas in the afterburner (14) . (16b) is the oxidising agent (e.g., air or water vapour) for the reformer (17), and (16c) is, in this case, the same oxidising agent for the afterburner (14) and is ingested by the exhaust gas (28) via the venturi noz- zle (21c) . The nozzle (21c) in this regard is arranged within the channel (27) and uses the exhaust gas (28) as propellant medium for supplying the afterburner (14) with the oxidising agent (16c). The valve (13c) controls the supply of the oxidisable agent (15b) through pipe (51) , which is connected to the flow channel (27) . The oxidising agents (16b) and (16c) are supplied to the venturi nozzles (21a) and (21c) via the pipes (52a) and (52b) .

Preferably, the exhaust gas (52) is then used to further preheat fresh air (16a) via, e.g., additional heat-transfer devices (not shown) .

Figures 6a and 6b:

Fuel cell system in accordance with Figure 5, in which the air supply for the cathode (9) is preheated by the hot exhaust gas from the cell and the entire air supply for the system is turned on and off by the same valve .

In this particular arrangement, this shared opening of the air supply takes place via the valve (13b) (see Figures 6a and 6b) .

In Figure 6a, air ingested through the inlet pipe (29) by the propellant nozzle (20) is preheated by the exhaust gas exiting from the fuel cell region (28) and is then supplied through the heat exchanger system (24) to the cathode (9) . The exhaust gas re- suiting from the system is removed through an outlet pipe (30) and perhaps put to further use. This can be achieved, e.g., by using the exiting gas to drive bucket wheels, so that the mechanical energy gained therefrom is used (e.g. to support the air supply with a blower or is used thermally by a Peltier element) . In a manner similar to the system shown in Figure 5, a further oxidisable gas can be added through the valve (13c) to the exhaust gas (28) .

Figure 6b shows additionally the possibility of adjusting the heat input into the medium transported through inlet pipe (29) via a supply of fuel gas (15c) through the pipe (52) leading into the flow channel (27) and the burner unit (14b) arranged in- side the flow channel (27) . Between the medium (16) in the pipe (29) and the medium (28) in the pipe (27) , heat transfer occurs at this point but no mass transfer. This fuel gas supply can be controlled via a valve (13d) . In principle, the heat exchanger (24) can be designed such that it encloses the reformer (17) and/or the burner unit (14a) such that an intense heat transfer occurs with these components. In this example shown in figure 6b the pipe which contains the reformer (17) passes through the pipe (27) at the point at which the burner (14a) is integrated into the pipe (27) . The burner (14a) is arranged as a sheath around the pipe which contains the reformer. This can be achieved with a simple bed of loose substances active as burner (14a) or by burners (14a) made from shapes having corresponding cavities for sheathing the reformer pipe. In a comparable manner, the burner (14b) also encloses the oxidising agent supply pipe (29) for the cathodes (9) . The pipes (51, 52 and 53) for the media (15b, 15c and 15) are connected to a fuel tank or an external fuel supply (not shown) .

The inlet pipe (29) of the cathode supply extends from a shared oxidising component (16) supply for the venturi nozzles (21c, 21a) into the heat exchanger (24) as a pipe sheathed by the flow channel (27) .

A reverse arrangement of the electrodes (anode outside, cathode inside the tubular SOFCs) is possible too in the context of the invention, with, in this case, the gas flows being adapted.

Figure 7 :

Figure 7 describes a possible arrangement of the heat exchanger (24) around a microtubular SOFC. The heat exchanger (24) consists on one side of windings (32) , which are wrapped around at least one cell or at least one stack of tubular SOFCs (8) and in which the hot exhaust gas, which is a combustion product of the afterburner (14) , is removed from the system via the outlet pipe (33) . The windings are wrapped in several layers around the cell or stack of tubular SOFCs (8) . For electrical insulation of the heat exchanger housing (54) , electrically insulating layers (55) made of, e.g., aluminium oxide, which can also act as gas seals, may be attached at the point (12) . In this special arrangement, the gas composition of the afterburner (14) is adjusted through an nozzle/pump (35) according to the invention, through which the air supply for the cathode (9) on the outside of the cell is regulated too. (34) refers to the anode ex- haust gas and (31) denotes the cathode exhaust gas. The pressurised anode exhaust gas (34) enters the nozzle (35) at point (56) and generates by means of the design of the nozzle (35) according to the invention a vacuum which ingests the cathode air (31) , which enters the nozzle (35) at the points (57) . At point (58), the mixture enters the afterburner (14) . At point (59) , oxidising component (16) enters the heat exchanger (24) . This passes through the channels (60) , which enclose the windings (32) , to the cathode (9) , as a result of which intense heat exchange takes place between the media in the pipes (32) and channels (60) .

Figure 8 :

Figure 8 shows a fuel cell system, which is comparable to the system shown in Figure 4. In this case, air or water or water vapour (16b) is ingested in the nozzle/pump (21a) at the anode side and a fuel to be reformed (such as propane, butane, methane, ethanol, methanol or other hydrocarbons that can serve as fuel) acts as propellant medium (15) . A reverse arrangement of the media is possible within the context of the invention in which the oxidising agent (16b) is used as propellant medium for the fuel to be re- formed (15) .

A preferred embodiment in which the temperatures of the jet pumps or venturi nozzles (21a, 21b) are above 100 ⁰C, especially above 500 ⁰C, uses a adequate choice of materials to avoid symptoms of poisoning of the fuel cell unit and carbon deposits in the nozzle. Furthermore the flow conditions must be adjusted such that there is no back diffusion of chromium compounds and/or other components that are damaging to cells . The materials used for this can be ceramics (e.g. aluminium oxide or zirconium oxide) or special high- temperature steels (e.g. Crofer 22 APU, perhaps coated with protective layers against, e.g., chromium evaporation) . The outflow zone of the mixture (5) (see Figure 1) here is equipped with apparatuses to improve mixing of the media (1) and (2) . These apparatuses can, for example, be baffles or packings.

The reference numbers (21a) and (21b) describe flexibly adjustable venturi nozzles and/or jet pumps according to the invention analogous to or with at least comparable functionality as in Figure 1. The nozzle (21a) in this case serves to mix the fuel (15) with the air (16b) . The mixture (62) (see (5) from Figure 1) then passes further to reformer (17) upstream of the fuel cell unit (8) , which consists of at least one microtubular SOFC. From this reformer (17), the resulting product gas passes further into the anode region of the fuel cell unit (37) for fur- ther electrochemical oxidation and perhaps also for internal reforming. The nozzle (21b) serves in this arrangement to prepare the mixture of the anode exhaust gas (22) and the cathode exhaust gas (23) . The nozzle (21b) is preferably designed such that there is no uncontrolled flame formation, this being pref- erably ensured by the fact that the flow channels in the burner (14) and/or in the nozzle (21b) have free flow cross-section with a diameter in the range of 1- 200 μm. This mixture is then used in the afterburner (14) to generate heat and reduce the oxidisable gases flowing out of the system (especially the poisonous carbon monoxide, usually a product of (17) in the case that (15) is, e.g., a reformable hydrocarbon) .

The oxidising gas - preferably air - (16a) flowing into the system is preheated by the heat exchanger

(24). In the simplest case, the air (16a) is ingested directly from the atmosphere. This heated medium then passes further to the cathode unit (9) of the fuel cell unit . Separation of the gas spaces of cathodes (9) and anodes (37) of the various fuel cells (8) is ensured by the electrolyte (38) arranged between these electrodes (9, 37) . The heat exchanger (24) can be realized in different embodiments. A special variant is shown in Figure 7. At points (36a), (36b) and (36c) seals are attached which prevent undesirable mixing of anode and cathode atmosphere. These seals can consist, for example, of glass and/or metal and/or ceramics. At point (36a), the fuel cell(s) (8) is/are installed in the gas supply pipe (61) coming from the reformer (17) and the reformate is fed into the internal anode (37) . To prevent the reformate from exiting the inside of the anode, the seal here must be attached at point (36a) . Similar considerations apply to the point (36c) . Point (36b) is where electrical contact is made between the anode (37) and the contact (11) . For this reason, the gas-tight electrolyte (38) must be interrupted in order that the contact (11) may touch the anode (37) . To prevent any of the anode gas atmosphere from exiting, a seal has been attached here .

Referring to Figure 1, media (1), (2) and (5) correspond in Figure 8 to the media fuel (15) , air (16b) and mixture (62) of air (16b) and fuel (15) of the nozzle (21a) and/or anode exhaust gas (22) , cathode exhaust gas (23) and mixture of anode exhaust gas (22) and cathode exhaust gas (23) of the nozzle (21b) .

Figure 9 :

Figure 9 describes a serial arrangement according to the invention of several venturi nozzles/jet pumps

(40) in the context of the invention, especially as a replacement for one of the venturi nozzles and/or jet pumps shown in the previous examples. The various media are connected and disconnected through the valves

(41) . In this regard, one or more valves can be integrated into the inlet tracts or in the outlet tract of each nozzle/pump (40) . Due to the ingesting medium (propellant medium) (42), different media (43, 45, 44) are ingested in accordance with the valve (41) position, and a resulting mixture (39) is created.

A corresponding parallel arrangement or a combination of serial and parallel arrangement of jet pumps/venturi nozzles is possible in the context of the invention. Thus, medium (43) can be air, medium (45) can be water vapour, medium (44) can be anode exhaust gas and medium (42) can be butane.

Claims

1. Fuel cell system whose anode gas supply, especially whose fuel gas supply, and/or whose cath- ode gas supply is realised via at least one ven- turi nozzle (3) and/or at least one jet pump, wherein the venturi nozzle (3) and/or the jet pump is/are configured such that with it/them, preferably under the condition that the avail - able static storage pressure of its/their pro- pellant gas (es) and/or its/their propellant fluid (s) (1) is constant, the ingested volume per time unit of at least one ingested (2) gas and/or at least one ingested (2) liquid is vari- able.

2. Fuel cell system in accordance with the preceding claim,

wherein the venturi nozzle (3) and/or jet pump is configured such that a flexible adjustment of the number of ingested (2, 6) gases and/or liquids and/or a flexible adjustment of the flow cross-section (46) of one or more in-flow pipe(s) (48, 50) of the ingested gas(es) and/or liquid (s) is made possible, and/or

wherein the venturi nozzle (3) and/or jet pump is configured such that a flexible adjustment of the number of ingesting (1) gases and/or liquids and/or a flexible adjustment of the flow cross- section (46) and thus of the volumetric flow of one or more in-flow ρiρe(s) (47) of the ingesting gas(es) and/or liquid (s) is made possible.

3. Fuel cell system in accordance with one of the preceding claims, wherein the fuel cell system is a solid oxide fuel cell system, preferably a fuel cell system having microtubular solid oxide fuel cells.

4. Fuel cell system in accordance with one of the preceding claims, wherein the ingesting gas(es) and/or liquid (s) (1) has/have at least one reducing component which is a fuel or which is adapted to be processed to a fuel for at least one electrode (anode and/or cathode) of at least one fuel cell of the fuel cell system.

5. Fuel cell system in accordance with the preceding claim,

characterised in that at least one of the reducing components comprises a hydrocarbon or an alcohol, preferably butane, propane, ethanol, methanol and/or methane preferably in pressurized form.

6. Fuel cell system in accordance with one of the preceding claims, wherein the ingesting (1) gas(es) and/or liquid (s) has/have at least one oxidising component which is a fuel or which is adapted to be processed to a fuel for at least one electrode (anode and/or cathode) of at least one fuel cell of the fuel cell system.

7. Fuel cell system in accordance with the preceding claim,

characterised in that the oxidising component comprises oxygen or air, preferably in pressurized form.

8. Fuel cell system in accordance with one of the preceding claims, wherein the volume of gas and/or liquid ingested (2) per time unit is adjustable through at least one variably adjust - able inlet aperture (46) and/or through one variably adjustable number of preferably variably adjustable inlet apertures (46) of the ingesting (1) gas(es) and/or liquid (s) and/or of the ingested (2) gas(es) and/or liquid (s) at and/or in the venturi nozzle and/or jet pump.

9. Fuel cell system in accordance with the preceding claim, wherein the inlet aperture (46) and/or the number of inlet apertures (46) is adjustable via a flap (4) and/or a slide (30) and/or a piston and/or a valve.

10. Fuel cell system in accordance with one of the preceding claims, wherein selectively at least one gas and/or at least one liquid (6) is adapted to be connected based on an additional, variably closable ingesting channel (50), wherein preferably the in- flow of said ingesting channel (50) is adapted to be regulated.

11. Fuel cell system in accordance with the preceding claim, wherein the selectively connectable gas and/or liquid (6) is adapted to be taken or is taken from the exhaust gas of the fuel cell system.

12. Fuel cell system in accordance with one of claims 10 or 11, wherein the selective connec- tions for the gas and/or the liquid (6) are realized in such a way that the stability of the fuel cell system is increased and/or that the flexibility with regard to the temperature man- agement of the fuel cell system is increased and/or that the efficiency of the fuel cell system is increased.

13. Fuel cell system in accordance with the preced- ing claim, wherein the stability increase is realized by a decrease or prevention of carbon deposits .

14. Fuel cell system in accordance with one of the four preceding claims, wherein the selectively connected gas(es) and/or liquid(s) (6) is/are adapted to influence the product gas of at least one reformer upstream of at least one fuel cell and/or to influence the product gas(es) produced in at least one fuel cell by internal reforming such, that an increased stability and/or efficiency and/or power density of the fuel cells is realized.

15. Fuel cell system in accordance with one of the preceding claims, wherein at least one of the venturi nozzles (3, 40) and/or jet pump contains in its out-flow channel (49) , at least one baffle, preferably in the shape of a spiral body, and/or at least one flow impediment, preferably in the shape of a packing material, which is/are configured such that a mixing occurs, preferably by an increase in turbulence, of the at least one ingested gas and/or liquid (2, 6, 16, 43, 44, 45) and/or of the at least one ingesting gas and/or liquid.

16. Fuel cell system in accordance with one of the preceding claims, wherein the at least one venturi nozzle and/or jet pump (3, 40) comprises a desulphurising com- ponent, preferably zinc oxide, activated charcoal and/or activated charcoal with additives,

and/or wherein the at least one venturi nozzle and/or jet pump (3, 40) contains preferably on the outgoing side, a reforming component.

17. Fuel cell system in accordance with one of the preceding claims, wherein at least one of the venturi nozzles and/or jet pumps (3, 40) comprises, as an extension, at least one microtubu- lar solid oxide fuel cell and/or a substrate for a microtubular solid oxide fuel cell, wherein preferably this venturi nozzle and/or jet pump (3, 40) is made by an injection moulding method.

18. Fuel cell system in accordance with one of the preceding claims, wherein the variation in the volume (2, 6, 16, 43, 44, 45) ingested per time unit is adapted to be adjusted on the basis of at least one parameter measured in the fuel cell system, preferably a temperature, a flow volume, a concentration, a pressure, an electric output and/or an operating period.

19. Fuel cell system in accordance with one of the preceding claims, wherein at least one of the venturi nozzles and/or jet pumps (3, 40) or a part thereof functions as fuel cell or as part of a fuel cell or as a fuel cell current collector.

20. Fuel cell system in accordance with one of the preceding claims, wherein a multi-stage arrangement and/or a series connection and/or a parallel connection of venturi nozzles and/or jet pumps (40) is configured for variation of the volume ingested per time unit and/or for variation of the number of the induced gases and/or liquids (43, 44, 45), wherein preferably the number and/or quantity of the ingested gases and/or liquids is adapted to be varied by connecting or disconnecting at least one stage (40) and wherein preferably the variation effected thereby in the resultant gas and/or liquid mix- ture (39) is adapted to be used for controlling the operating conditions of fuel cells and/or of fuel cell system components of the fuel cell system.