WO2005038972A2

WO2005038972A2 - Fuel cell, auxiliary device and energy generation installation

Info

Publication number: WO2005038972A2
Application number: PCT/NL2004/000744
Authority: WO
Inventors: Franklin Hagg
Original assignee: Stork Fokker Aesp B.V.
Priority date: 2003-10-20
Filing date: 2004-10-20
Publication date: 2005-04-28
Also published as: WO2005038972A3; NL1024571C2

Abstract

A fuel cell (24) comprises a housing (70) with an inlet (72) for an oxygen-containing gas and an outlet (74) for depleted oxygen-containing gas, which are in communication with one another via a number of fuel cell tubes (80) arranged parallel to one another, and an inlet (86) for a gaseous fuel and an outlet (88) for depleted fuel gas, which are in communication with one another via a chamber (79) arranged around the fuel cell tubes. Adjacent to the inlet (72), the housing (70) comprises a distribution chamber (82) for distributing incoming oxygen-containing gas to the fuel cell tubes (80), which distribution chamber (82) has a larger maximum cross-sectional area, as seen in the direction of flow, than the inlet (72) itself, as well as a collection chamber (84) for collecting depleted oxygen-containing gas at the end of the fuel cell tubes (80), which collection chamber (84) has a larger maximum cross-sectional area, as seen in the direction of flow, than the outlet (74). The tubes (80), distribution chamber (82) and collection chamber (84) are shaped in such a manner that the pressure drop across the fuel cell (24) is virtually negligible.

Description

Short title: Fuel cell, auxiliary device and energy generation installation

The invention relates firstly to a fuel cell for the generation of energy, in particular electricity and heat.

Fuel cells are generally known. In a fuel cell, an electrochemical reaction is used to convert hydrogen ions, derived from a fuel, combined with oxygen ions, derived from an oxygen-containing gas, into water with simultaneous generation of electricity. The fuel cell comprises an anode, along which the fuel flows, a cathode, along which the oxygen-containing gas flows, and an electrolyte arranged between the electrodes. The electrolyte permits ions to migrate between the electrodes . An external circuit connects the electrodes . Fuel cells can be classified according to the type of electrolyte, such as MCFC (molten carbonate fuel cell) , PEMFC (proton exchange membrane fuel cell) and SOFC (solid oxide fuel cells) , ^' etc. The partial reactions within the overall electrochemical reaction which occur at the corresponding electrodes and the transfer of ions through the electrolyte are also dependent on the type of electrolyte. In the case of a fuel cell of the SOFC type, oxygen, generally supplied in the form of air, is dissociated at the cathode, and the oxygen ions pass through the electrolyte, such as for example metal oxide, usually yttria-stabilized zirconium oxide, to the anode, where these oxygen ions combine with hydrogen, derived from a hydrogen-containing gas or vapour, to form water. A fuel cell of the SOFC type operates at a high temperature, usually between 650° - 1000°C, and at an optionally elevated pressure of 1-8 bar. The electrolyte and electrode materials used have to be able to withstand this high temperature. Water for the hydrogen shift reaction can be sprayed into the oxygen-containing gas supplied. Fuel cells are of interest since they have a very high efficiency compared to other conventional energy systems, such as an internal combustion engine.

The fuel cell can be used per se or in combination with existing conventional systems, such as a gas turbine. Examples of hybrid systems of this type are known, for example, from WO 96/056265 and US 6,213,234.

Various configurations of fuel cells are known. The configuration used most frequently is a sandwich structure (planar single cell) comprising anode, electrolyte and cathode. To obtain higher output voltages and powers, separate cells are connected to one another in series to form what is known as a stack. The removal of heat and the flows of gas impose considerable restrictions on this technology in practice. In the case of a tubular configuration, the anode, electrolyte and cathode form a tube. The outer side of the tube usually comprises an anode layer (hydrogen side) , which is covered with an electrolyte layer, followed by a cathode layer (oxygen side) . Tubes of this type are marketed, inter alia, by Siemens Westinghouse and generally have a length of 1.5 metres and a diameter of 2.2 cm. In this case too, the tubes are connected to one another in order to achieve the desired voltage and desired power.

In practice, however, the use of fuel cells as an energy source instead of or as addition to existing systems is limited, since in general there is insufficient readiness to make the extensive investment required for this purpose.

It is an object of the invention to provide a fuel cell which can be used in a simple way, without expensive additional measures, in combination with other energy provision system, in particular a gas turbine or a combined gas and steam turbine (STEG) .

The fuel cell according to the invention to this end comprises a housing with an inlet for an oxygen-containing gas and an outlet for depleted oxygen-containing gas, which are in communication with one another via a number of fuel cell tubes arranged parallel to one another, which fuel cell tubes each comprise an anode and a cathode with an electrolyte arranged between them, as well as an inlet for a gaseous fuel and an outlet for depleted fuel gas, which are in communication with one another via a chamber formed around the fuel cell tubes, the housing, adjacent to the inlet, comprising a distribution chamber for distributing incoming oxygen-containing gas to the fuel cell tubes, which distribution chamber has a larger maximum cross-sectional area, as seen in the direction of flow, than the inlet, and also a collection chamber for collecting depleted oxygen-containing gas at the end of the fuel cell tubes, which collection chamber has a larger maximum cross-sectional area, as seen in the direction of flow, than the outlet, the tubes, distribution chamber and collection chamber being shaped in such a manner that the pressure drop across the fuel cell is virtually negligible.

The invention is based on the insight that the integration of a fuel cell in an existing energy generation system, such as a gas turbine, is in part impeded by the costs of the equipment required to bring the corresponding outlet gases of the fuel cell up to the operating pressure required for the energy generation system, in particular the air flow. This is necessary in conventional systems in accordance with the prior art since the configuration of the fuel cell device and the flat or tubular fuel cell elements used therein causes a considerable pressure drop. In the configuration of the fuel cell according to the invention, by contrast, this pressure drop is scarcely present, on account of the shaping of the distribution chamber and collection chamber and the fuel cell tubes themselves. Also, in the invention there is no need for heat exchangers, which results in a cost saving; in existing integrated systems, such heat exchangers are used in order to exploit heat fluxes which are not otherwise utilized. Therefore, the fuel cell according to the invention can be fitted at relatively low cost as what is known as an add-on to an existing energy-supplying installation, for example a gas turbine. The distribution chamber has a larger cross section than the inlet, so that the velocity of the oxygen-containing gas decreases considerably when it enters, and therefore so does the pressure drop (proportionally to the square of the velocity) in the fuel cell tubes. The oxygen-containing gas is concentrated again at the collection chamber. Consequently, the pressure drop can be kept at a low level, with the result that the outlet gases can be fed directly to the main burner of a gas turbine system without intervening compression with the aid of compressors. Even if the fuel cell operation is less than optimum, for example with a degree of utilization of 10% of the fuel, the efficiency of the overall device is increased without major investment in peripheral equipment, such as compressors and the like, being required. With a view to achieving a low pressure drop, the tubes are advantageously straight pipes with a length which is less than that of the tubes currently used, for example less than 75 cm, more preferably with a length in the range from 20-60 cm. The diameter may be approximately equal to the diameter of the known Westinghouse tubes, i.e. approx. 2.2 cm. However, it is preferable for the pipes to have a larger diameter, 2.5 cm or more for example.

The distribution chamber and collection chamber are shaped in such a manner that the pressure drop is low. The distribution chamber advantageously has a gradual transition from the inlet to the maximum cross section of the housing. The shape of the collection chamber is similar. More preferably, the housing comprises a cylindrical centre section of constant diameter, with the wall of the housing which delimits the distribution chamber comprising a gradual transition from the inlet to the centre section. The housing is shaped in a similar way at the collection chamber. The gradual transitions are advantageously curved surfaces of the housing. In this embodiment, partitions are advantageously arranged on either side of the centre section, so as to define a chamber or space through which the fuel can flow. These partitions are provided with a number of bores through which the fuel cell tubes are fitted. The curved top side and the associated partition define the distribution chamber. The collection chamber is defined in a corresponding way by the curved wall surface of the housing and the corresponding partition. The ends of the fuel cell tubes are on one side in communication with the distribution chamber and on the other side open out into the collection chamber. The space or chamber which is delimited by the centre section of the housing and the partitions has an inlet for fuel and an outlet for used fuel gas. Baffle plates and other guide elements may be provided to ensure that the fuel is guided tightly along the outer side of the fuel cell tubes. The cathode (hydrogen side) of the fuel cell is located on the outer side of the fuel cell tubes.

The fuel cell is preferably of the SOFC type, in other words the electrolyte comprises a solid oxygen carrier. However, it is also possible for other types of fuel cells to be used in a similar way. In general, during operation all the fuel is passed across the fuel cell, as is some of the quantity of air required for the gas turbine. It is customary for the gas turbine to operate with excess air, for example 1.3-1.5 times the quantity of fuel on a molar basis (approx. 25-40 times on a volume basis), in order to cool the turbine.

According to a second aspect, the invention relates to an auxiliary device for improving the efficiency of an energy generation system, which device is provided with one or more fuel cells according to the invention, and the inlets of a first fuel cell are provided with a line with coupling for coupling to a corresponding line of the energy generation system, and the outlets of a last fuel cell are provided with a line with coupling for coupling to an associated line of the energy generation system. In particular, the inlets can be connected, via the said lines and couplings, to the discharge lines of the corresponding compressors of the energy generation system, and the outlets can be connected to the feed lines of the main burner. An excess of air (with respect to the quantity of fuel) is used in the main burner in a gas turbine as energy generation system. In the auxiliary device according to the invention, it is advantageous for some of the fuel and air already to have been used in order to heat the fuel and air to the temperature required for operation of the fuel cell with the aid of preheating devices. More preferably, the preheating devices are so called in-line combustion devices, from which the used gas (outlet gas) is fed, together with the corresponding heated gaseous fuel or air, to the fuel cell. Also, some of the fuel and the air is used by the fuel cell itself, specifically in such a manner that on account of the excess of air which is present, the original supply of air for the gas turbine itself can remain equal and can even be such that the inlet temperature of the turbine can remain equal, so that the gas turbine installation is scarcely affected.

The auxiliary device advantageously comprises a plurality of fuel cells according to the invention connected in series, the outlets of a fuel cell being in communication with the inlets of an adjacent, downstream fuel cell, the second and subsequent fuel cells also being provided with inlets for the introduction of cold oxygen-containing gas and cold fuel respectively. Since the overall electrochemical reaction in the fuel cell is an exothermic reaction, heat is released, with the result that the temperature can rise. However, the materials used in the auxiliary device are not able to withstand this elevated temperature. The partial supply of relatively cold reactants to the second and subsequent fuel cells ensures that the auxiliary device is cooled.

More preferably, the auxiliary device comprises a common feed line for cold fuel and one for cold oxygen-containing gas, which lines are provided with side lines leading to the corresponding fuel cells.

According to yet another aspect, the invention relates to an energy generation installation provided with an auxiliary device according to the invention. Advantageously, the installation comprises a compressor for compressing oxygen-containing gas, the outlet of which is connected to the inlet line for oxygen-containing gas of a fuel cell of the auxiliary device. In this preferred embodiment according to the invention, there is no need for a separate compressor for the auxiliary device. Furthermore, this embodiment permits the use of the excess of air from the original energy generation installation, with the supply of air associated with the energy generation installation and the outlet temperature of the burner remaining unchanged, so that the energy generation installation and/or the operational settings thereof need little if any modification. It is preferable for it to be possible for the auxiliary device to be switched off, so that, for example in the case of the auxiliary device failing, the energy generation installation itself can continue to operate in the original way. For this purpose, it is advantageous for the inlet lines of the auxiliary device to be coupled as side lines to the corresponding lines of the energy generation installation. Shut-off members/regulators are provided in the lines. Preferred embodiments of an energy generation installation of this type are a gas turbine and a combustion boiler. If desired, the gas turbine may be coupled to a steam turbine.

The invention is explained below on the basis of the appended drawing, in which: Fig. 1 shows an embodiment of a gas turbine system with an integrated fuel cell system according to the invention;

Fig. 2 shows an embodiment of a fuel cell according to the invention; and

Fig. 3 shows a diagrammatic preferred embodiment of an auxiliary device according to the invention with fuel cells connected in series .

In Fig. 1, an energy generation system in the form of a conventional gas turbine is shown beneath the dashed line. This gas turbine is provided with an auxiliary device according to the invention, which comprises a fuel cell according to the invention. Fuel, for example a lower hydrocarbon, such as methane, is fed to fuel compressor 12 via line 10 and is compressed therein. The compressed fuel is discharged via line 14. Air, supplied via line 16, is compressed in air compressor 18 and discharged from it via line 20. Line 14 is provided with a side line 22 which is suitable for transporting at least some of the compressed fuel to a fuel cell 24. Shut-off member 65 controls the quantity of fuel which passes to the fuel cell. The side line 22 is releasably coupled to the line 14. This coupling is denoted by reference numeral 26. The side line 22 is provided with a shut-off member 28. The side line 22 has two further side branches. A first side line 30 leads to a preheating device 32 for preheating compressed air. This preheating device 32 is an in-line burner in which the heat required for preheating is obtained by burning a part of the fuel with some of the compressed air. Via a second side line 34, a part of the compressed fuel is passed to a preheating device 36 for preheating the compressed fuel, supplied via side line 22. This preheating device 36 is likewise an in-line burner, in which the remaining fuel, supplied via the end of side line 22, is heated through combustion of the said partial .quantities of compressed fuel and compressed air. It is necessary to preheat the reactants for the fuel cell 24 since the electrochemical reaction which occurs therein only takes place at elevated temperatures. For compressed air to be supplied to the preheating devices, the discharge line 20 is provided with a side line 38, which can also be decoupled by means of coupling 40. The side line 38 is provided with a shut-off member 39. The discharge gases of the preheating devices are fed to fuel cell 24 via discharge lines 42 and 44, respectively. Details of the fuel cell are explained below with reference to Fig. 2. In the fuel cell 24, an electrochemical reaction takes place between fuel and air, with the electricity which is generated being tapped off in the usual way via lines 46. Even if the fuel cell 24 does not operate optimally, for example operates at a degree of fuel utilization of approximately 10%, the overall efficiency of the system as a whole is increased by a few per cent. The flows of reaction products from the fuel cell, which may still contain a considerable quantity of fuel and/or air, are passed via discharge lines, provided with shut-off members 48, 50, for fuel 52 and for air 54, respectively, to the main burner 56. More particularly, the discharge line 52 is coupled to line 14 via coupling 58. The discharge line 20 for compressed air from the compressor also opens out into the main burner 56. Further combustion takes place in the main burner 56. The exhaust gases are fed in the customary way to the turbine section 60 of the gas turbine, and electricity is generated with the aid of generator 62. The discharge gases 64 from the turbine section 60 can be utilized, for example, in a steam turbine (not shown) . Another option is to use the discharge gases 64 for recuperation if such a measure was already in use in the original gas turbine.

Fig. 2 shows an embodiment of a fuel cell according to the invention in more detail. The fuel cell 24 comprises a cylindrical housing 70 with, in the case illustrated, an air inlet 72 for compressed air at the top side and an air outlet 74 provided at the underside. The housing 70 comprises a centre section 76 of constant diameter. Partitions 78 are provided in the interior, in the vicinity of the boundaries of this centre section 76. A number of parallel fuel cell tubes 80, generally in a regular distribution, are fitted through bores in these partitions 78 and connect the air distribution chamber 82 at the top to the collection chamber 84 at the bottom of the housing 70. The top side of the housing 70, which together with the upper partition delimits the distribution chamber 82, gradually widens from the air inlet 72 to the centre section 76. The underside of the housing 70, which together with the bottom partition delimits the collection chamber 84, is gradually narrowed in a corresponding way from the centre section 76 towards the air outlet 74. A fuel chamber 79, which is provided with gas inlet 86 and gas outlet 88 located diametrically opposite one another, is formed between the partitions 78 and the wall of the housing of centre section 76. The fuel cell tubes 80 are short pipes with a length of 60 cm and a relatively large diameter of 2.5 cm. The shaping of the distribution chamber and collection chamber in combination with the relatively short fuel cell tubes 80 means that the pressure drop in the fuel cell 24 is low. The direction of flow of the various reactants and reaction products is indicated by arrows. At the top partition, there is a fixed seal between the fuel tubes 80 and the partition 78, while at the bottom partition there is a movable seal in the form of a labyrinth.

On account of the shaping of the fuel cell, the pressure drop across the fuel cell for the air ΔP-_.-_JJ. is comparable to the pressure drop ΔPi-_m across the line 20 which is normally used (cf. Fig. 1) .

Fig. 3 shows a series circuit of fuel cells in accordance with the invention. This is intended in particular for situations in which, as a result of a higher degree of utilization, a temperature rise occurs, which is disadvantageous for the materials used in the cells and the construction thereof. In the embodiment illustrated, the circuit comprises four fuel cells 24a to 24d, each with a basic configuration as explained above with reference to Fig. 2. The fuel cells 24 are arranged in a cylindrical housing 100, which at one end has a central air entry 102 for preheated air for the first fuel cell 24a, and a central outlet 104 for the outlet gas, which still contains a residual quantity of air. Preheated gas is fed via gas entry 106 to the first fuel cell 24a. The fuel outlet of the first cell 24a is in communication with the fuel inlet of the next cell 24b via intermediate line 108, etc. The flow of exhaust gas with a residual quantity of fuel is removed from the last fuel cell 24d via outlet 110. To cool the fuel cells 24, cold air is supplied via common feed line 112, and via corresponding side openings 114 to the second fuel cell 24b and subsequent fuel cells, the fresh cold air being mixed with the air discharge gas from the preceding fuel cell 24a. In a corresponding way, cold fuel is supplied via a common feed line 116 with side lines 118 to the second and subsequent fuel cells, where the fresh fuel is mixed with the fuel discharge gas from the preceding fuel cell. As a result of fresh cold air and fuel being supplied at the start of each subsequent stage of the series circuit, the gases will be cooled and the operating temperature can be controlled. In addition, the preheating devices can be made smaller, since a smaller quantity of air and fuel has to be heated.

Claims

1. Fuel cell (24) for the generation of energy, comprising a housing (70) with an inlet (72) for an oxygen-containing gas and an outlet (74) for depleted oxygen-containing gas, which are in communication with one another via a number of fuel cell tubes (80) arranged parallel to one another, which fuel cell tubes each comprise an anode and a cathode with an electrolyte arranged between them, as well as an inlet (89) for a gaseous fuel and an outlet (88) for depleted fuel gas, which are in communication with one another via a space (79) located around the fuel cell tubes, the housing (70) , adjacent to the inlet (72) , comprising a distribution chamber (82) for distributing incoming oxygen-containing gas to the fuel cell tubes (80) , which distribution chamber (82) has a larger maximum cross-sectional area, as seen in the direction of flow, than the inlet (72) , and also a collection chamber (84) for collecting depleted oxygen-containing gas at the end of the fuel cell tubes (80) , which collection chamber (80) has a larger maximum cross- sectional area, as seen in the direction of flow, than the outlet (74), the tubes (80), distribution chamber (82) and collection chamber (84) being shaped in such a manner that the pressure drop across the fuel cell (24) is virtually negligible.

2. Fuel cell according to claim 1, characterized in that the fuel cell tubes (80) have a length of less than 75 centimetres.

3. Fuel cell according to claim 2, characterized in that the fuel cell tubes (80) have a length in the range from 20 to 60 centimetres.

4. Fuel cell according to one of the preceding claims, characterized in that the housing (70) comprises a cylindrical centre section (76) with a constant diameter, the wall of the housing (70) which delimits the distribution chamber (82) comprising a gradual transition from the inlet (72) to the centre section (76) .

5. Fuel cell according to one of the preceding claims, characterized in that the housing (70) comprises a cylindrical centre section (76) of constant diameter, the wall of the housing (70) which delimits the collection chamber (84) comprising a gradual transition from the outlet (74) to the centre section (76) .

6. Fuel cell according to one of the preceding claims, characterized in that the electrolyte comprises a solid oxygen carrier.

7. Auxiliary device for improving the efficiency of an energy generation system, which device is provided with one or more fuel cells (24) according to one of the preceding claims, and the inlets

(72, 86) of a first fuel cell (24) are provided with a line (22, 38) with coupling (26, 40) for coupling to a corresponding line of the energy generation system, and the outlets (74, 88) of a last fuel cell (24) are provided with a line (52, 54) with coupling (58) for coupling to an associated line (14) of the energy generation system or system itself.

8. Auxiliary device according to claim 7, characterized in that the inlet lines (22, 38) are provided with preheating devices (32, 36), preferably in-line combustion devices.

9. Auxiliary device according to claim 7 or 8, characterized in that the device comprises a plurality of fuel cells (24a-24d) according to one of the preceding claims 1-6 connected in series, the outlets (74, 88) of a fuel cell (24a) being in communication with the inlets (72, 86) of an adjacent, downstream fuel cell (24b), the second and subsequent fuel cells (24b-24d) also being provided with inlets (112, 114; 116, 118) for the introduction of cold oxygen- containing gas and cold fuel.

10. Auxiliary device according to claim 9, characterized in that the auxiliary device comprises a common feed line (112) for cold oxygen-containing gas, which is provided with side lines (114) leading to the second and subsequent fuel cells (24b-24d) .

11. Auxiliary device according to claim 9 or 10, characterized in that the auxiliary device comprises a common feed line (116) for cold fuel, which is provided with side lines (118) leading to the second and subsequent fuel cells (24b-24d) .

12. Energy generation installation provided with an auxiliary device according to one of the preceding claims 7-11.

13. Energy generation installation according to claim 12, characterized in that the installation comprises a compressor (18) for compressing oxygen-containing gas, the outlet (20) of which is connected to the inlet line (38) for oxygen-containing gas of a fuel cell (24) of the auxiliary device.

14. Energy generation installation according to claim 12 or 13, characterized in that the inlet lines (22, 38) of the auxiliary device are coupled, as side lines, to the corresponding lines (14, 20) of the energy generation installation.

15. Energy generation installation according to one of claims 12- 14, characterized in that the energy generation installation is a gas turbine.

16. Energy generation installation according to one of claims 12- 14, characterized in that the energy generation installation is a combustion boiler.