DK144257B - POWER PLANT WITH ONE OR MORE FUEL CELLS UNDER PRESSURE - Google Patents

Description

(19) DENMARK (X ^ @ (12) PUBLICATION NOTICE 11 + 4257 6

DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No. 416/76 (51) IntCI.3 H 01 H 8/04 (22) Filing date Feb 2 1976 (24) Running day Feb 2 1976 (41) Aim. available 15 Aug 1976 (44) Submitted 25 · Jan * 1982 (86) International Application No. - (86) International Filing Day - (85) Continuation Day - (62) Master Application No. -

(30) Priority Feb 12 1975 * 549598 * US Feb 12 1975, 54961c *; JS Feb 12 1975 * 549601, US

(71) Applicant UNITED TECHNOLOGIES CORPORATION * Hartford * US.

(72) Inventor Michael Bernard Landau * US: Ronald _Cohen * US: David

Peter Bloomfield * US.

(74) Solicitor Larsen & Birkeholm Patent Office.

(54) Power plants with one or more fuel cells under pressure.

The invention relates to a power plant for generating electricity consisting of a fuel cell stack having a plurality of fuel cells electrically connected in series through a load, each cell consisting of a cathode, anode and a here-OQ between arranged electrolyte and a cathode gas compartment and anode gas space. on the side facing away from the electrolyte, respectively.

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C \] show the cathode and anode, the fuel used contains J-J- *

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2 144257 hydrogen, a fuel treatment unit which includes means for producing steam, a steam decomposition reactor and a reactor burner for producing heat for said decomposition reactor, means for supplying untreated fuel under pressure and steam under pressure to said reactor.

In the field of fuel cell technology, efforts have been made to improve cell performance by searching forwards along three different paths.

The first path involves raising the fuel cell operating temperature 10. However, this resort is limited by material degradation and - if an acid is used as an electrolyte - by evaporation of the acid. The second way involves seeking to increase the amount of catalyst per liter. square centimeters of the surface area of the electrodes. However, this resort is limited by the increased cost and practical limits of how much catalyst can be applied in any way to a particular electrode area. A third way involves increasing the pressure of the reaction participants (hereinafter referred to as the "reactants") within the fuel cell. It is well known that fuel cell performance 20 increases as reactant pressures increase. A major stumbling block on this path is that a considerable amount of energy is required to put the reactants under pressure. For example, it was envisaged that the energy to pressurize the reactants should be constituted by the electrical energy generated by the fuel cell which would be used to operate a compressor. The problem, however, is that about 30% of the electrical output of the cell stack is required to operate a compressor if it is to produce a reactant pressure of a reasonable size. This means that the fuel cell would need to be made approximately 50% larger to offset the loss of available electrical power. Since it is the fuel cell itself that is the most expensive part of a fuel cell power plant, the increased performance will be outweighed by the increased costs due to the cells being larger. As the total electrical output power of the cell stack 35 becomes larger, other parts of the power plant must be proportionally increased, such as the condensation equipment and the fuel treatment unit. In this way, the power plant becomes larger and 144257 3 more expensive. Furthermore, there are other apparent disadvantages of high-pressure reactant power plants, such as the cost of the auxiliary equipment to pressurize the reactants, the need for more expensive sealing devices, and the additional cost of using larger-strength parts for to withstand the higher pressures. In view of the above considerations and in the case of power plants using air as the oxidizing agent, the perception has always been that no net improvement could be achieved, but probably the opposite, when switching to power plants using reactants under high pressure in the fuel cell stack. For the above reasons, so far only reactants have been used at atmospheric pressure in these fuel cell power plants.

It is an object of the invention to provide the design of an economically advantageous fuel cell power plant using pressurized reactants, which plant has a higher efficiency than heretofore, and which, compared with prior art plants of the same kind and the same maximum performance, has a smaller size 20 and lower overall costs for the equipment included in the plant.

This object is accomplished by means of a compressor operably connected to a turbine adapted to be driven by the energy of a hot gaseous medium for compressing air to a pressure higher than two atmospheres. for supplying compressed air from the compressor into the cathode gas compartment, means for supplying pressurized fuel from the vapor decomposition reactor into the anode gas compartment, means for delivering at least a portion of the gases from the anode gas compartment into the reactor burner, and means for conducting waste energy , which is produced by the power plant, into the turbine in the form of a hot gaseous medium under pressure to operate the turbine. As a result, the size of the condensation equipment is reduced in relation to known equipment. Furthermore, it is achieved that no electrical output of the cell must be applied to the compressor, so it is not necessary to make the fuel cell stack 144257 4 larger to maintain the same maximum output in the power plant. On the contrary, the improvement in the performance of the fuel cell stack can be benefited in such a way that the stack can produce more electrical energy without having to be increased.

The power plant according to claim 2 can be characterized in that the means for conveying waste energy produced in the power plant into the turbine include means for passing gases from the cathode gas space into the turbine. In this way, the waste energy from the cathode gas space is utilized.

The power plant according to claim 3 may be characterized in that the means for passing the exhaust gases from the cathode gas chamber into the turbine comprise a conduit for first passing the exhaust gases from the cathode gas space into the capacitor, a conduit for passing condensed water from the capacitor to a condenser. boiler, as well as a conduit for passing steam from the boiler into the vapor decomposition reactor. Hereby the waste energy is further utilized to heat the boiler water of the power plant.

The power plant according to claim 4 may be characterized in that it comprises a conduit for conveying a portion of the compressed air from the compressor into the reactor burner. This results in improved burner efficiency.

The power plant according to claim 5 may be characterized by means for conducting a portion of the compressed air from the compressor outside the cathode gas space, and auxiliary burner for supplying extra heat to the gases fed into the turbine, whereby the means for passing the exhaust gases into the turbine includes means for conveying said outside compressed air into the turbine. Hereby it is obtained that the heat content of the gases at the inlet to the turbine is the same at reduced output as at full output.

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The power plant according to claim 6 can be characterized in that the means for conducting compressed air outside the cathode gas space include a bypass branch and the auxiliary burner is located in this branch. This embodiment is advantageous in that it is simpler and more economical to allow combustion to take place in the diverting branch.

The power plant according to claim 7 may be characterized in that the means for passing the exhaust gas from the cathode gas space into the turbine include conduits for passing the exhaust gas from the anode gas space and / or exhaust gas from the reactor burner together with the cathode gas space exhaust gases prior to their delivery to the turbine. This embodiment is convenient where the burner has its own fuel supply.

15

The power plant according to claim 8 can be characterized in that the wires for connecting gases from the reactor burner with the cathode gas room exhaust gases are located on the downstream side of the capacitor. In this embodiment, only water 20 is condensed for use in the reactor from the exhaust gas from the cathode gas chamber.

The power plant according to claim 9 can be characterized in that the wires for connecting gases from the reactor burner with the cathode gas room gases are located on the upstream side of the capacitor. In this embodiment, it is not necessary to use special fuel in the burner.

The power plant according to claim 10 can be characterized in that the conduit for supplying steam to the vapor decomposition reactor is connected to conduits for passing at least part of the gases from the anode gas space into the vapor decomposition reactor. In this embodiment, little or no equipment is required to recover water from the anode gases. 1

The power plant according to claim 11 can be characterized in that the means for delivering hydrogen from the vapor decomposition reactor into the anode gas space include means for removing heat 6 to reduce the temperature of the gases to less than the temperature of said fuel cell stack. This results in cooling of the fuel cell stack.

The power plant according to claim 12 may be characterized in that the means for delivering fuel from the vapor decomposition reactor into the anode gas space include means for first feeding the fuel into an upstream monoxide reactor located on the upstream side of the anode gas compartment. Thereby, utilization of the heat in the 10 carbon monoxide component contained in the gas flow from the reactor is achieved.

The power plant according to claim 13 can be characterized in that the means for delivering fuel from the vapor decomposition reactor to the anode gas room include means for delivering fuel from the reactor into a selective oxidation reactor and that compressed air is fed through a compressor via a conduit. the selective oxidation reactor for the anode gas compartment. This provides an even better utilization of the bound heat energy in the carbon monoxide component in the gas flow from the reactor.

20

Finally, the power plant according to claim 14 may be characterized in that said steam generating means comprise means for delivering a cooling fluid through a cooling loop in heat exchange communication with the fuel cell stack and the boiler.

Hereby an advantageous embodiment is obtained.

As mentioned above, it is the idea in one of the embodiments of the power plant according to the invention that the pressure in the cathode air is increased by means of a compressor driven by a turbine (ie a turbocharger). The turbine is driven by exhaust gases, both from a burner belonging to a vapor decomposition reactor and from the fuel cell. While driving at reduced output, part of the compressed air coming from the turbocharger, which would otherwise have been introduced into the cathode gas compartment and in other parts of the power plant, is diverted outside the fuel cell and passed through the turbine along with the other exhaust gases in the power plant. During reduced performance driving, an auxiliary burner is used to heat the gases flowing into the turbine. In this way, the mass flow rate and heat content of the turbine's propellant gases are the same at reduced output as at full output, so that the compressor can be operated at the same speed, thereby delivering compressed air at the same high pressure at reduced output as at full output.

This feature of the invention makes it possible to run the fuel cell with reduced output with less air than at full output, while maintaining the pressure in this air at the same level as the pressure in the full-use air. This is necessary if the advantages of a high-pressure power plant are to be fully maintained while driving at reduced output, as will be explained in more detail in the description of preferred embodiments.

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BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail below with reference to the exemplary embodiment of power plants according to the invention, fig. 1 is a schematic representation of a first embodiment of a power plant with an alternate version plotted in broken line; FIG. Figure 2 is an axial section through a turbocharger that can be used in a power plant according to the invention; 3> 4-, 5 schematically show further exemplary embodiments of the power plant; FIG. 6 shows fuel curves for fuel cells used in power plants according to the invention; FIG. 7 shows working curves for a vapor decomposition reactor used in power plants according to the invention, and FIG. 8 shows a working curve for a carbon monoxide reactor at various pressures.

As an exemplary embodiment of a plant according to the invention, one can take what is shown schematically in FIG. 1, The power plant is denoted as a unit by 10, and it comprises one as a whole with 12 designated fuel cell stack, one as a whole with 14 denoted compressor assembly, one as a whole with 16 denoted fuel processing unit, a capacitor 18, a boiler 20, a regenerator 22 and an air flow divider or air control box 25. The fuel cell stack 12 may comprise fuel cells of any conventional kind working with gaseous reaction participants (hereinafter referred to as "reactants"). In this example, the oxidizing agent is made up of air and the fuel is hydrogen, but this is only one example and other oxidizing agents and other fuels can be used. The stack 12 will normally comprise a plurality of fuel cells electrically connected through a load, but for the sake of clarity, the stack is shown here as consisting of only a single cell 13, and it also comprises a heat transfer portion 15. Each such cell shown comprises a cathode 24 , spaced apart from anode 26, and an electrolyte support 28 disposed between these parts. X This preferred embodiment is the electrolyte of liquid phosphoric acid, but it is not intended that the invention be limited thereto, since in a power plant according to the invention, both acidic and basic electrolytes as well as solid electrolytes, such as e.g. metal oxide electrolytes or solid polymer electrolytes. The electrodes 24 and 26 are connected in series through a load 29. Each cell 15 also includes a cathode gas compartment 30 on the away side of the electrolyte 24 and an anode gas compartment 52 on the away side of the electrolyte 26. In this embodiment, the fuel processing assembly 16 comprises a steam reforming reactor 34 and a reactor burner 36. The compressor assembly 14 is constituted by a turbocharger comprising a compressor 38 driven by a shaft 39 by a gas turbine. 40. Like the other parts of the power plant 10, the compressor assembly 14 is described in more detail below.

Referring to FIG. 1, it can be seen that during operation, air enters compressor 38 through an air intake line 41 and is compressed. Any pressure higher than atmospheric pressure will bring certain advantages over "pressureless" power plants; however, a pressure of two atmospheres or more is desirable in order to obtain significant benefits for the total power plant. This compressed air enters the air control box 25 through a conduit 43. The air control box 25 comprises control means and valves for properly distributing the air flow to the various parts of the plant. A portion of the air stream is passed through a charge 42 to the cathode gas compartment 30 and caused to react electrochemically within the cathode 24 with the phosphoric acid electrolyte in the carrier mass 28 to generate electricity and water, some of the water evaporating back to the air flow flowing through the cathode gas compartment 30. The moist and hot exhaust gas from the cathode leaves the cathode gas compartment 30 through a gas conduit 44 and passes through the regenerator 22 and thence to the capacitor 18. Cooling air enters the condenser 18 through a cooling air conduit 46 and leaves it in a heated state through another cooling air conduit 48. in the capacitor 18, the exhaust gas is cooled to the point where the water is condensed and collected for use in the fuel treatment assembly 16, as will be discussed below. The relatively cool cathode exhaust leaves the capacitor 18 through a conduit 50 and flows back through the regenerator 22, wherein the exhaust gas regains some of its lost heat. The reheated cathode exhaust leaves the regenerator 22 and is combined with the flow of anode exhaust and the exhaust gas flow from the reactor burner 36. It then flows through a conduit 52 into the turbine 4o, which receives power and thereby drives the compressor 58. If necessary, an auxiliary burner with its own fuel supply may not be used to increase the energy of the combined gas stream before it enters turbine 40. After the gas has passed through turbine 40, any additional energy in the gas stream can be either discarded through a conduit. 58 or used elsewhere in the power plant.

On the anode side, a hydrogen-containing liquid, e.g. naphtha, whose pressure by a pump 60 has been increased to about the same as the pressure in the air flowing into the cathode gas compartment 50, at a mixing site 61 mixed with water vapor from the boiler 20 and enters the vapor decomposition reactor 54 through a conduit 62.

Although not shown, it is preferred that the fuel be atomized as it is brought along with the water vapor in the mixing site 61 so that the flow introduced into the reactor 54 is in the vapor state.

If desired, the boiler 20 may be equipped with its own burner and fuel supply, but as can be seen from the illustrated embodiment, the boiler 20 is operated with waste heat generated in the fuel cell stack 12. In the embodiment shown, a refrigerant such as e.g. . a silicone oil, into the heat transfer portion 15 of the stack 12 through a conduit 64, absorbs heat generated in the stack 12 and flows out again through a conduit 66. Water from the capacitor 18 is introduced into the boiler 20 through a conduit 67. the boiler 20 and delivers its heat to the boiler water so that water vapor is formed. The cooling fluid exits the boiler 20 and flows into a cooler ("radiator") 68, in which additional heat can be released before the cooling fluid is pumped back to the stack 12 by means of a pump 69.

Process-treated fuel in the form of hydrogen gas and possibly some impurities leaves the vapor decomposition reactor 54- through a conduit 70, whereupon the fuel enters the anode gas compartment 52 of the fuel cell 15 where it reacts electrochemically with the electrolyte. In this embodiment, the idea is that the anode gas stream should have about the same pressure as the cathode gas stream in order to reduce the risk of gas flowing from the anode gas chamber to the cathode gas chamber or vice versa. The flow of anode exhaust leaves the anode gas compartment 32 through a conduit 72 and is passed along with the cathode exhaust stream at a mixing location 75 and together with the burner exhaust gas at a mixing location 74, whereupon the mixture flows into the turbine 40 and drives the compressor 38 as discussed above.

In this embodiment, the burner 36 of the vapor decomposition reactor has its own supply of fuel which is supplied to the burner through a conduit 75 and combined with compressed air from the air control box 25 which flows into the burner through a conduit 76.

The air and fuel burn in the burner 36 and generate heat to the reactor 34-. Then the burner of gas is fed through a conduit 77 to the mixing site 7 ^ where it is combined with the exhaust gas streams from the anode and cathode.

The important feature of the invention is that the waste energy generated by the power plant is used to drive the compressor, which in turn compresses the air or oxidizing agent used in the fuel cells. Most of this energy comes in the form of pressurized hot gases coming from the various parts of the power plant and supplied to a turbine which in turn drives the compressor. Of course, it is advantageous to utilize as much as possible of what would otherwise be waste energy, in order to obtain the greatest possible advantages of the invention. However, advantages over the prior art can be obtained, even if only the exhaust gas from the cathode gas compartment was used as hot compressed gas to power the turbine. In that case, the gases from the reactor mixer and from the anode gas compartment would not be fed to the turbine, but instead either be released to the atmosphere or their energy content could be used for other purposes. For example, the waste energy from the burner could be used to superheat the boiler water vapor before flowing into the reactor. If it were really such that only the exhaust gas from the cathode gas room was used to power the turbine, it would be more likely that a (not shown) auxiliary burner with its own fuel supply could be needed to further increase the cathode gas flow energy just before this gas flows in in the turbine. Also, if the burner exhaust is not to be used to operate the turbine, it should be preferred to use a low pressure burner, thereby eliminating the need to compress the combustion air to the burner. If, in that case, the anode exhaust were nevertheless to be used to supply the burner with fuel, it would be necessary to lower its pressure to the atmospheric pressure after leaving the fuel cell and before entering the burner, e.g. by means of a thruster.

In the embodiment of FIG. 1 as well as in the preferred embodiment shown in FIG. 3 and 5, preferred embodiments to be described in more detail below, the energy from both the anode exhaust, the cathode exhaust and the burner exhaust are used together to drive the turbine to compress the oxidant.

Although the water to the reactor 34- in this embodiment is supplied by condensing water from the cathode exhaust stream, it may occur that the power plant is located near a water supply in the form of e.g. a river, a lake or a large water reservoir. If so, it will be possible to omit the condensing equipment and to supply water to the reactor from one of these other sources. In that case, the need for the regenerator 22 would also lapse.

Although the fuel processing assembly of the embodiment shown in FIG. 1 only comprises a vapor decomposition reactor and a reactor burner, it is contemplated that the fuel treatment unit in power plants according to the invention may comprise other parts such as e.g. a shift converter and / or a selective oxidation reactor. What requirements. provided to the fuel processing equipment depends in part on the nature of the raw fuel used and on the particular design of the cells in the fuel cell stack. In fact, the fuel treatment assembly may comprise a partial oxidation hydrogen generator instead of a vapor decomposition reactor and a reactor burner. Ball of these other constituents are included in the FIG. 3 and 4 illustrate examples of power plants according to the invention.

Fig. 2 shows an example of a turbocharger suitable for use in a power plant designed in accordance with the invention. Ambient air flows in through a suction duct 200 and strikes a single-stage centrifugal compressor wheel 202 which communicates the air with moving energy or dynamic pressure. The air, which now has a high velocity, flows into a diffuser 204 in which the dynamic pressure is converted to static pressure. In the embodiment of FIG. 1, the air would leave the diffuser 204 through conduit 43 and, after passing through the air control box 25, would enter the cathode gas compartment 30 and the reactor burner 36. On the other hand, hot gases flow in through a turbine inlet 206 (e.g. Figure 1 shows conduit 52) and flows through a centrifugal turbine rotor 208 which converts the thermal energy of the gas stream into mechanical energy on a shaft 210 connected to the compressor wheel 202. The gases are ejected through a turbine outlet duct 212.

The FIG. 2 turbochargers are only an illustrative example of the type preferred for use in a power plant according to the invention. Any turbocharger available on the market may be used, the size of which is sufficient to provide the required flow rate and pressure for the fuel cell stack selected for the power plant concerned. In a power plant of e.g. 1200 kW, where it is desired that the reactor gases supplied to the fuel cell stack must have a pressure of about 3.5 atmospheres, a Brown Boveri type RR150 turbocharger may be suitable. This particular model is capable of generating a mass flow rate of up to

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1.36 kg / sec. at a pressure of 3.5 kg / cm. Although the term "turbocharger" usually brings the tank to a centrifugal compressor, as shown here, this term should also be considered to cover axial compressors. Centrifugal compressors are preferred as they have the advantage of having a high efficiency and high compression ratio in a single step, which is usually not the case for axial flow compressors. Furthermore, the purpose of the embodiment of FIG. 2 turbochargers include a centrifugal turbine - that turbochargers with axial flow turbines should be usable in power plants according to the invention.

Although in FIG. 2 is a typical example of what is known in the art as a "turbocharger", the invention is not intended to be limited thereto, but may include any machine in which the energy of a hot gas under pressure (usually exhaust gas) is used to compress another gas. For example, For example, any heat power machine capable of operating a compressor is capable of being operated by a flow of hot gas under pressure. A Comprex® pressure charger (registered trademark of Brown Boveri & Co. AG, Bade, Switzerland) may also be used in which air is compressed by direct transfer of energy from an expanding gas using compression and expansion waves, or a another machine that works on similar principles. The principle of the Comprex pressurized chargers is well known in the art and is more fully described in an ASME publication 58-GTP-16 entitled "The Comprex ____ A New Concept of Diesel Supercharging" by Max

Berchtold and E.J. Curtains, published in March 1958.

Another feature of this embodiment is that it is easier to maintain the same pressures in the anode and cathode gas compartments 30 and 32, respectively, since the gas streams from these compartments are joined at the mixing site 73 where they thus naturally have the same pressure. The pressure regulators usually needed for this purpose can thus be omitted.

An altered version of the hitherto mentioned in FIG. 1 is shown by means of the broken lines in FIG.

1. In this alternative embodiment, the exhaust gas from the anode gas compartment 32 to the burner 36 is passed through a conduit 100 rather than being directly combined with the cathode exhaust stream through conduit 72 at the mixing site 73 · The anode exhaust gas contains enough unburned hydrogen that it is not necessary to supply the burner. 36 with fuel through conduit 75- The burner 36 generates heat to the reactor 34. The burner exhaust, which in this version comprises the anode exhaust stream, passes through a heat exchanger or regenerator 101, where it is combined with the cathode exhaust stream at a mixing site 102 through a conduit 104 instead of being This device causes the water to be removed from both the cathode exhaust stream and the anode exhaust stream in the capacitor 18, which is advantageous as it is not certain that the cathode exhaust stream alone can provide enough water for the reactor 34. The combined gas streams leave the capacitor 18 , 15 U4257 recovers some of it lost heat in the regenerator 22 and then passed through the regenerator 101 so that its temperature is further increased by absorbing heat from the combined gas stream from the burner and the anode. Thereafter, the hot gas stream flows into the turbine 40 which drives the compressor 38. The function of the heat exchangers 101 will be explained in greater detail below when the operation of the capacitor 18 is explained in more detail.

FIG. 3 shows another embodiment of a power plant according to the invention. The reference numerals which are the same as in FIG. 1, refers to the same parts as in FIG. 1. This embodiment works in a similar manner to that of FIG. 1, but is somewhat more complicated as the fuel treatment unit 16 (cf. Fig. 1) has been equipped with a carbon monoxide reactor 105 and a selective oxidation reactor 106. In addition, the power plant has been equipped with four additional heat exchangers and a fuel boiler. In the carbon monoxide reactor 105, the carbon monoxide component is reduced in the gas stream leaving the reactor 34. In the carbon monoxide reactor 105, carbon monoxide reacts with water in the presence of a catalyst to form hydrogen, carbon dioxide and heat in accordance with the well-known reaction equation as follows: CO + H -S * + CO2 + heat (l) In the selective oxidation reactor 106, most of any residual carbon monoxide is reacted with oxygen in the presence of a catalyst to generate additional carbon dioxide and heat in accordance with the following reaction equation: CO + + heat (2)

The oxygen for the selective oxidation process is provided in the form of compressed air through the conduit 108 from the air control box 25. In this embodiment, the combined anode and cathode gas streams leaving the capacitor 18 are passed through heat exchangers in both the selective oxidation reactor and the carbon monoxide reactor. these parts generated additional heat that could otherwise be wasted.

Although in this embodiment the fuel treatment assembly is shown as comprising a vapor decomposition reactor, a reactor burner 16 m 257 there, one. carbon monoxide reactor and a selective oxidation reactor, the fuel treatment equipment of a power plant according to the invention may contain other constituents, requirements which are made to the fuel treatment equipment, depend in part on the nature of the raw fuel used and the particular design of the fuel cells included in the stack 12. For example, the fuel treatment assembly may include a partial oxidation hydrogen generator instead of a vapor decomposition reactor and a reactor burner.

In this embodiment, waste energy is transferred from the fuel treatment assembly to the turbine 40 by introducing the reactor burner exhaust gases into the turbine. If the power plant did not include a vapor decomposition reactor and therefore no reactor burner, other means would have to be provided to transfer waste energy from the fuel treatment unit to the turbine, such as the turbine. a heat exchanger which is in working communication with the fuel treatment unit and with any other gas stream introduced into the turbine.

In the FIG. 1, the steam leaves the boiler 20 and is fed directly to the reactor 34- after receiving fuel from line 62. In the embodiment shown in FIG. 3, the steam passes through three heat exchangers before entering reactor 34-. The steam first passes through a heat exchanger 116 in which it is superheated by heat from the gas stream leaving the carbon monoxide reactor 105. Then the steam takes up crude fuel at the mixing site 114- and additional heat in a heat exchanger 118 from compressed air (i.e., the compression heat) which flows through the heat exchanger 118 from line 76. The fuel and superheated steam then pass through yet another heat exchanger 120, thereby increasing the temperature of the gas stream to what is appropriate for the vapor decomposition reaction in the reactor 34, i.e. about 558 ° C. From the reactor 34- the partially process fuel is returned through the heat exchanger 120, where a large part of its heat is returned.

The only feature of this embodiment which differs from that of FIG. 1, the heat exchanger is 122. The anode exhaust gas passes through the heat exchanger 122 via the conduit 100 and is heated therein before it is introduced into the burner 36. The burner 36 generates heat for the vapor decomposition reaction in the reactor 34 and the burner gases comprising the anode exhaust gas stream , are cooled before arriving at capacitor 18 by passing them through heat exchangers 101 and 122 to reduce the load of capacitor 18, as will be discussed below.

A third embodiment of a power plant according to the invention is shown schematically in FIG. 4. The parts which fully correspond to parts in the above-described embodiments are denoted by the same reference numerals. However, the fuel cell stack has been assigned a new reference number, namely 300, since it - for reasons to be explained in more detail below - does not include a heat transfer part. The cell itself now carries the reference numeral 302 and comprises a cathode 304, an anode 306, anode gas compartment 308, a cathode gas compartment 310, and an electrolyte 312.

It should be noted that this embodiment is similar to that of FIG. 3, where exhaust gases from the anode gas compartment 308 are fed to the reactor burner 36 together with air from the compressor 38. In addition, the exhaust gases from the reactor burner 36 are combined with the exhaust gases from the cathode gas compartment 310 and then fed into the turbine 40 to drive the compressor 38.

And. An important difference between this embodiment and the other exemplary embodiments of power plants according to the invention consists in that the steam to the vapor decomposition reactor is produced directly from the anode exhaust without the need for water recovery equipment. In the embodiment of FIG. 4, the exhaust gases including vapor (i.e. water) generated in the cells will leave the anode gas space 308 through a conduit 314 and then pass through a distribution valve 316. The distribution valve 316 conducts a portion of the gases to the reactor burner 36 through a conduit 318 and a second portion to the vapor decomposition reactor 34- through a conduit 320.

This latter portion, comprising steam, is mixed in the reactor 34 with non-processed fuel under pressure, which is fed to the reactor 34 through a conduit 322. Partial process-treated fuel leaves the steam decomposition reactor 34 through a conduit 324, is cooled in a cooler 326 and fed to a carbon monoxide reactor ("change converter") 105 for further process processing. Process-treated fuel leaves the carbon monoxide reactor 105 and passes through a conduit 330 to a further cooler 328, wherein the gases are further cooled before being introduced into the anode gas compartment 308 through a conduit 332.

This embodiment also includes heat exchangers 334 and $ 33 for transferring heat from the turbine exhaust stream to the fuel gas flowing into the reactor burner 36 or the compressed air stream introduced into the reactor burner, respectively. A further heat exchanger 340 is arranged to heat the gas entering the reactor 34. It should be appreciated that the use and arrangement of heat exchangers can change from one power plant to the next depending on the components used in that power plant and the devices and needs that apply in each case. The FIG. 4, the arrangement of the heat exchangers is not intended to limit the scope of the invention, but is shown by way of example only.

In addition to providing steam for the reactor 34, the recirculated or recycled anode exhaust gas stream is used to cool the fuel cell stack 300. This is achieved by cooling the gas entering the anode gas compartment 308 to a temperature substantially lower than the temperature to be maintained in the stack. The final cooling of the gas takes place in the cooler 328 and is controlled by controlling the amount of cooling air passing into the cooler 328 through a cooling air line 341. A sufficient flow of cooling gases through the anode gas chamber is ensured by a pump 342. The gas stream is also cooled by means of the heat exchanger 340 and the cooler 326. The cooler 326 cools the gas entering the carbon monoxide reactor 105, this reactor being in this embodiment being of a kind adapted to operate at low temperatures. The reaction in the carbon monoxide reactor is exothermic and therefore raises the temperature of the gas stream as it passes through the reactor, making it necessary to use the second cooler 328. One purpose of the heat exchanger 340 is - in addition to cooling it flowing from the reactor 34 144257 19 - heating the gases flowing into the reactor 34, as already mentioned. In fact, it is sufficient to use any combination of heat exchangers to heat or cool the gases flowing into and out of the reactor, respectively, provided that a substantial part of the heat in the reactor exhaust is not wasted.

As mentioned above, it is necessary that a sufficient amount of steam is introduced into the reactor 34 in the exhaust gas from the anode gas chamber. To ensure a sufficient vapor volume, the mass flow rate through the anode gas chamber is maintained by the pump 34-2. The required flow rate through the anode gas compartment, as well as the required and controlled distribution between the reactor burner and the reactor itself, is determined by the pressure of the gases, the required reactor efficiency, and the amount of fuel required in the reactor burner to generate the sufficient heat to drive the vapor decomposition level. .

In the FIG. 1, 3 and 5 of the embodiment of the power plant according to the invention, the steam supplied to the reactor 34 is generated from a boiler located in the refrigerant circuit of the fuel cell stack. The pressure in the gases entering the anode gas chamber is limited by the pressure in the vapor, which is mixed with the fuel. The pressure in the steam developed in the boiler depends on the temperature of the refrigerant within the refrigerant circuit, which in turn is limited by the temperature of the stack. For example, if the temperature of a phosphoric acid cell is limited due to corrosion problems, the vapor pressure is accordingly limited. The FIG. The embodiment shown in Figure 4 is not subject to this limitation, although a phosphoric acid electrolyte can be used in the cell. The reason is that the steam evaporates into the anode gas compartment 308, regardless of the total pressure in that gas compartment, instead of the steam developing in a boiler which is driven by waste heat from the stack. Continuity requires removing water from the cell. The water must represent a certain mole fraction of the gas streams flowing from the cell stack. Since the vapor pressure is simply the total pressure times the mole fraction of water, the continuity requires that if the total pressure increases, then the vapor pressure must be increased. For this reason, at a certain stack temperature, the electrolyte becomes more diluted as the total pressure rises and the vapor pressure of the water above the electrolyte increases. Thus, if desired, it is possible to use much higher reactant gas pressure, which is a particular advantage of this embodiment.

Pig. 5 shows another embodiment of a power plant according to the invention. The reference numerals which are the same as in FIG. 1, refers to the same parts as in FIG. 1. Although this exemplary embodiment has many things in common with the previous embodiments, it includes some features which have not yet been described but which could easily be added to those of FIG. 1 and 3, if desired. One of these features consists in an improved device of the condensing equipment, which device is only possible in the pressurized power plant according to the invention. The second feature consists of the addition of equipment which enables the power plant to be operated at reduced capacity without losing the benefits of operating the system at full capacity. Both of these features are described in more detail below.

The FIG. 3 power plant thus comprises one as a whole with 12 designated fuel cell stack, one as a whole with 14 designated compressor assembly, one as a whole with 16 designated fuel treatment unit, an auxiliary burner 17, capacitors 18 and 19, a boiler 20, a cooler 68 and an air flow divider or air control box. 25. In this embodiment - as in FIG. 1, the fuel treatment assembly 16 comprises only a vapor decomposition reactor 34- with associated reactor burner 36, although it is not intended to limit the scope of the invention thereto. With the exception of the auxiliary burner 17 and the capacitor 19, all of the above-mentioned parts are in the FIG. 1.

During the operation of the device shown in FIG. 5, the air enters compressor 38 through the air intake line 4-1, whereupon it is compressed. This compressed air flows through a bypass control valve 27 on its way to the air control box 25. It is now assumed for a moment that the bypass control valve 27 is set to direct all air from the compressor 38 to the air control box 23 j U42.57 21 whatever. this will be the case when the power plant is running at full capacity. The air control box 25 contains control means and valves for proper distribution of the air flow to the various parts of the system, as is also the case with the other embodiments described above. Part of the air is fed into cathode gas space 30 through a conduit 42 and to the burner 36 through a conduit 76. Humid and hot cathode exhaust gas leaves the cathode gas compartment 30 through a gas conduit 44 and flows into the capacitor 18. Inside the capacitor 18, the cathode exhaust gas is cooled to a temperature at which condensed water is collected for use in the fuel treatment assembly 16, as will be explained below.The cathode exhaust leaves the capacitor 18 through a conduit 50 and mixes at a mixing location 51 Heat of the gas stream from the reactor burner 36 and passes with it into the turbine 40 so that it is energized to drive the compressor 38. Although not shown in this embodiment, the power plant may contain a regenerator similar to the regenerator 22 shown in Fig. 1 through which the cathode exhaust could pass through. it flowed into and after it flowed out of capacitor 18, as it does in the embodiment shown in Figure 1. ørelseseksempel.

On the anode side, pressurized fuel is mixed with pressurized steam at the mixing site 61 and flows into the vapor decomposition reactor 34- · The process-treated fuel leaves the vapor decomposition reactor 34- through a conduit 70, whereupon it flows into the anode gas compartment 32. The anode gas stream has about the same pressure as 'the cathode gas flow, thereby reducing the risk of gas flowing from the anode gas chamber to the cathode gas chamber or vice versa. The exhaust gas from the anode gas compartment 32 is fed into the capacitor 19 and from it to the burner 36. The anode exhaust gas contains a sufficient amount of unburnt hydrogen that no separate fuel supply is needed for the burner 36. The burner 36 'generates heat for the reactor 34-. The burner exhaust comprising the anode gas stream is combined at the mixing site 51 with the cathode exhaust stream, as discussed above, whereupon it flows into the turbine 40.

22 UA 257

In this embodiment, although the gas from the anode gas compartment is shown to flow into the burner 36, the fuel of which it constitutes, it may in some cases be more desirable not to pass the anode exhaust gas to the burner, but instead combine it directly with the gas flowing in line 50 from the cat-degas room. In that case, it would be necessary to equip the burner with its own fuel supply.

It is now assumed that one wants to run the power plant with reduced performance. During reduced performance operation, fuel cells need less fuel and less air, and they will also generate less water. Therefore, if the mass flow rate of air through the cathode gas chamber is not reduced by reduced output, then - as the cell produces less water - the partial pressure of the water in the cathode gas stream will be substantially lower than at full output. This is highly undesirable as very low partial vapor pressures in the e.g. Cathode exhaust flowing through the capacitor 18 makes it difficult to condense the water required for the reactor, or a much larger capacitor must be used. In addition, the fuel cell stack produces less heat at reduced output than at full output, and - as too much air flows through the stack at reduced output - the stack can be cooled too much so that it operates at a temperature below the optimum. In this case, an auxiliary burner may be required to heat the cell stack to a temperature where it operates efficiently, but this results in a low efficiency and is uneconomical.

Detailed considerations regarding the benefits of using pressurized reactants in all parts of the power plant must be set forth below; however, if these benefits are to be fully maintained during reduced-performance driving, it is necessary that the fuel cell reactants be maintained at the same high pressure during reduced-performance driving as during full-service driving. At the same time, it is also necessary to decrease the mass flow rate of the air through the cathode gas compartment of the fuel cells in order to avoid the problems mentioned in the preceding paragraphs. In the embodiment shown in FIG. 5, the geometry of the turbocharger is unchangeable, and therefore cannot provide the same high compressor pressure when the mass flow rate through the turbine is reduced while driving at reduced output, nor if the temperature of the turbine propellants is lower at reduced output, if the turbocharger Id, designed to be variable in geometry, is capable of delivering compressed air at the same pressure while driving at reduced output as when operating at full output, the mass flow rate through turbine 40 and the temperature of the gases flowing through should be approximately the same. reduced performance as with full-service driving. Any decrease in the energy in the gases flowing in turbine 40 would cause it to run slower, and as a result, both the air pressure and the mass flow of the air supplied by the compressor 38 will decrease.

It would be conceivable that this problem could be solved by introducing the excess air (supplied by the turbocharger when running at reduced output) into the reactor burner 36 via the air control box 23. However, the stack 12 consumes less fuel at reduced output and thus there is less unburned fuel in the exhaust gas flowing from the anode gas compartment to the burner 36. Of course, less heat is required from the burner 36 when driving at reduced output, and therefore less air is also required for the burner 36 from the air control box 25. If the excess air supplied by the compressor 38 pass through burner 36, it must heat all this air to keep the burner temperature at the required level. This would require extra fuel for the burner and lead to very low efficiencies.

All of the above problems are avoided by the one shown in FIG. 5. The bypass control valve 27 is adapted to respond to the electric current produced by the fuel cell.

At full output, all air from the compressor 38 is directed to the air control box 25. As the output diminishes, the valve · 27 opens and thereby directs a portion of the air around the stack through the diverting branch 400. This diverted air is combined with the exhaust gas from the burner 36 at a mixing location 402 and with the exhaust gas from the cathode gas compartment 30 at the mixing site 51 and flowing through the turbine 40.

24 U4Z57

Although the temperature of the gas from the cathode gas compartment and the temperature of the gas from the burner 36 may be the same at reduced output as at full output, these gases due to their reduced mass will contain less heat. An auxiliary burner 17 is disposed in the diverting branch 4-00 and heats the diverted air to a sufficiently high temperature that when combined with the other exhaust streams, the combined heat (and mass) content of the combined stream will be approximately the same. as in full performance. If no auxiliary aperture 17 was found, the diverted air would lower the temperature of the gas flowing into the turbine 4-0, which in turn would cause the turbine 4-0 to run slower, so that the mass flow rate and pressure in it from the compressor 38 outflowing air would be diminished. The auxiliary burner 17 is supplied with fuel through a line 4-04- from the same source as the fuel for the reactor 34 ·. The fuel flow to the auxiliary burner 17 is controlled by a fuel valve 4-06, which may be adapted to depend on any of a number of the plant's process variables in order to obtain the correct temperature in the gases flowing in the turbine 4-0.

If desired, the auxiliary burner could be located anywhere from the diverting branch 4-00 provided that the diverted air flows through it on its way to the turbine 4-0. The auxiliary burner can e.g. be placed in line 4-08, as indicated at 4-10 by a "box" in the dash. However, an auxiliary burner located in conduit 4-08 would receive oxygen at a more dilute concentration than a burner 4-00 burner, since the bypass air has now been mixed with various gases which generally lack oxygen. Thus, it is much easier and more economical to allow the combustion to take place in the diverting branch 4-00. In this embodiment, although the auxiliary burner burns crude fuel, it could also be feasible to burn the process-treated fuel which could then be removed from line 70. However, this could make it necessary to supply the reactor 34- additional fuel to offset that of the auxiliary burner. spent fuel.

144257 25

In order that the advantages and operation of the power plant according to the invention can be fully understood, reference is made to the curves in FIG. 6, which compares the working performance of a fuel cell in which the reactants have atmospheric pressure with the working performance of the same cell when the reactants have a total pressure of e.g. ca. 3> 5 atmospheres, here are several process variables to consider when comparing cells. The rate of reactant utilization is the ratio of, on the one hand, the mass flow rate of the reactants at either the anode or cathode consumed in the cell during the electrochemical reaction, and on the other (i.e., in the denominator of the fraction) the mass flow rate of the cell flowing hydrogen or oxygen. Thus, in a fuel cell that works with oxygen and hydrogen, there is oxygen utilization (Uq) at the cathode and hydrogen utilization (U an) at the anode, the Rer-like ^ reactant utilization is increased, the reactants' partial pressure towards the anode and cathode is automatically lowered. a larger amount of reactants is withdrawn from the gas stream per minute. unit mass flow through the cell; in this way, the average reactant amount in the gas flow across the electrode surface becomes smaller in the direction from the inlet towards the outlet, leg curve, as in FIG. 6 are marks "1.0 ATM", showing how the cell works with a particular hydrogen utilization and oxygen utilization. The fully drawn curve, labeled "3.5 ATM", corresponds to the mode of operation of the cell at the same reactant utilization fraction. It is also assumed that the cells to which each of these curves relate operate at the same temperature. According to the well-known Tafel equation, the cathode output (i.e. voltage) must increase as the oxygen partial pressure is increased. This equation is set out below.

Ahatode = K (mv) l0 «- C5) u0 (ref) where K is a constant. According to the Nernst equation, there must be an increase in the performance of the anode (i.e., an increase in cell voltage) when the hydrogen partial pressure is increased. The Nernst equation is given below.

Δ Voda = «" ί la -3- W

^^ (ref) 144257 26 where O is a constant. It will be appreciated that at a constant temperature and a constant rate of utilization, an increase in the total pressure of the reactants will result in an increase in the partial pressure of the reactants, leading to an improvement in performance, both at the cathode and at the anode. in the performance of the fuel cell can simply be shown as follows: ^^ total ~ '^ cathode + ^ anode equation 5's left side is graphically shown in FIG. 6 as the difference in voltage between points A and B at a constant current density. . From the curves of FIG. 6 it can further be seen that by working with a reactant pressure of 355 atmospheres, the cell can be made smaller without reducing the cell's output voltage, e.g. by working at point C.

The dashed curves of FIG. 6 also corresponds to cell performance at reactant pressures of 1.0 and 3 »5 atmospheres, respectively, as indicated by the mark. These curves correspond to the performance of cells which are in all ways similar to the cells corresponding to the fully drawn curves, with the one exception that the cells are arranged for a higher degree of reactant utilization.

It should be noted that at 3? 5 atmospheres, the cell can operate at a higher reactant utilization rate and yet show an improvement over the prior art, such as e.g. an increase in cell voltage by operating at point B 'or an increase in current density (i.e., a decrease in cell size). for the same cell voltage by working at point C1. On the other hand, it should be noted that in a cell in which the reactants have atmospheric pressure, an increase in the utilization rate will either mean that the cell must be made larger in order to maintain the same cell tension or that a lower voltage must be found for to maintain the same cell size. The importance of working with a higher degree of hydrogen utilization without sacrificing any of the performance or making the cell larger will be apparent from the considerations set forth below regarding the operation of the vapor decomposition reactor 3 in the preferred embodiment of a power plant according to the invention.

27 U62S7

With regard to improving the performance of the fuel cell, the one shown in FIG. 4 shows a particular mention in the invention. In this power plant, there is some recycling of carbon dioxide through the anode gas compartment. This causes the partial pressure in the hydrogen flowing into the anode gas chamber to be somewhat lower than in the other embodiments, as there is more carbon dioxide in the gas stream. According to the equation (3), this should lower the fuel cell's performance. However, the improvement in cell performance at the cathode as well as the other improvements and advantages of this embodiment, discussed above and hereinafter - such as e.g. the omission of the water recovery equipment - that this power plant will still be preferable for certain applications. Also, in this embodiment, there is no limitation of pressure due to the temperature of the fuel cell stack, higher reactant pressures can be used so that the partial pressure of the hydrogen entering the anode gas space becomes higher (instead of lower) than in the other embodiments, so that this Exemplary embodiment becomes even more preferable in these circumstances. In prior art fuel cells with phosphoric acid as electrolyte operating at temperatures above 14-9 ° C and at atmospheric pressure, the phosphoric acid electrolyte is evaporated. Due to this evaporation of the acid, it is necessary to regularly add additional acid during the life of the plant. The acid evaporation is a function of the mass flow rate of air through the cathode gas compartment, the partial pressure of the acid and the total gas pressure in the cathode gas compartment in accordance with the following equation: acid loss = ^ | flow rate x j (6)

From the above formula, it can be seen that an increase in the total pressure of the gases flowing through the cathode gas chamber reduces the acid loss. It is also a fact that an increase in the total pressure causes a decrease in the vapor pressure of the acid due to the dilution of the electrolyte, which further reduces the acid loss. Also, thanks to the higher reactant pressures, the fuel cells built into power plants according to the invention can be kept in operation with higher oxygen utilization rates, and therefore the mass flow rate of the air through the cathode gas space is lowered and the acid loss is further reduced. It has been found that the aforementioned factors in combination reduce the acid loss by a factor of the order of 10.

FIG. 7 shows working joints for a vapor decomposition reactor (Eng.

"steam reforming reactor"). The efficiency of the reactor 0} g) is plotted along the vertical axis, and the ratio of the mass flow rate (λ) of the process-treated gas stream to (in the denominator) the heat transfer area (A ^) of the reactor is plotted along the horizontal axis. Since the joint A ^ is directly proportional to the size of the reactor, it means that the reactor becomes smaller as you go right along the horizontal axis. The efficiency of the reactor is defined by the following equation: TR = (K) υΗ2 (Λ * Ιϊ) (7) where K is a constant, Ug is the hydrogen utilization rate in the fuel cell, and the product) is the fuel conversion in the reactor, expressed as the percentage of carbon in it. added fuel which is converted into CC ^. It is an expression of the amount of hydrogen generated by the vapor decomposition reaction. In FIG. 7, fuel conversion curves of 90 and 75% are shown together with a hydrogen utilization curve labeled Ug and a hydrogen utilization curve labeled U'-p. , of which the latter ^ corresponds to a higher degree of hydro ά2 reuse. For the sake of comparison, it is assumed that Ug is the same hydrogen utilization rate corresponding to the fully drawn curves of FIG. 6, and that Ut is the hydrogen utilized IXp. degree corresponding to the dashed curves of FIG. 6. As discussed with reference to FIG. 6, fuel cells using atmospheric reactants were bound or restricted to operate at a certain degree of hydrogen utilization Ug to thereby obtain a certain cell voltage for a specific cell size (i.e., at work, for example, at point A). Thus, after a certain degree of hydrogen utilization has been selected, it is required that the working point of the vapor decomposition reactor should lie somewhere on the hydrogen utilization curve labeled Ug. Thus, it is important to select the best combination of Reactor efficiency and reactor size for that cell. In the prior art reactors, the fuel conversion is generally about 90% in order to keep the size of the reactor within reasonable limits. Hereby, the working point of a vapor decomposition reactor used in conjunction with a fuel cell of the prior art would be at point D.

It will now be clearly understood why it is so important that it is possible to keep the fuel cell in operation with a higher degree of hydrogen utilization. Eg. it is possible to work along the curve 11 'with a power plant according to the invention. - tip

Hereby, a smaller size steam decomposition reactor can be used without sacrificing any of the efficiency, since the reactor can now be run with a lower fuel conversion. The corresponding operating point is marked E in FIG. 7 · If preferred, it is of course possible to maintain the same reactor size and achieve a great improvement in reactor efficiency, e.g. by working at point F. It is important to note that although the performance of the fuel cell diminishes somewhat when operating at higher utilization rates (cf. Fig. 6), the whole picture of the cell's performance is nevertheless significantly improved, and furthermore significant improvements can be achieved in the vapor decomposition reactor. This is in contrast to previous power plants, where - although a higher degree of reactant utilization in the fuel cell could bring benefits in the vapor decomposition reactor - the benefits are outweighed by the detrimental effect on fuel cell performance.

Of course, when it comes to designing and calculating a power plant according to the invention, it will be necessary to "switch off" between, on the one hand, seeking improvements in reactor performance and, on the other, seeking improvements in fuel cell performance. Thus, the reactant utilization rate, cell size, cell output voltage, reactor size, reactor efficiency, and reactor fuel conversion coefficient are selected depending on the targets being targeted by the power plant concerned.

In the preferred embodiment, it is intended to use naphtha as fuel and for the vapor decomposition reactor 34- to be of the well known kind in which a nickel catalyst is used.

However, any ordinary apparatus for producing hydrogen may be used as a reactor. For example, although the efficiency is less than that of a vapor decomposition reactor, a partial oxidation hydrogen generator can be used which will benefit significantly from the higher reactant gas pressures. In some cases, even the fuel processing unit may be omitted, e.g. if pure hydrogen is available as fuel for the fuel cell stack.

In power plants designed according to FIG. 1, 3 and 5? For example, capacitors that are significantly smaller than the capacitors of previous fuel cell power plants can be used. According to Faraday's law, the fuel cell produces a constant volume of water when the flow is constant. This water leaves the cell in the exhaust streams. It is known that the vapor decomposition reaction requires a certain amount of water, as in the prior art - similar to those in FIG.

1, 3 and 3 - at least partly recovered from the cathode gas stream. This water was removed from the cathode gas stream by a capacitor.

In previous fuel cell power plants, in which the electrolyte consists of phosphoric acid and where the gas stream is at atmospheric pressure, the dew point of the gas stream is so low that to condense a sufficient amount of water to keep the vapor decomposition reaction going, the gas stream temperature at the outlet of the condenser must be only a few degrees higher than the surrounding cooling air. As a result, very large capacitors are required. As previously discussed, the capacitors are the parts of prior art fuel cell power plants that occupy the most space. In power plants according to the invention in which overpressure prevails, the dew point of the gas flow flowing from the cathode gas space will be considerably higher than in the previous technique thanks to the higher pressure of the gas flow.

For example, the dew point of a gas stream leaving a fuel stack of 14-9 ° C with a pressure of 3> 2 kg / cm 2 would be about 34 ° C higher than the dew point of a gas stream leaving an IA-9 ° C - stack with atmosphere a jerk. This means that in order to condense the same amount of water, the temperature of the gas stream need not be brought down as far as in the "pressureless" plants. In other words, there will be a significant difference between the temperature of the condenser cooling air and the temperature of the gas leaving the condenser. Assuming that cooling air with a temperature of 144257 31 32 ° C is used both at power plants with and without overpressure, it is estimated that the capacitor can be reduced in size to about half or third. This reduction in size of the condensing equipment is one of the greatest advantages of the invention. and "contributes to making the power plant significantly cheaper".

Referring to FIG. Referring to the modified version or alternative embodiment mentioned in 1, the anode exhaust stream after passing through the burner 36 is combined with the cathode exhaust stream at the mixing site 102. This flow is very hot and contains a considerable amount of moisture bed. With regard to the work that the capacitor 18 is to perform, it is of course desirable that the temperature of the gas stream flowing into the capacitor 18 be as close to the dew point as possible. At the outlet of the fuel treatment assembly 16, the temperature of the anode exhaust stream may be about 671 ° C. From the capacitor's point of view, it would prohibit itself to combine these extremely hot gases with the cathode exhaust gas stream and direct them to the capacitor. Therefore, these gases are first passed through the regenerator 101, where they are cooled to about 260 ° C. They are then combined with the gases from the cathode gas compartment 30. The combined gases flow into the heat exchangers 22 where they are further cooled. In order for the gas stream to have sufficient energy to power the turbine, the gas stream after the outlet from the capacitor is heated to about 316 ° C, by bringing the gas back to the regenerators 22 and 101.

In previous power plants, it is often the case that not enough water can be provided for the vapor decomposition reactor alone from the cathode gas space. In some cases, even power plants with the reactants under pressure can run into the same problems. In the former fuel cell power plants, in which reactors without overpressure are used, additional water is usually recovered from the exhaust gas stream from the reactor burner. In the embodiment of a power plant according to the invention shown in FIG. 35, the additional water required for the vapor decomposition reactor is recovered from the anode exhaust stream before entering the reactor burner.

This was not possible in the earlier "pressureless" fuel cell power plants because the amount of water condensable from the "pressureless" gases from the anode gas room and cathode gas room was nonetheless insufficient for the vapor decomposition reactor; instead, the condensation equipment was placed downstream from the reactor fuel. in order to recover the additional water in this produced together with the water in the exhaust gas from the anode gas chamber, which caused further problems because the very high temperature in the exhaust gas from the reactor burner made it necessary to use a very large regenerative heat exchanger to cool the gases before In the embodiment shown in Figure 5 for a power plant according to the invention, the need for such a regenerative heat exchanger is avoided which constitutes a significant advantage of the invention. higher dew point in the exhaust gases from the anode gas compartment in a power plant one according to the invention makes it possible to recover a sufficient amount of water from these gases (before flowing into the reactor burner) by means of a condensation equipment of a reasonable size, so that when this water is combined with water which has been recovered from the exhaust gases from the cathode gas chamber, there is enough water for the vapor decomposition reactor. The removal of the water from the exhaust gas from the anode gas compartment prior to the inlet of the reactor burner also helps to reduce the size of the vapor decomposition reactor, thanks to the higher temperature of the burner as most of the water vapor has been removed from the gas stream.

Referring now to FIG. 8, showing a working curve of the carbon monoxide reactor (constant-temperature) in the gas stream. Note that in FIG. Examples 3 and 4 include a CO reactor. The curve shows that there is a direct correlation between the performance of the CO reactor and the pressure in the process gases flowing through the reactor. Thus, when operating at higher gas pressures, the activity of the catalyst is increased, which can also be understood to mean that the reactor can be made smaller, or alternatively a more complete shifting with a reactor of the same size can be achieved. It can be readily appreciated that the activity of the conversion catalyst doubles as the pressure of the gases flowing through the reactor is raised from the atmospheric pressure to about 4.2 kg / cm. This improved reactor performance is a further advantage which is achieved by the ability to allow fuel cell stacks to operate with high reactant gas pressures in accordance with the invention.

Claims (13)

34 U4257 1. Power plant for generating electricity consisting of a fuel cell stack having a number of fuel cells electrically connected in series through a load, each cell consisting of a cathode, anode and an electrolyte disposed therebetween, and a cathode gas compartment and an anode gas compartment on it away from the electrolyte facing side of the cathode and anode, respectively, the fuel used containing hydrogen, a fuel treatment assembly which includes steam generating means, a vapor decomposition reactor and a heat burner reactor for said decomposition reactor, means for delivering untreated fuel under pressure and steam pressurized to said reactor, characterized by a compressor (38) operatively connected to a turbine (40) adapted to be driven by the energy of a hot gaseous medium for compressing air to a pressure which is higher than two atmospheres, means (43, 42) for the delivery of compressed air from the compressor (38) into the cathode gas compartment (30), means (70) for supplying pressurized fuel from the vapor decomposition reactor (34) into the anode gas compartment (32), means (314,320) for supplying at least a portion of the gases from the anode gas compartment (32). ) into the reactor burner (36), as well as means (40,50,73,72,74,52) to transfer waste energy produced by the power plant into the turbine (4o) in the form of a hot gaseous medium under pressure to operation of the turbine (40). Power plant according to claim 1, characterized in that the means for conveying waste energy produced in the power plant into the turbine (40) include means (44, 50, 73, 52) for passing gases from the cathode gas space (30) into the turbine. Power plant according to claim 1 or 2, characterized in that the means (44, 50, 73, 52) for passing the exhaust gases from the cathode gas compartment (30) into the turbine comprise a conduit (44) for first passing the exhaust gases from the cathode gas compartment (30). ) into the condenser (18), a conduit (67) for passing condensed water from the condenser (18) to a boiler (20), and a conduit (62) for introducing steam from the boiler (20) into the vapor decomposition reactor. (3¾). Power plant according to claim 1, 2, 3 or 4, characterized in that it comprises a conduit (76) for passing a portion of the compressed air from the compressor (38) into the reactor burner (36). A power plant according to claim 1, 2, 3 or 4, characterized by means (27, 400, 402) for conducting a portion of the compressed air from the compressor (38) outside the cathode gas space (30) at reduced power output. an auxiliary burner (17, 410) for supplying extra heat to the gases fed into the turbine (40), thereby providing the means (44, 50, 72, 73, 74, 52) for passing the gases into the turbine (40) includes means (402, 408) for conveying said outside compressed air into the turbine (40). Power plant according to claim 5, characterized in that the means (27, 400, 402) for conducting compressed air outside the cathode gas space (30) include a bypass branch (400) and the auxiliary burner (410) is located in this branch (400). . Power plant according to one or more of claims 1 to 6, characterized in that the means (44, 50, 72, 73, 74, 52) for passing the exhaust gases from the cathode gas chamber into the turbine include conduits (72, 77, 74) to conducting the exhaust gases from the anode gas compartment (32) and / or exhaust gas from the reactor burner (36) with the cathode gas compartment exhaust gases prior to their delivery to the turbine (40). Power plant according to claim 7, characterized in that the wires (77, 74) for connecting gases from the reactor burner (36) with the cathode gas room exhaust gases are located on the downstream side of the capacitor (18). 144257 36 Power plant according to one or more of claims 1-7, characterized in that the conduits (102, 104) for connecting gas from the reactor burner (36) with the cathode gas room exhaust are located on the upstream side of the capacitor (18). Power plant according to one or more of claims 1-9, characterized in that the conduit (62) for supplying steam to the steam decomposition reactor (34) is connected to conduits (314, 320) for conveying at least part of the exhaust gases from the anode gas compartment (32) into the vapor decomposition reactor (34). Power plant according to claim 10, characterized in that the means (324, 330, 332) for delivering hydrogen from the vapor decomposition reactor into the anode gas space (308) include means for removing heat (340, 326, 328) for reducing the temperature of the gases. to less than the temperature of said fuel cell stack. Power plant according to claim 10, characterized in that the means (70 or 324, 330, 332) for delivering fuel from the vapor decomposition reactor (34) into the anode gas space (32 or 30) include means for first feeding the fuel into a carbon monoxide reactor ( 105) located on the upstream side of the anode gas compartment (32 or 308). Power plant according to claim 12, characterized in that the means (70) for delivering fuel from the vapor decomposition reactor (34) to the anode gas compartment (32) include means for delivering fuel from the reactor (105) into a selective oxidation reactor (106), and from the compressor (38) via a conduit (108) compressed air is passed through the selective oxidation reactor (106) to the anode gas compartment (32).