WO2012166040A1

WO2012166040A1 - Energy generation using a stack of fuel cells

Info

Publication number: WO2012166040A1
Application number: PCT/SE2012/050567
Authority: WO
Inventors: Kurt Dahlberg
Original assignee: Metacon Ab
Priority date: 2011-05-30
Filing date: 2012-05-28
Publication date: 2012-12-06

Abstract

The invention concerns an energy generation arrangement and method for generating energy. The energy generating arrangement (10) comprises a cooling chamber in which fuel cells (FC1, FC2, FC3, FC4, FC5, FC6, FC7, FC8, FC9. FC10, FC11, FC12, FC13, FC14) are provided in a stack and including at least a first fluid circulating area (12), a fluid propagating unit (16), and primary CHA6, CHA7, CHB1, CHB2, CHB3, CHB4, CHB5, CHB6, cooling fluid channels (CHA1, CHA2, CHA3, CHA4, CHA5, 10CHB7, CHB8) passing in parallel by the fuel cells of the fuel cell stack and connected to the first fluid circulating area (12).

Description

ENERGY GENERATION USING A STACK OF FUEL CELLS

FIELD OF INVENTION The present invention generally relates to cooling of fuel cells. More particularly the present invention relates to an energy generation arrangement and a method for generating energy using fuel cells in a stack .

BACKGROUND

Fuel cells have been known for some time, and are getting increasingly more interesting for generating electric power due to their lack of C02 emissions.

There exist a number of different types of fuel cells, such as Proton Exchange Membrane (PEM) , High

Temperature Protone Exchange Membrane (HTPEM) and Solid Oxide Fuel cells (SOFC) . Here the PEM cell typically operates at temperatures of maximum 80 C, HTPEM at temperatures of 160 - 180 C and SOFC at about 800 C. It can furthermore be mentioned that of these types the PEM cells are commercially available today, while SOFC need some further development before they are

commercially viable. Of special interest in this regard are the HTPEM cells, the use of which is starting to emerge on an industrial level . However, because of the temperature range they are active in they face a number of problems. One problem is that they are complicated to cool. Water cooling is for instance unsuitable for this reason. There is therefore a need for an improvement in the way energy is generated using fuel cells, which improvement may involve cooling of the fuel cells, which improved cooling may with advantage be used with HTPEM cells.

SUMMARY OF THE INVENTION

The present invention is therefore directed towards providing an improved energy generation that may operate at high temperatures .

One object of the present invention is to provide an improved energy generation arrangement that is based on a fuel cell stack.

This object is according to a first aspect of the present invention obtained through an energy generation arrangement and comprising:

- a stack of fuel cells,

a cooling chamber in which said stack of fuel cells is provided and including at least a first fluid circulating area,

a fluid propagating unit, and

- primary cooling fluid channels passing in parallel by the fuel cells of the fuel cell stack and

connected to the first fluid circulating area for circulating a first cooling fluid in a loop in order to cool the fuel cells in the stack.

Another object of the present invention is to provide an improved method for generating energy using a stack of fuel cells. This object is according to a second aspect of the present invention obtained through a method for

generating energy using fuel cells in a stack placed in a cooling chamber, comprising the steps of:

generating electric power using the fuel cells, and continuously transporting a first cooling fluid in a loop in the cooling chamber in parallel past the fuel cells of the stack for cooling the fuel cells.

The present invention has a number of advantages. It allows efficient cooling that can be based on a gas such as air. The cooling is also even and the

temperature differences between fuel cells in the stack kept low. The invention furthermore allows a high speed of the circulation of the first cooling fluid to be used, which leads to a good heat transfer to a second cooling fluid if such a second fluid is used. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will in the following be

described with reference being made to the accompanying drawings, where fig. 1 schematically shows a fuel cell used for

generating electrical power,

fig. 2 schematically shows a traditional fuel cell stack with a traditional cooling arrangement,

fig. 3 schematically shows a cooling arrangement according to a first embodiment of the invention for cooling a fuel cell stack, fig. 4 shows a flow chart of a number of method steps in a method for cooling the stack of fuel cells

according to the first embodiment of the invention, fig. 5 schematically shows a cooling arrangement according to a second embodiment of the invention for cooling a fuel cell stack,

fig. 6 schematically shows a cooling arrangement according to a third embodiment of the invention for cooling a fuel cell stack, where the cooling

arrangement is also used for providing heating, fig. 7 schematically shows how fuel cells are connected to an inverter for supply of electric power to a power network, and

fig. 8 schematically shows a variation of a chamber with a stack of fuel cells where the cooling fluid only passes by the fuel cells once.

DETAILED DESCRIPTION OF THE INVENTION As is well known within the art a fuel cell is a device where a chemical reaction causes ions to flow between two electrodes and thereby electrical power is

generated. In the chemical process the gases hydrogen and oxygen are used.

There exist a number of fuel cell types, where the most common type is the protone exchange membrane (PEM) fuel cell. Other known types are Solid Oxide Fuel Cell

(SOFC) and High Temperature PEM (HTPEM) . The PEM type is most common because it typically operates at below 80 C. The SOFC cell operates at about 800 C and has some way to go yet before it can be used industrially. The HTPEM cell operates at temperatures of about 160 - 180 C.

These HTPEM cells are now becoming more and more interesting to use in various applications. However, because of the temperature range they operate in, the cooling of these cells is a problem, especially if they are placed together in stacks. The traditional way to cool PEM cells is to use water flowing in a cooling block attached to an end of such a stack. This is obviously no solution for an HTPEM stack, because of the temperature range in which the cells operate.

The present invention addresses this problem. The present invention is therefore directed towards

generating electric power using a set of fuel cells combined with cooling these fuel cells, which cooling can be provided for fuel cells operating at high temperatures, i.e. at temperatures above the boiling temperature of water, i.e. at above 100 C.

Before the details of the present invention are

described, the functioning of a fuel well will briefly be discussed with reference being made to fig. 1. Fig. 1 shows a fuel cell FC in schematic form. A fuel cell FC includes two electrodes El and E2, where one is typically anode and the other a cathode. An electrode is typically provided in the form of a porous carbon felt that is impregnated with a catalyst, typically platinum. The electrode is on one side facing an electrolyte and on an opposite side facing a gas. This gas is used in a chemical reaction that causes the generation of electrical energy. The gas is thus a chemical substance used in the chemical reaction. In order to control this chemical reaction the fuel cell is provided with a bipolar or guiding plate that forms a number of chemical substance channels and here thus gas channels for making the chemical substance in the form of the gas to pass by the electrode. There is thus a first guiding plate GP1 joined to a first side of a first electrode El, which plate is designed for forming a number of fuel channels FCH with a gas, which gas is here hydrogen H₂. The first guiding plate GP1 thus guides the fuel H₂ past the first side of the first electrode El. The second, opposite side of the first electrode El is provided in an electrolyte and faces a corresponding second side of a second electrode E2. This second electrode E2 has a first side opposite of the second side along which chemical substance channels in the form of gas channels are provided through a second guiding plate GP2. The gas channels are here provided for an oxidation medium and are therefore also named oxidation channels OCH. The oxidation medium is here oxygen 0₂ which is normally supplied for the chemical reaction through providing a flow of air past the first side of the second electrode E2. Between the two electrodes El and E2 there is finally a membrane M. In operation ions flow from one electrode to the other through the membrane M causing an electric potential V_FC between the electrodes El and E2. This is

exemplified in fig. 1 through hydrogen ions 2H+ flowing from the first electrode El to the second electrode E2 via the membrane M. It should here be realized that it is also possible with an opposite flow of ions, i.e. from the second electrode E2 to the first electrode El. Such an ion flow through the electrolyte and membrane M thus causes an electric potential to appear between the two electrodes and thereby the cell can supply

electrical energy. The potential provided by one cell is typically in the range between 0.5 and 0.7 V DC.

The power that can be generated by one cell is in many applications not enough and therefore fuel cells are normally grouped together in stacks so that energy from a group of fuel cells, for instance eighty or one hundred fuel cells is used for obtaining electric power. A traditional stack is schematically shown in fig. 2. The top of the stack is here provided with a first cooling block or cooling plate CPl, while the bottom of the stack is provided with a second cooling block or cooling plate CP2. In such a stack ST, i.e. in between the first and second cooling plates CPl and CP2, there are provided a number of fuel cells. As an example, there may be a first group of fuel cells FC1, FC2, FC3 and FC4 stacked onto each other and separated from a second group of fuel cells FC5, FC6, FC7 and FC8 also stacked onto each other, via a third cooling plate CP3. The second group of fuel cells may be separated from a third group of fuel cells FC9, FC10, FC11 and

FC1 also stacked onto each other, via a fourth cooling plate CP4. In this way it is possible to group fuel cells depending on the amount of electrical power needed. It should here be realized that the number of groups and the number of fuel cells in each group may be varied. The cooling plates are typically provided through a suitable cooling material having good thermal conductivity, for instance a metal like aluminum, and normally include a number of cooling fluid channels, where a cooling fluid, typically a cooling liquid such as water, is passed for cooling the fuel cell stack. This type of cooling functions well for ordinary PEM fuel cells. However, they will normally not function too well for HTPEM fuel cells, especially if water is used. The reason is that the operational temperature of HTPEM cells is too high to be cooled with water. The cooling is furthermore uneven and not equal of the fuel cells in the stack.

There is therefore a need for an alternative energy generation arrangement with an improved cooling of the fuel cells. The present invention addresses this need.

Now a first embodiment of the invention that allows efficient cooling of HTPEM fuel cells will be described with reference being made to fig. 3 and 4, where fig. 3 schematically shows an energy generating arrangement according to this first embodiment of the invention and fig. 4 shows a flow chart of a number of method steps in a method for generating energy according to the first embodiment of the invention. The arrangement is provided for circulating a first cooling fluid in a loop, with advantage in a closed loop, in parallel past the fuel cells in the fuel cell stack in order to cool these fuel cells while at the same time generating electrical power.

In fig. 3 there are a number of fuel cells FC1 - FC14 placed together in a stack, where the top and bottom of the stack is provided with a first and a second cooling block or cooling plate CP1 and CP2, typically made of a material having good thermal conductivity for instance a metal such as aluminum. There is thus a cooling plate in each end of the stack.

In this first embodiment of the invention there is provided a number of primary cooling fluid channels between all the elements of the stack, i.e. between the fuel cells as well as between fuel cells and

neighboring cooling plates. The primary cooling

channels thus pass in parallel by the fuel cells of the fuel cell stack. This means that each fuel cell is separated from each neighboring fuel cell by at least one primary cooling fluid channel. There is here a cooling fluid channel CHBl provided between the first cooling plate CP1 and a first fuel cell FC1, a cooling fluid channel CHB2 provided between the first fuel cell FC1 and a second fuel cell FC2, a cooling fluid channel CHB3 provided between the second fuel cell FC2 and a third fuel cell FC3, a cooling fluid channel CHB4 provided between the third fuel cell FC3 and a fourth fuel cell FC4, a cooling fluid channel CHA1 provided between the fourth fuel cell FC4 and a fifth fuel cell FC5, a cooling fluid channel CHA2 provided between the fifth fuel cell FC5 and a sixth fuel cell FC6, a cooling fluid channel CHA3 provided between the sixth fuel cell FC6 and a seventh fuel cell FC7, a cooling fluid channel CHA4 provided between the seventh fuel cell FC7 and an eighth fuel cell FC8, a cooling fluid channel CHA5 provided between the eighth fuel cell FC8 and a ninth fuel cell FC9, a cooling fluid channel CHA6 provided between the ninth fuel cell FC9 and a tenth fuel cell FC10, a cooling fluid channel CHA7 provided between the tenth fuel cell FC10 and an eleventh fuel cell FC11, a cooling fluid channel CHB5 provided between the eleventh fuel cell FC11 and a twelfth fuel cell FC12, a cooling fluid channel CHB6 provided between the twelfth fuel cell FC12 and a thirteenth fuel cell FC13, a cooling fluid channel CHB7 provided between the thirteenth fuel cell FC13 and a fourteenth fuel cell FC14 and a cooling fluid channel CHB8 provided between the fourteenth fuel cell FC14 and the second cooling plate CP2. Here it can also be mentioned that as an alternative it is possible that the cooling fluid channels CHB1 and CHB8 may be omitted.

The fuel cells are further provided in a cooling chamber, with advantage a closed cooling chamber, which chamber includes at least one fluid circulating area and in this first embodiment includes a first fluid circulating area 12 and a second fluid circulating area 14. The chamber has walls surrounding the stack as well as the first and second fuel circulating areas. The chamber is here filled with a first cooling fluid CF1. The chamber is furthermore sealed and the first and second cooling plates CP1 and CP2 are provided as parts of the walls of the chamber. In this embodiment they are furthermore provided in a first and second side wall Wl and W2 of the chamber, which side walls are essentially provided in parallel with the fuel cells or perpendicular to the stacking direction of the fuel cells. The chamber also includes a first and second end wall W3 and W4, which end walls can be seen as having a general orientation in parallel with the stacking direction. However, as can be seen in fig. 3 these walls can have parts that are angled in relation to this general orientation. They can also be curved. Such angled parts or curvature is provided in order to influence the flow of the first cooling fluid CF1. The stack of fuel cells is here provided in-between the first and second fluid circulating areas and ensure that the first cooling fluid can be passed from the first fluid circulating area 12 to the second fluid circulating area 14, as well as from the second cooling fluid circulating area 14 to the first cooling fluid circulating area 12. The primary cooling fluid channels are thus connected to the first fluid circulating areas as well as to the second fluid circulating area. The fuel cells may furthermore be provided in groups, where a first group includes the fourth, fifth, sixth, seventh, eighth, ninth, tenth and eleventh fuel cells FC4, FC5, FC6, FC7, FC8, FC9, FC10 and FC11, while a second group includes the first, second, third, fourth, eleventh, twelfth, thirteenth and fourteenth fuel cells FC1, FC2, FC3, FC4, FC11, FC12, FC13 and FC14. In this first embodiment the first group is furthermore made up of a first combination including the fourth, fifth, sixth, seventh and eighth fuel cells FC4, FC5, FC6, FC7 and FC8 and a second combination including the eighth, ninth, tenth and eleventh fuel cells FC8, FC9, FC10 and FC11. In a similar manner the second group is also made of a first combination including the first, second, third and fourth fuel cells FC1, FC2, FC3, and FC4 and a second combination including the eleventh, twelfth, thirteenth and fourteenth fuel cells FC11, FC12, FC13 and FC14.

In this first embodiment of the invention there are provided two main parallel circulating flows from the first fluid circulating area to the second fluid circulating area and back. Therefore the chamber is provided with a first, second and third partition PA1, PA2 and PA3 in order to provide these two parallel main flows. The first partition PA1 is here provided at one end of the fourth fuel cell FC4 and stretches into the first circulating area 12 perpendicular to the stacking direction, the second partition PA2 is here provided at one end of the eleventh fuel cell FC11 and also

stretches into the first circulating area 12

perpendicular to the stacking direction, while the third partition PA3 is provided at one end of the eighth fuel cell FC8 and stretches into the second circulating area 14 also perpendicular to the stacking direction. It should here be realized that it is not necessary that the partitions are perpendicular to the stacking direction. They may also stretch out from other fuel cells than the fourth, eighth and eleventh Here the first and the second partitions PA1, PA2 stretch about halfway from the stack to the parts of first end wall W3 that is parallel with the stacking direction, while the third partition stretches all the way from the stack to the second end wall W4. In this way the second circulating area is divided into two halves 14-1 and 14-2 in order to enable cooling of the fuel cells via two main circulating paths. The cooling fluid channels CHA1 - CHA7 here make up a first set of cooling fluid channels, while the channels CHB1 - CHB8 make up a second set of cooling fluid channels. Here the first set of cooling fluid channels are used for transporting cooling fluid from the first fluid

circulating area 12 to the second fluid circulating area 14, while the second set of cooling fluid channels are used for transporting cooling fluid from the second fluid circulating area to the first fluid circulating area. The first set of primary cooling fluid channels thus passes by the first group of fuel cells and connects the first fluid circulating area with the second fluid circulating area, while the second set of primary cooling fluid channels passes by the second group of fuel cells and connects the second fluid circulating area with the first fluid circulating area. The first and second sets of cooling fluid channels thus each includes a number of parallel cooling fluid channels for transporting the first cooling fluid in parallel past fuel cells of the first and the second groups of fuel cells, respectively.

Since there are two main flows provided in parallel, this means that the first cooling fluid CF1 is passed in a first path through a first group CHA1 - CHA4 of the first set of channels to the first half 14-1 of the second fluid circulating area and returned to the first fluid circulating area 12 via a first group CHB1-CHB4 of the second set of channels. The first cooling fluid CF1 is also passed from the first circulating area 12 in a second path through a second group CHA5 - CHA7 of the first set of channels to the second half 14-2 of the second circulating area and then returned via a second group CHB5 - CHB8 of the second set of channels to the first circulating area 12.

At least some of the walls of the chamber and in this first embodiment only the end walls W3 and W4 may be provided with or include secondary cooling fluid channels CHC for a circulating second cooling fluid CF2, which second cooling fluid is with advantage a liquid, for instance water, and is provided for cooling the first cooling fluid CF1. These channels CHC are provided in the interior of the end walls W3 and W4 and thereby the second cooling fluid CF2 is separated from the first cooling fluid by these end walls. The cooling plates CP1 and CP2, which are optional, include

tertiary cooling fluid channels CHD for circulating a third cooling fluid CF3, which is with advantage also a liquid for instance oil. These channels CHD are

likewise provided in the interior of these plates and thus in the interior of the first and second side walls Wl and W2 and thereby the third cooling fluid CF3 is separated from the first cooling fluid by these side walls .

The chamber can thus be divided into sections, where each section is to provide one main flow of cooling fluid. As mentioned earlier there are two such main flows in this first embodiment of the invention. There are therefore two sections of each end wall in the first embodiment. However, it should be realized that it is possible with only one main flow as well as to provide more main flows, like three. In these cases each end wall will have as many sections are there are parallel main flows. Here the mid point of the end wall of such a section is provided in parallel with the stacking direction. This part may be surrounded by angled parts. Alternatively the end walls may be curved and then the tangential of the mid point of such a section will be parallel with the stacking direction. As can be seen in fig. 3, the walls of the chamber and here the end walls of the fluid circulating areas are placed in relation to the cooling fluid channels for forcing the first cooling fluid to flow past these walls in order to be cooled.

In order to provide circulation of the first cooling fluid the chamber is provided with at least one fluid propagating unit 16, which is with advantage a fan. This is placed for circulating the first cooling fluid CF1 through the closed chamber. The fluid propagating unit and primary cooling fluid channels are placed in relation to the chamber walls for forcing the first cooling fluid to pass by the walls having secondary cooling fluid channels. For this reason the fan 16 may be placed in the first fluid circulating area 12, for instance between the first and second partition PAl and PA2 and in front of the first set of channels CHA1 - CHA7. In order to provide circulation the fan 16 may be joined to a motor 18 via a shaft going through the first end wall W3.

In operation the first cooling fluid CF1 in the chamber is kept at a high pressure typically in the range of 1 - 5 bars and then preferably at 3 bars. Some fuel cell membranes may not be able to withstand pressures above 3 bar, in which case the pressure is kept below this limit. The pressure could thus be selected to be below the pressure fuel cells and especially the membranes are designed to withstand. The fan 16 then forces the first cooling fluid CF1 to circulate in the chamber at a speed in the range of 0.5 - 5 m/s and preferably at a speed of about 1 m/s. In operation the fuel cells generate electric power based on air and hydrogen, step 19, in which process also heat is generated. The fan 16 ensures that the first cooling fluid is circulated in the cooling chamber in a loop and thus continuously transports the first cooling fluid in parallel past the fuel cells of the stack. This is in the first embodiment done through the fan 16 causing the first cooling fluid CF1 to leave the first fluid circulating area 12 and pass in

parallel by the first group of fuel cells through passing in parallel through the first set of channels into the second circulating area 14 and then back past the second group of fuel cells through passing in parallel through the second set of channels, into the first fluid circulating area 12. As can be seen the fan 12 therefore transports the first cooling fluid CF1 in parallel past the first group of fuel cells FC4 - FC11 via the first set of cooling fluid channels CHA1 - CHA7 and into the second fluid circulating area, step 20.

Here the fan furthermore transports the first cooling fluid CF1 from the first fluid circulation area to the second fluid circulation area past the first

combination of the first group of fuel cells via the first group of the first set of cooling fluid channels in the first main flow as well as past the first combination of the second group of fuel cells via the second group of the first set of cooling fluid channels in the second main flow. As the first cooling fluid CF1 then passes by the first group of fuel cells, these are cooled. However, in the process of this cooling, the first cooling fluid CF1 has also been heated. Therefore the first cooling fluid CF1 is passed by or transported past the walls of the second fluid circulating area, where the fluid is cooled by these walls and in this embodiment cooled by the end wall W4 using the second cooling fluid CF2 in the secondary cooling fluid channels CHC, step 22. The first cooling fluid CF1 is thus transported past a wall of a fluid circulating area provided between the first and second sets of primary cooling fluid channels in the fluid

transportation direction.

After a transport of the first cooling fluid past the stack, the first cooling fluid is thus cooled using the second cooling fluid. Thereafter the first cooling fluid CF1 is passed in parallel past the second group of fuel cells FC1 - FC4, FC11 - FC14 via the second set of channels CHB1 - CHB8, step 24, from where it returns to the first fluid circulating area 12. In the first main flow, the first cooling fluid is thus passed by the first combination of the second group of fuel cells via the first group of the second set of cooling fluid channels and in the second main flow passed by the second combination of the second group of fuel cells via the second group of the second set of cooling fluid channels. The first cooling fluid CF1 is here passed by the end wall W3 of the first fluid circulating area 12, where the first cooling fluid CF1 is again cooled using the second cooling fluid CF2. Thereafter the fan again causes the first cooling fluid to leave the first fluid circulating area and pass in parallel by the first group of fuel cells into the second circulating area 14 and then back past the second group of fuel cells into the first fluid circulating area. The above method steps are thus repeated continuously. In this way the generation of electrical power combined with efficient cooling is provided, which cooling can be based on air. The cooling is furthermore even and the temperature differences between fuel cells in the stack kept low. The high speed of the circulation of the first cooling fluid furthermore leads to a good heat transfer to the second cooling fluid. The

invention thus provides a highly efficient hybrid cooling system with an inner cooling circuit using the first cooling fluid and an outer cooling circuit using the second cooling fluid, which fluids are separated to eliminate the risk for leakage of coolant into the fuel cell electrochemical process areas. The outer liquid cooling circuit is embodied as channels in the air tight chamber wall, which may be made of metal, in a similar fashion as in engine blocks of conventional combustion engines for cars. The hybrid cooling concept with two loops of cooling fluid makes it possible to use water as the second cooling fluid, since is not in direct contact with the high temperature cells, and the use of sophisticated and expensive cooling oils or steam is avoided. Furthermore, by providing the fuel cell with hybrid cooling and air circulation according to the invention, the power density of the fuel cell can be increased by 100 to 150 %, and the size, weight and cost can be reduced. Since the two cooling circuits can be safely separated, the reliability, durability and

maintainability of the arrangement can be greatly improved . The specific power of the stack can because of the invention be increased from approximately 0.13 W per square centimeter active area, to approximately 0.5 W/cm2.

The third cooling fluid CF3 assists in cooling the first cooling fluid as well as in cooling the fuel cell stack as the first cooling fluid passes through the first and the last channels CHB1 and CHB8 in the second set of cooling fluid channels.

In this way an even cooling of the fuel cells is obtained. In this way it is also possible to cool the fuel cells using air.

A second embodiment of the present invention is shown in fig. 5. In this embodiment the same way of

generating electric power combined with cooling the fuel cell stack is used as in the first embodiment. However, as air is used as the first cooling fluid, it is also used for supplying one chemical substance used in the chemical reaction of the fuel cells. The first cooling fluid is thus also used for supplying the oxidation medium. The first cooling fluid is thus supplied for use in the chemical process of the fuel cells, i.e. in the process of generating electric power. This means that the primary cooling fluid channels are also acting as chemical substance inlets for the chemical reaction of the fuel cells. This means that the primary cooling fluid channels passing by the fuel cells are also combined with the oxidation

channels. The oxidation channels OCH1, OCH2, OCH3, OCH4, OCH5, OCH6, OCH7, OCH8, OCH9, OCH10, OCH11, OCH12, OCH13 and OCH14 of the fuel cells are thus here a part of the primary cooling fluid channels. It is here possible that the primary cooling fluid channels are solely made up of these oxidation channels and that the elements of the fuel cell stack, i.e. fuel cells and possibly also the optional cooling plates, are placed in direct contact with each other. In the second embodiment all fuel cells are supplied with oxidation medium using the first cooling fluid. It should be realized the fewer fuel cells could be provided with the oxidation medium in this way, for instance only one .

This type of cooling does result in that air will be used also in the chemical process. This means that the oxygen content of the first cooling fluid is lowered. The first cooling fluid content is thus changed. There is because of this a need to remove used cooling fluid and supply new cooling fluid. In order to do this, there is in this embodiment provided a first

controllable cooling fluid inlet 28 leading to the chamber, through which inlet the first cooling fluid is supplied or controlled via a compressor 30. The inlet is thus controllable to supply first cooling fluid to the chamber during operation of the fan. This inlet 28 does with advantage lead to at least one of the fluid circulating areas and here to the first fluid

circulating area 12. Here it is possible to provide inlets also at other locations, for instance in the second fluid circulating area 14, either instead of or in addition to said inlet 28. There is also a

controllable cooling fluid outlet 32 leading from the chamber and here from one of the fluid circulating areas, which may be the other fluid circulating area and in this second embodiment is the second fluid circulating area 14. The outlet is thus controllable to remove first cooling fluid from the chamber during operation of the fan 16. The outlet 32 is with

advantage controlled through a pressure reducing valve 34 that will open the outlet if the pressure is above a given level. This level may be in the above described pressure range and can for instance be 3 bars. In this way it is possible to supply new first cooling fluid and remove used first cooling fluid and thus to keep a supply of oxidation medium/cooling fluid together with retaining a desired cooling medium pressure. In this case the chamber is not completely sealed, but semi- sealed.

Since air is also the electrochemical fuel on the cathode side of each cell, the cooling air flow can also be used to increase the air flow rate for the process and thereby increase the power density of the fuel cell. By supplying the air for cooling and process fuel at an increased pressure, the efficiency of cooling as well as the process efficiency are

increased, and this increase in power is significantly higher than the power needed for the compression and circulation of the air. Since the over pressured circulating air is given a relatively high speed, all parts of its multi-function role, to absorb heat from the stack, to provide oxygen for the process and to transfer the excess heat to the liquid cooled chamber walls by air-to-metal heat convection, can be made with high efficiency. Even considering the increased parasitic power for the compressor, the net increase in specific power is in the order of 4 times, giving the same reduction of stack volume, number of cells, need of catalyst and cost of the stack as in the first embodiment.

In one variation of this second embodiment, the gas flow pattern, which is normally made on the surface of the bipolar plates, is instead made in an electrode/gas diffusion layer component which is placed between the bipolar plate and the membrane. This is possible in combination with the over pressure, and also reduces cost of manufacturing. Fig. 6 shows a third embodiment of the present

invention. Here there are three chambers surrounding a stack ST of fuel cells, where each chamber provides a circulating flow of first cooling fluid CF1 through a part of the stack through the use of a first and a second fluid circulating area 12A, 14A, 12B, 14B, 12C, 14C and primary cooling fluid channels (not shown) . As mentioned earlier the cooling of the first cooling fluid leads to the second cooling fluid being heated. The energy transferred in this way can also be used, for instance in the heating of a premises. For this reason the cooling fluid channels CHC carrying the second cooling fluid CF2 are connected to fluid

transportation means in the form of pipes or ducts 36 leading to another entity in the form of a first heat exchanger 38, to which heat exchanger 38 further fluid transporting means in the form of pipes or ducts 40 are connected. In this embodiment also cooling fluid channels CHD carrying the third cooling fluid CF3 are connected to fluid transporting means in the form of pipes or ducts 42 leading to another entity in the form of a second heat exchanger 44, from which heat

exchanger 44 further fluid transporting means in the form of pipes or ducts 46 are provided. The further pipes or ducts 40 and 46 of this first and second heat exchanger 38 and 44 can be transporting heating fluid HF1 and HF2 such as a liquid like water and for this reason be connected to heating equipment, such as radiators of the premises. In this way it is possible to transport the second cooling fluid CF2 to the first heat exchanger 38 and the third cooling fluid CF3 to the second heat exchanger 44 in order to use the energy transferred to the first cooling fluid from the fuel cells also for other purposes like the heating of said premises. It should here be realized that the pipes or ducts of the heat exchangers carrying heating fluid can be connected in the same heating system and thus carry the same heating fluid.

This last embodiment shows that since the arrangement is intended for Combined Heat and Power (CHP)

applications, where hot water at temperatures +80 to + 110°C is preferred as output thermal energy, the hybrid cooling concept provides a reliable and straight^¬ forward interface to external heating systems .

The electric power generated by a stack of fuel cells may be supplied to a power network, such as to a power distribution network. This type of network is typically a three-phase network operating at an AC voltage such as 400 V. As mentioned above, the voltage contribution of a fuel cell is between 0.5 and 0.7 V DC and a stack may comprise about 80 - 100 cells. A stack may thus provide 40 - 70 V, which is not sufficient. For this reason a stack may be connected to a DC/DC converter which converts the DC voltage to a higher DC level for instance 400 V. It is furthermore also necessary to convert the DC voltage to an AC voltage such as a three-phase AC voltage. It is here also possible to have more than one stack, for instance two. Fig. 6 schematically shows how a first and a second stack STl and ST2 are connected to a corresponding DC/DC

converter 48 and 50, respectively, in order to raise the DC voltage. Both these DC/DC converters 48 and 50 are also connected to a DC/AC converter or inverter 52 for supplying three-phase AC power to a power

distribution network.

As mentioned above, the cooling fluid need only pass by a stack of fuel cells once. One way in which this may be realized is schematically shown in fig. 8, where the cooling fluid enters cooling fluid channels at one end of a single fluid circulating area 12 and exits the same cooling fluid channels at an opposite end of the single fluid circulating area 12. The bipolar plates of fuel cells may typically be formed through graphite, while cooling plates and other elements like fastening elements may be made of a material with good thermal conductivity, like aluminum. The bipolar plates may as an alternative also be provided as metal bipolar plates. The superior

electrical and thermal conductivity and the much higher mechanical strength of such metal plates gives further improved power efficiency, cooling and heat

controllability and a more compact and low cost design.

However, at the high temperature used, mechanical distortion due to temperature cycling frequently cause deformations and leakage in the multiple joints of the fuel cell stack. In order to address this problem it is possible that the stack structure may be formed through the use of an intermetal, such as superaluminum. This material has a good ability to retain its shape at temperatures up to 200°C. By selecting high performance aluminum alloys for casing, stack end plates and other parts, distortion due to the temperature cycling can be avoided at the same time as heat conductivity is improved.

The superaluminum may be in the so-called RM-lOx group supplied by Powder Light Metals GmbH. It can thus be a superaluminum denoted RM-100, RM-101, RM-102, RM-103 or RM-104. These alloys are produced through reactor milling of aluminum powder together with graphite powder. During milling sub-micron aluminum oxide AI₂O₃ and aluminum carbide particles are generated, which give high-strength properties at elevated temperatures. These alloys also exhibit good corrosion resistance and improved creep strength. RM-104 does for instance have a higher yield strength at 300°C than Aluminum at room temperature .

In the example above the fuel propagating unit was described as a fan. This fan may be operated by an air motor, in which case no lubricant is needed. It is also possible that the fuel propagating unit is provided through the use of a fluid injection nozzle provided in a fluid guiding tube.

The fuel cells do normally need to be heated to an operational temperature before they can be put into operation for producing electric power, which

operational temperature may be about 100°C. It normally takes some time to reach this operational temperature. It is possible to lower this time through providing one or more pre-heating elements in relation to the

chamber, either inside the chamber or outside the chamber at or in the inlets leading to the chamber. The forced air flow in combination with such pre-heating elements enables this operational temperature to be reached quickly. Once the operational temperature is reached, the pre-heating elements are turned off.

The hydrogen for the fuel cells may be provided through a reformer, which may obtain hydrogen from natural gas or biogas .

In the preferred variations of the invention HTPEM fuel cells are used. These cells have the advantage of providing high-value heat energy, due to the operating temperature of +160 to +180 degrees C. Another

advantage is that they are not excessively sensitive to the purity of the hydrogen. They can accept reformate gas which contains several % CO, thereby strongly reducing the cost and complexity of the reformer.

There are a number of further variations that can be made of the energy generating arrangement of the present invention apart from the ones already mentioned. First of all it should be realized that the first, second and third embodiments of the invention can be combined in every possible way and that any variations described in relation to one embodiment can be made in relation to another embodiment. There are further variations that are possible. The secondary cooling fluid channels have been described as being provided in the end walls of a chamber. However, it should be realized that they may also be provided in the side walls. It is furthermore possible that only one fluid circulating area is provided in the chamber and that all primary cooling fluid channels carrying the first cooling fluid are passed simultaneously in parallel past the fuel cells of a chamber from an entry point in a single main flow. After passing the stack the first cooling fluid is then cooled by the second cooling fluid and returned to the entry point, for instance through return piping. It is also possible to use more fluid propagation units, for instance one for each main flow, which fluid propagating unit may be placed in the second fluid circulation area

Above air was given as an example of a suitable gas to be used for cooling. It is possible with other gases, like for instance SF6. As mentioned above examples on cooling liquids are water and oil. The fuel cells described above are with advantage HTPEM. It should however be realized that the invention is not limited to this type but that for instance PEM and SOFC cells can be used.

From the foregoing discussion it is evident that the present invention can be varied in a multitude of ways. It shall consequently be realized that the present invention is only to be limited by the following claims .

Claims

1. An energy generation arrangement (10) and comprising :

- a stack of fuel cells (FC1, FC2, FC3, FC4, FC5, FC6, FC7, FC8, FC9. FC10, FC11, FC12, FC13, FC14), a cooling chamber in which said stack of fuel cells is provided and including at least a first fluid circulating area (12),

- a fluid propagating unit (16), and

primary cooling fluid channels (CHA1, CHA2, CHA3, CHA4, CHA5, CHA6, CHA7 , CHB1, CHB2, CHB3, CHB4, CHB5, CHB6, CHB7, CHB8) passing in parallel by the fuel cells of the fuel cell stack and connected to the first fluid circulating area (12) for

circulating a first cooling fluid (CF1) in a loop in order to cool the fuel cells in the stack.

2. The energy generation arrangement according to claim 1, further comprising a second fluid circulating area (14), wherein the fuel cells of the stack are provided in a first (FC4, FC5, FC6, FC7, FC8, FC9.

FC10, FC11) and a second (FC1, FC2, FC3, FC4, FC11, FC12, FC13, FC14) group, the primary cooling fluid channels are provided in a first (CHA1, CHA2, CHA3,

CHA4, CHA5, CHA6, CHA7 ) and a second set (CHB1, CHB2, CHB3, CHB4, CHB5, CHB6, CHB7, CHB8) of primary cooling fluid channels, the first set of primary cooling fluid channels passes by the first group of fuel cells and connects the first fluid circulating area with the second fluid circulating area, while the second set of primary cooling fluid channels passes by the second group of fuel cells and connects the second fluid circulating area with the first fluid circulating area.

3. The energy generation arrangement according to any previous claim, wherein the chamber has walls (Wl,

W2, W3, W4) surrounding said at least one fluid

circulating area, wherein at least one (W3, W4) of said walls is provided with secondary cooling fluid channels (CHC) .

4. The energy generation arrangement according to claim 3, wherein the fluid propagating unit and primary cooling fluid channels are placed in relation to the chamber walls for forcing first cooling fluid to pass by said at least one wall having secondary cooling fluid channels.

5. The energy generation arrangement according to any previous claim, wherein at least one primary cooling fluid channel is also acting as a chemical substance inlet for the generation of electric power of a corresponding fuel cell.

6. The energy generation arrangement according to claim 5, further comprising a controllable cooling fluid inlet (28) leading to the chamber and a

controllable cooling fluid outlet (32) leading from the chamber, the inlet being controllable to supply first cooling fluid and the outlet to remove first cooling fluid during operation of the fluid propagating unit.

7. The energy generation arrangement according to any previous claim, further comprising a first and a second cooling plate (CP1, CP2) provided at each end of the stack.

8. The energy generation arrangement according to claim 7, wherein the cooling plates include tertiary cooling fluid channels (CHD) .

9. The energy generation arrangement according to any previous claim, wherein the first cooling fluid is a gas provided in the chamber at a pressure in the range of 1 - 5 bars.

10. The energy generation arrangement according to any previous claim, wherein the propagating unit is controllable to circulate the first cooling fluid through the chamber at a speed in the range of 0.5 - 5 m/s .

11. The energy generation arrangement according to any previous claim, further comprising an inverter (52) configured to receive electric DC power generated by the fuel cells of the stack and convert the DC power to AC power for delivery to an AC power system.

12. The energy generation arrangement according to any previous claim, wherein the stack is made of an intermetal, such as superaluminum.

13. The energy generation arrangement according to any previous claim, further comprising at least one pre-heating element for heating the first cooling fluid in order to heat the fuel cells to an operational temperature .

14. A method for generating energy using fuel cells (FC1, FC2, FC3, FC4, FC5, FC6, FC7, FC8, FC9. FC10, FC11, FC12, FC13, FC14) in a stack placed in a cooling chamber , comprising the steps of:

generating (19) electric power using the fuel cells, and

continuously transporting a first cooling fluid (CF1) in a loop in the cooling chamber in parallel past the fuel cells of the stack for cooling the fuel cells.

15. The method according to claim 14, further comprising the step of cooling (22, 24) the first cooling fluid using a second cooling fluid (CF2) after a transport of the first cooling fluid past the stack of fuel cells.

16. The method according to claim 15, wherein the step of cooling the first cooling fluid comprises transporting the first cooling fluid past a wall (W3, W4 ) of a fluid circulating area (12, 14), where said wall includes secondary cooling fluid channels (CHC) with the second cooling fluid.

17. The method according to claim 15 or 16, further comprising the step of transporting the second cooling fluid to another entity (38, 44) for using the energy transferred from the first cooling fluid to the second cooling fluid during the step of cooling the first cooling fluid.

18. The method according to any of claims 14 - 17, wherein the fuel cells of the stack are divided into at least a first (FC4, FC5, FC6, FC4, FC5, FC6, FC7, FC8, FC9. FC10, FC11) and a second group (FC1, FC2, FC3, FC4, FC11, FC12, FC13, FC14) and the step of

continuously transporting the first cooling fluid comprises transporting (20) the first cooling fluid past the first group of fuel cells and transporting (24) the first cooling fluid past the second group of fuel cells after the first group of fuel cells has been passed .

19. The method according to claim 18, wherein the step of transporting the first cooling fluid past the first group of fuel cells comprises transporting the first cooling fluid in a first set of primary cooling fluid channels (CHA1, CHA2, CHA3, CHA4, CHA5, CHA6, CHA7 ) and the step of transporting the first cooling fluid past the second group of fuel cells comprises transporting the first cooling fluid in a second set of primary cooling fluid channels (CHB1, CHB2, CHB3, CHB4, CHB5, CHB6, CHB7, CHB8) .

20. The method according to any of claims 14 - 19, further comprising the step of supplying said first cooling fluid for use in the generating of electric power when performing the step of continuously

transporting said first cooling fluid past the stack.

21. The method according to claim 20, further comprising the steps of supplying new first cooling fluid and removing used cooling fluid as the step of continuously transporting said first cooling fluid past the stack is performed.