WO2014063908A1

WO2014063908A1 - Disc shaped fuel cell

Info

Publication number: WO2014063908A1
Application number: PCT/EP2013/070563
Authority: WO
Inventors: Kurt Dahlberg
Original assignee: Metacon Ab
Priority date: 2012-10-23
Filing date: 2013-10-02
Publication date: 2014-05-01

Abstract

The invention concerns an energy generation arrangement that comprises at least one fuel cell (FC) being shaped as a circular disc with a hollow center (14) and comprising at least one primary fluid channel (PCH) provided on one side of the disc and stretching from the periphery (12) to the hollow center (14) and at least one secondary fluid channel provided on an opposite side of the disc, where the primary fluid channel is provided with an inlet (CHI) at the periphery (12) and an outlet (CHO) at the hollow center (14) of the disc.

Description

DISC SHAPED FUEL CELL

FIELD OF INVENTION The present invention generally relates to cooling of fuel cells. More particularly the present invention relates to an energy generation arrangement comprising at least one fuel cell. BACKGROUND

Fuel cells have been known since the middle of the nineteenth century, 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 have uneven temperature distribution, which reduces the efficiency of the fuel cell. 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 fuel cell structure for operation at high temperatures .

One object of the present invention is to provide an improved energy generation arrangement.

This object is according to a first aspect of the present invention obtained through an energy generation arrangement comprising at least one fuel cell shaped as a circular disc with a hollow center, the fuel cells each comprising at least one primary fluid channel provided on one side of the disc and stretching from the periphery to the hollow center and at least one secondary fluid channel provided on an opposite side of the disc, wherein a primary fluid channel is provided with an inlet at the periphery and an outlet at the hollow center (of the disc.

According to one variation of the invention, the energy generation arrangement comprises more than one disc shaped fuel cell in a stack, and the arrangement further comprises: a cooling chamber surrounding the stack, at least one fluid propagating unit configured to make a first fluid pass in a flow through the primary fluid channels) of the discs of the stack from the periphery to the hollow center and up along a center axis of the stack. Thereby the first fluid acts as a chemical substance involved in the generation of electric power as well as a coolant for cooling the stack . The present invention has a number of advantages. It allows the temperature of the fuel cell to be more even and thereby the efficiency of the fuel cell may be raised . 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 the principles of a fuel cell used for generating electrical power,

fig. 2 schematically shows a disc shaped fuel cell according to a first embodiment of the invention, fig. 3 schematically shows some angular relationships of the fuel cell according to the first embodiment, fig. 4 shows a perspective view of a first side of a specific realization of a disc shaped fuel cell

according to the first embodiment,

fig. 5 shows a perspective view of a second side of the specific fuel cell realization according to the first embodiment, fig. 6 schematically shows a fuel cell according to a second embodiment of the invention,

fig. 7 schematically shows a first variation of an energy generation arrangement using a stack of disc shaped fuel cells,

fig. 8 schematically shows a second variation of an energy generation arrangement using a stack of disc shaped fuel cells,

fig. 9 schematically shows a third variation of an energy generation arrangement, which is also used for providing heating, and

fig. 10 schematically shows how fuel cells are

connected to an inverter for supply of electric power to a power network.

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, there are still some problems with these that need to be addressed.

The conventional layout of a fuel cell is in the form of a rectangular block and such a block may be placed in a stack with other blocks . One way to cool HTPEM fuel cells is to use air. The cells may thus be provided as rectangular block through which air may be blown.

However, when using this traditional block structure, the fuel cells have shown to be cooled unevenly. They thus have different temperatures in different areas of the cell. This has a negative effect on the efficiency of the operation. There is therefore a need for improvement in this regard. The present invention addresses this problem. The present invention is therefore directed towards providing an energy generating arrangement comprising at least one fuel cell, where the fuel cells have a more even temperature and therefore operate more efficiently .

One object of the invention is to provide a fuel cell that is improved in that the temperature variations are reduced. Another object is to use this cell structure in a stack in an energy generation arrangement in order to obtain a more efficient use of the cells in the stack. In this arrangement generation of electric power is performed using a stack of fuel cells combined with cooling of 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 cell 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 an 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 with a gas, which gas may be hydrogen ¾ . The first guiding plate GP1 thus guides the fuel ¾ 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. The oxidation medium is here oxygen O2 which is normally supplied for the chemical reaction through providing a flow of air past the first side of the second electrode E2. The oxidation channels are here also termed primary fluid channels PCH and the fuel channels are termed secondary fluid channels SCH. 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. In fig. 2 and 3 there is shown an exemplifying fuel cell realization according to a first embodiment of the invention. The fuel cell FC is provided as a circular disc with a circular periphery 12 and a hollow center 14. There is thus a hole in the center of the disc, which hole 14 may also be circular in shape. In the disc there are a number of fluid channels. In fig. 2 and 3 there is only shown one primary fluid channel PCH, which is a channel for a primary fluid, which fluid in this example is air. The primary fluid channel PCH is provided at one side of the disc and stretches from the periphery 12 to the center 14. Secondary fluid channels aligned with corresponding primary fluid channels are provided at the opposite side of the disc (not shown) for a second fluid, which secondary fluid is the fuel of the cell. For the shown primary fluid channel PCH there is thus a secondary fluid channel on the opposite side of the disc being aligned with the primary fluid channel PCH. The primary fluid channel PCH has a channel inlet CHI provided at the periphery 12 and a channel outlet CHO provided at the hollow center 14. There is thus an opening in the periphery forming the channel inlet and an outlet leading out to the hollow center. The channel inlet CHI has a first area Al and the channel outlet CHO has a second area A2 , where the first area Al is larger than the second area A2. The first area Al is also a cross-section of the primary channel PCH at the channel inlet CHI and the second area A2 is the cross-section of the primary channel PCH at the channel outlet CHO.

As can be seen in fig. 2 the primary channel CHI according to the first embodiment is not radial. The channel is at the inlet CHI provided at an angle a to the radius R of the disc and at the outlet provided at an angle β to the radius R of the disc. The normal of the first area thus forms an angle a with a radial axis of the disc, while the normal of the second area A2 forms an angle β with the radial axis of the disc. The direction of flow at the channel inlet CHI is thereby also angled to the radius R with the angle a, which angle is with advantage below ninety degrees. The direction of flow at the channel outlet CHO is in turn angled to the radius R with the angle β, which angle is with advantage smaller than the angle a. In the first embodiment the primary fluid channel PCH is furthermore curved. The curvature may be the curve of a spiral, with the radius of the curvature being smaller than the radius of the disc. The center of the curvature of the channel may furthermore be displaced from the center of the disc.

In fig. 2 and 3 only one channel on one side is shown. It should however be realized that normally there are several such channels on each side of the disc. As an example there may be as many as 100 - 200 primary channels and 100 - 200 secondary channels.

One example of a physical realization is shown in fig.

4 and 5, where fig. 4 shows a perspective view of a first side of a specific realization of a disc shaped fuel cell FC according to the first embodiment and fig.

5 shows a perspective view of a second side of the specific fuel cell realization according to the first embodiment. As can be seen in fig. 4 there are a great number of curved primary channels PCH symmetrically distributed around the center 14 of the disc. As can be seen in fig. 5 there may also be a corresponding number of secondary channels SCH with a similar curvature symmetrically distributed around the center 14 of the disc. However, this is in no way any requirement. The number of secondary channels may differ. There may for instance be more secondary channels. They do also not have to have the same shape. As can be seen in the figure the primary channels PCH of this exemplifying disc stretch all the way between periphery 12 and hollow center 14, while the secondary channels do not, they start and end in the interior of the disc. The reason for this will be explained shortly. It can also be seen that although the secondary fluid channels SCH are aligned with the primary fluid channels PCH, they do not have to have the same dimensions. The channels may for instance be smaller. However, the shape and distribution of secondary fluid channels may differ considerably from the primary fluid channels. It can generally be said that the secondary fluid channels SCH are designed for obtaining the best possible exchange with the membrane. The first area Al is with advantage at least 1.5 times larger than the second area A2. In one preferred variation it is at least 2.5 times the second area.

It should be realized that the shape of the channels may differ. It is for instance possible to use radial channels PCH, as can be seen fig. 6, which shows a second embodiment of the fuel cell FC . This type of channel is thus aligned with the radial direction R. The normal of the first and second areas Al and A2 thus coincide with the radial axis of the disc. Also in this second embodiment the first area Al is larger than the second area A2. The width of the channel may however be fixed . The fuel cell structure above has many advantages compared with the traditional block shape, where one advantage is a more even temperature variation, which in turn leads to a more efficient fuel cell. The power that can be generated by a single fuel cell is in many applications not enough and therefore fuel cells may be grouped together in stacks so that energy from a group of fuel cells, for instance eighteen or twenty fuel cells is used for obtaining electric power. However, it is also possible with as many as 200 fuel cells .

Now a first variation of the invention that provides stable and efficient generation of electric power together with efficient cooling of HTPEM fuel cells will be described with reference being made to fig. 7, which schematically shows an energy generating

arrangement according to the first variation of the invention. The arrangement 16 is provided for

circulating a first cooling fluid CF1 in a loop, with advantage in a closed loop, through fuel cell discs FC1 - FC6 in a fuel cell stack in order to cool these fuel cells while at the same time generating electrical power .

In fig. 5 there are therefore a number of fuel cells FC1 - FC6 placed together in a stack. As an example there are only six fuel cells in the chamber. It should however be realized that there may be more or fewer fuel cells, for instance eighteen or twenty.

The fuel cells are further provided in a cooling chamber 14, with advantage a closed cooling chamber, 14. The chamber has walls surrounding the stack, a floor on which the stack rests and a ceiling opposite the floor. There is here a clearance between the ceiling and the top of the stack in order to allow a cooling fluid flow in the chamber. The chamber 14 is filled with a first cooling fluid CF1, which also acts as an oxidation medium. The chamber 14 is furthermore semi-sealed.

In this first variation of the invention there is provided a number of primary fluid channels PCHl - PCH6 through all the discs of the stack, i.e. through the fuel cells. The primary fluid channels PCHl - PCH6 thus pass radially through the discs of the fuel cell stack from the periphery to the hollow center. There is here a first group of primary fluid channels PCHl provided in a first fuel cell FC1, a second group of primary fluid channels PCH2 provided in a second fuel cell FC2, a third group of primary fluid channels PCH3 provided in a third fuel cell FC3, a fourth group of primary fluid channels PCH4 provided in a fourth fuel cell FC4, a fifth group of primary fluid channels PCH5 provided in a fifth fuel cell FC5 and a sixth group of primary fluid channels PCH6 provided in a sixth fuel cell FC6. The channels stretch through the cells in the way shown in fig. 2 and 3 or 4, i.e. from the periphery of the discs to the hollow center of the discs.

There is also provided a number of secondary fluid channels SCH1 - SCH6 in all of the discs of the stack, i.e. in the fuel cells. The secondary fluid channels also pass radially through the discs of the fuel cell stack in a direction from the periphery towards the hollow center. However, in this example they do not pass all the way through the discs. Rather there is a first tube 30 stretching through the floor of the chamber 14 up through the cells to the channel inlets of the secondary cells and a second tube 32 stretching from the channel outlets through the cells down through the floor of the chamber. There is here a first group of secondary fluid channels SCH1 provided in the first fuel cell FC1, a second group of secondary fluid channels SCH2 provided in the second fuel cell FC2, a third group of secondary fluid channels SCH3 provided in the third fuel cell FC3, a fourth group of secondary fluid channels SCH4 provided in the fourth fuel cell FC4, a fifth group of secondary fluid channels SCH5 provided in the fifth fuel cell FC5 and a sixth group of secondary channels FCH6 provided in a sixth fuel cell FC6, where the channels stretch through the cells in the way shown in fig. 5. It should be realized that other ways of realizing the secondary channels are possible. They may as an example also stretch all the way from periphery to hollow center. What is important though is that they are separated from the primary fluid channels. The flow of the fuel thus has to be completely separated form the flow of the oxidation medium.

In the center of the stack, in a direction along a central axis of the stacked cells, there is a flow guiding unit, here in the form of a hollow tube 21. The hollow tube 21 has cone shaped outer wall and a cylinder shaped inner wall. The tube 21 stretches from the bottom to the top of the stack, where the cone is turned upside down, meaning that the wider walls of the cone shaped exterior of the tube 21 are provided at the top of the stack and the narrower walls at the tip of the cone are provided at the bottom of the stack. There is in this first variation provided a group of cooling fluid tubes 20A, 20B, 20C and 20D through the walls of the chamber 14. Openings of these tubes form first cooling fluid inlets of the chamber 14, through which the first cooling fluid CF1 is supplied to the chamber 14. The supply may optionally be controlled via a compressor (not shown) . The inlets may thus be controllable to supply first cooling fluid CF1. In order to provide circulation there is a number of corresponding fluid propagating units 18A, 18B, 18C and 18D, here in the form of nozzles. Through the tube openings being provided in the center of the nozzles, the shape of the nozzles will force the cooling fluid exiting from the tubes 20A, 20B, 20C and 20D to

circulate in the chamber 14. The cooling fluid inlets may be provided evenly spaced around the walls

surrounding the stack. There is also a controllable cooling fluid outlet 22 leading out from the chamber 14 and here lead out from the ceiling of the chamber. The outlet 22 is thus controllable to remove first cooling fluid CF1 from the chamber 14 during operation of the arrangement. The outlet 22 is with advantage controlled through a pressure reducing valve 24 that will open the outlet 22 if the pressure is above a given level. In this way it is possible to supply new first cooling fluid CF1 and remove used first cooling fluid and thus to keep a supply of cooling fluid together with

retaining a desired cooling medium pressure.

In this first variation of the invention there is a main circulating flow of first cooling fluid CF1 from the tube and nozzle combinations 18A, 18B, 18C, 18D, 20A, 20B, 20C and 20D to the exterior or the periphery of the cells FC1 - FC6 in the stack, through the primary fluid channels PCH1 - PCH6 and into the hollow center of the stack, where the cooling fluid CFl is guided towards the bottom of the stack by the shape of the guiding unit, i.e. by the shape of the exterior of the tube 21. The cooling fluid CFl then enters the center of tube 21 and rises upwards towards the ceiling of the chamber 14, from where it then returns to the outside or periphery of the cells FC1 - FC6 of the stack .

At least some of the walls of the chamber 14 may be provided with or include tertiary cooling fluid

channels TCH 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 CFl. These channels TCH are provided in the interior of the walls and thereby the second cooling fluid CF2 is separated from the first cooling fluid CFl .

In operation the first cooling fluid CFl in the chamber is kept at a high pressure, typically in the range of 1 - 5 bars and then preferably at 3 bars. The pressure may be regulated by the valve 24. Some fuel cell membranes may not be able to withstand pressures above 3 bar, in which case the pressure may be 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 nozzle tube combinations 18A, 18B, 18C, 18D, 20A, 20B, 20C, 20D continuously supplies the first cooling fluid CFl for circulation 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, in which process also heat is generated, where the hydrogen is supplied to and from the secondary channels SCH1 - SCH6 using the tubes 30 and 32. The fluid propagating units ensure that the first cooling fluid CF1 is circulated in the cooling chamber 14 in a loop comprising the fuel cells FC1 -

FC6 and thus continuously transports the first cooling fluid CF1 past the fuel cells of the stack. This is in the first embodiment done through the tubes 20A, 20B, 20C, 20D and nozzles 18A, 18B, 18C, 18D causing the first cooling fluid CF1 to enter the primary fluid channels PCH1 - PCH6 at the periphery of the stacked cells FC1 - FC6 and pass through these primary fluid channels to the hollow interior, from there down to the bottom of the stack through the center of the tube 21 to the top of the stack and then back to the periphery.

As the first cooling fluid CF1 then passes by the fuel cells, 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 fluid channels are also acting as chemical substance inlets for the chemical reaction of the fuel cells. The cooling fluid which is not used for generating energy is thus used for cooling the cells. However, in the process of this cooling, the first cooling fluid CF1 has also been heated. Therefore the first cooling fluid CF1 may be passed by or transported past the walls, where the fluid is cooled by these walls using the second cooling fluid CF2 in the tertiary fluid channels TCH.

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 fluid propagating unit again causes the first cooling fluid CF1 to leave the exterior of the stack and pass through the primary fluid channels PCI - PCH6 into the hollow interior, down to the bottom of the stack, up through the middle of the guiding unit 21 to the top of the stack and then back to the periphery of the cells. The flow is thus repeated continuously in this first variation.

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 different parts of a fuel cell are 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. In this way 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 is obtained. These fluids are furthermore separated to eliminate the risk for leakage of coolant into the fuel cell electrochemical process areas. An outer liquid cooling circuit is embodied as channels in the 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.

The first and second areas of the primary fluid channel inlets and outlets are typically dimensioned for providing an even flow speed. A larger area typically provides a lower speed than a smaller area. However, as some of the fluid is consumed then the difference in area is designed for counteracting the lower flow rate caused by the loss of the fluid.

The angling of the inlet and outlet areas makes it easier to design the two areas for obtaining a desired flow rate relationship. It is possible to optimize the absorption of oxygen in relation to absorption of hydrogen. The angling may thus provide a flow rate variation of the fluid when passing through the channel that improves absorption of oxygen. The flow rate may for instance be higher at the inlet than during the passage through the channel. The curved channels furthermore improves the speed with which the fluid propagates and therefore also the cooling. The use of spiral shaped channels, perhaps together with the guiding unit can be used for obtaining a cyclone effect on the flow of the first cooling fluid, which improves the flow considerably. Because of this the fuel cell provides improved efficiency and a more even

temperature distribution. The use of tubes an nozzles provide a further advantage in that no moving parts are needed in the chamber.

Furthermore, by providing the fuel cell with hybrid cooling and air circulation the power density of the fuel cell can be increased 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.

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.

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. Fig. 8 shows a second variation of the arrangement. This figure also shows that the stack of fuel cells are connected between two circular discs 33 and 34 of electrically conducting material, between which the anodes and cathodes of the fuel cells are connected in a known manner. A first of the discs 33 is here

connected to a first electric terminal 36 and the second 34 is connected to a second electric terminal 37. The stack thereby provides an output voltage V between the first and second electric terminals 36 and 37. The stack with guiding unit 21 and first and second plates 33 and 35 are furthermore fastened to the ceiling of the chamber using a clamping nut 35. Here the second disc 34 also functions as a pressure plate. The tubes 30 and 32 where hydrogen is supplied and removed does in the second variation also stretch through the ceiling, while the primary cooling fluid CF is provided through the chamber wall. As the whole stack structure is fastened to the ceiling of the chamber the top of the guiding unit 21 provides a flow of primary cooling fluid out through the ceiling. The cooling fluid inlets , fluid propagating units and cooling fluid outlet may be provided in the same as in the first variation and have therefore been omitted. Since the stack is fastened to the ceiling, there is no recirculation of first cooling fluid from the top of the stack to the periphery of the fuel cell discs.

Fig. 9 shows a simplified third variation of the arrangement. Here the elements in the interior of the chamber have been omitted for clarity purposes . As mentioned earlier the cooling of the first cooling fluid leads to the second cooling fluid CF2 being heated. The energy transferred in this way can also be used, for instance in the heating of a premises. For this reason the tertiary fluid channels TCH carrying the second cooling fluid CF2 are connected to fluid transportation means in the form of pipes or ducts 39 leading to another entity in the form of a heat

exchanger 38, to which heat exchanger 38 further fluid transporting means in the form of pipes or ducts 40 are connected. The further pipes or ducts 40 of this first heat exchanger 38 can be transporting heating fluid HF1 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 heat exchanger 38 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 variation 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. A stack may provide an insufficient voltage. 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. 10 schematically shows how a first and a second stack ST1 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.

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.

In the example above the fuel propagating units were described as a combination of fluid injection nozzles and fluid guiding tubes. However, other types of fluid propagating units may be used. One type that may be used is a fan placed in the chamber. In order to provide circulation such a fan, it may be joined to a motor via a shaft going through a wall. The motor may be an air motor, in which case no lubricant is needed.

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. The tubes 30 and 32 in fig. 7 may thus be connected to a reformer.

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. The arrangement can vary from only

comprising a fuel cell, a fuel cell stack as well as be a stack in a chamber with fuel propagating unit. It should also be realized that the first, second and third variations of the invention can be combined in every possible way and that any variations described in relation to one variation can be made in relation to another embodiment. It is also possible to omit the tertiary fluid channels and the second cooling fluid. The fuel cell discs may be varied considerably. The primary fluid channels may have virtually any shape as long as they start at the periphery and end at the hollow center. It is also not necessary that the first area of the fluid channel inlet is larger than the second area of the fluid channel outlet. The opposite situation may exist. The areas may in one variation furthermore be equal. It should also be realized that the guiding unit may be omitted. It is furthermore possible to place the fuel cells anywhere in the chamber .

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 (16)

comprising at least one fuel cell (FC; FC1, FC2, FC3, FC4, FC5, FC6) being shaped as a circular disc with a hollow center (14), the fuel cells each comprising at least one primary fluid channel (PCH; PCH1, PCH2, PCH3, PCH3, PCH4, PCH5, PCH6) provided on one side of the disc and stretching from the periphery (12) to the hollow center (14) and at least one secondary fluid channel (SCH; SCH1, SCH2, SCH3, SCH3, SCH4, SCH5, SCH6) provided on an opposite side of the disc, wherein a primary fluid channel is provided with an inlet (CHI) at the periphery (12) and an outlet (CHO) at the hollow center (14) of the disc.

2. The energy generation arrangement according to claim 1, wherein the primary channel is angled with a first angle (a) to the radial direction (R) at the inlet and angled with a second angle (β) to the radius (R) at the outlet.

3. The energy generation arrangement according to claim 2, wherein the primary fluid channel is shaped as a spiral.

4. The energy generation arrangement according to any previous claim, wherein the primary fluid channel inlet has a first area (Al) and the primary fluid channel outlet has a second area (A2), where the area of the primary fluid channel inlet is larger than the area of the primary fluid channel outlet .

5. The energy generation arrangement according to claim 4, wherein the first area is at least 1.5 times larger than the second area.

6. The energy generation arrangement according to claim 4, wherein the first area is at least 2.5 times larger than the second area 7. The energy generation arrangement (16) according to any previous claim, wherein there is more than one disc shaped fuel cell (FC1, FC2, FC3, FC4, FC5, FC6) provided in a stack, the arrangement further comprising :

- a cooling chamber (14) surrounding said stack,

at least one fluid propagating unit (18A, 18B, 18c, 18D, 20A, 20B, 20C, 20D) configured to make a first fluid pass in a flow through the primary fluid channels (PCH1, PCH2, PCH3, PCH3, PCH4, PCH5, PCH6) of the discs of the stack from the periphery to the hollow center and up along a center axis of the stack, said first fluid thereby acting as a chemical substance involved in the generation of electric power as well as a coolant for cooling the stack.

8. The energy generation arrangement according to claim 7, further comprising a guiding unit (21) in the center of the stack, said guiding unit being shaped for guiding the flow of first fluid to the bottom of the stack and from there up through the center to the top of the stack.

9. The energy generation arrangement according to claim 8, wherein the guiding unit is a tube externally shaped as a cone with walls of increasing width along the length of a stack axis.

10. The energy generation arrangement according to any of claims 7 - 9, wherein the chamber has walls surrounding said stack, wherein at least one of said walls is provided with tertiary fluid channels (TCH) .

11. The energy generation arrangement according to any of claims 7 - 10, further comprising at least one cooling fluid inlet (20A, 20B, 20C, 20D) leading to the chamber and a controllable cooling fluid outlet (22) leading from the chamber, the inlet being configured to supply first cooling fluid and the outlet to remove first cooling fluid during operation of the fluid propagating unit.

12. The energy generation arrangement according to claim 11, wherein the cooling fluid outlet (22) is controlled through a pressure reducing valve configured to open the cooling fluid outlet if the pressure is above a given level .

13. The energy generation arrangement according to any of claims 7 - 12, wherein the first cooling fluid is a gas provided in the chamber at a pressure in the range of 1 - 5 bars .

14. The energy generation arrangement according to any of claims 7 - 13, 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.

15. The energy generation arrangement according to any of claims 7 - 14, 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.

16. The energy generation arrangement according to any of claims 7 - 15, wherein the fluid propagating unit is provided as a tube (20A, 20B, 20C, 20D) with an opening provided in a nozzle (18A, 18B, 18C, 18D) .

17. The energy generation arrangement according to any of claims 7 - 16, wherein said at least one fluid propagating unit is further configured to make said flow of first fluid return back to the periphery of the discs of the stack