EP2332203A1

EP2332203A1 - Draining means for a fuel cell system and related adjustment mode

Info

Publication number: EP2332203A1
Application number: EP09800054A
Authority: EP
Inventors: Sadok Garnit; Francis Roy; Guillaume Joncquet; Jean-Philippe Poirot-Crouvezier
Original assignee: Commissariat a lEnergie Atomique CEA; Peugeot Citroen Automobiles SA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: PSA Automobiles SA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2008-07-25
Filing date: 2009-07-22
Publication date: 2011-06-15
Also published as: US20110189552A1; JP2011529246A; BRPI0916854A2; KR20110033944A; WO2010010105A1; CN102160222A; FR2934420A1; FR2934420B1

Abstract

The invention relates to a draining device for a fuel cell (FC). The effluents of a hydrogen FC including a recirculation circuit must be drained regularly in order to ensure optimal operation. The draining devices of the prior art are characterised by great variations in the effluent hydrogen content. The invention comprises integrating the draining means into the device for separating the liquid and gaseous phases of the effluents. Advantageously, fine adjustment means for the drainage flow rate are provided, which reduces the hydrogen losses in the drained effluents.

Description

PURGE MEANS FOR FUEL CELL SYSTEM AND ASSOCIATED REGULATION MODE

This invention applies to the field of the fuel cell (PAC), and more particularly to applications operating at low temperature and using a membrane as electrolyte. The cells concerned are those supplied with pure or almost pure hydrogen. Even in the so-called "recirculation" modes of operation where the hydrogen is reinjected into the cell, it is necessary to purge the system regularly to evacuate the pollutants and to prevent the increase of the nitrogen concentration from deteriorating the system performance. . Several purge modes have been devised, the two main ones being the periodic opening of a purge valve, described as "dead end" or frontal mode by those skilled in the art, and the other the production of a calibrated orifice in depending on the desired purge rate. The present invention relates to this second mode which theoretically has mainly the advantage over the first mode to avoid sudden variations in hydrogen flow inherent in the first mode. However, prior art calibrated orifice bleeders have the disadvantage that the effluents which contain water in the liquid phase, which constitutes the majority of the operating cases, create irregularities in the purge flow which, finally, recreate the disadvantages of the first mode. The following patent applications (US 2002/006534, US 2005/233191 and US 2006/086074) attempted to solve this problem by providing an adjustable purge function coupled with a phase separation function. These patents and patent applications, however, do not allow the purge flow rate to be adjusted throughout the operating range of a fuel cell. WO 2007/010372 addressed this problem by providing two purge valves whose flow rates can be combined to extend the operating range. This improvement, however, does not provide sufficient flexibility to allow easy adaptation to the possible scenarios of use of the fuel cell.

The present invention solves this problem by providing purge means coupled with the phase separation function, said means being Easily configurable to handle most possible scenarios of fuel cell use

For this purpose, the invention discloses a fuel or oxidant recycling circuit coupled to a fuel cell comprising means for purging the products of the reactions of the cells and means for separating the phases of said products, said purge means constituting a output of the phase separation means and comprising a plurality of calibrated output ports each controlled by an electromechanical valve whose opening and closing are controlled to select the group of active output ports at a given time, said recycling circuit being characterized in that said calibrated orifices are arranged in a housing whose inner face to the phase separation means is provided with at least one hole of dimensions adapted to the calibres of the outlet orifices and is able to move to conceal a portion of the calibrated orifices under control of selected means in the group of electrical and pneumatic means.

Advantageously, the housing has substantially the shape of a barrel and in that the movement of the inner face of said cavity is a rotating movement. Advantageously, the inner face of the separation means is provided with a single hole whose position corresponds to either the activation of only one of the outlet or the complete passivation of the purge means. Advantageously, the internal face of the phase separation means is provided with a single hole whose position corresponds either to the activation of at least two of the associated outlets or to complete passivation of the purge means.

Advantageously, a module is provided at the outlet of the purge means for performing effluent treatment chosen in the dilution, catalytic combustion group. The invention also discloses a method for producing electric current in a fuel cell comprising a set of elementary cells having an anode and a cathode, said assembly being supplied with fuel and with oxidant, one or the other being constituted by a gas mixture recycling circuit, said method comprising a product purge step of the reactions of the cells whose effluent flow in the purge step is controlled by alternating opening / closing of several calibrated orifices, said method being characterized in that said calibrated orifices are arranged in a housing whose internal face to the phase separation means is provided with at least a hole of dimensions adapted to the calibres of the outlet orifices and in that said method comprises a step of setting said internal face of said housing in motion by means selected from the group of electrical and pneumatic means for concealing a portion of the calibrated orifices. Advantageously, the mode of control of the effluent flow at the outlet of the purge step is combined with a variation of the pressure in the hydrogen supply line.

The invention also has the advantage of providing greater compactness since two functions, realized in the prior art in two physically distinct devices, are integrated in a single assembly having the dimensions of the most bulky of them ( the phase separator). In addition, several embodiments allow wide operating power ranges, where appropriate by providing barrels carrying one or more orifices possibly controlled by one or more valves, each cylinder being optimized for one of the operating ranges. Finally, it will be apparent from the description that the concept and the organ are simple and inexpensive to produce, maintain and control.

The invention will be better understood, its various features and advantages will emerge from the following description of several embodiments and its accompanying figures, including:

FIG. 1 represents an architecture of the prior art of a heat pump with recirculation of hydrogen according to the patent application US200601 10640; FIG. 2 represents the block diagram of a phase separator integrating a calibrated orifice for purging gas in one embodiment of the invention;

FIG. 3 represents a selector of one of three calibrated gas purge orifice in one embodiment of the invention; FIG. 4 represents a zero selector, one or two calibrated gas purge orifices out of five in one embodiment of the invention;

FIG. 5 represents an example of the prior art of regulating the nitrogen concentration in the hydrogen line by periodic purge;

FIG. 6 represents an example of regulation of the nitrogen concentration in the hydrogen line by opening and closing alternatively of a purge line incorporating a calibrated orifice in one embodiment of the invention.

FIG. 1 represents the architecture of a PAC 10 of the prior art with recirculation of hydrogen 30. A PAC is a stack of elementary cells 20 in which an electrochemical reaction takes place between two reagents which are introduced continuously. The fuel is brought into contact with the anode, the oxidant in contact with the cathode. The reaction is subdivided into two half reactions (oxidation and reduction), which take place on the one hand at the anode / electrolyte interface and on the other hand at the cathode / electrolyte interface. They can only take place if there is an ionic conductor between the two electrodes (the electrolyte) and an electronic conductor (the external electrical circuit). The stack of cells is only the place of the reaction: the reagents must be brought there, the products and the non-reactive species must be evacuated, just like the heat produced. Finally, the electrical circuit must be connected to the two terminals of the stack. In systems using hydrogen and atmospheric air as reagents, the air is fed to the cell by a compressor and passes through a series of components (filter, heat exchanger, humidifier, etc.) before entering the cell. battery at the cathode. At the cathode outlet, the air is generally charged with liquid water and steam. Part of this water is recovered for the purposes of humidification, then the residual gas is often discharged via a discharge device to maintain pressure line. Anode side hydrogen can be from a large number of different sources, which are usually also sources of pressure to avoid the use of a gas compression device. It is therefore most often brought to the battery after passing through one or more regulators or solenoid valves applying the expected pressure in the line. At the stack outlet, several scenarios are possible: either the gas leaving the anode is sufficiently pure and it can be partly reinjected into the battery inlet so as to ensure sufficient water supply to the battery, or it is simply purged at regular intervals to evacuate pollutants while minimizing the amount of hydrogen purged. In the first case we speak of recirculation of hydrogen, and it is the most common mode of operation on systems fed with hydrogen and air. The transfer of nitrogen through the membrane between the cathode side and the anode side is the main reason why one of these two modes of operation must be applied to the anode. And even in the case of recirculation, purging is necessary to prevent the nitrogen concentration from reaching values that greatly degrade the performance of the cell. The most common operation thus accumulates recirculation and purge. In FIG. 1, the purge valve 40 is shunt-mounted on the recirculation circuit 30. In this embodiment of the prior art, no phase separator is provided. However, this component is generally essential for the proper functioning of the PAC system incorporating recirculation. Indeed, the passage of liquid water in the body driving the recycled gas (pump or ejector) can alter the operation of the battery or the auxiliary member due to the large difference in density between the hydrogen (very light ) and liquid water. Or at the battery outlet anode side of the liquid water is present in most cases of operation. Moreover, if the purge is carried out continuously via a calibrated orifice, the passage of a two-phase fluid can also pose a problem by creating irregularities in the purge flow. In addition, the water recovered at the outlet of the phase separator can be reinjected into the humidifier 60. The humidification of the electrolytic membranes of the cells of the heat pump is indeed an essential function for its proper functioning.

As shown in FIG. 2, which represents the schematic diagram of a phase separator incorporating a calibrated gas purge orifice, in one embodiment of the invention, a phase separator 50 is provided as a bypass of the recirculation circuit. . An additional outlet is provided in the phase separator chamber and comprises a purge means 40. In this example, the purge means is an orifice whose caliber is chosen according to the purge flow rate to ensure. Advantageously, the orifice is located in an area near the outlet of the separator, where the gas is removed from all the liquid present at the inlet. As an indication, the gas purge flow rate, for a 20 kW rated power cell, varies between 1 and 2 NL / min for gas and gas purges.

10 and 60 ml / min for the purges of water.

In this embodiment, the purge rate can not be adjusted.

It is however possible to provide a periodic opening / closing valve downstream of the calibrated orifice which will allow fine adjustment. By adjusting the opening and closing times of the valve, it is possible to reduce the hydrogen losses.

In cases where a finer regulation of the purge flow would be required, typically ^Λ A at ³ A Nl / min of purge gas depending on the operating point, several purge lines with calibrated orifices of different section can be implanted on the separator. Each purge line thus created can be connected to a valve that will make it active or not during the operation of the system. Alternatively, an orifice selection device can be implanted directly in the phase separator. If the orifices are arranged on the same line can be used a pierced plate that is translated so as to coincide the hole or holes in the plate with one or more calibrated orifices. Nevertheless the most advantageous configuration, especially in terms of compactness is that where the orifices are arranged in a circle. The selector is then a pierced disk that simply rotate so that the hole or holes it contains coincide with one or more orifices.

Figures 3 and 4 show two examples of selectors that provide a better understanding of the operation of this device. In Figure 3, the disk on the inner face of the barrel is provided with a single hole whose diameter is greater than that of the largest calibrated orifices of the separator. It can take three open positions, each corresponding to one of the orifices, the purge being deactivated in all other positions of the disc. In Figure 4, the disc also has a single hole but a particular configuration that ensures the opening of two connected ports simultaneously, which allows to select five different rates. As an indication, for a stack of 20 kW, all calibrated can be 0.15, 0.2 and 0.25 mm in diameter. This diameter distribution will control the purge flow in all life situations. Note that during startup, the hydrogen pressure is low so the selector will be positioned on the largest hole. When the pressure increases, the selector will change position to ensure a regular purge flow. This dimensioning depends on the pressures, temperatures and battery core technology used.

The separators incorporating one or more orifices as described above can be connected directly to an air dilution module or to a catalytic burner. This connection can also be done via a valve which will ensure a tight closure of the purge in certain operating phases. Finally a phase separator such as those described above may be integrated with the cylinder head or one of the end plates of the fuel cell to which it is connected, in order to further reduce the compactness of the PAC system. The separators incorporating one or more orifices as described above can be connected directly to an air dilution module or to a catalytic burner. This connection can also be done via a valve which will ensure a tight closure of the purge in certain operating phases.

The management of the purge with the different phase separators described above is more or less flexible according to the described cases: with a single orifice, the purge flow rate depends only on the hydrogen pressure in the phase separator. One way to modulate this flow may be to vary the pressure in the hydrogen line: it will vary depending on the power provided by the battery; in this case a low pressure will be used for low power operation because the performance of the system is improved by a decrease in the purge rate; if necessary, it will also be possible for weak powers to return to a mode of operation by periodically opening a valve downstream of the orifice; with several orifices, the flow variations are simple to achieve using a selector such as those described above. The selector may be moved by electrical and / or pneumatic means; it is possible to associate as in the previous case a variation of the hydrogen pressure as a function of the power level provided by the battery; a mode of operation by periodic opening of a valve downstream of the orifices is also possible here.

The periodic opening of a valve located downstream of the orifices makes it possible to finely regulate the concentration of nitrogen in the hydrogen line. It differs from the purge systems used in the prior art because the rate of decrease in concentration during the opening phase of the valve is much lower, which makes the regulation more precise.

Figure 5 shows an example of the prior art of regulating the nitrogen concentration in the hydrogen line by periodic purge. The nitrogen concentration in the hydrogen line drops sharply (from 60% to zero) when the purge valve opens, while it slowly increases when the valve is closed. It is therefore possible to take advantage of this slow kinetics by associating a purge valve with a calibrated orifice device as described above. To limit the loss of hydrogen through this orifice in certain operating phases, the periodic closing of the purge valve greatly reduces the outflow (for example by a factor of 2 for a ratio of opening time / closing time). of 1), while regulating the nitrogen concentration in a range compatible with efficient operation of the fuel cell. We are then in the presence of a system almost equivalent to a smaller orifice.

FIG. 6 represents an example of this mode of operation of the hydrogen line by opening and closing an alternative purge line incorporating a calibrated orifice in one embodiment of the invention. In this case, the opening and closing times of the orifice are closer and the range of variation of the nitrogen concentration remains narrow (here between 30 and 40%). The examples described above are given by way of illustration of embodiments of the invention. They in no way limit the scope of the invention which is defined by the following claims.

Claims

A fuel or oxidizer recycling circuit (30) coupled to a fuel cell (10) comprising purge means (40) for the products of cell reactions and phase separating means (50) of said products, said purge means constituting an output of the phase separation means and comprising a plurality of calibrated output orifices each controlled by an electromechanical valve whose opening and closing are controlled to select the group of active outlet orifices at a given moment, said circuit recycling device being characterized in that said calibrated orifices are arranged in a housing whose inner face to the phase separation means is provided with at least one hole of dimensions adapted to the calibres of the outlet orifices and is able to move to conceal a part of the orifices calibrated under control of means selected from the group of electrical and pneumatic means.

2 recycling circuit according to claim 1 characterized in that the housing has substantially the shape of a barrel and in that the movement of the inner face of said cavity is a rotary movement.

3 recycling circuit according to claim 2 characterized in that the inner face of the separation means is provided with a single hole whose position corresponds to the activation of only one of the outlet or the complete passivation means purge.

Recirculation circuit according to Claim 2, characterized in that the internal face of the phase separation means is provided with a single hole whose position corresponds to either the activation of at least two of the associated output ports or to the complete passivation of the purging means.

5 recycling circuit according to one of the preceding claims characterized in that a module is provided at the outlet of the purge means for performing effluent treatment selected in the group dilution, catalytic burning.

A method of producing electric current in a fuel cell comprising a set of elementary cells having an anode and a cathode, said assembly being supplied with fuel and oxidant, one or the other consisting of a recycling circuit of the gaseous mixture, said process comprising a step of purging the products of the reactions of the cells whose effluent flow rate at the outlet of the purge step is controlled by alternative opening / closing of several calibrated orifices, said method being characterized in that said calibrated orifices are arranged in a housing whose inner face to the phase separation means is provided with at least one hole of dimensions adapted to the calibres of the outlet orifices and in that said method comprises a step of moving said face internal of said housing by means selected from the group of electrical and pneumatic means to obscure a portion of the calibrated orifices.

Electrical power generation method according to claim 6, characterized in that the recycling circuit is produced according to claim 2.

8 process for producing electric current according to claim 7 characterized in that the mode of control of the effluent flow at the outlet of the purge step is combined with a variation of the pressure in the hydrogen supply line.