FR2534072A1 - LEAKING GASKET JOINING LEAKS FOR FUEL CELL SYSTEM AND METHOD OF IMPLEMENTING SAME - Google Patents

Abstract

THE INVENTION RELATES TO A MANIFOLD GASKET WHICH ALLOWS LEAKS. THIS GASKET IS USED IN A SYSTEM OF FUEL CELLS INCLUDING A STACK 10 OF SEVERAL FUEL CELLS 12, EXTERIOR REACTIVE GAS COLLECTORS 24, 26, 28, 30 ATTACHED TO THIS STACK 10, GAS-TIGHT ELEMENTS 29 ARRANGEMENTS BETWEEN THESE MANIFOLDS 24, 26, 28, 30 AND STACKING 10, A MEANS FOR CONDUCTING THE REACTIVE GASES FROM THE FUEL CELLS 12 INTO THE MANIFOLDS 24, 26, 28, 30 AT A FIRST PRESSURE AND A MEANS FOR DELIVERING INERT GAS INTO A SPACE 15 FROM A PRESSURE VESSEL 14 TO A SECOND PRESSURE GREATER THAN THE FIRST. THE INVENTION IS USED TO PREVENT REAGENT GAS LEAKS FROM A FUEL CELL SYSTEM INCLUDING EXTERNAL REACTIVE GAS COLLECTORS.

Description

2534072-

  Collector gasket letting leaks.

  The present invention relates to systems

of fuel cells.

  Fuel cell systems such as fuel cell power plants for power generation typically include a large number of fuel cells that are stacked and

  electrically connected in series to form an

  pumping A fuel cell system can contain

  number of stackings Collectors are used to carry reactive gases to the batteries,

  as well as to receive spent reactive gases

  coming from these These collectors are fixed

  hermetically against the lateral surfaces of the

  and a gasket or sealing material

  is placed between the surface of the stack and the edge of the collector to try to prevent

  reactive gas leaks out of the collectors

  Nos. 1 and 2 of US Pat. No. 4,345,009 of the Applicant illustrate a stack of fuel cells whose electrolyte is made of phosphoric acid and to the sides of which are fixed

  external collectors for the reactive gases.

  The ability to positively seal the edges

  collectors against the surfaces of the stack

  several factors, in particular the pressure of the reactive gases, the operating temperature and the type of electrolyte used in the cells, thus limiting

  sealants that can be used.

  There may also be a limitation as to how much force can be used

  to press the external collectors against the over-

faces of the stack.

  Fuel cells including electrolyte

  consists of a molten carbonate, can function-

  at temperatures of the order of 6490 C and with reactive gas pressures of the order of 9.9 bar

  or even more when put into service

  Beyond atmospheric pressure, stacking is

  placed inside a pressure vessel

  is very difficult to completely prevent the escape

  reactive gases out of the collectors under such conditions, although this is necessary

  to prevent the accumulation of combustible gases in the

  inside the pressure vessel surrounding the stack,

  as well as to maintain a high yield.

  An object of the present invention is to prevent

  expensive reactive gas leaks out of a stack of fuel cells with gas collectors

external reagents.

  According to the present invention, a stack of

  fuel cells with external collectors

  takes seals between the collectors

  and the stacking surfaces, the latter being

  inside a pressure vessel which is continuously fed with an inert gas at a higher pressure than the reactive gases contained

  in the stack, the inert gas contained in the recipe

  of pressure continuously escaping through the aforementioned joints to enter the collectors of

gas reagents -

  Rather than trying to prevent leaks,

  the fuel cell system of the present invention.

  tion lets them pass; however, this system ensures that these leaks take place in the reactant gas manifolds and not outside them and also

  that they are virtually harmless to the system.

  tem, thus removing the awkward task of creating a positive seal in a

very hostile.

  The invention is particularly well suited

  for use with fuel cell systems

  Since the electrolyte is made of molten carbonate, it has not been possible to create an outer collector gasket that does not leak through this type of fuel cell stack. As used here, the expression

  * "inert gas" means a gas that does not contain any

  present in sufficient quantities to react

  detrimental to the components of the

  pounding, this gas does not significantly reduce the

  of batteries as it passes through the

  Thus, for security reasons,

  the inert gas can not contain significant quantities

  oxidizing or oxidizable constituents (eg

  ple, 02 'Cl, CO, CH 4 and H 2) which could react to the operating temperatures of the cell, since the combination of these constituents can cause an explosion Constituents-which could accelerate the corrosion of the constituent parts of the cells or of the

  collectors are also prohibited.

  In a preferred embodiment, molten carbonate is used as the electrolyte in the stack fuel cells; in addition, the gas

  Exhausted fuel leaves the outlet manifold.

  fuel and is burned to eliminate

  all combustible constituents such as oxy-

  carbon, unreacted hydrogen,

  other hydrocarbons This gas burned, or a part

  part of it, is then introduced into the

  pressure as inert gas.

  know to which have been submitted several piles of

  at 20 stacks of 0.09 m 2, it has been shown that

  inert gas generation in the stack via

  collector seals could be maintained at one

  calf that reduces the efficiency of the battery system to

less than 0.1% fuel.

  The aforementioned objects, features, and advantages of the present invention, as well as other

  appear more clearly on reading the

  DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS DETAILED WITH REFERENCE TO THE APPENDIX BRIEFLY IN WHICH FIG. 1 is a partly diagrammatic view and partly in the form of a block diagram illustrating a fuel cell system embodying implement the features of the present invention; and FIG. 2 is a graph illustrating the effects of leaks at the collectors on the

  fuel cell system performance.

  Reference will now be made to FIG. 1 which illustrates, by way of example, a battery system with

  fuel according to one embodiment of the present invention.

  In this system, a stack of

  the fuel is generally designated by the reference numeral 10 This stack 10 consists of a plurality of fuel cells 12 which are

  superimposed and electrically connected in series.

  Each of these cells contains an electrolyte consisting of a molten carbonate disposed between two electrodes; adjacent piles are separated by plates

  electrically conductive and impervious to gases.

  The construction of these piles is well known in the

  technique and is not part of the character of new-

  of the present invention Stacking 10 is arranged

  inside a pressure-tight container 14.

  A gas space 15 is thus defined between the stack

  and the container 14 surrounding the latter.

  At each of the four sides 16, 18, 20 and 22 of the stack, a reagent gas manifold 24, 26, 28, 30 is respectively attached by a means

  who is not represented, but who could be

  It is considered that the method of attaching the collectors to the sides of the stack does not have to be fitted with suitable collars around the stack 10 as illustrated in the aforesaid US Pat. No. 4,245,009.

  is not part of the present invention.

  The "frame-like" seal type 29 is clamped between each of the side faces 16, 18, 20, 22

  of the stack 10 and a peripheral rim 31 of the collar

  associated reader 24, 26, 28, 30 The seals 29 do not

  are not gas-tight. They can be, for example,

  ply, ceramic fiber joints that are porous and

  compressible, while being virtually inert

  molten carbonates of the type generally used

  as an electrolyte in fuel cells.

  The collector 24 is the fuel gas inlet manifold to which a hydrogen-rich gaseous stream is conveyed via a pipe 32. The collector 24 conveys the fuel gas to the stacks 12 and this gas flows across the stack from which it passes through. The exhausted fuel gas (i.e., most of the hydrogen reacted) leaves the manifold 28 via a pipe 34.

  manifold 26 is the oxidizing gas inlet manifold.

  It receives the oxidizing gas via a pipe 36 and it

  This oxidizing gas flows across the stack from which it passes through the different cells in a direction-perpendicular to that followed by the fuel gas, to end in the outlet manifold of the oxidizing gas.

  the manifold 30 via a pipe 38.

  In the simple fuel cell system

6 2534072

  shown in FIG. 1, a feedstock

  which may be a liquid hydrocarbon or

  Zeux, is put under a pressure to which the fuel cells are able to operate, by means not shown (The batteries can operate at atmospheric pressure, but it is advantageous to

  put into operation beyond the atmospheric pressure

  that together with water vapor at the same pressure, this fuel is introduced into a conditioning apparatus such as a steam reforming apparatus 40 In this reforming apparatus 40, hydrogen is formed by reaction of the vapor

  water and carbon load in the presence of a

  a suitable catalyst, such as nickel on a support in

  The heat for the endogenous reaction

  is provided by a burner 42

  The hydrogen-rich reforming feedstock contains, by volume, about 50% hydrogen, 10% CO, 10% CO 2 and 30% H. This fuel is reformed.

  is routed via line 32 of the

  forming with water vapor 40 in the collector

  fuel gas 24 of the stack 10.

  Exhausted fuel gas leaving the collector

  fuel gas outlet 28 via line 34,

  carbon dioxide, hydrogen having no

  unreacted, carbon monoxide and water vapor.

  This gaseous stream then passes through a condenser 44 and the water is removed via a pipe 46 This water is transformed into steam in a boiler 48 and this steam is conveyed from the boiler into the steam reforming apparatus of water 40 via a

driving 50.

  Compressed air supplied by a compressor 54

  driven by a turbine 56 is routed in the col-

  gas-oxidant reader 26 of the stack 10 via the con-

  36, and constitutes the oxidizing gas for the

  The fuel 12 As is known in the art,

  that the air does not contain a sufficient amount of carbon dioxide to effectively initiate the reaction in fuel cells whose electrolyte is a molten carbonate;

  the C 02 contained in the exhaust gas effluent

  must be added to the air introduced into the stack

  but, before making this addition, es-

  all the combustible substances

  In this way, the spent fuel gas which is now relatively dry is fed from the condenser 44 into the burner 42.

  the compressor 54 is also fed into the burner

  Their 42 via a pipe 58 The supplied air burner and the oxidizing gas inlet manifold 26 is at the

  same pressure as the fuel entering the

  same as steam reforming 40, so that there is a minimum pressure difference across each stack 12 and that the pressure in the outer manifolds 24, 26, 28 and 30 differs only as a result of inevitable pressure drops occurring in the system Preferably, the amount of air introduced into the burner 42 is just sufficient to ensure substantially complete combustion of hydrogen, carbon monoxide and other combustible substances, such as so that

  the effluent leaving the burner 42 does not contain substantially

  only carbon dioxide, nitrogen,

  as well as a small amount of water.

  After the passage of the oxidizing gas through the

  batteries, the hot exhausted oxidant gas

  both the outlet manifold 30, through a heat exchanger 62 to generate the heat required for the boiler 48 The exhaust gas stream exhausted which still contains considerable energy, can

  then be used to drive the turbine 56.

  According to the present invention, a small amount of burner effluent from line 60 is diverted into line 64 and its pressure is slightly increased by any suitable means such as a blower 66.

  whose pressure is now slightly higher than

  to that of the reactive gases introduced into the

  10, is conveyed into the gas space 15 of the

  pressure container 14, and it escapes continuously

  by the seals 29 to enter the col-

reactive gas readers.

  As mentioned above, the ef-

  fluent burner contains essentially only

  carbon dioxide, nitrogen, and a small amount of

  The amount of water vapor is obviously quite unreactive and non-corrosive within the stack. The carbon dioxide entering the collectors is, of course, also harmless, since Carbon dioxide is a required constituent of the oxidizing gas and is a by-product of the reaction taking place in the fuel-side fuel cell. Water in small quantities is

  equally harmless If, for any reason whatsoever,

  the burner effluent 42 should contain a quantity

  unacceptable degree of hydrogen or other

  or an unacceptable quantity of water, an additional burner and / or condenser (s) could then be inserted in the pipe 64

  to reduce the amounts of these constituents.

  It is thought that it might be acceptable for gas

  inert introduced into the pressure vessel con-

  up to about 1.0% oxygen, up to about

  2.0% hydrogen and up to about 1.0% methane.

  The limiting factor is the system performance

  and it does not matter whether the substance limits

busses are exceeded.

  FIG. 2 is a graph illustrating the effect of the inert gas entering the stack manifolds on the overall efficiency of a molten carbonate fuel cell power plant assuming that the plant has stackings. each made up of

  525 cells, each battery having an active surface area of

  viron 1.44 m 2 In this graph, leakage to

  readers are given in m 3 per hour and stacked

  By scaling the leakage rate actually occurring during battery stack tests with an active area of 0.09 m 2 each, it is estimated that the much larger piles of 525 cells could have leaks at a flow rate of about 6.94 m 3 per hour The graph shows that at a leak rate of 6.94 m 3 / hour, the efficiency of the power station decreases by less than

  0.1% (compared to the return obtained in the

  Leakage) - The loss of efficiency associated with a leakage rate of three or four times higher might be acceptable. One reason that the yield loss is so low is that the inert gas used for pressure

  and, therefore, most of the energy it

  firm, are not lost to the system In a

  test of the present invention, a stack of 20

  the molten carbonate electrolyte constituted each

  30.5 cm x 30.5 cm square was enclosed in a steel pressure vessel. On each of the four sides of the stack was a stainless steel reactive gas collector. zirconia fibers 0.254 cm thick as a joint material between the side surfaces

  stacking and the outer edges of the collectors.

  Reactive gases were sent to the

  At a pressure of 9.8 bar, an inert gas consisting of equal parts by weight was used.

  nitrogen and carbon dioxide to simulate ef-

  gaseous flue gas This gas was fed into the pressure vessel at a water column of 2.54

  at 7.62 cm beyond the pressure of the reactive gases.

  When operating in steady state, then

  that the operating temperature of the batteries was approximately

  6490 C, it has been determined that the inert gas

  pressure vessel was leaking into the

  reactive gas at a flow rate of approximately 0.51 m 3 / hr

  re, compared to reactive gas flow rates of

  6.75 m 3 / hour for the combustible gas and 12.1 m 3 / hr

  re, for the oxidizing gas Stacking functioned normally

  maliciously during this test If this stacking

  was part of a power plant, making it

  of the latter could be reduced by less than 0.1% as a result of the penetration of inert gas into flow-reactive gas

  above Although the invention has been illustrated

  described and described with reference to a form of

  preferred combination of the latter, a person skilled in the art

  take that various modifications and omissions may

  be considered both in its form and in its

  details, without departing from his mind and his

dre.

Claims (7)

  A fuel cell system comprising a stack (10) of a plurality of fuel cells; collective reactive gas reactors (24, 26, 28, 30) attached to this stack; gas-tight members (29) disposed between the gas manifolds (24, 26, 28, 30) and the stack (10); and means (32) for conveying the reactive gases of the fuel cells (12) into the manifolds (24, 26, 28, 30) at a first pressure;   characterized in that it also comprises a recipe   pressure pillar (14) surrounding the stack (10) and   the collectors (24, 26, 28, 30) by defining a   gas pace (15) between them; a source of an inert gas; and means (64, 66) for conveying inert gas from said source into the gas space (15) defined within the pressure vessel (14) at a second pressure greater than first; the gastight elements (29) being designed and arranged to allow the continuous passage of gas at   through, so that the inert gas escapes   from the gas space (15) and into the reactant gas manifolds (24, 26, 28, 30).   by these gastight elements (29).   2 Fuel cell system according to the   1, characterized in that the fuel cells   (12) each contain an electrolyte based on a molten carbonate.   A fuel cell system comprising: a stack (10) of a plurality of fuel cells (12) each containing an electrolyte based on a molten carbonate; external reactive gas collectors (24, 26, 28, 30) attached to said stack (10) and comprising   a fuel gas inlet manifold (24) for   fuel to the batteries (12), a col-   fuel gas outlet reader (28) for receiving the spent fuel from the batteries   (12), an oxidizing gas inlet manifold (26) of   to feed the oxidizing gas to the batteries, as well as   an oxidizing gas outlet manifold (30) for   see the spent oxidizing gas from the cells (12); gas-tight members (29) disposed between the gas manifolds (24, 26, 28, 30) and the stack   means (32) for conveying a fuel gas   at a first pressure in the collector of   fuel gas (24) and (36) an oxidizing gas at said first pressure in the oxidant gas inlet manifold (26); and means (34, 52, 60, 36) for conveying at least a portion of the spent fuel gas from the fuel gas outlet manifold (28) into the oxidizing gas manifold (26);   characterized in that it also comprises a recipe   pressure pusher (14) surrounding the stack (10) and the collectors (24, 26, 28, 30) defining a gas gap (15) therebetween; a burner (42);   means (34) for conveying at least one   exhausted fuel gas from the exhaust manifold   fuel gas (28) in this burner (42) for   to produce an inert gas; and means (64, 66) for   to convey at least a portion of this inert gas from the burner   their (42) in the gas space (15) defined inside   of the pressure vessel (14) to a second   greater than the first; the gastight elements (29) being designed and arranged to allow the continuous passage of gas at   through, so that the inert gas escapes   of the gas space (15) defined in the   pressure vessel (14) and enters the fuel gas (24, 28) and oxidizing gas (26, 30) inlet and outlet collectors through these sealed elements with gases (29).   4 Fuel cell system according to the   3, characterized in that an apparatus for con-   fuel assembly (40) is provided outside the pressure vessel (14) for converting a carbonaceous fuel into a hydrogen-rich gas, the means (32) for conveying a fuel gas through   the fuel inlet manifold comprising an element   the hydrogen-rich gas produced in this fuel conditioning apparatus (40), while the burner (42) is in a heat exchange relationship with this fuel conditioning apparatus (40). ) to provide heat to the latter.   A method of commissioning a fuel rod system according to claim 1, 2, 3 or 4,   this system comprising a stack (10) of several pins   the fuel (12), as well as   fuel gas (24, 28) and oxidant (26, 30) attached to the sides (16, 18, 20, 22) of   this stack (10) for conveying these gases to the fuel cells.   tible (12) of the stack (10) and to receive the spent fuel and oxidant reactive gases from these   batteries (12), the reactive gases contained in the   tors (24, 26, 28, 30) and the stack (10) being at a   first pressure, while the stack (10) is   placed in a pressure vessel (14) which defines a gas space (15) around the latter, characterized in that it comprises the steps of;   ensure a continuous supply of   in the above-mentioned gas space (15) at a second   pressure greater than the first; and let this inert gas continually escape   gas space (15) and enter the   reactant gases (24, 26, 28, 30).   6 Method for implementing a system of   fuel cells according to claim 5,   characterized in that the step of charging an inert gas into the gas space (15) comprises burning at least a portion of the spent fuel gas to an inert gas, and   least a first part of this combustible gas   burnt in the gas space (15).   7 Method for implementing a system of   fuel cells according to claim 6,   characterized in that each of the fuel cells (12)   This process also includes the step of introducing into the inlet manifold of oxidizing reactive gas (26) a second portion of the oxidant reactant gas (26). spent fuel gas burned.   8 Method for implementing a system of   fuel cells according to claim 7,   characterized in that a condition apparatus is provided   fueling (40) for transforming   a hydrocarbon fuel into a gas rich in hydro-   which is the combustible reactive gas for the batteries (12), the combustion step providing, to the device   of fuel conditioning (40), the heat generated   necessary for the conversion of hydro-   carbon dioxide into a combustible gas-rich reactive gas gene.