MXPA00001685A - Producing electrical energy from natural gas using a solid oxide fuel cell - Google Patents

Abstract

A process of generating electricity from natural gas (1) comprises supplying air (37) to the cathode side (20) of a solid oxide fuel cell (10);converting at the anode side (15) of the fuel cell the natural gas to hydrogen and carbon monoxide and allowing the cathode and anode reactions to take place to produce a potential difference betweem anode and cathode wherein an anode off-gas is produced which comprises water and carbon dioxide and feeding the anode off-gas from the anode side (15) to a ceramic afterburner (75) in which any unburned carbon monoxide and hydrogen are combusted without addition of nitrogen to the anode off-gas.

Description

A PROCEDURE WILL PRODUCE ELECTRICAL ENERGY FROM NATURAL GAS USING A BATTERY OF COMBUSTIBLE FUEL SOLID OXIDE FIELD OF THE INVENTION The present invention relates to a process for producing electric power from natural gas using a solid oxide fuel cell or battery. BACKGROUND OF THE INVENTION A fuel cell is an electrochemical cell that can continuously convert the chemical energy of a fuel and an oxidant into electrical energy by means of a process comprising an electrode-electrolyte system which does not vary. Here, the expression "cell" or "fuel cell" is also used to refer to a multiplicity of cells, which can be ordered in series or in parallel. A solid oxide fuel cell is a fuel cell comprising one side of the anode and one side of the cathode separated from each other by means of a solid electrolyte. The solid electrolyte is, for example, a mixture of yttria and zirconia. The REF .: 32731 charge transfer through the cathode electrolyte to the anode is performed by oxygen ions. The general reaction of the cathode of a solid oxide fuel cell is: 1/2 (a + b) 02 + 2 (a + b) e- - > (a + b) 02-; and the general reaction of the anode is: aH2 + bCO + (a + b) 02- - > aH20 + bC02 + 2 (a + b) e-. The anode waste gas therefore comprises carbon dioxide and water. The applicant is particularly interested in operating the fuel cell near a well that produces hydrocarbon fluids from an underground reservoir, this can be a gas well or an oil well that also produces associated gas. In both cases gas containing high pressure methane (25-50 MPa) is available. The carbon dioxide obtained as an effluent from the process is stored in a receptacle, which can be an underground reservoir. For this purpose the carbon dioxide has to be compressed to a pressure that allows to inject the carbon dioxide in the underground reservoir. The underground reservoir can be the reservoir from which hydrocarbon fluids or an aquifer layer are recovered. Therefore there are no carbon dioxide emissions. It is known from a European patent specification No. 482,222 the generation of electricity from natural gas at high pressure using a solid oxide fuel cell. The known method comprises the steps of: (a) supplying oxidant to the cathode side of the fuel cell; (b) convert natural gas to hydrogen and carbon monoxide on the side of the fuel cell node and allow the reactions between cathode and anode to produce a potential difference between the anode and the cathode, where produces an anode waste gas comprising water and carbon dioxide; (c) removing the oxidant, in which the oxygen from the outlet on the cathode side was exhausted and the waste gas was removed from the anode from the outlet on the anode side; (d) feeding the waste anode waste gas from the anode side outlet of the fuel cell to a delayed combustion plant; (e) partially condensing the waste gas from the anode and removing the water from the waste gas from the anode to produce a stream rich in carbon dioxide; (f) compressing the carbon dioxide-rich stream to a predetermined pressure; (g) cooling the compressed stream rich in carbon dioxide at least partially by means of an indirect heat exchange with the stream of natural gas that is supplied to the fuel cell to obtain an at least partially liquefied stream rich in carbon dioxide. carbon; (h) separating non-condensable gas from the at least partially liquefied stream, rich in carbon dioxide; (i) store the current by l? less partially liquefied, rich in carbon dioxide in a receptacle. Other fuel cell or fuel cell systems in which the waste gases are treated in various ways described in Japanese Patent JP-A-6203845, in the European patent application 473152 and in the US patent No. 4,250,230. In the process disclosed in European Patent Specification No. 482,222 a conventional retarded combustion plant is used which is a high temperature oxidation process where a substantial amount of nitrogen is added to the anode waste gas. An object of the present invention is to provide an improved method for producing electricity from natural gas using a solid oxide fuel cell which is provided with a delayed combustion plant where the addition of nitrogen to the anode waste gas is minimal or has been eliminated.

BRIEF DESCRIPTION OF THE INVENTION In the method according to the present invention a retarded combustion plant is used where the combustion of carbon monoxide and hydrogen that were not burned is carried out, without the addition of a substantial amount of nitrogen to the gas Anode scrap. The nitrogen forms a substantially non-condensable gas that is difficult to remove from the anode waste gas and thus complicates the storage process of the anode waste gas in a receptacle.

The present invention provides an integrated process, wherein low pressure electric power can be obtained from natural gas at high pressure, and where liquefied carbon dioxide is produced at high pressure, which can be injected into an underground reservoir. In the method of the invention, the energy obtained by expansion of the natural gas supplied to the fuel cell is suitably used to compress at least in part a current rich in carbon dioxide discharged by the cell or fuel cell. A solid oxide fuel cell operates at high temperatures, at approximately 1000 ° C and this allows at least part of the conversion of methane to hydrogen and carbon monoxide in the solid oxide fuel cell, a reaction that It is catalyzed by metals at the anode. Properly, therefore, step (b) comprises allowing, on the anode side of the fuel cell, the stream of heated low pressure natural gas to react with water to form hydrogen and monoxide. of carbon, and allow the cathode and anode reactions to be performed to produce a potential difference between the anode and the cathode, where an anode waste gas comprising water and carbon dioxide is produced. Initially, a little water must be added to the natural gas to initiate the methane conversion reaction, however, subsequently, the water obtained in the reaction of the anode will react with methane. The invention also relates to a solid fuel cell that is equipped with a delayed combustion plant. According to the invention, the delayed combustion plant comprises a ceramic membrane which is substantially permeable to oxygen and substantially impermeable to nitrogen, the membrane through which oxygen is supplied to the waste gas of the anode for the oxidation of non-toxic components. burned in the anode waste gas. Preferably the ceramic membrane is a high temperature oxygen ceramic oxide membrane that conducts oxygen ions. Suitably, the fuel cell and the retarded combustion plant are equipped with a series of ceramic membrane tubes which are closed at one end and through which air circulates.

Reference is now made to U.S. Patent Specification No. 4,751,151. This publication discloses a process for producing electrical energy from a fossil fuel that is first converted into a reformer in a hydrogen-rich fuel gas that also contains carbon dioxide. The known process comprises supplying the hydrogen-rich gaseous fuel to the anode-side inlet of a fuel cell; supplying air to the cathode side of the fuel cell and removing the exhausted air from the outlet on the cathode side; allow the reaction of the anode (H2-> 2H + + 2e-) and the cathode reaction (1/2 02 + 2H- + 2e- -> H20) to produce a potential difference between the anode and the cathode; removing the waste gas from the anode, in which the hydrogen was exhausted, from the anode side; and removing the carbon dioxide from the waste gas of the anode, in which the hydrogen was exhausted.

In the known method a non-alkaline fuel cell is used in the form of an acid fuel cell that tolerates the dioxide of carbon. Thus, the carbon dioxide produced as a by-product in the conversion of fossil fuel to hydrogen does not adversely affect the performance of the fuel cell. Removal of the carbon dioxide from the anode waste gas is done by absorbing carbon dioxide in an aqueous absorption solution that is regenerated to recover the carbon dioxide for a useful purpose. This publication is not relevant to the present invention since it does not disclose an integrated process for producing electrical energy from natural gas at high pressure. Furthermore, this publication does not reveal the recovery of carbon dioxide by means of its liquefaction at high pressure.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example in greater detail with reference to the accompanying drawings, in which: Fig. 1 schematically shows a plant for carrying out the present invention; and Fig. 2 schematically shows a solid oxide fuel cell provided with a ceramic delayed combustion plant.

DESCRIPTION OF THE PREFERRED MODALITIES Fig. 1 shows a flow diagram of the method for generating electricity according to the present invention. The high pressure natural gas is supplied through line 1 to an expansion motor in the form of a turbo expander 3, turbo expander 3 in which the natural gas is expanded at high pressure to a lower pressure. The turbo expander 3 drives a load in the form of an electrical generator 6. The low pressure natural gas passes through the conduit 8 to a solid oxide fuel cell 10. The low pressure natural gas passing through the conduit 8 is heated by means of indirect heat exchange in the heat exchanger 11. The solid oxide fuel cell 10 comprises a side of the cathode 15 having an inlet 17 and an outlet 18, and a side of the node 20 having an inlet 25 and an outlet 26. Between the side of the cathode 15 and the side of the node 20 is located a solid electrolyte 30, provided with a node '33 on the side of the solid electrolyte facing the anode side 15 and a cathode 35 in the opposite side of the solid electrolyte 30.

An oxidant in the form of air is supplied to the inlet 25 on the cathode side 20 of the solid oxide fuel cell 10 through the conduit 37. The heated low pressure natural gas is supplied with water supplied through the conduit 39 to the inlet 17 on the cathode side 15 of the solid oxide fuel cell 10. On the cathode side 15 the natural gas at low pressure is converted into hydrogen and carbon monoxide. The conversion is carried out according to the reaction H20 + CH4 - > 3H2 + CO. The cathode reaction is carried out at the cathode 35, where oxygen ions are produced which can pass through the solid electrolyte 30 to the node 33, where the anode reaction is carried out, where a waste gas is produced from the node which comprises water and carbon dioxide. A potential difference occurs between the anode 33 and the cathode 35. The terminals of the node 33 and the cathode 35 are connected to a load 44, through electrically conductive wires 41 and 42. The air in which the oxygen was exhausted it is withdrawn through the conduit 46 of the outlet 26 of the cathode side 20 and the waste gas from the node is withdrawn through the conduit 47 of the outlet 18 of the anode side 15. In the heat exchanger 49 the gas is cooled of waste from the node and is partially condensed so as to remove water from the waste gas of the node in the separator 51. The water is removed from the separator 51 through the conduit 54 and the waste gas from the node having a water content Reduced is passed through conduit 56 to a compressor 57. The waste gas from the node, a current rich in carbon dioxide, is compressed in the compressor 57 at a predetermined pressure that allows to inject the current into an underground reservoir (which is not shown). The predetermined pressure is selected in such a way that the carbon dioxide, after further cooling, can be injected into the underground reservoir by means of an injection pump 9 (not shown). The compressor 57 is driven by the electric motor 58 driven at least partially by the electrical energy generated by the electric generator 6. The compressed stream rich in carbon dioxide is passed through the conduit 60 by a water separating device 70. to the heat exchanger 11. The water separating device 70 discharges the separated water through a conduit 71 and an exchanger heat 72 in the separator 51. From the carbon dioxide-rich stream flowing from the water separating device 70 the water is removed so that the water level is sufficiently low to exhibit the formation of carbon dioxide hydrates. The water separating device 70 is preferably a device in which the. fluid stream is induced to flow at supersonic velocity through a conduit so as to lower the temperature of the fluid below the water point of condensation, device further comprising elements imparting a whirling movement, which impart a whirling movement to the fluid stream so that the condensed water droplets are separated from the gas stream by means of centrifugal forces. A water separating device of this type is disclosed, for example, in Dutch patent application No. 8901841.

In the heat exchanger 11 the compressed stream is at least partially cooled by means of an indirect heat exchange with the natural gas stream at low pressure in the conduit 8 upstream of the solid electrolyte fuel cell 10. From the heat exchanger 11 a partially liquefied stream rich in carbon dioxide is removed, which is passed through the separator 63. If required, a heat exchanger (not shown) upstream of the separator 63 may be included, where more carbon dioxide is condensed by means of indirect heat exchange with a suitable refrigerant which is cooled in a separate cycle (not shown). The refrigerant is, for example, propaho or ammonia. In the separator 63, the non-condensable gas is separated from the liquefied stream rich in carbon dioxide. The non-condensable gas is withdrawn through line 66, and the liquefied stream rich in carbon dioxide is withdrawn through line 67. The "liquefied waste stream rich in carbon dioxide is supplied to an underground reservoir (not shown). ), where it is stored.

In the heat exchanger 49, the heated low pressure natural gas can be further heated to the required operating temperature before it enters the solid oxide fuel cell 10. Additionally, the air that is supplied to the inlet 25 on the side of the cathode 20 of the solid oxide fuel cell 10 through the conduit 37 can be heated by means of indirect heat exchange (not shown) with the waste gas of the anode, or with the air in which the oxygen leaving the side of the cathode 20 through the conduit 46. In the embodiment of the invention as described with reference to Fig. 1, the conversion of methane to hydrogen and carbon monoxide is done on the side of the node of the solid oxide fuel cell. At least part of this reaction can be performed upstream of the solid oxide fuel cell in a separate reactor. When the non-condensable gas from the separator 63 contains hydrogen or unused carbon monoxide, it can be recycled to the side of the node 15 of the solid oxide fuel cell 10. According to the invention, the solid oxide fuel cell is provided with a ceramic delayed combustion section where combustion of carbon monoxide and hydrogen, which were not burned, is performed substantially completely without adding nitrogen to the waste gas of the node. This is achieved by providing the solid electrolyte fuel cell with a delayed combustion section 75 comprising a high temperature ceramic oxide membrane 76, through which oxygen (02) is supplied to the gas stream of Anode scrap. The membrane 76 is preferably an oxygen permeable membrane that is a good conductor of oxygen ions. Suitable materials for a membrane 76 of this type are described in a "Ceramic Fuel Cells" article by Nguyen Q. Minh in J.A. Ceramic Society, vol. 76 (3), 563-588, 1993. Suitably, the solid oxide electrolyte is a mixture of 8% by mass of yttria and 92% by mass of zirconia, the anode comprises nickel and zirconia and the cathode comprises lanthanum manganite. The operating temperature of the solid oxide fuel cell is between 900 and 1000 ° C and its operating pressure is between 0.1 and 1 MPa (gauge). The temperature of the liquefied stream rich in carbon dioxide is between 5 and 200C and its pressure is between 3 and 8 MPa (gauge). The oxidant is suitably air, however, pure oxygen or air enriched with oxygen can also be used instead. The liquefied carbon dioxide can be stored in a receptacle that can be an underground reservoir, and which is properly, the underground reservoir from which methane (CH4) is produced. In the embodiment as described with reference to Fig. 1, the compressor 57 is driven by an electric motor 58. However, the turbo expander 3 can be connected directly to the compressor 57. In the described embodiment the turbo expander 3 as well as the compressor 57 comprise a single machine, however , may include more than one machine, wherein the turbo expander comprises more than one machine interconnected in the known manner and wherein the compressor comprises more than one machine interconnected in the known manner. Referring now to Fig. 2, a solid oxide fuel cell 80 is shown therein comprising an air supply 81 and a series of fuel cell tubes 82 through which air is circulated through the air ducts. supply of air 83 to an exhaust duct 84 for discharge of nitrogen-rich air, in which "oxygen was exhausted, from fuel cell 80. Methane (CH) containing natural gas is supplied to a series of compartments interconnected 85 of the fuel cell 10 through a gas inlet opening 86. The outer surfaces of the tubes 82 of the fuel cell form the anode side and the inner surfaces of the fuel cell tubes 82 form the cathode side of the fuel cell 80. A description of the operation of the tubes 83 of the fuel cell as illustrated in Fig. 2, can be obtained from "Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition, volume 11, pages 1114-1121, published by John Wiley & amp;; Sons, Inc. The fuel cell 80 is provided with a delayed combustion plant 87 comprising a series of ceramic oxygen separation tubes 88 to which air is supplied through the air supply conduits 89 which are similar. to the air supply ducts 83 of the tubes 82 of the fuel cell. The compartments 85 are connected in fluid communication with each other and with the interior of the retarded combustion plant 87 through the openings 90. The valves 91 are present in the exhaust duct 84 and the interior of the delayed combustion plant to control and compensating the fluid flow through the fuel cell 80 and the delayed combustion plant 87. The oxygen separation tubes 88 are made of a high temperature ceramic oxide membrane material which is permeable to oxygen and which it is an oxygen ion conductor, but it is substantially impermeable to nitrogen. Therefore, only a minimal amount of nitrogen, if any, is added to the waste gas stream from the anode 92, while substantially pure oxygen is added for the combustion of any carbon monoxide and unburned hydrogen in said stream. 92 in the delayed combustion plant 87. Therefore, a waste gas stream from the node that is rich in carbon dioxide and poor in carbon monoxide, hydrogen and nitrogen flows from the delayed combustion plant 87 to the exhaust duct of anode waste gas 93, wherein a fuel inlet 94 is present which is a communication with a conduit 94 for the supply of wet gas to a pre-reformer. The waste gas conduit 93 of the anode waste gas may be further connected to a drying, cooling and compressing equipment in the same manner as that illustrated with respect to the waste gas conduit of the anode 47 shown in FIG. 1. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (11)

1. Procedure for generating electricity from natural gas using a solid oxide fuel cell, comprising the steps of: (a) converting natural gas to hydrogen and carbon monoxide on the anode side of the fuel cell and letting the reactions of the cathode and the anode are carried out to produce a potential difference between the anode and the cathode, where an anode waste gas comprising water and carbon dioxide is produced; (b) removing the oxidant, in which the oxygen was exhausted, from the outlet on the side of the cathode and removing the waste gas from the anode from the outlet on the anode side; (c) feeding the anode waste gas from the anode side outlet of the fuel cell in a delayed combustion plant; (d) partially condensing the waste gas from the anode and removing the water from the waste gas from the anode to produce a stream rich in carbon dioxide; (e) compressing the carbon dioxide-rich stream at a predetermined pressure; (f) cooling the compressed stream rich in carbon dioxide at least partially by means of indirect heat exchange with the stream of natural gas that is supplied to the fuel cell to obtain a stream at least partially liquefied, rich in dioxide carbon; (g) separating non-condensable gas from the at least partially liquefied stream rich in carbon dioxide; and (h) injecting the at least partially liquefied stream, rich in carbon dioxide, into a receptacle; characterized in that the step (c) of feeding the waste gas from the anode in the delayed combustion plant comprises feeding the waste gas from the anode in a delayed combustion plant to which oxygen is supplied through a selective ceramic membrane which it separates the oxygen from the nitrogen and where the combustion of unburned carbon monoxide and hydrogen is carried out without the addition of a substantial amount of nitrogen to the anode waste gas.

2. The process according to claim 1, characterized in that step (a) comprises letting the heated low pressure natural gas stream, on the anode side of the solid oxide fuel cell, react with water to form hydrogen and monoxide of carbon, and allow the cathode and anode reactions to be performed to produce a potential difference between the anode and the cathode, where an anode waste gas comprising water and carbon dioxide is produced.

3. The process according to claim 1, characterized in that a ceramic delayed combustion plant comprising a high temperature ceramic oxide membrane, which is permeable to oxygen and which is an oxygen ion conductor, is used and is supplied oxygen through the membrane to the anode waste gas.

4. The process according to claim 1, characterized in that in step (d) the water is separated from the carbon dioxide-rich stream by means of a water separating device wherein the fluid stream is induced to circulate at supersonic velocity through a conduit so that the temperature of the fluid is below the point of condensation of water, a conduit that is provided with elements that impart a whirling movement, which induces the condensed water droplets to be separated from the current of fluid by centrifugal forces.

5. The method according to claim 1, characterized in that the receptacle is formed by the pore spaces of an underground ground formation.

- 6. - The method according to claim 5, characterized in that the formation of underground ground is a formation having oil and / or natural gas.

7. The process according to claim 6, characterized in that the liquefied stream rich in carbon dioxide is injected into the formation having oil and / or natural gas from which the natural gas that is supplied to the fuel cell is produced.

8. The method according to claim 7, characterized in that it comprises the steps of expanding the natural gas at a lower pressure in an expansion motor to produce energy and heating the low pressure natural gas stream through indirect heat exchange before feeding the natural gas stream to the solid oxide fuel cell.

9. A solid oxide fuel cell which is equipped with a delayed combustion plant, characterized in that the delayed combustion plant comprises a ceramic membrane which is substantially permeable to oxygen and substantially impermeable to nitrogen through which oxygen is supplied from the membrane to the anode waste gas for oxidation of unburned components in the anode waste gas.

10. The solid fuel cell with delayed combustion plant according to claim 9, characterized in that the ceramic membrane is a high temperature oxygen oxide ceramic membrane that conducts oxygen ions.

11. The solid fuel cell with retarded combustion plant according to claim 10, characterized in that the fuel cell and the delayed combustion plant are equipped with a series of ceramic membrane tubes that are closed at one end and through the which circulates air.