Patent Application
20250046839
The present disclosure relates generally to direct carbon fuel cells and specifically to detecting or controlling carbon buildup in a direct carbon fuel cell.
The pursuit of direct carbon conversion to electrical power has been explored for more than a century, with past focus primarily on high carbon fuel stocks such as coal and biomass. Recent interest continues to be motivated by concerns over energy and the environment. Direct carbon fuel cells (DCFCs) are characterized by high efficiencies (theoretically 100%) and low emissions, since the primary output product is pure carbon dioxide (CO2) which can be sequestered or used as an industrial feedstock in various processes. However, DCFC technology is characterized by numerous technical challenges, and has not yet reached a development stage where it is suitable for widespread commercially adoption.
Direct carbon conversion is a high temperature process that can be achieved with different fuel cell technologies, solid-oxide fuel cells (SOFC) and molten carbonate fuel cells (MCFC) being the most common types of DCFCs.
A typical molten carbonate direct carbon fuel cell (MC-DCFC) 100, is illustrated schematically in
Cathode: O2+2CO2+4e−→CO32− (1)
Anode: C(s)+2CO32−→3CO2+4e− (2)
Net reaction: C(s)+O2→CO2 (3)
During the reaction, carbon is introduced and flows through a porous anode. Depending on the particle size distribution of the carbon and pore size of the anode, some carbon particles will flow through the anode and some will become lodged into the pores. These lodged particles will begin to react to form CO2 and electrons. As the reaction continues, the particles get consumed and are replaced by new carbon particles fed to the cell.
When the amount of carbon fed to the DCFC is greater than the amount consumed, carbon particles will begin to build up on the anode surface. In some DCFC cell designs, the carbon fuel is mixed with the carbonate electrolyte and this mixture flows into the gap between the anode and cathode. Some of the carbon/electrolyte mixture flows past the anode and is recirculated but some flows through the porous anode structure. Therefore, a build-up of carbon on the anode could provide a conductive bridge between the anode and the cathode and lead to a short circuit of the cell.
The amount of carbon consumed by the DCFC can be inferred from the voltage and current produced. However, this is a gross, macro measurement and does not address the localized problem address above. A direct means to detect carbon buildup on the anode surface is required which will allow the system to control the amount of carbon fed into the cell and prevent short circuiting and/or to allow for potential mitigation strategies to be implemented to prevent localized buildup.
According to a first aspect of the disclosure, there is provided a direct carbon fuel cell system (DCFC) comprising: a fuel cell comprising a porous anode, a porous cathode and an electrolyte flow field chamber in between the anode and the cathode and containing a molten carbonate electrolyte; a conductive mesh in the electrolyte flow field chamber and spaced from the anode; a fuel supply apparatus for flowing a fuel slurry comprising carbon particles and a carbon carrier fluid into the electrolyte flow field chamber, wherein the carbon carrier fluid has a same composition as the molten carbonate electrolyte; an oxidant supply apparatus for flowing an oxidant stream to the cathode; an electrolyte circulation apparatus for circulating the molten carbonate electrolyte to the electrolyte flow field chamber; and a controller in electrical contact with and operable to measure the resistance between the anode and the conductive mesh and compare the measured resistance against a set-point indicating carbon particle build-up on the anode is contacting the conductive mesh and forming a conductive pathway. The molten carbonate electrolyte can comprise one or a combination of Li, Na and K molten salt.
The controller can be operable to send a carbon-build-up detected signal when the measured resistance is at or below the set-point. Alternatively, the controller can further comprise a processor and a memory having encoded thereon instructions executable by the processor to: measure the resistance between the anode and the conductive mesh; when the measured resistance is greater than the set-point; control the fuel supply apparatus to increase a feed rate of carbon particles to the fuel slurry; and when the measured resistance is at or less than the set-point, control the fuel supply apparatus to reduce the feed rate of carbon particles to the fuel slurry.
The DCFC can further comprise a cathode protection barrier positioned between the cathode and fuel slurry in the electrolyte flow field chamber and configured to impede or prevent the carbon particles from electrically contacting the cathode. The cathode protection barrier can be a micro surface coating on the cathode or a porous felt. The conductive mesh can be mounted on the cathode protection barrier and facing the anode
According to another aspect, there is provided a method for detecting carbon build-up in a direct carbon fuel cell comprising a porous anode, a porous cathode, an electrolyte flow field chamber in between the anode and the cathode and containing a molten carbonate electrolyte, and a conductive mesh in the electrolyte flow field chamber and spaced from the anode. The method comprises: measuring a resistance between the anode and the conductive mesh; comparing the measured resistance to a set-point indicating a carbon build-up on the anode is contacting the conductive mesh and forming a conductive pathway; and sending a carbon build-up detected signal when the measured resistance is at or below the set-point.
According to another aspect, there is provided a method for controlling carbon build-up in a direct carbon fuel cell comprising a porous anode, a porous cathode, an electrolyte flow field chamber in between the anode and the cathode and containing a molten carbonate electrolyte, and a conductive mesh in the electrolyte flow field chamber and spaced from the anode, the method comprising: measuring a resistance between the anode and the conductive mesh; when the measured resistance is greater than a set-point indicating a carbon build-up on the anode is contacting the conductive mesh and forming a conductive pathway, increasing a feed rate of carbon particles to a fuel slurry supplied to the electrolyte flow field chamber; and when the measured resistance is at or less than the set-point, reducing the feed rate of carbon particles to the fuel slurry supplied to the electrolyte flow field chamber
Further aspects and example embodiments are illustrated in the accompanying drawings and/or described in the following description.
The accompanying drawings illustrate non-limiting example embodiments of the disclosure. The drawings are not intended to be to scale, and in most cases are schematic or simplified intended to clearly illustrate various aspects of the disclosure.
Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the disclosure. However, the disclosure may be practiced without these particulars. In other instances, well known aspects or features have not been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive sense.
Embodiments described herein relate to a DCFC having a conductive mesh in an electrolyte flow field chamber between an anode electrode and a cathode electrode of the DCFC. The conductive mesh is positioned and secured at a specified gap distance from the anode surface. As the DCFC is operated, carbon/carbonate fluid is introduced into the DCFC, a portion flows through the conductive mesh and though the porous anode. If the rate of carbon introduced into the DCFC is greater than the amount consumed, carbon will begin to build up on the surface on the anode electrode. Once the thickness of the carbon buildup equals the gap distance between the mesh and the anode surface, a conductive path will be created between the mesh, carbon particles and anode electrode. A controller in contact with the conductive mesh continuously or periodically measures the resistance between the conductive mesh and the anode electrode and when the measured resistance falls to or below a defined set-point indicating a resistance when a conductive path between the anode and conductive mesh has formed, the controller can send a carbon build-up detected signal, and/or execute mitigation actions to reduce the amount of carbon delivered to the cell.
Referring to
Slurry 116 passes through the electrolyte flow field chamber 119 in contact with the porous anode 118. Some of the slurry permeates the anode 118, and carbon from the slurry is trapped and consumed at the anode 118. The anode 118 comprises a porous electrode separating the carbon slurry 116 from the electrolyte 104 in an electrolyte return chamber 102. The porosity of the electrode facilitates carbon contact, sufficient to promote electrochemical exchange of electrons at triple phase boundary (TPB) sites where the carbon fuel is in electrical contact with the anode 118, and in ionic contact with the electrolyte 104. The molten carbonate, as the carbon carrier fluid, helps ensure the carbon is wetted, which facilitates contact with carbonate ions in the electrolyte 104. The porous anode 118 permits some of the carbon carrier fluid (MC) to pass into and, in this case, through the anode 118, and serve to effectively trap or filter the carbon fuel from the slurry. The carbon carrier fluid (MC) having passed through the anode 118 rejoins the bulk electrolyte 104 in the electrolyte return chamber 102. Solid carbon particles, which are trapped at the porous anode 118, are consumed in the oxidation reaction forming product CO2 gas, which accumulates in the headspace 120 in the upper portion of the electrolyte return chamber 102.
Electrolyte 104 that passes through anode 118 enters the electrolyte return chamber 102. The remainder of the electrolyte slurry 116, with a depleted carbon loading, exits flow field chamber 119 at outlet 106 and is combined with electrolyte 104 from the electrolyte return chamber 102 via conduit 138. The combined electrolyte stream can be cooled in a heat exchanger 108, have more carbon added at mixer 114, and be recirculated back to flow field chamber 119.
The ratio of flow of electrolyte (slurry) through outlet 106 versus through anode 118 and into electrolyte return chamber 102 can be controlled to some degree by the anode porosity. A flow restriction 140 can also be positioned in the main electrolyte loop, for example, to ensure that there is sufficient pressure drop across the anode to force carbon particles to TPB sites and to flush product CO2 into the (substantially) carbon-free electrolyte slipstream in return chamber 102. Flow restriction 140 may be a passive orifice restriction, an active back-pressure regulator or similar or other suitable device. In other embodiments, the ratio of flow of electrolyte (slurry) through outlet 106 versus through anode 118 and into electrolyte return chamber 102 can be further controlled by having two independent pumps and flow paths, such as shown in
To some extent, the configuration of system 100 enables decoupling of two electrolyte flow stream functions: (1) the “slipstream” delivery of carbon particles to the anode with (2) the entrainment of product CO2 gas away from the carbon bed and the bulk flow of electrolyte as a heat exchange medium. In the illustrated embodiment, the electrolyte 104 from return chamber 102 and the bulk electrolyte (depleted slurry) flow from flow field chamber 119 are re-combined upstream of heat exchanger 108. It can be appreciated that these streams can be combined downstream of the heat exchanger, kept independent or otherwise configured to accomplish the desired goals for each stream.
The product CO2 gas accumulated in the headspace 120 in the electrolyte return chamber 102 is discharged from the fuel cell. A portion of the CO2 can then be circulated to the cathode 132 for the cathode carbonate formation reaction. In system 100, product CO2 gas is split into two streams at 125, with one DCFC exhaust stream 126, and one recirculation stream 128 which is circulated via a recirculation compressor 130 to a cathode flow field chamber 133, together with an oxidant stream (such as air or pure oxygen). Unreacted CO2 gas can be discharged from the cathode flow field chamber 133 at exhaust port 144.
A conductive mesh 150 extends along the length of the electrolyte flow field chamber 119 generally parallel to and spaced from the anode 118. The gap spacing between the conductive mesh 150 and anode surface 118 can be selected depending on the amount of carbon build-up on the anode 118 is tolerable before mitigation action is taken. The mesh material can be made from materials known in the art that are compatible for use with molten carbonates in terms of temperature and corrosion resistance and be of a pore size which allows the carbon entrained in the slurry 116 to freely pass through.
A controller 152 is in electrical contact with the conductive mesh 150, anode 118 and cathode 132, and is operable to measure the resistance between the anode 118 and the conductive mesh 150 to detect carbon build up in the fuel cell, and in some embodiments to control or mitigate against carbon build in the fuel cell. In a basic embodiment, the controller 152 operates as a monitor and sends a carbon build-up detected signal when a measured resistance falls to or below a set-point value, indicating that carbon build up has reached the anode 118 to form a conductive pathway. In another embodiment the controller 152 comprises a processor and a memory having encoded thereon program code executable by the processor to perform a carbon build-up mitigation operation when the measured resistance falls to or below the set-point value.
Referring now to
First recirculation pump 205 can be used to appropriately regulate the flow and pressure drop across the anode to ensure appropriate carbon accumulation and CO2 product gas management. The flow rate of second recirculation pump 210 can be set to provide the desired heat extraction in heat exchanger 208, for example, to maintain a preferred stack temperature and/or temperature rise across the fuel cell or stack(s). This type of configuration can be used to introduce an additional degree of control freedom at the cost of additional balance of plant equipment. An optional flow restriction 240 can also be positioned in the main electrolyte loop to provide further control of flow of electrolyte (slurry) through outlet 206 versus through anode 218 and into electrolyte return chamber 202.
Like the first embodiment, a conductive mesh 250 extends along the length of the electrolyte flow field chamber 219 generally parallel to and spaced from the anode 218. The gap spacing between the conductive mesh 250 and anode surface 218 can be selected depending on the amount of carbon build-up on the anode 218 is tolerable before mitigation action is taken.
Like the first embodiment, a controller 252 is in electrical contact with the conductive mesh 250, anode 218 and cathode 232, and is operable to measure the resistance between the anode 218 and the conductive mesh 250 to detect carbon build-up in the fuel cell, and in some embodiments to control or mitigate against carbon build-up in the fuel cell. In a basic embodiment, the controller 252 operates as a monitor and sends a carbon build-up detected signal when a measured resistance falls to or below a set-point value, indicating that carbon build-up has reached the anode 118 to form a conductive pathway. In another embodiment the controller 252 comprises a processor and a memory having encoded thereon program code executable by the processor to perform a carbon build-up mitigation operation when the measured resistance falls to or below the set-point value.
A cathode protection barrier (not shown) can be used in any of the various MC-DCFC systems 100, 200 described herein, which have carbon slurry between the anode and cathode, to mitigate potential oxidation of carbon particles at the cathode, which could otherwise lead to increased heat generation and reduced cell efficiency.
Referring now to
Throughout the disclosure where a controller is referenced it may include one or more controllers in communication with each other through one or more networks or communication mediums. Each controller generally comprises one or more processors and one or more computer readable mediums in communication with each other through one or more networks or communication mediums. The one or more processors may comprise any suitable processing device known in the art, such as, for example, application specific circuits, programmable logic controllers, field programmable gate arrays, microcontrollers, microprocessors, virtual machines, and electronic circuits. The one or more computer readable mediums may comprise any suitable memory devices known in the art, such as, for example, random access memory, flash memory, read only memory, hard disc drives, optical drives and optical drive media, or flash drives. In addition, where a network is referenced it may include one or more suitable networks known in the art, such as, for example, local area networks, wide area networks, intranets, and the Internet. Further, where a communication to a device or a direction of a device is referenced it may be communicated over any suitable electronic communication medium and in any suitable format known to in the art, such as, for example, wired or wireless mediums, compressed or uncompressed formats, encrypted or unencrypted formats.
Unless the context clearly requires otherwise, throughout the description and the
Specific examples of systems, methods, and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this disclosure. This disclosure includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.
While particular elements, embodiments and applications of the present disclosure have been shown and described, it will be understood, that the disclosure is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions, and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2022/051472 | 10/5/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63292137 | Dec 2021 | US |
