# US 2019/0245225 A1 · Methods for Transitioning a Fuel Cell System between Modes of Operation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0245225 A1 - Document ID: US20190245225A1 - Status: Published application - Kind: A1 - Application number: 15/887,720 - Filed: 2018-02-02 - Published: 2019-08-08 - Earliest claimed: 2018-02-02 - Assignees: LG Fuel Cell Systems Inc. - Applicants: LG Fuel Cell Systems, Inc. - Inventors: Mark V. Scotto; Ted Ohrn; Shung-Ik Lee; JaeBong Choi - Web page: https://patentgrep.com/patent/US20190245225A1 ## CPC - H01M 8/04097: {with recycling of the reactants (H01M8/04119, H01M8/04104 take precedence)} - H01M 8/04302: applied during start-up - H01M 8/04708: {of fuel cell reactants} - H01M 8/04731: {of other components of a fuel cell or fuel cell stacks} - H01M 8/04753: {of fuel cell reactants} - H01M 8/0625: {in a modular combined reactor/fuel cell structure} - H01M 8/1246: the electrolyte consisting of oxides - H01M 8/2483: characterised by internal manifolds - H01M 2008/1293: {Fuel cells with solid oxide electrolytes} - Y02E 60/50: Fuel cells - H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract Systems and methods for transitioning a fuel cell system between operating modes. The fuel cell system may be a SOFC system comprising Ni-containing anodes. The transitions may be from a shutdown mode to a hot standby mode, from a hot standby mode to a power ready hot standby mode, from a power ready hot standby mode to an operating mode, from an operating mode to a power ready hot standby mode, from a power ready hot standby mode to a hot standby mode, from a hot standby mode to a shutdown mode, and from an operating mode to a shutdown mode. ## Claims ### Claim 1 A method of transitioning between operating modes of a fuel cell system, the fuel cell system comprising: a fuel cell stack comprising: a plurality of solid oxide fuel cells, each solid oxide fuel cell comprising an anode, a cathode, and an electrolyte; an anode loop comprising: an in-block fueling flowpath comprising a fuel supply manifold, a fuel exhaust manifold, and one or more fueling channels in fluid communication with said fuel supply manifold and said fuel exhaust manifold, wherein each anode is exposed to a fuel flowing in one or more of said fueling channels; an anode ejector having a fuel supply input, a fuel recycle input, and a combined fuel output; a fuel recycle conduit in fluid communication with said anode ejector fuel recycle input and said in-block fueling flowpath fuel exhaust manifold; and a combined fuel supply conduit in fluid communication with said anode ejector combined fuel output and said in-block fueling flowpath fuel supply manifold; a fuel supply conduit in fluid communication with said anode ejector fuel supply input; a source of SOFC fuel in fluid communication with said fuel supply conduit; a source of transition fuel in fluid communication with said fuel supply conduit; a cathode loop comprising: an in-block oxidizing flowpath comprising an oxidant supply manifold, an oxidant exhaust manifold, and one or more oxidizing channels in fluid communication with said oxidant supply manifold and said oxidant exhaust manifold, wherein each cathode is exposed to an oxidant flowing in one or more oxidizing channels; a cathode ejector having an oxidant supply input, an oxidant recycle input, and a combined oxidant output; an oxidant recycle conduit in fluid communication with said cathode ejector oxidant recycle input and said in-block oxidizing flowpath oxidant exhaust manifold; a combined oxidant supply conduit in fluid communication with said cathode ejector combined oxidant output and said in-block oxidizing flowpath oxidant supply manifold; and a heat source positioned to heat an oxidant flowing in the cathode loop; an oxidant supply conduit in fluid communication with said cathode ejector oxidant supply input; and an oxidant source in fluid communication with said oxidant supply conduit; the method of transitioning the fuel cell system from a shutdown mode wherein: oxidant is flowing through the cathode loop at ambient temperature; no fuel is flowing in the anode loop; and no RCB is applied to the fuel cell stack; to a hot standby mode wherein: oxidant is flowing through the cathode loop at a hot standby temperature; transition fuel is flowing from the source into the anode loop at a mass flow rate sufficient to prevent oxidation of the anode; RCB is applied to the fuel cell stack; and anode fuel utilization is with an anode-protection fuel utilization range; said method of transitioning comprising: maintaining flow of oxidant through the cathode loop; controlling a heat up of the fuel cell stack by controlling the mass flow rate and temperature of the oxidant flowing through the cathode loop; when the temperature of the fuel cell stack reaches a predetermined temperature between ambient temperature and hot standby temperature, flowing transition fuel into the anode loop at a mass flow rate sufficient to prevent anode oxidation; when the temperature of the fuel cell stack is at or below the predetermined temperature, applying RCB to the fuel cell stack; and maintaining control of the heat up of the fuel cell stack by controlling the mass flow rate and temperature of the oxidant flowing through the cathode loop until the temperature of the fuel cell stack reaches a hot standby temperature. ### Claim 2 (depends on 1) The method of claim 1 comprising maintaining flow of oxidant through the cathode loop in the range of 50% to 100% of a full load mass flow rate. ### Claim 3 (depends on 2) The method of claim 2 comprising maintaining flow of oxidant through the cathode loop at about 100% of the full load mass flow rate. ### Claim 4 (depends on 1) The method of claim 1 comprising controlling the heat up of the fuel cell stack by controlling the heat source. ### Claim 5 (depends on 1) The method of claim 1 wherein the hot standby temperature is in the range of 800 C. to 1000 C. ### Claim 6 (depends on 5) The method of claim 5 wherein the hot standby temperature is about 850 C. ### Claim 7 (depends on 1) The method of claim 1 wherein the predetermined temperature is in the range of 450 C. to 750 C. ### Claim 8 (depends on 7) The method of claim 7 wherein the predetermined temperature is about 650 C. ### Claim 9 (depends on 1) The method of claim 1 comprising controlling the heat up of the fuel cell stack from ambient temperature to the predetermined at a rate in the range of 1 C. to 5 C. per minute. ### Claim 10 (depends on 9) The method of claim 9 comprising controlling the heat up of the fuel cell stack from ambient temperature to the predetermined temperature at a rate of about 3 C. per minute. ### Claim 11 (depends on 1) The method of claim 1 comprising controlling the heat up of the fuel cell stack from the predetermined temperature to the hot standby temperature at a rate in the range of 1 C. to 5 C. per minute. ### Claim 12 (depends on 11) The method of claim 11 comprising controlling the heat up of the fuel cell stack from the predetermined temperature to the hot standby temperature at a rate of about 3 C. per minute. ### Claim 13 (depends on 1) The method of claim 1 comprising controlling the heat up of the fuel cell stack from ambient temperature to about 850 C. at a rate in the range of 1 C. to 10 C. per minute. ### Claim 14 (depends on 13) The method of claim 13 comprising controlling the heat up of the fuel cell stack from ambient temperature to about 850 C. at a rate of about 3 C. per minute. ### Claim 15 A method of transitioning a fuel cell system from a shutdown mode to a hot standby mode, the fuel cell system having a fuel cell stack comprising a plurality of solid oxide fuel cells, each fuel cell comprising an anode and a cathode spaced apart by an electrolyte, an anode loop for providing a fuel to the anodes, and a cathode loop for providing an oxidant to the cathodes, wherein conditions of the fuel cell system in the shutdown mode include: an oxidant flowing through the cathode loop at a mass flow rate in the range of about 50% to 100% of a full load mass flow rate at ambient temperature; no fuel is flowing in the anode loop; and no RCB is applied to the fuel cell stack; wherein conditions of the fuel cell system in the hot standby mode include: an oxidant flowing through the cathode loop at a mass flow rate in the range of about 50% to 100% of a full load mass flow rate at a temperature in the range of 800 C. to 1000 C.; transition fuel is flowing from the source into the anode loop at a mass flow rate sufficient to prevent oxidation of the anode; RCB is applied to the fuel cell stack; and anode fuel utilization is with an anode-protection fuel utilization range; said method comprising: maintaining flow of oxidant through the cathode loop at a mass flow rate in the range of about 50% to 100% of a full load mass flow rate; controlling the heat up of the fuel cell stack from ambient temperature to a predetermined temperature in the range of 600 C. to 700 C. by controlling the mass flow rate and temperature of the oxidant flowing through the cathode loop; when the fuel cell stack reaches a predetermined temperature between ambient temperature and a temperature in the range of 800 C. to 1000 C., begin flowing the transition fuel into the anode loop at a mass flow rate sufficient to prevent oxidation of the anode; when the temperature of the fuel cell stack reaches the predetermined temperature or earlier, applying RCB to the fuel cell stack; and controlling the heat up of the fuel cell stack from the predetermined temperature to a hot standby temperature in the range of 800 C. to 1000 C. by controlling the mass flow rate and temperature of the oxidant flowing through the cathode loop. ### Claim 16 (depends on 15) The method of claim 15 wherein the predetermined temperature is about 650 C. ### Claim 17 (depends on 15) The method of claim 15 comprising controlling the heat up of the fuel cell stack at a rate in the range of 1 C. to 10 C. per minute. ### Claim 18 (depends on 17) The method of claim 17 comprising controlling the heat up of the fuel cell stack at a rate of about 3 C. per minute. ### Claim 19 A method of transitioning a fuel cell system having a stack comprising a plurality of fuel cells from a shutdown mode at ambient temperature wherein anodes of the fuel cells are substantially free of oxidized metal, to a hot standby mode at a temperature in the range of 800 C. to 1000 C. wherein the anodes of the fuel cells comprise oxidized metal, the method comprising: flowing an oxidant in a cathode loop of the fuel cell system; heating the oxidant flowing in the cathode loop to thereby effect heating of the fuel cell stack; allowing oxidation of a metal contained in the anodes of the fuel cells while the fuel cell stack heats up to a predetermined temperature below the hot standby mode temperature; and inhibiting further oxidation of the metal in the anodes of the fuel cells while the fuel cell stack heats up from the predetermined temperature to the standby temperature by: applying an RCB to the fuel cell stack while the fuel cell stack is at or below the predetermined temperature; and flowing a transition fuel in an anode loop of the fuel cell system at a mass flow rate sufficient to prevent oxidation of the metal in the anodes. ### Claim 20 (depends on 19) The method of claim 19 wherein the predetermined temperature is in the range of 600 C. to 700 C. ### Claim 21 (depends on 20) The method of claim 20 comprising controlling the heat up of the fuel cell stack at a rate in the range of 1 C. to 10 C. per minute by controlling the mass flow rate and temperature of oxidant flowing in the cathode loop.