# How a High-Temperature Fuel Cell System Starts, Stops, and Recycles Fuel > This patent describes a fuel cell system that uses a smaller, secondary fuel cell to power itself during startup and shutdown, and to recycle hydrogen from its exhaust during normal operation. - **Patent:** US 7846599 - **Original title:** Method for high temperature fuel cell system start up and shutdown - **Owner:** Bloom Energy - **Granted:** 2010 - **Status:** Active - **Times cited:** 26 - **Field:** energy, power_generation, fuel_cells, industrial_equipment ## What it does The patent outlines a method for operating a fuel cell system, specifically focusing on its start-up and shut-down phases, and how it handles fuel during normal operation. During normal, "steady state" operation, a main "fuel cell stack" (like a Solid Oxide Fuel Cell or Molten Carbonate Fuel Cell, per claims 7 and 13) converts fuel into electricity. The exhaust from this main stack then goes to a "PEM stack" (a Proton Exchange Membrane fuel cell/electrolyzer). This PEM stack operates in "electrolysis mode" (claim 4) to separate hydrogen from the exhaust and feeds that hydrogen back into the main fuel cell stack's fuel supply, making the system more efficient. When starting up or shutting down, the PEM stack switches roles. It receives its own fuel and air (claims 1 and 9) and generates power to run "auxiliary components" (claim 1) of the system, such as pumps or heaters, ensuring a smooth and controlled transition. ## What it does NOT cover - Fuel cell systems that do not include a separate PEM stack for both power generation and hydrogen recycling. - Systems where the PEM stack does not provide power to auxiliary components during start-up or shut-down. - Systems where the PEM stack does not operate in electrolysis mode to separate hydrogen from the main fuel cell stack's exhaust. - Methods that do not involve recycling separated hydrogen from the PEM stack back into the main fuel cell stack's fuel inlet stream. - Fuel cell systems that do not involve a 'fuel cell stack' (specifically SOFC or MCFC in some claims) and a 'PEM stack' working together in these defined roles. ## The clever bit The cleverness lies in using a single PEM stack for two distinct, critical functions: acting as a small fuel cell to provide power for the system's own start-up and shut-down needs, and then switching to an electrolyzer during normal operation to recycle hydrogen from the exhaust, boosting overall efficiency. ## Real-world examples 1. Bloom Energy Servers 2. Stationary fuel cell power plants 3. Combined heat and power (CHP) systems using SOFCs ## Why it matters High-temperature fuel cells, such as Solid Oxide Fuel Cells (SOFCs) and Molten Carbonate Fuel Cells (MCFCs), are very efficient but require careful control during start-up and shut-down to prevent damage. This patent provides a way to manage these critical phases reliably and efficiently. By using a PEM stack to power auxiliary systems and recycle hydrogen, it makes these complex fuel cell systems more robust and self-sufficient, reducing operational costs and improving their lifespan. ## Frequently asked questions ### What does How a High-Temperature Fuel Cell System Starts, Stops, and Recycles Fuel cover? This patent describes a fuel cell system that uses a smaller, secondary fuel cell to power itself during startup and shutdown, and to recycle hydrogen from its exhaust during normal operation. ### Who owns patent US 7846599? Bloom Energy owns this patent, granted in 2010. ### When does this patent expire? This patent is expected to expire on June 3, 2028, when the invention enters the public domain. ### What is patent US 7846599 cited by? This patent has been cited by 26 later patents that build on its ideas. ### What problem does this patent solve? High-temperature fuel cells, such as Solid Oxide Fuel Cells (SOFCs) and Molten Carbonate Fuel Cells (MCFCs), are very efficient but require careful control during start-up and shut-down to prevent damage. This patent provides a way to manage these critical phases reliably and efficiently. By using a PEM stack to power auxiliary systems and recycle hydrogen, it makes these complex fuel cell systems more robust and self-sufficient, reducing operational costs and improving their lifespan. ### What does this patent NOT cover? Fuel cell systems that do not include a separate PEM stack for both power generation and hydrogen recycling. **Full plain-English explainer:** https://patentbrief.org/patent/us/7846599/method-for-high-temperature-fuel-cell-system-start-up-and-shutdown **Original patent:** https://patents.google.com/patent/US7846599 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Fuel Cells Reuse Exhaust Hydrogen for High Efficiency](https://patentbrief.org/patent/us/7833668/fuel-cell-system-with-greater-than-95-fuel-utilization) — This patent describes a fuel cell system that captures and recycles over 95% of the unused hydrogen from its exhaust stream using a special pump, significantly boosting efficiency. - [How Fuel Cells Capture Carbon Dioxide While Making Electricity](https://patentbrief.org/patent/us/9553321/integrated-power-generation-and-carbon-capture-using-fuel-cells) — This patent describes a system that uses special fuel cells to generate electricity and capture carbon dioxide from power plant exhaust, by recycling unused fuel back into the system. - [How to Prepare a Fuel Cell for Faster, Cheaper Startup](https://patentbrief.org/patent/us/20140045086/pre-activation-method-for-fuel-cell-stack) — This patent describes a method for 'pre-activating' a fuel cell stack by injecting humidified hydrogen, sealing it, and storing it, which helps reduce the time and hydrogen needed for its first full operation. - [Boosting Fuel Cell Power for Vehicles Using Oxygen Injection](https://patentbrief.org/patent/us/5346778/electrochemical-load-management-system-for-transportation-applications) — A system that boosts a vehicle's fuel cell power by injecting pure oxygen into the air supply when the engine needs extra energy. - [How a Special Reactor Makes Methane Fuel Without Constant Electricity](https://patentbrief.org/patent/us/10145018/method-for-operating-an-soec-type-stack-reactor-for-producing-methane-in-the-abs) — This patent describes a method for a Solid Oxide Electrolyser Cell (SOEC) reactor to produce methane, even when electricity is scarce, by switching from electrolysis to a heat-generating chemical reaction.