Electrolyzer system and method of operating same in standby mode

Abstract

A method of operating an electrolyzer system includes operating the electrolyzer system in a steady state mode by providing steam, heat and electric power to at least one stack of electrolyzer cells to electrolyze the steam and generate a hydrogen containing product stream that is provided to a hydrogen processor; and operating the electrolyzer system in a hot isolated standby mode by stopping the provision of the steam to the at least one stack of electrolyzer cells, stopping the provision of the hydrogen containing product stream to the hydrogen processor, recycling the hydrogen containing product stream through the at least one stack of electrolyzer cells while providing the heat to the at least one stack of electrolyzer cells, and not providing external hydrogen from outside the electrolyzer system to the at least one stack of electrolyzer cells.

1 . A method of operating an electrolyzer system, comprising:
 operating the electrolyzer system in a steady state mode by providing steam, heat and electric power to at least one stack of electrolyzer cells to electrolyze the steam and generate a hydrogen containing product stream that is provided to a hydrogen processor; and   operating the electrolyzer system in a hot isolated standby mode by stopping the provision of the steam to the at least one stack of electrolyzer cells, stopping the provision of the hydrogen containing product stream to the hydrogen processor, recycling the hydrogen containing product stream through the at least one stack of electrolyzer cells while providing the heat to the at least one stack of electrolyzer cells, and not providing external hydrogen from outside the electrolyzer system to the at least one stack of electrolyzer cells.   
     
     
         2 . The method of  claim 1 , wherein:
 the step of providing the heat comprises heating the at least one stack of electrolyzer cells using at least one heater; and   the step of recycling the hydrogen containing product stream comprises using a recycle blower to recycle the hydrogen containing product stream from an outlet of the at least one stack of electrolyzer cells through a recycle conduit to an inlet of the at least one stack of electrolyzer cells.   
     
     
         3 . The method of  claim 2 , further comprising operating the electrolyzer system in a start-up mode by providing the external hydrogen from outside the electrolyzer system to the at least one stack of electrolyzer cells,
 wherein:   the external hydrogen is provided from a hydrogen storage device to the at least one stack of electrolyzer cells through an open hydrogen valve and a stored hydrogen conduit during the start-up mode;   the steam is provided to the at least one stack of electrolyzer cells through an open water control valve and a steam conduit from a steam source during the steady state mode; and   the hydrogen containing product stream is provided from the at least one stack of electrolyzer cells to the hydrogen processor through an open product valve and a product conduit during the steady state mode.   
     
     
         4 . The method of  claim 3 , wherein the hydrogen valve, the water control valve and the product valve are closed in the hot isolated standby mode to fluidly isolate the at least one stack of electrolyzer cells from the hydrogen storage device, the steam source and the hydrogen processor. 
     
     
         5 . The method of  claim 2 , further comprising operating the electrolyzer system in a voltage controlled start-up mode by providing electric power to the at least one stack of electrolyzer cells without providing the external hydrogen from outside the electrolyzer system to the at least one stack of electrolyzer cells,
 wherein:   a hydrogen valve is closed on a stored hydrogen conduit fluidly connecting a hydrogen storage device to the at least one stack of electrolyzer cells during the voltage controlled start-up mode;   the steam is provided to the at least one stack of electrolyzer cells through an open water control valve and a steam conduit from a steam source during the voltage controlled start-up and the steady state modes; and   the hydrogen containing product stream is provided from the at least one stack of electrolyzer cells to the hydrogen processor through an open product valve and a product conduit during the voltage controlled start-up and the steady state modes.   
     
     
         6 . The method of  claim 1 , wherein the electric power is not provided to the at least one stack of electrolyzer cells during the hot isolated standby mode. 
     
     
         7 . The method of  claim 6 , further comprising alternately operating the electrolyzer system in the hot isolated standby mode and in an isolated electrolysis mode, wherein in the isolated electrolysis mode, the electric power is provided to the at least one stack of electrolyzer cells while recycling the hydrogen containing product stream through the at least one stack of electrolyzer cells and providing the heat to the at least one stack of electrolyzer cells, while not providing the steam or the external hydrogen from outside the electrolyzer system to the at least one stack of electrolyzer cells, and not providing the hydrogen containing product stream to the hydrogen processor. 
     
     
         8 . The method of  claim 7 , further comprising:
 reacting the hydrogen in the recycled hydrogen containing product stream with oxygen to generate steam at fuel electrodes of the at least one stack of electrolyzer cells operating in the hot isolated standby mode until the hydrogen level reaches a low threshold value;   operating the at least one stack of electrolyzer cells in the isolated electrolysis mode by supplying the electric power to at least one stack of electrolyzer cells to electrolyze the steam into the hydrogen and the oxygen until the hydrogen level reaches a high threshold value, wherein the oxygen is transported from the fuel electrodes to air electrodes through electrolytes of the at least one stack of electrolyzer cells during the isolated electrolysis mode; and   operating the at least one stack of electrolyzer cells in the hot isolated standby mode by stopping the provision of the electric power to the at least one stack of electrolyzer cells when the hydrogen level reaches a high threshold value in the isolated electrolysis mode.   
     
     
         9 . The method of  claim 1 , further comprising controlling the electric power that is provided to the at least one stack of electrolyzer cells to a cell voltage within a predetermined cell voltage tolerance range during the hot isolated standby mode. 
     
     
         10 . The method of  claim 9 , wherein the electric power is provided to the at least one stack of electrolyzer cells during the hot isolated standby mode is controlled to the cell voltage at which neither an electrolysis reaction nor a reverse steam generation reaction comprising oxidation of the hydrogen dominate, and substantially no hydrogen is created or depleted during the hot isolated standby mode. 
     
     
         11 . The method of  claim 1 , wherein:
 the at least one stack of electrolyzer cells comprises a plurality of the stacks of electrolyzer cells;   the electrolyzer system comprises a plurality of electrolyzer modules each containing a respective hotbox housing a respective portion of the plurality of the stacks of electrolyzer cells;   in the steady state mode, the steam is provided to the plurality of electrolyzer modules through a common steam line, and the hydrogen containing product stream is provided from the plurality of electrolyzer modules to the hydrogen processor through a common product line;   in the hot isolated standby mode, the common product line is fluidly isolated from the hydrogen processor, the steam is provided to least one hydrogen-generating module of the plurality of electrolyzer modules without providing the steam to remaining hydrogen-consuming modules of the plurality of electrolyzer modules, electrolyzing the steam in the at least one hydrogen-generating module to generate the hydrogen containing product stream, and providing the hydrogen containing product stream to the hydrogen-consuming modules through the common product line.   
     
     
         12 . The method of  claim 1 , further comprising providing air to the at least one stack of electrolyzer cells during both the steady state mode and the hot isolated standby mode, wherein the at least one stack of electrolyzer cells comprises at least one stack of solid oxide electrolyzer cells. 
     
     
         13 . The method of  claim 1 , further comprising operating the electrolyzer system in voltage controlled shutdown mode by providing electric power to the at least one stack of electrolyzer cells, providing the hydrogen containing product stream to the hydrogen processor, recycling the hydrogen containing product stream through the at least one stack of electrolyzer cells without providing the heat to the at least one stack of electrolyzer cells, and not providing external hydrogen from outside the electrolyzer system to the at least one stack of electrolyzer cells. 
     
     
         14 . The method of  claim 13 , wherein the voltage controlled shutdown mode comprises a voltage controlled gradual cool down mode in which the steam is provided to at least one stack of electrolyzer cells. 
     
     
         15 . The method of  claim 13 , wherein the voltage controlled shutdown mode comprises a voltage controlled process stop mode in which the steam is not provided to at least one stack of electrolyzer cells. 
     
     
         16 . An electrolyzer system, comprising:
 at least one stack of electrolyzer cells;   at least one heater configured to provide heat to the at least one stack of electrolyzer cells;   a power supply electrically connected to the at least one stack of electrolyzer cells;   a steam conduit fluidly connecting a steam source to an inlet of the at least one stack of electrolyzer cells;   a water control valve located on the steam conduit;   product conduit fluidly connecting an outlet of the at least one stack of electrolyzer cells to a hydrogen processor;   a product valve located in fluid communication with the product conduit;   a recycle conduit fluidly connecting the inlet of the at least one stack of electrolyzer cells to an outlet of the at least one stack of electrolyzer cells;   a recycle blower located in fluid communication with the recycle conduit and configured to recycle a hydrogen containing product stream from the outlet to the inlet through the recycle conduit; and   a controller configured to:
 operate the electrolyzer system in a steady state mode by opening the steam valve, turning on the at least one heater, the recycle blower and the power supply to provide electric power to the at least one stack of electrolyzer cells to electrolyze the steam to generate the hydrogen containing product stream, and opening the product valve to provide the hydrogen containing product stream to the hydrogen processor; and 
 operate the electrolyzer system in a hot isolated standby mode by closing the steam valve and the product valve, while continuing to operate the at least one heater and the recycle blower without providing external hydrogen from outside the electrolyzer system to the at least one stack of electrolyzer cells. 
   
     
     
         17 . The electrolyzer system of  claim 16 , further comprising:
 an external hydrogen storage device;   a stored hydrogen conduit fluidly connecting the external hydrogen storage device to the inlet of the at least one stack of electrolyzer cells; and   a hydrogen valve located on the external hydrogen storage device or on the stored hydrogen conduit;   wherein the controller is configured to open the hydrogen valve in a start-up mode and to close the hydrogen valve in the hot isolated standby mode.   
     
     
         18 . The electrolyzer system of  claim 16 , wherein the controller is configured to turn off the power supply during the hot isolated standby mode. 
     
     
         19 . The electrolyzer system of  claim 18 , wherein the controller is configured to alternately operate the electrolyzer system in the hot isolated standby mode and in an isolated electrolysis mode by turning on the power supply during the isolated electrolysis mode and turning off the power supply during the hot isolated standby mode. 
     
     
         20 . The electrolyzer system of  claim 16 , wherein the controller is configured to control the power supply such that the electric power is provided to the at least one stack of electrolyzer cells during the hot isolated standby mode at a level such that neither an electrolysis reaction nor a reverse steam generation reaction comprising oxidation of the hydrogen dominate, and substantially no hydrogen is created or depleted during the hot isolated standby mode. 
     
     
         21 . The electrolyzer system of  claim 16 , wherein:
 the at least one stack of electrolyzer cells comprises a plurality of the stacks of electrolyzer cells;   the electrolyzer system comprises a plurality of electrolyzer modules each containing a respective hotbox housing a respective portion the plurality of the stacks of electrolyzer cells;   a common steam line is configured to provide the steam from the steam source to the steam conduits of the plurality of electrolyzer modules in the steady state mode;   a common product line is configured to provide the hydrogen containing product stream from the product conduits of the plurality of electrolyzer modules to the hydrogen processor in the steady state mode; and   the controller is further configured to operate the electrolyzer system in the hot isolated standby mode by fluidly isolating the common product line from the hydrogen processor by closing the product valve which is located the common product line, opening the water control valve on the steam conduit of at least one hydrogen-generating module of the plurality of electrolyzer modules, and closing the water control valves on the steam conduits of remaining hydrogen-consuming modules of the plurality of electrolyzer modules to electrolyze the steam in the at least one hydrogen-generating module to generate the hydrogen containing product stream, and to provide the hydrogen containing product stream to the hydrogen-consuming modules through the common product line.   
     
     
         22 . The electrolyzer system of  claim 16 , further comprising an air blower configured to provide air to the at least one stack of electrolyzer cells during both the steady state mode and the hot isolated standby mode. 
     
     
         23 . The electrolyzer system of  claim 16 , wherein the at least one stack of electrolyzer cells comprises at least one stack of solid oxide electrolyzer cells.