Starting method of high-pressure water electrolysis system and starting method of water electrolysis system

Abstract

A starting method includes determining whether a depressurizing current was supplied to a water electrolyzer while at least a cathode side of the water electrolyzer was depressurized in an immediately previous stop of a water electrolysis system after electrolyzing water. A first current is supplied to the water electrolyzer at a first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was supplied to the water electrolyzer in the immediately previous stop. A second current is supplied to the water electrolyzer at a second supply rate lower than the first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was not supplied to the water electrolyzer in the immediately previous stop.

What is claimed is: 
     
         1 . A starting method of a high-pressure water electrolysis system that includes a high-pressure water electrolysis device which electrolyzes supplied water, produces oxygen on an anode side, and produces hydrogen at a higher pressure than the oxygen on a cathode side, the starting method comprising:
 a step of determining whether or not depressurization on at least the cathode side is performed while a depressurizing current is applied in a previous stop of the high-pressure water electrolysis system;   a step of performing starting by applying a starting current to the high-pressure water electrolysis device at a normal current application rate in a case where a determination is made that an electrolysis depressurization process, in which depressurization is performed while the depressurizing current is applied, is performed in the previous stop; and   a step of performing the starting by applying the starting current to the high-pressure water electrolysis device at a current application rate that is lower than the normal current application rate in a case where a determination is made that an electroless depressurization process, in which depressurization is performed while the depressurizing current is not applied, is performed in the previous stop.   
     
     
         2 . The starting method according to  claim 1 , wherein before starting applying the starting current to the high-pressure water electrolysis device, water is caused to circulate only in a prescribed time in which an inside of the high-pressure water electrolysis device is filled with the water. 
     
     
         3 . The starting method according to  claim 1 , further comprising:
 a step of detecting a hydrogen concentration in a fluid that is discharged from the anode side of the high-pressure water electrolysis device while the starting current is applied to the high-pressure water electrolysis device at the current application rate; and   a step of raising a starting current value of a current that is applied to the high-pressure water electrolysis device to a rated current value in a case where the detected hydrogen concentration becomes a prescribed value or lower.   
     
     
         4 . The starting method according to  claim 1 , wherein as a start pressure of the electroless depressurization process is higher, the current application rate is set lower. 
     
     
         5 . A starting method of a water electrolysis system including a water electrolyzer, the starting method comprising:
 determining whether a depressurizing current was supplied to the water electrolyzer while at least a cathode side of the water electrolyzer was depressurized in an immediately previous stop of the water electrolysis system after electrolyzing water to produce oxygen with a first pressure on an anode side and hydrogen with a second pressure higher than the first pressure on the cathode side;   supplying a first current to the water electrolyzer at a first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was supplied to the water electrolyzer in the immediately previous stop; and   supplying a second current to the water electrolyzer at a second supply rate lower than the first supply rate to start the water electrolysis system in a case where it is determined that the depressurizing current was not supplied to the water electrolyzer in the immediately previous stop.   
     
     
         6 . The starting method according to  claim 5 , wherein before starting supplying the first or second current to the electrolyzer, water is caused to circulate only in a prescribed time in which an inside of the electrolyzer is filled with the water. 
     
     
         7 . The starting method according to  claim 5 , further comprising:
 detecting a hydrogen concentration in a fluid that is discharged from the anode side while the first or second current is supplied to the electrolyzer; and   raising a starting current value of a current that is applied to the electrolyzer to a rated current value in a case where the detected hydrogen concentration becomes a prescribed value or lower.   
     
     
         8 . The starting method according to  claim 5 , wherein as a start pressure of an electroless depressurization process is higher, the first supply rate or the second supply rate is set lower.