| CPC C25B 9/65 (2021.01) [C25B 1/04 (2013.01); C25B 9/67 (2021.01); C25B 9/77 (2021.01); C25B 15/021 (2021.01); C25B 15/027 (2021.01); C25B 15/029 (2021.01); C25B 15/085 (2021.01); C25B 15/087 (2021.01)] | 4 Claims |
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1. A method of operating a water electrolysis system of which durability is improved by preventing performance degradation of an inner portion of a water electrolysis stack,
wherein the water electrolysis system comprises:
the water electrolysis stack (101) having a structure in which a plurality of unit cells and separating plates are stacked in series and configured to produce hydrogen and oxygen through a water electrolysis reaction by electric energy;
a cell voltage reducer (102) which detects that a cell voltage of the water electrolysis stack (101) is lowered from a predetermined cell operating voltage in real time;
a current variable converter (103) which supplies the electric energy to the water electrolysis stack (101);
a breaker (103-1) which is provided at one side of the current variable converter (103) and blocks current from flowing to a back-pressure regulator (120) and the water electrolysis stack (101);
a circulating water tank (104) which is provided at one side of the water electrolysis stack (101) and supplies circulating water thereto;
a liquid pump (105) positioned on an oxygen generation line on which oxygen is generated at an anode (OER; oxygen evolution reaction) electrode of the water electrolysis stack and configured to circulate circulating water, which is an electrolyte;
a pressure sensor (106) provided at front end of the water electrolysis stack (101);
a flow sensor (107) provided at one side of the pressure sensor (106) and configured to detect a flow rate of the circulating water;
a temperature sensor (108) which is provided at rear end of the water electrolysis stack (101) to monitor an increase in a temperature of the circulating water at the rear end of the water electrolysis stack (101) due to a mixing phenomenon of hydrogen and oxygen when a pinhole is generated in an ion-exchange membrane;
an air-cooled heat exchanger (109) which maintains a constant temperature of the circulating water tank (104);
a water electrolysis system controller which detects a dangerous state due to the mixing phenomenon of hydrogen and oxygen;
a circulating water auxiliary tank (110) which supplies as much water as an amount of water consumed in the circulating water tank (104) in real time;
a cooling heat exchanger (114) which cools hydrogen produced at a cathode (HER) electrode of the water electrolysis stack (101);
a pressurizer which is provided on a hydrogen production line and prevents water coming through the ion-exchange membrane from a side of the anode electrode toward the cathode electrode;
a check valve which prevents water from flowing back through the ion-exchange membrane;
a water separator (115) which separates moisture transferred with hydrogen;
an absorber (117) positioned at one side of the water separator (115);
a microfilter (118) which is provided at one side of the absorber (117) and allows hydrogen purity to be improved with the absorber (117);
a pressure sensor (119) provided at rear end of the water electrolysis stack (101);
the back-pressure regulator (120) provided at one side of the pressure sensor (119) and adjusts a hydrogen production pressure; and
an explosion-proof oxygen sensor (121) which detects a concentration of oxygen in produced hydrogen gas,
wherein the method comprises:
in a start process of the water electrolysis system, the electrolyte circulating water of the water electrolysis stack is circulated while heated to a temperature of 60° C., and power with a current of 30 mA/cm2 based on an active area of the water electrolysis stack is supplied to the water electrolysis stack until the temperature of the electrolyte circulating water reaches the temperature of 60° C.; and
in a shut down process of the water electrolysis system, power with a current of 50 mA/cm2 based on an active area of the water electrolysis stack is supplied to the water electrolysis stack, and the electrolyte circulating water is cooled to a temperature of 40° C.
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