High differential pressure water electrolysis system and method for starting the same

A method for starting a high differential pressure water electrolysis system that includes:

• a high differential pressure water electrolysis device configured to electrolyze water to generate oxygen and high pressure hydrogen which has a pressure higher than a pressure of the oxygen;
• a water supply tank to store the water to be supplied to the high differential pressure water electrolysis device;
• a high pressure gas-liquid separator to separate liquid from the high pressure hydrogen output from the high differential pressure water electrolysis device;
• a hydrogen outlet line connecting the high differential pressure water electrolysis device and the high pressure gas-liquid separator;
• a drain line to drain a liquid water separated by the high pressure gas-liquid separator;
• a low pressure gas-liquid separator disposed in the drain line;
• a water return line connecting the low pressure gas-liquid separator and the water supply tank;
• and
• a pressure application line connecting a midpoint of the hydrogen outlet line and the low pressure gas-liquid separator,
• the method comprising:
• determining whether or not a pressure in the low pressure gas-liquid separator is lower than a pressure in the water supply tank;
• introducing the high pressure hydrogen output from the high differential pressure water electrolysis device into the low pressure gas-liquid separator through the pressure application line when it is determined that the pressure in the low pressure gas-liquid separator is lower than the pressure in the water supply tank;
• and
• opening the water return line to return water in the low pressure gas-liquid separator to the water supply tank when it is determined that the pressure in the low pressure gas-liquid separator is higher than the pressure in the water supply tank.