Water Electrolysis System Explosion

An explosion occurred in an electrolysis system in a commercial facility. Electrolysis of a potassium hydroxide solution is used to produce hydrogen for a hydrogenation processes. The circular electrolysis cells are 1.5 m in diameter and 25 mm thick. Design current for the electrolyzer is 6,000 amps at 1.78 volts. Operating temperature and pressure is 70-90 °C and 435 psig. Hydrogen and oxygen product gases are separated from the electrolyte in separating drums. The system had been operating at the plant for 13 years prior to the explosion. Operating experiences had been generally favorable except for the need to periodically flush the system with water to remove sludge formations.

According to the investigative report, sludge deposits in the electrolyte passages started the following sequence of events, culminating in the explosion.

Reduced electrolyte flow rates caused by sludge blockage resulted in increased cell temperatures and electrolyte concentrations. The increased electrolyte concentrations and linear velocities (due to obstructed passages) eventually led to severe corrosion/erosion damage of the cell electrodes and separators (hydrogen embrittlement may have also been a contributing factor). Physical breakdown of the cell separators allowed hydrogen and oxygen to mix and hydrogen to enter the oxygen separator drum. The gas mixture was ignited causing a violent explosion which ruptured the separator drum. A plant operator in the electrolysis room at the time of the explosion was fatally burned by the caustic solution sprayed from the ruptured drum.