Fires in ion membrane electrolyzers occur from time to time in chlor-alkali enterprises, with minor incidents causing damage to the electrolyzer and production halts for several hours, and severe cases leading to casualties. Based on the analysis of a fire incident involving an ion membrane electrolyzer in a chlor-alkali enterprise, the causes were examined and a series of preventive measures were proposed. These measures aim to serve as a reference for other chlor-alkali enterprises, with the goal of improving the industry’s overall ability to prevent such incidents and promoting the safe and high-quality development of the chlor-alkali sector.
1. Incident Overview of the Fire
During a routine inspection in the electrolyzer section of a workshop, the shift supervisor on duty heard two abnormal sounds at intervals of 3 seconds while inspecting the first floor of the electrolyzer plant. Shortly afterward, they noticed liquid leaking onto the ground from a pipe hole in the ceiling leading to the second floor. Simultaneously, the central control room of the chlor-alkali facility notified the on-site supervisor via radio about abnormal current fluctuations in circuit #5. The supervisor immediately led the team to the second floor of the electrolyzer plant, where they found a fire on top of the electrolyzer in position 10 of circuit #5.
The supervisor reported the incident to senior management and instructed the team to use dry powder fire extinguishers to fight the fire. However, the fire intensified. The on-site personnel then opened the nitrogen valves on both ends of the electrolyzer in circuit #5, ensuring that the cathode side was under positive pressure. They used the emergency stop button to shut down circuit #5, switched the gas and liquid phases of the electrolyzer to waste chlorine and waste hydrogen, and closed the anode and cathode inlet valves. As nitrogen was pumped into the system, the fire gradually subsided, and the fire at the top of the electrolyzer was extinguished. The team then carried out shutdown procedures for the electrolyzer.
2. Cause Analysis of the Fire Incident
The brine system of the workshop’s electrolyzer had been in continuous operation for an extended period. The CPVC pipes and rubber gaskets used in the electrolyzer’s brine system were exposed to high temperatures (around 90°C, the operating temperature of the ion membrane electrolyzer) and free chlorine, which caused them to corrode, age, and deteriorate. The detached debris from the gaskets and pipes flowed with the brine to the anode feed manifold (which has an inner diameter of 6 mm), eventually blocking the manifold opening for unit 64# of electrolyzer 10# in circuit #5. As a result, brine could not enter the anode chamber of unit 64, leading to a rapid increase in both voltage and temperature within the anode chamber. The pressure inside the unit rose, deforming and leaking the electrolyzer gaskets. As the liquid level inside the unit dropped, the upper part of the ion membrane dried out and was punctured by the direct current.
Once the ion membrane in unit 64# was punctured, the contact between the electrolyzer’s anode and cathode resulted in a discharge, producing sparks. The leaking hydrogen was quickly ignited, causing the fire in the ion membrane electrolyzer.
At the same time, the manifold opening for unit 64# in electrolyzer 10# of circuit #5 became blocked, coinciding with the moment when the DCS (Distributed Control System) operator disconnected the circuit voltage interlock switch to adjust the interlock threshold (a process that takes 1 minute). During this period, the electrolyzer’s voltage protection system was not interlocked, and when the voltage anomaly occurred, the interlock protection for the circuit’s rectifier system was not activated. Consequently, the direct current to the electrolyzer was not cut off in time, leading to the puncturing of the ion membrane in unit 64#, hydrogen leakage, and the resulting fire.
3. Fire Prevention Measures for Ion Membrane Electrolyzers
3.1 Replacement of Pipes and Gaskets Around the Ion Membrane Electrolyzer: The non-metallic pipes around the electrolyzer, previously made from CPVC, should be replaced with fiberglass-reinforced PTFE-lined pipes. The gaskets should be upgraded from low calcium-magnesium rubber to PTFE gaskets or rubber gaskets wrapped in PTFE. This will reduce or eliminate the likelihood of CPVC pipes and rubber gaskets deteriorating, shedding debris that could block the feed hose. During annual shutdowns for maintenance, the brine, caustic soda feed pipes, filters, and electrolyzer outlet pipes should be cleaned. Additionally, the secondary refined brine tank and anolyte circulation tank must also be cleaned.
3.2 Upgrade of the Ion Membrane Electrolyzer Voltage Interlock Protection System: The voltage interlock protection system should be upgraded to include a forced interlock mechanism for the ion membrane electrolyzer voltage. This interlock should remain engaged at all times and must not be manually disabled. Even when the DCS personnel make minor adjustments to the accurate protection value of the electrolyzer voltage (which should be calculated based on current density), an additional layer of voltage protection will still be in place. This prevents the direct current supply from continuing if the voltage rises abnormally high. During every shutdown and startup, the reliability of the voltage interlock should be tested to ensure it functions as expected. Additionally, the authority to disable the voltage interlock should be elevated, requiring approval from senior company and division leadership. Once approved, the adjustment of the voltage protection value should be completed within 5 to 8 seconds, and the interlock must be immediately re-engaged.
3.3 Enhancing the Emergency Response Capabilities of Operators: The current dry powder fire extinguishers located on the second floor of the electrolyzer plant are insufficient to control the spread of fire in ion membrane electrolyzer incidents. Therefore, CO2 fire extinguisher carts and nitrogen gas hoses should be added to effectively control and extinguish fires. Regular targeted emergency drills should be conducted to ensure that operators are trained to handle fires involving ion membrane electrolyzers, preventing the escalation of incidents and controlling them at an early stage.
3.4 Adding Pneumatic Valves for Full Remote Control of the Ion Membrane Electrolyzer: Currently, cutting off the gas and liquid phases and operating the nitrogen protection system for each circuit of the ion membrane electrolyzer requires on-site personnel to manually operate valves on the second floor of the electrolyzer plant. In case of a leak, operators face risks such as hydrogen combustion and explosion, chlorine poisoning, burns, or electric shock when manually performing these operations. By adding pneumatic valves, the ion membrane electrolyzer can be fully automated and remotely controlled, allowing for quick and efficient operation without requiring personnel to enter the hazardous second floor, thereby significantly reducing the risk of injury.
4. Conclusion
The electrolysis process is a key hazardous process under strict supervision, and ensuring the safe and stable operation of electrolyzers is one of the main control tasks for chlor-alkali enterprises. The issue of electrolyzer fires has long troubled these enterprises. With increasingly stringent safety and environmental protection regulations, it is necessary to invest in upgrading ion membrane electrolyzer systems to improve their intrinsic safety and prevent fire incidents. The goal is to ensure that ion membrane electrolyzers can operate safely and stably throughout each maintenance cycle, continuously generating economic benefits for chlor-alkali enterprises.