【Haichuan Chemical Salary News】Explosion Accident During Maintenance at Anhui Bayi Chemical Plant

Preliminary investigations indicate that the accident occurred in Reactor No. 3 in the p-aminophenol production area of this company – a pressure vessel located ahead of the membrane filter and serving as a buffer tank for the hydrogenation reaction. Two workers from the subcontracting company, Jiangsu Xinseng Construction Engineering Co., Ltd., were involved in the accident while removing bolts and opening the manhole cover of Reactor No. 3. Monitoring records from the control room show that at 10:21, there was an abnormal temperature rise in Reactor No. 3; at 10:17, the concentration of flammable gases in the surrounding area increased abnormally, while the pressure inside the reactor remained at normal levels. According to the preliminary analysis by experts, the cause of the accident may have been the presence of hydrogen in Reactor No. 3. When the external contractors opened the manhole cover, hydrogen mixed with air; sparks were generated as a result of contact with metal tools or due to static electricity from human bodies, leading to an explosion. The shock wave caused one person to die on the work platform at the manhole site, while another person was injured after falling to a lower platform about 2 meters below. The specific cause of the accident is under further investigation.

Preliminary investigations indicate that the accident occurred in Reactor No. 3 in the p-aminophenol production area of this company – a pressure vessel located ahead of the membrane filter and serving as a buffer tank for the hydrogenation reaction. Two workers from the subcontracting company, Jiangsu Xinseng Construction Engineering Co., Ltd., were involved in the accident while removing bolts and opening the manhole cover of Reactor No. 3. Monitoring records from the control room show that at 10:21, there was an abnormal temperature rise in Reactor No. 3; at 10:17, the concentration of flammable gases in the surrounding area increased abnormally, while the pressure inside the reactor remained at normal levels. According to the preliminary analysis by experts, the cause of the accident may have been the presence of hydrogen in Reactor No. 3. When the external contractors opened the manhole cover, hydrogen mixed with air; sparks were generated as a result of contact with metal tools or due to static electricity from human bodies, leading to an explosion. The shock wave caused one person to die on the work platform at the manhole site, while another person was injured after falling to a lower platform about 2 meters below. The specific cause of the accident is under further investigation.

Boom accident occurs during hydrogen venting. Accident name: Boom occurs during hydrogen venting. Date of occurrence: April 30, 1988. Incident location: A factory in Zhejiang. Accident sequence: After a row of hydrogen cylinders at the hydrogen filling station in the compressed hydrogen section of the plant had been filled, the operator released the remaining high-pressure hydrogen from the pipeline system. Immediately thereafter, a loud explosion occurred above the plant building. Around the outlet of the hydrogen release pipe on the roof of the compressed hydrogen plant, a fire ignited first; the diameter of this fire ball was nearly 1 meter. After 3 to 5 seconds, it turned into a cloud of black smoke, and the accident did not spread any further. Cause analysis: Since the outlet of the hydrogen vent pipe is only 1 meter away from the eaves gutter, the discharged hydrogen accumulates in the eaves gutter. Calculations show that approximately 0.3 m3 of chlorine gas was released at that time (under normal pressure and temperature), and it mixed with the air in the gutter to form a explosive mixture. This hydrogen gas at a pressure of nearly 14.7 lMPa was discharged rapidly from the vent opening, causing static electricity to build up and sparks to be generated, which led to a deflagrating combustion. Yan Sheng’s fire was caused by the ignition of the roof’s waterproof asphalt layer.

Lesson: (1) When installing the hydrogen vent pipe, its exhaust outlet should extend more than 3 meters above the roof, and the end of the exhaust pipe should face an open area. To ensure that the released hydrogen can diffuse promptly ； (2) Static grounding of hydrogen storage equipment and pipelines should be provided ； (3) All materials used in the compressed air plant shall be constructed from non-combustible materials.

I. Accident course and hazards: Around 2 p.m. on December 18, 2000, the employees on duty at a power company noticed an unusual odor in the hydrogen-oxygen workshop, so they inspected the workshop and found that the paint on the inlet pipe of the No. 3 drying tower, which was in operation, had been scorched. Gas sampling and analysis of the inlet pipeline to the drying tower revealed that the oxygen content in the hydrogen gas in that pipeline was above the allowable level. After 10 minutes of emergency nitrogen filling to protect the 300m3 wet hydrogen storage tank in the workshop’s purification system, a popping sound was heard from the pipeline of the hydrogen deoxygenation tower; subsequently, the 300m3 wet hydrogen storage tank exploded. The bell cover of the storage tank rose about 2 meters (with the bottom of the tank not above the water surface) before falling back, causing severe damage to the bell cover; hydrogen leaked from the cracks in the bell cover, leading to a fire.

II. Analysis of the accident causes: Based on the conditions at the accident site and surrounding areas, as well as the data from the accident investigation, the power company held a meeting to analyze the cause of the accident, bringing together relevant experts to conduct a thorough analysis. It was determined that there are two possible causes for the explosion of the 300m3 wet hydrogen storage tank: (1) The guide wheel at the 180m3 mark became stuck, preventing the tank from moving up and down freely. The operation of the compressor creates a negative pressure inside the storage tank, causing the tank to deform and leading to cracks at the welds of the bell cover. Outside air enters the storage tank through these cracks, resulting in the formation of a hydrogen-oxygen mixture in certain areas of the tank. Since the deoxygenation tower was still in operation, intense oxidation reactions occurred under the catalysis of the catalysts in that tower, generating a large amount of heat. This heat caused the paint on the inlet pipes of the drying tower to burn off. When the hydrogen concentration in the storage tank reached its explosive limit, an explosion occurred due to the ignition source in the deoxygenation tower, resulting in the destruction of the storage tank and the outbreak of a fire.

(2) The quality of the recycled nitrogen used in the process system was poor (the oxygen content in the nitrogen was above the specified limit). Due to the inadequate sealing of the valves in the hydrogen drying tower, oxygen present in the nitrogen mixed into the hydrogen system, forming a hydrogen-oxygen mixture. Under the catalytic action of the catalysts in the deoxidation tower, a violent oxidation reaction occurred, releasing large amounts of heat; this caused the paint on the inlet pipes of the drying tower to burn away. When emergency nitrogen filling was carried out to protect a 300 m3 wet hydrogen storage tank, the high oxygen content in the nitrogen used resulted in the hydrogen inside the tank reaching its explosive limit in some areas. An explosion occurred as a result of an ignition source in the deoxidation tower, causing the tank to be damaged and triggering a fire. Since there may be two possible causes for the accident, further technical analysis is conducted.

【Explosion incident of 300m3 wet hydrogen tank – Haichuan Chemical Industry Forum】https://bbs.hcbbs.com/forum.php?mip=1&mod=viewthread&tid=1178310

Hydrogen explosions: Hydrogen can explode when ignited in air. Theoretical calculations show that the explosion limit for hydrogen is 4.0% to 75.6% (in terms of volume concentration); this means that if the volume concentration of hydrogen in air is within this range, it will explode upon contact with a flame. However, when the hydrogen concentration is less than 4.0% or greater than 75.6%, no explosion will occur even in the presence of a flame.

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