On April 3, a large accident of aluminum explosion occurred in a melting and casting workshop of Guangdong Qingyuan Exquisite Special Profile Co., Ltd., resulting in 5 deaths.
After preliminary investigation, when the accident occurred, the No. 9 deep well casting plate watchman left the post without authorization in violation of the operating procedures, resulting in a leakage of aluminum water for up to 1 minute and 32 seconds without being discovered, the emergency situation could not be dealt with in time, and a large amount of high-temperature aluminum water flowed into the casting deep well to cause an explosion, which then caused the explosion of the nearby No. 6 casting deep well.
Moreover, the accident enterprise did not strictly comply with the relevant provisions of the state, the interface between the flow trough and the casting die plate, and the crystallizer cooling water system were not set up in accordance with the specifications of the monitoring and alarm devices, and the quick shut-off valve and emergency discharge valve on the flow slot were not interlocked.
A number of experts said that the accident once again exposed the problem of the low safety level of equipment and facilities of some aluminum processing enterprises. The installation of automatic monitoring and early warning and interlocking devices to strengthen the safety training and education of enterprise employees is still the next step of rectification.
In Qingyuan, Guangdong, an aluminum explosion accident occurred in the melting and casting workshop of Exquisite Special Profiles Co., Ltd., and the accident site was a mess, and rescue personnel were carrying out disposal work.
The main power of the "aluminum hydrum explosion" comes from chemical reactions
According to the data, Guangdong Exquisite Special Profile Co., Ltd. was established in 2010, with a registered capital of 650 million yuan and 1302 employees, mainly engaged in non-ferrous metal smelting and calendering processing, and its products are mainly aluminum profiles and casting deep processing components. The company has 10 melt casting production lines, equipped with 10 stationary melting furnaces, supporting the use of wire rope hoisting traction of deep well casting system.
It is reported that Deep Well Casting is in the middle of the aluminum industry chain, and the aluminum solution generated by upstream electrolysis is made into an aluminum rod for use in the downstream manufacturing industry.
The casting process of this process is: the aluminum ingot is melted into molten aluminum through the melting furnace, and the molten aluminum enters the crystallizer through the flow groove, and then solidifies into a bar by water cooling. In the process of aluminum rod making, once the high-temperature aluminum liquid leaks and is in improper contact with the cooling water, it will explode, which is also a high-risk point in the deep well casting process.
In September 2020, an accident occurred in the Gansu Hongda aluminum casting workshop due to improper operation of on-site workers, resulting in a large amount of aluminum liquid entering the cooling shaft and causing an explosion, which caused 4 deaths and 6 injuries.
Surveillance video at the scene of the accident showed that at 11:10:22 on April 3, a leak occurred in a diversion hole of the crystallizer. After that, due to the lack of timely standardized disposal, a large amount of aluminum water quickly leaked into the deep well, resulting in an explosion.
Why does molten aluminium leak from the crystallizer? "When the crystallizer cannot smoothly solidify the molten aluminum from the liquid to a solid state, the molten aluminum may leak out of the crystallizer." Aluminum expert He Yongping told reporters, "This situation is mainly related to the state of the crystallizer, the temperature of the aluminum liquid, the cooling strength and other parameters." ”
In addition, expert Mi Jian introduced that in the entire casting process, the refractory materials from the aluminum mouth of the smelting furnace are damaged, the refractory materials in the flow groove are damaged or the refractories do not meet the requirements, and the gate valve is not closed in place, which may lead to the leakage of aluminum liquid.
Why is the "aluminum water explosion" so powerful? It is understood that the so-called "aluminum water explosion" contains both physical and chemical processes.
"After the molten aluminum liquid and the water contact, due to the huge temperature difference and the boiling point of the water is much lower than the temperature of the molten aluminum, the water temperature quickly reaches the boiling point above the boiling point and enters a superheated state, the water instantly evaporates into a gas, and the volume expands by more than 1,000 times." Especially under the narrow space conditions of the casting well, a pressure wave of a certain amplitude will be formed, and the expansion will produce energy, and the explosion will occur. Expert Mi Jian said.
He pointed out that steam explosions, physical explosions, are not very powerful, and the main damage comes from subsequent chemical explosions. "Aluminum is a very chemically active metal element, and the chemical reaction of molten aluminum with oxygen in water or air will release huge amounts of energy, especially in a relatively enclosed space like a well pit, where the explosive power will be further amplified."
The watchman left his post without authorization
Continuous leakage of molten aluminum was not detected in time
Zhou Yingquan, an aluminum expert, said that a small amount of aluminum molten slowly entered the casting deep well and did not react violently. "A large amount of molten aluminum covered the water, and the expanding water vapor had nowhere to go, and the explosion occurred. In other words, if you are not afraid of 'water-wrapped aluminum', you are afraid of 'aluminum-clad'. ”
It is understood that the accident enterprise No. 9 deep well casting disk, near the console usually has 3 workers, from the surveillance video can be seen, the Incident No. 9 deep well to see the plate workers violated the operating procedures, unauthorized departure, the casting site is unsupervised, aluminum leakage up to 1 minute and 32 seconds but was not found. When the operators discovered the molten aluminum leak and took measures to plug the leak, a more serious situation occurred – a large amount of aluminum water quickly entered the deep well, and the explosion followed.
According to experts, due to the process characteristics of aluminum processing (deep well casting), the casting regulations stipulate that there must be a special person responsible for supervising the watchdog on the spot. The company's system also stipulates that three people must be present at the same time.
"The fact that the company's management system has not been implemented shows that the company's safety training and education for employees is not in place." Zhou Yingquan said that the entry threshold of the aluminum processing industry is low, the cultural level of employees is generally not high, and safety training and education are particularly important.
"In actual production, in order to prevent the leakage of aluminum molten, before casting, the mold is generally maintained by applying sludge, cleaning the cooling water eye, etc.; when casting, it is necessary to control the temperature and casting speed of the aluminum liquid, adjust the matching cooling water flow in time, in addition, the on-site personnel should pay close attention to the state of each crystallizer, the formation of the aluminum rod, etc." He Yongping said.
Expert Mi Jian introduced that in the casting process, once the aluminum leakage is found, the correct disposal method is to terminate the casting, immediately cut off the amount of aluminum liquid entering the leakage area, discharge the high-temperature aluminum liquid into the emergency pit for disposal, and the personnel should stay as far away from the aluminum leakage site as possible.
Set up sensors and alarm devices
And the automatic interlocking device is the direction of rectification
According to the Guangdong Provincial Emergency Management Department, the accident enterprise fixed smelting furnace high-temperature aluminum water outlet did not set up a mechanical locking device, deep well casting crystallizer and other water-cooled components of the cooling water system only equipped with alarm devices, did not configure emergency cut interlocking devices, does not meet the national "aluminum seven" requirements. The "seven aluminum articles" mentioned in the circular are the "Key Matters of Safety Production Law Enforcement Inspection of Aluminum Processing (Deep Well Casting) Enterprises" issued by the Ministry of Emergency Management, which has three requirements for equipment and facilities, emphasizing the setting of sensors, alarm devices and automatic interlocking devices in key parts of key equipment.
According to the investigation, the liquid level sensor installed at the interface between the flow tank and the casting die plate of the accident enterprise deep well has only a high level alarm function, no low level alarm function, and cannot monitor the sharp drop of the aluminum water level in the flow groove; the cooling water system of the deep well casting crystallizer is installed with inlet water temperature, pressure, flow monitoring and alarm device, no outlet water temperature monitoring and alarm device is installed, and the rapid rise of the cooling water temperature in the casting well cannot be monitored, which does not meet the requirements of the national "aluminum seven".
The lack of these safety equipment makes it impossible to automatically monitor the leakage of aluminum water in the crystallizer, nor to cut off the aluminum water flowing into the crystallizer in time and divert it to the emergency pit, thus causing the accident to occur.
The reporter noted that the use of automated devices to monitor, warn and dispose of abnormal conditions such as aluminum leakage in the casting process is also a requirement of the state in recent years. The "Criteria for Determining the Hidden Dangers of Major Production Safety Accidents in the Industry and Trade Industry (2017 Edition)" lists a series of behaviors such as "the water cooling components of the smelting furnace are not equipped with temperature, the detection and alarm device of the inlet and outlet water flow difference, and the safety facilities (such as: rapid shut-off valves, etc.) that prevent a large amount of cooling water from entering the furnace are not set up.
"Through the instrument can be the melting and casting process of the liquid level, cooling water temperature, cooling water flow, cooling water pressure and other important parameters to monitor and warn, when the parameters are abnormal, with automatic interlocking control instead of human operation, you can terminate the casting at the first time of risk occurrence, reduce and control the risk." If the company's monitoring and early warning and interlocking devices are standardized and installed, the aluminum leakage will be immediately and automatically disposed of, and this accident can be completely avoided. Expert Mi Jian said.
The entry threshold of the aluminum processing industry is low, and the safety level of equipment and facilities is common. Experts said that some small businesses do not meet the design requirements and have more hidden risks.
Zhou Yingquan said that at present, aluminum processing enterprises are in the process of industrial adjustment, and some large enterprises with advanced management concepts can achieve timely transformation and update of automation equipment. Investigators revealed that the accident company is a wholly-owned subsidiary of Guangdong Haomei New Material Co., Ltd. Guangdong Haomei New Material Co., Ltd. was established in 2004, and in 2017, it won the title of "Top Ten Enterprises of China's Construction Aluminum Profiles", and in 2020, it was listed on the small and medium-sized board of the Shenzhen Stock Exchange.
With such a strong background in the parent company, why is it delayed in updating the equipment? "In the final analysis, enterprises still do not pay enough attention to safe production, and do not coordinate the relationship between development and safety." That's what the experts say.
Guangdong: 150 aluminum processing enterprises in the province were transformed into safety technologies
The lack of employee safety training and education and automation devices exposes that the main responsibility of the enterprise has not been implemented, taking production safety as a slogan, and ignoring safety production laws and regulations.
Investigators found that not even a single safety warning sign could be seen in the factory area of the accident company. The relevant person in charge of the enterprise said that on March 4, the employees of the casting workshop were organized to watch the video of the "2.18" accident in Huizhou and carry out accident warning education and safety training, but they could not find any training records. The investigators questioned the training host and the participants, and they did not know what to do.
The hidden dangers in the safety hazard inspection record sheet of the accident enterprise in June 2021 are required to complete rectification on July 1, but there is no record of the rectification of the hidden danger problem in the July record table. "It shows that the security risk investigation of the enterprise is a formality, and the problems found are not rectified." Experts say.
The above situation violates the relevant provisions of Article 41 of the Work Safety Law: Production and business units shall establish, improve and implement a system for the investigation and management of hidden dangers of production safety accidents, adopt technical and management measures, and timely discover and eliminate hidden dangers of accidents. The investigation and management of hidden dangers of accidents shall be truthfully recorded, and employees shall be informed through methods such as employee assemblies or employee congresses, information bulletin boards, etc.
According to incomplete statistics, there are 150 aluminum processing (deep well casting) enterprises in Guangdong Province, mainly concentrated in 12 cities such as Foshan, Guangzhou, Shenzhen, Zhuhai, Shaoguan, Jiangmen, Zhanjiang, Zhaoqing, Qingyuan, Dongguan, Zhongshan, Yunfu, etc., of which Foshan has the most, reaching 80. On April 8, Guangdong deployed 150 aluminum processing (deep well casting) enterprises in the province to carry out system governance, implement safety technology transformation such as monitoring and alarm interlocking, and ensure the normal installation and use of equipment and facilities such as monitoring alarm interlocking.
"This accident warns us that it is very necessary to configure a mechanical locking device, a liquid level monitoring alarm, a cooling water system monitoring alarm device and an emergency shut-off device interlock." He Yongping said that in order to prevent the recurrence of such accidents, the national "seven aluminum" requirements should be effectively implemented, and new, reform and expansion projects should be strictly reviewed. At the same time, qualified enterprises recommend using tilting furnaces and hydraulic casting machines with higher intrinsic safety levels instead of fixed melting furnaces and wire rope casting machines.
"In addition to the requirements for equipment and facilities, the 'Aluminum Seven' put forward corresponding requirements for the inspection and replacement of steel wire ropes, emergency storage facilities, and personnel control to prevent the occurrence of major accidents and mass casualties." Zhou Yingquan said.
It is understood that the Ministry of Emergency Management has asked emergency management departments at all levels to issue a warning video of this accident to the relevant aluminum processing (deep well casting) enterprises, urging enterprises to learn the lessons of the accident, conscientiously carry out investigation and rectification in accordance with the "Aluminum Seven Articles", effectively strengthen on-site safety management, and resolutely curb the recurrence of similar accidents.
At the same time, emergency management departments at all levels will accurately carry out law enforcement inspections in accordance with the requirements of the "Seven Articles of Aluminum", and will strictly investigate the responsibility of enterprises for "repeated prohibitions and repeated penalties".