Reactors and stills (including rectification tanks) are among the most commonly used equipment in the chemical industry. In recent years, leaks of reactors and distillation stills, fires, and explosions have occurred frequently. Since the kettle is often filled with toxic and hazardous chemicals, the consequences of the accident are more serious than the general explosion.
1. "What is the reactor?"
The reactor refers to a batch reactor equipped with a stirring device, and the chemical reaction can be carried out under conditions of open, sealed atmospheric pressure, pressure or negative pressure depending on the pressure required by the process.
Second, "What is the distillation pot?"
A still pot is a device used to separate a homogeneous liquid mixture.
Third, the risk of existence
(1) inherent danger
The inherent risks of reactors and distillation stills are mainly as follows:
1, materials
The materials in the reactor and the still are mostly hazardous chemicals. If the material is a substance with a low self-ignition point and a low flash point, once it leaks, it will form an explosive mixture with the air. If it encounters an ignition source (open flame, spark, static electricity, etc.), it may cause fire and explosion; if the material is poisonous, once it leaks It may cause poisoning and suffocation.
Accident case:
On March 27, 1994, a reaction kettle exploded in an antistatic agent workshop of an auxiliary plant in Shaoxing City, killing 4 people and seriously injuring 8 people. The reaction vessel is mainly ethylene oxide having an explosion limit of 3% to 100%.
The main cause of the accident:
The air in the kettle was not completely replaced by nitrogen, and the mixed concentration with ethylene oxide reached the explosion limit.
The factory is a newly established township and village enterprise. The pressure vessels used have never been tested. The operators have low cultural and technical quality. They have not been specially trained. They do not understand the danger degree of the production process and the methods for handling the faults.
Before the project was put into production, it was not reviewed by "three simultaneous". There was no complete safety operation procedure and technical measures. It was impossible to display the air in the reactor completely through the instrument, nor did the laboratory test procedure be established. The workers operated with experience and feeling. .
2. Manufacturing problems of equipment
Unreasonable design of the reactor and distillation vessel, discontinuous shape of the equipment, improper weld placement, etc., may cause stress concentration; improper material selection, welding quality when manufacturing containers, and improper heat treatment may reduce the toughness of the material. The container shell is corroded by corrosive media, the strength is reduced or the safety accessories are missing, which may cause the container to explode during use.
Accident case one:
On December 1, 2007, a pressure vessel (steaming kettle) of a fly ash aerated concrete block production workshop of a building material co., Ltd. in Baoding City, Hebei Province exploded, causing five deaths and one minor injury.
The main cause of the accident:
According to the investigation, the management personnel of the company changed the process parameters without authorization, and reduced the total number of connecting bolts of the autoclave and the kettle lid from 60 to less than 30, and the replacement was not timely, and the safety valve of the steaming kettle was not timely. Calibration, long-term overpressure, over temperature operation, resulting in an accident.
Case 2 of the accident:
On September 4, 2000, during the operation of a jacketed glass-lined reactor of a biochemical reagent factory in Yiyang City, Hunan Province, the lid of the kettle suddenly rushed out, and a large amount of acetone medium was sprayed out to mix with air to form an explosive gas. The explosion killed two people and injured six.
The main cause of the accident:
The main cause of the accident was the aging of the gasket on the sealing surface of the reactor, the leakage during operation, and the tightening of the worker with the pressure, causing the lid to escape and causing an explosion. This reactor was an old pressure vessel, which was untested before use and was installed illegally. The operator was also untrained.
(2) Operational process hazards
The reaction kettle and the distillation still have the following risks in the production operation:
1, the reaction is out of control caused by fire and explosion
Many chemical reactions, such as oxidation, chlorination, nitration, and polymerization, are strong exothermic reactions. If the reaction is out of control or sudden power outages and water cuts, the reaction heat is accumulated, and the temperature inside the reactor rises sharply and the pressure increases. Its pressure resistance will cause the container to rupture.
The material is ejected from the rupture, which may cause a fire and explosion accident; the explosion of the reactor causes the equilibrium state of the vapor pressure of the material to be destroyed, and the unstable superheated liquid will cause 2 explosions (steam explosion); the ejected material will rapidly diffuse and react. The space around the kettle is covered by mist or steam of flammable liquid, and three explosions (mixed gas explosion) occur in the ignition source. The main reasons for the uncontrolled reaction are: the reaction heat has not been removed in time, the reaction materials are not evenly dispersed and the operation is faulty.
Accident case:
On March 16, 2007, a chemical company in Dongtai City, Jiangsu Province, in the process of illegally testing the new product ethoxymethanylmalononitrile by using the original production equipment, the distillation tower suddenly exploded, causing 4 deaths and 1 injury.
The main cause of the accident:
The ethoxylated methylidene malononitrile crude product is over-distilled, causing high boilers to block the packing layer, the pressure in the distillation pot is increased, a physical explosion occurs, and the tower section below the packed tower is blown up, which in turn causes combustion and chemistry of the material. explosion.
2. The high pressure material of the reaction vessel is introduced into the low pressure system to detonate
The atmospheric or low-pressure equipment connected to the reaction vessel explodes due to the intrusion of the high-pressure material and exceeds the pressure limit of the reaction vessel.
Accident case:
On August 22, 1991, a major fire accident occurred at the Resin Factory in Pingdingshan City, Henan Province.
The main cause of the accident:
Due to overpressure in the reactor section of the polymerization section, the valve leading to the foam trap (normal pressure equipment) was not completely closed when the on-duty staff urgently disposed, causing an explosion, which subsequently caused the explosion of the combustible mixture in the entire section.
3. An accident occurs when water vapor or water leaks into the reaction vessel.
If the water vapor for heating, the heat transfer oil, or the water for cooling leaks into the reaction vessel or the distillation pot, it may react with the materials in the kettle to liberate heat, causing a sharp rise in temperature pressure, material rushing out, and a fire accident.
4, the distillation condensing system lacks cooling water to explode
During the distillation process, if the cooling water of the overhead condenser is interrupted, and the material in the kettle is still continuing the distillation cycle, the system will change from the original atmospheric pressure or negative pressure state to positive pressure, which will explode beyond the capacity of the equipment. .
Accident case:
On July 28, 2006, the explosion accident of Yancheng Fluoride Chemical Co., Ltd. in Sheyang County, Yancheng City, Jiangsu Province.
The main cause of the accident:
That is, because there is no cooling water in the condenser of the chlorination reaction tower, and there is no product outflow at the top of the tower, there is no immediate stop, and the heating is continued erroneously, so that 2,4-dinitrofluorobenzene is in a high temperature state for a long time, eventually resulting in It breaks down the explosion.
5, the container caused by explosion caused by heat
The reaction vessel is ignited by external combustibles or subjected to heat radiation from a high-temperature heat source, causing the temperature inside the vessel to rise sharply, and the pressure is increased to cause a flushing or explosion accident.
Accident case:
At 6:50 on October 8, 1991, in the pilot room of Jiangsu Huaiyin Organic Chemical Plant, a 100L high pressure reactor for the production of high molecular polyether suddenly exploded, and the fastening bolts connecting the lid and the kettle body were broken. The lid of the weight of about 80kg flew to more than 80 meters from the original place, and the safety valve and pressure gauge installed on the high-pressure reactor were also blown up. The air waves generated by the explosion collapsed the roof, and the 20m3 pilot room collapsed completely. Three operators were killed on the spot.
Analysis of the cause of the accident:
The explosion of the high-pressure reactor is caused by over-temperature and overpressure. The production process of producing high-molecular polyether from ethylene oxide and propylene oxide requires the operator to strictly operate according to the regulations. "Addition, control the amount of feed to avoid the risk of loss of control after the reaction is severe. However, the operator of the plant violated the operation process and adopted the “batch†addition method. The feed was too much at one time and the reaction speed was too fast.
6, the material in and out of the container improper operation caused an accident
Many low-flashing Class A flammable liquids enter the reactor and distillation tank from the pipeline by liquid pump or vacuum. Most of these materials are insulating materials, and the conductivity is poor. If the material flow rate is too fast, it will cause accumulation. Static electricity cannot be removed in time, and a burning explosion accident occurs.
Accident case one:
On March 30, 1993, a major explosion accident occurred in the Jingzhou Petrochemical Complex, killing 4 people. The direct cause of the explosion is that the ethylene oxide feed rate is too fast. In less than 2 hours, the feed in the autoclave has reached 500 kg, causing ethylene oxide to react with propynol and accumulating in the autoclave. The pressure in the autoclave rises rapidly, and the high-pressure gas is rapidly ejected, exploding in the presence of static electricity.
Analysis of the cause of the accident:
The reason for the too fast feed is that the reactor only manually controls the feed rate with the valve, and the flow meter is not installed. Workers do not know what the main ingredients are put into the reactor and should be placed according to what standards. However, the technology transfer party refused to disclose the name and amount of raw materials to the petrochemical general factory on the grounds of technical confidentiality.
Case 2 of the accident:
On April 22, 2002, a chemical reactor accident occurred in a chemical company in Yuanping City, Shanxi Province, causing one death and one serious injury. The explosion shock wave will almost completely open the roof of the prefabricated panel of about 200m2. All the windows of the south wall will be broken, the slag will fly farthest about 50m, and the 40 M20 bolts on the reaction head will be pulled or pulled off.
Analysis of the cause of the accident:
The cause of the accident is that during the discharge process of the reactor, the mixture of carbon disulfide, isopropanol and oxygen in the kettle is pressed and discharged under the gauge pressure of 0, 2 MPa. When the material leaks from the flange, there is a pressure difference between the inside and the outside, and leakage The material flows out at a certain speed, and static electricity is formed in the process. When the liquid material in the kettle is basically drained, the static electricity at the edge of the flange accumulates to a certain energy and forms a discharge gap to generate a static spark, which ignites a mixed gas of carbon disulfide, isopropanol and oxygen, and rapidly ignites into the reactor to cause a chemical explosion. .
7, the workers thought relaxed, did not find the accident in time
The reaction vessel is generally subjected to a reaction under normal pressure or openness, and the distillation vessel is generally operated under normal pressure or under reduced pressure.
Some people think that the risk of operation under normal pressure, open or negative pressure is not great, and it is often lax in thought and can not detect and deal with the sudden accidents in time, and eventually lead to an accident.
In fact, in a reactor with a normal pressure or an open mouth, the pressure on the wall of the kettle is greater than that of the reactor under pressure in the kettle, and the risk is also greater.
For the distillation still, if the operator fails the operation, the reaction of the reaction is out of control and the pipeline valve system is blocked. Under normal conditions, the normal pressure and the vacuum state become positive pressure. If the treatment cannot be found in time, there is no emergency pressure relief device, and it is easy to cause fire. Explosion accident.
Accident case:
On November 27, 2007, Jiangsu Yancheng Lianhua Technology Co., Ltd. was experiencing an explosion of diazotization reactor.
Analysis of the cause of the accident:
Because the steam valve of the diazotization reactor is not shut down, a large amount of steam still enters the reactor jacket during the heat preservation stage, causing the temperature in the reactor to rise rapidly, and the diazotized salt is decomposed violently and then exploded. On-duty operators did not monitor the kettle temperature, and failed to find the temperature abnormality in the kettle in time, delaying the best time to deal with abnormal conditions.
Fourth, security measures
The biggest role of the reactor is to achieve the process of raw material gathering, which can meet the raw material production process and achieve the desired production. However, it is necessary to pay attention to the standard operation. If the reactor is used, the wrong operation steps will cause damage and affect production. Below we will briefly understand the precautions for the use of chemical reactors.
1. Operate in strict accordance with the system
Strictly regulate the operation of the system, which is the most basic requirement for operation. Before operating the chemical reactor, you should understand the standard operating system of the equipment. Although the specification information provided on the equipment manual is not very detailed, some systems that must be observed must be done to ensure the safe operation of the equipment.
2, check before operation
Check the equipment before operating the chemical reactor to check for abnormalities. If the device is in normal operation, the upper cover and the touch panel must not be opened to avoid electric shock. It is strictly forbidden to carry out pressure operation during operation, which not only damages the equipment, but also poses a safety hazard. In the process of nitrogen pressure test, it is necessary to pay attention to its changes to avoid excessive pressure.
3, pay attention to observation
When operating the chemical reactor, pay attention to observation and observe each operation step. Especially when the reactor is heated to a certain degree, it must not be in contact with the kettle body to avoid burns. After the experiment is completed, firstly, it is necessary to carry out cooling treatment, waiting for the temperature to cool, so as to avoid damage to the equipment caused by excessive temperature, and also unplug the power supply in time.
4, pay attention to maintenance
Equipment operation should not only pay attention to the operation process, but also pay attention to equipment maintenance. Equipment maintenance is not an easy task. Only by learning to maintain it can the equipment perform its better performance and at the same time prolong the service life of the equipment. Otherwise, it will seriously affect the operation performance of the equipment.
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