First, the fire risk of ethylene production enterprises

Ethylene is one of the important basic raw materials for petrochemical production and is widely used in the production of synthetic fibers, synthetic rubber and plastics. The production of ethylene represents the level of development of a country's petrochemical industry.
The raw materials for the production of ethylene are naphtha, natural gas, and deep processing of refinery products such as atmospheric diesel and vacuum diesel. Ethylene production has greater fire and explosion hazard than refining. The pressure and temperature in production are higher (the highest working pressure is 11.28MPa, the maximum temperature is 1010°C, the device is more complicated, the continuity is stronger, and there is still deep Cold operation (minimum temperature - 170 ° C); the material in the production process is mostly gaseous, so fire and explosion protection work is extremely important.

The fire hazards of ethylene producers are:

(1) The solution process is carried out under high temperature and high pressure conditions, and there may be fires and explosions.

1. The temperature in the cracking furnace is as high as 750-1000 ° C, and the cracking reaction is carried out in a high-temperature gas phase. The main products obtained are gaseous flammable substances at normal temperature and pressure, and once it leaks, whether it is light diesel or not, The cracked gas can immediately ignite and burn, causing a fire.

2. If the cracking gas is at a high temperature, if the water pressure is greater than the water pressure due to insufficient water or water pressure or due to misoperation, the equipment will be burned and the fire will be caused.

3. If the induced draft fan fails or the damper opening is insufficient, the furnace pressure will rise and cause an explosion if it is severe.

4. The negative pressure of the cracking furnace furnace may change with the wind direction and the wind. If you do not pay attention to the adjustment, it may cause a fire.

5. When the winter starts, if the condensate is brought into the furnace, it will cause the positive pressure in the furnace to temper, so that the cracking furnace interlocks and stops, the fire comes out from the fire hole, and it is easy to burn the instrument and electrical equipment around the furnace. Tempering can cause deflagration in the furnace.

6. Before driving, if there is an explosive mixture in the furnace without replacement by ventilation or replacement by steam, it will cause an explosion if it is ignited.

(2) The danger of the compression process

Compression is the compression of raw materials through the compressor to 3.0-4.0MPa, the equipment is not good, poor maintenance or long-term maintenance, misuse, etc., and negative pressure due to compressor cooling, poor lubrication, pipeline equipment, If a material leaks due to a crack, an explosion or flushing of the equipment may occur, causing a fire accident.

(3) Fire hazard of cryogenic separation

The cryogenic separation is carried out at an ultra-low temperature of -30 ° C to -165 ° C. If the raw material gas is not dry and the equipment system remains moisture, "freezing plugging" will occur. When the equipment is venting materials, if the equipment is not strictly controlled, it will cause the equipment to burst cold and brittle, resulting in a large amount of flammable materials leaking, causing fire and explosion accidents.

(4) Fire hazard in the hydrogenation process

The hydrogenation process is the addition of hydrogen to acetylene, carbon three, and gasoline. Hydrogen is a flammable, explosive, and highly permeable gas, so the hydrogenation process is very strict. If the hydrogen or alkyne ratio of the hydrogenation reactor is improper, it will cause the hydrogenation reactor to heat up sharply. If the reaction temperature of the reactor is too high, it will cause coking of the catalyst, causing the reactor to "fly". If the "flying temperature" is severe, the temperature of the reactor will rise sharply, which will cause thermal creep of the wall, causing a fire or even an explosion.

(5) Fire hazard of substances in ethylene production

Ethylene plants should pay attention to fire prevention during the start-up, operation, and maintenance of the ethylene plant. Because the raw materials, intermediate products and products used in the production of ethylene are mostly flammable, explosive, toxic gases or liquids. In the production of ethylene, the material is prone to electrostatic charge under certain external conditions (such as friction, induction, polarization, adhesion, flow, spray and droplets), and can cause fire and explosion caused by static electricity.

Because ethylene production has the characteristics of high temperature (1010 ° C), high pressure (10 MPa), deep freezing (-196 ° C), and there are corrosive media such as sulfur and alkali, it is easy to cause corrosion, perforation and crack in pressure vessels, equipment and pipelines. , fracture, hydrogen is a greater risk of fire in production.

Second, the fire safety work of ethylene production enterprises

(1) Strengthening fire safety management

1. Establish and improve various safety systems, strictly operate according to the "Safety Technical Regulations for Ethylene Plants", and control temperature, pressure, material flow, flow rate and liquid to prevent accidents caused by "flying temperature" overpressure, negative pressure and static electricity.

2. Establish fire prevention files and ledgers; improve fire safety organizations and voluntary fire brigades, and conduct training and study.

3. Strictly control the fire source and establish a strict hot fire system. It is strictly forbidden to bring fire and nail shoes into the factory, and it is forbidden to hit the equipment with iron.

4. Every year, the device must be overhauled, and key equipment, containers, and key parts should be organized for analysis and consultation by engineering and technical personnel, and modern inspection methods and methods such as physical operation and filming should be applied for careful maintenance.

5. Develop emergency parking solutions and fire fighting plans.

(2) The design of the device shall comply with the requirements for fire prevention and explosion protection.

The safety specifications of the general layout should be strictly observed during the design phase of the installation. Limit the number of inflammable and explosive materials within a certain boundary within a certain boundary, and maintain a certain fire separation distance between the boundaries. The electronic computer, instrument and electrical system should ensure safe operation. The selection of electrical equipment shall comply with the national regulations on the division of electrical fire and explosion sites.

(3) Taking safety measures according to the characteristics of the process

The operating conditions of the ethylene production process are complex, and various process parameters, such as temperature, pressure, flow, liquid level, etc., correctly indicate the change of production, which is the premise of ensuring safe production during the operation. Therefore, the realization of automatic control of process parameters is also a prerequisite for ensuring safe production.

1. temperature control

If the temperature is too high, it may cause the material to be washed. If the temperature is too low, the reaction will be stagnant. Once the temperature returns to normal, the material will react excessively and even explode. Whether the temperature is too high or too low directly affects the cracking depth of light diesel oil, thus affecting the purity of ethylene and propylene production.

For the ethylene cracking and separation process, such a high degree of automation and continuous production equipment, temperature control is required to achieve automatic temperature measurement, automatic recording, automatic adjustment, automatic interlocking, and important parts should be provided with lower limit temperature and upper limit temperature. Call the police. When the limit temperature is exceeded, the fire should be automatically extinguished and the feed should be cut off. The cracking gas at high temperature may not be cooled due to water stoppage and water pressure, or may be cooled due to malfunction of the gas pressure greater than the water pressure, which may cause the fire to be caused by burning the equipment. In order to ensure production safety, two power sources and water sources should be equipped to ensure smooth water pressure. It is found that the water stop or the air pressure is greater than the water pressure, and it is urgent to vent and stop the treatment. In particular, when the device is opened or stopped, the process operation rules must be strictly implemented to determine the process parameters such as oven heating curve, constant temperature and temperature drop. During the hydrogenation process, it is necessary to closely monitor whether the control of hydrogen and alkyne ratio meets the requirements of the process and prevent the hydrogenation reactor from rapidly heating up; if the interlocking device fails during sudden temperature rise, the hydrogen and materials should be cut off, the heating should be stopped, and the inlet and outlet valves should be closed. And the emergency measures to vent to the torch.

2. Pressure control

In the process of ethylene production, if the pressure is too high, it will cause equipment, pipes to burst or react violently and explode. If the positive pressure production equipment and pipelines form a negative pressure, the air is sucked into the equipment and pipes, and mixed with flammable and explosive substances, there is a danger of fire and explosion. Equipment and pipelines produced under negative pressure may explode when flammable or explosive materials leak out, and fire and explosion accidents may occur. Therefore, accurate measurement of the pressure of various parts of the process system is an important condition to ensure the safe production of ethylene. In order to accurately determine the true pressure of the system, when selecting the pressure gauge, it should be noted that the pressure gauge installed on the pressure vessel should have a maximum range that is compatible with the working pressure of the vessel (1.5-3.0 times); the pressure selected The gauge shall be of sufficient accuracy to be periodically calibrated; the gauge pull tube shall be directly coupled to the body of the pressurized vessel. Continuous, dangerous and large compression and cryogenic and separation processes should automatically adjust the pressure to achieve automatic measurement, automatic recording, automatic adjustment, automatic alarm, automatic switching to ensure safe production. The automatic alarm should be equipped with low voltage, high pressure alarm, dangerous pressure alarm and interlocking.

3. Flow level control

Controlling the flow rate of materials is a dangerous production process in ethylene production. Hydrocarbon gases and liquids in ethylene production generate static electricity. To limit the generation of static electricity, the flow rate of materials in the pipeline should be strictly controlled. Excessive feeding, volume expansion after heating the material can cause equipment or container to burst. The liquid level of the tower and tank container must be strictly monitored. If the liquid level is too low, it is easy to pump equipment. If the liquid level is too high, it is easy to run the material. To ensure safe production, low liquid level and high liquid level should be set on the tower and tank container. Alarm and automatic switching control system for feeding and discharging. In particular, the liquid level of the suction tank of each section of the compressor should be strictly controlled to prevent the high liquid level from causing the instrument chain to malfunction. The gas carries the liquid into the compressor, causing vibration, resulting in damage to the tank body and a large amount of material spilling and causing a major accident.

(4) Safety measures for production equipment

1. Pressure vessel, compressor, etc. should be installed with explosion-proof pressure relief device

When the pressure in the high pressure equipment of the safety valve or the rupture disc and the pressure vessel exceeds 1.10 times of the normal pressure, the safety valve can automatically open the exhaust gas (liquid) to reduce the pressure and prevent the equipment and the pressure vessel from rupturing and exploding. Safety valves should be installed in equipment and vessels with pressures above 9.8X10-: MPa in production, and shut-off valves should not be provided at the outlet of safety valves. The shut-off valve must be opened during production if required by the process.

Bursting discs are a type of safety device and are most commonly used in reactors. When the production is not normal and the pressure rise is not enough to cause an explosion, the damage is first caused, and the pressure is lowered to prevent the container from breaking or exploding.

The safety valve on the flammable and explosive toxic material container should be led to the flare system for burning when it is drained. A flame arrester or water seal should be installed on the pipeline connected to the high temperature equipment or the open flame heating furnace to prevent the fire from expanding when the fire is on fire. It is strictly forbidden to use copper pressure gauges and valve parts on ammonia and acetylene pipelines and equipment. Pressure gauges must be installed vertically on pipes and equipment. A check valve is installed on the pipe produced between different pressures or between the equipment to prevent the gas or liquid from flowing backward. Install a breathing valve on the tank to prevent the tank from being twitched or overpressured. All explosion-proof pressure relief and safety devices or accessories must be visually inspected monthly for periodic calibration to ensure accuracy and safety.

2. Pipelines should be regularly tested and replaced

The ethylene production process has high temperature, high pressure and strong corrosiveness. The long-term production is flushed, the pipe wall is gradually thinner, and it is prone to leakage or breakage accident. Therefore, during the overhaul, not only the equipment should be inspected for flaw detection, but also the inspection of process pipelines and furnace tubes should not be ignored, and problems should be solved in time.

3. Install the necessary ventilation

Forced ventilation of the plant can reduce the accumulation of flammable gases, liquid vapours or combustible dust, making them unable to reach the limits of the explosion. Non-open compression workshops and pump rooms should be provided with good ventilation.

4. Set up safety insurance and monitoring devices

The safety device is a device that can automatically act to eliminate the danger when a dangerous situation occurs in production. For example, the backup power supply can be automatically used when a sudden power failure occurs. Safety monitoring is an important measure to prevent fires. It is easy to produce flammable gas and liquid vapor. A flammable gas alarm should be installed to monitor the concentration of flammable substances in the air at any time to eliminate fire and explosion hazards and ensure production safety.

(5) The corresponding fire extinguishing facilities

According to the characteristics of the device, the corresponding fire extinguishing facilities should be equipped. Such as cooling water system, foam fire extinguishing system, water sprinkler system, steam fire extinguishing system. When a large amount of flammable and explosive substances leaks from the device, in order to avoid explosion in contact with the open flame heating furnace, an automatic detection and alarm of flammable gas and a chain fixed fire extinguishing system may be provided between the open flame zone and the flammable gas leakage zone. The installation of a steam fire extinguishing system has a special effect on the initial fire of high-temperature equipment.

Monel Pipe/Tube

Monel 400,Monel 400 Tube,Monel 400 Pipe

Ningbo Qiyi Precision Metals Co., Ltd. , http://www.qiyi-metal.com

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