Prevention of the hottest fire and explosion

1.2 danger of high temperature operation

high operating temperature in petrochemical production is an important factor causing ignition and explosion of process gas. Because the surface of high-temperature equipment and pipes is easy to cause the combustible materials in contact with it to catch fire; Combustible gases and mixtures under high temperature, once the air is pumped into the system to mix and reach the explosion limit, are very easy to explode in equipment and pipelines; Once the oil or combustible gas whose temperature reaches or exceeds the spontaneous combustion point leaks, it can cause combustion and explosion; High temperature makes the metal material creep inside, changes the metallographic structure, reduces the mechanical strength of the equipment, leads to leakage, and even causes explosion; High temperature enlarges the explosion limit of combustible gas. For example, the lower explosion limit of gas at room temperature is 6.0%, while it decreases to 4% at 400 ℃. For example, the explosion limit of ammonia at room temperature is 15.5% - 27%, and it changes to 14.5% - 29.5% at 100 ℃. As the explosion range is widened, the danger is increased

1.3 danger caused by high-pressure operation

high pressure can widen the explosion limit of combustible gas, especially the upper limit. For example, the upper explosion limit of methane is 15% under normal pressure, and it increases to 45.7% at 12.5mpa, which increases the explosion risk. In addition, electrostatic sparks generated by the friction between the high-pressure air flow and the nozzle can also cause ignition and explosion

2 general principles for preventing combustion and explosion

the basic principles for preventing combustion and explosion are: take measures to prevent combustion and explosion accidents; Once an accident occurs, the scope of the disaster will be limited or reduced, the loss of the accident will be reduced, and it will be evacuated to a safe place in time

the prevention plan or scheme generally includes two aspects:

(1) management of explosive substances

(2) management of ignition sources that constitute explosions

in order to prevent the components of the mixed gas from reaching the explosion range, the production process can take measures to make the components of the mixed gas below the lower explosion limit or above the upper explosion limit; Replace air with inert gas; Measures such as keeping the oxygen concentration below the limit value. At the same time, in order to prevent the discharge and leakage of combustible gas into the air and prevent the air from entering the combustible gas system, a mixed gas danger alarm device, a safety coupling device for cutting off materials, automatic venting and parking should be installed

in order to control the ignition source, we should master the conditions of 9 ignition sources, such as impact friction, open fire, high-temperature surface, adiabatic compression, natural heating, electrical spark, electrostatic spark, thermal radiation, optical radiation, so as to take corresponding countermeasures, fire control and prevention

3 prevention of fire and explosion in petrochemical production

3.1 control or formation of fire-fighting combustion and explosion conditions

3.1.1 the design should comply with the specifications

petrochemical production devices should fully consider the risk of fire and explosion in this industry when designing. First of all, it is necessary to meet the safety technical requirements of fire and explosion prevention, adopt advanced process technology and reliable fire and explosion prevention measures, adopt advanced automatic control and troubleshooting advanced devices, and use no or less flammable and combustible substances, so as to reduce the factors contributing to combustion and explosion and increase the safety factor

3.1.2 operate correctly and strictly control the process index

(1) control the temperature and prevent overheating. Controlling the reaction temperature well is not only the need to stabilize production and ensure product quality, but also necessary for fire and explosion prevention. If the temperature is too high and the heating rate is too fast, the reaction will be violent and the pressure will rise. Rapid temperature rise (fall) will also cause rapid expansion and contraction of equipment and pipelines due to sudden temperature change and local overheating, resulting in equipment damage, material leakage and fire and explosion accidents

(2) control pressure. Increasing the pressure can speed up the reaction, improve the yield and equipment capacity. However, pressurized production also brings many unsafe factors. When the strength exceeds the equipment can bear, it will cause equipment damage or even explosion, and material leakage will also cause secondary explosion or combustion. In addition, pressurized operation also widens the explosion range of combustible gas and increases its risk

(3) prevent misoperation. Petrochemical production units are mostly technology intensive production units. The technical quality and safety awareness of employees are one of the most fundamental reasons that affect the occurrence of various accidents. Therefore, strengthening the post technical training, strengthening the safety education of employees and strengthening the working spirit of employees are the guarantee of safe production

in addition, controlling the feeding speed, feeding proportion and feeding sequence, forbidding excessive storage, and controlling the purity of raw materials are all key process control links that must be paid attention to

3.1.3 strengthening maintenance and ensuring equipment integrity

ensuring maintenance quality and equipment integrity, strengthening safety supervision and detection of pressure vessels, safe and reliable safety devices and safety interlocks are all powerful guarantees to avoid and reduce accidents

3.1.4 strengthen ventilation and exhaust to prevent the accumulation of combustible gases

production posts with explosion risk should make full use of natural ventilation, adopt local or comprehensive mechanism forced ventilation, and discharge the leaked combustible gases in time to prevent the accumulation from causing explosion

3.1.5 adopt automatic control and safety protection devices

in order to effectively prevent overheating and overpressure, technical specification for ultrasonic detection of concrete defects CECS 21:2000, overload, strictly control the oxygen content in the system and strengthen gas monitoring, safety interlocking and automatic control technical measures such as automatic detection and analysis, automatic adjustment, automatic alarm, automatic shutdown, automatic emission, automatic power removal and so on should be adopted, This is an important technical measure to prevent fire and explosion

3.1.6 use inert gas protection

add non combustible inert gases such as nitrogen, carbon dioxide and steam to flammable and explosive equipment, which can dilute the concentration of combustible gases, reduce the oxygen content to a safe value, and destroy its combustion and explosion conditions. SuiXing gas can also be used as a protective gas for transporting flammable liquids

3.2 measures to prevent the spread of fire

it is very important to adopt various measures to prevent the spread of fire to reduce accident losses

in addition, setting fire doors, firewalls, fire curtains, fire lifts and maintaining fire safety distances are all measures to prevent the spread of fire

3.3 explosion proof and pressure relief measures

when the equipment is overpressured, in order to relieve the pressure in time and prevent explosion accidents, explosion-proof leakage facilities must be set up for process devices. The workshop with explosion risk shall have sufficient pressure relief area

3.4 strengthen the control and management of fire sources

the fire sources that petrochemical enterprises can encounter, in addition to the heating furnace fire and anti coupling agent in the production process, which can improve the compatibility between inorganic fillers, inorganic fibers and matrix resin, heat stress and electric spark, as well as maintenance fire, mechanical friction heat, impact spark, etc. These fire sources are often the root causes of the ignition and explosion of inflammables and explosives. Controlling these fire sources and strict fire management are very important for fire prevention and explosion prevention

3.4.1 control of open fire

3.4.1.1 control of heating fire

(1) try to avoid using open fire to heat flammable liquids

(2) the arrangement of open flame heating equipment in the device should be as far away from the process equipment and storage tank area that may leak flammable gas and steam as possible, and should be arranged in the crosswind or upwind direction of the equipment that emits flammable and explosive materials

3.4.1.2 control of fire for maintenance

(1) it is strictly prohibited to carry out hot work in places with inflammable and explosive materials

(2) the fire for maintenance should be strictly controlled, that is, fire ticket, blind plate and chemical analysis

(3) the welding handle wire should be well insulated, and the metal components connected with the production equipment should not be used as the welding ground wire

(4) hot work in flammable and explosive places shall be carried out according to the hot work system, and the "three no hot work" shall be achieved

(5) strengthen the management of motor vehicles driving in flammable and explosive areas

3.4.2 prevention of friction and impact

the two parts of the impact should be made of different metals. For example, if it is easy to change the speed, the operation in the flammable and explosive area should be impacted with a tool made of bronze or a wooden hammer; It is not allowed to wear clothes that can generate static electricity only by wearing nail shoes, and enter flammable and explosive areas; Do not throw or hit metal equipment and pipelines at will; Bearings should be well protected and lubricated

3.4.3 control of other fire sources

(1) inflammable materials should be prevented from contacting high-temperature equipment and pipelines. Inflammables or their discharge outlets should be away from high-temperature surfaces, and heat insulation measures should be taken on high-temperature surfaces

(2) oil rags and oil cotton yarn are prone to spontaneous combustion and cause fire. They should be placed in a safe place or put into metal barrels and transported out in time

(3) smoking is strictly prohibited in the petrochemical production plant

3.5 strengthen the management of flammable and explosive substances

for raw materials, intermediates and finished products of a petrochemical production plant, we must understand and master their physical and chemical properties, so as to recognize the degree of danger. In order to better prevent the occurrence of fire and explosion accidents