Familiar with the analysis and control of the explosion of the oil tank! Typical accident case in the vicinity of the year

Some fire and explosion accidents that have occurred in recent years, although the specific reasons are different, but all reveal the loopholes and hidden dangers in the safety production of relevant units. The seemingly accidental incentives that led to the accident are actually caused by a series of inevitable factors.

The oil storage tank is an important equipment of the oil depot. It stores a large number of oils that are flammable, explosive, volatile and easy to lose. It is difficult to estimate the damage caused by the explosion.

In the past 20 years, the development of oil tanks has become a significant trend. With the increase in oil and gas reserves, the size and number of oil storage tanks have also increased significantly.

Oil tank fires caused by open flames ranked first, mainly due to poor management or weak measures in the use of electrical, welding and oil storage equipment.

For example, the maintenance pipeline does not add a blind plate; when there is oil in the tank, the repair welding nail does not add measures; when the pipeline is welded, the pipeline is not cleaned beforehand, and the pipeline is not blinded; the weeds and combustibles around the tank are not removed. Clean and so on.

Another important reason is to carry and use contraband such as matches, lighters, lights, etc. in the restricted area of ​​the oil depot and the place where oil vapor is easy to accumulate or to smoke in the above-mentioned places.

The so-called electrostatic fire refers to a fire or explosion accident caused by an electrostatic discharge spark that ignites combustible materials such as combustible gases, combustible liquids, and steam.

The essence of static electricity is the presence of residual charge.

When two different objects contact or rub, electrons gain and loss between the objects, under certain conditions, the charge of the object can not be lost and accumulate, which will produce a high static voltage, when two with different charges When objects are separated or contacted, sparks will appear between the objects, and the energy of electrostatic discharge (ESD) electrostatic discharge is related to the nature of the charged body and the form of discharge.

The forms of electrostatic discharge include corona discharge, brush discharge, spark discharge, and the like. Among them, the spark discharge energy is larger and the risk is the greatest.

(1) There are conditions for generating static electricity.

Generally, flammable liquids have large electrical resistance, and static electricity can be generated during collision, transportation, transportation or production due to collision, splashing and wall friction or impact. Especially when there is no conductive particles in the liquid, the inner surface of the conveying pipe is rough, and the liquid flow rate is too fast, a strong friction is generated, thereby generating static electricity.

(2) Static electricity is accumulated and reaches an electrostatic voltage sufficient to cause a spark discharge.

The physical properties of the oil material determine that the electrostatic charge generated therein is difficult to be lost and accumulates in a large amount. The voltage can reach tens of thousands of volts. When the discharge condition is encountered, it is easy to generate a discharge and cause a fire.

(3) There is enough explosive mixture around the static spark.

The evaporation of the oil, the oil mist generated during the splashing, and the good accumulation conditions of the oil storage tank cause the oil to form an explosive mixture of oil and gas in the upper surface of the oil.

(4) The spark energy of the electrostatic discharge reaches the minimum ignition energy of the explosive mixture.

When the spark energy generated by the electrostatic discharge reaches or is greater than the minimum energy (0.2-0.25 mJ) of the ignition of the oil vapor, the combustible gas mixture is ignited, causing a combustion explosion.

Fire and explosion accidents caused by electrostatic discharge (ESD) are common, and electrostatic fires have certain characteristics of suddenness, easy explosion, difficulty in fighting, and easy to cause casualties. Therefore, how to better prevent static electricity has always been An important part of safety management.

Spontaneous combustion is a spontaneous ignition process of a substance, usually caused by a slow redox reaction. That is, a substance undergoes a redox reaction at a normal temperature without heating, and self-heating, which is hindered by heat dissipation, and heat is accumulated. Combustion caused by the point of spontaneous combustion.

Therefore, there are three conditions for spontaneous combustion, namely, redox reaction, heat release, and heat accumulation. The main processes are oxidation, heat accumulation, temperature rise, and ignition.  

In general, there are three main reasons for causing spontaneous combustion of storage tanks:

Electrostatic self-ignition, spontaneous combustion of phosphine, and spontaneous combustion of sulfur.

Electrostatic auto-ignition As described above, in the process of frequent loading and unloading of oil tanks, the oil or moving parts rub against the inner wall, flapping the oil surface, the liquid level fluctuates, the moving parts slosh, and the oil is hydrated and the quality is high. It is easy to generate static electricity, and forms a huge floating electrified body in moving parts and oil tanks. Static electricity discharges through contact points and protruding parts to generate static sparks.

Phosphine spontaneous combustion originates from phosphine in the oil. According to relevant data, the phosphine in the oil exists in the form of PH3 or P2H4.

PH3 is usually present in the gaseous phase of the oil tank in a gaseous form, and its content is extremely low. Its self-ignition point is 100 ° C, and generally there is no possibility of spontaneous combustion. P2H4 is usually present in liquid form in the liquid phase space of the oil tank, which reacts with air. The activation energy is very low, and spontaneous combustion can occur at normal temperature. However, since the polarity of the gasoline is strong, a small amount of P2H4 is dissolved therein, and it is isolated from the air, and combustion does not occur.

Sulphur self-ignition is caused by spontaneous combustion of iron sulfide. Iron sulfide is the main product of sulfur corrosion in petroleum storage tanks. Iron sulfide reacts strongly with heat when it comes into contact with air. If heat accumulation occurs, the temperature will increase and spontaneous combustion will occur.

The sulfur in crude oil is divided into active sulfur and inactive sulfur, and elemental sulfur, hydrogen sulfide and low molecular sulfur yeast are collectively referred to as active sulfur.

The active sulfur has high corrosiveness to the metal, and the corrosion of the sulfur to the equipment can be divided into low temperature wet H2S corrosion, high temperature sulfur corrosion, etc., and the corrosion of the oil storage tank belongs to low temperature wet H2S corrosion.

There are two ways of corrosion in low temperature wet H2S corrosion:

One is that hydrogen sulfide gas is dissolved in the water on the tank wall to form hydrogen sulfuric acid, and the hydrogen sulfuric acid and the tank wall metal iron are electrochemically corroded:

The other is a wet hydrogen sulfide gas in the storage tank, which is electrochemically corroded with the corrosion product of the iron on the inner wall of the storage tank, iron oxide and its hydrate, in the absence of oxygen. The main products of both types of corrosion are ferrous sulfide.

The inner wall of the tank in the gas phase space is particularly corroded, and the inner anticorrosive coating is vulcanized into a gel film, while the inner anticorrosive layer in the liquid phase has no obvious corrosion marks. Because the colloidal membrane has a protective effect on FeS, Therefore, when FeS is oxidized, the heat of oxidation is not easily released in time, which accelerates the self-ignition rate.

In the vicinity of the tank top vent, FeS is in contact with air, rapidly oxidizing, and heat is not easily accumulated. In the lower part of the tank, the closer to the gas phase space of the float, the lower the oxygen content, and some FeS is not completely oxidized to form single crystal sulfur. The single crystal sulfur has a yellow particle shape, a low ignition point, and is doped in a massive, loose structure of iron pyrosulfide, which provides sufficient combustion conditions for the spontaneous combustion of FeS in the pyrosulfide iron.

When the oil tank is in the oil-receiving state, a large amount of air fills the gas phase space of the oil tank, and the FeS originally immersed under the floating plate and hidden in the anti-corrosion film is gradually exposed, and the oxidation occurs first in the weak portion of the gel film, and rapidly Fever and spontaneous combustion, causing single crystal sulfur rubber, rubber seals to burn, and even lead to fire and explosion accidents.

The oil and gas mixture present in the tank area is subject to lightning strikes, even if the tank is grounded, it will cause a fire. The floating roof tank lightning strike is often caused by poor connection of the floating roof and the tank wall or poor sealing performance of the tank.

The so-called human management is to try every means to prevent explosions caused by illegal operations, illegal operations, and illegal command.

It is necessary not only to strengthen the training and education of workers' safety, but also to recognize the danger and seriousness of the explosion of oil storage tanks; it is necessary to further standardize the behavior of employees and strictly follow the operating procedures, especially the operational details, such as wearing anti-static Work clothes, do not wear chemical fiber clothes and rubber shoes to work, and so on.

According to the conditions of combustion and explosion of combustibles, in order to avoid fire and explosion in the storage tank, oxygen or air must be prohibited from entering the storage tank.

For the large floating inner tank, the charging and mixing operation mode can be implemented to make the floating plate float in a small range, and the chance of the ferrous sulfide exposed to the air in the space below the floating plate is reduced; the high liquid level operation is adopted. , reduce the gas phase space of the oil tank, reduce the corrosion range; adopt the method of inert gas replacement (nitrogen protection), which can realize the oxygen-free operation and prevent the formation of explosive mixed gas; when the oil tank is oiled, the injection steam or nitrogen gas is taken. Protection measures, after stopping the injection of steam, should be injected with nitrogen in time to prevent air from entering the tank.

Improve the "one off four injection" process of the atmospheric pressure device to reduce the sulfur content; use the oil residue hydroconversion process to reduce the sulfur content of the atmospheric residue; the oil is effectively dehydrated before the tank is introduced to reduce the water content; A corrosion inhibitor is added at the top to form a protective film on the surface of the steel to act as a corrosion inhibitor, and an antistatic agent is added to the oil to improve the electrical conductivity of the oil.

Use corrosion-resistant steel where it is susceptible to corrosion;

Spraying corrosion-resistant metal or plating corrosion-resistant materials on the inner surface of corrosive equipment;

Use antistatic coatings on the inner wall of the storage tank in strict accordance with the standard to eliminate the hazards caused by electrostatic discharge or various production obstacles caused by electrostatic attraction;

The top spray technology is adopted to effectively reduce the temperature of the oil tank, delay the corrosion of sulfur, and dissipate the heat released by the oxidation of iron sulfide in time; strengthen the electrostatic leakage by electrostatic grounding, bridging, and setting an electrostatic mitigator to prevent static electricity from accumulating; Effectively avoid the hazard of lightning;

Strengthen tank sealing inspection and maintenance; install flammable gas alarm devices, fire extinguishing and cooling facilities for large oil tanks.

Take the bottom oil to reduce the entry of air, the generation of static electricity and the generation of oil mist; increase the diameter of the oil injection pipe to control the flow rate to reduce the generation of static electricity; detect and sample in the detection well, and avoid static electricity by standing for a few minutes The use of pickling, high pH solvent, multi-stage oxidant, passivation and other methods to remove ferrous sulfide deposits; regular clearing tanks to eliminate the accumulation of water in the tank; strengthen the daily equipment maintenance, The safety inspection and inspection work in the tank area eliminated the accident in the bud.

(1) Establish a suitable corrosion monitoring network to control and prevent sulfur corrosion failure. Through on-line monitoring and off-line monitoring through reasonable selection and distribution, long-period coupons combined with instantaneous corrosion rate measurement can fully grasp the corrosion situation, so as to take timely measures to prevent problems before they occur.

(2) Detect the environment with a flammable gas alarm to control the concentration of combustible gas, flammable liquid vapor and dust below the limit of the explosion.

(3) Automatic fire alarm and automatic fire extinguishing system are adopted for fireproof design of flammable and explosive working places. The detectors for automatic alarm shall be of explosion-proof type, and the fire extinguishing agent for automatic fire extinguishing shall be CO2 gas fire extinguishing agent.

This article mainly specifies the requirements for the management of the use of oil and gas storage tanks. The storage medium, storage temperature, pressure and liquid level of oil and gas storage tanks must conform to the design process conditions and process control indicators. If these indicators exceed the control range, they will bring safety risks such as leakage and fire.  

In the design stage, the tank is designed according to a certain storage medium. The factors considered in the design are limited to the physical and chemical properties of the medium and the storage and transportation process requirements. In order to change the storage medium, the design conditions of the established tank must be considered. Whether the storage requirements of the medium are met and the tank is safely operated. Changing storage media or storage tanks at will may pose a safety hazard and cause an accident.

On March 31, 1984, an explosion occurred in the oil tank of the petrochemical plant in Baoding City, Hebei Province, causing 16 deaths and 6 serious injuries. The main cause of the accident was the illegal input of residual oil (formerly boiler fuel tank), and the oil temperature was too high. A large amount of gas is mixed with the air in the tank to form an explosive gas, which is triggered by a spark.

This article mainly stipulates the management requirements for manual water cutting, canning and loading and unloading operations in the storage tank area. Manual water cutting refers to manually opening the water cutting valve to interrupt the water deposited on the bottom of the oil and gas storage tank; cutting the tank means switching the incoming and outgoing materials from one storage tank to another; loading and unloading vehicles means loading the materials in the storage tank The vehicle transports material from the transport vehicle to the storage tank. The operation steps such as water cutting, canning, loading and unloading vehicles shall strictly abide by the safety operation standards, procedures and systems, and shall be carried out under the supervision of the guardian on-site and under full supervision. If the guardian is not in place, it will easily cause oil and gas leakage and cause an accident.

On October 22, 1988, a liquefied gas explosion occurred in the Xiaoliangshan ball tank area of ​​the Shanghai Gaoqiao Petrochemical Company refinery, causing 26 deaths and 15 burns. The main cause of the accident was that the operator opened the valve for the liquefied balloon. When water is used, it is not operated according to the operating procedures, and it is not monitored at the site, so that the liquefied gas is discharged together with the water, and the disposal is not timely, and the liquefied gas is exposed to an open flame. On July 16, 2015, Shandong Shida Technology Petrochemical Co., Ltd. liquefied balloon tank was on fire and explosion accident. When the water cut operation was carried out in the tank area, the operator left the scene, the liquefied gas leaked, and the disposal was not timely.

This article mainly specifies the safe operation requirements of safety valves and pressure relief systems. Safety valve shut-off valve refers to the shut-off valve installed before and after it to facilitate the verification or replacement of the safety valve. The pressure relief discharge system refers to a system that can discharge the pressure of the tank quickly, usually referred to as a flare system or a dedicated discharge system. The safety valve shut-off valve is closed or the pressure relief system plus the blind plate will make the pressure of the storage tank in the event of overpressure or emergency, and the storage tank may cause a serious accident such as explosion or fire due to overpressure.

On July 16, 2015, Shandong Shida Technology Petrochemical Co., Ltd. ignited a liquefied balloon tank, causing two firefighters to be slightly injured, seven fire engines to be destroyed, and some spherical tanks and surrounding facilities and structures to be damaged to varying degrees. The direct cause of the accident was that during the tanking operation, after the water in the No. 6 tank was completely cut out, the liquefied petroleum gas leaked and spread from the water cut pipe, and the ignition source burned, causing the liquefied hydrocarbon tank area to catch fire; the spherical tank was closed due to the safety valve. The pressure relief system adds a blind plate, causing an explosion and expanding the consequences of the accident.

This article specifies the management requirements for alarm and interlocking systems for key parameters such as temperature, pressure, liquid level, flammable and toxic gases in the oil and gas tank area. Oil and gas storage tanks shall be equipped with liquid level gauges, thermometers, pressure gauges, flammable (toxic) gas alarms, high liquid level alarms and high liquid level automatic interlocks to cut off feeding measures according to the standards and specifications. The alarm signal shall be sent to The operator is in the control room or operation room, and the alarm should set the sound and light alarm to detect the abnormality and deal with it in time. Therefore, it is necessary to ensure that the alarm and interlock system are in good condition and in use.

On December 11, 2005, a fire and explosion accident occurred in the Bangsfield oil depot in the United Kingdom. More than 20 large oil storage tanks were burned and 43 people were injured. The direct economic loss was 250 million pounds. The main cause of the accident was the failure of the automatic measurement system of the storage tank. The electronic monitors of some tanks and piping systems and related alarm equipment are in an abnormal working state.

This article mainly stipulates the requirements for the management of hot fires and restricted space operations in oil and gas tanks. Before the hot work, it is necessary to analyze and detect the content of flammable gas around the fire point in the oil and gas tank area. Before entering the restricted space, the flammable, toxic gas and oxygen content in the tank should be analyzed.

The hot fire and the entry into confined space have always been the frequent incidents. The oil and gas tanks store a lot of materials. In the event of an accident, the consequences are often serious. The management must be strictly examined and approved, and the dangerous and harmful factors that may exist at the job site and during the operation process are identified. The corresponding safety measures shall be formulated and implemented, and relevant personnel shall sign and confirm according to the authority. During the operation, guardians shall be on-site for monitoring. The specific management procedures shall comply with the requirements of the “Special Operation Safety Regulations for Chemical Production Units” (GB30871).

On June 2, 2010, an explosion and fire accident occurred in the petrochemical tank of Dalian Petrochemical of PetroChina, causing four deaths. The direct cause of the accident was that illegally subcontracted contractor operators illegally carried out gas cutting in the tank of the Sanbenzene tank area. In the fire operation, the cutting flame ignites the inflammable and explosive gas such as toluene leaking, and tempering into the tank causes the tank to explode.

On October 27, 2004, an oil tank explosion accident occurred in PetroChina Daqing Petrochemical, causing 7 deaths. The main cause of the accident was the leakage of explosive mixed gas in the tank from the weld crack, and the open flame or splash melting of the gas cutting pipeline operation. The slag caused an explosion.

This article mainly specifies the requirements for the liquid level of the inner floating roof tank. The bottom of the floating plate means that the floating plate falls on the support leg due to the low liquid level of the storage tank. During normal operation, the float plate will form a gas phase space between the floating plate and the oil surface. When the material flow rate is too fast, the static electricity of the material line pipe is easy to accumulate, which may easily cause a fire explosion accident.

On August 29, 2011, PetroChina Dalian Petrochemical diesel tanks exploded and fire accidents. The main cause of the accident was the low liquid level caused by the oil supply from the accident storage tanks, and the formation of gas phase space between the floating plate and the diesel oil surface, causing air to enter; The operation of the upstream device fluctuates, and the light component content of the diesel fuel entering the accident storage tank increases, forming an explosiveness under the floating disk.

Mixed gas; plus the flow rate of the oil is too fast, a large amount of static electricity can not be exported in time to generate a discharge, causing an explosion and fire.

This article stipulates the safety management requirements for the use of various additives and additives in the process of oil and gas processing and blending. Before adding and using, it is necessary to understand the physicochemical properties of additives and additives, and conduct risk assessment, formulate corresponding control measures and emergency plans, and use a special dosing system in the operation process to strictly implement the operating procedures.

On July 16, 2010, Dalian PetroChina International Storage and Transportation Co., Ltd. suffered an explosion and fire accident in the oil pipeline of the tank area. The main cause of the accident was the continued desulfurization of crude oil containing strong oxidants into the oil pipeline when the crude oil tanker had stopped unloading operations. The agent reacts violently in the oil pipeline, causing an explosion and causing a fire.

This article mainly specifies the requirements for the use of explosion-proof equipment in oil and gas tanks. The medium stored in the oil and gas tank area is generally characterized by inflammable and explosive. The use of non-explosion-proof tools, electrical facilities, communication equipment, etc. in the oil and gas tank area has serious safety hazards and is prone to accidents.

On June 29, 2010, a deflagration accident occurred in the crude oil storage tank of PetroChina Liaoyang Petrochemical, causing five deaths and five injuries. The main cause of the accident was that the hydrocarbon combustibles in the crude oil tank reached the explosion limit during the tank operation. An electric spark generated by a non-explosion-proof general lighting lamp that enters a crude oil storage tank, causing a deflagration accident.

This article mainly stipulates the training requirements for post operators and the management requirements of contractors and outsiders and motor vehicles. Operators in the oil and gas tank area must be qualified for training and have the ability to work. Contractors entering the tank area have the corresponding qualifications to ensure the safety of the operation. The free entry of outsiders and motor vehicles into the tank area will bring many uncontrollable safety risks.

On October 21, 1993, Sinopec Jinling Petrochemical Refinery suffered a tank explosion accident, causing two deaths. The main cause of the accident was that the operator violated the operating procedures, causing gasoline leakage, forming an explosive mixture in the air, and encountering contractor driving. The hand-held tractor exhaust pipe exhausts Mars and a fire explosion occurs.

This article mainly specifies the management requirements for equipment and facilities in oil and gas tanks. Tanks, pipeline fittings, safety accessories, lightning protection, anti-static, fire emergency and other equipment and facilities in the oil and gas tank area should be regularly maintained and guaranteed to operate in good condition.

On January 7, 2010, CNPC Lanzhou Petrochemical carbon four-ball tank exploded and fire accident, causing 6 deaths and 6 injuries. The main cause of the accident was the failure of the elbow of the cracked carbon four-ball tank outlet pipeline, material leakage, and leaking cracked carbon. Fourth, the explosion limit is reached, and a space explosion occurs in the ignition source, which causes leakage, fire and explosion of the surrounding storage tank.