Analysis method of damage probability distribution of most unfavorable area of lightning-induced explosion of floating roof tank

Abstract

The present application relates to the field of chemical safety technology, especially to a lightning-induced floating roof tank explosion most unfavorable area damage probability distribution analysis method. The present application studies the characteristics of floating roof tank, lightning-induced explosion process and explosion probability, from the key events in the process of floating roof tank explosion induced by lightning, the probability of lightning-induced floating roof tank explosion is obtained. The present application also studies the area damage probability distribution and the most unfavorable situation of floating roof tank explosion, based on the tank explosion damage evolution theory, the tank explosion damage evolution model and the area damage probability distribution are obtained, the lightning-induced tank explosion probability is taken as the detonation probability of the detonation tank, the tank explosion damage evolution process is established, the area damage probability distribution considering the lightning-induced tank explosion is obtained, the necessity of lightning protection of the detonation tank is determined by integrating the area damage probability distribution, the importance ranking of the tank lightning protection and the most unfavorable area damage probability distribution are obtained.

Description

Technical Field

[0001] This invention relates to the field of chemical safety technology, and in particular to a method for analyzing the probability distribution of damage in the most unfavorable area of ​​a floating roof tank explosion induced by lightning strike. Background Technology

[0002] Tank explosions in chemical industrial parks are a very serious problem, posing a significant threat to human health and the environment. Chemical industrial parks integrate numerous chemical plants and related facilities. These plants typically store large quantities of hazardous materials, and the tanks are used to store various chemical liquids. If an explosion occurs, it can cause immense damage to surrounding personnel and the environment. Tank explosions in chemical industrial parks can be divided into two parts: the explosion of the tank itself, and the explosion of one tank leading to the explosion of other surrounding tanks. The former is the starting point of the explosion process and is primarily controlled as a hazard source; the latter is the propagation process of the explosion, requiring consideration of the evolution of the explosion between tanks and primarily controlled as a propagation pathway.

[0003] There are many causes of storage tank explosions, which can be categorized into natural disasters, human error, and spontaneous generation. Natural disasters include lightning strikes, floods, earthquakes, and tornadoes. Human error includes violations of safety regulations, unauthorized welding or other open-flame operations, or smoking in no-smoking areas. Spontaneous generation occurs when the substances inside the storage tank mix with air to reach their explosive limits, forming an explosive mixture that explodes upon contact with open flames or high temperatures.

[0004] The explosion processes of different types of storage tanks also differ. For example, fixed-roof tanks, internal floating-roof tanks, and external floating-roof tanks all have different explosion processes. This is also related to the physicochemical properties of the substances stored inside the tank. Furthermore, in chemical industrial parks, multiple storage tanks exist in an open space in some distribution pattern. When one tank explodes, the shock wave and heat radiation can severely affect surrounding tanks, reducing their structural strength, causing safety facilities to fail, and altering the stored substances. This can easily lead to further explosions in nearby tanks, creating a chain reaction of explosions. Especially when a tank explosion occurs suddenly, it is difficult to take effective measures to prevent the spread of the explosion's effects in an emergency, easily leading to a chain reaction of tank explosions in the chemical industrial park. Lightning strikes are highly likely to cause this phenomenon.

[0005] Research on tank explosions, lightning strikes, and chain reactions of tank explosions is gradually increasing. These studies include: Liu Xuejun et al.'s research on lightning risk prevention and control for external floating roof tanks; Liu Xiangke et al.'s research on direct lightning overvoltage tests on external floating roof oil tanks based on artificial lightning induction technology; Fu Bangjie's proposal on the causes and prevention strategies for lightning-induced fires in oil depots; Yu Qingqing's evaluation of the vulnerability of storage tanks in stations to lightning-induced domino effects; Liu Xuan's research on lightning early warning and protection technologies for crude oil tank areas; Zheng Xiaoming's proposal on key points and prevention strategies for fire safety in petrochemical enterprises; Wang Zhibin et al.'s discussion on lightning fire prevention technologies for large floating roof tanks; Zhang Yingjie et al.'s research on lightning protection design for aluminum dome tanks based on the rolling ball method; Deng Xin's discussion on lightning protection technology for large external floating roof tanks; Xu Wei et al.'s research on lightning protection measures for urban gas stations and facilities; Li Wenkai's research on lightning fire analysis and safety evaluation of floating roof tanks; and Sun Cuilin et al.'s research on the differences in lightning protection standards for large oil storage tanks at home and abroad. These findings involved field analysis, simulation experiments, and theoretical derivation for different scenarios, resulting in effective theories, technologies, and methods for predicting, preventing, and managing lightning strikes on storage tanks in various situations.

[0006] However, these studies mainly focus on tank structure, auxiliary equipment, stored materials, and statistical analysis. In reality, while focusing on single tank explosions caused by lightning strikes, it is even more important to study the chain reaction explosions resulting from multiple tanks being struck by lightning in chemical industrial parks. Research in this area remains lacking.

[0007] Therefore, how to provide an analytical method for the evolution of a lightning-struck floating roof tank explosion considering multiple tanks has become an urgent technical problem to be solved. Summary of the Invention

[0008] The purpose of this invention is to provide a method for analyzing the damage probability distribution of the most unfavorable area in a lightning-induced explosion of a floating roof tank, in order to solve the problem that the existing technology only considers the lightning explosion of a single tank and does not consider the evolution process of multiple tanks being struck by lightning.

[0009] According to a first aspect of the present invention, a method for calculating the probability of a lightning-induced explosion of a floating roof tank is provided, comprising the following steps:

[0010] Assume the storage tank is a vertical cylinder with an average attraction area A. C The calculation is shown in equation (6):

[0011]

[0012] In the formula: D L H represents the outer diameter of the storage tank, in meters ( / m). L The height of the storage tank is given in meters (m).

[0013] Ground lightning density n L / km -2 ·a -1This reflects the frequency and severity of lightning events; it is measured by the ground lightning density n. L and average attraction area A C The product of represents the probability P1 of lightning striking the storage tank, as shown in equation (7):

[0014] P1 = n L A c (7)

[0015] The probability P of lightning breaking through the outer shell of the storage tank C As shown in equation (8):

[0016]

[0017] Considering the probability of oil leakage, the probability P2 of lightning breakdown leading to oil leakage is obtained, as shown in equation (9):

[0018]

[0019] Where: H N The liquid level in the tank is expressed in meters (t). L The tank wall thickness is expressed in meters (m).

[0020] The failure probability of the automatic fire extinguishing system is 1%, i.e., P3 = 0.01;

[0021] P4 represents the conditional probability of lightning striking the floating roof of the storage tank, as shown in equation (10):

[0022]

[0023] Where: H B The height of the lightning rod is expressed in meters (m).

[0024] The probability of the sealing ring igniting, P5, is equal to the probability of ignition, P. f The probability P of petroleum vapor concentration reaching the explosion limit lim The product of is shown in equation (11):

[0025]

[0026] Where: P for non-metallic storage tanks lim Take 0.04, metal storage tank P lim Take 0.19;

[0027] Where, k1 = 31, k2 = 2.6; n s The number of conductive plates is determined by installing one plate every 1.8 to 3 meters along the perimeter of the tank wall.

[0028] The probability of a lightning strike triggering an explosion in a floating roof tank is P. F=P1P3P4P5+P1P2P3(1-P4); The basic parameters of the floating roof tank are expressed as shown in equation (12):

[0029]

[0030] Finally, the probability of lightning-induced explosion of floating roof tanks is calculated using equation (12).

[0031] According to a second aspect of the present invention, a method for analyzing the damage probability distribution of the most unfavorable area in a lightning-induced floating roof tank explosion is provided, comprising the following steps:

[0032] When there are N storage tanks in a chemical industrial park, consider the probability distribution of regional damage induced by lightning strikes. Equation (13) is obtained;

[0033]

[0034] Equation (13) can determine the regional damage probability after the evolution of damage from a storage tank explosion caused by lightning strike at all locations in a chemical industrial park; P F The probability of a lightning-induced floating roof tank explosion is obtained according to the method described in claim 1.

[0035] Consider all storage tanks O = {o1,...,o} in the chemical industrial park. N By taking each lightning-induced explosion as an initiating tank, the explosion evolution process and regional damage probability distribution of all tanks in the park that are lightning-induced explosion tanks can be obtained.

[0036] The risk probability distribution within the chemical industrial park is determined by integrating the risk distribution, as shown in equation (14):

[0037]

[0038] Equation (14) means the detonation tank. n The sum of damage probabilities at all node locations within the area; for all storage tanks... The calculation will yield the result. The numerical ranking shows that the larger the value, the greater the necessity for lightning protection of the corresponding explosion-inducing storage tank. The maximum value corresponds to the most unfavorable situation of lightning-induced explosion of floating roof storage tanks in chemical industrial parks.

[0039] Furthermore, the analysis method for the damage probability distribution of the most unfavorable area in a lightning-induced floating roof tank explosion also includes the following steps:

[0040] Based on the study of the shock wave, the functional relationship between the lateral overpressure ΔP and the atmospheric pressure P0 of a TNT explosion on flat ground is shown in equation (1):

[0041]

[0042] Where: ΔP is the peak explosion overpressure at point r, Pa; P0 is the ambient pressure, Pa; α is the vapor cloud equivalent coefficient, 0.02%-14.9%, taken as 4%; W f Q represents the total mass of fuel in the vapor cloud, in kg; f Q is the heat of combustion of a combustible material, expressed in kJ / kg. TNT The heat of explosion of the combustible material is taken as 4120-4690 kJ / kg; r is the distance between the measuring point and the explosion source, in meters.

[0043] Let Z X×Y The area designated as the chemical industrial park is abbreviated as Z, where X is the wide boundary (m); x∈{0,1,...,X} are grid coordinates; Y is the high boundary (m); y∈{0,1,...,Y} are grid coordinates; and O is the tank set, O={o1,...,o N}, where N is the number of storage tanks, n∈[1,N], o n Let n be the nth storage tank, with coordinates (x, y, y). n ,y n ); any position in Z and o n The distance is shown in equation (2); replacing r in equation (1), then the storage tank o n The overpressure of the explosion in region Z is As shown in equation (3):

[0044]

[0045]

[0046] Let o n The probability of damage caused by the explosion is An atmospheric pressure vessel fails when the pressure exceeds 22 kPa; L = 1 represents atmospheric pressure. A high pressure vessel fails when the pressure exceeds 17 kPa; L = 2 represents high pressure. Therefore... This can be further specified as equation (4);

[0047]

[0048] The probability distribution of damage from tank explosion is as follows It is an X×Y matrix, with unit values ​​of so For all locations The N storage tanks constitute the set of probability distributions of storage tank explosion damage.

[0049] Let o n To detonate the storage tank, o n ∈O; other storage tanks o i ∈O, i≠n; on The maximum probability of damage to the remaining storage tanks from the explosion is o n Explosion pair (x i ,y i Storage tank at location o i The probability of damage caused; at this time o i Let O = O / o be the storage tank most likely to continue exploding. n This means removing the o from O. n , express Objects added in sequence n ;

[0050] The model for the evolution of damage from a storage tank explosion can be described as follows: First, let's assume o... n To detonate the storage tank, O = O / o i ,n=i; the second time at o n The probability of damage to other storage tanks is affected during the traversal. O = O / o i n = i; intermediate processes omitted; the (N-2)th time at o n The impact on determining the probability of damage to the last two storage tanks. O = O / o i n = i; N-1th time: final determination O = φ, stop analysis;

[0051] At this time o n The set of tank explosion sequences corresponding to the maximum probability of damage to the detonating tank, Q = [100%, Q1, Q2, ..., Q...]. N-1 ] represents the corresponding damage probability;

[0052] The above has been obtained Q = [100%, Q1, ..., Q] N-1 ]and o n The probability distribution of regional damage obtained from the most unfavorable explosion evolution process is shown in equation (5):

[0053]

[0054] Based on Equation (5), the damage probability of all locations in the chemical industrial park is represented by a matrix, which is the regional damage probability distribution of the tank explosion; Equation (13) is obtained by combining Equation (5) and Equation (12).

[0055] This invention utilizes the technical solution of the present invention to study the characteristics of floating roof tanks, the lightning-induced explosion process, and the explosion probability. The study concludes that external floating roof tanks have significant advantages and are widely used in chemical industrial parks for storage. However, due to the complex structure of external floating roof tanks, they are highly susceptible to lightning-induced explosions. Based on key events in the process of a floating roof tank exploding after being struck by lightning, the probability of lightning striking the tank, the probability of lightning breakdown leading to leakage, the probability of automatic fire suppression system failure, the probability of lightning striking the external floating roof, and the probability of the sealing ring igniting were calculated. Ultimately, the probability of a lightning-induced floating roof tank explosion was obtained. This invention also studies the regional damage probability distribution and the worst-case scenario of a floating roof tank explosion. Based on the tank explosion damage evolution theory, a tank explosion damage evolution model and regional damage probability distribution were obtained. The probability of a lightning-induced tank explosion was used as the initiation probability of the tank to establish the tank explosion damage evolution process. The probability distribution of damage in the area considering lightning-induced tank explosions was obtained. By integrating it, the necessity of lightning protection for the tank that was about to explode can be determined, and the importance ranking of the tank's lightning protection and the probability distribution of damage in the most unfavorable area can be obtained.

[0056] Based on the implementation methods provided in the above aspects, this application can be further combined to provide more implementation methods.

[0057] It should be noted that letters in this invention, unless otherwise specified, are intermediate variables in the calculation process or have meanings known to those skilled in the art. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0059] Figure 1 The probability distribution of tank explosion damage for storage tank O1 is shown.

[0060] Figure 2 The probability distribution of tank explosion damage for storage tank O2 is shown.

[0061] Figure 3 The probability distribution of tank explosion damage for storage tank O3 is shown.

[0062] Figure 4 The probability distribution of tank explosion damage for storage tank O4 is shown.

[0063] Figure 5 The diagram shows the probability distribution of area damage when storage tank O1 is the initiating tank induced by a lightning strike;

[0064] Figure 6 The diagram shows the probability distribution of area damage when storage tank O2 is the initiating tank induced by a lightning strike;

[0065] Figure 7 The diagram shows the probability distribution of area damage when storage tank O3 is the initiating tank induced by a lightning strike;

[0066] Figure 8 The diagram shows the probability distribution of regional damage when storage tank O4 is the initiating tank induced by a lightning strike. Detailed Implementation

[0067] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0068] This invention provides an analytical method for the evolution of a lightning-struck floating roof tank explosion and the probability distribution of damage in the most unfavorable area.

[0069] With the increasing number of floating roof tanks in chemical industrial parks, which are increasingly threatened by lightning strikes, this invention establishes a method for calculating the evolution of lightning-induced explosions of floating roof tanks in chemical industrial parks and the probability distribution of damage in the most unfavorable area. First, the theory, analytical methods, and mathematical models of tank explosion damage evolution are introduced. Second, the characteristics of external floating roof tanks, the lightning-induced explosion process, and the explosion probability are studied. Finally, a method for calculating the regional damage probability distribution is constructed, and the damage probability distribution in the most unfavorable area is determined. Research shows that the probability of lightning-induced tank explosions can be used as the initiation probability of the initiating tank to establish the tank explosion damage evolution process; it can obtain the regional damage probability distribution of all tanks acting as initiating tanks, the ranking of the necessity of lightning protection for tanks, and the damage probability distribution in the most unfavorable area. An example illustrates the analytical process, yields ideal calculation results, and discusses the value of the method and future research directions. This research can provide an analytical method for understanding the importance of lightning and explosion protection for floating roof tanks in chemical industrial parks.

[0070] To address the aforementioned issues, this invention, based on the theory of tank explosion damage evolution, uses multiple external floating roof tanks in a chemical industrial park as examples to calculate the probability of lightning-induced explosions of these tanks; analyze the tank explosion damage evolution process; and calculate the damage probability distribution in the explosion area. The regional damage probability distribution after each tank, acting as the initiating tank, undergoes tank explosion damage evolution is analyzed. Finally, the importance of lightning protection for each tank is ranked, providing an analytical method for lightning protection of tanks in chemical industrial parks.

[0071] The following is an introduction to the theory of damage evolution in storage tank explosions:

[0072] The evolution of damage from tank explosions requires consideration not only of the stored materials, geometry, and structural characteristics of each tank, but also of the damage caused by the interactions between tanks due to the explosion. Since multiple tanks exist within a chemical industrial park, the explosion of these tanks will damage other tanks throughout the park. In other words, the damage evolution process of a tank explosion is a superposition of the effects of explosions on other tanks. To study the evolution of tank explosion damage, relevant concepts and methods include: tank explosion damage probability, tank explosion damage probability distribution, tank explosion damage evolution process, and regional damage probability distribution. Since these are not the focus of this invention, they are only briefly introduced here.

[0073] The following is an introduction to the probability of damage from a storage tank explosion:

[0074] The explosion effect mainly exists in the form of thermal radiation and shock wave. Considering the energy attenuation with distance, the impact of shock wave on other storage tanks is much greater than that of thermal radiation. Therefore, the explosion process of storage tanks is studied based on shock wave. The functional relationship between the lateral overpressure ΔP and the atmospheric pressure P0 of TNT explosion on flat ground is shown in Equation (1).

[0075]

[0076] Where: ΔP is the peak explosion overpressure at point r, Pa; P0 is the ambient pressure, Pa; α is the vapor cloud equivalent coefficient, 0.02%-14.9%, taken as 4%; W f Q represents the total mass of fuel in the vapor cloud, in kg; f Q is the heat of combustion of a combustible material, expressed in kJ / kg. TNT The heat of explosion of the combustible material is taken as 4120-4690 kJ / kg; r is the distance between the measuring point and the explosion source, in meters.

[0077] Let Z X×Y (Hereinafter referred to as Z) is the chemical industrial park area, where X is the wide boundary, / m; x∈{0,1,...,X} are grid coordinates; Y is the high boundary, / m; y∈{0,1,...,Y} are grid coordinates. O is the tank set, O={o1,...,o N}, where N is the number of storage tanks, n∈[1,N], o n Let n be the nth storage tank, with coordinates (x, y, y). n ,y n Any position in Z and o n The distance is shown in equation (2); replacing r in equation (1), then the storage tank o n The overpressure of the explosion in region Z is As shown in equation (3).

[0078]

[0079]

[0080] Let o n The probability of damage caused by the explosion is An atmospheric pressure vessel fails when the pressure exceeds 22 kPa (L = 1); a high pressure vessel fails when the pressure exceeds 17 kPa (L = 2). Therefore... It can be specified as equation (4).

[0081]

[0082] The following is an introduction to the probability distribution of damage from storage tank explosions:

[0083] The probability distribution of damage from tank explosion is as follows It is an X×Y matrix, with unit values ​​of so For all locations The N storage tanks constitute the set of probability distributions of storage tank explosion damage.

[0084] The following is an introduction to the damage evolution model of a storage tank explosion:

[0085] Let o n To detonate the storage tank, o n ∈O; other storage tanks o i ∈O(i≠n). o n The maximum probability of damage to the remaining storage tanks from the explosion is o n Explosion pair (x i ,y i Storage tank at location o i The probability of causing damage. At this point, o i Let O = O / o be the storage tank most likely to continue exploding. n This means removing the o from O. n , express Objects added in sequence n .

[0086] The model for the evolution of damage from a storage tank explosion can be described as follows: First, let's assume o... n To detonate the storage tank, O = O / o i ,n=i; the second time at o n The probability of damage to other storage tanks is affected during the traversal. O = O / o i n = i; intermediate processes omitted; the (N-2)th time at o n The impact on determining the probability of damage to the last two storage tanks. O = O / o i n = i; N-1th time: final determination O = φ, stop analysis.

[0087] At this time o n The set of tank explosion sequences corresponding to the maximum probability of damage to the detonating tank, Q = [100%, Q1, Q2, ..., Q...]. N-1 ] represents the corresponding damage probability.

[0088] The following is an introduction to the probability distribution of regional damage:

[0089] The above has been obtained Q = [100%, Q1, ..., Q] N-1 ]and o n The probability distribution of regional damage obtained from the most unfavorable explosion evolution process is shown in Equation (5).

[0090]

[0091] Based on Equation (5), the damage probability of all locations in the chemical industrial park is traversed, and the area damage probability distribution of the tank explosion is represented in matrix form.

[0092] The following section introduces the characteristics of floating roof tanks and how lightning strikes can induce explosions:

[0093] Floating roof tanks are divided into external floating roof tanks and internal floating roof tanks. External floating roof tanks have a floating roof that floats on the liquid surface, rising and falling with the liquid level; external floating roof tanks reduce oil loss by approximately 80% compared to fixed-roof tanks. Internal floating roof tanks have a roof, and their disadvantages compared to domed roof tanks include higher steel plate consumption and more demanding construction requirements; compared to external floating roof tanks, they are less convenient to maintain and less suitable for large-scale production. Therefore, this invention uses external floating roof tanks as an example for research; unless otherwise specified, "floating roof tank" in the following text refers to external floating roof tanks.

[0094] The characteristics of floating roof tanks are described below:

[0095] In general, external floating roof tanks offer advantages such as reduced evaporation losses, good stability, excellent insulation, reduced environmental pollution, ease of maintenance, high safety, and applicability to various liquid storage applications. They are widely used in large-scale petrochemical, chemical, and oilfield industries, primarily for storing liquefied petroleum products and chemicals such as liquefied gas, liquid oxygen, liquid ammonia, ethylene, benzene, gasoline, and diesel. They are also commonly used in the aviation and pharmaceutical industries, as well as for storing and transporting volatile organic compounds such as petroleum, methanol, and hydrocarbons. They are a primary storage facility and equipment in chemical industrial parks.

[0096] The following describes the process by which lightning strikes trigger explosions in floating roof storage tanks:

[0097] External floating roof tanks are vulnerable to lightning strikes, primarily because they are located in the open environment of chemical industrial parks. Cases of lightning strikes on external floating roof tanks are not uncommon worldwide.

[0098] Lightning protection measures for external floating roof tanks generally include grounding, installing lightning rods, and installing conductive plates. The tank top of an external floating roof tank floats with the rise and fall of the liquid level. The air gaps inside the tank are extremely small, preventing the formation of explosive mixtures, and the floating roof and tank wall are sealed, thus ensuring high safety. The floating metal tank top is connected to the metal tank body and grounded through the tank body; its grounding resistance should not exceed 10Ω. However, if lightning protection measures are inadequate, external floating roof tanks can still be struck by lightning. For example, problems with the discharge of the encased conductive plates can lead to a flash explosion if the concentration of flammable gas in the secondary sealed internal cavity reaches the explosive limit. Poor bridging of the floating roof ladder and excessive transition resistance can also cause lightning strikes. Once an external floating roof tank is struck by lightning, it may cause major safety accidents such as fires and explosions. Therefore, lightning protection measures for external floating roof tanks should be taken seriously and regularly inspected and maintained. Especially in chemical industrial parks with multiple tanks, it is necessary not only to ensure the lightning protection safety of each tank but also to study the impact of lightning-induced tank explosions on surrounding tanks to avoid chain reactions caused by lightning-induced tank explosions.

[0099] The following section introduces the calculation of the probability of a floating roof tank explosion induced by lightning strikes:

[0100] Related technologies describe the process by which a floating roof tank explodes after being struck by lightning, and provide an event tree analysis diagram. The main factors initiating a lightning strike-induced tank explosion include: whether the lightning strike hits the tank, whether it hits the floating roof, the sealing ring igniting, the ring breaking down and causing leakage, and the failure of the automatic fire suppression system. The evolutionary process is not discussed in detail here; only the probability of these key events is given.

[0101] 1) The probability P1 of lightning striking the storage tank.

[0102] The probability of lightning attraction was calculated. Based on randomness, simulations were performed using the Monte Carlo method. The average attraction distance of buildings with regular shapes was calculated, thus yielding the lightning capture area. Storage tanks in typical chemical industrial parks are vertical cylinders, and their average attraction area A is... C The calculation is shown in equation (6).

[0103]

[0104] In the formula: D L H represents the outer diameter of the storage tank, in meters ( / m). L The height of the storage tank is given in meters (m).

[0105] Ground lightning density n L / km -2 ·a -1 This reflects the frequency and severity of lightning events. The ground lightning density n... L and average attraction area A C The product of represents the probability P1 of lightning striking the storage tank, as shown in equation (7).

[0106] P1 = n L A c (7)

[0107] 2) The probability P2 of lightning strike causing oil leakage.

[0108] Regarding the probability of lightning strikes causing oil leaks, the probabilities of lightning strikes breaking down the tank shell and oil leaks can be considered separately. Related technologies provide the probability P of lightning strikes breaking down the tank shell. C As shown in equation (8).

[0109]

[0110] Further considering the probability of oil leakage, the probability P2 of lightning breakdown leading to oil leakage is obtained, as shown in equation (9).

[0111]

[0112] Where: H N The liquid level in the tank is expressed in meters (t). L The thickness of the storage tank wall is given in meters (m).

[0113] 3) Failure probability P3 of automatic fire suppression system

[0114] To determine the effectiveness of the automatic fire suppression system, the relevant technology yielded a failure probability of 1%, i.e., P3 = 0.01.

[0115] 4) The conditional probability P4 of lightning striking the floating roof of the storage tank.

[0116] Let P4 represent the conditional probability of lightning striking the external floating roof of the storage tank, as shown in equation (10).

[0117]

[0118] Where: H B The height of the lightning rod is in meters (m).

[0119] 5) Probability of sealing ring ignition P5

[0120] The relevant technology gives the sealing ring ignition probability P5 as equal to the ignition probability P. f The probability P of petroleum vapor concentration reaching the explosion limit lim The product of is shown in equation (11).

[0121]

[0122] Where: P for non-metallic storage tanks lim Take 0.04, metal storage tank P lim Take 0.19.

[0123] Related technologies obtained the probability distribution of lightning strike current amplitude through a lightning location system, calculating k1 = 31, k2 = 2.6; n s The number of conductive plates is determined by installing one plate every 1.8 to 3 meters along the perimeter of the tank wall.

[0124] 6) The probability P of a lightning strike triggering an explosion of a floating roof tank. F

[0125] Based on the vapor cloud explosion event tree analysis of floating roof tanks using relevant technologies, the probability of a lightning-induced explosion is determined by five probabilities: the probability of lightning striking the tank (P1), the probability of lightning causing breakdown and oil leakage (P2), the probability of automatic fire suppression system failure (P3), the probability of lightning striking the external floating roof (P4), and the probability of the sealing ring igniting (P5). The probability of a lightning-induced explosion of a floating roof tank is P. F =P1P3P4P5+P1P2P3(1-P4). The basic parameters of the floating roof tank are expressed as shown in equation (12).

[0126]

[0127] Finally, the probability of lightning-induced floating roof tank explosion is calculated using equation (12), which serves as the basis for analyzing the evolution process and worst-case scenario of lightning-induced floating roof tank explosion.

[0128] The following section describes the probability distribution of regional damage and the worst-case scenario in the case of a floating roof tank explosion:

[0129] Calculating the regional damage probability distribution requires addressing the impact range and extent of each storage tank explosion in the chemical industrial park, the explosion process of the storage tanks, and the probability of lightning-induced storage tank explosions.

[0130] The extent and severity of the impact zone from each storage tank explosion were determined based on the aforementioned information. Let represent the set of probability distributions of explosion damage to all storage tanks in the chemical industrial park.

[0131] The evolution of the storage tank explosion process, as determined by the aforementioned content, is Q = [100%, Q1, ..., Q]. N-1 The value represents the probability of damage to all storage tanks after an explosion at a storage tank in a chemical industrial park.

[0132] The probability of a lightning strike triggering an explosion in a floating roof tank is determined by the aforementioned factors, i.e., P. F The original assumption was that the probability of the initiating tank exploding was 100%. After considering the probability of a lightning-induced explosion of a floating roof tank, the probability of the initiating tank exploding changes from 100% to the probability of a lightning-induced explosion, P. F The subsequent evolution of the tank explosion was centered around P. F It is based on the foundation and its evolutionary process remains unchanged.

[0133] So, when there are N storage tanks in a chemical industrial park, what is the probability distribution of regional damage induced by lightning strikes? Combining equations (5) and (12), we obtain equation (13).

[0134]

[0135] Equation (13) can determine the regional damage probability after the evolution of damage from a storage tank explosion caused by lightning strikes at all locations in the chemical industrial park. Furthermore, if we consider all storage tanks in the chemical industrial park O={o1,...,o...} N By identifying storage tanks that explode due to lightning strikes as the initiating tanks, the explosion evolution process and regional damage probability distribution of all storage tanks in the industrial park that experience lightning-induced explosions can be obtained. Due to differences in stored materials, geometric characteristics, and relative locations, the evolution process and damage probability distribution of different lightning-induced explosions will vary. Given limited human, financial, and material resources, it is crucial to determine the optimal lightning protection scheme to minimize the risk to the chemical industrial park. Specifically, this involves determining the risk level of each storage tank by analyzing the regional damage probability distribution of lightning-induced explosions, thereby focusing lightning and explosion protection efforts on the tanks that cause the most unfavorable regional damage probability distribution.

[0136] The above process is actually a comparison of the regional damage probability distribution after the evolution of lightning strikes and explosions in each storage tank. Since the risk and safety of a chemical industrial park take into account the overall situation of the park, different regional damage probability distributions also need to be considered in the context of the entire park. This can be determined by integrating the regional risk probability distribution within the chemical industrial park area, as shown in equation (14).

[0137]

[0138] Equation (14) means the detonation tank. n The sum of damage probabilities at all node locations within the area. This is applied to all storage tanks. The calculation will yield the result. The numerical ranking shows that the larger the value, the greater the necessity for lightning protection for the corresponding explosion-inducing storage tank. This situation represents the most unfavorable scenario for lightning-induced explosions of floating roof storage tanks in chemical industrial parks.

[0139] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings:

[0140] For example, Table 1 shows the relative positions, material parameters, and geometric parameters of four storage tanks O = {o1, o2, o3, o4} in a chemical industrial park. The chemical industrial park is a 1000m × 1000m area, i.e., x∈{0,1,...,1000}m, y∈{0,1,...,1000}m.

[0141] Table 1. Relative location, material parameters, and geometric parameters of storage tanks

[0142] Table 1 Relative position, material parameters, and geometric parameters of storage tanks

[0143]

[0144] The chemical industrial park is located in a province in northern my country. According to standard calculations, the ground flash density is 1.78 flashes / km². 2 ·a, therefore n L = 1.78 / (1000×1000) times / m 2 •a. Based on relevant technologies and storage volume, the tank parameters are obtained according to specifications, including tank type, height, outer diameter, liquid level inside the tank, and wall thickness, as shown in Table 1. The liquid level inside the tank is obtained by multiplying the ratio of storage volume to calculated capacity by the tank height.

[0145] Based on the method described above, the probability distribution of tank explosion damage for the four storage tanks was obtained, as follows: Figures 1 to 4As shown. Since this is not the main research content, the results are given directly here.

[0146] Based on the foregoing, assuming O2 is the detonating storage tank with a probability of 100%, the explosion evolution process can be analyzed as follows: First comparison: O2→O1 = 18.70%, O2→O3 = 10.59%, O2→O4 = 10.86%, therefore Q1 = 18.70%; Second comparison: O2→O1→O3 = 18.70% + (1 - 18.70%) × 10.51% = 27.25%, O2→O1→O4 = 18.70% + (1 - 18.70%) × 11.99% = 28.45%, therefore Q2 = 28.45%; Third comparison: O2→O1→O4→O3 = 28.45% + (1 - 28.45%) × 13.89% = 38.39%, i.e., Q3 = 38.39%. Therefore, we get Q = [100%, 18.7024%, 28.45%, 38.39%], and the explosion sequence is o2→o1→o4→o3.

[0147] Calculate the probability P of a floating roof tank explosion induced by a lightning strike. G The probability P1 of lightning striking the storage tank is calculated according to equation (7), where n L = 1.78 / 1000 / 1000 times / m 2 •a; The storage tank o2 parameter is D L =40.65m, H L =17.8m, according to equation (6), A C =1396.4m², P1 = 0.0025. Calculate the probability P2 of lightning strike causing oil leakage, t L =0.15m=150cm, according to equation (8), P C =0.0259; According to equation (9), P2 = 0.0142. The failure probability of the automatic fire extinguishing system is P3 = 0.01. Calculate the conditional probability P4 of lightning striking the external floating roof of the storage tank, H B =20m, H N =15.52m, calculated using equation (10) yields P4 = 0.8120%. Calculate the ignition probability P5 of the sealing ring, and the metal storage tank P... lim =0.19, k1=31, k2=2.6, From equation (11), we get P5 = 0.1518. Therefore, the probability P of a storage tank explosion caused by a lightning strike is... F P can be determined using equation (12). F =3.1305×10⁻⁶. The probability distribution of regional damage induced by lightning strikes is determined according to equation (13). The result is as follows Figure 6 As shown. The sum of the regional damage probabilities is obtained according to equation (14).

[0148] Similarly, following the above process, let o1 be the detonating tank with a probability of 100%. The tank explosion process is as follows: First comparison: o1→o2 = 17.57%, o1→o3 = 10.51%, o1→o4 = 11.99%, therefore Q1 = 17.57%; Second comparison: o1→o2→o3 = 17.57% + (1 - 17.57%) × 10.59% = 26.3%, o1→o2→o4 = 17.57% + (1 - 17.57%) × 10.86% = 26.52%, therefore Q2 = 26.52%; Third comparison: o1→o2→o4→o3 = 26.52% + (1 - 26.52%) × 13.8909% = 36.73%, i.e., Q3 = 36.73%. Therefore, Q = [100%, 17.57%, 26.52%, 36.73%], and the explosion sequence is o1→o2→o4→o3. P1 = 0.0014, P2 = 0.0150, P3 = 0.0100, P4 = 0.6609, P5 = 0.1701, P... F =1.6453×10⁻⁶ Regional damage probability distribution as follows Figure 5 As shown.

[0149] Let O3 be the detonating tank with a probability of 100%. The explosion process is as follows: First comparison: O3→O1 = 10.32%, O3→O2 = 9.20%, O3→O4 = 12.92%, therefore Q1 = 12.92%; Second comparison: O3→O4→O1 = 12.92% + (1 - 12.92%) × 12.76% = 24.03%, O3→O4→O2 = 12.92% + (1 - 12.92%) × 10.34% = 21.92%, therefore Q2 = 24.03%; Third comparison: O3→O4→O1→O2 = 24.03% + (1 - 24.03%) × 17.57% = 37.38%, therefore Q3 = 37.38%. Therefore, Q = [100%, 12.92%, 24.03%, 37.38%], and the explosion sequence is o3→o4→o1→o2. P1 = 0.0014, P2 = 0.0135, P3 = 0.0100, P4 = 0.5640, P5 = 0.1701, P... F =1.4256×10⁻⁶ Regional damage probability distribution as follows Figure 7 As shown.

[0150] Let o4 be the detonating storage tank with a probability of 100%. The explosion process is as follows: First comparison: o4→o1 = 12.76%, o4→o2 = 10.34%, o4→o3 = 13.89%, therefore Q1 = 13.89%; Second comparison: o4→o3→o1 = 13.89% + (1 - 13.89%) × 10.32% = 22.78%, o4→o3→o2 = 13.89% + (1 - 13.89%) × 9.20% = 21.81%, therefore Q2 = 22.78%; Third comparison: o4→o3→o1→o2 = 22.78% + (1 - 22.78) × 17.57% = 36.35%, therefore Q3 = 36.35%. Therefore, Q = [100%, 13.89%, 22.78%, 36.35%], and the explosion sequence is o4→o3→o1→o2. P1 = 0.0025, P2 = 0.0107, P3 = 0.0100, P4 = 0.6011, P5 = 0.1518, P... F =2.3742×10⁻⁶ Regional damage probability distribution as follows Figure 8 As shown.

[0151] Figures 5 to 8 This paper presents the evolution of four storage tanks in a chemical industrial park after being struck by lightning, i.e., the regional damage probability distribution. Clearly, areas with high damage probabilities are concentrated near the initial explosion tank, assuming that the initial explosion was directly induced by the lightning strike. After the initial explosion, the damage evolution of the remaining tanks is a superposition of probabilities, so the probability of subsequent explosions gradually decreases. Under these circumstances, the regional damage probability distribution of all tanks during the superposition of the explosion evolution process highlights the regional damage probability distribution of the initial explosion tank.

[0152] The different regional damage probability distributions of storage tanks induced by lightning strikes vary significantly due to differences in their geometric parameters, stored materials, evolutionary processes, and relative locations. Therefore, the impact of lightning strikes on their explosions differs. From the perspective of ensuring the safety of the chemical industrial park and reducing its risks, it is necessary to determine the order in which lightning protection measures should be implemented for each storage tank. The above calculation yields the sum of the regional damage probabilities for each storage tank induced by lightning strikes. This indicator shows that, This indicates that the order of lightning strike hazard and importance of lightning protection for each storage tank is: storage tank O2 > O4 > O1 > O3. Therefore, under limited conditions, lightning protection measures for storage tank O2 should be prioritized to avoid excessive risks to the chemical industrial park area.

[0153] Of course, Equation (14) is a comparison result considering the most unfavorable area damage probability distribution within the entire chemical industrial park. It can also be calculated for a specific area within the chemical industrial park; or the gradient of the regional damage probability distribution can be analyzed to determine the lightning strike hazard and the importance of lightning protection for each tank. This requires developing a method for comparing the regional damage probability distribution of each tank based on different objectives.

[0154] The main objective of this invention is to determine the regional damage probability distribution in a chemical industrial park under lightning strikes. This regional damage probability distribution forms the basis for further analysis. For example, damage gradient analysis can be achieved by differentiating the damage probability distribution; optimal evacuation routes can be determined based on the damage probability distribution; the effectiveness of solutions can be analyzed by incorporating lightning protection and explosion-proof measures; and even the effects of multiple lightning strikes on tank explosions can be considered. All these studies are meaningful and require a basis in the regional damage probability distribution. The application of this invention to the regional damage probability distribution lies in determining the damage probability distribution of the most unfavorable region, thereby determining the lightning strike hazard of each tank and the ranking of the importance of lightning protection, providing an analytical method for lightning and explosion prevention of storage tanks in chemical industrial parks.

[0155] The beneficial technical effects of the present invention include at least the following:

[0156] 1) This study investigated the characteristics of floating roof tanks, the lightning-induced explosion process, and the explosion probability. The study concluded that external floating roof tanks have significant advantages and are widely used in chemical industrial parks. However, due to the complex structure of external floating roof tanks, they are highly susceptible to lightning-induced explosions. Based on key events in the lightning-induced explosion process, the probability of lightning striking the tank, the probability of lightning breakdown leading to leakage, the probability of automatic fire suppression system failure, the probability of lightning striking the external floating roof, and the probability of the sealing ring igniting were calculated. Ultimately, the probability of a lightning-induced floating roof tank explosion was obtained.

[0157] 2) The regional damage probability distribution and worst-case scenario of floating roof tank explosions were studied. Based on the tank explosion damage evolution theory, a tank explosion damage evolution model and regional damage probability distribution were obtained. The probability of a lightning-induced tank explosion was used as the initiation probability of the initiating tank to establish the tank explosion damage evolution process. The regional damage probability distribution considering lightning-induced tank explosions was obtained. Integrating this distribution determines the necessity of lightning protection for the initiating tank, resulting in the ranking of the importance of tank lightning protection and the worst-case regional damage probability distribution.

[0158] 3) The algorithm flow is demonstrated through examples. The evolution process and regional damage probability distribution of four storage tanks as lightning-initiated explosion tanks are obtained. The ranking of the sum of regional damage probabilities is then calculated, determining the ranking of lightning strike hazard and the importance of lightning protection for each tank. Finally, the significance and future development direction of the research are explained.

[0159] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for calculating the probability of a lightning-induced explosion of a floating roof storage tank, characterized in that, Includes the following steps: Assume the storage tank is a vertical cylinder with an average attraction area A. C The calculation is shown in equation (6): In the formula: D L H represents the outer diameter of the storage tank, in meters ( / m). L The height of the storage tank is given in meters (m). Ground lightning density n L / km -2 ·a -1 This reflects the frequency and severity of lightning events; it is measured by the ground lightning density n. L and average attraction area A C The product of represents the probability P1 of lightning striking the storage tank, as shown in equation (7): P1=n L A c (7) The probability P of lightning breaking through the outer shell of the storage tank C As shown in equation (8): Considering the probability of oil leakage, the probability P2 of lightning breakdown leading to oil leakage is obtained, as shown in equation (9): In the formula: H N The liquid level in the tank is expressed in meters (t). L The tank wall thickness is expressed in meters (m). The failure probability of the automatic fire extinguishing system is 1%, i.e., P3 = 0.01; P4 represents the conditional probability of lightning striking the floating roof of the storage tank, as shown in equation (10): In the formula: H B The height of the lightning rod is expressed in meters (m). The probability of the sealing ring igniting, P5, is equal to the probability of ignition, P. f The probability P of petroleum vapor concentration reaching the explosion limit lim The product of is shown in equation (11): Where: P for non-metallic storage tanks lim Take 0.04, metal storage tank P lim Take 0.19; Where, k1 = 31, k2 = 2.6; n s The number of conductive plates is determined by installing one plate every 1.8 to 3 meters along the perimeter of the tank wall. The probability of a lightning strike triggering an explosion in a floating roof tank is P. F =P1P3P4P5+P1P2P3(1-P4); The basic parameters of the floating roof tank are expressed as shown in equation (12): Finally, the probability of lightning-induced explosion of floating roof tanks is calculated using equation (12).

2. A method for analyzing the probability distribution of damage in the most unfavorable area of ​​a floating roof tank induced by a lightning strike, characterized in that, Includes the following steps: When there are N storage tanks in a chemical industrial park, consider the probability distribution of regional damage induced by lightning strikes. Equation (13) is obtained; Equation (13) can determine the regional damage probability after the evolution of damage from a storage tank explosion caused by lightning strike at all locations in a chemical industrial park; P F The probability of a lightning-induced floating roof tank explosion is obtained according to the method described in claim 1. Consider all storage tanks O = {o1,...,o} in the chemical industrial park. N By taking each lightning-induced explosion as an initiating tank, the explosion evolution process and regional damage probability distribution of all tanks in the park that are lightning-induced explosion tanks can be obtained. The risk probability distribution within the chemical industrial park is determined by integrating the risk distribution, as shown in equation (14): Equation (14) means the detonation tank. n The sum of damage probabilities at all node locations within the area; for all storage tanks... The calculation will yield the result. The numerical ranking shows that the larger the value, the greater the necessity for lightning protection of the corresponding explosion-inducing storage tank. The maximum value corresponds to the most unfavorable situation of lightning-induced explosion of floating roof storage tanks in chemical industrial parks.

3. The method for analyzing the probability distribution of damage in the most unfavorable area of ​​a lightning-induced floating roof tank explosion according to claim 2, characterized in that, It also includes the following steps: Based on the study of the shock wave, the functional relationship between the lateral overpressure ΔP and the atmospheric pressure P0 of a TNT explosion on flat ground is shown in equation (1): Where: ΔP is the peak explosion overpressure at point r, Pa; P0 is the ambient pressure, Pa; α is the vapor cloud equivalent coefficient, 0.02%-14.9%, taken as 4%; W f Q represents the total mass of fuel in the vapor cloud, in kg; f Q is the heat of combustion of a combustible material, expressed in kJ / kg. TNT The heat of explosion of the combustible material is taken as 4120-4690 kJ / kg; r is the distance between the measuring point and the explosion source, in meters. Let Z X×Y The area designated as the chemical industrial park is abbreviated as Z, where X is the wide boundary (m); x∈{0,1,...,X} are grid coordinates; Y is the high boundary (m); y∈{0,1,...,Y} are grid coordinates; and O is the tank set, O={o1,...,o N }, where N is the number of storage tanks, n∈[1,N], o n Let n be the nth storage tank, with coordinates (x, y, y). n ,y n ); any position in Z and o n The distance is shown in equation (2); replacing r in equation (1), then the storage tank o n The overpressure of the explosion in region Z is As shown in equation (3): ΔP on =F Δp (x n ,y n ,P o ,α,W f ,Q f ,Q TNT ) (3) Let o n The probability of damage caused by the explosion is An atmospheric pressure vessel fails when the pressure exceeds 22 kPa; L = 1 represents atmospheric pressure. A high pressure vessel fails when the pressure exceeds 17 kPa; L = 2 represents high pressure. Therefore... This can be further specified as equation (4); The probability distribution of damage from tank explosion is as follows It is an X×Y matrix, with unit values ​​of so For all locations The set of N storage tanks constitutes the probability distribution of storage tank explosion damage. Let o n To detonate the storage tank, o n ∈O; other storage tanks o i ∈O, i≠n; o n The maximum probability of damage to the remaining storage tanks from the explosion is o n Explosion pair (x i ,y i Storage tank at location o i The probability of damage caused; at this time o i Let O = O / o be the storage tank most likely to continue exploding. n This means removing the o from O. n , express Objects added in sequence n ; The model for the evolution of damage from a storage tank explosion can be described as follows: First, let's assume o... n To detonate the storage tank, The second time in o n The probability of damage to other storage tanks is affected during the traversal. Intermediate process omitted; N-2th time at o n The impact on determining the probability of damage to the last two storage tanks. N-1th time: Final confirmation Stop analysis; At this time o n The set of tank explosion sequences corresponding to the maximum probability of damage to the detonating tank, Q = [100%, Q1, Q2, ..., Q...]. N-1 ] represents the corresponding damage probability; The above has been obtained Q = [100%, Q1, ..., Q] N-1 ]and o n The probability distribution of regional damage obtained from the most unfavorable explosion evolution process is shown in equation (5): Based on Equation (5), the damage probability of all locations in the chemical industrial park is represented in matrix form as the regional damage probability distribution of the tank explosion. Combining equations (5) and (12), we obtain equation (13).

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