Fireball thermal radiation hazard analysis method for oil tank farm

Abstract

This invention relates to a method for analyzing the thermal radiation hazards of fireballs in oil tank areas, belonging to the field of oil tank area safety control technology. It aims to solve the problem that traditional fireball hazard models in existing technologies neglect the height of the radiated target. This approach treats the radiated target as a point mass, limiting its study to hazards to personnel. However, oil tank fires can cause far more serious hazards, failing to provide a reliable reference for safety control work in complex situations. The proposed method, based on collected environmental parameters, references empirical coefficients for fireballs with different fuels, substitutes the mass of fuel in the fireball to determine the fireball's combustion characteristics, and calculates the thermal radiation energy on the fireball's surface. It introduces the positional height variable on the oil tank's main line to improve the traditional fireball hazard model, calculating the thermal radiation flux at different locations on the oil tank. Finally, it combines thermal radiation flux criteria to determine the thermal damage level of the radiated target.

Description

Technical Field

[0001] This disclosure relates to a method for analyzing the thermal radiation hazards of fireballs to oil tank areas, belonging to the field of flammable fuel storage and transportation safety control technology. Background Technology

[0002] With the continuous growth of my country's oil consumption demand and the rapid development of the petrochemical industry, energy reserves are becoming increasingly large, making the construction of large fuel storage tanks an inevitable trend. Among these, liquefied petroleum gas (LPG) storage tanks can become heat sources. LPG is formed under high pressure and possesses combustion and explosion hazards; fireball accidents caused by its leakage have occurred frequently in recent years, with a wide range of hazards and strong destructive power. According to standard API 581, the probabilities of safe discharge, jet flame, fireball fire, and vapor cloud explosion from gas leaks are 0.8, 0.1, 0.06, and 0.04, respectively, indicating that fireballs are relatively easy gas-related disasters. Fireball accidents are characterized by high heat radiation; the resulting fireball's heat radiation can cause skin and retinal burns to nearby personnel, and in severe cases, death. Current research on fireball hazards mainly focuses on the harm to personnel. Because people are at a relatively low height, most researchers have ignored the height of the radiation target, treating the research object as a point mass. However, the chain reaction threat of fireball accidents in energy storage areas is obviously much greater; once a fire occurs, it will be a disaster. Many specialized equipment have considerable heights, with large oil tanks reaching tens of meters in height. Traditional fireball hazard models tend to underestimate the impact of fireballs on oil tank areas. Therefore, it is necessary to study the thermal radiation hazards of fireballs on oil tank areas. Summary of the Invention

[0003] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for analyzing the thermal radiation hazard of fireballs on oil tank areas, so as to solve the problems of underestimating the thermal radiation effect of fireballs on oil tanks in the prior art, and the traditional fireball hazard model ignoring the height of the radiated target, which leads to calculation errors. The main impacts are on the observation factor and atmospheric transmittance.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows.

[0005] A method for analyzing the thermal radiation hazard of a fireball to an oil tank area. The method denotes the height of the oil tank as h0, the target height on the nearest oil tank line to the fireball as h, and uses the following fireball hazard model to calculate the thermal radiation flux q(r, h) received at the target height h, in units of kW / m². 2 :

[0006] q(r, h) = E p ·F v (h)·τ atm (h), 0 < h ≤ h0

[0007] In the fireball hazard model:

[0008] E p The thermal radiation energy of the fireball surface is calculated using the following formula:

[0009]

[0010] Where: χ r M is the thermal radiation factor of a fireball combustion. f H represents the mass of fuel in the fireball, expressed in kilograms. c The heat of combustion of fuel, expressed in kilojoules per kilogram; D f t represents the maximum diameter of the fireball, in meters; t represents the duration of the fireball, in seconds.

[0011] F v (h) is the observation factor, calculated using the following formula:

[0012]

[0013] In the formula: r is the horizontal distance from the target's altitude position to the center of the fireball, in meters; H f This represents the maximum height the fireball can reach.

[0014] τ atm (h) is the atmospheric transmittance, calculated using the following formula:

[0015]

[0016] In the formula: P w This represents the partial pressure of water at ambient temperature T0, expressed in Pa.

[0017] In the above technical solution, the severity of damage caused by the fireball to the target depends on the magnitude of the received thermal radiation flux. This flux is determined by the radiant energy on the fireball's surface, the observation factor, and the atmospheric transmittance of the area. Considering the actual site conditions, many special equipment pieces have a certain height and key protected locations. Introducing the variable 'h' improves the accuracy of calculating the target's received thermal radiation flux. The fireball's thermal radiation hazard range is much larger than the flame size, requiring further calculation of the thermal radiation flux. The magnitude of the target's received thermal radiation flux is affected by environmental factors, primarily corrected by the observation factor and atmospheric transmittance. For larger targets, different parts need to be considered; therefore, the above technical solution establishes observation factor functions and atmospheric transmittance functions related to the target height variable 'h'.

[0018] In the above technical solution, the maximum diameter of the fireball can be obtained by calculating it using the following formula:

[0019]

[0020] The duration of the fireball is calculated using the following formula:

[0021]

[0022] Where: a, b, c, and d are empirical coefficients for the combustion of fireballs with different fuels.

[0023] In the above technical solution, the fireball undergoes a process of generation, expansion, elevation, and disappearance, and the fireball has a certain elevation height. The elevation height of the fireball is uncertain. This invention considers the maximum elevation height of the fireball to be 1.23 times its maximum diameter. The maximum elevation height of the fireball is calculated as follows:

[0024] H f =1.23D f .

[0025] In the above technical solution, the partial pressure of water at the ambient temperature T0 can be obtained by calculating the following formula:

[0026]

[0027] In the formula: RH is the relative humidity, with a value of 0 to 1; P0 is the ambient pressure, in Pa.

[0028] As a further improvement to the above technical solution, after calculating the thermal radiation flux q(r,h) received at height h, the thermal flux corresponding to the failure of the production equipment is determined based on the calculated thermal radiation flux and with reference to the thermal radiation flux criterion, thereby determining the degree of thermal damage. The method of this invention enhances the rationality of safety assessment and can provide a more accurate basis for decision-making regarding the safety distance of oil tank areas, the thermal insulation design of safety devices, and emergency rescue. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating one implementation method;

[0030] Figure 2 This is a schematic diagram illustrating the spatial distribution of the height of the radiated target in one implementation method;

[0031] Figure 3 This is a schematic diagram showing the actual working conditions and measurement point locations in one implementation method.

[0032] Figure 4 This is a schematic diagram of a comparative verification in one implementation method. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0034] In one implementation, the improved model method of the present invention is compared with the traditional model method, and the flowchart is shown below. Figure 1 As shown. Operations in a flowchart do not have to be performed in sequence. Instead, operations can be performed in reverse order or simultaneously. Furthermore, one or more additional operations can be added to the flowchart. One or more operations can be removed from the flowchart. Figure 1 The method includes the following steps:

[0035] Step 1: Collect fireball combustion parameters and spatial distribution data of oil tanks.

[0036] To facilitate the verification of experimental results, this embodiment selects the following set conditions and uses fire simulation software (FDS) to numerically simulate a fireball accident under the same conditions. The mass of propane in the fireball is set to 200 kg, the ambient pressure to be standard atmospheric pressure, the ambient temperature to be 20°C, the fireball combustion heat radiation factor to be 0.3, and the relative humidity to be 1. The spatial distribution parameters of the oil tank include the nearest horizontal distance from the center of the fireball to the oil tank to be 20 m and the height of the oil tank to be 21 m.

[0037] Step 2: Based on the fireball combustion parameters and referring to the empirical coefficients for fireball combustion of different fuels, select the corresponding combustion model and calculate the maximum diameter, combustion time, and maximum rising height of the fireball using the following formula.

[0038] (1) Maximum diameter D of the fireball f :

[0039]

[0040] (2) Combustion time t:

[0041]

[0042] (3) Maximum rising height H of the fireball f :

[0043] H f =1.23D f (3)

[0044] In equations (1)-(3), M f D represents the mass of fuel in the fireball, expressed in kilograms. f t represents the maximum diameter of the fireball in meters; t represents the duration of the fireball in seconds; a, b, c, and d are empirical coefficients for the combustion of fireballs with different fuels.

[0045] Referring to Table 1, the combustion coefficient of the propane fireball is selected. Substituting the mass of propane (200 kg) in the fireball from step one into formulas (1)-(2), the maximum diameter of the fireball is calculated to be approximately 37 m and the combustion time is approximately 6 s. Substituting the maximum diameter of the fireball into formula (3), the maximum rising height of the fireball is approximately 46 m.

[0046] Table 1 Empirical coefficients for fireballs with different fuels

[0047]

[0048] Step 3: Based on the maximum diameter of the fireball, the burning time, and the mass of propane in the fireball, calculate the surface thermal radiation energy E of the fireball using the following formula. p :

[0049]

[0050] In equation (4), E p The surface thermal radiation energy of the fireball, kW / m 2 ;χ r The heat radiation factor of a fireball is generally between 0.2 and 0.4; H c The heat of combustion of the fuel is expressed in kJ / kg.

[0051] Substituting the calculated maximum fireball diameter of 37m, combustion time of 6s, and propane mass of 200kg in the fireball from step two into formula (4), it can be calculated that the thermal radiation energy of the fireball surface in this embodiment is approximately 117kW / m². 2 .

[0052] Step four, introduce the variable h, which represents the height of a certain position on the main line of the oil tank closest to the fireball, such as... Figure 2 As shown.

[0053] Step 5: Establish the observation factor function and atmospheric transmittance function for variable h.

[0054] The formulas for the traditional model observation factor and atmospheric transmittance are as follows:

[0055] 1) Observation factor F v :

[0056]

[0057] In the formula, r is the horizontal distance from the target to the center of the fireball, in meters.

[0058] 2) Atmospheric transmittance τ atm :

[0059]

[0060] In the formula, P wLet be the partial pressure of water at ambient temperature T0, in Pa.

[0061]

[0062] In the formula, RH is the relative humidity from 0 to 1; T0 is the ambient temperature in K; and P0 is the ambient pressure in Pa.

[0063] For large targets exposed to radiation, different parts need to be considered separately. Therefore, the heat flux calculated by traditional model formulas is relatively small. Substituting h into formulas (6) and (7), we establish the observation factor function and atmospheric transmittance function for the target height variable h:

[0064]

[0065]

[0066] In this embodiment, considering the tank height h0 = 21m, the range of variable h is 0–21m. To verify the improved fireball hazard model using real-world conditions, eight test points were selected on the generatrix closest to the fireball. A schematic diagram of the test point locations is shown below. Figure 3 For measuring points 1 to 8, h is 0m, 3m, 6m, 9m, 12m, 15m, 18m, and 21m respectively. Among them, h = 0m is the result calculated by the traditional hazard model. Finally, r = 20m is substituted into formulas (8) and (9), and then substituted into step six for calculation.

[0067] Step 6: Based on the observed factors, atmospheric transmittance, and thermal radiation energy of the fireball surface, calculate the thermal radiation flux received by the target using the improved fireball hazard model formula.

[0068] The formula for calculating the thermal radiation flux in a traditional fireball hazard model is as follows:

[0069] q(r)=E p ·F v ·τ atm (10)

[0070] In the formula, q(r) is the thermal radiation flux received by the target, kW / m². 2 Substituting the improved observation factor function and atmospheric transmittance function into the traditional fireball hazard model formula (10), its expression is as follows:

[0071] q(r, h) = E p ·F v (h)·τ atm (h) (11)

[0072] In the formula, q(r, h) is the thermal radiation flux received at position h corresponding to the target, in kW / m². 2 .

[0073] The thermal radiation energy of the fireball surface calculated in step three is 117 kW / m². 2 Then, the results calculated in step five based on the improved observation factor and atmospheric transmittance formula are substituted into formula (11) to calculate the thermal radiation flux received by the target. The results are shown in Table 2.

[0074] Table 2. Thermal radiation flux calculated at different measuring points

[0075]

[0076] Step 7: Analyze the degree of thermal damage to the target by combining the thermal radiation flux criterion.

[0077] The thermal radiation flux criterion is a commonly used standard that uses heat flux as an indicator to measure whether a target has been damaged. When the thermal radiation flux received by a target is greater than or equal to the critical value that causes damage, the target suffers the corresponding level of damage. Referring to Table 3 of the thermal radiation flux criterion, the oil tank itself and its protective facilities suffered severe damage, corresponding to a thermal radiation flux of 37.5 kW / m². 2 The corresponding locations of the damaged oil tank are measuring points 7 and 8; the deformation of the steel structure and metal pipelines of the oil tank itself corresponds to a thermal radiation flux of 25.0 kW / m². 2 The corresponding locations of the damaged oil tank are measuring points 4, 5, and 6; the non-metallic installation accessories were damaged, with a corresponding thermal radiation flux of 12.5 kW / m². 2 The corresponding damaged locations of the oil tank are measuring points 1, 2, and 3.

[0078] Table 3: Criteria for Thermal Radiation Flux

[0079]

[0080] Step 8: Numerical simulation, collecting thermal radiation flux at the corresponding measuring points to verify the calculation results.

[0081] A propane fireball combustion model was established using FDS software. Thermal radiation flux acquisition devices were installed at various measuring points to collect thermal radiation flux data. The theoretical calculation values ​​from step six were compared with the simulation calculation results from this step. The results are as follows: Figure 4 As shown in the figure, the results calculated by the improved prediction model are in good agreement with the simulation data, and the rationality of the model has been verified by numerical simulation.

[0082] This invention incorporates the height of the radiated target into the fireball hazard model formula, reducing the error caused by the traditional fireball hazard model neglecting the height of the research object when performing thermal damage analysis. This greatly improves the accuracy of calculating the thermal radiation flux received by the target, enhances the rationality of safety assessment, and can provide more accurate decision-making basis for oil tank area safety distances, thermal insulation design of safety devices, and emergency rescue.

[0083] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for analyzing the thermal radiation hazards of fireballs to oil tank areas, characterized in that: The method denotes the height of the oil tank as h0 and the target height on the nearest oil tank line to the fireball as h. Using the following fireball hazard model, the thermal radiation flux q(r, h) received at the target height h is calculated, with units of kW / m². 2 : q(r,h)=E p ·F v (h)·τ atm (h),0<h≤h0 In this fireball hazard model: E p The thermal radiation energy of the fireball surface is calculated using the following formula: Where: χ r M is the thermal radiation factor of a fireball combustion. f H represents the mass of fuel in the fireball, expressed in kilograms. c The heat of combustion of fuel, expressed in kilojoules per kilogram; D f t represents the maximum diameter of the fireball, in meters; t represents the duration of the fireball, in seconds. F v (h) is the observation factor, calculated using the following formula: In the formula: r is the horizontal distance from the target's altitude position to the center of the fireball, in meters; H f This represents the maximum height the fireball can reach. τ atm (h) is the atmospheric transmittance, calculated using the following formula: In the formula: P w This represents the partial pressure of water at ambient temperature T0, expressed in Pa.

2. The method according to claim 1, characterized in that, The maximum diameter of the fireball is calculated using the following formula: The duration of the fireball is calculated using the following formula: Where: a, b, c, and d are empirical coefficients for the combustion of fireballs with different fuels.

3. The method according to claim 1, characterized in that, The maximum height of the fireball is calculated using the following formula: H f =1.23D f 。 4. The method according to claim 1, characterized in that, The partial pressure of water at the ambient temperature T0 is calculated using the following formula: In the formula: RH is the relative humidity, with a value of 0 to 1; P0 is the ambient pressure, in Pa.

5. The method according to claim 1, characterized in that, After calculating the thermal radiation flux q(r, h) received at height h, the thermal flux corresponding to the failure of the production equipment is determined based on the calculated thermal radiation flux and with reference to the thermal radiation flux criterion, and then the thermal damage level is determined.

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