Method for evaluating the installation location of explosion suppression devices using flame speed and acceleration

Abstract

The present invention discloses a method for evaluating the installation position of an explosion suppression device using flame speed and acceleration, and relates to the field of prediction technology. The method comprises: using a volume balance calculation method to list the variation of the combustion gas volume over time; using a numerical analysis method to calculate the laminar combustion speed of gases with different concentrations, different components, and different proportions; then calculating the gas concentration in front of the flame at different times based on the relationship between the flame position and concentration, and calculating the laminar combustion speed at different times through the above steps. Obtain the flame acceleration; finally, using the relationship between the flame speed and acceleration, find the moment of maximum relative distance between the two, substitute this moment into the velocity equation, obtain the flame position information at this moment, and use this position as the optimal position for placing the explosion suppression device. The present invention can reflect the explosion mutation time and the transition position from deflagration to detonation, and provide theoretical guidance for the placement of explosion suppression sensors and explosion suppression devices in the direction of predicting flame acceleration and shock wave velocity.

Description

Technical Field

[0001] The present invention relates to the field of prediction technology, and in particular to a method for predicting the installation position of an explosion suppression device. Background Art

[0002] Gas pipelines, as widespread infrastructure, play a vital role in both residential life and industrial production. However, due to the inherent flammability and explosiveness of gas, the safe operation of gas pipelines presents significant risks. Therefore, equipping large gas pipelines and coal mine tunnels with explosion suppression devices is particularly important to ensure safe production.

[0003] At present, the existing technology has made requirements for the application and selection of explosion suppression devices. For example, according to the application method, they mainly include embedded explosion suppression devices and placed explosion suppression devices. In terms of the selection of explosion suppression devices, it is necessary to select explosion suppression devices with waterproof, moisture-proof and dust-proof properties, and maintain good mechanical and electrical properties for safety. However, no in-depth research has been conducted on the installation location of the explosion suppression device.

[0004] This shows that the prior art needs to be further improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for evaluating the installation location of an explosion suppression device using flame speed and acceleration, and to predict the flame speed and explosion pressure wave acceleration of combustible gas explosions in multi-scale locations through numerical calculations, thereby determining the explosion development intensity and the delay time of the flame and pressure wave, and thus determining the installation location of the explosion suppression device.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for evaluating the installation position of an explosion suppression device using flame speed and acceleration comprises the following steps:

[0008] Step 1: Use the volume balance calculation method to list the change of combustion gas volume over time, as shown in formula (1):

[0009]

[0010] In formula (1): V b is the total volume of the burning gas, t is the time, E is the ratio of the density of the unburned gas to the density of the burned gas, S is the surface area of ​​the flame front position, U L is the laminar combustion velocity.

[0011] Step 2: Use numerical analysis methods to calculate the laminar combustion velocity of gases with different concentrations, different components, and different proportions.

[0012] Step 3: According to the law of conservation of mass, the concentration of combustible gas is calculated as a function of time, as shown in formula (2):

[0013]

[0014] In formula (2), c is the concentration of combustible gas and D is the diffusion rate.

[0015] Combining formula (2) to calculate the relationship between the flame position and concentration of combustible gas, as shown in formula (3):

[0016]

[0017] In formula (3): η is the mass fraction of combustible gas combustion, r * is the aspect ratio.

[0018] Combine step 2, equation (2) and equation (3) to obtain the laminar flame speed at a certain moment.

[0019] Step 4: Calculate the laminar flame acceleration by differentiating equation (1).

[0020] Step 5: Using the relationship between laminar flame velocity and laminar flame acceleration, find the moment of maximum relative distance between the two, substitute this moment into the velocity equation to obtain the position information of the flame at this moment, and use this position as the optimal location for installing the explosion suppression device.

[0021] In the above-mentioned method for evaluating the installation location of an explosion suppression device using flame speed and acceleration, in step 1, the combustion gas is hydrogen, methane, ethane, propane, butane, ethylene, acetylene, propylene or hydrogen sulfide.

[0022] In the above method of using flame speed and acceleration to evaluate the installation position of the explosion suppression device, in step 3, the laminar flame speed equation is shown in equation (4):

[0023]

[0024] Substituting equation (4) into equation (1) yields the laminar flame speed, as shown in equation (5):

[0025]

[0026] In formula (5): Z tip is the flame position, δ is the coefficient 1.13, r is the radius of the container, and τ is the characteristic time.

[0027] In the above method of using flame speed and acceleration to evaluate the installation position of explosion suppression device, in step 4, the calculation formula of laminar flame acceleration is shown in formula (6):

[0028]

[0029] In formula (6), g is the laminar flame acceleration; the value of e is 2.7.

[0030] In the above-mentioned method for evaluating the installation position of an explosion suppression device using flame speed and acceleration, the explosion suppression device is installed in a tunnel or a gas pipeline.

[0031] In the above-mentioned method of using flame speed and acceleration to evaluate the installation position of the explosion suppression device, in step 2, the laminar combustion velocity of gases with different concentrations, different components, and different proportions is calculated by using the Chemkin solution reaction kinetic mechanism.

[0032] The above-mentioned method for evaluating the installation position of an explosion suppression device using flame speed and acceleration is for use in coal mines or gas pipelines.

[0033] In the above-mentioned method for evaluating the installation position of an explosion suppression device using flame speed and acceleration, in step 4, when there is an obstacle in the container, the turbulent combustion velocity is calculated.

[0034] The above method of using flame speed and acceleration to evaluate the installation position of explosion suppression device, when calculating the turbulent combustion velocity, the normal velocity of the flame surface fold U n The calculation is shown in formula (7):

[0035]

[0036] In formula (7), L M is the Markstein length of the flame, R F is the curvature radius of the flame.

[0037] Turbulent combustion speed U T It is expressed as formula (8):

[0038]

[0039] In formula (8), b1, b2, b3, and b4 are adjustment coefficients, which are 1, 0.7, 3 / 4, and 1 / 4 respectively.

[0040] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0041] (1) Formulas are used to calculate the speed and acceleration of different types of flames and the economically reasonable location for the placement of explosion suppression devices. This has very important practical significance for people to formulate relevant laws, regulations and industry standards, better prevent and control explosions of mixed gases, and assist in accident investigations and time-space inversion.

[0042] (2) Compared with setting up an experimental device, the present invention adopts a calculation method, which is easy to operate and more flexible to use. It can arbitrarily adjust the gas mixture components and the size of the explosion space, and understand the explosion trend of multi-component gases in different spaces, rather than being limited to a single gas. It has a wide range of uses, high flexibility, and high accuracy, and can guide engineering applications.

[0043] (3) Accurately understand the changes in the propagation speed of the explosion flame and the changes in the speed parameters over time, and can comprehensively and systematically understand the explosion of multiple gases, understand the explosion parameters from multiple angles and directions, and judge the distance required for the deflagration to turn into explosion or even detonation based on the trend of the explosion parameters. It can also judge the relative positions of temperature and pressure, and reasonably and economically place the explosion suppression device based on the specific area obtained.

[0044] In summary, the method provided by the present invention for evaluating the installation position of an explosion suppression device using flame speed and acceleration has the advantages of data analysis, comprehensive analysis, accurate numerical values, not limited to a single gas and space, a wide range of uses, the ability to determine the effective location of the explosion suppression device according to different gases and different pipeline tunnels, and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a flow chart of the present invention for evaluating the installation position of explosion suppression devices using flame speed and acceleration.

[0046] Figure 2 This is a specific model diagram of laminar combustion velocity.

[0047] Figure 3 The flame speed diagram of hydrogen laminar flow at different ratios.

[0048] Figure 4 It is a time distance graph. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0050] The technical solution of the present application is further described in detail below with reference to the accompanying drawings.

[0051] The main technical concept of the present invention is to provide a method for placing an explosion suppression device, which selects the placement area of ​​the explosion suppression device in an economical and reasonable manner, and specifically includes the following steps:

[0052] Step 1: Propose the equation of combustion volume changing with time, introduce the volume ratio before and after combustion and laminar combustion velocity into the equation. Use the volume balance calculation method to list the equation of combustion gas volume changing with time

[0053]

[0054] U L is the laminar flame speed, S is the surface area of ​​the flame front, and E is the unburned gas density ρ u and the burned gas density ρ h Ratio, where unburned gas and combustible gas are introduced into the equation. The gaseous products produced by combustion of different types of gases are different, so it is applicable to different types of gases. The laminar combustion velocity U L There are also differences, and this value can be obtained through experiments.

[0055] Step 2: Calculate the laminar combustion velocity at different times and proportions using numerical analysis methods. This paper addresses the lack of experimental flexibility for different types of gases, different components, and different concentrations. This paper simplifies the experimental process by proposing a numerical simulation method, using Chemkin to solve reaction kinetics and thermodynamic files to flexibly calculate the laminar combustion velocity of gases of different concentrations, different components, and different proportions. S represents the surface area of ​​the flame front, and this value can be adjusted based on the flame shape. Generally, the flame develops in a hemispherical shape, and this parameter is affected by the radius and cross-sectional area of ​​the pipe and tunnel.

[0056] Step 3: During the flame propagation process, the gas concentration in the front of the flame is constantly consumed and changes due to the influence of turbulence. In addition, the gas is often concentrated in a certain place in an enriched state before the explosion. During the explosion, the gas is continuously dissipated in the front of the flame. Therefore, it is necessary to calculate the change of the concentration of the combustible material in front of the flame with time at different times. According to the law of conservation of mass, the formula for the change of the combustible gas concentration with time is:

[0057]

[0058] Calculate the relationship between flame position and concentration, as shown in formula (3):

[0059]

[0060] r * is the aspect ratio; η is the combustion mass fraction; by calculating the flame concentration range at a certain moment and combining it with the Chemkin solution to solve the reaction kinetics mechanism, the laminar combustion velocity of the flame at that moment is calculated.

[0061] Calculate the speed of the flame after it contacts the wall. In the early stage of flame development, without obstacles or other external influences, it is approximately in a laminar state. The laminar flame speed can be expressed as Substituting this equation into equation (1), we can obtain the flame speed when the flame contacts the wall, as shown in equation (4):

[0062]

[0063] In formula (4): Z tipis the flame position, δ is the coefficient 1.13, r is the pipe radius, and τ is the characteristic time.

[0064] Calculate the flame acceleration to determine the time required for the flame and the flame shock wave to reach the same speed. Differentiate the above equation again to obtain the flame acceleration, as shown in equation (5):

[0065]

[0066] When the calculation location is in the tunnel and there are obstacles, the laminar flame formula will not be applicable. When there are many obstacles in the research target, the flame will evolve into a turbulent flame, and folds will occur in front of the flame. Since the flame surface area cannot be accurately evaluated, the above formula is not applicable to obstacles and pipelines that are greatly affected by external conditions. Turbulence is used to calculate the flame speed, where the normal speed of the flame surface folds U n , the normal velocity of the curved flame is shown in formula (6):

[0067]

[0068] In formula (6): L M is the Markstein length of the flame, R F is the curvature radius of the flame.

[0069] The turbulent combustion speed U T As shown in formula (7):

[0070]

[0071] b1, b2, b3, b4 are adjustment coefficients, which are calculated to be 1, 0.7, 3 / 4, 1 / 4, U t is the root mean square velocity fluctuation. Under conditions of obstacles and air flow disturbance, the flame speed is expressed using this formula. It is currently believed that the explosion pressure wave velocity is independent of the combustible gas reaction rate. The pressure wave is approximated as the speed of sound, and acceleration is used to calculate the time required for the flame to reach the speed of sound. This time is considered the moment when the flame speed exceeds the pressure wave, and the distance between them gradually decreases. This moment is considered the maximum relative distance between the flame and the pressure wave during the explosion. This moment is combined with the flame speed and acceleration formula to obtain the flame speed at that moment.

[0072] The present invention will be further described below with reference to Example 1.

[0073] Example 1:

[0074] The present invention uses flame speed and acceleration to evaluate the installation position of the explosion suppression device, and its flow chart is as follows: Figure 1 As shown in the figure, the flame position is calculated by combining numerical simulation and experimental methods, and the results are compared and analyzed with the calculation results.

[0075] Taking a circular semi-open pipe with a length of 4m and a diameter of 0.1m as an example, hydrogen gas with an equivalent ratio concentration is collected and ignited within a distance of 1m from the left end of the pipe. The approximate location of the explosion suppression device is calculated. The equation for the change of combustion volume with time is proposed:

[0076]

[0077] The calculations were performed using the hydrogen mechanism described by O'Connaire et al., using a laminar combustion velocity model such as Figure 2 As shown, the unburned gas temperature is set to 300K, the combustion end distance is 1cm, the intermediate products HO2, H2O2, H, OH and the product H2O are used as the starting reaction conditions, the hydrogen concentration is set to 30vol% and the injection speed is 40cm / s. To improve the calculation accuracy, the time step is 1000 steps and the step size is 10 -6 , the calculation results are derived to calculate the combustion rate value. Under the equivalence ratio conditions, such as Figure 3 As shown, the laminar combustion velocity of hydrogen with different concentrations is obtained by introducing the existing mechanism into the chemical reaction processor Chemkin.

[0078] Under standard meteorological conditions, the complete combustion of 1 mole of hydrogen (H2) and 0.5 moles of oxygen (O2) produces 1 mole of water vapor (H2O). According to the ideal gas equation (PV = nRT) in gas chemistry, equal quantities of substances have equal volumes at the same temperature and pressure. Therefore, it can be inferred that at the same temperature and pressure, the density of water vapor after combustion will be close to the density of hydrogen before combustion, with the ratio of the density of hydrogen before and after combustion being approximately 1:1. The combustion density of hydrogen in air is E = 1.

[0079]

[0080] The hydrogen concentration in front of the flame at different times is calculated by formula (3). Under the initial enrichment condition, the hydrogen concentration in front of the flame is continuously consumed and diluted as the flame propagates. At this time, the hydrogen mass fraction in the pipeline is 0.0289, and the pipeline aspect ratio is r * =40, and use Figure 3 The data is aimed at obtaining the laminar combustion velocity data of the flame at each moment during the flame propagation process.

[0081]

[0082] According to this formula, the time for the flame to reach each point is calculated as follows: Figure 4 As shown in the figure, the calculation results show that the flame acceleration reaches its peak after 2.5m in the pipeline, and it is most appropriate to install an explosion suppression device before this point.

[0083] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present application and are not intended to limit the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection claimed in the present application.

Claims

1. A method for evaluating the installation position of an explosion suppression device using flame speed and acceleration, characterized in that: The following steps are involved: Step 1: Use the volume balance calculation method to list the change of combustion gas volume over time, as shown in formula (1): In formula (1): V b is the total volume of the burning gas, t is the time, E is the ratio of the density of the unburned gas to the density of the burned gas, S is the surface area of ​​the flame front position, U L is the laminar flame speed; Step 2: Calculate the laminar combustion velocity of gases with different concentrations, different components, and different ratios using numerical analysis methods; Step 3: According to the law of conservation of mass, the concentration of combustible gas is calculated as a function of time, as shown in formula (2): In formula (2): c is the concentration of combustible gas, D is the diffusion rate; Combining formula (2) to calculate the relationship between the flame position and concentration of combustible gas, as shown in formula (3): In formula (3): η is the mass fraction of combustible gas combustion, r * is the aspect ratio; Combining step 2, equation (2) and equation (3) we can get the laminar flame speed at a certain moment; Step 4: Calculate the laminar flame acceleration by differentiating equation (1); Step 5: Using the relationship between laminar flame velocity and laminar flame acceleration, find the moment of maximum relative distance between the two, substitute this moment into the velocity equation to obtain the position information of the flame at this moment, and use this position as the optimal location for installing the explosion suppression device.

2. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 1, wherein: In step 1, the combustion gas is hydrogen, methane, ethane, propane, butane, ethylene, acetylene, propylene or hydrogen sulfide.

3. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 1, wherein: In step 2, the equation for the laminar flame speed is shown in equation (4): Substituting equation (4) into equation (1) yields the flame speed at which the flame contacts the wall, as shown in equation (5): In formula (5): Z tip is the flame position, δ is the coefficient 1.13, r is the radius of the container, and τ is the characteristic time.

4. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 1, wherein: In step 4, the calculation formula of laminar flame acceleration is shown in formula (6): In formula (6), g is the laminar flame acceleration; the value of e is 2.

7.

5. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 1, wherein: The explosion suppression device is installed in the tunnel or gas pipeline.

6. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 1, characterized in that: In step 2, the laminar combustion velocity of gases with different concentrations, different components, and different ratios is calculated by using the Chemkin solution reaction kinetic mechanism.

7. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 1, characterized in that: The explosion suppression device is an explosion suppression device for coal mines or an explosion suppression device for gas pipelines.

8. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 1, wherein: In step 4, when there is an obstacle in the container, the turbulent combustion velocity is calculated.

9. The method for evaluating the installation position of an explosion suppression device using flame speed and acceleration according to claim 8, characterized in that: When calculating the turbulent combustion velocity, the normal velocity of the flame surface folds U n The calculation is shown in formula (7): In formula (7), L M is the Markstein length of the flame, R F is the curvature radius of the flame; Turbulent combustion speed U T The calculation of is shown in formula (8): In formula (8), b1, b2, b3, and b4 are adjustment coefficients, which are 1, 0.7, 3 / 4, and 1 / 4 respectively.

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