Method for evaluating installation position of explosion suppression device by using flame speed and acceleration

Abstract

The invention discloses a method for evaluating the installation position of an explosion suppression device by using flame velocity and acceleration, and relates to the technical field of prediction. The method comprises the following steps: listing a change formula of a combustion gas volume along with time by utilizing a volume equilibrium calculation method; calculating laminar flow combustion speeds of gases with different concentrations, different components and different proportions by using a numerical analysis method; and then calculating the gas concentration in front of the flame at different moments according to the relationship between the flame position and the concentration, and calculating the laminar combustion speed at different moments through the above steps. Solving the flame acceleration; and finally, finding out the moment of the maximum relative distance between the flame velocity and the acceleration by utilizing the relationship between the flame velocity and the acceleration, substituting the moment into the velocity equation to obtain the position information of the flame at the moment, and taking the position as the optimal position for placing the explosion suppression device. According to the invention, the explosion sudden change time and the transition position from deflagration to detonation can be reflected, and theoretical guidance is provided for the placement positions of the explosion suppression sensor and the explosion suppression device in the prediction of the flame acceleration and the shock wave velocity direction.

Description

Technical Field

[0001] The 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] As a widely distributed infrastructure, gas pipelines play an important role in residents' lives and industrial production. However, due to the flammability and explosiveness of gas itself, there are huge risks in the safe operation of gas pipelines. In recent years, especially with the acceleration of urban infrastructure construction in my country, pipeline explosion accidents have occurred frequently. Therefore, it is particularly important to equip large gas pipelines and coal mine tunnels with explosion suppression devices to ensure safe production.

[0003] At present, the existing technology has made requirements on 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. Regarding 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 position of an explosion suppression device using flame speed and acceleration, predicting the flame speed of a combustible gas explosion and the acceleration of an explosion pressure wave in a multi-scale location through numerical calculation, determining the explosion development intensity and the delay time of the flame and pressure wave, and determining the installation position 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 combustion 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, and U is the 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 changes with 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] Combining step 2, equation (2) and equation (3), we can get the laminar flame speed at a certain moment.

[0019] Step 4: By differentiating equation (1), the laminar flame acceleration is calculated.

[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, obtain the flame position information at this moment, and use this position as the best location for installing the explosion suppression device.

[0021] In the above-mentioned method for evaluating the installation position 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 the explosion suppression device, in step 4, the calculation formula of the 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 method for evaluating the installation position of the explosion suppression device using flame speed and acceleration, in step 2, the laminar combustion speed 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, the explosion suppression device is an explosion suppression device for a coal mine or an explosion suppression device for a gas pipeline.

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

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

[0038]

[0039] In formula (8), b1, b2, b3, 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) The formula is used to calculate the flame speed and acceleration of different types and the economical and reasonable location for the explosion suppression device. This has very important practical significance for people to formulate relevant laws, regulations and industry standards, better prevent and control the explosion of the mixed gas, and assist in accident investigation 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. The gas mixture components and the size of the explosion space can be adjusted at will to 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 multi-gas explosion situation, understand the explosion parameters from multiple angles and directions, and judge the distance required for the deflagration to turn into an explosion or even a detonation based on the trend of the explosion parameter changes, judge the relative position 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 position 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 the explosion suppression device using flame speed and acceleration.

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

[0047] Figure 3 This is a diagram of the laminar flame speed of hydrogen 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 clearly and completely described 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 in conjunction with 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 by economical and reasonable means, and specifically includes the following steps:

[0052] Step 1: Propose the equation for the change of combustion volume over time, introduce the volume ratio before and after combustion and the laminar combustion velocity into the equation. Use the volume balance calculation method to list the equation for the change of combustion gas volume over 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 the unburned gas and combustible gas are introduced into the equation. The gaseous products produced by the 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, which can be obtained by experiment.

[0055] Step 2: Use numerical analysis methods to calculate the laminar combustion speed of flames at different times and in different proportions. In view of the lack of experimental flexibility for different types of gases, gases of different components, and gases of different concentrations, the present invention simplifies the experimental process and proposes a numerical simulation method. It uses Chemkin to solve reaction kinetics and thermodynamic files to flexibly calculate the laminar combustion speed of gases of different concentrations, different components, and different proportions. S is the surface area of ​​the flame front position, and the numerical change can be adjusted according to the flame shape. Generally speaking, the flame develops in a hemispherical shape, and the parameters are affected by the radius and cross-sectional area of ​​the pipeline 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 turbulence. The gas is often concentrated in a certain place in an enriched state before the explosion. During the explosion, the gas is constantly dissipated in the front of the flame. Therefore, it is necessary to calculate the change of the concentration of combustible substances in front of the flame at different times over time. According to the law of conservation of mass, the formula for the change of combustible gas concentration over 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 the Chemkin solution to 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 apply. When there are many obstacles in the research target, the flame will evolve into a turbulent flame, and wrinkles 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 velocity of the folds on the flame surface is 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 radius of curvature 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 fluctuation of velocity. Under the conditions of obstacles and air flow disturbance, the flame speed is expressed by this formula. At present, it is believed that the explosion pressure wave velocity has nothing to do with the reaction rate of the combustible gas. The pressure wave is approximated as the speed of sound, and the acceleration is used to calculate the time required for the flame to reach the speed of sound. This time is regarded as the flame speed exceeding the pressure wave, and the distance between the two gradually shortens. This moment is regarded as the maximum relative distance between the flame and the pressure wave during the explosion. The flame speed at this moment is obtained by combining this moment with the flame speed and acceleration formula.

[0072] The present invention will be further described below in conjunction with Example 1.

[0073] Embodiment 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, the flame position is calculated by combining numerical simulation method with experimental method, and the calculation results are compared and analyzed.

[0075] Taking a circular semi-open pipe with a length of 4m and a diameter of 0.1m as an example, hydrogen with an equivalent ratio concentration is gathered within a distance of 1m from the left end of the pipe and ignited, and the approximate location of the explosion suppression device is calculated. The equation for the change of combustion volume over 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 conditions for starting the reaction, 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 length 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 speed of hydrogen with different concentrations is obtained by introducing the existing mechanism into the chemical reaction processor Chemkin.

[0078] Under standard meteorological conditions, 1 mole of hydrogen (H2) and 0.5 moles of oxygen (O2) will produce 1 mole of water vapor (H2O) after complete combustion. According to the ideal gas state equation (PV=nRT) of gas chemistry, the same amount of substance has the same volume 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, and the density ratio of hydrogen before and after combustion is roughly close to 1:1. The combustion density ratio 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 mass fraction of hydrogen in the pipeline is 0.0289, and the aspect ratio of the pipeline 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, it can be seen from the calculation results that the flame acceleration reaches its peak value after the flame is 2.5m into 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 only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope 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 combustion 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, and U is the L is the laminar flame speed; Step 2: Calculate the laminar combustion velocity of gases with different concentrations, different components and different proportions by using numerical analysis methods; Step 3: According to the law of conservation of mass, the concentration of combustible gas changes with 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: By differentiating equation (1), the laminar flame acceleration is calculated; 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, obtain the flame position information at this moment, and use this position as the best 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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 proportions is calculated by using Chemkin to solve the reaction kinetics 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, characterized in that: In step 4, when there is an obstacle in the container, the turbulent combustion speed is calculated.

9. A 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 U of the flame surface folds is 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, b4 are adjustment coefficients, which are 1, 0.7, 3 / 4, and 1 / 4 respectively.

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