Hydrogen-doped natural gas pipeline leakage safety assessment method, system and equipment

Abstract

The invention discloses a hydrogen-doped natural gas pipeline leakage safety assessment method, system and equipment, and relates to the field of natural gas pipeline safety, and the method comprises the steps: determining the flow of actual fluid passing through a crack and a corrosion pit according to the size of the crack of the natural gas pipeline and the depth of the corrosion pit; determining a flaring structure correction coefficient based on the obtained inclination angle of the blow-down pipe of the hydrogen-doped natural gas pipeline; the leakage flow is determined based on the defect area, the flow when actual fluid passes through the crack and the corrosion pit and the flaring structure correction coefficient; performing multi-scale computational fluid dynamics (CFD) simulation according to the leakage flow and the gas characteristic parameters under the current hydrogen doping ratio, and determining a simulation result of hydrogen concentration field distribution; determining an explosion lower limit according to the obtained volume fraction of hydrogen in the hydrogen-doped natural gas pipeline, and determining a safe concentration threshold according to the explosion lower limit; and when the simulation result of the hydrogen concentration field distribution is greater than or equal to a safe concentration threshold value, carrying out risk early warning.

Description

Technical Field

[0001] This invention relates to the field of natural gas pipeline safety technology, and in particular to a method, system and equipment for safety assessment of leaks in hydrogen-blended natural gas pipelines. Background Technology

[0002] As a key carrier for achieving the "dual carbon" goal, hydrogen-blended natural gas faces inherent safety bottlenecks in its application in urban pipeline networks: the molecular weight of hydrogen (2g / mol) is only 1 / 8 that of methane (16g / mol), and its diffusion coefficient is 3.8 times higher (NIST data), resulting in a leakage rate increase of more than 40% under isobaric conditions; the explosion limit of hydrogen (4%-75%) is far greater than that of natural gas (5%-15%), and its minimum ignition energy is as low as 0.02mJ (only 1 / 10 of that of natural gas), meaning it can be ignited by a small amount of static electricity; the hydrogen embrittlement effect may accelerate the propagation of pipeline cracks, increasing the probability of sudden leaks.

[0003] The existing natural gas pipeline safety system has serious deficiencies in hydrogen-blended scenarios: neither domestic standards (GB 50251-2015, GB 50183-2004) nor international standards (ASME B31.8, API 521) specify leakage control parameters for hydrogen-blended conditions; vent pipe design specifications (such as API 537) are designed for active emission scenarios and cannot address accidental leakage problems. Methane sensor-based leak detection systems are not sensitive enough to hydrogen (cross-sensitivity <30%); the acoustic / negative pressure wave method suffers from misjudgments due to the sound velocity characteristics of hydrogen (1300 m / s vs. methane 430 m / s), making it difficult to achieve quantitative safety assessment of leak accidents. Summary of the Invention

[0004] This invention provides a method, system, and equipment for safety assessment of leaks in hydrogen-blended natural gas pipelines, to solve the aforementioned problems in the prior art, namely, the problem of accurately assessing leak accidents in the prior art. This invention provides a method for safety assessment of leaks in hydrogen-blended natural gas pipelines, which includes: The defect area, crack size, and corrosion pit depth of the natural gas pipeline under test are obtained. Based on the crack size and corrosion pit depth, the flow rate of the actual fluid passing through the crack and corrosion pit is determined. Based on the obtained tilt angle of the vent pipe of the hydrogen-blended natural gas pipeline, the flare structure correction coefficient is determined. The corresponding leakage flow rate is determined based on the defect area, the actual flow rate of fluid passing through cracks and corrosion pits, and the correction factor for the flared structure. Based on the leakage flow rate and the gas characteristic parameters obtained under the current hydrogen blending ratio, a multi-scale computational fluid dynamics (CFD) simulation is performed to determine the simulation results of the hydrogen concentration field distribution. Based on the hydrogen gas integral number obtained in the hydrogen-blended natural gas pipeline and the hydrogen blending ratio, the lower explosion limit is determined. Based on the lower explosion limit, a safe concentration threshold is determined. When the simulation results of the hydrogen concentration field distribution are greater than or equal to the safe concentration threshold, a risk warning is issued.

[0005] Optionally, the acquisition of the leaked traffic specifically includes: The leakage flow rate is obtained using the following formula: ; in, For leakage flow; K g C is the correction factor for the flared structure; where, when the pipe contains a 33° flared structure, the correction factor for the flared structure is taken as 1.13; d is the flow coefficient, representing the ratio of the actual flow rate of fluid passing through cracks and corrosion pits to the theoretical flow rate; A is the defect area; ρ mix ΔP is the density of the gas mixture; ΔP is the pressure difference between the inside and outside of the pipe.

[0006] Optionally, the step of determining the lower explosive limit based on the obtained hydrogen gas fraction in the hydrogen-blended natural gas pipeline and the hydrogen blending ratio, and then determining the safe concentration threshold based on the lower explosive limit, specifically includes: Based on the obtained hydrogen gas integral and the hydrogen doping ratio, the lower explosive limit is obtained using the following formula: ; in, yH2 is the lower explosive limit; yH2 is the hydrogen gas integral number, representing the ratio of hydrogen volume in natural gas to the total volume of natural gas, with a value range of 0-30%; 4.0 is the reference value for the lower explosive limit of pure hydrogen; 1.5 is the hydrogen blending ratio coefficient. Based on the lower explosive limit, the safe concentration threshold is obtained using the following formula: in, For safe concentration thresholds, k This is for the safety factor.

[0007] Optionally, the gas characteristic parameters can be generated by calling the NIST property database.

[0008] This invention provides a safety assessment system for leaks in hydrogen-blended natural gas pipelines, comprising: The flared structure correction coefficient determination module is used to obtain the defect area, crack size, and corrosion pit depth of the natural gas pipeline under test. Based on the crack size and corrosion pit depth, the flow rate of the actual fluid passing through the crack and corrosion pit is determined respectively. Based on the obtained tilt angle of the vent pipe of the hydrogen-blended natural gas pipeline, the flared structure correction coefficient is determined. The leakage flow rate determination module is used to determine the corresponding leakage flow rate based on the defect area, the actual flow rate of fluid passing through cracks and corrosion pits, and the flared structure correction coefficient. The safety assessment module is used to perform multi-scale computational fluid dynamics (CFD) simulations based on the leakage flow rate and the gas characteristic parameters obtained under the current hydrogen blending ratio, to determine the simulation results of the hydrogen concentration field distribution; based on the obtained hydrogen gas integral number in the hydrogen-blended natural gas pipeline and in combination with the hydrogen blending ratio, to determine the lower explosive limit, and based on the lower explosive limit, to determine the safe concentration threshold; when the simulation results of the hydrogen concentration field distribution are greater than or equal to the safe concentration threshold, a risk warning is issued.

[0009] The present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-mentioned method for safety assessment of leakage in hydrogen-blended natural gas pipelines.

[0010] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention provides a method for safety assessment of leaks in hydrogen-blended natural gas pipelines. This method achieves dynamic calculation of gas characteristics through the constructed hydrogen-blended physical property data, improving the accuracy of the evaluation model for different hydrogen blending ratios. Simultaneously, based on the defect area, the actual flow rate of fluid passing through cracks and corrosion pits, combined with the hydrogen-blended physical property data and the obtained flared structure correction coefficient, the accuracy of leak flow rate calculation is improved. Accurate assessment of leak accidents based on the obtained leak flow rate provides reliable data support for subsequent simulations and risk assessments, preventing safety accidents caused by natural gas leaks. Furthermore, based on the obtained leak flow rate and gas characteristic parameters, multi-scale computational fluid dynamics (CFD) simulation is performed, achieving dynamic simulation of the entire leak accident process. This enables real-time detection of the degree of natural gas pipeline leakage and graded alarms, preventing safety accidents caused by natural gas leaks. Attached Figure Description

[0011] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0012] Figure 1 A flowchart of a method for assessing the safety of hydrogen-blended natural gas pipeline leaks, provided as an embodiment of the present invention; Figure 2 Risk heatmap provided for embodiments of the present invention; Figure 3 A schematic diagram of a computer device for a hydrogen-blended natural gas pipeline leakage safety assessment method provided in an embodiment of the present invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0014] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0015] Figure 1 This is a flowchart of a method for assessing the safety of hydrogen-blended natural gas pipeline leaks, as provided in an embodiment of the present invention. Figure 1 As shown in the figure, this embodiment illustrates a method for safety assessment of leaks in hydrogen-blended natural gas pipelines, including: S1: Obtain the defect area, crack size, and corrosion pit depth of the natural gas pipeline under test. Determine the flow rate of the actual fluid passing through the crack and corrosion pit based on the crack size and corrosion pit depth, respectively. Determine the flare structure correction coefficient based on the obtained tilt angle of the vent pipe of the hydrogen-blended natural gas pipeline.

[0016] For example, structural damage such as crack length / width or corrosion pit depth can be detected, including crack size (length L, width W) and corrosion pit depth d. If the pipe outlet has a flared structure: when the inclination angle is 33°, the leakage flow correction factor is taken as 1.13; for other inclination angles, the correction factor can be adjusted according to the piecewise linear relationship between the pipe outlet inclination angle and the leakage flow correction factor.

[0017] S2: Determine the corresponding leakage flow rate based on the defect area, the actual flow rate of fluid passing through cracks and corrosion pits, and the correction factor for the flared structure.

[0018] For example, the leakage flow can be obtained using the following formula: Among them, K g C is the correction factor for the flared structure, taken as 1.13. d , where A is the flow rate coefficient (default 0.62) and A is the defect area (m²). ρ mix ΔP is the density of the mixed gas (kg / m³), and ΔP is the pressure difference between the inside and outside of the pipe (Pa).

[0019] For example, natural gas pipeline data may include pipeline operating pressure P (MPa), hydrogen blending ratio yH2, ambient temperature Tenv (°C), and atmospheric pressure Patm (kPa); gas characteristic parameters may include the density and diffusion coefficient of the mixed gas; wherein the density and diffusion coefficient of the mixed gas can be automatically generated by calling the NIST physical property database.

[0020] S3: Based on the leakage flow rate and the gas characteristic parameters obtained under the current hydrogen blending ratio, perform multi-scale computational fluid dynamics (CFD) simulation to determine the simulation results of the hydrogen concentration field distribution; based on the obtained hydrogen gas integral number in the hydrogen-blended natural gas pipeline and in combination with the hydrogen blending ratio, determine the lower explosion limit; based on the lower explosion limit, determine the safe concentration threshold; when the simulation results of the hydrogen concentration field distribution are greater than or equal to the safe concentration threshold, issue a risk warning.

[0021] For example, the execution of a multi-scale computational fluid dynamics (CFD) simulation may include the following two stages: Phase 1: Perform near-field shock wave simulation, which may include: (1) Mesh generation: refine the mesh near the wall (y+<1), with a mesh count ≥ 200,000. Solve the governing equations:

[0022] Among them, Y k D is the mass fraction of component k (H2 / CH4). k Let k be the diffusion coefficient of component k (m² / s). This represents the chemical reaction source term (kg / (m³·s)).

[0023] Phase 2: Conduct far-field atmospheric diffusion, which may include: (1) Couple urban environmental data: import real-time wind speed and direction and three-dimensional building cluster GIS data; (2) Simulate the diffusion of combustible clouds: use large eddy simulation (LES) to track hydrogen concentration distribution and dynamically adjust grid density: automatically densify the grid in areas with large concentration gradients.

[0024] For example, the lower explosive limit can be calculated based on the hydrogen doping ratio (the higher the hydrogen ratio, the lower the lower explosive limit); the laminar combustion rate can be quantified (increasing the hydrogen ratio will lead to a decrease in combustion rate), and the lower explosive limit can be obtained using the following formula: Where yH2 is the hydrogen gas integral (0-30%), 4.0 is the lower explosive limit reference value of pure hydrogen (GB / T 50493), and 1.5 is the hydrogen doping ratio coefficient (experimental calibration value).

[0025] For example, based on the lower explosive limit, the safe concentration threshold can be obtained using the following formula: Where k=0.6 (red / orange warning) and k=0.3 (yellow warning).

[0026] For example, when a 300mm diameter pipeline (containing 25% hydrogen) in a certain urban area experiences a crack and leak, and a natural gas pipeline also leaks, during the execution process, the physical property library calculates the lower explosive limit (LFLmix) to be 4.375% (because the hydrogen content is higher than that of pure natural gas); a 33° flared structure is detected in the pipeline, and the leakage flow rate is corrected by 1.13 times; CFD simulation shows that the hydrogen concentration in the primary school playground reaches 2.1% after 38 seconds, exceeding the safety threshold. =2.625% × 0.6 = 1.575%.

[0027] Risk Decision Output: Triggering an orange alert: Automatically reducing pipeline pressure; isolating the area within 150 meters of the leak point. Prevention and Control Effect: The explosion suppression system successfully prevented the spread of the flammable cloud to the playground; the actual number of evacuees was reduced by 67% compared to traditional methods. As can be seen from the above implementation methods, this invention has a simple structure, low testing losses, and a high degree of automation in the testing process, significantly reducing the workload of personnel, and can achieve a cross-dimensional breakthrough from "equipment design" to "urban public safety".

[0028] like Figure 2 As shown, when making dynamic risk assessment: (1) real-time monitoring of risk indicators: extracting H2 concentration field CH2; (2) when the simulation result of hydrogen concentration field distribution is greater than or equal to the safe concentration threshold, triggering graded early warning, specifically including: when the hydrogen concentration in densely populated areas such as schools and hospitals is ≥ the lower explosive limit (LFL) mix A red alert is triggered when the hydrogen concentration in a normal area is ≥60% of the lower explosive limit (LFL). mix A hydrogen concentration of 60% triggers an orange alert; when the hydrogen concentration reaches the lower explosive limit (LFL)... mix A yellow alert is triggered when the level is between 30% and 60%. For example, when a red alert is triggered, the upstream valve can be immediately shut off, the explosion suppression nitrogen system can be activated, and personnel within a 300-meter radius can be evacuated; when an orange alert is triggered, the pipeline operating pressure can be reduced, and a 150-meter warning isolation zone can be set up; when a yellow alert is triggered, inspection personnel can be dispatched, and ventilation reminders for residential areas can be issued.

[0029] The above are one or more embodiments of the hydrogen-blended natural gas pipeline leakage safety assessment method provided in this specification. Based on the same idea, this specification also provides a corresponding hydrogen-blended natural gas pipeline leakage safety assessment system, including: The flared structure correction coefficient determination module is used to obtain the defect area, crack size, and corrosion pit depth of the natural gas pipeline under test. Based on the crack size and corrosion pit depth, the flow rate of the actual fluid passing through the crack and corrosion pit is determined respectively. Based on the obtained tilt angle of the vent pipe of the hydrogen-blended natural gas pipeline, the flared structure correction coefficient is determined. The leakage flow rate determination module is used to determine the corresponding leakage flow rate based on the defect area, the actual flow rate of fluid passing through cracks and corrosion pits, and the flared structure correction coefficient. The safety assessment module is used to perform multi-scale computational fluid dynamics (CFD) simulations based on the leakage flow rate and the gas characteristic parameters obtained under the current hydrogen blending ratio, to determine the simulation results of the hydrogen concentration field distribution; based on the obtained hydrogen gas integral number in the hydrogen-blended natural gas pipeline and in combination with the hydrogen blending ratio, to determine the lower explosive limit, and based on the lower explosive limit, to determine the safe concentration threshold; when the simulation results of the hydrogen concentration field distribution are greater than or equal to the safe concentration threshold, a risk warning is issued.

[0030] Specific limitations regarding the safety assessment system for hydrogen-blended natural gas pipeline leaks can be found in the limitations of the safety assessment method for hydrogen-blended natural gas pipeline leaks mentioned above, and will not be repeated here. Each module in the aforementioned safety assessment system for hydrogen-blended natural gas pipeline leaks can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the corresponding operations of each module.

[0031] The present invention also provides Figure 3 The schematic diagram of the computer device shown is as follows: Figure 3 As shown, at the hardware level, the computer device includes a processor, an internal bus, a network interface, memory, and non-volatile memory, and may also include other hardware required for business operations. The processor reads the corresponding computer program from the non-volatile memory into memory and then runs it to implement the hydrogen-blended natural gas pipeline leakage safety assessment method provided in the above embodiments.

[0032] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided by this invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0033] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this invention.

Claims

1. A method for safety assessment of leaks in hydrogen-blended natural gas pipelines, characterized in that, include: The defect area, crack size, and corrosion pit depth of the natural gas pipeline under test are obtained. Based on the crack size and corrosion pit depth, the flow rate of the actual fluid passing through the crack and corrosion pit is determined. Based on the obtained tilt angle of the vent pipe of the hydrogen-blended natural gas pipeline, the flare structure correction coefficient is determined. The corresponding leakage flow rate is determined based on the defect area, the actual flow rate of fluid passing through cracks and corrosion pits, and the correction factor for the flared structure. Based on the leakage flow rate and the gas characteristic parameters obtained under the current hydrogen blending ratio, a multi-scale computational fluid dynamics (CFD) simulation is performed to determine the simulation results of the hydrogen concentration field distribution. Based on the hydrogen gas integral number obtained in the hydrogen-blended natural gas pipeline and the hydrogen blending ratio, the lower explosion limit is determined. Based on the lower explosion limit, a safe concentration threshold is determined. When the simulation results of the hydrogen concentration field distribution are greater than or equal to the safe concentration threshold, a risk warning is issued.

2. The method for safety assessment of hydrogen-blended natural gas pipeline leakage as described in claim 1, characterized in that, The acquisition of the leaked flow specifically includes: The leakage flow rate is obtained using the following formula: ； in, For leakage flow; K g C is the correction factor for the flared structure; where, when the pipe contains a 33° flared structure, the correction factor for the flared structure is taken as 1.13; d is the flow coefficient, representing the ratio of the actual flow rate of fluid passing through cracks and corrosion pits to the theoretical flow rate; A is the defect area; ρ mix ΔP is the density of the gas mixture; ΔP is the pressure difference between the inside and outside of the pipe.

3. The method for safety assessment of hydrogen-blended natural gas pipeline leakage as described in claim 1, characterized in that, The process involves determining the lower explosive limit based on the hydrogen gas fraction within the hydrogen-blended natural gas pipeline and the hydrogen blending ratio, and then determining the safe concentration threshold based on the lower explosive limit. This process specifically includes: Based on the obtained hydrogen gas integral and the hydrogen doping ratio, the lower explosive limit is obtained using the following formula: ； in, yH2 is the lower explosive limit; yH2 is the hydrogen gas integral number, representing the ratio of hydrogen volume in natural gas to the total volume of natural gas, with a value range of 0-30%; 4.0 is the reference value for the lower explosive limit of pure hydrogen; 1.5 is the hydrogen blending ratio coefficient. Based on the lower explosive limit, the safe concentration threshold is obtained using the following formula: in, For safe concentration thresholds, k This is for the safety factor.

4. The method for safety assessment of hydrogen-blended natural gas pipeline leakage as described in claim 1, characterized in that, The gas characteristic parameters are generated by calling the NIST property database.

5. A safety assessment system for leaks in hydrogen-blended natural gas pipelines, characterized in that, include: The flared structure correction coefficient determination module is used to obtain the defect area, crack size, and corrosion pit depth of the natural gas pipeline under test. Based on the crack size and corrosion pit depth, the flow rate of the actual fluid passing through the crack and corrosion pit is determined respectively. Based on the obtained tilt angle of the vent pipe of the hydrogen-blended natural gas pipeline, the flared structure correction coefficient is determined. The leakage flow rate determination module is used to determine the corresponding leakage flow rate based on the defect area, the actual flow rate of fluid passing through cracks and corrosion pits, and the flared structure correction coefficient. The safety assessment module is used to perform multi-scale computational fluid dynamics (CFD) simulations based on the leakage flow rate and the gas characteristic parameters obtained under the current hydrogen blending ratio, to determine the simulation results of the hydrogen concentration field distribution; based on the obtained hydrogen gas integral number in the hydrogen-blended natural gas pipeline and in combination with the hydrogen blending ratio, to determine the lower explosive limit, and based on the lower explosive limit, to determine the safe concentration threshold; when the simulation results of the hydrogen concentration field distribution are greater than or equal to the safe concentration threshold, a risk warning is issued.

6. A computer device, characterized in that, It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the hydrogen-blended natural gas pipeline leakage safety assessment method according to any one of claims 1-4.

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