Non-isothermal gas pipeline leakage monitoring technology! Sichuan Provincial Key Discipline Construction Project, No .: KaW / Zhang Hongbing, Li Changjun Southwest Petroleum Institute, Chengdu Road, Sichuan, leaked. Establishing a pipeline real-time leak monitoring system can minimize economic losses and environmental pollution. The article introduces the research results of leak monitoring of unequal-temperature gas pipelines based on the transient mathematical model of the pipeline: mathematical model of leak monitoring, principle of leak monitoring, and method of pipeline leak location. Tests show that this technology is a highly feasible method for gas pipeline leak detection.
Pipeline transportation has the advantages of easy management and control, low cost and high safety, and is widely used in the transportation of oil and gas.
However, with the extension of the age of the pipeline, corrosion, abrasion and some human factors have caused pipeline leakage accidents. This not only affects the normal operation of the pipeline, causes waste of resources, but also pollutes the environment and threatens human life and property. Therefore, it is very important to study the real-time diagnosis technology of gas pipeline leakage faults, quickly find the leakage accidents and accurately locate them.
With the continuous development of computer technology and the establishment of oil and gas pipeline systems, various leak detection technologies based on software systems have also been continuously developed, such as mass balance method, pressure and flow signal monitoring method and transient model method. This paper introduces the research results of real-time pipeline leakage monitoring based on the transient mathematical model of the non-isothermal gas pipeline, and the model is solved by the characteristic line method.
Mathematical model of leakage monitoring The flow of gas in the pipeline follows the unsteady flow of one element, which must meet the laws of conservation of mass, momentum and energy. Therefore, the continuity equation, momentum equation and energy equation of natural gas flow can be established according to fluid mechanics and thermodynamics. These equations describe the relationship between fluid pressure, temperature, flow, etc. in the construction period of petroleum engineering-gas density-time variable-gas flow rate-variable along the tube length-gas pressure in the pipeline-gravity acceleration-the pipeline and The inclination angle between the horizontal planes—hydraulic friction coefficient; —the inner diameter of the pipeline—the enthalpy of the gas—the total heat transfer coefficient of the pipeline—the temperature of the gas in the pipeline—the characteristics of the hyperbolic partial differential equation system composed of the equations considered by the temperature of the pipeline buried depth The characteristic line equations describing the transient flow of the gas pipeline are obtained: the left characteristic line equation, the right characteristic line equation, the temperature characteristic line equation,-gas velocity-gas constant pressure specific heat-gas compression factor.
The principle of leakage monitoring can be used to solve the equation by the explicit characteristic line method, that is, the partial differential equation is converted into an ordinary differential equation along different characteristic line directions, but in order to ensure the stability and convergence of the solution, it must be satisfied! , The difference format is shown in the figure.
We can use point parameters to find point parameters. The establishment of the characteristic finite difference equation is relatively intuitive, and the solution is easy to implement. The calculation using the explicit characteristic difference method will be satisfactory. This is mainly because the calculation time of this method is quite small, the characteristic line is short and it is close to a straight line, and the establishment of the difference The assumptions in the equation are consistent.
Using the method described above, divide the pipeline into segments. As shown in the figure, use the collected pipeline starting data pressure, temperature, flow and layer transient simulation data to first calculate the point time layer data, then the point time layer data, ... until the time layer, at this point, the data preparation for the leak detection at the starting point is completed. In the same way, using the gas data at the end of the pipeline, the characteristic line differential network volume end of the end point to the starting point can be established to prepare the data from the end point to the starting point. At this time, the simulation curves of the entire pipeline from the start point to the end point and the end point to the start point can be obtained respectively.
The pipeline system is used to collect the data obtained from both ends of the pipeline in real time, and the simulation of the pipeline from the start point to the end point and the end point to the start point is performed respectively. Compare the end point parameter obtained by the starting point parameter simulation with the actual measured parameter value or the end point parameter obtained by the end point parameter simulation and the measured parameter value. When one or more of the differences exceeds the threshold, it can be determined that the pipeline has occurred Leakage is determined by the shortest time at which the leak is detected. Among them, the time for the disturbance generated by the leak to reach the end of the pipeline, the time for the disturbance to reach the start of the pipeline, and the time for the entropy change process to reach the end of the pipeline.
However, during the operation of the pipeline, it is inevitable to start and stop the compressor, close the valve, or change the opening of the valve. The parameters of the pipeline start and end points will momentarily fluctuate and the monitoring data of the start and end points will occur. If the difference from the measured data exceeds the threshold, the system will issue an alarm signal. In order to eliminate or reduce false alarms in this situation, we do not consider the alarms that occur when the disturbance caused by the change operation propagates to the first and last time intervals.
After the leak location system finds the alarm, it will locate the leak point according to the real-time monitoring curve. Assuming that a leakage accident occurs from the beginning of the pipeline, after a certain period of time, its disturbance will be transmitted to both ends of the pipeline. The monitoring curve is shown in the figure. The straight line is the square distribution of the pressure across the pipeline when no leakage occurs. The straight line is the pipeline pressure distribution obtained from the front-to-back leakage monitoring of the pipeline using the starting point boundary conditions after the leakage occurs.
The simulation result to the section is close to the actual situation of the pipeline operation, and the simulation result to the section deviates from the actual situation, and the farther away from the location, the greater the degree of deviation; Similarly, the pipeline end operating parameters are used as boundary conditions Carry out the simulation from back to front, as shown by the straight line, the simulation result to the section is close to the actual situation of pipeline operation.
To the paragraph is wrong. In this way, the straight line will intersect at the point, and at this time, it can be determined that the pipeline corresponding to the point has leaked. The positioning accuracy depends on the distance step of the pipe section. You can improve the positioning accuracy by reducing the distance step of the pipe section, but you cannot reduce the distance step of the pipe section without limit. Generally, the pipe length is sufficient.
Example The long wall thickness of a gas pipeline in Sichuan is 5 '', the operating pressure! . 10! 9. A leakage point was artificially created at the end temperature. The monitoring software sends out a leak alarm signal afterwards, and then locates the leak everywhere, with an error of. 0: /.
Conclusion The visual monitoring software compiled with the leak monitoring technology introduced in this article has the following characteristics: it can accurately propagate the leak signal to the start and end points.
The two simulations of the pipeline from the starting point to the end point and from the end point to the starting point can accurately and timely determine the location and amount of leakage.
The gas pipeline leakage monitoring system can stably and reliably monitor the operation of the gas pipeline, display the real-time operation data of the pipeline, and combine with the database system to facilitate query and analysis of historical operation data.
On the basis of the gas pipeline leakage monitoring system, it can be targeted for improvement, and can be developed into other pipeline leakage monitoring systems such as urban gas pipeline networks, with a wide range of applications.
However, this monitoring method is only applicable to dry gas pipeline transportation, and there is only one leakage point at a time. For wet natural gas pipeline transportation, the gas phase and liquid phase must be considered separately to establish a mathematical model; Point leakage or the situation where a leakage occurs after the disturbance has not been transmitted to both ends after a leakage occurs is not applicable, and the monitoring method needs to be changed.
= Li Changjun0 natural gas pipeline transportation = 70 Beijing: Petroleum Industry Press, ... 0 Zhang Hongbing graduated from Jiangsu Petrochemical College and is currently a Ph.D. candidate in oil and gas storage and transportation engineering of Southwest Petroleum Institute, mainly engaged in the research of pipeline network simulation and accident diagnosis jobs.
Zhang Hongbing et al: Leak Monitoring Technology for Unequal Temperature Gas Transmission Pipeline
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