A natural gas pipeline online simulation ground temperature calculation method

Abstract

The application discloses a kind of natural gas pipeline online simulation ground temperature calculation method, comprising the following steps: S1, data acquisition;S2, calculate simulated ground temperature approximation;S3, calculate Joule-Thomson effect coefficient;S4, calculate the temperature drop correction value caused by pressure drop;S5, calculate the simulation ground temperature obtained after correction.It is characterized by: by the arithmetic mean of the inlet temperature of multiple stations and users near the end of the pipeline as the method of pipeline simulation ground temperature, the problem that natural gas pipeline simulation ground temperature cannot be obtained is solved;At the same time, inspired by the Joule-Thomson effect, the temperature drop caused by the pressure drop of natural gas flow in the pipeline is quantitatively calculated, and the value is used to correct the calculated ground temperature of the natural gas pipeline, making up for the error between the average ground temperature and the true ground temperature.The application has clear calculation process, strong operability, small calculation amount, high precision, and is convenient for personnel in the technical field and natural gas pipeline simulation development and use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas pipeline simulation, in particular to a natural gas pipeline online simulation ground temperature calculation method. BACKGROUND

[0002] The transportation of natural gas mainly relies on a huge pipeline network, and the safety, stability and economy of the pipeline are key factors for the sustainable development of the natural gas industry. The natural gas pipeline online simulation method uses computer technology to simulate the real-time hydraulic, thermal and equipment operation state of the pipeline, and truly reproduces the flow law in the pipeline, thereby providing protection for the safe operation of the pipeline.

[0003] The ground temperature varies due to factors such as seasonal changes, geographical location, soil type and humidity, and the fluctuation of the ground temperature indirectly affects the transportation efficiency of the natural gas through heat exchange with the natural gas in the pipeline, thereby affecting the simulation calculation accuracy of the natural gas pipeline. The traditional ground temperature measurement and calculation method has many limitations, such as limited measurement points, poor real-time performance, high calculation complexity and difficult data acquisition, etc. These problems result in that the natural gas pipeline online simulation system cannot obtain accurate ground temperature data.

[0004] Since the natural gas exchanges heat with the outside through the pipe wall when flowing, the temperature of the natural gas will infinitely approach the ground temperature when the pipeline is far enough. Therefore, the commonly used method at present is to take the average value of the natural gas inlet temperature at multiple stations and users near the end of the pipeline as the approximate ground temperature value for the natural gas simulation of the region. However, in actual operation, there is an error of 1-2℃ between the actually measured ground temperature data and the calculated ground temperature data, and at present, the error is usually manually removed by adding a constant based on personal experience, but the accuracy of this method is poor, and accurate ground temperature data cannot be obtained. SUMMARY

[0005] The present application aims to provide a natural gas pipeline online simulation ground temperature calculation method, which can reflect the ground temperature change along the natural gas pipeline in real time, simply and accurately, and has important significance for ensuring the safe operation of the pipeline, optimizing the pipeline design and maintenance.

[0006] The present application is implemented by the following technical solutions:

[0007] A natural gas pipeline online simulation ground temperature calculation method, comprising the following steps:

[0008] S1, data acquisition: obtaining the natural gas inlet temperature at each station and user near the end of the pipeline through the SCADA system;

[0009] S2, calculating the simulated ground temperature approximation value: calculating the simulated ground temperature approximation value of the pipeline online simulation system by using the natural gas inlet temperature obtained in the data acquisition of S1;

[0010] S3, calculating the Joule-Thomson effect coefficient;

[0011] S4, calculating the temperature drop correction value caused by pressure drop: taking the Joule-Thomson effect coefficient calculated in S3 as the temperature drop coefficient caused by pipeline pressure drop, and calculating the temperature drop correction value caused by pressure drop;

[0012] S5, calculating the simulated ground temperature after correction: correcting the simulated ground temperature approximation value obtained in S2 by using the temperature drop correction value caused by pressure drop obtained in S4 to obtain the simulated ground temperature T0.

[0013] Further, the method of S2, calculating the simulated ground temperature approximation value, is as follows:

[0014] Arithmetic average is performed on the natural gas inlet temperature obtained in the data acquisition of S1, and the arithmetic average is taken as the approximation value T1 of the pipeline online simulation system ground temperature calculation simulation;

[0015]

[0016] In formula (1), T1 is the simulated ground temperature approximation value, ℃; T Zi is the natural gas inlet temperature at the end of the pipeline, ℃; n is the number of obtained natural gas inlet temperature data;

[0017] Further, the formula of S4, calculating the temperature drop correction value caused by pressure drop, is as follows:

[0018]

[0019] In formula (2), T2 is the temperature drop correction value caused by pressure drop, ℃; p Q is the natural gas pipeline starting pressure, MPa; p z is the natural gas pipeline terminal pressure, MPa; L is the pipeline length, m; ζ is the temperature drop effect coefficient, ℃ / MPa; a is the calculation coefficient, and the expression is shown in formula (3):

[0020]

[0021] In formula (3), K is the total heat transfer coefficient of the pipeline, W / (m 2 gK); D is the pipeline outer diameter, m; M is the gas mass flow, kg / s; c p is the gas mass constant pressure heat capacity, J / (kggK).

[0022] Further, the formula of S5, calculating the simulated ground temperature after correction, is as follows:

[0023] T0 = T1 + T2 (4)

[0024] In formula (4), T0 is the corrected simulated ground temperature, ℃.

[0025] In the present application, the specific method for calculating the Joule-Thomson effect coefficient S3 is as follows:

[0026] Since the process of natural gas flowing in the pipeline can be regarded as an isenthalpic flow process, the Joule-Thomson effect coefficient D i of natural gas is as shown in the following formula (5):

[0027]

[0028] In formula (5), D i is the Joule-Thomson effect coefficient, ℃ / MPa; T is the temperature of the gas, ℃; p is the pressure of the gas, Pa; and h is the enthalpy of the gas, J / kg.

[0029] Based on the basic thermodynamic differential equation, the complete differential equation of entropy, the Maxwell relation and the constant-pressure specific heat thermodynamic equation, as shown in the following formula (6) to formula (9), the dh equation with temperature and pressure as independent variables, i.e., the following formula (9), can be obtained.

[0030] dh = Tds + vdp (6)

[0031]

[0032] In the formula, s is the entropy of the gas, kJ / (kg gK), v is the flow rate of the gas, m / s; C p is the specific heat capacity of the gas at constant pressure, J / (kg gK).

[0033] According to the physical meaning of the temperature drop effect coefficient caused by pressure drop and the constraint of isenthalpic change of natural gas flow, the expression of the Joule-Thomson effect coefficient D i is as shown in the following formula (10):

[0034]

[0035] In formula (10), σ is the thermal expansion coefficient, K -1 , and its calculation formula is as shown in the following formula (11):

[0036]

[0037] Based on the thermodynamic relation of p-V-T, as shown in formula (12), introducing formula (11) and rearranging it into formula (13), the expression format of the more commonly used Joule-Thomson effect coefficient D i can be obtained.

[0038]

[0039]

[0040] Based on the BWRS state equation, the following can be obtained and As follows formula (14) and formula (15).

[0041]

[0042] In the formula, all parameters can be solved from the BWRS state equation, and the corresponding Joule-Thomson effect coefficient can be solved by substituting formula (14) and formula (15) into formula (13).

[0043] The temperature drop effect coefficient ζ used in the application is the Joule-Thomson effect coefficient D calculated in the foregoing under the same pressure and temperature conditions i , and here ζ is used only to represent the temperature drop coefficient caused by the pressure drop along the pipeline.

[0044] Advantages of the application:

[0045] The application solves the problem that the ground temperature of the pipeline area is not easy to obtain, resulting in the lack of key parameters of the simulation system by taking the average value of the inlet temperature of the station near the end of the natural gas pipeline or the user as the pipeline simulation ground temperature.

[0046] Meanwhile, the method is inspired by the Joule-Thomson effect, and the temperature drop caused by the pressure drop of the natural gas flow in the pipeline is quantitatively calculated, and the value is used to correct the ground temperature of the natural gas pipeline, making up for the error between the average ground temperature and the real ground temperature, making the simulation system calculation temperature more close to the real ground temperature, and improving the ground temperature calculation precision of the simulation system.

[0047] The application has clear calculation process, strong operability, small calculation amount, high precision, and is convenient for personnel in the technical field and development and use of natural gas pipeline simulation. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 A natural gas pipeline online simulation ground temperature calculation method flowchart based on Joule-Thomson effect compensation is provided for the application.

[0049] Figure 2 A broken line change graph of the ten-hour measured ground temperature, average ground temperature and calculated ground temperature is provided for the calculation case of the application.

[0050] Figure 3 A error value comparison columnar chart of the ten-hour calculated temperature before and after correction is provided for the calculation case of the application. DETAILED DESCRIPTION

[0051] As Figure 1 shown, the present application provides a natural gas pipeline online simulation ground temperature calculation method based on Joule-Thomson effect compensation, which calculates the measured inlet temperature of a gas pipeline for 10 consecutive hours, the end station and four user places, which is an embodiment, the gas pipeline is 98.7km long, the starting pressure of the gas pipeline is 8.05MPa, and the end pressure is 7.20MPa. The calculated ground temperature is compared with the measured ground temperature, which mainly includes the following steps:

[0052] S1, data acquisition: obtaining the natural gas inlet temperature at each station near the end of the pipeline and the user through the SCADA system; obtaining the natural gas inlet temperature data obtained by the SCADA system every hour as shown in Table 1.

[0053] Table 1: Inlet temperature of each station for 10 hours and measured ground temperature (unit ℃)

[0054]

[0055]

[0056] S2, calculating the simulated ground temperature approximation: calculating the arithmetic mean of the natural gas inlet temperature obtained in S1, data acquisition, and taking it as the approximation T1 of the pipeline online simulation system ground temperature simulation, and the calculation formula is shown as formula (1).

[0057]

[0058] In formula (1), T1 is the simulated ground temperature approximation, ℃; T Zi is the natural gas inlet temperature at the end of the pipeline, ℃; n is the number of obtained natural gas inlet temperature data;

[0059] In this embodiment, T Zi is the inlet temperature value of five points at the same time at the end station and four users, and the calculation according to formula (1) can obtain the simulation ground temperature approximation result for 10 consecutive hours as shown in Table 2.

[0060] Table 2: Ten-hour average simulation ground temperature approximation T1 (unit ℃)

[0061]

[0062] S3, calculating the Joule-Thomson effect coefficient;

[0063] The calculation formula of the Joule-Thomson effect coefficient D i is shown as formula (13).

[0064]

[0065] Based on the existing pipeline data, and based on the BWRS state equation, the result is substituted into equation (13) to solve, that is, the value of D i in this case, the Joule-Thomson effect coefficient D i should be taken as 3.0.

[0066] S4, calculate the temperature drop correction value caused by pressure drop: introduce the factors such as the starting and ending pressure of the pipeline and the pipe length, and take the Joule-Thomson effect coefficient obtained by solving S3 as the temperature drop coefficient caused by the pressure drop of the pipeline, calculate the temperature drop correction value T2 caused by the pressure drop, and the calculation relationship is shown in equation (2).

[0067]

[0068] In equation (2), T2 is the temperature drop correction value caused by pressure drop, ℃; p Q is the starting pressure of the natural gas pipeline, MPa; p z is the ending pressure of the natural gas pipeline, MPa; L is the length of the pipeline, m; ζ is the temperature drop effect coefficient, ℃ / MPa; a is the calculation coefficient, and the expression is shown in equation (3):

[0069]

[0070] In equation (3), K is the total heat transfer coefficient of the pipeline, W / (m 2 gK); D is the outer diameter of the pipeline, m; M is the mass flow of gas, kg / s; c p is the specific heat capacity of gas at constant pressure, J / (kggK). Based on the existing pipeline operation data, substitute into equation (2) to calculate the temperature drop correction value data caused by pressure drop in the pipeline, which is shown in Table 3.

[0071] Table 3 Temperature drop value T2 caused by pressure drop based on ten hours (unit ℃)

[0072]

[0073] S5, calculate the simulated ground temperature after correction: use the temperature drop correction value T2 caused by pressure drop obtained in S4 to correct the approximate simulated ground temperature T1 obtained in S2 to obtain the simulated ground temperature T0.

[0074]

[0075] In equation (4), T0 is the simulated ground temperature after correction, ℃.

[0076] Substitute T1 and T2 calculated in steps 2 and 4 into equation (4) respectively to obtain the corrected calculated ground temperature T0, and the specific calculated ground temperature value is shown in Table 4.

[0077] Table 4 ten hours calculated simulation ground temperature T0 (unit ℃)

[0078]

[0079] As Figure 2 shown by the ten hours average temperature, calculated temperature and measured ground temperature, the calculated ground temperature after compensation by Joule-Thomson effect is closer to the measured ground temperature.

[0080] As Figure 3 shown, after the pipeline simulation ground temperature is corrected by Joule-Thomson effect, the ground temperature deviation is greatly reduced.

[0081] The natural gas pipeline online simulation ground temperature calculation method based on Joule-Thomson effect compensation provided by the present application has good calculation precision, solves the problem that the simulation system is difficult to obtain ground temperature data, and reduces the calculation error of the simulation system.

[0082] In the embodiment, the precision of the calculated ground temperature data is improved by 15% compared to the simulated ground temperature approximate value, and thus it can be seen that the present application can accurately simulate the real-time hydraulic, thermal and equipment operation state of the pipeline, and provides protection for the safe operation of the pipeline.

[0083] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for calculating in-line simulation ground temperature of a natural gas pipeline, characterized in that, Comprise the following steps: S1, data acquisition: through the SCADA system to obtain the natural gas inlet temperature of each station and user near the pipeline end; S2, calculating the simulated ground temperature approximation value: calculating the simulated ground temperature approximation value of the pipeline online simulation system by using the natural gas inlet temperature obtained in S1; wherein, the method for calculating the simulated ground temperature approximation value is as follows: taking the arithmetic average of the natural gas inlet temperature obtained in S1 as the approximation value of the ground temperature calculation simulation of the pipeline online simulation system : （1） In formula (1), is an approximate value of the ground temperature, ℃; is the natural gas inlet temperature at the end of the pipeline, ℃; is the number of obtained natural gas inlet temperature data; S3, calculate the Joule-Thomson effect coefficient; S4, calculate the temperature drop correction value caused by pressure drop: the Joule-Thomson effect coefficient calculated in S3 is taken as the temperature drop coefficient caused by pipeline pressure drop, and the temperature drop correction value caused by pressure drop is calculated; wherein the Joule-Thomson effect coefficient is determined based on the BWRS state equation; S5, calculating the simulated ground temperature after correction: the simulated ground temperature after correction is obtained by correcting the simulated ground temperature approximation value obtained in S2 by using the temperature drop correction value caused by the pressure drop obtained in S4 ; wherein, the formula for calculating the simulated ground temperature after correction is as follows: （4） In formula (4), is the corrected simulated ground temperature, ℃; is the approximate value of the simulated ground temperature, ℃; is the temperature drop correction value caused by pressure drop, ℃.

2. The method for calculating the ground temperature on-line in a natural gas pipeline according to claim 1, characterized in that, The formula of S4, calculating the temperature drop correction value caused by pressure drop, is as follows: （2） In formula (2), is a temperature drop correction value caused by pressure drop, ℃; is a natural gas pipeline starting pressure, MPa; is a natural gas pipeline ending pressure, MPa; L is a pipeline length, m; is a temperature drop effect coefficient, ℃ / MPa; a is a calculation coefficient, and an expression is shown in formula (3): （3） In formula (3), K is the total heat transfer coefficient of the pipe, W / (m 2 gK); D is the outer diameter of the pipe, m; M is the mass flow of the gas, kg / s; Cpgis the specific constant pressure heat capacity of the gas, J / (kg g K).

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