Natural gas pipeline on-line simulation ground temperature calculation method

Abstract

The invention discloses a natural gas pipeline on-line simulation ground temperature calculation method. The method comprises the following steps: S1, data acquisition; s2, calculating a simulated ground temperature approximate value; s3, calculating a Joule-Thomson effect coefficient; s4, calculating a temperature drop correction value caused by the pressure drop; and S5, calculating the simulated ground temperature obtained after correction. The method has the advantages that the problem that the natural gas pipeline analogue simulation ground temperature cannot be obtained is solved by taking the arithmetic average value of the inlet temperatures of a plurality of stations and users near the tail end of the pipeline as the pipeline analogue ground temperature; meanwhile, the method is inspired by the Joule-Thomson effect, the temperature drop caused by the pressure drop of natural gas flowing in the pipeline is quantitatively calculated, the value is used for correcting the calculated ground temperature of the natural gas pipeline, and the defect that errors often exist between the average ground temperature and the real ground temperature is overcome. The method is clear in calculation process, high in operability, small in calculation amount, high in precision and convenient for personnel in the technical field and natural gas pipeline analogue simulation development and use.

Description

Technical field:

[0001] The invention relates to the technical field of natural gas pipeline simulation, and in particular to a method for calculating geotemperature of a natural gas pipeline online simulation. Background technology:

[0002] The transportation of natural gas mainly depends 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 online simulation method of natural gas pipeline uses computer technology to simulate the real-time hydraulic, thermal and equipment operating status of the pipeline, truly reproduce the flow law in the pipeline, and provide guarantee for the safe operation of the pipeline.

[0003] Ground temperature varies due to seasonal changes, geographical location, soil type, humidity and other factors. The fluctuation of ground temperature will indirectly affect the transportation efficiency of natural gas through heat exchange with natural gas in the pipeline, and thus affect the accuracy of natural gas pipeline simulation calculation. Traditional ground temperature measurement and calculation methods have many limitations, such as limited measurement points, poor real-time performance, high calculation complexity and difficulty in data acquisition. These problems make it impossible for the natural gas pipeline online simulation system to obtain accurate ground temperature data.

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

[0005] The purpose of the present invention is to provide a method for calculating the geothermal temperature of a natural gas pipeline in an online simulation manner, which can reflect the geothermal changes along the natural gas pipeline in real time, simply and accurately, and is of great significance for ensuring the safe operation of the pipeline and optimizing the design and maintenance of the pipeline.

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

[0007] A method for calculating geothermal temperature of a natural gas pipeline online simulation includes the following steps:

[0008] S1. Data collection: The SCADA system is used to obtain the natural gas inlet temperature at each station near the end of the pipeline and at the user;

[0009] S2. Calculate the approximate ground temperature of the simulation: use the natural gas inlet temperature obtained in S1. data collection to calculate the approximate ground temperature simulated by the pipeline online simulation system;

[0010] S3. Calculate the Joule-Thomson effect coefficient;

[0011] S4. Calculate the temperature drop correction value caused by the pressure drop: use the Joule-Thomson effect coefficient calculated and solved in S3 as the temperature drop coefficient caused by the pipeline pressure drop to calculate the temperature drop correction value caused by the pressure drop;

[0012] S5. Calculate the corrected simulated ground temperature: Use the temperature drop correction value caused by the pressure drop obtained in S4 to correct the simulated ground temperature approximation obtained in S2 to obtain the simulated ground temperature T0.

[0013] Furthermore, the method of calculating the simulated ground temperature approximate value in S2 is as follows:

[0014] Take the arithmetic average of S1 and the natural gas inlet temperature obtained in data collection, and use it as the approximate value T1 of the geothermal calculation simulation of the pipeline online simulation system;

[0015]

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

[0017] Furthermore, the formula for calculating the temperature drop correction value caused by the pressure drop in S4 is as follows:

[0018]

[0019] In formula (2), T2 is the temperature drop correction value caused by pressure drop, °C; Q is the starting pressure of the natural gas pipeline, MPa; p z The terminal pressure of the natural gas pipeline, MPa; L is the pipeline length, m; ζ is the temperature drop effect coefficient, °C / MPa; a is the calculation coefficient, as 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 outer diameter of the pipe, m; M is the gas mass flow rate, kg / s; c p Heat capacity of gas mass at constant pressure, J / (kggK).

[0022] Furthermore, the formula for calculating the corrected simulated ground temperature in S5 is as follows:

[0023] T0=T1+T2(4)

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

[0025] In the present invention, S3, the specific method for calculating the Joule-Thomson effect coefficient 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 of natural gas D i 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; h is the enthalpy of the gas, J / kg.

[0029] Based on the basic thermodynamic differential equation, the complete differential equation of entropy, Maxwell's relations and the constant pressure specific heat thermodynamic equation, as shown in equations (6) to (9), the dh equation with temperature and pressure as independent variables can be obtained, that is, equation (9).

[0030] dh=Tds+vdp (6)

[0031]

[0032] Where s is the entropy of the gas, kJ / (kg gK), v is the flow rate of the gas, m / s; C p is the heat capacity of 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 equal enthalpy change of natural gas flow, the Joule-Thomson effect coefficient D can be obtained. i The expression of is shown in the following formula (10):

[0034]

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

[0036]

[0037] Based on the thermodynamic relationship of pVT, see formula (12), introduce formula (11) and rearrange it into formula (13), we can get the more commonly used Joule-Thomson effect coefficient D i The expression format of .

[0038]

[0039]

[0040] Based on the BWRS state equation, we can get and As shown in equations (14) and (15).

[0041]

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

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

[0044] Advantages of the present invention:

[0045] The present invention solves the problem that the ground temperature in the area where the pipeline is located is difficult to obtain, resulting in the loss of key parameters of the simulation system, by taking the average value of the station temperature near the end of the natural gas pipeline or the inlet temperature at the user as the pipeline simulation ground temperature.

[0046] At the same time, inspired by the Joule-Thomson effect, this method quantitatively calculates the temperature drop caused by the pressure drop of natural gas flowing in the pipeline, and uses this value to correct the calculated ground temperature of the natural gas pipeline, making up for the error that often exists between the average ground temperature and the actual ground temperature, making the temperature calculated by the simulation system closer to the actual ground temperature, and improving the ground temperature calculation accuracy of the simulation system.

[0047] The present invention has clear calculation process, strong operability, small calculation amount and high precision, which is convenient for personnel in this technical field and for natural gas pipeline simulation development and use. Description of the drawings:

[0048] Figure 1 A flow chart of a method for calculating the online simulated ground temperature of a natural gas pipeline based on Joule-Thomson effect compensation provided by the present invention.

[0049] Figure 2 This is a line chart showing the changes in the ten-hour measured ground temperature, average ground temperature and calculated ground temperature for the calculation case provided by the present invention.

[0050] Figure 3 This is a bar chart comparing the error values ​​before and after the temperature correction for the calculation case provided by the present invention for ten hours. Specific implementation method:

[0051] like Figure 1 As shown, the present invention provides a method for calculating the geothermal online simulation of a natural gas pipeline based on Joule-Thomson effect compensation. The inlet temperature measured at the terminal and four users of a gas pipeline for 10 consecutive hours is calculated as an embodiment. The gas pipeline is 98.7 km long, the starting pressure of the gas pipeline is 8.05 MPa, and the terminal pressure is 7.20 MPa. The calculated geothermal temperature is compared with the measured geothermal temperature, which mainly includes the following steps:

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

[0053] Table 1: Entrance temperature and measured ground temperature at each station in ten hours (unit: °C)

[0054]

[0055]

[0056] S2. Calculate the approximate value of the simulated ground temperature: Take the arithmetic average of the natural gas inlet temperature obtained in the data collection using S1, and use it as the approximate value T1 of the ground temperature simulation of the pipeline online simulation system. The calculation formula is shown in formula (1).

[0057]

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

[0059] In this implementation, T Zi is the intake air temperature value at the same time at five points at the terminal and four users. According to formula (1), the approximate value of the simulated ground temperature for ten consecutive hours can be obtained as shown in Table 2.

[0060] Table 2 Approximate value of ten-hour average simulated ground temperature T1 (unit: °C)

[0061]

[0062] S3. Calculate the Joule-Thomson effect coefficient;

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

[0064]

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

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

[0067]

[0068] In formula (2), T2 is the temperature drop correction value caused by pressure drop, °C; Q is the starting pressure of the natural gas pipeline, MPa; p z The terminal pressure of the natural gas pipeline, MPa; L is the pipeline length, m; ζ is the temperature drop effect coefficient, °C / MPa; a is the calculation coefficient, as shown in formula (3):

[0069]

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

[0071] Table 3 Temperature drop value T2 (unit: °C) obtained based on pressure drop in ten hours

[0072]

[0073] S5. Calculate the corrected simulated ground temperature: Use the temperature drop correction value T2 caused by the pressure drop obtained in S4 to correct the simulated ground temperature approximation value T1 obtained in S2 to obtain the simulated ground temperature T0.

[0074]

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

[0076] Substituting T1 and T2 calculated in step 2 and step 4 into formula (4) respectively, the corrected calculated ground temperature T0 can be obtained. The specific calculated ground temperature values ​​are shown in Table 4.

[0077] Table 4 Ten-hour calculated simulated ground temperature T0 (unit: °C)

[0078]

[0079] like Figure 2 As shown, from the average temperature of ten hours, the calculated temperature and the measured ground temperature, it can be seen that the calculated ground temperature after compensation using the Joule-Thomson effect is closer to the measured ground temperature.

[0080] like Figure 3 As shown in the figure, after the Joule-Thomson effect was used to correct the simulated ground temperature of the pipeline, the ground temperature deviation was greatly reduced.

[0081] The method for calculating geothermal temperature of a natural gas pipeline online simulation based on Joule-Thomson effect compensation proposed by the present invention has good calculation accuracy, solves the problem that it is difficult for the simulation system to obtain geothermal data, and reduces the calculation error of the simulation system.

[0082] In this embodiment, the calculated geothermal data is 15% more accurate than the simulated geothermal approximation. This shows that the present invention can simulate the real-time hydraulic, thermal and equipment operating conditions of the pipeline more accurately, thus providing a guarantee for the safe operation of the pipeline.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calculating geothermal temperature of a natural gas pipeline online simulation, characterized in that: The following steps are involved: S1. Data collection: The SCADA system is used to obtain the natural gas inlet temperature at each station near the end of the pipeline and at the user; S2. Calculate the approximate ground temperature of the simulation: use the natural gas inlet temperature obtained in S1. data collection to calculate the approximate ground temperature simulated by the pipeline online simulation system; S3. Calculate the Joule-Thomson effect coefficient; S4. Calculate the temperature drop correction value caused by the pressure drop: use the Joule-Thomson effect coefficient calculated and solved in S3 as the temperature drop coefficient caused by the pipeline pressure drop to calculate the temperature drop correction value caused by the pressure drop; S5. Calculate the corrected simulated ground temperature: Use the temperature drop correction value caused by the pressure drop obtained in S4 to correct the simulated ground temperature approximation obtained in S2 to obtain the simulated ground temperature T0.

2. A method for calculating geothermal temperature of a natural gas pipeline online simulation according to claim 1, characterized in that: The method of calculating the approximate value of the simulated ground temperature in S2 is as follows: Take the arithmetic average of S1 and the natural gas inlet temperature obtained in data collection, and use it as the approximate value T1 of the geothermal calculation simulation of the pipeline online simulation system; In formula (1), T1 is the simulated ground temperature approximation, °C; T Zi is the natural gas inlet temperature at the end of the pipeline, ℃; n is the number of natural gas inlet temperature data obtained.

3. A method for calculating geothermal temperature of a natural gas pipeline online simulation according to claim 2, characterized in that: The formula for calculating the temperature drop correction value caused by the pressure drop in S4 is as follows: In formula (2), T2 is the temperature drop correction value caused by pressure drop, °C; Q is the starting pressure of the natural gas pipeline, MPa; p z The terminal pressure of the natural gas pipeline is MPa; L is the pipeline length, m; ζ is the temperature drop effect coefficient, °C / MPa; a is the calculation coefficient, and the expression is shown in formula (3): In formula (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 gas mass flow rate, kg / s; c p Heat capacity of gas mass at constant pressure, J / (kggK).

4. A method for calculating geothermal temperature of a natural gas pipeline online simulation according to claim 3, characterized in that: The formula for calculating the corrected simulated ground temperature in step S5 is as follows: T0=T1+T2=i=1n+ζ(4p)Q In formula (4), T0 is the simulated ground temperature after correction, ℃.

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