Calculation method for calculating transportation difference of natural gas pipeline

Abstract

The invention discloses a calculation method for calculating the transportation difference of a natural gas pipeline, which is characterized in that an original calculation mode based on the volume is upgraded into a calorific value calculation mode, a unit calorific value is added into the volume, and the transportation difference is determined according to a calorific value unification rule, the amount of entering heat and the amount of exiting heat except for bottom gas laying. And the heat of the natural gas is more accurately metered by taking the nitrogen content as an auxiliary means, so that the transportation difference of the natural gas pipeline is accurately calculated. The calorific value calculation method is not influenced by external temperature and pressure, and the nitrogen content is only increased but not reduced under accurate measurement, so that the pipeline natural gas transportation difference is accurately measured and calculated, and metering equipment runs more accurately.

Description

Technical Field

[0001] This invention relates to the field of oil and gas pipeline technology, and specifically to a method for calculating the transmission loss of natural gas pipelines. Background Technology

[0002] Natural gas pipeline transmission loss is the difference between the changes in gas input and output and gas inventory in a pipeline caused by metering errors, pipeline leaks, and venting. It is commonly referred to as "pipeline transmission loss" or simply "transmission loss". Natural gas pipeline transmission loss refers to the difference between the total input (including gas extraction), changes in gas inventory, and the total sales (including gas injection), and the amount of gas consumed by the pipeline within a certain statistical period, under standard reference conditions (101.325 kPa and 293.15 K in China).

[0003] The formula for calculating transmission loss is: △Q1=Qe+Qs1-Qo-Qs2; where: △Q1--pipeline transmission loss under standard reference conditions, m3; Qe--total input metering under standard reference conditions (including gas intake from gas storage facilities), m3; Qs1--initial pipeline inventory under standard reference conditions, m3; Qo--total output metering under standard reference conditions (including gas sales, gas consumption, and gas injection into gas storage facilities), m3; Qs2--final pipeline inventory under standard reference conditions, m3.

[0004] The assessment of pipeline loss management is generally conducted using the pipeline loss rate. The natural gas pipeline loss rate refers to the percentage of pipeline loss to the sum of total input and pipeline inventory changes within a certain statistical period under standard reference conditions. Its calculation formula is: Qr=△Q1 / (Qe+Qs1)*100%; where: Qr--pipeline loss rate (abbreviated as loss rate).

[0005] All values ​​in the formula are based on natural gas volume. Pipeline storage is greatly affected by the temperature, pressure, and composition of the natural gas within the pipeline, and will fluctuate in real time without accurate measurement methods. For example, even with a valve closed and pressure maintained on a section of natural gas under completely leak-free conditions, changes in temperature and pressure will still cause changes in the natural gas storage within the pipeline. When the pipeline's physical capacity and the natural gas storage are large, this can significantly interfere with the accurate calculation of transmission differentials. This calculation method needs improvement to more accurately calculate natural gas transmission differentials. Summary of the Invention

[0006] The purpose of this invention is to provide a method for calculating the transmission difference of natural gas pipelines. This method uses calorific value instead of volume to calculate the transmission difference of natural gas pipelines, with nitrogen content as an auxiliary factor, and uses dual-line metering to accurately measure the transmission difference of pipelines.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention provides a method for calculating the transmission loss of natural gas pipelines, characterized by the following steps:

[0009] Step 1: Convert all the volume of natural gas in the formula for calculating the transmission loss and natural gas pipeline transmission loss rate into the energy E of natural gas, that is, E = Q * q, where q is the unit calorific value of natural gas at a certain time, which can be measured by a gas chromatograph.

[0010] Step 2: In practical applications, the differential calculation data is obtained from the flow computer. The pipe inventory in a certain pipeline section is the heat measured by the flow computer during natural gas replacement, and the pipe inventory is E. s =E1-E2, where E1 is the energy of natural gas entering the pipeline, and E2 is the energy of natural gas distributed and output; therefore, E s It will be unaffected by changes in pressure and temperature in natural gas, and there is no need to use average components to estimate the compressibility factor, thus resulting in more accurate measurement;

[0011] Step 3: Verify the accuracy of the unit calorific value. Except for nitrogen, all gases in liquefied natural gas (LNG) are combustible hydrocarbon compounds. The accuracy of the unit calorific value can be verified by calculating the nitrogen content in natural gas. When the total nitrogen content increases, the total calorific value will definitely decrease. In a closed natural gas pipeline, the nitrogen content in natural gas remains unchanged. Due to the need for maintenance and replacement, the nitrogen content will increase. Therefore, the nitrogen content in natural gas will only increase and will not decrease.

[0012] The beneficial effects of this invention are as follows: the method of this invention eliminates the volume measurement method and uses natural gas heat measurement instead, which can overcome the changes in pipeline storage caused by temperature, pressure and composition, and better meet the needs of the natural gas industry.

[0013] The calorific value calculation method of this invention is not affected by external temperature and pressure. Under accurate measurement, the nitrogen content will only increase and not decrease, thereby accurately calculating the pipeline natural gas transmission difference and making the metering equipment operate more accurately. Detailed Implementation

[0014] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1

[0016] A method for calculating the transmission loss of natural gas pipelines includes the following steps:

[0017] Step 1: Convert all the volume of natural gas in the formula for calculating the transmission loss and natural gas pipeline transmission loss rate into the energy E of natural gas, that is, E = Q * q, where q is the unit calorific value of natural gas at a certain time, which can be measured by a gas chromatograph.

[0018] Step 2: In practical applications, the differential calculation data is obtained from the flow computer. The pipe inventory in a certain pipeline section is the heat measured by the flow computer during natural gas replacement, and the pipe inventory is E. s =E1-E2, where E1 is the energy of natural gas entering the pipeline, and E2 is the energy of natural gas distributed and output; therefore, E s It will be unaffected by changes in pressure and temperature in natural gas, and there is no need to use average components to estimate the compressibility factor, thus resulting in more accurate measurement;

[0019] Step 3: Verify the accuracy of the unit calorific value. Except for nitrogen, all gases in liquefied natural gas (LNG) are combustible hydrocarbon compounds. The accuracy of the unit calorific value can be verified by calculating the nitrogen content in natural gas. When the total nitrogen content increases, the total calorific value will definitely decrease. In a closed natural gas pipeline, the nitrogen content in natural gas remains unchanged. Due to the need for maintenance and replacement, the nitrogen content will increase. Therefore, the nitrogen content in natural gas will only increase and will not decrease.

[0020] Application examples:

[0021] 1. A natural gas pipeline under the jurisdiction of Guangdong Provincial Pipeline Company of China National Pipeline Network Corporation is over 500 kilometers long, with one intake point and several distribution points. It is mainly divided into two parts: 315 kilometers from west to east and 172 kilometers from south to north, with the LNG receiving terminal intake point in between. The daily intake is 13 million cubic meters, with the eastern section producing 20,000 cubic meters per day. The vast majority of the natural gas is distributed from south to north. The total natural gas pipeline capacity is 20 million Nm3. Due to the insufficient gas flow from west to east, the pipeline is shut off. However, daily fluctuations in natural gas pressure and temperature still cause significant variations in the pipeline capacity, affecting the calculation of the overall regional transmission difference.

[0022] On November 5, 2023, with the westbound pipeline valve closed, a daily gas deficit of 590,000 cubic meters occurred. This was because the methane content of the natural gas in the pipeline increased from 93% to 99% that day. The entire pipeline system was calculated based on 99%, leading to a higher compressibility factor and an underestimation of the natural gas volume in the entire pipeline. This problem can be avoided by using a calorific value. After the valve is closed, the calorific value of the natural gas in the pipeline is a fixed value on the flowmeter and will not change due to other conditions. All values ​​are taken from the flowmeter, eliminating the need to estimate the volume of natural gas in the pipeline, effectively reducing calculation errors related to transmission discrepancies.

[0023] After calculating the transmission difference through heat calculation, subtract the total nitrogen content of all distribution points from the total nitrogen content of the natural gas intake (the value can be found in the gas chromatograph analysis results). If the result is positive and the deviation rate is similar, the transmission difference is accurate and the equipment is operating well. If the result is negative or the deviation is large, further investigation is required.

[0024] 2. A certain LNG receiving terminal of CNOOC Gas & Power Group Co., Ltd. has several LNG storage tanks. Natural gas is liquefied in the tanks but gaseous when transported to the natural gas pipeline network. The conversion between these two states is cumbersome. If heat is used as the calculation method, no conversion is needed, and the transmission difference can be directly calculated, as shown in the table below.

[0025]

[0026] By starting with the differences in calculation results, a minor anomaly in the amount of gas transferred out for settlement on a certain day can be found, which may have caused the deviation. This method can effectively find anomalies in metering equipment or trade settlement, and greatly promotes the refined management of the natural gas industry.

[0027] The two cases above illustrate a novel method for calculating natural gas pipeline transmission differentials, using heat as the primary means and nitrogen quantity as an auxiliary method. This method can effectively identify any anomalies or defects in the metering equipment used in natural gas operations, and effectively control the overall efficiency and safety of natural gas operations. The prerequisite for using this calculation method is a thorough understanding of the overall situation of the operating area and a deep understanding of the conversion of various physical properties of natural gas. While the patent description cannot fully elaborate on all aspects, it provides a direction for further refinement and exploration of this method through meticulous operational practice, leading to further advancements in natural gas metering technology.

[0028] The method of this invention upgrades the original volume-based calculation method to a calorific value calculation method. It adds the unit calorific value to the volume, and except for the bottom gas, it uses the unified calorific value rule to determine the transmission difference based on the amount of heat entering and leaving the pipeline. This method is not affected by the temperature and pressure of the pipeline. Furthermore, it uses nitrogen content as an auxiliary means to more accurately measure the heat of natural gas, thereby achieving accurate calculation of the transmission difference of natural gas pipelines.

[0029] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method of calculating a natural gas pipeline delivery discrepancy, the method comprising: Comprising the following steps: Step 1: convert the volume of natural gas in the formula for calculating the transmission loss rate of natural gas pipeline into energy E, i.e., E=Q*q, q is the unit heat value of natural gas at a certain time, which can be measured by a gas chromatograph; Step 2: in practical application, the transmission loss calculation data are obtained from the flow computer, and the pipe storage in a certain pipe section is then replaced by natural gas, the heat measured in the flow computer, and the pipe storage in the pipeline is E s =E1-E2, E1 is the energy of natural gas entering the pipeline, and E2 is the energy of natural gas output in distribution; then E s It is not affected by the changes of pressure and temperature in natural gas, and it is not necessary to estimate the compression factor by averaging the components, so as to more accurately measure; Step 3: verify the accuracy of the unit heat value, the gas in liquefied natural gas (LNG) is a combustible compound of hydrocarbon except nitrogen, and the accuracy of the unit heat value can be verified by measuring the nitrogen content in natural gas, when the total nitrogen content increases, the total heat value must decrease, and the nitrogen content in the closed natural gas pipeline is constant, and the nitrogen content will increase due to the need for maintenance replacement, so the nitrogen content in natural gas will only increase and not decrease.

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