Gas hydrocarbon molecular weight and net heat value detection system and calculation method thereof

Abstract

The invention belongs to the technical field of ultrasonic flow meters, and particularly relates to a gas hydrocarbon molecular weight and net heat value detection system and a calculation method thereof.The gas hydrocarbon molecular weight and net heat value detection system comprises a mobile terminal, an ultrasonic flow meter, a data acquisition module, a temperature sensor, a pressure sensor and an ultrasonic transducer; the mobile terminal is connected with the data acquisition module through Bluetooth or a digital interface, and the data acquisition module is respectively connected with the ultrasonic flowmeter, the temperature sensor, the pressure sensor and the ultrasonic transducer; and the data acquisition module is integrated in the ultrasonic flowmeter. The method has the advantages that the hydrocarbon molecular weight in the natural gas is measured and estimated through the detection system with the flowmeter, the thermometer, the pressure gauge and the transducer as core function units, the net heat value of the gas is further calculated, and the hydrocarbon molecular weight is rapidly measured through the sound velocity, the temperature and the pressure of the natural gas; hydrocarbon molecular weight and net heat value data of the gas are rapidly obtained; the detection system is wide in application range, and installation cost and time can be saved.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrasonic flowmeters, and in particular relates to a gas carbon-hydrogen molecular weight and net calorific value detection system and a calculation method thereof. Background Art

[0002] At present, natural gas trade settlement mainly adopts volume measurement, that is, settlement is based on the volume of natural gas. However, this measurement method has limitations and cannot reflect the true value of natural gas. Natural gas from different origins and with different compositions may have very different energy contents. Secondly, the volume of natural gas will change with changes in temperature and pressure. Under different temperature and pressure conditions, the energy content represented by the same volume of natural gas will also be different. Therefore, the use of energy measurement for natural gas is more conducive to fair trade.

[0003] The main component of natural gas is methane, and it contains a small amount of ethane, propane, butane, and other hydrocarbons. Net Heating Value (NHV) is a key indicator for measuring fuel quality, focusing on the heat released when water vapor exists in liquid form after the fuel is burned. Compared with the gross calorific value (Higher Heating Value, HHV), HHV is the heat released when it is assumed that the water vapor in the combustion products exists completely in gaseous form. Taking hydrocarbon fuels as an example, if the water vapor generated during the combustion process changes from gas to liquid, it will release latent heat of vaporization. This part of the latent heat of vaporization is subtracted when calculating NHV, which more accurately reflects the actual available heat of the fuel.

[0004] At present, natural gas energy measurement is divided into direct measurement and indirect measurement. The indirect measurement method involves natural gas component analysis, which relies on chromatographs to determine the proportion of each component. This method has high accuracy, but the equipment is expensive and requires regular maintenance; the direct measurement method directly measures the heat released by natural gas combustion, but has high requirements for the combustion devices involved.

[0005] According to the speed of sound formula It can be seen that the actual gas sound velocity c will be affected by the gas molar mass M and the gas temperature and pressure, but since the volume fraction of the mixed gas is unknown, the conventional method cannot obtain the molecular weight information of the mixed gas. Summary of the invention

[0006] The purpose of the present invention is to provide a gas carbon and hydrogen molecular weight and net calorific value detection system and a calculation method thereof, which overcomes the shortcomings of the prior art, uses a detection system with a flow meter, a thermometer, a pressure gauge and a transducer as core functional units to measure and estimate the carbon and hydrogen molecular weight in natural gas, and further deduce the net calorific value of the gas, and quickly calculates the carbon and hydrogen molecular weight through the natural gas sound velocity, temperature and pressure, providing effective and fast reference data for testers, which helps testers to quickly conduct tests and find problems in time.

[0007] To achieve the above object, the present invention is implemented through the following technical solutions:

[0008] One of the technical solutions: A gas hydrocarbon molecular weight and net calorific value detection system includes a mobile terminal, an ultrasonic flow meter, a data acquisition module, a temperature sensor, a pressure sensor and an ultrasonic transducer. The mobile terminal is connected to the data acquisition module via Bluetooth or a digital interface. The data acquisition module is respectively connected to the ultrasonic flow meter, the temperature sensor, the pressure sensor and the ultrasonic transducer; the data acquisition module is integrated in the ultrasonic flow meter.

[0009] Furthermore, the ultrasonic transducer is placed in a box body, the top and left and right sides of the box body are covered with a stainless steel protective shell, and a high-strength magnet for rapid adsorption to a carbon steel natural gas pipeline is provided at the bottom of the box body; the temperature sensor and pressure sensor are both arranged in the natural gas pipeline.

[0010] Furthermore, the mobile terminal is an Android phone.

[0011] Furthermore, the model of the ultrasonic flowmeter is MT1600CL.

[0012] Furthermore, the model of the temperature sensor is MT1600CL-T; the model of the pressure sensor is MT1600CL-P; and the model of the ultrasonic transducer is MT1600CL-H.

[0013] Technical solution 2: A calculation method for a gas carbon-hydrogen molecular weight and net calorific value detection system, which uses a linear programming method to find the range of carbon-hydrogen molecular weights, and calculates the carbon-hydrogen molecular weights by compensating the previous methane content data of the gas field, and finally calculates the net calorific value of the natural gas through the corresponding hydrocarbon content information after compensation. The specific calculation steps are as follows:

[0014] 1) Obtain the natural gas sound velocity, temperature, and pressure in the current environment; compensate the sound velocity by temperature and pressure;

[0015] 2) Establish a linear programming model based on the speed of sound and the characteristics of natural gas; Establish a linear programming model; The formula of the linear programming model is:

[0016]

[0017] The formula is called the feasible solution of linear programming, and the feasible solution that makes the objective function (1) reach the maximum or minimum value is called the optimal solution;

[0018] 3) Model establishment: According to the existing data, the minimum methane content of natural gas is 61%, so the molecular weight model of natural gas carbon and hydrogen is:

[0019] y=16x1+30x2+44x3+58x4

[0020]

[0021] The maximum and minimum values ​​of the molecular weight of carbon and hydrogen at a certain sound speed are obtained through this model; where x1~x4 are the contents of methane, ethane, propane, and butane, c is the sound speed after compensation, and y is the molecular weight of carbon and hydrogen of the natural gas to be obtained;

[0022] 4) Result compensation: compensate the obtained molecular weight of hydrocarbons according to historical data;

[0023] 5) Net calorific value calculation: average the net calorific value range to estimate the final net calorific value of natural gas.

[0024] Furthermore, in the sound velocity compensation in step 1), it can be known from the sound velocity formula that temperature and pressure will affect the sound velocity. In order to eliminate the influence of temperature and pressure, the sound velocity needs to be compensated, and the sound velocity under all working conditions is converted to the sound velocity under standard conditions (temperature is 0°C, pressure is 1 standard atmosphere). The compensation formula is as follows:

[0025]

[0026] Where Z is the compression factor, which can be obtained by looking up the natural gas compression factor table according to temperature and pressure, and T' is the Celsius temperature.

[0027] Furthermore, in step 4), the maximum and minimum values ​​of the molecular weight of hydrocarbons and the corresponding contents of each component can be obtained through iteration. The range of the model parameters can be appropriately narrowed according to the previous field data. Finally, in order to obtain more accurate results, the data needs to be compensated. The result compensation formula is:

[0028]

[0029] where y max is the maximum molecular weight of carbon and hydrogen, y min is the minimum molecular weight of carbon and hydrogen, is the methane content corresponding to the maximum and minimum values ​​of the molecular weight of carbon and hydrogen; k is the compensation coefficient, and m is the historical data of the methane content of the natural gas in the pipeline, or 0 if there is none.

[0030] Furthermore, in the calculation of the net calorific value of the gas in step 5), the low calorific value is generally used in natural gas energy metering. This is because in practical applications, the exhaust gas after combustion is usually discharged at a higher temperature, and water exists in gaseous form;

[0031] The volume flow rate and molecular weight of hydrocarbons obtained from the flow meter are combined and calculated, and finally the net calorific value of the gas is estimated. The specific steps are as follows:

[0032] 1) The volume fractions of hydrocarbons in natural gas have been obtained by the above method, which are x1, x2, x3, and x4 respectively;

[0033] 2) Under standard conditions, the net calorific value of natural gas is calculated as follows (in kj / m 3 ):

[0034] Q=q1x1+q2x2+q3x3+q4x4

[0035] Among them, q 1 ~q 4 is the net calorific value of methane, ethane, propane and butane;

[0036] 3) The maximum and minimum net calorific value of natural gas is obtained by the hydrocarbon content corresponding to the maximum and minimum values ​​of the molecular weight of hydrocarbons, and then the final net calorific value is estimated by the arithmetic average method. The formula is as follows:

[0037]

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1) By using a detection system with flowmeter, thermometer, pressure gauge and transducer as core functional units to measure and estimate the molecular weight of carbon and hydrogen in natural gas, and further deduce the net calorific value of the gas, the molecular weight of carbon and hydrogen is quickly calculated through the natural gas sound velocity, temperature and pressure, and the molecular weight of carbon and hydrogen and net calorific value data of the gas are quickly obtained;

[0040] 2) The detection system has a simple structure, convenient and reliable installation, and a wide range of applications. It can greatly shorten the installation time and improve the test efficiency, realize flexible process monitoring and quality control, and save a lot of test costs, which is conducive to saving installation costs and time;

[0041] 3) Compared with traditional measurement methods, this method reduces the use cost, installation time and maintenance difficulty of the equipment, can achieve effective and fast online monitoring, provide effective and fast reference data for testers, provide strong support for real-time control and optimization in industrial production processes, and help testers to quickly conduct tests and find problems in a timely manner;

[0042] 4) The detection system and calculation method have high applicability and can meet the testing requirements under different conditions. They are mainly suitable for natural gas, liquefied gas, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic block diagram of the structure of an embodiment of a gas carbon-hydrogen molecular weight and net calorific value detection system of the present invention;

[0044] Figure 2 It is a schematic diagram of the external structure of an embodiment of a gas carbon-hydrogen molecular weight and net calorific value detection system of the present invention;

[0045] Figure 3 This is a schematic diagram of the working state of an embodiment of a gas carbon-hydrogen molecular weight and net calorific value detection system of the present invention;

[0046] Figure 4 It is a flow chart of the calculation method of an embodiment of the present invention.

[0047] In the figure: 1- high-strength magnet, 2- stainless steel protective shell, 3- ultrasonic flowmeter, 4- carbon steel medium pipeline, 5- box body. DETAILED DESCRIPTION

[0048] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0049] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the specific embodiments required to be used in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some implementation methods of the present invention. For ordinary technicians in this field, other specific embodiments can be obtained based on these specific embodiments without paying creative work.

[0050] The components of the embodiments of the present invention generally described and shown in the specific embodiments herein can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the specific embodiments is not intended to limit the scope of the invention claimed, but merely represents selected embodiments of the present invention.

[0051] like Figure 1-3 As shown, a schematic diagram of the structure of a gas hydrocarbon molecular weight and net calorific value detection system includes a mobile terminal, an ultrasonic flow meter, a data acquisition module, a temperature sensor, a pressure sensor and an ultrasonic transducer. The mobile terminal is connected to the data acquisition module via Bluetooth or a digital interface, and the data acquisition module is respectively connected to the ultrasonic flow meter, the temperature sensor, the pressure sensor and the ultrasonic transducer; the data acquisition module is integrated in the ultrasonic flow meter 3.

[0052] The ultrasonic transducer is placed in the box body 5. The top, left and right sides, front and back sides of the box body 5 are all covered with a stainless steel protective shell 2. A high-strength magnet 1 for rapid adsorption with the carbon steel natural gas pipeline 4 is provided at the bottom of the box body 5; the temperature sensor and the pressure sensor are both arranged in the carbon steel natural gas pipeline 4.

[0053] In the embodiment, the mobile terminal is an Android phone, and its functions are to calculate the molecular weight of hydrocarbons and the net calorific value, as well as to display or set the flow meter related parameters. It can display the standard volume flow rate, operating volume flow rate, standard mass flow rate, operating mass flow rate, temperature, pressure and other parameters, and can set the pipe diameter, wall thickness, pipe material, transducer frequency, measurement method and other parameters. The model of the ultrasonic flowmeter 3 is MT1600CL. The model of the temperature sensor is MT1600CL-T, which is used to obtain the pipe temperature; the model of the pressure sensor is MT1600CL-P, which is used to obtain the pipe pressure; the model of the ultrasonic transducer is MT1600CL-H, which is used to send and receive ultrasonic signals. Data acquisition module

[0054] See Figure 4 The present invention provides a calculation method for a gas carbon-hydrogen molecular weight and net calorific value detection system, which uses a linear programming method to find the range of carbon-hydrogen molecular weight, and calculates the carbon-hydrogen molecular weight by compensating the previous methane content data of the gas field, and finally calculates the net calorific value of the natural gas by the corresponding hydrocarbon content information after compensation. The specific calculation steps are as follows:

[0055] 1) Obtain the natural gas sound velocity, temperature, and pressure in the current environment; compensate the sound velocity by temperature and pressure; From the sound velocity formula, it can be seen that temperature and pressure will affect the sound velocity. In order to eliminate the influence of temperature and pressure, it is necessary to compensate the sound velocity and convert the sound velocity under all working conditions into the sound velocity under standard conditions (temperature is 0°C and pressure is 1 standard atmospheric pressure). The compensation formula is as follows:

[0056]

[0057] Where Z is the compression factor, which can be obtained by looking up the natural gas compression factor table according to temperature and pressure, and T' is the Celsius temperature.

[0058] 2) Establish a linear programming model based on the speed of sound and the characteristics of natural gas; Establish a linear programming model; The formula of the linear programming model is:

[0059]

[0060] The formula is called the feasible solution of linear programming, and the feasible solution that makes the objective function (1) reach the maximum or minimum value is called the optimal solution;

[0061] 3) Model establishment: According to the existing data, the minimum methane content of natural gas is 61%, so the molecular weight model of natural gas carbon and hydrogen is:

[0062] y=16x1+30x2+44x3+58x4

[0063]

[0064] The maximum and minimum values ​​of the molecular weight of carbon and hydrogen at a certain sound speed are obtained through this model; where x1~x4 are the contents of methane, ethane, propane, and butane, c is the sound speed after compensation, and y is the molecular weight of carbon and hydrogen of the natural gas to be obtained;

[0065] 4) Result compensation: compensate the obtained molecular weight of hydrocarbons according to historical data; the maximum and minimum values ​​of molecular weight of hydrocarbons and the corresponding content of each component can be obtained through iteration. The value range of model parameters can be appropriately narrowed according to the previous data on site. Finally, in order to obtain more accurate results, the data needs to be compensated. The result compensation formula is:

[0066]

[0067] where y max is the maximum molecular weight of carbon and hydrogen, y min is the minimum molecular weight of carbon and hydrogen, is the methane content corresponding to the maximum and minimum values ​​of the molecular weight of carbon and hydrogen; k is the compensation coefficient, and m is the historical data of the methane content of the natural gas in the pipeline, or 0 if there is none.

[0068] 5) Net calorific value calculation: the net calorific value range is averaged to estimate the final net calorific value of natural gas. In natural gas energy measurement, the low calorific value is generally used. This is because in practical applications, the exhaust gas after combustion is usually discharged at a higher temperature, and water exists in gaseous form;

[0069] The volume flow rate and molecular weight of hydrocarbons obtained from the flow meter are combined and calculated, and finally the net calorific value of the gas is estimated. The specific steps are as follows:

[0070] 1) The volume fractions of hydrocarbons in natural gas have been obtained by the above method, which are x1, x2, x3, and x4 respectively;

[0071] 2) Under standard conditions, the net calorific value of natural gas is calculated as follows (in kj / m 3 ):

[0072] Q=q1x1+q2x2+q3x3+q4x4

[0073] Among them, q1~q4 are the net calorific values ​​of methane, ethane, propane and butane;

[0074] 3) The maximum and minimum net calorific value of natural gas is obtained by the hydrocarbon content corresponding to the maximum and minimum values ​​of the molecular weight of hydrocarbons, and then the final net calorific value is estimated by the arithmetic average method. The formula is as follows:

[0075]

[0076] Since the composition of natural gas produced by different gas fields is slightly different, but the vast majority of the gas composition is methane, assuming that the number and type of gas components are known but the content of each component is unknown, first use the ultrasonic flowmeter 3 and the temperature and pressure sensor to accurately measure the natural gas sound velocity, temperature, and pressure, then substitute the sound velocity after temperature and pressure compensation into the linear programming model, and calculate the range of values ​​of the molecular weight of hydrocarbons. Finally, relevant compensation is performed through the past data of the methane content of the gas field to obtain the molecular weight of hydrocarbons. Finally, the net calorific value of the natural gas is calculated through the corresponding hydrocarbon content information after compensation.

[0077] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A gas carbon-hydrogen molecular weight and net calorific value detection system, characterized in that: It includes a mobile terminal, an ultrasonic flowmeter, a data acquisition module, a temperature sensor, a pressure sensor and an ultrasonic transducer. The mobile terminal is connected to the data acquisition module via Bluetooth or a digital interface. The data acquisition module is respectively connected to the ultrasonic flowmeter, the temperature sensor, the pressure sensor and the ultrasonic transducer. The data acquisition module is integrated in the ultrasonic flowmeter.

2. A gas carbon-hydrogen molecular weight and net calorific value detection system according to claim 1, characterized in that: The ultrasonic transducer is placed in a box body, the top and left and right sides of the box body are covered with a stainless steel protective shell, and a high-strength magnet for rapid adsorption to a carbon steel natural gas pipeline is provided at the bottom of the box body; the temperature sensor and pressure sensor are both arranged in the natural gas pipeline.

3. A gas carbon-hydrogen molecular weight and net calorific value detection system according to claim 1, characterized in that: The mobile terminal is an Android phone.

4. A gas carbon-hydrogen molecular weight and net calorific value detection system according to claim 1, characterized in that: The model of the ultrasonic flow meter is MT1600CL.

5. The system for detecting carbon-hydrogen molecular weight and net calorific value of a gas according to claim 1, characterized in that: The model of the temperature sensor is MT1600CL-T; the model of the pressure sensor is MT1600CL-P; and the model of the ultrasonic transducer is MT1600CL-H.

6. A method for calculating the carbon and hydrogen molecular weight and net calorific value detection system of a gas, characterized in that: The range of hydrocarbon molecular weight is obtained through linear programming method, and the hydrocarbon molecular weight is calculated by compensating the previous methane content data of the gas field. Finally, the net calorific value of the natural gas is calculated through the corresponding hydrocarbon content information after compensation. The specific calculation steps are as follows: 1) Obtain the natural gas sound velocity, temperature, and pressure in the current environment; compensate the sound velocity by temperature and pressure; 2) Establish a linear programming model based on the speed of sound and the characteristics of natural gas; Establish a linear programming model; The formula of the linear programming model is: The formula is called the feasible solution of linear programming, and the feasible solution that makes the objective function (1) reach the maximum or minimum value is called the optimal solution; 3) Model establishment: According to the existing data, the minimum methane content of natural gas is 61%, so the molecular weight model of natural gas carbon and hydrogen is: y=16x1+30x2+44x3+58x4 The maximum and minimum values ​​of the molecular weight of carbon and hydrogen at a certain sound speed are obtained through this model; where x1~x4 are the contents of methane, ethane, propane, and butane, c is the sound speed after compensation, and y is the molecular weight of carbon and hydrogen of the natural gas to be obtained; 4) Result compensation: compensate the obtained molecular weight of hydrocarbons according to historical data; 5) Net calorific value calculation: average the net calorific value range to estimate the final net calorific value of natural gas.

7. The calculation method of a gas carbon-hydrogen molecular weight and net calorific value detection system according to claim 6 is characterized in that: The speed of sound compensation in step 1) is known from the speed of sound formula that temperature and pressure will affect the speed of sound. In order to eliminate the influence of temperature and pressure, the speed of sound needs to be compensated, and the speed of sound under all working conditions is converted to the speed of sound under standard conditions (temperature is 0°C, pressure is 1 standard atmosphere). The compensation formula is as follows: Where Z is the compression factor, which can be obtained by looking up the natural gas compression factor table according to temperature and pressure, and T' is the Celsius temperature.

8. The calculation method of a gas carbon-hydrogen molecular weight and net calorific value detection system according to claim 6 is characterized in that: In step 4), the maximum and minimum values ​​of the molecular weight of hydrocarbons and the corresponding contents of each component can be obtained through iteration. The value range of the model parameters can be appropriately narrowed according to the previous field data. Finally, in order to obtain more accurate results, the data needs to be compensated. The result compensation formula is: where y max is the maximum molecular weight of carbon and hydrogen, y min is the minimum molecular weight of carbon and hydrogen, is the methane content corresponding to the maximum and minimum values ​​of the molecular weight of carbon and hydrogen; k is the compensation coefficient, and m is the historical data of the methane content of the natural gas in the pipeline, or 0 if there is none.

9. The calculation method of a gas carbon-hydrogen molecular weight and net calorific value detection system according to claim 6, characterized in that: In the step 5), the net calorific value of the gas is calculated. In natural gas energy measurement, the low calorific value is generally used. This is because in practical applications, the exhaust gas after combustion is usually discharged at a higher temperature, and water exists in gaseous form; The volume flow rate and molecular weight of hydrocarbons obtained from the flow meter are combined and calculated, and finally the net calorific value of the gas is estimated. The specific steps are as follows: 1) The volume fractions of hydrocarbons in natural gas have been obtained by the above method, which are x1, x2, x3, and x4 respectively; 2) Under standard conditions, the net calorific value of natural gas is calculated as follows (in kj / m 3 ): Q=q1x1+q2x2+q3x3+q4x4 Among them, q1~q4 are the net calorific values ​​of methane, ethane, propane and butane; 3) The maximum and minimum net calorific value of natural gas is obtained by the hydrocarbon content corresponding to the maximum and minimum values ​​of the molecular weight of hydrocarbons, and then the final net calorific value is estimated by the arithmetic average method. The formula is as follows:

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