CN111337071A - Natural gas measurement evaluation system - Google Patents

Abstract

The invention provides a natural gas measurement evaluation system, which includes a flow measurement device arranged in a natural gas pipeline and a flow computer arranged outside the natural gas pipeline; the flow measurement device includes a flow meter, a temperature transmitter, a pressure transmitter, a gas Chromatographic analysis instruments, the flowmeter, temperature transmitter, pressure transmitter, and gas chromatographic analysis instruments are used as primary measurement instruments to measure the flow, temperature, pressure and gas components of natural gas respectively; the flow computer is used as a secondary measurement instrument, through Collect the measurement value of the on-site primary measuring instrument to calculate, calculate the system uncertainty, and use the system uncertainty to evaluate the measurement accuracy of the on-site measuring system. The greater the uncertainty, the worse the measuring accuracy of the on-site measuring system. The invention calculates the calculation method verification and system uncertainty of the metering system by calling the natural gas physical property calculation dynamic calculation calling library and the measurement uncertainty calculation calling library, and the calculation method verification result is compared with the actual measurement result, and the on-site measurement system is directly obtained. Calculate deviation; and the results of measurement uncertainty calculation can directly evaluate the measurement accuracy of the field measurement system.

Description

A natural gas measurement and evaluation system

technical field

The invention relates to an evaluation system, in particular to a natural gas measurement evaluation system.

Background technique

As a high-quality, high-efficiency and clean low-carbon energy and chemical raw material, natural gas has become an important development trend in the world's energy applications. Since the beginning of the 21st century, my country's natural gas consumption has increased rapidly, from 150.9 billion cubic meters in 2012 to 188.4 billion cubic meters in 2014. Accelerating the development of the natural gas industry and increasing the proportion of natural gas in primary energy consumption has important strategic significance for my country to adjust the energy structure, improve people's living standards, promote energy conservation and emission reduction, and respond to climate change. In the next 20 years, the growth rate of my country's natural gas demand will significantly exceed that of coal and oil. It is estimated that by 2020, the proportion of natural gas in the total energy demand will exceed 10%, and the demand is expected to reach 251.7 billion cubic meters. With the rapid growth of natural gas trade volume and the increasing frequency of international natural gas transactions, the measurement of natural gas has received more and more attention and attention from both trading parties. In order to meet the needs of the development direction of high-pressure, large-flow, and high-accuracy measurement in natural gas trade, there are various types of ultrasonic flowmeters, turbine flowmeters, vortex flowmeters, Coriolis flowmeters, and standard orifice flowmeters. The natural gas flow meter is used in metering systems for natural gas custody transfer and process metering.

Since Sinopec implemented the strategy of "big development of natural gas", it has completed the construction of Sichuan-East Gas Pipeline, Yu-Ji Natural Gas Pipeline, Qingdao LNG, and started construction of key projects such as Guangxi LNG, Tianjin LNG, Zhongyuan and Jintan gas storages, etc. Within the scope, a gas supply market with "two lines and three districts" as the main body is formed. In terms of natural gas development, the Company will accelerate the promotion of key production capacity construction projects, strengthen the management of old gas fields such as Puguang, rationally adjust marketing strategies, expand total operating volume, and improve economic benefits; in terms of shale gas development, the first phase of Fuling’s 5 billion cubic meters of production capacity has been efficiently constructed and put into production. The daily production level of the well exceeded the design plan, forming a good situation for great development. In 2014, Sinopec produced about 20.288 billion cubic meters of natural gas, an increase of 8.5% year-on-year, and sold 18.31 billion cubic meters of natural gas, an increase of 8.7% year-on-year. The natural gas market area has expanded to more than 20 provinces and cities across the country, and natural gas has become a new economic growth point. In key projects such as Sinopec's new natural gas pipelines and LNG, ultrasonic flowmeters have become the main handover measuring instruments and are widely used. In 2014, Sinopec's major natural gas pipeline companies used nearly 800 natural gas flow meters in high-pressure natural gas metering systems.

At present, in the domestic natural gas metering system, the popularity of primary instruments such as flow meters, temperature transmitters, pressure transmitters, differential pressure transmitters, and gas chromatographic analyzers has been quite high, and secondary instruments such as flow computers, volume calculators, etc. The popularity is also getting higher and higher, and most natural gas custody transfer units can carry out effective periodic traceability/verification work for primary instruments, but in terms of secondary instrument verification, since there is no mandatory verification category, a considerable part of the two None of the sub-meters has a valid periodic check.

In a typical natural gas metering system, the measuring instrument configuration of the primary instrument, the management of the primary instrument, and the configuration parameter configuration of the flow computer will affect the measurement accuracy of the entire natural gas metering system. At present, the main guiding regulation for the overall evaluation of the entire natural gas metering system in China is GBT 35186-2017 "Natural Gas Metering System Performance Evaluation", but since it is not included in the mandatory verification, basically no evaluation work is performed, and the user level mainly focuses on one meter cycle. There is no corresponding evaluation system or implementation specification for sex tests and trade differences.

SUMMARY OF THE INVENTION

In view of the above technical problems, the present invention proposes a natural gas measurement and evaluation system, including a flow measurement device arranged in the natural gas pipeline and a flow computer arranged outside the natural gas pipeline; the flow measurement device includes a flow meter, a temperature transmitter, a pressure Transmitter, gas chromatographic analysis instrument, the flowmeter, temperature transmitter, pressure transmitter, and gas chromatographic analysis instrument are used as primary measuring instruments to measure the flow rate, temperature, pressure and gas components of natural gas respectively; the flow computer As a secondary measuring instrument, it is calculated by collecting the measurement value of the primary measuring instrument on site, and the system uncertainty is calculated, and the measurement accuracy of the on-site measuring system is evaluated by the system uncertainty. The measurement accuracy is worse.

Further, it also includes an instantaneous flowmeter of working conditions arranged in the natural gas pipeline, and the instantaneous flowmeter of working conditions collects the instantaneous flow of working conditions in the natural gas pipeline; the flow computer is used as a secondary measuring instrument, by collecting the primary measuring instrument on site. The measured value of the standard condition is calculated, and the instantaneous flow rate of the standard condition is also calculated, and the instantaneous flow rate of the standard condition is compared with the instantaneous flow rate of the working condition, so as to obtain the flow deviation of the on-site metering system.

Further, the flowmeter is an ultrasonic flowmeter, or a turbine flowmeter, or a waist wheel flowmeter, or a mass flowmeter, or a vortex flowmeter, and the uncertainty includes volume flow uncertainty, pressure uncertainty , temperature uncertainty, compression factor uncertainty;

The uncertainty formula is:

Analyze the uncertainty of each parameter item by item, where:

_ur (q _s,s ) is the uncertainty of the volume flow under operating conditions; read it from the nameplate of the flow meter equipment.

_ur (p _s ) is the operating pressure uncertainty; read from the nameplate of the flow meter device.

_ur (T _s ) is the operating temperature uncertainty; read from the nameplate of the flow meter device.

_ur (Z _s ) is the uncertainty of the compressibility factor of the operating condition; read it from the nameplate of the flow meter equipment.

u _r (p _f ) is the standard pressure uncertainty;

u _r (T _f ) is the standard temperature uncertainty;

u _r (Z _sf ) is the standard condition compression factor uncertainty;

The uncertainty function in the uncertainty formula comes from the calculation formula of the volume flow of the standard table method gas flow standard device, and the calculation formula of the volume flow of the standard table method gas flow standard device is:

In the formula: - the standard volume flow under the standard conditions of the flowmeter;

—Volume flow under the working conditions of the flowmeter; a working flowmeter device is arranged in the natural gas pipeline, and the working flowmeter device includes a working flowmeter, and the volume flow under the working conditions of the flowmeter comes from the working condition the measured value of the flowmeter;

- Pressure under standard conditions, take a constant, 101.325kPa;

- the temperature under standard conditions, take a constant, 20 degrees Celsius;

- the compression factor under standard conditions;

—Pressure under the working condition of the flowmeter; the natural gas pipeline is provided with a working condition flowmeter device, and the working condition flowmeter device includes a working condition pressure transmitter, and the pressure under the working condition of the flowmeter comes from the working condition The measured value of the pressure transmitter;

—The temperature under the working condition of the flowmeter; the natural gas pipeline is provided with a working condition flowmeter device, and the working condition flowmeter device includes a working condition temperature transmitter, and the temperature under the working condition of the flowmeter comes from the working condition The measured value of the temperature transmitter;

- Compression factor under the working conditions of the flowmeter; the compression factor at the flowmeter is calculated according to the method in the AGA NO.8 report or the GB/T17747.2-1999 standard, AGA NO.8 report and GB/T17747.2 - The method of calculating the compressibility factor at the flowmeter in the 1999 standard is a standard, which belongs to the well-known technology, and will not be described here;

Further, the flowmeter is a sonic nozzle and an orifice flowmeter, and the uncertainty includes the uncertainty of the cross-sectional area of the throat of the venturi nozzle of the boundary flow, the uncertainty of the outflow coefficient, the uncertainty of the critical flow function, and the stagnation. Pressure uncertainty, gas constant uncertainty, stagnation temperature uncertainty;

When a single critical flow Venturi nozzle participates in the flow measurement, the uncertainty formula of the mass flow measurement of the metering system is:

The formula for calculating the mass flow measured by the metering system is:

Analyze the uncertainty of each parameter item by item.

Further, it also includes a switch, and the flowmeter, temperature transmitter, pressure transmitter, and gas chromatographic analysis instrument are respectively connected with the switch, and data exchange is carried out through the TCP/IP protocol, and the flow computer is connected with the switch, and the flow computer is connected with the switch. /IP protocol to collect data from flow meters, temperature transmitters, pressure transmitters, and gas chromatography analysis instruments.

Further, it also includes a PLC programmable logic controller, a communication network and a diagnostic terminal, and the flowmeter, temperature transmitter, pressure transmitter, and gas chromatographic analysis instrument are respectively connected with the PLC programmable logic controller, through TCP/ IP protocol for data exchange, the communication network is responsible for the network communication between the PLC programmable logic controller and the diagnosis terminal, the flow computer is connected with the diagnosis terminal, and the flowmeter, temperature transmitter, pressure Data from transmitters, gas chromatography instruments.

The calculation methods of each measurement system verify the system uncertainty evaluation calculation, and call the natural gas physical property calculation dynamic calculation call library to calculate in the calculation process.

The instantaneous flow and cumulative flow calculation methods of several flowmeters are as follows:

1) Calculation of flow rate of ultrasonic flowmeter

Gas ultrasonic flowmeter is a flow measurement instrument composed of flowmeter body, electronic components, microprocessor system, ultrasonic transducer, etc. Ultrasonic transducers are usually installed along the pipe wall and are in direct contact with the gas and are subjected to the pressure of the gas. Ultrasonic pulses emitted by one ultrasonic transducer are received by another ultrasonic transducer and vice versa. Reflective channels are used in some flow meters, where the sound wave pulse is reflected one or more times on the pipe wall.

Ultrasonic pulses travel through pipes like a ferry across a river. If the gas is not flowing, the sound waves will travel in both directions at the same speed. When the gas velocity in the pipe is not zero, the pulses propagating downstream in the direction of the gas flow will speed up, while the pulses propagating countercurrent will slow down. Therefore, the time tD for forward flow travel will be shortened and the time tU for counter flow travel will increase relative to the case of no airflow, both of which are measured by the electronics. From these two travel times, the measured flow velocity can be calculated

where:

V—the average flow velocity of the gas, in meters per second (m/s);

L - channel length, in meters (m);

X——channel distance, in meters (m);

tU—the time for the acoustic pulse to propagate upstream, in seconds (s);

tD—the time that the acoustic pulse travels downstream, in seconds (s).

2) Calculation of instantaneous working condition flow rate of ultrasonic flowmeter

In a multi-channel gas ultrasonic flowmeter, the ultrasonic transducers are arranged in various forms. Channels can be parallel to each other, or other orientations are possible. The flowmeter can propagate sound waves directly or by reflection along two or more inclined strings. The method used to synthesize the measurements of the individual channels into an average flow velocity also varies with the specific configuration of the flowmeter. In particular, not all methods require the use of the aforementioned k-factor to calculate the average flow.

由于V可以表示为：In a multi-channel gas ultrasonic flowmeter, calculated from a series of discrete y-values

Since V can be expressed as:

计算出轴向平均流速V的近似值。其表达式如下：Here is the average flow velocity along the channel (the transverse position of the chord is Y), and the above equation can be integrated by using an appropriate digital integration technique, such as the Gaussian integration method. In this way, according to the

An approximation of the axial mean flow velocity V is calculated. Its expression is as follows:

是与所用积分技术有关的权重系数，yi是超声换能器的弦线横向位置。这是一种广泛使用的数字积分技术，在流量计中有多种方式能实现这种技术。所选择的声道位置应能使权重系数作为常数处理，而不要求对速度分布做假设，但这取决于所用的方法。here

is the weighting factor related to the integration technique used and yi is the transverse position of the ultrasonic transducer chord. This is a widely used digital integration technique that can be implemented in a flow meter in several ways. The channel positions are chosen such that the weight coefficients are treated as constants without requiring assumptions about the velocity distribution, but this depends on the method used.

The product of the average axial velocity and the flow area A is the volume flow qf under operating conditions:

q _f =VA………………(23)

The flowmeter is designed and manufactured using the principle of ultrasonic propagation and digital integration technology. The value measured according to formula (5) is the natural gas flow rate under working conditions. The flow rate under standard reference conditions should be calculated according to the gas state equation according to the static pressure and temperature of the gas flow measured online.

3) Calculation of instantaneous flow under standard reference conditions of ultrasonic flowmeter

In a multi-channel gas ultrasonic flowmeter, the ultrasonic transducers are arranged in various forms. Channels can be parallel to each other, or other orientations are possible. The flowmeter can propagate sound waves directly or by reflection along two or more inclined strings. The method used to synthesize the measurements of the individual channels into an average flow velocity also varies with the specific configuration of the flowmeter. In particular, not all methods require the use of the aforementioned k-factor to calculate the average flow.

由于V可以表示为：In a multi-channel gas ultrasonic flowmeter, calculated from a series of discrete y-values

Since V can be expressed as:

计算出轴向平均流速V的近似值。其表达式如下：Here is the average flow velocity along the channel (the transverse position of the chord is Y), and the above equation can be integrated by using an appropriate digital integration technique, such as the Gaussian integration method. In this way, according to the

An approximation of the axial mean flow velocity V is calculated. Its expression is as follows:

是与所用积分技术有关的权重系数，yi是超声换能器的弦线横向位置。这是一种广泛使用的数字积分技术，在流量计中有多种方式能实现这种技术。所选择的声道位置应能使权重系数作为常数处理，而不要求对速度分布做假设，但这取决于所用的方法。here

is the weighting factor related to the integration technique used and yi is the transverse position of the ultrasonic transducer chord. This is a widely used digital integration technique that can be implemented in a flow meter in several ways. The channel positions are chosen such that the weight coefficients are treated as constants without requiring assumptions about the velocity distribution, but this depends on the method used.

The product of the average axial velocity and the flow area A is the volume flow qf under operating conditions:

q _f =VA………………(26)

The flowmeter is designed and manufactured using the principle of ultrasonic propagation and digital integration technology. The value measured according to formula (5) is the natural gas flow rate under working conditions. The flow rate under standard reference conditions should be calculated according to the gas state equation according to the static pressure and temperature of the gas flow measured online.

4) Calculation of cumulative flow under standard reference conditions of ultrasonic flowmeter

The instantaneous flow rate under the standard reference conditions of the flowmeter is calculated as follows:

Where: qn——instantaneous flow under standard reference conditions, in cubic meters per hour (m3/h);

qf——Instantaneous flow under working conditions, in cubic meters per hour (m3/h);

Pn——absolute pressure under standard reference conditions, its value is 0.101325MPa;

Pf——absolute static pressure under working conditions, in megapascals (MPa);

Tn——The thermodynamic temperature under standard reference conditions, its value is 293.25K;

Tf - thermodynamic temperature under working conditions, in Kelvin (K);

Zn——compression factor under standard reference conditions, calculated according to GB/T17747;

Zf——compression factor under working conditions, calculated according to GB/T17747.

4. Calculation model of turbine flow metering system

A typical turbine metering system consists of a turbine flowmeter, a temperature transmitter, a pressure transmitter, a gas chromatographic analysis instrument, and a flow computer. The measuring instruments measure the flow rate, temperature, pressure and gas composition of natural gas respectively. The flow computer is used as a secondary measuring instrument to calculate the working condition compression factor and standard condition compression factor of natural gas by collecting the measured values of the primary measuring instrument on site. Calculate the instantaneous standard flow of natural gas.

The main procedures and specifications used by the turbine flow metering system are as follows:

JJG 1037 Turbine Flowmeter Verification Regulations

GB_T 21391-2008 Measuring natural gas flow with gas turbine flowmeter

ISO 9951 Measurement of Gas Flow in Closed Conduits–Turbine Meters

1) Calculation of instantaneous working condition flow rate of turbine flowmeter

Turbine flowmeter is a measuring device in which the impeller is rotated under the action of the measured airflow in the pipeline, and the impeller speed is a function of the gas volume flow. The measurement of the gas flow through the flowmeter is based on the number of pulses generated by the rotation of the measuring impeller. .

Turbine flowmeter volume flow is calculated by the following formula:

In the formula: qV-turbine flowmeter volume flow, cubic meters per hour (m3/h).

The value measured according to formula (8) is the natural gas flow rate under working conditions. The flow rate under standard reference conditions should be calculated according to the gas state equation according to the static pressure and temperature of the gas flow measured online.

2) Instantaneous flow calculation under standard reference conditions of turbine flowmeter

The instantaneous flow rate under the standard reference conditions of the flowmeter is calculated as follows:

Where: qn——instantaneous flow under standard reference conditions, in cubic meters per hour (m3/h);

qf——Instantaneous flow under working conditions, in cubic meters per hour (m3/h);

Pn——absolute pressure under standard reference conditions, its value is 0.101325MPa;

Pf——absolute static pressure under working conditions, in megapascals (MPa);

Tn——The thermodynamic temperature under standard reference conditions, its value is 293.25K;

Tf - thermodynamic temperature under working conditions, in Kelvin (K);

Zn——compression factor under standard reference conditions, calculated according to GB/T17747;

Zf——compression factor under working conditions, calculated according to GB/T17747.

3) Calculation of cumulative flow under standard reference conditions of turbine flowmeter

The cumulative flow under standard reference conditions is calculated as follows:

In the formula: Qn——the cumulative amount in a period from t0 to t under the standard reference condition, the unit is cubic meter (m3);

——对t0至t时间段的积分；

- the integral over the time period t0 to t;

dt - the integral increment of time.

5. Calculation model of waist wheel flow measurement system

A typical waist wheel metering system consists of a waist wheel flowmeter, a temperature transmitter, a pressure transmitter, a gas chromatography analysis instrument and a flow computer, among which the waist wheel flowmeter, temperature transmitter, pressure transmitter, gas chromatography analysis instrument The instrument is used as a primary measuring instrument to measure the flow rate, temperature, pressure and gas composition of natural gas respectively. The flow computer is used as a secondary measuring instrument to calculate the compression factor and standard condition compression factor of natural gas by collecting the measured values of the primary measuring instrument on site. factor, so as to calculate the instantaneous standard flow rate of natural gas.

The main procedures and specifications used by the waist wheel flow measurement system are as follows:

SY_T 6660-2006 Measuring natural gas flow with rotary positive displacement gas flowmeter

JJG 633-2005 Gas volumetric flowmeter

3. EN 12480 64_e_stf Gas meters-Rotary displacement gas meters

1) Calculation of instantaneous working condition flow rate of waist wheel flowmeter

The waist wheel flowmeter is a typical volumetric flowmeter. The waist wheel flowmeter is a measuring device in which the rotor is rotated under the force of the measured airflow in the pipeline, and its impeller speed is a function of the gas volume flow. It measures the gas passing through the flowmeter. The flow rate is based on measuring the number of pulses produced by the rotation of the rotor.

The volume flow of the waist wheel flowmeter is calculated by the following formula:

In the formula: qV - volume flow of waist wheel flowmeter, cubic meters per hour (m3/h).

The value measured according to formula (8) is the natural gas flow rate under working conditions. The flow rate under standard reference conditions should be calculated according to the gas state equation according to the static pressure and temperature of the gas flow measured online.

2) Calculation of instantaneous flow under standard reference conditions of waist wheel flowmeter

The instantaneous flow rate under the standard reference conditions of the flowmeter is calculated as follows:

Where: qn——instantaneous flow under standard reference conditions, in cubic meters per hour (m3/h);

qf——Instantaneous flow under working conditions, in cubic meters per hour (m3/h);

Pn——absolute pressure under standard reference conditions, its value is 0.101325MPa;

Pf——absolute static pressure under working conditions, in megapascals (MPa);

Tn——The thermodynamic temperature under standard reference conditions, its value is 293.25K;

Tf - thermodynamic temperature under working conditions, in Kelvin (K);

Zn——compression factor under standard reference conditions, calculated according to GB/T17747;

Zf——compression factor under working conditions, calculated according to GB/T17747.

3) Calculation of cumulative flow under standard reference conditions of waist wheel flowmeter

The cumulative flow under standard reference conditions is calculated as follows:

In the formula: Qn——the cumulative amount in a period from t0 to t under the standard reference condition, the unit is cubic meter (m3);

——对t0至t时间段的积分；

- the integral over the time period t0 to t;

dt - the integral increment of time.

6. Calculation model of vortex flow measurement system

Similar to ultrasonic flowmeter, turbine flowmeter and waist wheel flowmeter, vortex flowmeter is a typical velocity flowmeter, and a typical vortex flowmeter system consists of vortex flowmeter, temperature transmitter, pressure transmitter, gas It is composed of chromatographic analysis instrument and flow computer. Vortex flowmeter, temperature transmitter, pressure transmitter and gas chromatographic analysis instrument are used as primary measuring instruments to measure the flow rate, temperature, pressure and gas composition of natural gas respectively. The flow computer As a secondary metering instrument, the compression factor of natural gas under working conditions and the compression factor under standard conditions are calculated by collecting the measured values of the primary measuring instrument on site, so as to calculate the instantaneous flow rate of natural gas under standard conditions.

The main procedures and specifications used by the vortex flow metering system are as follows:

JJG 1029-2007 Vortex flowmeter

GB_T 25922-2010 Measurement of fluid flow in closed pipelines Method for measuring flow with a vortex flowmeter installed in a pipeline of circular cross-section filled with fluid

ISO TR12764:1997Measurement of fluid flow in closed conduits—Flowrate measurement by means of vortex shedding

1) Calculation of instantaneous working condition flow rate of vortex flowmeter

The vortex flowmeter is a measuring device that generates vortices under the action of the measured airflow in the pipeline, and the frequency of the vortex is a function of the gas volume flow. The measurement of the gas flow through the flowmeter is based on the number of pulses generated by the rotation of the measuring impeller. of.

When the fluid passes through the vortex generator composed of helical blades (see Figure 1), the fluid is forced to rotate violently around the axis of the generator, forming a vortex. When the fluid enters the diffusion section, the vortex flow is affected by the backflow and begins to perform secondary rotation, forming a gyroscopic vortex precession phenomenon. The precession frequency is proportional to the flow rate and is not affected by the physical properties and density of the fluid. The detection element measures the precession frequency of the secondary rotation of the fluid, and the flow rate is known. And good linearity can be obtained in a wide flow range. The flow calculation formula is:

K=f/q………………(34)

In the formula: K——flow meter coefficient l/m3;

f——vortex frequency Hz

q——volume flow m3/h

The meter coefficient of the flowmeter has nothing to do with the temperature, pressure, composition and physical properties (density, viscosity) of the fluid within certain structural parameters and the specified Reynolds number range.

The value measured according to formula (11) is the natural gas flow rate under working conditions. The flow rate under standard reference conditions should be calculated according to the gas state equation according to the static pressure and temperature of the gas flow measured online.

2) Calculation of instantaneous flow under standard reference conditions of vortex flowmeter

The instantaneous flow rate under the standard reference conditions of the flowmeter is calculated as follows:

Where: qn——instantaneous flow under standard reference conditions, in cubic meters per hour (m3/h);

qf——Instantaneous flow under working conditions, in cubic meters per hour (m3/h);

Pn——absolute pressure under standard reference conditions, its value is 0.101325MPa;

Pf——absolute static pressure under working conditions, in megapascals (MPa);

Tn——The thermodynamic temperature under standard reference conditions, its value is 293.25K;

Tf - thermodynamic temperature under working conditions, in Kelvin (K);

Zn——compression factor under standard reference conditions, calculated according to GB/T17747;

Zf——compression factor under working conditions, calculated according to GB/T17747.

3) Calculation of cumulative flow under standard reference conditions of vortex flowmeter

The cumulative flow under standard reference conditions is calculated as follows:

In the formula: Qn——the cumulative amount in a period from t0 to t under the standard reference condition, the unit is cubic meter (m3);

——对t0至t时间段的积分；

- the integral over the time period t0 to t;

dt - the integral increment of time.

7. Calculation model of orifice flow metering system

The standard orifice flowmeter is composed of the standard orifice plate, the orifice plate clamping device and the pressure taking pipeline, the front and rear straight pipe sections, the differential pressure transmitter, the gauge pressure transmitter, the temperature transmitter and the flow computer that we have just seen. The flow computer is used as a secondary measuring instrument to calculate the compression factor of natural gas under working conditions and the compression factor of standard condition by collecting the measurement value of the primary measuring instrument on site, so as to calculate the instantaneous standard condition flow of natural gas.

The main specifications of the orifice flow metering system are as follows:

1. SYT6143-2004 uses standard orifice flowmeter to measure natural gas flow

2. GBT 21446-2008 Measuring natural gas flow with standard orifice flowmeter

3.ISO 5167Orifice

1) Calculation of instantaneous working condition flow rate of orifice flowmeter

The measurement principle of the orifice flowmeter is very simple, that is, when the air flows through the standard orifice plate, a differential pressure will be generated on the upstream side and the downstream side of the orifice plate. The relationship between the air flow can be determined by measuring the differential pressure.

So specifically, the flow calculation formula of the standard orifice flowmeter is as follows, and in fact all standard differential pressure flowmeters follow this calculation formula:

it's here,

q _m —mass flow, kg/s;

C—outflow coefficient, dimensionless;

β—the ratio of the opening diameter of the standard orifice plate to the inner diameter of the upstream pipe, referred to as the diameter ratio, dimensionless;

ε—expansibility coefficient, dimensionless;

d—the opening diameter of the standard orifice plate, m;

Δp—differential pressure, Pa;

ρ ₁ —The air density at the upstream pressure taking port under working conditions, kg/m3.

2) Instantaneous flow calculation under standard reference conditions of orifice flowmeter

The practical formula for calculating the flow rate derived under natural gas conditions is as follows:

The value measured according to formula (8) is the natural gas flow rate under working conditions. The flow rate under standard reference conditions should be calculated according to the gas state equation according to the static pressure and temperature of the gas flow measured online.

3) Calculation of cumulative flow under standard reference conditions of orifice flowmeter

The cumulative flow under standard reference conditions is calculated as follows:

In the formula: Qn——the cumulative amount in a period from t0 to t under the standard reference condition, the unit is cubic meter (m3);

——对t0至t时间段的积分；

- the integral over the time period t0 to t;

dt - the integral increment of time.

8. Calculation model of nozzle flow metering system

A typical standard nozzle metering system consists of a standard nozzle, a temperature transmitter, a pressure transmitter, a gas chromatography analysis instrument and a flow computer, of which the standard nozzle, temperature transmitter, pressure transmitter, and gas chromatography analysis instrument are used as one measurement. The instrument measures the flow rate, temperature, pressure and gas composition of natural gas respectively. The flow computer is used as a secondary measurement instrument to calculate the compression factor of natural gas and the compression factor of standard conditions by collecting the measured values of the primary measurement instrument on site. Obtain the instantaneous standard flow rate of natural gas.

The main specifications of the standard nozzle flow metering system are as follows:

ISO 9300-2005 Measurement of gas flow with critical flow venturi nozzles

GB_T 21188-2007 Measuring gas flow with critical flow venturi nozzle

JJG 620-2008 Verification Regulations for Critical Flow Venturi Nozzles

BS EN ISO 5167.3-2003 Measurement of fluid flow with differential pressure devices inserted into pipes of circular section. Nozzles and venturi nozzles

1) Calculation of mass flow rate of critical flow Venturi nozzle under instantaneous operating conditions

The theoretical mass flow rate for critical flow Venturi nozzle metering is calculated by the following formula:

In the formula: A - nozzle throat area, cubic meters (m3);

C* - critical flow function;

p0 - stagnation pressure at the throat of the nozzle, MPa (MPa);

T0 - stagnation temperature at the nozzle throat, open (K).

2) Calculation of volume flow rate of critical flow Venturi nozzle under instantaneous operating conditions

The critical flow Venturi nozzle volume is calculated by:

In the formula: qV-critical flow Venturi nozzle volume flow, cubic meters per hour (m3/h);

Z0 - Compression factor of stagnant natural gas at the throat of the nozzle.

3) Calculation of instantaneous flow rate under standard reference conditions of critical flow Venturi jet

The instantaneous flow rate under the standard reference conditions of the flowmeter is calculated as follows:

Where: qn——instantaneous flow under standard reference conditions, in cubic meters per hour (m3/h);

qf——Instantaneous flow under working conditions, in cubic meters per hour (m3/h);

Pn——absolute pressure under standard reference conditions, its value is 0.101325MPa;

Pf——absolute static pressure under working conditions, in megapascals (MPa);

Tn——The thermodynamic temperature under standard reference conditions, its value is 293.25K;

Tf - thermodynamic temperature under working conditions, in Kelvin (K);

Zn——compression factor under standard reference conditions, calculated according to GB/T17747;

Zf——compression factor under working conditions, calculated according to GB/T17747.

4) Calculation of cumulative flow under critical flow Venturi spray standard reference conditions

The cumulative flow under standard reference conditions is calculated as follows:

In the formula: Qn——the cumulative amount in a period from t0 to t under the standard reference condition, the unit is cubic meter (m3);

——对t0至t时间段的积分；

- the integral over the time period t0 to t;

dt - the integral increment of time.

9 Coriolis flow metering system calculation model

A Coriolis flowmeter is a mass flowmeter. A typical Coriolis metering system consists of a Coriolis flowmeter, a temperature transmitter, a pressure transmitter, a gas chromatographic analysis instrument and a flow computer. The flowmeter, temperature transmitter, pressure transmitter, and gas chromatographic analysis instrument are used as primary measuring instruments to measure the flow rate, temperature, pressure and gas components of natural gas respectively, and the flow computer is used as a secondary measuring instrument. The measurement value of the measuring instrument is used to calculate the compression factor of the natural gas under the working condition and the compression factor of the standard condition, so as to calculate the instantaneous flow rate of the natural gas under the standard condition.

The main procedures and specifications used by the Coriolis flow metering system are as follows:

SYT 6659-2006 Measuring Natural Gas Flow with Coriolis Mass Flow Meters

JJG 1038-2008 Coriolis Mass Flow Meter Verification Regulations

ISO 10790:2015 gives guidelines for the selection, installation, calibration, performance, and operation of Coriolis flowmeters for the measurement of mass flow and density

1) Coriolis flowmeter instantaneous working condition flow calculation

The flowmeter is a novel instrument that directly and precisely measures the mass flow of fluids. The main body of the structure adopts two U-shaped tubes side by side, so that the return bends of the two tubes vibrate slightly towards each other, and the straight tubes on both sides will follow. Vibration, i.e. they will close together or open at the same time, i.e. the vibrations of the two tubes are synchronized and symmetrical. Coriolis flowmeter is a measuring device that measures the relative vibration of the measuring tube under the action of the measured gas flow in the pipeline, and the phase difference of the vibration of the two measuring tubes is a function of the gas volume flow. The measurement of the gas flow through the flowmeter is based on the measuring tube. The phase difference between them is obtained.

Coriolis flowmeter volume instantaneous volume flow is calculated by the following formula:

Where: q _m - Coriolis flowmeter mass flow, kilograms per hour (kg/h).

The value measured according to formula (21) is the mass flow rate of natural gas under working conditions. The flow under instantaneous volume flow and standard reference conditions should be calculated based on the static pressure, temperature and composition of the gas flow measured online.

2) Calculation of instantaneous flow under working conditions of Coriolis flowmeter

The instantaneous flow rate under the working conditions of the Coriolis flowmeter is calculated as follows:

where: q _m ——the instantaneous mass flow rate under working conditions, in kilograms per hour (kg/h);

q _f — instantaneous volume flow under working conditions, in cubic meters per hour (m3/h);

ρ _f —— Density under working conditions, its value is kilograms per cubic meter (kg/m3).

3) Calculation of instantaneous flow under standard reference conditions of Coriolis flowmeter

The instantaneous flow rate under the standard reference conditions of the Coriolis flowmeter flowmeter is calculated as follows:

where: q _m ——the instantaneous mass flow rate under working conditions, in kilograms per hour (kg/h);

q _n ——Instantaneous volume flow under standard reference conditions, in cubic meters per hour (m3/h);

ρ _n —— Density under the condition of standard reference condition, its value is kilogram per cubic meter (kg/m3).

4) Calculation of cumulative flow under standard reference conditions of Coriolis flowmeter

The cumulative flow under standard reference conditions is calculated as follows:

In the formula: Qn——the cumulative amount in the period from t0 to t under the standard reference condition, the unit is cubic meter (m ³ );

——对t0至t时间段的积分；

- the integral over the time period t0 to t;

dt - the integral increment of time.

The working principle of the invention: by calling the natural gas physical property calculation dynamic calculation calling library and the measurement uncertainty calculation calling library, the calculation method verification and system uncertainty of the measurement system are calculated, and the calculation method verification result is compared with the actual measurement result, and it is directly obtained. The field measurement system calculates the deviation; and the result of the measurement uncertainty calculation can directly evaluate the measurement accuracy of the field measurement system.

Select the type of system to be evaluated in the system, select the type and accuracy level of the on-site metering equipment, and input the on-site working conditions, such as temperature, pressure and natural gas composition, the software automatically calculates and obtains the instantaneous standard condition of this type of natural gas metering system The flow calculation results and system uncertainty can be compared with the measurement results of the measured flow measurement system to obtain the relative deviation between the measured measurement system and the theoretical measurement result, so as to evaluate the calculation accuracy and measurement uncertainty of the measured measurement system.

The system of the present invention studies the calculation method and uncertainty of the measurement system based on the ultrasonic flowmeter, the turbine flowmeter, the orifice flowmeter, the nozzle flowmeter, the precession vortex flowmeter, the Coriolis flowmeter and the waist wheel flowmeter. The degree evaluation method, combined with the physical property parameters of natural gas, can directly verify and evaluate different types of natural gas metering systems.

Instruction drawings

FIG. 1 is a network architecture diagram of the natural gas measurement and evaluation system of the present invention.

Implementation

Embodiment 1: a natural gas measurement evaluation system, including a flow measurement device arranged in a natural gas pipeline and a flow computer arranged outside the natural gas pipeline; the flow measurement device includes a flow meter, a temperature transmitter, a pressure transmitter, Gas chromatographic analysis instrument, the flowmeter, temperature transmitter, pressure transmitter, and gas chromatographic analysis instrument are used as primary measuring instruments to measure the flow, temperature, pressure and gas components of natural gas respectively; the flow computer is used as secondary measurement The instrument is calculated by collecting the measurement value of the primary measuring instrument on site, calculates the system uncertainty, and uses the system uncertainty to evaluate the measurement accuracy of the on-site measuring system. The greater the uncertainty, the worse the measuring accuracy of the on-site measuring system. .

Further, it also includes an instantaneous flowmeter of working conditions arranged in the natural gas pipeline, and the instantaneous flowmeter of working conditions collects the instantaneous flow of working conditions in the natural gas pipeline; the flow computer is used as a secondary measuring instrument, by collecting the primary measuring instrument on site. The measured value of the standard condition is calculated, and the instantaneous flow rate of the standard condition is also calculated, and the instantaneous flow rate of the standard condition is compared with the instantaneous flow rate of the working condition, so as to obtain the flow deviation of the on-site metering system.

Further, the flowmeter is an ultrasonic flowmeter, or a turbine flowmeter, or a waist wheel flowmeter, or a mass flowmeter, or a vortex flowmeter, and the uncertainty includes volume flow uncertainty, pressure uncertainty , temperature uncertainty, compression factor uncertainty;

The uncertainty formula is:

Analyze the uncertainty of each parameter item by item, where:

u _r (q _s,s ) is the uncertainty of volume flow under operating conditions;

u _r (p _s ) is the operating condition pressure uncertainty;

u _r (T _s ) is the operating temperature uncertainty;

u _r (Z _s ) is the uncertainty of the compression factor of the working condition;

u _r (p _f ) is the standard pressure uncertainty;

u _r (T _f ) is the standard temperature uncertainty;

u _r (Z _sf ) is the standard condition compression factor uncertainty;

The uncertainty function in the uncertainty formula comes from the calculation formula of the volume flow of the standard table method gas flow standard device, and the calculation formula of the volume flow of the standard table method gas flow standard device is:

In the formula: - the standard volume flow under the standard conditions of the flowmeter;

—Volume flow under the working conditions of the flowmeter; a working flowmeter device is arranged in the natural gas pipeline, and the working flowmeter device includes a working flowmeter, and the volume flow under the working conditions of the flowmeter comes from the working condition the measured value of the flowmeter;

- Pressure under standard conditions, take a constant, 101.325kPa;

- the temperature under standard conditions, take a constant, 20 degrees Celsius;

- the compression factor under standard conditions;

—Pressure under the working condition of the flowmeter; the natural gas pipeline is provided with a working condition flowmeter device, and the working condition flowmeter device includes a working condition pressure transmitter, and the pressure under the working condition of the flowmeter comes from the working condition The measured value of the pressure transmitter;

—The temperature under the working condition of the flowmeter; the natural gas pipeline is provided with a working condition flowmeter device, and the working condition flowmeter device includes a working condition temperature transmitter, and the temperature under the working condition of the flowmeter comes from the working condition The measured value of the temperature transmitter;

- Compression factor under the working conditions of the flowmeter; the compression factor at the flowmeter is calculated according to the method in the AGA NO.8 report. The method in the AGA NO.8 report is a well-known technology and will not be described here;

Take the uncertainty analysis of ultrasonic flowmeter, turbine flowmeter, waist wheel flowmeter, mass flowmeter and vortex flowmeter as examples

The calculation methods of ultrasonic flowmeter, turbine flowmeter, waist wheel flowmeter, mass flowmeter and vortex flowmeter are similar. Taking the turbine flowmeter measurement system as an example, the gas flowmeter measurement system consists of a turbine flowmeter and a temperature transmitter. , 1 pressure transmitter and 1 gas composition analyzer.

In the flow measurement process, the flow measurement uncertainty of a single turbine flowmeter is taken as the flow measurement uncertainty of the flow standard.

The calculation formula of the volume flow rate of the standard gas flow standard device by the standard table method is shown in formula (48):

In the formula: q _{s, f} — the standard volume flow under the standard conditions of the turbine flowmeter;

q _{s, s} — the volume flow under the working conditions of the turbine flowmeter;

p _f — pressure under standard conditions, take a constant, 101.325kPa;

T _f - the temperature under standard conditions, take a constant, 20 degrees Celsius;

z _f —compression factor under standard conditions;

p _s —pressure under the working conditions of turbine flowmeter;

T _s — temperature under working conditions of turbine flowmeter;

z _s — Compression factor under turbine flowmeter operating conditions.

Using the method and formula (48) in JJF 1059.1-2012 "Measurement Uncertainty Evaluation and Representation", the flow measurement uncertainty of the turbine flow measurement system is calculated as shown in formula (49):

Analyze the uncertainty of each parameter item by item:

(1) Uncertainty of volume flow of turbine flowmeter

Typically, taking the turbine flow meter of the turbine flow metering system traceable to the secondary flow metering system of the Nanjing substation as an example, the uncertainty of the measurement error is better than 0.24% according to previous calibration reports; the confidence probability is 95%. %, including factor k=2:

The relative expanded uncertainty of the volume flow of the turbine flowmeter is U _r (q _s,s )=0.24%, k=2.

The relative standard uncertainty of the volume flow of the turbine flowmeter is: _ur (q _s,s )=0.12%.

(2) Uncertainty of pressure at turbine flowmeter

The pressure measurement uncertainty at the turbine flowmeter is mainly due to the pressure transmitter. The pressure transmitter at the turbine flowmeter takes the pressure transmitter model 3051S produced by Rosemount as an example, and its maximum allowable error is ±0.025% , distributed uniformly.

The relative standard uncertainty of the pressure at the turbine flowmeter is:

(3) Uncertainty of temperature at turbine flowmeter

The temperature measurement uncertainty at the turbine flowmeter mainly comes from the temperature transmitter. The temperature transmitter at the turbine flowmeter takes the temperature transmitter model 3144P produced by Rosemount Company as an example. The expanded uncertainty of temperature measurement It is 0.05°C (k=2), and the absolute temperature is 0.05K, and the commonly used temperature is 293.15K.

The relative standard uncertainty for the temperature at the turbine flowmeter is:

(4) Uncertainty of compression factor at turbine flowmeter

The compression factor at the turbine flowmeter is calculated according to the method in the AGA NO.8 report, and its relative expanded uncertainty is 0.1% (k=2).

The relative standard uncertainty of the compression factor at the turbine flowmeter is:

Because the calculation method is the same, the uncertainty of the compression factor of the turbine flowmeter under the working condition and the standard condition is taken as the working condition, and the standard condition is not repeated calculation, and the value is 0.

The temperature and pressure of the turbine flowmeter are constant under standard conditions, and the uncertainty is 0.

Based on the above, the uncertainty of the volume flow of the metering system is shown in Table 1:

Table 1 Statistical table for the evaluation of the uncertainty of the volume flow of the turbine flow metering system

The relative expanded uncertainty of the volume flow of the turbine flow metering system is: U _r (q _v )=U _r (q _s,f )=0.29%, k=2.

Embodiment 2: a natural gas measurement evaluation system, comprising a flow measurement device arranged in a natural gas pipeline and a flow computer arranged outside the natural gas pipeline; the flow measurement device includes a flow meter, a temperature transmitter, a pressure transmitter, Gas chromatographic analysis instrument, the flowmeter, temperature transmitter, pressure transmitter, and gas chromatographic analysis instrument are used as primary measuring instruments to measure the flow, temperature, pressure and gas components of natural gas respectively; the flow computer is used as secondary measurement The instrument is calculated by collecting the measurement value of the primary measuring instrument on site, calculates the system uncertainty, and uses the system uncertainty to evaluate the measurement accuracy of the on-site measuring system. The greater the uncertainty, the worse the measuring accuracy of the on-site measuring system. .

Further, it also includes an instantaneous flowmeter of working conditions arranged in the natural gas pipeline, and the instantaneous flowmeter of working conditions collects the instantaneous flow of working conditions in the natural gas pipeline; the flow computer is used as a secondary measuring instrument, by collecting the primary measuring instrument on site. The measured value of the standard condition is calculated, and the instantaneous flow rate of the standard condition is also calculated, and the instantaneous flow rate of the standard condition is compared with the instantaneous flow rate of the working condition, so as to obtain the flow deviation of the on-site metering system.

Further, the flowmeter is a sonic nozzle and an orifice flowmeter, and the uncertainty includes the uncertainty of the cross-sectional area of the throat of the venturi nozzle of the boundary flow, the uncertainty of the outflow coefficient, the uncertainty of the critical flow function, and the stagnation. Pressure uncertainty, gas constant uncertainty, stagnation temperature uncertainty;

When a single critical flow Venturi nozzle participates in the flow measurement, the uncertainty formula of the mass flow measurement of the metering system is:

The formula for calculating the mass flow measured by the metering system is:

Analyze the uncertainty of each parameter item by item.

The gas flow measurement system composed of a critical flow Venturi nozzle or an orifice flowmeter has the same calculation method, and the measurement uncertainty of the mass flow of a single nozzle is taken as the measurement uncertainty of the measurement system.

When a single critical flow Venturi nozzle participates in the flow measurement, the mass flow measurement uncertainty of the metering system can be expressed as:

The formula for calculating the mass flow measured by the metering system is:

Analyze the uncertainty of each parameter item by item:

(1) Uncertainty of the cross-sectional area of the throat of the boundary flow Venturi nozzle:

Critical flow Venturi nozzle of metering system In the data processing system of the metering system, the throat cross-sectional area of the critical flow nozzle is used as a constant to participate in the flow calculation, and its value itself has no systematic error; the throat diameter used to calculate the throat cross-sectional area , using the nominal diameter used in the calibration of the Nanjing sub-station, so as to ensure that the outflow coefficient provided by the Nanjing sub-station can accurately and reliably correct the measured mass flow. However, in the actual measurement process, the cross-sectional area of the throat changes with the pressure and temperature, and the medium components in the measurement pipeline are not completely consistent in each measurement process, which has a certain impact on the measurement results of mass flow.

The simplified calculation formula of nozzle throat diameter with temperature and pressure is:

According to the above formula, it is easy to obtain the difference in pressure and temperature. The calculation formula of the change value of the nozzle throat diameter is:

where - d is the nominal throat diameter;

β is the coefficient of linear expansion of steel, the value is 10.5×10 ^-6 mm/(mm·℃);

E is the Young's modulus of steel, the value is 1.94×10 ¹¹ N/m ² ;

t is the nozzle wall thickness.

According to the test data of the Nanjing substation, the test pressures of the critical flow nozzles are 5.5, 6.0, and 6.5MPa, respectively, and the substations usually work at a pressure of (6.2 to 6.4) MPa; the test temperature of the critical flow nozzles is (12 to 14) ℃, The substation usually operates at a temperature of (5 to 20) °C. The maximum value of the nozzle throat diameter change can be calculated:

Then the maximum value of the change in the cross-sectional area of the nozzle throat is:

According to the uniform distribution, the expanded uncertainty of the nozzle throat cross-sectional area is:

So the relative uncertainty of the nozzle throat cross-sectional area is:

The relative uncertainty of the estimated nozzle throat cross-sectional area is: ur _(A) = 0.015%;

(2) Uncertainty of outflow coefficient:

Typically, the outflow coefficient of the critical flow Venturi nozzle of the critical flow Venturi nozzle gas flow measurement system can be traced back to the "mt" method gas flow measurement system of the Nanjing substation, and the uncertainty of the outflow coefficient has been found to be excellent through previous calibration reports. at 0.15%; confidence probabilities are all 95%, including factor k=2. The test data for traceability of its value can be found in the calibration certificate of the critical flow Venturi nozzle:

k＝2；Therefore, the traceability uncertainty of the outflow coefficient of the critical flow Venturi nozzle throat diameter of the critical flow Venturi nozzle gas flow measurement system is better than

k=2;

The data processing system of the critical flow Venturi nozzle gas flow measurement system adopts the linear fitting method, interpolates and calculates the outflow coefficient of the nozzle, and determines the outflow coefficient value involved in the calculation by calculating the Reynolds number of the nozzle throat.

According to the outflow coefficient corresponding to the Reynolds number of each nozzle in the inspection process provided in the nozzle report, the relationship between the outflow coefficient and the Reynolds number can be determined.

The formula for calculating the Reynolds number at the nozzle throat is:

由此引起的质量流量测量变化可以忽略不计。The dynamic viscosity of natural gas is a parameter related to temperature and gas composition. The uncertainty of the calculation result given by the relevant data is estimated to be 0.75%, but in the process of flow measurement, its sensitivity coefficient is very small.

The resulting change in mass flow measurement is negligible.

k＝2；The uncertainty of the critical flow Venturi nozzle outflow coefficient is:

k=2;

(3) Uncertainty of critical flow function:

The critical flow function is a function of stagnation pressure, stagnation temperature and gas composition. Its value is little affected by temperature and pressure, and the sensitivity coefficient is as follows:

The influence of stagnation pressure and stagnation temperature on the critical flow function can be ignored, and the uncertainty mainly comes from the mathematical model of calculating the critical flow function with gas components. The data processing system of the metering system uses the state equation provided by the AGA-NO.8 report to calculate it. Its ideal state equation has no error, but the deviation of the actual gas calculation result is 0.05%. According to the uniform distribution, the critical The expanded uncertainty of the flow function is:

⑷ Uncertainty of stagnation pressure:

The stagnation pressure at the upstream inlet of the critical flow Venturi nozzle is the static pressure at the nozzle inlet measured by a pressure transmitter, and is calculated by the thermodynamic formula. The calculation formula is:

The isentropic index is determined by the operating pressure, temperature and the measured natural gas composition; the Mach number is calculated from the nominal volume flow of the nozzle and the diameter of the pipe at the upstream inlet. These two parameters are used to calculate the stagnation pressure. The effect of the results is about 0.002%, which can be ignored. It is considered that the uncertainty of stagnation pressure mainly comes from the uncertainty of pressure measurement at the upstream inlet of the nozzle.

The uncertainty of pressure measurement mainly comes from the sum of the gauge pressure transmitter plus the absolute atmospheric pressure transmitter. The pressure transmitter of the Rosemount company's model 3051S is selected for the gauge pressure transmitter. After debugging and on-site verification , its indication error is better than 0.025%, the absolute pressure atmospheric pressure transmitter selected by Rosemount company's model is 3051C, its indication error is better than 0.05%, considering that the actual pressure is about 50 times the atmospheric pressure, so The maximum contribution value of the uncertainty of the absolute pressure transmitter is less than 0.05%/50=0.001%. According to the uniform distribution, the expanded uncertainty of the stagnation pressure is:

⑸ Uncertainty of gas constant:

The universal gas constant is introduced as a constant in the data processing system. During the calculation process, its value does not change, so it can be considered that there is no error in the universal gas constant; , the composition of natural gas is obtained by on-line chromatographic analysis, and the molar mass measurement accuracy is 0.1%. According to the uniform distribution, the relative uncertainty of the gas constant is obtained as:

⑹ Uncertainty of stagnation temperature:

The stagnation temperature at the upstream inlet of the critical flow venturi nozzle is the static pressure measured by the temperature transmitter, and is calculated by the thermodynamic formula. The calculation formula is:

The error of the stagnation temperature calculation result introduced by the error of the isentropic index and Mach number is 0.004%. It can be considered that the uncertainty of the stagnation temperature mainly comes from the measurement uncertainty of the static temperature. The indication value of the temperature transmitter The error is better than 0.1K, the common operating temperature is 293.15K, and the expanded uncertainty according to the uniform distribution of stagnation temperature is:

Based on the above, the flow measurement uncertainty of the metering system is as follows:

serial number symbol relative uncertainty 1 A 0.015% 2 C_d 0.15% 3 C_* 0.058% 4 P₀ 0.029% 5 R/M 0.115% 6 T₀ 0.039%

The uncertainty of mass flow measurement of critical flow Venturi gas flow measurement system is better than:

The confidence probability is 95%, and the inclusion factor is k=2.

Example 3:

As shown in Figure 1, a natural gas measurement and evaluation system includes a flow measurement device arranged in a natural gas pipeline and a flow computer 6 arranged outside the natural gas pipeline; the flow measurement device includes a flow meter 1, a temperature transmitter 2, Pressure transmitter 3, gas chromatographic analysis instrument 4, described flowmeter 1, temperature transmitter 2, pressure transmitter 3, gas chromatographic analysis instrument 4 are used as primary measuring instruments to measure flow, temperature, pressure and gas of natural gas respectively Components; the flow computer is used as a secondary measuring instrument, and it is calculated by collecting the measurement value of the primary measuring instrument on site to calculate the system uncertainty, and use the system uncertainty to evaluate the measurement accuracy of the on-site measuring system. The larger the value, the worse the measurement accuracy of the field metering system.

Further, it also includes an instantaneous flowmeter of working conditions arranged in the natural gas pipeline, and the instantaneous flowmeter of working conditions collects the instantaneous flow of working conditions in the natural gas pipeline; the flow computer is used as a secondary measuring instrument, by collecting the primary measuring instrument on site. The measured value of the standard condition is calculated, and the instantaneous flow rate of the standard condition is also calculated, and the instantaneous flow rate of the standard condition is compared with the instantaneous flow rate of the working condition, so as to obtain the flow deviation of the on-site metering system.

Further, it also includes a switch 5, the flow meter 1, the temperature transmitter 2, the pressure transmitter 3, and the gas chromatographic analysis instrument 4 are respectively connected with the switch 5, and data exchange is carried out through the TCP/IP protocol, and the flow computer 6 Connect to the switch 5, collect the data in the flow meter 1, the temperature transmitter 2, the pressure transmitter 3, and the gas chromatographic analysis instrument 4 through the TCP/IP protocol, and calculate the system uncertainty and the standard condition instantaneous flow.

Further, it also includes a PLC programmable logic controller 7, a communication network 8 and a diagnostic terminal 9, and the flowmeter 1, temperature transmitter 2, pressure transmitter 3, and gas chromatographic analysis instrument 4 are respectively connected with the PLC programmable logic. The controller 7 is connected, and data exchange is carried out through the TCP/IP protocol. The communication network 8 is responsible for the network communication between the PLC programmable logic controller 7 and the diagnosis terminal 9. The flow computer 6 is connected with the diagnosis terminal 9. /IP protocol collects data in flowmeter 1, temperature transmitter 2, pressure transmitter 3, and gas chromatographic analysis instrument 4, and calculates system uncertainty and instantaneous flow rate under standard conditions.

Further, the flowmeter is an ultrasonic flowmeter, or a turbine flowmeter, or a waist wheel flowmeter, or a mass flowmeter, or a vortex flowmeter, and the uncertainty includes volume flow uncertainty, pressure uncertainty , temperature uncertainty, compression factor uncertainty;

The uncertainty formula is:

Analyze the uncertainty of each parameter item by item, where:

u _r (q _s,s ) is the uncertainty of volume flow under operating conditions;

u _r (p _s ) is the operating condition pressure uncertainty;

u _r (T _s ) is the operating temperature uncertainty;

u _r (Z _s ) is the uncertainty of the compression factor of the working condition;

u _r (p _f ) is the standard pressure uncertainty;

u _r (T _f ) is the standard temperature uncertainty;

u _r (Z _sf ) is the standard condition compression factor uncertainty;

The uncertainty function in the uncertainty formula comes from the calculation formula of the volume flow of the standard table method gas flow standard device, and the calculation formula of the volume flow of the standard table method gas flow standard device is:

In the formula: q _s,f - the standard volume flow under the standard conditions of the flow meter;

q _{s, s} —volume flow under the flowmeter working condition; a working flowmeter device is provided in the natural gas pipeline, and the working flowmeter device includes a working flowmeter, and the volume flow under the flowmeter working condition The measured value from the working condition flowmeter;

p _f — pressure under standard conditions, take a constant, 101.325kPa;

T _f - the temperature under standard conditions, take a constant, 20 degrees Celsius;

z _f —compression factor under standard conditions;

p _s —pressure under the working conditions of the flowmeter; the natural gas pipeline is provided with a working condition flowmeter device, and the working condition flowmeter device includes a working condition pressure transmitter, and the pressure under the working condition of the flowmeter comes from The measured value of the working pressure transmitter;

T _s —the temperature under the working condition of the flowmeter; the natural gas pipeline is provided with a working condition flowmeter device, and the working condition flowmeter device includes a working condition temperature transmitter, and the temperature under the working condition of the flowmeter comes from The measured value of the working temperature transmitter;

z _s —compression factor under the working conditions of the flowmeter; the compression factor at the flowmeter is calculated according to the method in the AGA NO. stated;

Further, the flowmeter is a sonic nozzle and an orifice flowmeter, and the uncertainty includes the uncertainty of the cross-sectional area of the throat of the boundary flow Venturi nozzle, the uncertainty of the outflow coefficient, the uncertainty of the critical flow function, and the stagnation. Pressure uncertainty, gas constant uncertainty, stagnation temperature uncertainty;

When a single critical flow Venturi nozzle participates in the flow measurement, the uncertainty formula of the mass flow measurement of the metering system is:

The formula for calculating the mass flow measured by the metering system is:

Analyze the uncertainty of each parameter item by item.

Claims (6)

1. A natural gas measurement evaluation system is characterized in that: the flow meter comprises a flow metering device arranged in a natural gas pipeline and a flow computer arranged outside the natural gas pipeline; the flow metering device comprises a flow meter, a temperature transmitter, a pressure transmitter and a gas chromatographic analysis instrument, wherein the flow meter, the temperature transmitter, the pressure transmitter and the gas chromatographic analysis instrument are used as primary measuring instruments to measure the flow, the temperature, the pressure and the gas components of the natural gas respectively; the flow computer is used as a secondary metering instrument, the uncertainty of the system is calculated by collecting the measured value of the primary metering instrument on the spot, the measurement accuracy of the field metering system is evaluated by using the uncertainty of the system, and the greater the uncertainty is, the poorer the measurement accuracy of the field metering system is.

2. The natural gas metering and evaluating system according to claim 1, wherein: the natural gas pipeline working condition instantaneous flow meter is arranged in the natural gas pipeline and used for collecting working condition instantaneous flow in the natural gas pipeline; the flow computer is used as a secondary metering instrument, the measured value of the primary metering instrument on the site is collected to calculate, the instantaneous flow of the standard condition is also calculated, and the instantaneous flow of the standard condition is compared with the instantaneous flow of the working condition, so that the flow deviation of the on-site metering system is obtained.

3. The natural gas metering and evaluating system according to claim 1, wherein: the flowmeter is an ultrasonic flowmeter, a turbine flowmeter, a waist wheel flowmeter, a mass flowmeter or a vortex shedding flowmeter, and the uncertainty comprises volume flow uncertainty, pressure uncertainty, temperature uncertainty and compression factor uncertainty;

the uncertainty formula is:

analyzing the uncertainty of each parameter item by item, wherein:

u_r(q_s,s) The working condition volume flow uncertainty;

u_r(p_s) Working condition pressure uncertainty;

u_r(T_s) Working condition temperature uncertainty;

u_r(Z_s) Compression factor uncertainty for the operating conditions;

u_r(p_f) The standard condition pressure uncertainty;

u_r(T_f) Is standard condition temperature uncertainty;

u_r(Z_sf) The standard condition compression factor uncertainty;

the uncertainty function in the uncertainty formula is derived from a calculation formula of the volume flow of the standard meter method gas flow standard device, and the calculation formula of the volume flow of the standard meter method gas flow standard device is as follows:

in the formula: q. q.s_s,f-standard volumetric flow rate at standard conditions of the flowmeter;

q_s,s-volumetric flow rate under the conditions of the flowmeter; the natural gas pipeline is internally provided with a working condition flowmeter device, the working condition flowmeter device comprises a working condition flowmeter, and the volume flow under the working condition of the flowmeter is from the measured value of the working condition flowmeter;

p_f-pressure under standard conditions, constant, 101.325 kPa;

T_f-temperature under standard conditions, constant, 20 ℃;

z_f-compression factor under standard conditions;

p_s-pressure under flow meter conditions; the natural gas pipeline is internally provided with a working condition flowmeter device, the working condition flowmeter device comprises a working condition pressure transmitter, and the pressure of the flowmeter under the working condition is from the measured value of the working condition pressure transmitter;

T_s-temperature under flow meter conditions; the natural gas pipeline is internally provided with a working condition flowmeter device, the working condition flowmeter device comprises a working condition temperature transmitter, and the temperature of the flowmeter under the working condition is obtained from the measured value of the working condition temperature transmitter;

z_s-compression factor under flowmeter conditions; the compression factor at the flow meter is calculated according to the method in the AGA No.8 report, which is a well-known technique and not described in further detail herein.

4. The natural gas metering and evaluating system according to claim 1, wherein: the flow meter is a sonic nozzle and an orifice plate flow meter, and the uncertainty comprises uncertainty of sectional area of a throat part of a boundary flow Venturi nozzle, uncertainty of outflow coefficient, uncertainty of critical flow function, uncertainty of stagnation pressure, uncertainty of gas constant and uncertainty of stagnation temperature;

when a single critical flow venturi nozzle participates in flow measurement, the mass flow measurement uncertainty formula of the metering system is as follows:

the mass flow calculation formula measured by the metering system is as follows:

the uncertainty of each parameter is analyzed item by item.

5. The natural gas metering and evaluating system according to claim 1, wherein: the flow meter, the temperature transmitter, the pressure transmitter and the gas chromatography instrument are respectively connected with the switch, data exchange is carried out through a TCP/IP protocol, the flow computer is connected with the switch, and data in the flow meter, the temperature transmitter, the pressure transmitter and the gas chromatography instrument are collected through the TCP/IP protocol.

6. The natural gas metering and evaluating system according to claim 1, wherein: the flow computer is connected with the diagnosis terminal and collects data in the flow meter, the temperature transmitter, the pressure transmitter and the gas chromatography analyzer through the TCP/IP protocol.

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