Problems and Countermeasures in the measurement of

2022-08-20
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Problems and Countermeasures in natural gas measurement

1 current situation of natural gas measurement

China is a large country rich in natural gas resources The prospective reserves of natural gas reach 3.8*1013m3 (38 trillion m3), and the proven reserves at present are 1.6*1012m3 (1.6 trillion m3) Natural gas is an efficient, clean fuel and high-quality chemical raw material. Natural gas flow measurement has become an important constraint to the development of natural gas industry, and it is an important problem that must be solved in the use of natural gas. Flow measurement is not only the basis for trade settlement between natural gas suppliers and demanders, but also a technical indicator of gas consumption efficiency of production departments In the production and management of enterprises, flow measurement is an important technical basic work carried out daily. Accurate measurement of natural gas can not only make fair trade settlement, but also improve production technology, improve product quality, reduce product production costs, ensure safe production, and improve economic and social benefits

2 problems existing in natural gas measurement at present and their causes

there are many kinds of flow measurement instruments and various calculation models, such as standard orifice flowmeter, vortex flowmeter, vortex flowmeter, ultrasonic flowmeter, etc. in addition to standard orifice flowmeter, there is a lack of necessary standards or specification support

with the help of long-term international experimental research and practical experience, orifice flowmeter began to implement instrument dry calibration as early as the 1930s, and has been widely used since then China has formulated the standard orifice metering method (sy/) for natural gas flow in the natural gas industry, which stipulates the structural form, technical requirements, pressure tapping mode and application method of throttling device of the standard orifice, as well as the data of flow calculation and its uncertainty It provides a standard basis for natural gas flow measurement

however, there are still many problems in natural gas flow measurement with orifice flowmeter

orifice flowmeter consists of three parts: throttling device, differential pressure transmitter and flow indicator. Under the severe working conditions on site, the use and maintenance of throttling device, differential pressure transmitter and its connecting pressure pipeline are the key points. The standard orifice metering method for natural gas flow (sy/) points out that although natural gas is extracted from the formation and after separation, dust removal and filtration, its components are very complex. From single well calculation, gas injection metering to gas distribution metering, the gas components are different, so the corrosion of throttling devices in use is also different In particular, the erosion and corrosion of the right angle population edge of the orifice plate and the inner wall of the measuring pipe are particularly serious, which will affect the specified standard of the arc radius rk of the right angle inlet edge of the orifice plate and the relative roughness k/d of the inner wall of the measuring pipe, the outflow coefficient C will change, and the uncertainty of flow measurement will exceed the estimate

there are three main factors affecting the deviation of outflow coefficient C from the standard value

2.1 error caused by the instrument itself

(1) right angle sharpness of orifice plate inlet. (2) The pipe diameter is inconsistent with the calculation. (3) Orifice thickness error. (4) Steps and eccentricities are generated in the accessories of throttling parts. (5) Flatness of upstream end face of orifice plate. (6) The size of the ring chamber produces steps and eccentricity. (7) Pressure tapping position. (8) Welding, weld protrusion. (9) The pressure tapping hole is processed irregularly or blocked. (10) Throttling parts have different axial degrees

2.2 installation error

deviation of pipeline layout. The installation error caused by the deviation of pipeline layout is universal, and its main reason is that the length of straight pipe section cannot be met on site

2.3

(1) orifice plate bending (deformation). (2) Dirt is deposited on the upstream measuring pipe. (3) The casting of the laboratory machine manufacturer uses the casting method to make the metal material produce plastic deformation and deposit dirt on the upstream end face. (4) The right angle edge of orifice plate inlet becomes blunt and damaged. (5) The Reynolds number range does not conform to the standard. (6) The pipeline roughness is affected, and the pipeline roughness increases, and the pipeline roughness changes indefinitely

3 ways to solve natural gas measurement problems

3.1 strengthen management and improve personnel quality

the reason why orifice flowmeter is easy to deviate from the standard lies in the working principle and structural characteristics of the instrument itself. The error of the instrument itself is the installation and use error caused by the cooperation between the two sides to establish an advanced polymer micro processing platform. During manufacturing, the installation and use error is caused by fluid medium corrosion, wear, contamination, etc. during installation or long-term use Therefore, the flow metering system should be installed in strict accordance with the technical requirements to eliminate the installation error In the process of use, the operator should do a good job in the overhaul, maintenance and repair of the system, extend its service life and reduce the measurement error At the same time, we should strengthen the publicity and implementation of sy/t standard in practical application. The method of reducing error is mentioned in the standard orifice metering method (sy/) of natural gas flow In the appendix, the function treatment of the zigzag testing machine with partial deviation from the standard provisions in use stipulates that in practical application, two correction coefficients shall be added to the outflow coefficient C, namely, the orifice inlet sharpness correction coefficient and the pipe wall roughness correction coefficient, or the replaceable orifice throttling device shall be used. Therefore, in the practical application of natural gas measurement, we should study deeply, understand the essence of the standard orifice measurement method (sy/t) of natural gas flow, install, use and process data in strict accordance with the standard provisions, and ensure the accuracy of natural gas measurement

3.2 correct selection of measuring instruments

standard throttling device should be preferred for measuring instruments. When the flow change range is large, wide range intelligent differential should be considered. Other types of detection instruments should be carefully selected in the corresponding standard of measuring natural gas. The measurement model of secondary instruments should meet the requirements of sy/t. FZ can input components and calculate C value in real time

3.3 strengthen technical training, learn from foreign experience

introduce, digest and absorb the natural gas meter developed in recent years. Our technical masters have a good understanding of various performances of the machine and new technologies. From the perspective of foreign countries, energy measurement has almost completely replaced the traditional volumetric measurement in the international trade of natural gas, while volumetric measurement still occupies a dominant position in the field of natural gas measurement in China In order to be in line with international standards as soon as possible, users can jointly tackle key problems with various scientific research institutes, carry out the test work of natural gas energy measurement, and complete standardization on this basis. In order to speed up the test progress, it is suggested to introduce foreign advanced gas chromatography system and flow computer, and develop natural gas energy measurement system suitable for China's national conditions on the basis of digesting the imported technology

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