是将标准孔板与多参数差压变送器(或差压变送器、温度变送器及压力变送器)配套组成的高量程比差压流量装置，可测量气体、蒸汽、液体及天然气的流量，广泛应用于石油、化工、冶金、电力、供热、供水等领域的过程控制和测量。 Orifice flowmeter is a high-range specific differential pressure flow device composed of a standard orifice plate and a multi-parameter differential pressure transmitter (or differential pressure transmitter, temperature transmitter and pressure transmitter). It can measure gas, The flow of steam, liquid and natural gas is widely used in the process control and measurement of petroleum, chemical industry, metallurgy, electric power, heating, water supply and other fields.
1 Influence of measured fluid characteristics
Due to the nature of natural gas, complex changes will occur with changes in the external ambient temperature, which will affect the measurement accuracy of the flow meter. For the measurement of natural gas, the working temperature and pressure of natural gas must be determined first, because the change in external temperature will also change the pressure and temperature of natural gas, which may cause excessive changes in density and compression coefficient. Low-density gas is difficult for some measurement methods. At this time, the selected measurement method must be changed, or temperature and / or pressure must be corrected to ensure the accuracy of the measurement.
2 Impact of instrument performance
The main reasons for the error caused by the orifice plate flow meter are: the sharpness of the right angle of the orifice of the orifice; the size of the pipe diameter does not match the calculation; the thickness of the orifice plate is wrong; the accessories of the throttle are stepped or eccentric; Dimensions produce steps and eccentricity; take pressure position; welding, weld seam protrude; irregularity or blockage of pressure take hole processing; different axiality of throttle parts and so on. These factors may affect the repeatability of the orifice plate. Repeatability is determined by the principle of the instrument itself and manufacturing quality. It is an important indicator in process control applications. In addition to accuracy, it depends on the calibration system. In practical applications, the excellent repeatability of the meter is disturbed by many factors, including changes in fluid viscosity and density, which will affect the measurement accuracy. If the meter output characteristics are non-linear, this effect is more prominent.
3 Impact of Flowmeter Installation
The installation error caused by the deviation of the pipeline layout is universal, and the main reason is that the site cannot meet the required length of the straight pipe section.
4 Impact on environmental conditions
Although the installation of the flowmeter can be used normally, due to changes in the environmental conditions and expected conditions, some performance parameters and hardware aspects of the instrument have also changed, which will change the measurement results of the flowmeter.
Orifice flow meter measurement problem approach
1 Strengthen management. Improve personnel quality
易于偏离标准的原因在于仪表本身的工作原理与结构特点，仪器自身误差是制造时产生的，安装和使用误差则是在安装时或长期使用中由于流体介质腐蚀、磨损、沾污等造成的。 The reason for the orifice plate flowmeter to easily deviate from the standard lies in the working principle and structural characteristics of the meter. The error of the instrument itself is caused during manufacture. The installation and use errors are due to corrosion, wear and contamination of the fluid medium during installation or long-term use. Caused by. Therefore, the flow metering system should be installed in strict accordance with technical requirements to eliminate installation errors.
2 Correct selection of measuring instruments
The measuring instrument should be a standard throttling device. When the range of flow changes is large, a wide-range intelligent differential change should be considered. Other types of testing instruments should be selected carefully in the corresponding standard for measuring natural gas. The measurement model of the secondary instrument should comply with SY / T6143-1996 requires the calculation of Fz to be able to input components and calculate the C value in real time.
3 Strengthen technical training and learn from foreign experience
Introduce, digest and absorb new natural gas metering technologies developed in recent years. From the perspective of foreign countries, in the natural gas international trade, energy metering has almost completely replaced traditional volume metering, while China's gas metering field still occupies a controlling position. In order to be in line with international standards as soon as possible, users can work with various scientific research institutes to carry out experiments on natural gas energy measurement and complete standardization on this basis. In order to speed up the test progress, it is recommended to introduce advanced foreign online gas chromatography systems and flow computers, and develop a natural gas energy measurement system suitable for China's national conditions on the basis of digesting imported technologies.
机体现场清理过程是一个肮脏、粗笨、既花钱而又低效的工作。 Conventional orifice plate flowmeter body cleaning process is a dirty, clumsy, costly and inefficient task. It needs to pull the body of the flowmeter out of the tube, and then either place it on a fixed tube or hang it with a crane, and then use a large and expensive grindstone to rotate back and forth to clean it. This is a laborious and inefficient labor. Because it not only needs to spend money to lease special lifting equipment, hire skilled plumbers, but also to damage the inner surface of the flowmeter body due to the rotation of the grinding stone, and the final waste residue will also pollute the surrounding environment.
After observing the disadvantages of the traditional cleaning process, Mr. Robert A. Burns of Illinois, USA, developed a new method for on-line cleaning of the orifice flowmeter body after four years of intensive research. The online cleaning process of the flowmeter body named "Borns Cleanup Method" was inspired by himself and the engineering team when he observed the flowmeter cleaning process of a large natural gas underground storage facility in Illinois. .
The Borns online cleaning method uses a specially developed cleaning flange that can enter the inside of the flowmeter body. A high-pressure spray gun is installed on the flange. The spray gun uses a specially designed rotating nozzle to spray a non-hazardous and biodegradable hard surface cleaner into the body of the flow meter. The spray gun is engraved with a scale mark that passes through a certain part of the inside of the flowmeter body. It can not only reduce and remove all the glycol and grease dirt and debris adhering to the surface of the body, but also can finally trap dirt and debris under closed loop conditions. The technician came to the clean-up site to complete this kind of work by adopting the general contract work method (turn-key project), so no other client was needed.
The Borns flowmeter body cleaning method has the following advantages:
(1) Avoid the high costs caused by the preparation of related equipment, the employment of skilled plumbers and the complicated operation process;
(2) Get rid of the old method of using rotary grindstone scraping equipment, complete the expensive cleaning work in the past, and enhance the accuracy of flowmeter measurement;
(3) Reduced downtime of flowmeter cleaning, which can make it return to service quickly;
(4) All waste liquids can be finally processed in a closed loop system.