Guo Xu southwest China and China Petroleum Oil and Gas Branch (Chengdu 610213)
He Min Ji-Qin of China's oil industry flow of natural gas metering station (Chengdu 610215)

Abstract On the site of natural gas trading, many factors may influence the precision of settlement. These factors such as gas quality and installation are often beyond the control of the requirements of metering calibration. Some new-type flowmeters like ultrasonic flowmeters have been tested at verification stations and used at metering stations. It has been proved that the accuracy of measurement of ultrasonic flowmeters is higher than 0.5%, with such strong points as high accuracy, good repetitivity, broad range ratio, strong anti-interference, small amount of maintenance, and measurement of two-way flow.
Subject Headings Venturi nozzle for critical flow, Actual flow test, Ultrasonic flowmeter, Field application

Natural gas metering system and the status quo

At present, China's natural gas metering system to the main orifice flowmeter. As we all know, by cutting expenditure orifice flowmeter devices, guided pressure pipeline system, composed of differential. Its characteristics are smaller than the range, pressure loss, very sensitive to the pulsating, two-way flow, and so can not be measured. Although the orifice flowmeter has been a hundred years of history, but because measurement instrument error (device to cut expenditure for the design, manufacture, installation and use of the conditions do not meet the ISO5167-1 [1] the requirements of, or inappropriate choice of instrument) and the use of changes in conditions The error (longer period, traffic changes beyond the scope of the chosen instrument of measurement, or pulsating flow generated), tend to make the orifice flowmeter accuracy can not be better than 1.5%. Although ISO/TR3313 [2] has inhibited the flow of the pulse and error estimates provide some data for the use of reference, but to meet the needs of the scene there is still much to be desired: the scene of the type of resistance flow far more than the standard provided in the , And impacted the flow of the form of the ever-changing, the scene still some issues to be resolved (such as cyclone, the Department of the standards will be no requirement); pilot study will take a lot of manpower and resources; use Zheng Liuguan to shorten the length of the straight tube will bring additional pressure loss, but also increase the use of maintenance workload. Orifice not suitable for measuring pulse flow, because of differential signal for the non-linear relationship with the flow, with pressure pipelines to slow and signal distortion, cut expenditure on the pulse of a wave-generated obstacles, such as the reflection [3]. As the impact of trade settlement orifice flowmeter accuracy of many factors, resulting in gas measurement error was 2 percent. How to improve and enhance the accuracy of natural gas metering system is the industry issues of common concern, and the corresponding development of a large number of new flow meter. In many flow meter, China's natural gas flows through the metering station (the metering station) is natural gas flow testing and field application that Ultrasonic Flowmeter, intelligent Swirlmeter better results, it is worth promoting.

Overview of natural gas flow metering station

China's oil industry flow of natural gas metering station at the Asian investment is the largest natural gas metering station, with a time of quality (mt) a standard system (the uncertainty of 0.1 percent) and the critical flow Venturi nozzle sub-standard system (it does not Set of 0.25 percent). Calibration pressure range: 0.2 ~ 3.8 MPa, calibration of the traffic condition: 5 ~ 6000 m 3 / h. Diameter range: DN25 ~ DN400. So far, the United States, the Netherlands, Germany, Singapore, China and other countries a variety of flowmeter calibration with the flow than it is right, has accumulated tens of thousands of experimental data.

Ultrasonic Gas Meter is the flow calibration and field applications

A real flow calibration

Metering station uncertainty of 0.25 percent for the critical flow Venturi nozzle flow standards for the devices, according to AGA.NO.9 [4] with the draft report and verification protocols JJGl98-94 [5] conducted various tests the following: different Channel (5, 4, 3, 2, 1); different diameters (DN300, DN150); different installation conditions (ideal line conditions, non-ideal conditions pipeline; "ideal conditions" means the installation of better conditions , As no less than 170 D elbow, no transition components, such as pieces of non-resistance. Flow more stable, without the pulsating flow, without vortex flow; "non-ideal conditions" means in the upper reaches of ultrasonic flowmeter 13 D join the resistance of the former man-made , Double-bend, T-shaped bend, Shen Suqi, the tube, and so on); install different direction (flowmeters are, reverse the installation, channel level, vertical installation); different pressure (2.0 MPa, 1.2MPa, 0.8 MPa).
(1) Ultrasonic Flowmeter suitable for the high-pressure, large-calibre, the flow of working conditions, but especially for small flow inflection point (maximum flow of 10 percent, with Qt that) the following paragraph should be anti-flow (see Figure 1).

Figure 1 12 "Q.Sonic-5S ultrasonic flowmeter ideal and non-ideal line after line after test results (superscript status)
Description: Two-elbow after the test, in addition to traffic for the 240 m 3 / h, showing the relative value of error of 1.45 percent, the remaining points are the indicators.

(2) Ultrasonic Flowmeter the flow of gas from the measurement of the impact to the same degree of accuracy for two-way flow measures (see Figure 2).

Figure 2 12''4S Ultrasonic Flowmeter is ideal under the pipeline, the reverse flow indication error comparison chart (flowmeter coefficient 0.9962)

(3) of the same manufacturer of ultrasonic flowmeter, channel number, the more accurate measurement of the higher traffic, more reliable performance (see table 1).

Table 1 the same number of channels under the conditions of the impact of ultrasonic flowmeter

(4) Ultrasonic Flowmeter the pre-test and calibration flow is between a system error, the seizure of the factory stem qualified to be the real test flow calibration, sometimes due to the installation of the error might exceed 0.3 percent. Such as the 4 S Ultrasonic Flowmeter its factory set at 0.9962 flow coefficient, the ideal line test to ensure accuracy of better than 0.5%, but in non-ideal conditions under the pipeline flow is calibrated set of parameters, the "ideal pipeline Conditions "2.0 MPa and 0.7 MPa pressure tests, the error is greater than AGA.NO.9 impact on the pipeline installation of not more than 0.3% of the requirements and should therefore be based on the scene working conditions for real flow calibration