Application of Gas Rotary Flow Meter in Closed Measurement of Urban Civil Gas Area

1. Introduction

With the increase of natural gas exploration in China and the increasing urgency of urban environmental protection. Urban gasification has become a development trend in major and medium-sized cities across the country. Under the influence of the market economy, the metering work in urban gas transmission and distribution directly affects the survival and development of gas management departments, and is also an important assessment indicator for the work of these departments. Then, facing more than a dozen types and hundreds of varieties of gas flow meters at home and abroad, how to reasonably select and correctly design according to the various physical properties, flow states, installation requirements, environmental conditions, and economic efficiency of the fluid is the premise and basis for good metering work, and it is also an immortal theme for research and discussion by gas metering departments and professional designers in various cities. As a gas management department, we attach great importance to the metering and charging work in the jurisdiction area. According to the actual working conditions, we chose to try out the RTQ-ZC series intelligent gas waist wheel flowmeter produced by Jiangsu Ruite Instrument Co., Ltd. This volumetric flow meter is used as a metering instrument for the closed assessment of gas fees in civil communities. This series of meters not only has all the characteristics of a volumetric flowmeter, but also has a perfect combination with its intelligent integrator, which enables the flowmeter to obtain a wider range ratio without losing metering accuracy, and is particularly suitable for the metering of dry pipes with large fluctuations in gas consumption in residential areas.

2. The working principle and characteristics of the volumetric gas impeller flowmeter:

2.1 The working principle of the volumetric flowmeter:

The volumetric flowmeter is designed with a space of a certain volume inside. The rotor inside the flowmeter rotates under the pressure of the fluid flowing in from the inlet. As the rotor rotates, the fluid flows from the inlet to the outlet. At this time, during the rotation of the rotor, a certain volume space is formed between the rotor and the flowmeter housing, so that the fluid fills this space. As the rotor rotates, the fluid is continuously sent to the outlet. If the volume of the space is designed well and the number of rotations of the rotor is measured, the volume given by the space can be obtained, thereby obtaining the volume of the fluid flowing through. In addition, based on the number of rotations of the rotor measured per unit time, the instantaneous flow rate can be obtained. This is the measurement principle of the volumetric flowmeter.

2.2 The working principle of the impeller flowmeter;

When the measured fluid flows through the flowmeter, the dynamic pressure of the fluid forms a differential pressure between the inlet and outlet, which drives the impeller to rotate (as shown in Figure 1)

When the fluid drives the waist wheel on the D2 axis to rotate counterclockwise, Figure 1A, the driving gear connected to it drives the waist wheel on the D1 axis to rotate clockwise, and after rotating 90o, it becomes the state of Figure 1C. The upper waist wheel is driven by the fluid to rotate clockwise, and the driving gear drives the lower waist wheel to rotate counterclockwise. When the waist wheel rotates 360o, four times the effective volume of the metering chamber will discharge the fluid from the flow meter. In this way, the two waist wheels are driven to rotate alternately, and as the waist wheels rotate, the fluid is continuously discharged from the flow meter through the metering chamber. The volume of fluid discharged for each rotation of the waist wheel is a fixed value, that is, the discharge volume is proportional to the number of rotations of the waist wheel shaft. Through the waist wheel shaft and other transmission mechanisms, the number of rotations is decelerated and transmitted to the integrated display part. It is this working principle of the rotary flowmeter that determines that as long as the internal clearance design and assembly of the metering chamber are reasonable, this flowmeter will have higher accuracy and lower starting flow. This feature is extremely important in the gas metering of residential areas. It not only meets the metering accuracy of residents during normal gas use, but also overcomes the inability of other types of flowmeters to deal with the small amount of gas during low-peak gas use.

2.3 Working principle of the intelligent integration part of the RTQ-ZC series gas rotary flowmeter:
As shown in Figure 2, the integration part detects the number of rotations of the rotor shaft through the pulse sensor. This pulse signal is amplified by the circuit, filtered and shaped, and then sent to the microprocessor for counting processing. The microcomputer calculates according to the input instrument coefficient K value and the measured number of pulses. The formula is as follows:

Q=3600×f/K

Q——Volume flow rate of fluid flowing through the flow meter Unit: m3/h
f——Pulse frequency Unit: n/s
n——Number of pulses
k——Instrument coefficient Unit: n/m3

After the flow value is obtained, it is sent to the LCD drive circuit to drive the LCD to display the instantaneous flow of the fluid. At the same time, the Q value is accumulated and stored inside the flow meter. The accumulated gas volume measured by the flow meter can be viewed at any time through the function key. [page]

The integration part uses the method of inputting different instrument coefficients at five different flow points under the powerful support of the microprocessor to correct the nonlinear section of the characteristic curve of the volumetric flow meter so that the flow meter can obtain a wide range ratio. The curve comparison is shown in Figure 3:

It can be seen from the characteristic curve that the small flow part of the characteristic curve of the RTQ-ZC series intelligent gas waist wheel flowmeter has been significantly improved, which is exactly what we hope to achieve in the closed metering of civil gas areas.

3. Application of RTQ-ZC series intelligent gas waist wheel flowmeter in regional closed metering:

In order to cooperate with the work of reducing the difference, it is a feasible measure to adopt regional closed metering for civil gas, and to reduce the accounting unit. On the one hand, it can assess the work of the community toll collectors and analyze the operation status of the internal pipe network of the community through the difference between the total meter and the sub-meter of the community; on the other hand, it can grasp the gas volume distribution of the entire jurisdiction area through data analysis, which is conducive to the reasonable allocation of gas volume to ensure the gas use of residents.

Characteristics of closed metering in the community:

1) The peak and low peak of gas consumption are relatively concentrated, and the gas flow of the main pipe entering the area varies in a large range, requiring the total meter to have a wide range ratio.
2) The low peak gas flow of gas consumption is very small, sometimes only the gas consumption of several residents' stoves, requiring the total meter to have a very low starting flow.
3) Residents generally use diaphragm-type civil gas meters, which have high measurement accuracy and no gas loss under normal operation, requiring the total meter to have high measurement accuracy.
4) The total meter is installed after the pressure regulator and installed indoors, which is basically the same as the working conditions of residents' gas use. Both the total meter and the sub-meter use volumetric flowmeters to eliminate the difference caused by the change of gas components in different types of flowmeters.
5) Flow meter transformation work. The original process pipeline direction and installation space are greatly limited.

The total meter is required to have no front and rear straight pipe sections and flexible installation methods.

Practice has proved that the RTQ-ZC series intelligent gas waist wheel flowmeter, a volumetric flowmeter, can meet the above requirements. However, it should be noted that the measured medium flowing through the volumetric flowmeter must maintain a certain degree of cleanliness, that is, a gas filter must be installed before the flowmeter, otherwise it will affect the normal operation and reliable accuracy of the volumetric flowmeter.

Taking into account the renovation investment, the average living standard of the residential area, the living habits and geographical location of the residents, the size of the community and many other factors, the Fengheyuan 1045-household commercial residential area located on Kemao Street and the Rongqianxili 3736-household flat-to-renovation residential area located on Wangdingdi were selected as the most representative pilot areas in the city under the jurisdiction. Fengheyuan Community uses natural gas as the gas source. According to the gas usage conditions in the past, an RTQ-ZC-300 intelligent gas rotary flowmeter was selected. The maximum operating flow rate is 300m3/h, the accuracy is ±1%, the range ratio is 1:60 (i.e. 5-300m3/h), the starting flow rate is 3m3/h, and it is installed from top to bottom. A gas filter is installed before the meter. Rongqianxili Community uses natural gas as the gas source. According to the gas usage conditions in the past, an RTQ-ZC-450 intelligent gas rotary flowmeter was selected. The maximum working flow is 450m3/h, the accuracy is ±1%, the range ratio is 1:60 (i.e. 7.5-450m3/h), the starting flow is 4.5m3/h, the upper inlet and lower outlet are installed, and a gas filter is installed before the meter. Since it was put into trial operation in May 2000, it has achieved initial results. Taking the report data from July 20, 2000 to August 20, 2000 as an example, the total gas supply of Fengheyuan Community is 8520m3, the gas sales volume is 7991.5m3, and the difference between purchase and sales is 6.2%. The total gas supply of Qinrong Qianxili Community is 39830m3, the gas sales volume is 37318.27m3, and the difference between purchase and sales is 6.31%. The charging rates of the two communities have increased by about 10% compared with the same period last year. In addition, the closed metering method can accurately obtain the supply and sales difference rate of each closed community, which lays a good foundation for improving the management level of community operation and charging. On the one hand, it can timely discover and take measures for gas theft, gas leakage and "human relations" in charging work, so that the gas management department can reduce economic losses, and at the same time provide favorable monitoring means for safe gas supply; on the other hand, there are also rigid assessment indicators for the work of community toll collectors, which strengthens their sense of responsibility.

When the community is large and the peak flow rate of the inlet main pipe is high, it is necessary to take into account the upper limit flow rate and not lose gas at low flow rate, which invisibly increases the requirements for the range ratio of the inlet total meter. For example; assuming that the maximum flow rate of the inlet main pipe of a residential community is 600 m3/h and the minimum flow rate is 6m3/h, this requires the range ratio of the flow meter at this location to be 1:100. It is difficult for various flow meters to meet this parameter. At this time, we can solve this problem by installing two flow meters in parallel. In the above case, two RTQ-ZC-300 intelligent gas lumbar flowmeters are installed in parallel (Figure 4). The flow range of a single meter is 5-300m3/h with an accuracy of ±1%. During the peak of gas consumption, the two meters are put into operation at the same time, and the upper limit of measurement is 600m3/h, which means that it does not exceed the limit and can meet the measurement accuracy. When the gas consumption is low, one flowmeter is turned off, and the lower limit of measurement of a single operation is 5m3/h, which can meet the measurement requirements of the minimum flow. This switching process can be completed manually or automatically through electric valves and control circuits.

4. Conclusion and Suggestions

4.1 It is concluded from the above example that the working principle and structure of the volumetric flowmeter determine that the gas lumbar flowmeter is more suitable for closed measurement in urban residential gas consumption areas. It is used in conjunction with the intelligent totalizing display part to make this type of flow meter more perfect.

4.2 If conditions permit, use the RTQ-ZA series temperature and pressure compensation intelligent gas rotary flowmeter to directly convert the working flow into standard (20℃, 101.325Kpa) flow display and storage, which will bring greater convenience to the gas department's metering work. (end)