Chongqing Institute of Industrial Automation Instrumentation Sun Huai

1. preamble
According to information on the world energy development in the 1920s, coal is the peak period, the percentage of its total energy over 70 percent of the 1970s to the 1990s oil to replace coal, oil, energy percentage of 30% to 40%, to 21 Early century of natural gas will gradually replace petroleum, natural gas percentage of total energy forecast to exceed 50 percent. The alternative energy to replace its own internal and external reasons, its internal reasons in the past 20 to the slow increase in oil production, and natural gas are high-speed growth, from 1970 to 1996 the world more than doubled the annual output of natural gas and oil production basic Remain unchanged. Allegedly the world still contains a very rich natural gas resources, its natural gas industry for the development and laid a solid foundation.

alternative energy to replace the external causes for natural gas is a highly efficient, cleaner fuel and high-quality chemical raw materials, which greatly attracted by the user. The rapid deterioration of the urban environment of energy is the greatest driving force structural changes. Automobile exhaust emissions has reached the unbearable point, the frequency of acid rain city warning people can no longer maintain the existing energy structure.

rich natural gas resources in China is a big country, according to evaluation, long-term natural gas reserves of 38 trillion cubic meters, has proven reserves are 1.6 trillion legislature main meters. For a long time but the development of the gas industry has seriously lagged behind, but annual output has more than 200 billion cubic meters, only the energy consumption structure of 2% (and the world for more than 20 per cent), and natural gas resources in this large country is not proportionate. Recently the Government attaches great importance to the development of gas industry in making major policy decisions, "West-East Gas Pipeline" opened the start of China's energy structure adjustment of the major curtain. Cities are the end-user of natural gas use in urban users in both industrial enterprises, have common industrial city, it is a mixed group of users. In the use of natural gas in an important issue to be resolved, it is necessary to provide the socialist market economy requirements of the natural gas flow measurement system. Supply and demand of natural gas flow measurement is the basis for the settlement of bilateral trade and gas production sector is the main technical efficiency indicators. In enterprise production and management of day-to-day flow is a measure of the importance of technological foundation work. Accurate timely flow measurement can improve the production technology, improve product quality, reduce production costs, ensure safe production and rational management and to improve economic and social benefits. Now everyone has recognized as compressed natural gas vehicle fuels and urban enterprises and public utilities. To gas and coal as fuel is to improve the basic quality of the urban environment and the fundamental measures. These departments need to be tailored to the requirements of the user traffic measurement instruments. Because users extremely cumbersome, the flow of the requirements of diverse instrumentation, flowmeters product diversification is an inevitable trend. How is followed in such diverse types of flowmeters in the choice of a suitable instrument that problem. Urban natural gas flow meter and long pipelines for trade clearing of natural gas flowmeter have different requirements, it needs to solve the object generally to the measurement of low pressure (1.6 MPa below) and small and medium-sized flow (DN200 below) and installation of poor conditions (straight paragraph Inadequate length), maintenance management is weak in strength, functional easy to understand, easy to operate, maintenance-free, affordable, and so on. To meet these requirements, although there are many sophisticated instruments, to meet the requirement of the users still need a lot of development work, "adapt to the market, will always strive to" plant should be the motto.

2. gas flowmeter Profile

already using or is about to vote with the flowmeter generally have the following categories: Pressure-flow meters, turbine flowmeter, the fluid flow meter vibration, volume flow meter, ultrasonic flowmeter, target - Coriolis flowmeter and mass flowmeter, and so on.

1. Differential Flowmeter: including the detection of as the standard all-speed devices and cutting expenditure, etc.. It is the application of a long history and rich practical experience in mature and improve the standards (all except the speed), the different specifications of a complete flow meter, 20 10 in the 1950s before it may be the only natural gas flow meter. It has many inadequacies in: if the general accuracy, on-site installation of the terms and conditions, pressure loss, the scope of the narrow, and so on; address these shortcomings, in recent years, domestic production plant launched a series of improvements, if the style Pressure Meter, The value of cutting expenditure, expenditure for Orifice devices, a standard nozzle, and so on, plus the 1980s after the Differential Flowmeter two components: differential pressure and flow transmitter for a show that highlighted the progress , It is estimated that the future of such flowmeter will occupy an important position.

2. Turbine Flowmeter: in Europe and the United States Turbine Flowmeter is the orifice flowmeter after the second statutory gas flow meter, has developed more variety, the whole series, and more specifications, the scale of mass production of natural gas flowmeter . Standards are very complete, but some inadequacies in: the media measurement require a higher degree of cleanliness, the use of limited duration. However, according to the use of foreign department said: had the use of 240 of 8 to 15 Meter cycle test, found that the accuracy of the instrument is still within the framework of migration. In addition, the efficient use of a rectifier role of the rectifier coupled with the turbine flow sensors integrated into the structure of the gas turbine flow meter, flow resistance in the upstream side of the elbow or semi-open valve closing conditions, only 2 D straight paragraph Length, with the city to install the narrow space, it is a very prominent feature.

3. fluid vibration Flowmeter: there are two kinds of such flowmeter type: Vortex Flowmeter and precession (vortex precession) flowmeter.

vortex flowmeter has many features, such as the output pulse frequency signals, and traffic signals for the linear relationship, for the total measurement, the scope of relief, pressure loss of small, it is undeniable dynamic components, simple structure , Easy to install, such as maintenance, inadequacies in the rules for the flow field of higher and will take a longer straight, the stress of pipelines and mechanical vibration-sensitive and should not be used in place strong vibration. Practice has proved that for many years, Vortex Flowmeter Selection (a suitable measuring range) is essential, should pay special attention to installation requirements, sometimes at the appropriate adjustment is necessary, increase the use of these effects are the key.

precession Flowmeter features and Vortex is basically the same, but there are two differences: Flowmeter much greater pressure loss and a shorter length of straight pipe requirements. Production plant launched direct-reading (live show) flowmeter users are welcome Incidentally, all cities are using natural gas should be the development of direct-reading scene shows flowmeter, it should be used as one of the basic varieties, is a measurement for the total to The main instrument.

4volume flowmeter include: Roots flowmeter, the film flow meter (domestic gas meters). It is the use of a long history and huge amount of natural gas flow meter, a comprehensive standard specifications. Moderate precision, the wide range of special (150:1), suitable for small and medium-sized flow of direct-reading, without the need of energy and straight tube, and so on.

5. ultrasonic flowmeter

20 in the 1990s ultrasonic gas flow meter started in the gas industry in the application, with its excellent properties caused considerable international attention, became the orifice, the vortex after a major natural gas flow Dollars. It features: high precision, the scope of the very wide and can adapt to very low flow rate (0.5 m / s below) and installed a short length of the straight tube (a multi-channel varieties). Inadequacy of the present: only applicable to large-caliber, high prices, and so on.

6. Target flowmeter

new target flowmeter of a contingency force sensor, has many outstanding features. Such as high accuracy (aggregate measure up to 0.5% ~ 0.1%), the scope of wide (10:1), the application of small and medium-calibre (DN15 above), there is no moving parts, simple structure and easy maintenance, and can be implemented Ganjiao A post-mortem (re-pegging), such as simplified approval cycle.

7. Coriolis mass flow meter

compressed natural gas as vehicle fuels must be resolved to promote the use of the vehicle filling stations measurement issues. Coriolis mass flow meter in the successful application of liquid to gas people in the hope to promote to, but encountered a problem for low-density gas, can not meet the needs of instrumentation to `seek. High-pressure gas to the gas density substantially increase just to meet this demand.

3. Flowmeter Selection of natural gas

the face of so many varieties of gas flow meter, for the average user selection became a problem. How to scientifically and objectively select the best flowmeter is an issue of concern. We believe that selection should follow the appropriate rules, the manufacturers try to avoid misleading publicity for themselves the right to find a flow meter, it is their ideals flowmeter.

Selection may be five areas: performance instrumentation, fluid characteristics, installation conditions, environmental conditions and economic factors. To consider all aspects of the following factors:

1. instrument performance: accuracy, repeatability, linearity, scope, the pressure loss, the limits of traffic, the signal output characteristics, such as response time;

2. fluid characteristics: fluid pressure, temperature, density, viscosity, lubrication and chemical properties, wear and corrosion, scaling, dirt, gas compression factor, such as entropy index, the heat capacity, Conductivity, the speed of sound, mixed-phase flow, such as fluctuating flow;

3. installation conditions: pipeline layout direction of the flow direction, on the lower reaches of pipeline length, diameter pipeline, maintaining space, pipe vibration, grounding, power supply, an auxiliary equipment (filters, sewage), Explosion And so on;

4. Environmental conditions: temperature, humidity, safety, electromagnetic interference, and so on;

5. Economic factors: acquisition, installation fees, maintenance fees, check fees, service life, operating costs (energy consumption), spare parts, and so on.

Selection steps are as follows:

1. primaries based on five factors as the type of available instruments;

2. eliminated in a comparison of selected 2-3 types, from the order;

3. again by five careful assessment, the final out to a type of instrument.

selection depends largely on the success of the Instrument Selection staff quality and performance measurement of the precise targets of understanding. The Instrument of quality manufacturers should pay particular attention to the false propaganda and misleading. Measuring the exact targets of understanding is very important, users do not object to their measurements are accurate understanding of the failure of many selection is not accurate because the parameters provided by the. Some of the objects to go through in-depth investigation to find out the.