With the energy saving and emission reduction, environmental protection has become an important assessment indicators of all levels of government and all kinds of industrial enterprises, so that the scope of natural gas is increasing, the number of natural gas trade settlement increased year by year. Measurement of natural gas flow is the most important part in the industry of natural gas pipeline. It is the main factor that the enterprise carries on the trade, the reverse is the operating result of the enterprise, the internal economic analysis and the operation cost are the main factors that affect the economic benefit of the enterprise and the user interest. At present, the main flow measurement instruments in natural gas transmission pipeline are orifice plate differential pressure type flowmeter, gas turbine flowmeter and gas ultrasonic flow meter. Ultrasonic flow meter is a kind of flow measuring instrument which has just arisen in recent years, because it has the advantages of traditional instrument which is not unique and has been widely welcomed by users.
The advantages of ultrasonic flow meter in flow measurement accuracy is almost not affected by the temperature, pressure, viscosity, density and other parameters, and can be made into non contact and portable measuring instruments, so that it can be easily used and portable, so it is difficult to measure the flow measurement of other types of flow meter, such as non electric, strong corrosive, radioactive and flammable and explosive media. In addition, in view of the non contact measurement features, can also be equipped with a reasonable electronic circuit, an ultrasonic flowmeter can be adapted to a wide range of measurement and measurement of a wide range of flow. So the ultrasonic flow meter has the ability to adapt to other traffic flow.
Firstly, we make a general understanding of the basic principle of ultrasonic flowmeter:
1, ultrasonic flowmeter probe
2. The technical characteristics of the time through principle
DANIEL / ultrasonic flowmeter is time through ultrasonic flowmeter
- the sound wave is transmitted from one probe to another, and is not reflected by the wall.
The acoustic wave is transmitted from the upstream to the downstream (due to the acoustic wave is pushed by the air current) of the time (the acoustic wave is the reverse of the air flow).
- the difference between the two time and the velocity of the gas flow is a kind of relationship.
- the average velocity and the velocity of sound waves can be calculated from the measured transmission time.
The metrological administrative department under the State Council shall be responsible for establishing various measurement datum instruments, as the highest basis for unifying national quantity.
According to "the people's Republic of China National Measurement Method" Ninth provisions: the Department and enterprise, public institution of the highest measurement standard apparatus, and for trade settlement of the work measurement apparatus, the compulsory verification.
Metrological verification shall be carried out in accordance with the principle of economic and reasonable.
Secondly, it is about how to test the ultrasonic flowmeter
Test Center (hereinafter referred to as measurement center) is the main function: first, the calibration for trade settlement and measurement of the flow meter, and the pressure, temperature, the amount of the test and calibration; two is for the social pressure, large diameter, large flow of traffic flow meter calibration services; three is to carry out natural gas measurement technology research.
The metering center can operate under the pressure of near 7.5MPA, in which the flow rate of various types of gas flow meters with no more than 400 mm in the operating mode flow is 8 m3 / h to 12000 m3 / h.
Real flow verification is in the process of testing to allow testing fluid flow through the flow meter, and flow standard device or standard instrument to determine the standard flow rate as the basis, assess the flow meter accuracy, stability and other measurement performance, or the flow meter calibration or calibration, and determine whether it is qualified. Strictly speaking, the basic characteristics of online real flow verification is the installation and use of the flow meter in the verification and the actual use of the process.
Third is about how the ultrasonic flowmeter is removed
Two kinds of combination scheme, the difference between the two is the difference between the selection of process valve, so that there are some small differences in the work principle.
Pressure regulating lever in the normal work, all the process valve is opened, pressure regulating pry melody, following a road reserve, six valve set point are not the same. SSV valve is in the open state, and the other two valve PCV and PV are in the closed state. And the same tone of the working principle, after about pressure regulating lever regulating valve after the pressure reaches 4.0 MPa, if pressure regulator failure occurred in a PCV07603, monitor regulator PV07602A replace melody adjust the voltage, valve after the pressure reaches 4.1MPa. If there is a failure to monitor the PV07602A, there are two kinds of situations:
First, monitoring the regulator PV07602A to shut down, then this way will lose the role of pressure adjustment, and temporarily cut off the gas supply, then the pressure will fall. When the pressure drop to reach 3.9Mpa at 3 days and alternate road monitoring regulator PV07602B open, but due to the main regulator PCV07603B closed, so the valve pressure continue to decline, when the pressure decreased to 3.8mpa, the main regulator PCV07603B open. Then, alternate road is really began to work the.
Second, monitor PV07602A regulator can not be closed, then the road will rise, when the valve after the pressure reached SSV07601A, the 5.0MPa will automatically shut down, the road will lose the role of pressure, and the same as the first principle, alternate road to start work.
So no matter tone tone control voltage regulator which happens and, by adjusting pressure can be a good automatic switching of high pressure, and pressure effect is very good.
The above is figure 1 the most common way of work, there is one, is the same as the setting point of the two valves, one way to work, the other way in front of the process valve closed, when the work of the road, when the other way to open another.
Figure 2 in each way more than one electric ball valve, there is a way in the pressure at the same time, another standby, when one of the way is a failure, then open the electric valve, and the other way to start working, the set points are the same. Our company is the use of such a front with an adjustable pressure valve.
Fourth is for the flow control valve for the use and its application
1, flow control
In theory, the control valve can achieve the flow of control, but in practice there are the following problems.
(1) self operated pressure relief valve to valve and valve after the pressure for the flow of the flow adjustment, the direct reference to the object is the pressure, it is difficult to achieve accurate adjustment of flow.
(2) to adjust the pressure valve for flow regulation, the need for the re setting of its command, affected by the operating conditions, the site operation is difficult, but it takes longer time.
(3) the pressure value of the setting of the adjustable pressure valve is adjusted on-line, which is easy to cause the instantaneous stop gas or flow over the range.
(4) the influence of the supply and demand of gas, the actual setting value of the pressure valve and the valve after the pressure is not necessarily equal, when the relationship between supply and demand is reversed, prone to accidents.
Electric control valve to control the flow, directly regulate the flow section, the site operation is convenient, fast and safe.
2, protection technology and equipment
(1) protection valve. Flow switching is a gas station the most frequent operation, in the process of the switching valve is opened, flow dramatic challenge erosion of the valve sealing surface, resulting in leakage within the equipment. According to the process of switching operation rules, using flow regulating valve structure of the advantages, in the before and after the valve is fully open, slowly open the flow control valve can focus shock in the flow control valve, reduce or even eliminate the process of switching on the upstream and downstream of the valve at the instant of impact and prolong the service life of the equipment.
(2) protection of surge valve. Air transmission pipeline pressure system is the use of the Chinese FISHER pry body, which is easy to pick up the pressure valve for the valve cover, valve, the valve body. By adjusting the valve and flow valve to work, reasonable adjustment of flow control valve opening, as far as possible to make the valve sleeve in the large open motion, in order to increase the flow section of the pressure valve, dispersed erosion surface. Practice has proved that the pressure regulating valve and flow control valve, can be extended to the replacement of the valve parts of the replacement cycle, reduce production and operation costs.
3, inhibition of asthma
Small flow gas supply, often occurs when the flow phenomenon, that is, the flow is quasi periodic and large and small. The analysis thinks, in the small flow section, the sensitivity of the pressure drop, easy to adjust the instantaneous lag or instantaneous excess phenomenon, resulting in a surge of breath. By reducing the opening of the regulation valve, inhibiting the instantaneous excess process, it can achieve the suppression of the breath flow.
