How should the natural gas flowmeter be selected? Look here!
2021-06-26
In the use of natural gas flowmeters, the first problem is the selection of instruments. Natural gas flow meter selection is not an easy thing, it has to consider a lot of factors. There are generally: instrument performance, fluid characteristics, installation requirements, environmental conditions, and price factors. A decision can only be made after careful analysis and comparison. If the decision is wrong, the entire measurement may fail. Among them, the exact understanding of the measurement object (that is, the actual condition of the fluid) is very important, it should be pointed out here that not the user has an accurate understanding of his measurement object, and often requires in-depth investigation by the selection designer to find out.
In the design of metering and regulating station of city gas system, which flowmeter should be selected, there are roughly such aspects.
For the metering personnel who have worked in the oil metering system for decades, for the measurement of natural gas and other gases, they often choose orifice plate natural gas flowmeters without thinking, and they will think that this is already a conclusion. However, after in-depth analysis, it is clear that the orifice plate is not suitable. The downstream of the city gas metering and regulating station is often a large number of scattered users, and some are even all residents. In the cooking time, everyone uses gas, the flow is large, and the gas is basically not used between two meals, the flow is small. Fluctuation of such a large flow range with a range ratio of 3 :1 orifice plate is definitely not applicable, less than the orifice small flow is not measured. For example, the measuring range of a hole plate is 300 ~ 900m3/h, when only a few residents are using gas, and the gas flow is less than 300m3/h, the gas supply side will lose money.
At present, orifice plate natural gas flowmeters are often used in the following occasions :① large diameter occasions, when the diameter is greater than 600m, there is generally no other instrument to choose, only the orifice plate can be used;
(2) In the whole measuring process, the flow rate is relatively constant, and the flow fluctuation range does not exceed the range ratio of 3 :1 of the hole plate;
(3) For industrial monitoring and measurement, even if the fluctuation range is large, the range of a group of continuous aperture plates (more than ten pieces) can be covered, and the part of natural gas leakage that is not measured when the orifice plate is replaced (refers to the orifice valve that can not stop the orifice plate for replacement) is not considered. Another principle of flowmeter selection for oilfield personnel is to choose a flowmeter without moving components, which is considered to be wear-free and durable.
Therefore, the vortex gas flowmeter is considered. However, after analysis, it is believed that the scope of use of vortex gas flowmeter is limited due to the Strauha number St (Re≥4000), that is, when the downstream flow rate of the metering regulator station is small, the flow rate can not meet the requirements, and it can not be measured accurately, so the selection of vortex gas flowmeter is not appropriate.
As mentioned earlier, if the waist wheel gas flow meter is stuck, it is equal to cutting off the gas source, so the waist wheel can not be used.
Because of the large pressure loss (and the domestic meter has poor anti-interference ability), the precession vortex gas flowmeter is not suitable for the pressure regulator station.
Selected turbine gas flowmeter, mainly using foreign advanced high-quality gas turbine gas flowmeter. It has a wide measuring range, and the measuring range can reach 15:1 ~ 30:1, and the measuring range can be increased under high pressure gas transmission. Low pressure loss; The accuracy is not less than 1 level, which is less affected by the change of flow field than the orifice flowmeter. In comparison, turbine gas flowmeters are compact in structure and small in size. Easy to install, low cost. Another notable feature is: pulse output, more convenient to use with the computer. They all solve the problems of durability, resistance to dirty media, anti-interference, and minimal maintenance of impeller bearings. For example, the bearing adopts Boeing aircraft engine bearing materials and is designed to be fully sealed, so that dirty media is difficult to affect the bearing part. According to the data, the natural gas flowmeter can ensure that the original accuracy can be maintained after 8 to 15 years of use.
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