Steam flow meter

The steam flow meter is a special instrument for measuring the cumulative mass flow of steam, which has two structural forms: mechanical and intelligent; The quality of all steam flowing through the meter can be accurately read through the on-site display of the indicator dial (mechanical) or LCD (intelligent), and the pulse signal can also be output. At the same time, it has the function of manual pressure compensation or automatic temperature compensation. Because of its simple structure, moderate price, and wide measuring range, the flow meter is widely used in the petroleum, chemical industry, textile, heat supply, and other occasions where a steam flow meter is needed.

Principle

The vortex flow meter is a volume flow meter that measures the volume flow of gas, steam, or liquid, the volume flow of standard conditions, or the mass flow according to the Karman vortex street principle. It can also be used as a flow transmitter in the automatic control system.

The instrument adopts advanced differential technology, in combination with isolation, shielding, filtering, and other measures to overcome the problems of poor seismic resistance and small signal data disorder of similar products, and adopts unique sensor packaging technology and protective measures to ensure the reliability of the product. There are two types of products: basic type and composite type. The basic type measures a single flow signal; The compound type can realize the measurement of temperature, pressure, and flow at the same time. Each type has an integral and separate structure to adapt to different installation environments.

The measuring principle of vortex street flow meter Saturated steam flow measurement was generally adopted by a standard orifice flow meter in the 1980s. However, from the development of flow instruments, the orifice flow meter has a long history and a wide range of applications; It is also the most fully studied and the test data is the most perfect, but there are still some shortcomings in measuring saturated steam flow with standard orifice flowmeter: first, the pressure loss is large; Secondly, the impulse pipe, three groups, and connect joints are easy to leak; Third, the measuring range is small, generally 3 to 1, which is easy to cause low measurement value due to large flow fluctuation. The vortex flow meter has a simple structure, and the vortex transmitter is directly installed on the pipeline to overcome pipeline leakage. In addition, the pressure loss of the vortex flow meter is small, the range is wide, and the measuring range ratio for saturated steam can reach 30 to 1. Therefore, with the maturity of vortex flow meter measurement technology, the use of vortex flow meters is more and more popular.

The vortex street flowmeter measures flow by applying the fluid oscillation principle. When fluid passes through a vortex street flow transmitter in the pipeline, two rows of vortices directly proportional to the flow velocity are generated alternately up and down behind the vortex generator of the triangle column. The vortex release frequency is related to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator, which can be expressed by the following formula:
f=Stv/d
Where: f is the vortex release frequency, Hz; V is the average velocity of the fluid flowing through the vortex generator, m/s; D is the characteristic width of vortex generating body, m; St is Strouhal number, dimensionless, and its numerical range is 0.14-0.27.
St is a function of the Reynolds number, St=f (l/Re).

When the Reynolds number Re is in the range of 102~105, the value of St is about 0.2. Therefore, in the measurement, the Reynolds number of the fluid should be in the range of 102~105, and the vortex frequency f=0.2v/d.

It can be seen that the average velocity v of the fluid flowing through the vortex generator can be calculated by measuring the vortex frequency, and then the flow q can be calculated by the formula q=VA, where A is the sectional area of the fluid flowing through the vortex generator. Applications: power generation, cogeneration, and heating industries; Aviation, aerospace, shipbuilding, nuclear energy, and weapons industries; Machinery, metallurgy, coal mine, and automobile manufacturing industries; Petroleum and chemical industries; Pharmaceutical, food, and cigarette manufacturing industry; Forest industry, agricultural reclamation, light industry, etc.

Classification

(1) Electrical principle: the instruments used for this principle include electromagnetic type, differential capacitance type, inductive type, strain resistance type, etc.
(2) Acoustic principle: ultrasonic and acoustic (shock wave) flow measurement methods are used.
(3) Thermal principle: there is a thermal type, direct calorimetric type, indirect calorimetric type, etc. that uses the thermal principle to measure flow.
(4) Optical principle: laser type, photoelectric type, etc. Are instruments of this kind.
(5) Original physical principles: nuclear magnetic resonance type, nuclear radiation type, etc. are instruments of this kind
(6) Other principles: labeling principle (tracing principle, nuclear magnetic resonance principle), related principles, etc.

Main features 

1. Temperature and pressure compensation function is integrated into the meter body, which can measure the standard volume flow or standard mass flow of fluid.
2. Fully intelligent and digital circuit design, which can automatically compensate for the density of the measured fluid or the standard volume calculation.
3. The new digital filtering and correction function makes the flow measurement more accurate and reliable.
4. The battery-powered type can work continuously for more than two years without an external power supply.
5. New dot matrix Chinese character LCD display, more convenient to use and operate.

Characteristic

1. The highly reliable flow sensor uses the sensing components and control circuits of integrated production, the sensing part has no mechanical movement, and the driving part uses high-quality relays, thus greatly improving the reliability. 

2. The extremely wide flow range flow sensor is only sensitive to the flow rate of the fluid, so it can monitor the flow of different sizes by matching different pipe diameters. The size of the monitored flow is almost unlimited. 

3. The feature of a full straight flow pipe flow sensor is of great significance in many applications. In the production of petroleum, chemical industry, heavy industry, light industry, and bioengineering medicine, which may lead to production accidents such as flow blockage of pipes. The flow switch can implement online monitoring without affecting the flow to avoid production accidents. 

4. The concise and intuitive indication flow sensor has power indication and flows status indication. The flow status in the current pipeline can be displayed visually. 

5. It is applicable to a variety of fluid medium flow sensors. The flow switch of the same model can be used for both gas and liquid, such as water and oil. The flow of gas and liquid can be monitored by adjusting the knob in the flow switch. 

6. The special integrated manufacturing method of the non-pressure loss flow sensor enables the probe to achieve a very small size, so there is almost no pressure loss for the fluid. In many cases, directly replacing the pressure switch will make the system more reliable and more widely applicable.

Characteristics of measurement

The steam we send to hot users is superheated steam. However, after long-distance transmission, with the change of working conditions (generally temperature and pressure), superheated steam will enter a saturation or supersaturation state due to the decrease of heat loss temperature (pressure 0.58 MPa temperature 164 ℃ is superheated steam, Dongyue pressure 0.6MP temperature 245 ℃, and Lumei food pressure 0.58MP temperature 162 ℃), That is to say, the steam received by the remote heat user may become saturated steam. We usually measure the quality of saturated steam with dryness X (the water content in saturated steam). The best is dry saturated steam, which is generally called superheated saturated steam, or superheated steam for short, and its water content is negligible (X=1); The wet saturated steam with poor dryness is called wet saturated steam, and the water content can reach 30% at most, which leads to the problem of "two-phase flow" of saturated steam.

Progress

1. A brief review of natural gas measurement at home and abroad The measurement of natural gas as a high-quality, energy and chemical raw material has been paid more and more attention. Developed countries with higher industrialization levels, such as Europe and the United States, started the research on natural gas measurement technology earlier, invested more capital and scientific and technological strength, and attached great importance to the measurement of trade natural gas. In terms of flow meter selection, turbine and waist wheel flow meters are mainly used in Europe. For example, turbine and waist wheel flow meters in the Netherlands account for about 80%, turbine flow meters in Canada account for about 90%, and steam is mainly used in the United States, accounting for about 80%. On the whole, in terms of the use of flow meters, steam was used in the 1970s, a turbine flow meter was used in the 1980s, and an ultrasonic flow meter was used in the middle and late 1990s.

2. Steam flow meter In recent years, China's natural gas metering technology has made new progress. The metering technology of the steam throttling device and its secondary instrument double bellows differential pressure gauge, which is widely used in China, has inherent defects, such as continuous wear and corrosion of steam during use; The combination forms of on-site resistance parts are far more than the 7 cases specified in the standard; The influence factors of on-site vortex flow and pulsating flow are complex; Poor adaptability to the situation of large gas volume fluctuation and high change frequency; The impulse pipe is easy to cause signal hysteresis, which cannot ensure its measurement accuracy, which brings new research topics to flow workers.