Basic information of orifice flow meter

An orifice flow meter is a high-range ratio differential pressure flow device consisting of a standard orifice and multi-parameter differential pressure transmitter (or differential pressure transmitter, temperature transmitter, and pressure transmitter), which can measure the flow of gas, steam, liquid, and natural gas.

It is widely used in process control and measurement in the petroleum, and chemical industry, metallurgy, electric power, heat supply, water supply, and other fields. The orifice flowmeter is widely used in coal, chemical industry, transportation, construction, light textile, food, medicine, agriculture, environmental protection and people's daily life, and other fields of the national economy. It is an important tool to develop industrial and agricultural production, save energy, improve product quality, and improve economic efficiency and management level. In process automation instruments and devices, flow instruments have two major functions: as a detection instrument of process automation control system and a total table for measuring material quantity.

Verification and detection

This flowmeter has a wide range of applications. All single-phase flow rates can be measured, and some mixed-phase flows can also use this product. Due to the two-phase flow, it can not be accurately measured, and even water hammer may occur, which may damage the pipe fittings. If an annular orifice is used, condensate can flow away from the edge of the annular orifice. The minimum flow surface is a circle close to the inner wall of the pipe, while the minimum flow surface of the standard orifice is a concentric circle at the center of the pipe. The flow rate of impurities in the fluid is low, which generally flows close to the pipe wall. New types of throttling devices are constantly emerging and being promoted. The differential pressure transmitter and display instrument matched with the throttling device are developing rapidly in terms of performance and quality.

The orifice flowmeter, which should be a sharp right angle at the inlet edge, has become a bell mouth, changing the discharge coefficient, resulting in large errors, and has to be replaced. It can be seen that this product is the best choice for measuring the flow of high-temperature fluid.

Design style

The fluid flows through the throttling device in the pipeline, causing local contraction near the throttling element, increasing the flow rate, and generating static pressure differences on both sides of the upstream and downstream.

The throttling device of the orifice flowmeter is simple in structure, firm, stable, and reliable in performance, long in service life, and low in price. It is a commonly used flow-measuring instrument in the industry. The entire processing process adopts international standards and has undergone strict verification and testing.

The orifice flowmeter increases the flow rate and lowers the static pressure, so a pressure drop is generated before and after the throttling element, that is, the pressure difference. The larger the flow of the medium, the greater the pressure difference before and after the throttling element. Therefore, the orifice flowmeter can measure the fluid flow by measuring the pressure difference. This measurement method is based on the law of conservation of energy and the law of continuity of flow.

The orifice flowmeter can measure the flow of various fluids in the pipeline. The measurable mediums include liquid, gas, and steam. It is widely used in the petroleum, chemical industry, metallurgy, light industry, coal mine, and other industrial sectors.

A static pressure difference is generated before and after the orifice flowmeter, which has a certain functional relationship with the flow. The greater the flow, the greater the pressure difference. The differential pressure signal is transmitted to the differential pressure transmitter, which is converted into 4-20ma DC analog signal output and is transmitted to the flow totalizer to realize the measurement of fluid flow. A mass flow meter, using an intelligent differential pressure transmitter, realizes the measurement of fluid mass flow.

The orifice flowmeter shall supply hot air, and the hot blast furnace is generally close to the blast furnace, with many elbows. In the past, standard orifices were used, and the error was large because the straight pipe section was not long enough. Since the instrument has a grading ring and multiple pressure taps, a 2D long straight pipe section is required. After being installed on the air supply pipe of the hot blast stove, the application is very satisfactory. More than thirty hot blast stoves have been installed with annular orifice flowmeters, which have been running for more than three years without failure.

Scope of application

• Nominal diameter: 15 mm ≤ DN ≤ 1200mm orifice steam flowmeter
• Nominal pressure: PN ≤ 40MPa
• Working temperature: - 50 ℃ ≤ t ≤ 550 ℃
• Range ratio: 1:10, 1:15
• Accuracy: Grade 0.5, Grade 1

Model Selection

Pipeline conditions:

(1) The straight pipe section in front of and behind the throttling element must be straight without visible bending.

(2) The straight pipe section used for installing the throttling element shall be smooth. If it is not smooth, the flow coefficient shall be multiplied by the roughness correction coefficient.

(3) In order to ensure that the fluid flow forms a fully developed turbulent velocity distribution at 1D in front of the throttling element, and make this distribution into a uniform axisymmetric shape, 1) the straight pipe section must be round, and the roundness requirements for the 2D range in front of the throttling element are very strict, and there are certain roundness indicators.

(4) The length of the straight pipe section between the first resistance part and the second resistance part on the upstream side of the throttling part can be determined according to the form of the second resistance part β= 0 7 (regardless of the actual situation β What is the value) 1/2 of the value listed in Table 1

(5) When the upstream side of the throttling element is an open space or a large container with a diameter ≥ 2D, the length of the straight pipe between the open space or larger container and the throttling element shall not be less than 30D (15D). If there are other local resistance parts between the throttling element and the open space or the large container, except that the minimum straight pipe section length 1 specified in Table 1 is set between the throttling element and the local resistance parts, The total length of the straight pipe section from the open space to the throttling element shall not be less than 30D (15D).

Instrument introduction

working principle
Under the condition that the relevant parameters are known, the relationship between differential pressure and flow rate can be derived according to the flow continuity principle and Bernoulli equation to obtain the flow rate. The basic formula is as follows:
C - Discharge coefficient dimensionless
D - Diameter of orifice or throat of throttling element under operating conditions
D - Inner diameter of upstream pipe under operating conditions
QM - mass flow Kg/s
QV - Volume flow m/s
D/D-diameter ratio dimensionless
The density of fluid Kg/m
Expandability coefficient dimensionless

Orifice flow meter structure

Throttling parts: standard orifice plate, standard nozzle, long diameter nozzle, 1/4 round orifice plate, double orifice plate, eccentric orifice plate, circular orifice plate, tapered inlet orifice plate, and other pressure tapping devices: ring chamber, pressure tapping flange, clamping ring, pressure pipe and other connecting flanges (national standards, various standards, and flanges of other design departments), fasteners. Measuring tube.

Installation requirements for orifice flow meter: the requirements for the straight pipe section are generally the first 10D and the second 5D. Therefore, when purchasing an orifice flow meter, it is necessary to select the flowmeter suitable for the site industry and mining, according to the on-site industrial and mining conditions of the flow meter.

When the fluid that fills the pipeline flows through the throttling device in the pipeline, the flow beam will form local contraction at the throttling element of the throttling device, thus increasing the flow rate.

Orifice plate flow

• The structure of the throttling device is easy to copy, simple, and firm, with stable and reliable performance, long service life, and low price.
• Orifice plate calculation adopts international standards and processing
• Wide application range, all single-phase flows can be measured, and some mixed-phase flows can also be used.
• The standard throttling device can be put into use without real flow calibration.
• The all-in-one orifice plate is simpler to install, without a pressure pipe, and can be directly connected to a differential pressure transmitter and pressure transmitter. Intelligent features
• Imported monocrystalline silicon intelligent differential pressure sensor
• High precision, perfect self-diagnosis function
• The measuring range of an intelligent orifice flow meter can be adjusted by self-programming.
• Cumulative flow, instantaneous flow, pressure, and temperature can be displayed at the same time.
• In addition to online and dynamic full compensation functions, it also has a self-diagnosis and self-setting range.
• Equipped with multiple communication interfaces
• High stability
• Wide range, greater than 10:1

Intelligent technical indicators

• High precision: ± 0.075%
• High stability: better than 0.1% FS/year
• High static pressure: 40MPa
• No need for adjustment after 5 years of continuous operation
• The influence of temperature and static pressure can be ignored
• High overvoltage resistance

Characteristics of intelligent orifice flow meter

• Imported monocrystalline silicon intelligent differential pressure sensor
• High precision, perfect self-diagnosis function
• Intelligent orifice flow meter The measuring range of the intelligent orifice flow meter can be adjusted by self-programming.
• The intelligent orifice flow meter can simultaneously display the accumulated flow, instantaneous flow, pressure, and temperature.
• In addition to online and dynamic full compensation functions, the intelligent orifice flow meter also has a self-diagnosis and self-setting range.
• Equipped with multiple communication interfaces
• High stability
• Wide range, greater than 10:1

Required parameters

• Pipe diameter (pipe diameter * wall thickness)
• Pipe material
• Medium measured by an orifice flow meter
• The working temperature of the measured medium
• Working pressure of the measured medium (maximum pressure, minimum pressure, normal pressure)
• Working flow of the measured medium (maximum flow, minimum flow, normal flow)
• The viscosity of the measured medium

Precautions

Transmitter

The high range ratio differential pressure flow device matched with the transmitter can measure the flow of gas, steam, liquid, and natural gas. An orifice plate throttling device is a standard throttling element, which can be directly produced according to national standards without calibration.

All single-phase flow rates can be measured, and some mixed-phase flows can also use this product. The HNLG orifice flow meter is simple to install and does not need a pressure pipe. It can be directly connected to a differential pressure transmitter or a pressure transmitter for measurement. It can simultaneously display the cumulative flow, instantaneous flowmeter, pressure, and temperature of the fluid, and is equipped with a variety of communication interfaces.

When the fluid filled with pipe flows through the orifice plate, it will produce local contraction, flow beam concentration, flow rate increase, and static pressure decrease, so a static pressure difference will be generated before and after the orifice plate.

The structural principle of the orifice flow meter is that an orifice plate is installed on the pipeline, and the two sides of the orifice plate are connected with pressure measuring pipes, which are respectively connected with the U-shaped differential pressure gauge. The orifice plate flow meter uses the throttling effect of fluid passing through sharp holes to increase the flow rate and reduce the pressure, resulting in the pressure difference between the front and back of the orifice plate, as the basis for measurement. If the pipe diameter is d1, the orifice plate sharp hole diameter is d0, the diameter of the shrink pulse formed after the fluid flows through the orifice plate is d2, and the fluid density is ρ。 Velocity at the interface I and II, i.e. at the pressure measuring pipe in front of the orifice plate and at the contraction pulse.

debugging
1. Connect the signal line and power line
2. Open the inlet and outlet valves with the same opening
3. Open the stainless steel three-valve group balance valve, slowly open the valve at the high and low pressure ends of the orifice plate, and close the stainless steel three-valve group balance valve after the fluid passes through the flowmeter.
8 Product Classification

Since the application of the orifice flow meter in the industrial field, its application scope has been expanded, and the original product specifications and standards can not better adapt to the development of rapidly changing industrial machinery. Therefore, the production researchers of orifice flowmeters have developed two kinds of orifice flowmeters that can meet the needs of various industries, including integrated orifice flowmeters and intelligent orifice flowmeters.

The difference between the two is:

1. The integrated orifice flow meter is a differential pressure generator for measuring flow. It can measure the flow of various fluids in the pipeline with various differential pressure gauges or differential pressure transmitters. The orifice flow meter throttling device includes annular orifice plates, nozzles, etc.

2. The intelligent orifice flowmeter is a new generation flowmeter that integrates flow, temperature, and pressure detection functions, and can automatically compensate for temperature and pressure. The orifice flowmeter adopts advanced microcomputer technology and new micro power consumption technology, with strong functions, compact structure, simple operation, and convenient use.

Classification

Standard orifice plate

The standard orifice plate is a standard throttling device with the most specifications, which is widely used in various fluids, especially in gas flow measurement. The structure of the orifice plate is different due to different pressures, diameters, and pressure measurement methods. The standard orifice plate can be divided into three types according to the common pressure tapping methods: corner joint pressure tapping, flange pressure tapping, and diameter distance pressure tapping.

Round hole plate
Pressure tapping mode: flange pressure tapping
Eccentric orifice
Pressure tapping mode: corner connection

Eccentric orifices and circular orifices are only suitable for installation on horizontal or inclined pipes, and cannot be used on vertical pipes. If the measured fluid contains solid particles, the opening or notch shall be placed below; If gas is separated from the liquid, the opening or notch shall be placed above; The pressure tap is located on the opposite side of the tangent point between the circular notch or eccentric opening and the pipe.

Embedded orifice plate

This type of orifice plate is a combination of the orifice plate and measuring pipe, which is generally used for small pipe diameter (DN ≤ 50mm), so it is also called a small pipe diameter orifice plate.

characteristic:

(1) Compact structure, durable and reliable.
(2) It can measure small flow and is convenient for on-site installation.
(3) It is required to prepare a straight pipe section (the first 5D and the second 2D require precision machining).

Service conditions:

(1) Nominal diameter: 15-50mm
(2) Nominal pressure: ≤ 6.3 MPa
(3) . Accuracy (uncertainty): 2.5%

Restriction orifice

It is used for pressure reduction and flow restriction during fluid transportation. Use the characteristics of the pressure loss of the throttling element to achieve the purpose of reducing pressure and limiting flow. Features: simple structure, durable and reliable. It is not necessary to measure the differential pressure.

Annular orifice

The annular orifice plate is applicable to all kinds of fluid (gas, steam, liquid) media. In addition to the simple and firm structure and convenient installation and use of standard orifice plates, it also has the following advantages:
1. It is more suitable for measuring saturated steam, superheated steam, gas, cooling water, and other dirty fluids.
2. It is easier to adapt to the flow measurement of high-temperature and high-pressure fluids.
3. It is more reliable and more accurate than round and eccentric orifice plates.
4. The corrosion-resistant type is made at a lower cost, and the flow of corrosive fluid is measured.
5. Because of its simple external shape, the product is easy to be made into a jacket with moisture retention type, and steam is passed in the jacket, which can prevent the measured fluid (such as heavy oil, residual oil, etc.) from condensation or adhesion in the measuring pipe section; The cooling liquid can prevent the liquid easy to vaporize from forming vapor-liquid two-phase flow when flowing through the flow measuring plate.
6. The pressure equalizing ring structure is adopted to reduce the source of measurement error, which leads to the average static pressure of the cross-section of the pressure tapping pipe at the upstream and downstream of the flow measuring plate. It weakens the influence of the velocity distribution distortion caused by the upstream local resistance on the accuracy, and the actual accuracy is closer to the basic accuracy.
7. Front and rear straight pipe sections with low requirements
8. The integrated structure is adopted to reduce pipeline laying.
9. The differential pressure transmitter with a remote transmission capsule can be used to measure the flow of dirty liquids such as pulverized coal and residual oil. Working principle: Like the ordinary standard orifice, the annular orifice throttling device is based on the fluid continuity equation and the Bernoulli equation. When the annular orifice plate is installed in the round pipe, when the liquid flows through the throttling device, the pressure difference between the upstream and downstream sides will be generated.
Connection mode: flange connection and welding connection.