Vortex flowmeters gradually replace orifice flowmeters in many industries

The orifice flowmeter is composed of a throttle pressure-receiving device and a differential pressure transmitter. The pressure-guiding pipe needs to have a heat-treating measure for a place that is easy to freeze, and a static sealing point of a flow measurement circuit is about 20, The following problems exist in use:
It is easy to freeze, easy to block, easy to leak, and heat is easy to cause aging of differential pressure transmitter device. In some cases, the pressure guiding tube needs to be added with isolation liquid. Due to heat or process instability, positive and negative pressure guiding tube isolation liquid The lines are often unequal, resulting in a liquid column difference that makes the flow indication inaccurate.
All of the above will change the flow coefficient, and the measurement accuracy will be reduced. The tube shortens the pressure guiding tube and directly installs the differential pressure transmitter on the pipeline, but there is still a dead zone of flow.
The vortex flowmeter has only three static sealing points, which are not easy to leak, no dead zone of flow, no heat insulation, no influence on fluid gravity, temperature, pressure, and viscosity. The flow coefficient is unchanged for a long time. .

However, when the vortex flowmeter is used in the presence of vibration, the flow measurement may be inaccurate. At present, anti-vibration vortex flowmeters have been introduced on the market to overcome the impact of vibration on flow measurement inaccuracy.
(1) Initial investment
An imported vortex flowmeter is about 20,000 RMB (DN15-DN50), and a throttling device including differential pressure transmitter, orifice plate and flange, pressure guiding tube, valve, incubator or protection box are also required. 15,000 yuan, from a long-term perspective, the use of vortex flowmeters is still cost-effective.
(2) Installation costs
The vortex  installation is simple, just ensure that there is a certain straight pipe section before and after the flowmeter. The straight section of the orifice plate, the concentricity, the pressure guiding pipe, the transmitter, the incubator have certain installation requirements, and the installation cost is the vortex. Several times.
(3) Maintenance costs
In addition to the periodic calibration of the vortex flowmeter, there is generally no failure, but the orifice plate is not, the leakage, the regular discharge, the isolation of the liquid, the replacement of the pressure control pipe, the valve, the insulation, the cleaning orifice, etc. There is a certain amount of maintenance. For example, 200 sets of flow orifice measuring circuit (heating and heating), every two years, the heating and heating system transformation has to invest a certain maintenance fee, which does not include the update of the differential pressure transmitter, the orifice renewal cost. Calculate enough to buy a certain number of imported vortex.
(4) Operating costs
1. Steam consumption costs
For example, 200 sets of flow orifice measuring circuits (heating and heat tracing required), each with a hot gas consumption of 0.02t/h, if the average annual calculation is 4300 hours, the steam cost is 40 yuan / ton, then the annual steam consumption cost is about 688,000 yuan, the annual cost per circuit is 0.344 million yuan.
2. Energy costs
The pressure loss of the vortex flowmeter is smaller than that of the orifice plate, which is about 1/15 of the orifice plate. Therefore, long-term operation requires less energy for pumps and fans. The orifice plate is 15 times larger than that of the vortex. When used for gas or steam flow measurement, the density is small, the flow volume of the same pipe diameter is large, the pressure loss is more serious, and the energy consumption is higher.
3. Leakage charges
The sewage discharge fee depends on the number of sewage discharges, which is about 20 times per year. The discharged pollutants and materials pollute the atmospheric environment. If the sewage exceeds the standard, the environmental protection department must also impose a fine.
(5) Long-term operation accuracy
The design accuracy of the orifice plate system is 1.5%-2.5%. Since the differential pressure and the flow rate are linear relations of phenanthrene, when the flow rate is lower than 30%, the error increases, the gas is too serious, and on the other hand, due to the long-term wear of the medium used, The acute angle becomes dull, causing the flow coefficient to change, which is also an important reason for the accuracy.
Due to the special structure of the vortex, the accuracy is almost constant when the accuracy is actually determined (about 0.5% - 1% of the measured value).
(6) Interchangeability
The same vortex can measure the flow of gas, liquid and steam. Electronic circuit boards and sensitive components are common to flowmeters with different diameters. The signal output usually has three forms: pulse, analog and digital signals. It can be switched by the switch of the board, and the user can switch to another output signal at any time according to his own needs. Changing the range is also very easy. For the analog output, just change the input pulse frequency line.
The orifice plate is not. The pore size is designed for a specific medium. The interchangeability is poor, and it is difficult to change the range. The orifice plate needs to be recalculated.
(7) Range ratio
Since the output frequency of the vortex flowmeter is linear with the flow rate, the flow ratio can be 20:1-80:1. For example, Foxboro's vortex flowmeter measures the gas to vapor range ratio of 80:1. The measuring range of the measuring liquid is 40:1, which can adapt to the requirements of the process flow measuring range, and the accuracy can still be guaranteed.
The differential pressure of the differential pressure flowmeter has a nonlinear relationship with the flow rate. When the flow rate is small, the measurement is not accurate, and the range ratio is only 3:1-5:1. If you increase the turndown ratio, you must try to improve the accuracy of the differential pressure transmitter.
(8) Reliability
There is now a more reliable vortex .It has two sets of electronic circuits and two sets of sensitive components installed on one body, which are independent of each other and can be used for important flow measurement occasions. It is difficult to do this with differential pressure flow meters. point.
(9) Energy saving effect
For example, the amount of steam is 120t/h, the pressure is 3.9Mpa, and the temperature is 445oC. If the vapor is measured by orifice plate, the pressure loss is 0.03-0.05Mpa. If calculated according to 0.03Mpa, the energy consumption of this orifice is 82kW. According to 300 days a year, the annual consumption of 590,000 kW/h is 68.5 tons of standard coal. If the vortex energy consumption is only 1/15-1/20 of the orifice plate, if it is 1/20, then It consumes only 3.34 tons of coal per year, accounting for only 3.33% of the energy consumption of the orifice.
(10) The influence of the flow characteristics of the primary component on the control system
Since the output frequency of the vortex is linear with the flow rate, when it is combined with the regulating valve and the regulator level into a control system, it is equivalent to a hysteresis link with a time lag and a small time negligence, which can be regarded as a proportional link. The characteristics of the generalized object depend entirely on other links in the loop, and have little effect on the control system.
The orifice flowmeter is not. Because its output is linear with the flow rate, the loop gain varies with the flow rate. Although the flow characteristics of the regulating valve are used to compensate the linear influence of the generalized object, the effect is not obvious, so it must be introduced. The introduction of the squarer and the squarer makes the characteristics of the generalized object not change with the working point, which obviously changes the adjustment quality, but the response is fast, sensitive and easy to cause the system at a small flow rate, and the adjustment error increases.
In summary, vortex flowmeters are versatile in many flow measurements to replace orifice plates, saving money and effort, and it does have many benefits for flow measurement.

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