Recently, many customers ask us whether the vortex flowmeter can replace the orifice flowmeter? Today we will explain to you whether these two products can be substituted.1. About vortex flowmeter productsThe basic structure of the vortex flowmeter is composed of a vortex generator, a detection element, and a signal processing amplifying circuit. At present, the research on the vortex generator has reached a fairly complete level. The triangular generator is used as the shape, and the detection elements are: Thermistor, strain gauge, piezoelectric crystal, differential capacitor, ultrasonic, etc. Many of the signal processing parts have been microcomputerized. The vortex flowmeter has the advantages of easy installation (can be installed directly on the pipeline), small size, strong interchangeability, high long-term operation accuracy, and can be applied to most liquid, gas and vapor measurement. At present, the sales of vortex flowmeters in the world market are increasing by about 30% every year.2. About orifice flowmeter productsOrifice flowmeter is a high turndown differential pressure flow device composed of standard orifice plate and multi-parameter differential pressure transmitter (or differential pressure transmitter, temperature transmitter and pressure transmitter). It can measure gas, The flow rate of steam, liquid and natural gas, orifice plate throttling device due to its simple structure, low cost and reliability, it is suitable for almost all media measurement, and the matching differential pressure transmitter has developed rapidly, making it its own The shortcomings can be made up. It is widely used in process control and measurement in the fields of petroleum, chemical industry, gold, electricity, heating, water supply, etc. At present, the technical development level of orifice flowmeters is still based on a certain empirical formula. In 1980, the International Organization for Standardization set R541 Merged with the two standards of R781 into the standard ISO5167 (1980).3. Comprehensive performance evaluation of the two productsThe vortex flowmeter (referred to as the vortex street) has only 3 static sealing points, which is not easy to leak, has no dead zone for flow, does not need heat preservation, and is not affected by fluid gravity, temperature, pressure, and viscosity, and the flow coefficient remains unchanged for a long time. .The orifice flowmeter (orifice plate for short) is composed of a throttling piece pressure taking device and a differential pressure transmitter. The pressure guiding tube needs heat tracing measures for places that are susceptible to freezing. There are about 20 static sealing points for a flow measurement loop. There are the following problems in use: easy to freeze, easy to block, easy to leak, heat tracing easily causes the aging of the differential pressure transmitter device, and in some cases the pressure guiding tube needs to be added with isolating liquid, due to heat tracing or unstable process operation, positive and negative The isolation liquid line of the pressure guiding tube is often unequal, resulting in a liquid column difference, which makes the flow indication inaccurate. All of the above will change the flow coefficient and reduce the measurement accuracy. The pipe shortens the pressure guiding tube and installs the differential pressure transmitter directly on the pipeline, but there is still a dead zone for flow.However, when the vortex street is used in a vibration environment, the flow measurement will be inaccurate. At present, the anti-vibration type vortex street has been introduced on the market to overcome the influence of vibration on the inaccurate flow measurement.(1) Initial investmentAn imported vortex street is about 20,000 yuan (DN15-DN50), and a throttling device including differential pressure transmitter, orifice plate and flange, pressure guiding pipe, valve, incubator or protective box also needs 1. 50,000 yuan, from a long-term point of view, the use of vortex street is still cost-effective.(2) Installation costThe installation of the vortex street is simple, only need to ensure that there are certain straight pipe sections before and after the flowmeter. The straight section of the orifice plate, concentricity, pressure guiding tube, transmitter, and incubator have certain installation requirements, and the installation cost is vortex street Several times.(3) Maintenance costsIn addition to the periodic calibration required for measurement, the vortex street generally does not fail, but the orifice plate does not. It eliminates leakage, regularly drains the sewage, fills the isolation fluid, replaces the pressure tube, valve, heat preservation, cleans the orifice, etc., there are certain The amount of maintenance. For example, for 200 sets of flow orifice plate measurement loops (requires heat preservation and heat tracing), every two years, the transformation of the heat preservation and heat tracing system has to invest a certain amount of maintenance cost, which does not include the update of the differential pressure transmitter and the update of the orifice plate. Calculate enough to buy a certain amount of imported vortex street.(4) Operating cost1. The cost of steam consumption is 200 sets of flow orifice plate measurement loops (requires heat preservation and heat tracing), and each hot spot consumes 0.02t/h of steam. If the annual average is 4300 hours, the steam cost is 40 yuan/ton, then every year The cost of steam consumption is about 688 thousand yuan, and the annual cost of each circuit is 0.344 million yuan.2. Energy consumption cost The pressure loss of the vortex street is smaller than that of the orifice plate, about 1/15 of that of the orifice plate. Therefore, long-term operation costs less energy consumption for pumps and fans. The orifice plate is 15 times that of the vortex street. When used for gas or steam flow measurement, due to the low density, the large volume flow of the same pipe diameter, the pressure loss is more serious, and the energy consumption is higher.3. Leakage discharge fee discharge fee depends on the number of discharges, generally about 20 times a year. The discharged dirt and materials pollute the atmosphere, and the sewage exceeds the standard, and the environmental protection department will also fine it.(5) Long-term operation accuracy The design system accuracy of the orifice plate is 1.5%-2.5%. Because the differential pressure and the flow rate are linearly related, when the flow rate is less than 30%, the error increases, and the gas is too serious. On the one hand, due to the long-term wear and tear of the medium used, the acute angle becomes blunt, which changes the flow coefficient, which is also an important reason that affects the accuracy. Due to the special structure of the vortex street, when the accuracy is actually determined (approximately 0.5-1% of the measured value), the accuracy is almost unchanged.(6) Interchangeability The same vortex can measure the flow of gas, liquid and steam. Electronic circuit boards and sensitive components are common to flow meters of different calibers. The signal output usually has three forms: pulse, Analog and digital signals. It can be switched by the switch on the circuit board, and the user can switch to another output signal at any time according to his needs. It is also easy to change the range. For analog output, only the input pulse frequency is required. The orifice plate is not the case. The aperture is designed for a specific medium, and the interchangeability is poor. It is also difficult to change the range, and the orifice plate needs to be recalculated.(7) Turndown ratio Since the output frequency of the vortex street is linear with the flow rate, the flow rate turndown ratio can reach 20:1-80:1. For example, some vortex flowmeters measure gas and steam with a turndown ratio of 80:1 , The measuring range ratio of the liquid is 40:1, which can meet the requirements of a larger measuring range of process flow, and the accuracy can still be guaranteed. The differential pressure of the differential pressure flowmeter has a non-linear relationship with the flow rate, and the measurement is not accurate when the flow rate is small, and the range ratio is only 3:1-5:1. If you expand the turndown ratio, you must try to improve the accuracy of the differential pressure transmitter.(8) Reliability There is now a more reliable vortex street, which has two sets of electronic circuits and two sets of sensitive components installed on one meter body, and they are independent of each other. They can be used in important flow measurement occasions, differential pressure flow It is difficult to do this.(9) Energy-saving effect. For example, if the steam consumption is 120t/h, the pressure is 3.9Mpa, and the temperature is 445oC, if the orifice is used to measure the steam, the pressure loss will be 0.03-0.05Mpa, such as 0.03Mpa. The power consumption of a perforated plate is 82kW. Based on 300 days a year, the annual power consumption of 590,000 kW/h is converted to 68.5t of standard coal. If the vortex street is used, the energy consumption is only 1/15-1 of that of the perforated plate. /20, if calculated as 1/20, only 3.34 tons of coal is consumed each year, accounting for only 3.33% of the energy consumption of the orifice plate.(10) The influence of the flow characteristics of the primary element on the control system. Because the output frequency of the vortex street has a linear relationship with the flow rate, when it forms a control system with the regulating valve and the regulator stage, it is equivalent to a time lag and a time constant. A hysteresis link that is small enough to be ignored can be regarded as a proportional link. The characteristics of the generalized object completely depend on other links in the loop and have little effect on the control system. The gain changes with the flow rate. Although the flow characteristics of the regulating valve are used to compensate for the linear influence of the generalized object, the effect is not obvious. Therefore, a square extractor must be introduced. Although the introduction of the square extractor makes the characteristics of the generalized object not follow the operating point The change obviously changes the adjustment quality, but the response is fast and sensitive when the flow is small, and it is easy to cause the system to increase the adjustment error.To sum up: It is feasible to use vortex street instead of orifice plate in many flow measurement. It saves money and labor. It does bring many benefits to flow measurement.
Post time: 21-09-21