Metal Works,Wind Generator Shaft,Wind Turbine Part Olym Metal Products Co., Ltd. , http://www.china-steel-casting.com
Keywords: Flow Measurement Orifice Speed ​​Tube With the rapid development of the power industry, a variety of high-efficiency new technologies and new processes have been put into use. Advanced processes require high-precision control and measurement. Accurate and accurate measurement of various media flows of steam, water, smoke, and wind in boilers and turbines is one of the necessary conditions for the safe and economical operation of the unit.
A wide variety of flow measurement products, according to the most extensive classification can be divided into: positive displacement flowmeter, differential pressure flowmeter, float flowmeter, turbine flowmeter, electromagnetic flowmeter, vortex flowmeter and mass flowmeter. Various flow meters have their own characteristics. There is no measurement method or flow meter can adapt to a variety of fluids and all kinds of flow conditions. Different measurement methods and structures require different measurement operations, methods of use, and conditions of use. Each type of flowmeter has its own unique advantages and disadvantages. Therefore, based on a comprehensive understanding of various measurement methods and instrument characteristics, select the optimal flow measurement product that is suitable for specific production features, which is safe, reliable, economical and durable. .
1 Comparison of differential pressure type flow measurement orifice and constant velocity tube 1.1 Types of differential pressure type flow measurement device Currently, the most widely used industrial measurement is differential pressure flow measurement. The mainstream of differential pressure type is throttling (hole) Boards, Venturis, etc.) and Dynamic Pressure Heads (Average Speed ​​Tubes).
The use of differential pressure principle for flow measurement is the most classic and reliable flow detection method in engineering today. Differential pressure flow meter is based on the differential pressure, known fluid conditions, and test pieces and pipes generated in the flow detection device installed in the pipeline. Geometry to calculate traffic. The differential pressure flowmeter consists of a primary device (test piece) and a secondary device (differential pressure conversion and flow display instrument). Differential pressure flowmeters are usually classified in the form of test pieces, such as orifice flowmeters, venturi flowmeters, and constant velocity tube flowmeters.
The greater the differential pressure generated by the flow detection devices in the pipeline, the more beneficial the differential pressure transmitter selection and cost, as well as the accuracy of the measurement. However, since the flow rate measurement device usually selects the shrinkage ratio (orifice, nozzle) according to the flow rate, the pressure difference increases and the pressure loss increases. The increase in the permanent pressure loss in the pipeline makes it necessary to increase the pipeline power, which requires high-powered fans, pumps, etc., which increases the energy consumption and increases the operating costs of the entire system.
The representative product of differential pressure flowmeter is orifice plate, because people are very familiar with its installation, use, and overhaul, and the orifice plate is easy to copy, simple, solid, stable and reliable performance, long service life, low price, so long-term application universal. However, the use of orifices for a long time will result in a sharp drop in accuracy, requiring regular inspection and cleaning.
1.2 Measurement principle of the equal flow tube flowmeter The average flow tube flowmeter replaces the cross-sectional flow velocity of the orifice plate by measuring the flow velocity at a certain diameter. With the constant development of the cross-section technology and the opening technology of the constant velocity tube, the measurement accuracy of the velocity flow tube continuously increases. Germany's Systec-Controls company and Germany's famous Erlangen University jointly launched the Delta Bar equal flow tube flowmeter with a streamlined tubular design. Flow detection is performed by inserting two rows of evenly distributed tubes in the medium velocity tube. A pressure tap is taken to detect the differential pressure generated by the fluid, resulting in an average differential pressure resulting from the average flow rate, and this differential pressure is transmitted through the interface to the transmitter. Through a plurality of uneven pressure holes, the average flow velocity in the pipeline can be reflected as realistically as possible. This makes it not only maintains high accuracy, high strength, and large range ratio in the flow measurement, but also greatly reduces pressure loss in the pipeline. Compared with the use of orifice plates, the use of plug-in flow probes has a significant economic benefit due to the reduction of pressure loss in the pipeline. At the same time, the unique probe design can meet the requirements of small pressure loss and high differential pressure at the same time, facilitating the selection of the transmitter.
Take a single-point signal plug-in flow sensor (such as plug-in turbine, vortex, electromagnetic, etc.) to detect the flow velocity at a certain point in the pipeline. Then analyze the detection point through the flow profile on the empirical chart to infer the average flow velocity. Complex conditions such as pipelines and fluids are complex and changeable. Most of them are non-fixed velocity profiles. Using a single point of measurement to replace the average flow velocity is inaccurate, leading directly to poor measurement accuracy and low repeatability.
1.3 Delta Bar Flow Probe Advantages (1) Can measure a variety of media, a wide range of applications, minimal impact on physical properties and pipeline characteristics. Diameter range can be from 3mm to 15m; high temperature and high pressure probe can work in 650°C, 28MPa steam environment, if choose 1.4828, X15CrNiSi20-12 probe, its working temperature can be up to 1040°C; also choose 1.4539 (A904 alloy, X1NiCrMoCu25 -20-5) and HC4 type probes, working with SO, SO2 flue gas or strong acid and alkali media.
Delta Bar flow probes can be used to: 1 Various types of gas measurements, including air, moist gases, various flue gases before and after purification, high-temperature flue gas, compressed air, primary air, secondary air, etc.; Measurements, including steam, saturated steam, superheated steam; 3 various types of liquids, including water, fuel, and benzene.
(2) High accuracy, good repeatability and large range ratio (1:30). Delta Bar flow probes are non-uniform openings and open points are based on computational software complex calculations. Manufacturing parameters are determined based on pipe diameter, media, and major process parameters. The improved measurement accuracy of the probe makes the adjustment of the measured parameter more accurate.
(3) The probe is designed with pressure holes to prevent blocking. The maximum opening of the probe is 8mm. As long as the dust or particles in the medium is not more than 130mg/m3, maintenance and purging are not required. The addition of a nitrogen purge line allows accurate metering of high-dust gases such as blast furnace gas, coke oven gas, converter gas, and sintering flue gas in large pipelines.
(4) streamline probe cavity design, measurement signal stability, small fluctuations. The number and distribution of the pressure taps before and after are completely symmetrical, and the two-way measurement can also be achieved without fear of mounting.
(5) The permanent pressure loss of the pipeline is small, and the requirement for the straight pipeline segment is low. The plug-in flow probe guarantees 1% accuracy in very short straight sections (first 4D, last 3D) and uses a non-shrink throttling design that is at least 90% lower than the permanent pressure loss of the orifice.
(6) The installation cost is low, basic maintenance free, and online installation and maintenance.
2 The use of deltabar flow probes in main steam measurement and thermal network reconstruction Deltaba flow probes are widely used, and have been widely used in 300MW/600MW large-scale thermal power units. The measurement of saturated steam at Tianwan Nuclear Power Station in Jiangsu proves more Its safety and measurement accuracy.
The delta flow probes in the main steam measurement and thermal network retrofit have their unique advantages of energy savings in micro pressure loss.
(1) The accurate measurement of the main steam flow is to meet the requirements of the unit detection and control, and the output of the steam turbine is adjusted through accurate steam measurement. The main steam flow of a general 300 MW/600 MW unit is measured by an indirect method, that is, to measure the turbine regulation pressure, and to derive the power of the steam according to the mathematical model provided by the host manufacturer. The accuracy of the main steam flow measurement depends not only on the accuracy and accuracy of the mathematical model and the accuracy of the sensor, but also on the changes in the structure and operating conditions of the steam turbine equipment, the location of the installation of the parameter measurement points, and the representativeness of the measured parameters. The accuracy of the measurement, the calculation accuracy is difficult to meet the operating requirements.
If the main steam flow measurement is set, the flow measurement point should be placed in front of the turbine, and the high temperature, high pressure, and high flow rate. If the probe breaks, the consequences of damaging the rear turbine will be disastrous. Delta Bar's high-temperature and high-pressure flow measurement device is the highest application of 69MPa, 1200 °C, the probe selection is based on the pipe's maximum pressure and maximum temperature through the corresponding software online calculation automatically generated with a higher safety factor. In high temperature and high pressure conditions, Delta Bar probe material selection 1.4828, its materials and manufacturing process to ensure the design life can reach 200,000 h, can be used for long-term use of high temperature steam below 650 °C, the main steam flow before the turbine can be completely Direct measurement. For the main steam flow measurement, the condenser outlet is equipped with a condensing kettle to rapidly cool the high-temperature steam in the condensing kettle (the lower end is condensed water and the upper end is steam). When the normal operating medium temperature reaches 550°C, the globe valve can be protected and The differential pressure transmitter is protected from high temperatures and ensures reliable flow measurement. Since the condensing kettle is welded and pressure tested at the factory, the user only needs to install the three-valve manifold and the transmitter for the integrated product, and the split product is welded after the cut-off valve. Leakage caused by high temperature and high pressure and on-site workload. Due to the low pressure loss, the delta bar flowmeter increases the steam production of the boiler and also makes the operation of the boiler and steam pipeline more safe and reliable.
The direct measurement of the high-temperature and high-pressure main steam flow of the Delta Bar Flowmeter has been widely used in Europe. Since it was put into use, there have been hundreds of examples of high-temperature and high-pressure applications, which have gradually been recognized and widely used in China.
(2) The measurement of the flow meter is the basis for the metering and charging of the heating system. Therefore, the flow meter is required to have a high measurement accuracy. In the past, orifice flowmeters and ultrasonic flowmeters were used more often in thermal network metering. Recently, deltabar flowmeters are increasingly used in heat network steam and circulating water applications. Not only because of its measurement accuracy can fully meet the measurement requirements of the heating network steam and circulating hot water, and when the pipe temperature is lower than 100 °C, the pressure is less than 1MPa, the existing pipeline can be implemented with pressure hole and installation, etc. Suitable for heating network and other technological transformation projects. The delta bar flowmeter can use the online plug-in flow probe, which meets the need for on-line demolition and maintenance of probes for long-term pipelines that cannot be stopped, and solves the problems of difficult installation and maintenance of orifices and other metering devices.
The main performance indicators of several common flowmeters in heat network applications are shown in Table 1. 
references:
[1] Zhou Qunfeng. Flow measurement scheme and application of Delta Tuba integrated velocity control in large thermal power plant [Z].
Application of Averaging Tube Flowmeter in Power Plant
Abstract : The measurement principle of differential pressure flow measurement device is introduced. The orifice plate and equal velocity tube in differential pressure flow measurement device are deeply compared. The advantages of plug-in flow probe in power plant and the safety and precision of the probe are discussed. Conditions and precautions for use. 3 Flow meter installation The use of the equal flow tube flowmeter is a high-precision sensor that can work normally under very complicated conditions and maintain good performance. In order to achieve the best performance, the flowmeter needs to be properly installed and maintained. The inner diameter of the measuring tube must be provided accurately when selecting this product. Because the design of the probe pressure distribution hole is calculated according to the center of the pipe, if there is a large error in the diameter of the pipe, it will cause the probe and the pipe to be measured and cause greater measurement error. As a measuring flow meter, it is recommended to use a probe inserted with a full tube, especially when the straight tube section does not meet the requirements. The velocity control tube replaces the cross-sectional flow velocity of the orifice plate by measuring the flow velocity at a certain diameter, and the flow velocity is not completely the same on different diameter lines (unless the straight tube segment in its position is long enough), so if the installation position and direction are not Appropriate measurement will result in invalid measurement or measurement without accuracy. Therefore, when selecting a model, theoretical analysis and calculation should be performed according to the installation conditions, and the proper installation position and installation method should be selected in order to achieve the best results. The installation of the flowmeter probe is recommended to be installed under the guidance of the manufacturer to prevent large errors in measurement due to the probe installation.