Abstract: This paper introduces the working principle of the elbow flow meter. Compared with other flow meters, the elbow flow meter features simple structure, low pressure loss, maintenance-free operation, strong adaptability, and high accuracy. Based on the improvements made to the flow meters of the three 65-ton/unit boilers and three 12,000 kW units at the Qianjin Thermal Power Plant, the energy metering problem has been effectively solved.
Keywords: Bend tube flow meter; differential pressure; features; energy saving
Chinese Library Classification Number: TP399 Document Code: A
Characteristic and applied analysis of Pipe flow meter
Liu Xiao-li
Work professional school Shandong Changle 262400
Abstract: Introduced the pipe flow meter's principle of work. Through with orifice well tester's contrast, the elbow piece flow meter has the structure to be simple, the damaged due to pressing small, exempts the maintenance, the compatible strong precision higher characteristic. Before entering the thermal power plant to have three 65 ton/boilers, three 12,000 kilowatt unit's flow meter improvement situations, the good solution energy measurement question.
Keywords: Pipe flow meter; Differential; Characteristic; Energy conservation
1. Overview
With the development of modern industrial production scale, enterprises are paying increasing attention to energy requirements. Issues related to energy regulation, such as process control, production cost accounting, and energy metering assessment, rely more and more on flow measurement. Therefore, accurate measurement of the flow rate of media such as steam, natural gas, and water is becoming increasingly important for industrial energy conservation. The research and design of bent-tube flow meters has a history of over 80 years, but their industrial application has faced significant difficulties due to various technological limitations. With advancements in bent-tube processing and measurement technologies, they have received widespread attention and effective promotion in recent years. This paper compares the application performance of traditional flow meters and bent-tube flow meters. Through comparison, calculation, and analysis, it is found that bent-tube flow meters have advantages such as low pressure loss, easy maintenance, high measurement accuracy, and good repeatability, and can effectively solve energy metering problems.
2. Working principle of the bend pipe flow meter
Like traditional orifice plate flow meters, bend flow meters belong to the category of differential pressure flow meters. However, the way a bend flow meter generates differential pressure differs from that of an orifice plate flow meter. Orifice plates generate differential pressure based on the principle of fluid expansion and contraction, while bend flow meters utilize the principle of fluid inertia. When fluid passes through the bend, it is forced into a circular motion due to the constraint of the bend. The centrifugal force generated during this circular motion acts on the inner and outer sides of the bend, creating a pressure difference between the inner and outer sides of the bend flow meter. The magnitude of this pressure difference depends on the fluid density, average flow velocity, radius of curvature of the pipe, and inner diameter of the pipe, and its expression is:
Where v is the fluid value, representing the average flow velocity in the bend.
R—radius of curvature at the center of the bend;
D—Inner diameter of the bend
—Radius of curvature at the center of the bend;
ΔP—The differential pressure generated when fluid passes through the bend sensor;
—The density of the medium;
Flow rate of fluid in the pipe
As can be seen from the above, as long as the pressure difference is accurately measured, and the influence of temperature and pressure on the density of the medium is taken into account during the calculation, the flow rate of the medium can be accurately measured.
3. Features of the bend pipe flow meter and its performance comparison with other flow meters
1.1 Simple structure and high cost performance
Simple in structure and low in price. The bend sensor is essentially a standard 90-degree elbow; there is no flow sensor with a simpler structure. With the development of the machining industry and the continuous improvement of industry standardization and regulation, the quality of standard machine-made elbows used as bend sensors is improving, and their prices are decreasing. Flange-type pressure-tapping orifice plate flow meters are the cheapest flow meters on the market, and the price of bend flow meters is completely comparable.
1.2 Sensors capable of measuring media that are easily soiled or clogged.
Coal gas (including blast furnace gas, coke oven gas, producer gas, etc.) and flue gas are considered contaminated media, easily clogging and sticking to critical parts of sensors, directly affecting measurements. Traditional orifice plate flowmeters and vortex flowmeters generally cannot guarantee long-term accuracy and stability. Circulating water has poor quality, significantly impacting flow measurement devices. The throttling elements of orifice plate flowmeters or the insertion parts of vortex flowmeters are easily contaminated or clogged by circulating water, especially the right-angled sections of the orifice plate throttling orifice; even slight contamination can greatly affect measurement accuracy. The adaptability of bent-tube sensors to media like coal gas and circulating water is unquestionable; even long-term operation ensures the normal operation of bent-tube flowmeters and guarantees sufficient measurement accuracy.
1.3 Flexible and adaptable, with a wide measuring range and minimal requirements for straight pipe sections. Any fluid flow rate that can be measured using orifice plates, vortex flow meters, or averaging pitot tube flow meters can also be measured using elbow flow meters. Furthermore, elbow flow meters are far superior to other flow meters in terms of resistance to high temperatures, high pressures, impacts, vibrations, moisture, and dust. The usability of vortex flow meters is quite limited due to their measurement principle; the actual measurement results produce significant additional errors, affecting measurement accuracy and leading to inaccuracies. All these problems have almost no impact on elbow flow meters. Moreover, high temperatures and high pressures can be easily addressed by using standard elbows made of the same material as the process pipeline.
The range ratio of a bent-tube flow meter can reach 1:10. This wide range refers to two aspects: firstly, the bent-tube flow meter is applicable to a wide range of flow velocities of the measured medium. For steam or other gaseous media, the velocity range is 0~70 m/s, which can well meet the requirements of steam flow measurement; for liquid media, the velocity range is 0~5 m/s. There are no strict limitations on the velocity range mentioned above. If there is no upper limit to the velocity of the measured medium, the velocity range can be even larger; with a sufficiently accurate differential pressure transmitter, the lower limit of the fluid velocity can be very small. The application of high-quality differential pressure transmitters enables bent-tube flow meters to adapt to the requirements of low-velocity, low-signal measurements. In short, the range of the bent-tube flow meter can fully meet the flow measurement requirements of different objects. Another aspect of the wide range is that there are no limitations on the geometric dimensions of the bent-tube sensor; the pipe diameter can range from tens of millimeters to one meter or even more than two meters.
The less stringent requirements for straight pipe sections are also a crucial characteristic of elbow flow meters in field applications. Many flow measurement devices cannot perform measurements or guarantee their accuracy because the straight pipe sections in the field cannot meet the requirements. Due to its unique measurement principle, the elbow flow meter has less stringent requirements for straight pipe sections in practical applications, generally requiring only 5D before and 2D after the pipe, which is far lower than the requirements of other flow measurement devices.
1.4 The elbow flow meter has high accuracy and good repeatability. The measurement accuracy can reach 1% and the repeatability accuracy can reach 0.02%. After one installation, it does not need to be disassembled and reassembled repeatedly. Therefore, its installation accuracy can be guaranteed to the best.
1.5 No additional throttling devices or inserts are required, resulting in no additional pressure loss and energy savings.
For orifice plate flow meters, the pressure loss of fluid on the orifice plate is irreversible, and can reach 60% to 80% of the differential pressure generated by the orifice plate at that flow rate. The most important advantage of elbow flow meters compared to other flow meters is that they have no additional throttling or insertion components, eliminating the problem of additional pipeline resistance losses. The throttling loss of the orifice plate can be simply viewed as the energy-saving effect of the elbow flow meter, which is particularly beneficial for large systems, large pipe diameters, high flow rates, and low pressure measurements. This characteristic brings significant convenience and economic benefits to the industrial application of elbow flow meters.
1.6 Maintenance-free flow sensor
The bent-tube flow meter sensor is wear-resistant and insensitive to minor wear. It will not deform, twist, or vibrate under high-speed fluid impact. Under long-term high and low temperature operating conditions, the sensitive element will not age or deteriorate, thus maintaining stability and sensitivity. It is insensitive to environmental factors such as vibration, dust, humidity, and electromagnetic interference. Its stability, sensitivity, and accuracy will not change significantly after long-term operation, minimizing the risk of sensor fouling, scaling, and blockage. In contrast, the orifice of an orifice plate flow meter is highly sensitive to minor wear. Generally, the orifice plate of a metering orifice plate flow meter must undergo mandatory wear checks once or more per year; this is essential for ensuring accurate measurement. For large-diameter orifice plates and steam orifice plates, the difficulty of disassembly and installation, and the high maintenance costs, impose an additional burden on users. Due to its wear resistance, maintenance-free operation, and long-term high-precision operation, the bent-tube sensor uses a direct welding method for installation, completely solving the problem of leaks and spills in the field.
1.7 Measurement data can be directly connected to the DCS system.
Measurement data can be directly input into the DCS system. The dedicated host is equipped with RSR-232 and 485 communication interfaces.
4. Application Analysis of Bend Pipe Flow Meters
The analysis is based on the improvement of flow meters for the existing three 65-ton/day boilers and three 12,000-kilowatt units in the Qianjin Thermal Power Plant.
4.1 Improvement Plan
The original production process of the three 65-ton/hour boilers is shown in Figure 1. Each boiler originally had two orifice flow meters installed on its main steam pipeline, totaling six. Since the orifice flow meters calculate steam flow based on the principle of pressure difference generated by flow interception, pressure loss occurs when steam flows through the orifice. Measurements show that the pressure loss caused by steam flowing through the orifice flow meters is approximately 0.05 MPa. Steam entering the turbine from the boiler needs to pass through two orifice flow meters, resulting in a pressure loss of approximately 0.1 MPa at these flow meters. Adding the pressure loss from the steam pipeline and valves, the pipeline loss between the boiler superheater header outlet and the turbine inlet reaches 0.4 MPa. Even with the boiler operating at its maximum pressure (3.82 MPa), the turbine inlet pressure can only reach 3.4 MPa (the design inlet pressure is 3.47 MPa), leading to increased steam consumption and coal consumption for power generation. This results in a loss of 4.2 million kWh of electricity annually, equivalent to 4200 tons of raw coal per year, and an increase in sulfur dioxide emissions of 21.5 tons.
Figure 1 Original production process diagram
Fig1Originaltechniqueofproductionchart
Replacing the orifice plate flow meter with a bend pipe flow meter, the bend pipe sensor is installed at the 90-degree bend in the original pipeline, effectively replacing the original 90-degree elbow. This eliminates any pressure loss, completely eliminating the pressure loss generated by the orifice plate flow meter device. The improved process is shown in Figure 2. Calculations show that this will reduce the pressure loss in the steam pipeline by 0.1 MPa. This allows for a 0.1 MPa increase in the turbine inlet pressure to 3.5 MPa while maintaining the boiler operating conditions. According to the load characteristic curve of a 12MW turbine, at full load, the inlet pressure increases from 3.4 MPa to 3.5 MPa, increasing the load by 200 kWh and reducing power generation steam consumption by 0.1 kg/kWh. This achieves the goal of energy saving and consumption reduction.
4.2 Economic Benefit Analysis After Improvement
Figure 2 Improved process diagram
Fig2 Improvementcraft Chart
(1) Energy saving benefits
According to the load characteristic curve of the 12MW steam turbine, due to the resistance of the existing orifice plate, the inlet steam pressure drops from 3.5MPa to 3.4MPa under full load, resulting in a 200kWh reduction in power generation. After this project is put into operation, this steam pressure drop energy loss will be avoided, and the turbine steam consumption rate will be reduced by 0.1kg/kWh. The energy-saving economic benefits of this project are significant. Considering only the reduction in steam heat loss and the increase in power generation under the same steam volume or the saving of steam consumption under the same power generation, it saves 4200 tons of raw coal per year, reduces production costs by 2.1 million yuan, and has an investment payback period of only 3 months. This project is an effective energy-saving and resource-saving clean production project.
(2) Environmental benefits
This project is an engineering project to reduce and control pollutant generation at its source. After it is put into operation, it will save 4,200 tons of raw coal per year. This will reduce sulfur dioxide production by 54 tons per year, reduce sulfur dioxide emissions by 21.5 tons per year, and reduce flue gas emissions by 35.7 million m3 per year. Therefore, the environmental benefits are significant.
5. Conclusion
5.1 The pressure loss of orifice plate flowmeters should not be underestimated, as it results in significant energy consumption (generally around 60% of the orifice plate differential pressure), which should be given high priority by enterprises.
5.2 The elbow flow meter has no additional resistance loss, requires no maintenance, is resistant to high temperature and high pressure, and its measurement accuracy fully meets the needs of the field.
5.3 By adopting new technologies through technological upgrades, energy conservation and consumption reduction can be achieved, creating considerable economic and social benefits for the enterprise.
References:
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[3] Duan Baobao, Li Hu, Song Hongpeng. Application Study of Bent-tube Flowmeter in Large Fluidized Bed Boiler, Power Plant System Engineering, 2011.01, Vol.27, No.131-33
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[Author Biography] Mu Aixia (1983–), female, Han nationality, from Zibo, Shandong Province, is a teacher at Shandong Industrial Vocational College. Her main research and teaching areas include automated testing and intelligent sensor applications.
Mailing Address: Department of Architecture and Information Engineering, Shandong Industrial Vocational College, No. 69, High-tech Development Zone, Zibo City, Shandong Province, 256414, China
