In energy monitoring instruments, in addition to electricity meters and solid-state coal weighing meters, other gaseous and liquid energy sources (such as crude oil, refined oil, heavy oil, residual oil, natural gas, liquefied gas, and gas...) and energy carriers Quality (water, steam) must use flow meters. Even for solid-state energy coal, a flush-plate flowmeter or a gas-solid two-phase microwave flowmeter can be used in the continuous operation in the process industry. Therefore, the flow meter plays an important and irreplaceable role in energy monitoring instruments.
During the “Eleventh Five-Year Plan†period, the Central Government will make the greatest determination to regard energy conservation and consumption reduction as the top priority in economic construction. While ensuring that GDP is doubled, the energy consumption per unit of production value should drop by 20% within five years. China's industrial energy consumption accounts for 68% of total energy, and people's life consumes only 11.4%. Therefore, the focus of energy conservation should be on industry, especially high-energy-consuming industries such as electricity, metallurgy, steel, petrochemicals, building materials, transportation, etc. .
Comparison of several energy monitoring flow meters 1, throttling device: based on throttling produce differential pressure, measuring the square root of the differential pressure to know the size of the flow. For a long time, these instruments have been able to withstand harsh working conditions and have been based on international standards. They used to occupy 60 to 70% of the market for flow meters, with up to two to 30 types.
2. Plug-in: simple structure, easy installation, low cost, and continuous flow and fold, but the accuracy is low. It is only suitable for large pipeline flow detection, and can be used in energy monitoring for occasions where the accuracy is not high.
1 measuring speed: measuring the flow rate of a point in the pipeline instrument, such as double venturi; plug-in vortex, turbine, electromagnetic, pitot tube. According to ISO7145, the accuracy is ±3%. If the straight pipe is less than 30D, the accuracy will be less than ±5%*3.
Among the L-type pitot parameters:
â—Ž Pitot tube measuring medium: Gas or liquid compatible with 304 stainless steel.
â—Ž Pitot tube main purposes: measuring the total pressure in the pipeline, static pressure, dynamic pressure (ie pressure difference), but also to calculate the flow rate and flow.
â—Ž Pitot tube instrument connection: It can connect various pressure instruments (such as U-type pressure gauge, tilt micro pressure gauge, inclined tube differential pressure gauge, digital micro pressure gauge, compensation micro pressure gauge, etc.) and differential pressure transmitter, secondary Instrumentation and imports of various pressure gauges.
◎ Pitot tube use temperature: ≤600°C ◎ Execution standard: National standard JJG518-98 ◎ Pitot tube use Humidity: ≤HR45% ◎ Measurement flow rate range: Air flow rate ≤ 40m/s; Water flow rate ≤ 25m/s
â—Ž Pitot tube standard coefficient: L type pitot tube is between 0.99 and 1.01; S type skin tube is between 0.81 and 0.86.
Recently introduced in the market a test tube similar to the deformation of the skin, the biggest advantage is not easy to block, put three in the top of the pipeline, each need to use a differential pressure transmitter, the price is more expensive. Allegedly designed according to ISO 3966, but did not meet the requirements of the standard required to arrange 20 measuring points in the cross-section. The relevant article did an error analysis on it*4, but did not consider that when the velocity distribution is not ideal, the interference coefficient γ*5 that affects the accuracy is the greatest. Therefore, the measurement error will exceed ±3%.
2 measured radial multi-point flow rate: A typical instrument for the average speed tube, due to many measuring points, the accuracy of the insertion rate can be better than the measuring point speed. Usually only measuring the multi-point flow velocity in the cross-sectional diameter direction, in the need to improve the accuracy, can also be inserted into each other into the two average velocity tube 900, it is more in line with ISO3966 measuring point requirements.
3, no resistance flow meter. This type of instrument is characterized by a simple mechanical structure, no resistance within the pipeline, small pressure loss, high accuracy, is the most potential development of flow meters, such as ultrasound, Coriolis, electromagnetic, the annual growth rate of the market in the past five years respectively 10.4%, 6.9%, 2.4%.
Development trend: At present, there are many types of flow meters, and they are in a state of “Spring and Autumn and Warring Statesâ€. However, with the rapid development of science and technology, new types of instruments such as electromagnetic, ultrasonic, and Coriolis are increasingly favored by users because of their simple structure and perfect functions. . The classic type (orifice, nozzle, venturi) or large pressure loss, requiring long straight pipe lengths are difficult to meet and other shortcomings, the market development is declining, the annual growth rate is -2.3%. New throttling devices are also emerging, so the replacement of classic traditional instruments with new flow meters will be a long process and not a one-time event.
In addition to measuring the aircraft speed, the Pitot tube also has many other functions. In scientific research, production, teaching, environmental protection, and tunnels, mine ventilation, and energy management departments, Pitot tubes are commonly used to measure the airflow velocity in ventilation ducts, industrial ducts, and kiln flue ducts, and the flow rate can be determined through conversion to measure the water flow in the ducts. speed. The use of Pitot tube to measure the speed and determine the flow rate has a reliable theoretical basis and is easy to use and accurate. It is a classic and extensive measurement method. In addition, it can also be used to measure the pressure of a fluid.
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