Sincere sharing on the selection analysis of DN300 oxygen flow meters

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Operating conditions on-site: The oxygen pipeline has a diameter of 300 mm, operates at normal temperature and pressure. The maximum flow rate is 9000 m3/h, while the minimum flow rate is 900 m3/h. The gauge is required to display both the instantaneous flow rate and the cumulative flow rate, as well as to output a current signal of 4-20 milliamps. Oxygen is a colorless and odorless gas, the most common elemental form of oxygen. Oxygen is needed in the oxidation of hydrocarbons, wastewater treatment, rocket propellants, and for breathing by animals and humans in aviation, spaceflight, and diving. Animal respiration, combustion, and all oxidation processes (including those of organic substances**) consume oxygen. Selection analysis: Several commonly used flowmeters that can measure oxygen flow include vortex flowmeters, target flowmeters, differential pressure flowmeters, metal tube float flowmeters, and thermal mass flowmeters. Let’s take a closer look at them. (1) Vortex flowmeter for measuring oxygen: It is not resistant to vibrations, has a relatively high starting flow rate, and can measure media with high flow rates. Oxygen being a small-molecule gas, it is not possible to measure low flow rates using this device. The flow range corresponding to a DN300 vortex flowmeter is 4500–45000 m3/h; therefore, when selecting such a flowmeter, flows below 4500 cubic meters per hour cannot be measured. (2) Target flow meter for measuring oxygen: This type of flow meter is primarily used to measure media that are highly viscous, contain many impurities, are prone to clogging, and exist under conditions of high or low temperature as well as strong corrosivity. Oxygen is a pure gas and a small-molecule gas, with a low flow rate; therefore, target flow meters are not suitable for measuring it. (3) Differential pressure flow meters (such as bar-type series flow meters, orifice plates, wedge-shaped devices, nozzles, V-cones, etc.) for measuring oxygen: All of these are types of throttling devices. During measurement, pressure is taken at the pressure tapping points, and this pressure is then converted into a flow signal by a transmitter. In the process of converting the flow signal, the transmitter is prone to zero drift, making it difficult to ensure flow stability. It has a higher pressure loss compared to other flowmeters, and it is difficult to achieve accurate measurements under low-pressure and low-flow conditions. It is prone to dirt and blockages, requires extensive maintenance, can be used for basic process control; when there is no interference at the site, its accuracy exceeds 2.5%. Installing it in large-diameter pipes is time-consuming and labor-intensive. (4) Metal tube float flow meter for measuring oxygen: This is a mechanical flow meter designed specifically for measuring low-flow rates of gases, with a measurement accuracy of 2.5% grade. It has no advantages when measuring large-diameter pipes, hydrogen, or oxygen. For DN300, the flow rate range is 600–6000 m3/h; the upper limit of the flow rate is only 6000 cubic meters per hour, which is insufficient to meet the actual flow requirements on site. Large-diameter pipes are expensive and difficult to install. (5) Measurement of oxygen using a thermal mass flow meter: Oil-free and degreasing treatments have been carried out prior to leaving the factory, ensuring the reliable operation of the flow meter in its intended operating conditions. Its range can reach 400–10,000 m3/h, covering the required flow rate range entirely. It features built-in temperature and pressure compensation, offering high measurement accuracy and good stability. It is simple to install and requires no special maintenance; it is thus a high-precision, maintenance-free gas flow meter. Based on the analysis of the above flowmeters, it is recommended that users use thermal gas mass flowmeters. It has the following features: 1. A true mass flow meter that includes built-in temperature and pressure compensation for gas flow measurement, ensuring convenient and accurate readings. The mass flow rate or standard volume flow rate of the gas can be obtained. 2. It features a wide range ratio, enabling the measurement of gases with flow speeds as high as 100 Nm/s and as low as 0.1 Nm/s; the flow rate ratio is 1:100, making it suitable for gas leak detection. 3. It has a wide range of applicable media; when measuring corrosive media, anti-corrosion sensors can be used to extend the service life of the flow meter and improve its precision and reliability. 4. The sensor has no moving parts or pressure-sensing components, so vibrations do not affect its measurement accuracy. 5. Easy to install and maintain. It can be manufactured in segmental or plug-in types according to on-site requirements, reducing the amount of installation work. Where site conditions permit, installation and maintenance can be carried out without shutting down production. (Special customization required) 6. Digital design. Overall digital circuit measurement, providing accurate results and ease of maintenance. 7. The use of RS-485 or HART communication enables factory automation and integration. Diverse power supply options, with the choice between 220VAC and 24VDC.