Principles for selecting flowmeter instruments
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I attended a review meeting last time, where I met a professional who spoke at length about the selection of flow meters. While I don’t entirely agree with his views, I would like to share my personal insights from a different perspective. In the petrochemical industry, there are various ways to classify flow meters based on the process medium. The first classification is by type of medium: liquids (clean liquids, turbid liquids or those containing particles, liquids with different viscosities)； Gases (mixed gases and ideal gases) ； Steam (saturated steam and unsaturated steam). The second classification is by process type: 1. Instantaneous accuracy ； 2. Accurate cycle timing ； 3. High stability (low accuracy requirements). Next, let’s discuss the second category: 1. Instantaneous accuracy: These types of meters are primarily used in commercial metering, and internationally, three types of meters are recognized in this category: mass flow meters, twin-rotor volume flow meters, and velocity-type turbine flow meters. But such instruments share several common features: high accuracy (Class 0.2) ； Small caliber ； Generally applicable to liquids. They are widely used in the loading and unloading areas of various petrochemical plants. The main requirement is instant accuracy; among the commonly used weighing devices, flow meters for measuring liquids during transfer also have the advantage of online calibration (standard volume tubes: piston-type or ball-type). 2. Periodic accuracy: Such instruments are mainly used for the transfer of materials between different units as well as for production measurement within these units. Some companies may also use mass flow meters in this process, and such flow meters require high stability and precision, making them suitable for team-level measurements, monthly calculations, annual calculations, etc. The accuracy required for these instruments can be lower than that of the first category. 3. Metering instruments used for measurement and regulation within a device are intended for their basic functions only; their accuracy can be relatively low, but they must be stable. Especially in the case of instruments used for regulation, the actual regulatory effect is verified through other process parameters, so high accuracy is not required. A special case of this situation is that certain chemical processing units used for ratio-based reactions are not suitable for this purpose; in such cases, instruments from category one or category two can be selected as appropriate.
I fully agree with the original poster’s view. The selection of a flowmeter involves a comprehensive assessment and analysis; it is necessary to take into account the process conditions at the site, the operating environment, the required performance characteristics, as well as the technical features of various instruments before making a choice.
Metering instruments used for measurement within a device and with regulatory functions are intended for basic applications only; their accuracy can be relatively low, but they must be stable. Especially in the case of instruments used for regulation, the actual regulatory effect is verified through other process parameters, so high accuracy levels are not required. A special case in this situation is that certain chemical processing units used for reactions involving specific ratios are not suitable for this purpose; depending on the circumstances, instruments from category one or category two can be selected as a reference
In my opinion, what the original poster has mentioned should not be called \"principles for selecting flow meters\", but rather a brief overview of the knowledge related to flow meters； The selection principles for flowmeter instruments should take into account various factors such as performance requirements, the functional characteristics of the flowmeter, the properties of the fluid being measured, installation conditions, environmental conditions, and economic considerations. (The book \"Methods of Flow Measurement and Selection of Instruments\" is recommended; it contains a dedicated chapter that provides detailed information on the selection of flowmeter instruments.)
In summary, I have such a medium, and I need to determine which functions it should fulfill; the selection is made based on the first two factors.
The original poster is right. Ensure the pipe is full during use to avoid two-phase flow.
Being rigidly bound by principles can, if things go wrong, kill people. The result is what matters most, because cheap items are not necessarily of poor quality, and expensive items are not necessarily better; the difference between expensive and cheap products can sometimes be minimal. Moreover, people’s purchasing power has improved these days.
It seems that in the chemical industry, cumulative meters are generally not used; instead, the accumulation is done directly within the program.
Turbine flowmeters have high accuracy, with ratings of 0.5 grade, 0.2 grade, and 0.1 grade; they are also inexpensive, which is great.