Common Flow Meters in the Chemical Industry and Selection

Accurate measurement and regulation of fluid flow are fundamental to ensuring safety, improving product quality, and reducing energy consumption in petrochemical production. Due to the complexity and diversity of flow measurement media, there is no universal flow meter that suits all conditions. Each type of flow meter has its advantages and limitations, with different principles, structures, and functions suited to specific applications. Therefore, selecting a flow meter requires adherence to standard regulations and selection principles while considering various factors that affect flow measurement. 

Principles and Selection of Common Flow Meters

Vortex Steam Flow Meter: Principle and Selection

The vortex steam flow meter operates based on the Kármán vortex street principle. It maintains measurement accuracy within a specified range, unaffected by the medium's pressure, temperature, viscosity, or density. This type of flow meter can directly measure the volumetric flow of steam, air, and gases. It features a simple structure, easy installation and maintenance, long service life, high versatility, and excellent stability, making it widely used.

However, vortex steam flow meters require a relatively high fluid velocity to generate vortices, which may cause noise. Their measurement accuracy typically ranges from 1.0% to 2.0%. They are generally suitable for pipe diameters up to 300 mm; for larger sizes, an insertion-type model is required.

Electromagnetic Water Meter: Principle and Selection

Electromagnetic water meters use electromagnetic induction to measure flow. They determine the flow rate by detecting the induced electromotive force generated when a conductive fluid moves through a magnetic field. These meters can only measure conductive fluids with a conductivity of at least 5 μS/cm, such as saline solutions, acids, alkalis, and water. They are also suitable for measuring slurries, such as mud, pulp, and mining slurry.

Electromagnetic water meters cause minimal pressure loss and have a wide measurement range, typically with a turndown ratio of 1:20 or more. Their output signal is linear with flow rate, and their measurement accuracy exceeds 0.5%. Since they measure volumetric flow, they are unaffected by the viscosity, density, or temperature of the fluid. Once calibrated with water, they can be used to measure other conductive liquids. Industrial electromagnetic flow meters are available in sizes ranging from 6 mm to 2.2 m, with some models reaching diameters of up to 3 m.

Coriolis Mass Flow Meter: Principle and Selection

Fluid volume varies with temperature and pressure, while mass remains constant. In applications requiring high accuracy, such as process control, quality monitoring, trade settlement, and consumption measurement, volume-based flow meters (e.g., vortex flow meters, electromagnetic flow meters, and orifice flow meters) may not suffice, as they require corrections for pressure, temperature, and density variations. These intermediate calculations introduce potential errors.

To address this, mass flow meters were developed to measure fluid mass directly. The main types include differential pressure mass flow meters, thermal mass flow meters, and Coriolis mass flow meters.

Coriolis mass flow meters function by utilizing the Coriolis force generated when a fluid moves in a rotating system. These meters directly measure mass flow with high accuracy, excellent stability, high reliability, a wide measurement range, and suitability for high-viscosity fluids. As a result, they are widely used in chemical production.

Common Issues in Flow Meter Selection and Use

1. Selecting Based Solely on Pipe Size

Oversizing is a common selection error that often leads to suboptimal measurement performance. This is not a flaw in the flow meter itself but a result of improper sizing. Each type of flow meter has a specific operating range and application conditions.

2. Improper Installation

Each flow meter has specific installation requirements to ensure accurate measurement. Many require specific upstream and downstream straight pipe lengths, as well as horizontal or vertical installation configurations. It is essential to carefully review the user manual before installation.

3. Incorrect Parameter Settings

This issue often arises with battery-powered flow meters. Some users assume that factory settings are sufficient and fail to adjust parameters before use. However, actual production conditions in chemical plants—such as fluid temperature, pressure, and density—may differ from design specifications, leading to significant measurement errors.

4. Lack of Regular Maintenance

Routine maintenance is essential to ensuring the accuracy of measurement instruments. Flow meters may experience gradual accuracy degradation over time. Each type of flow meter has specific maintenance requirements that must be followed to ensure long-term reliability.

Every flow meter has its advantages and limitations. Proper selection is critical to the efficient operation of chemical plants. Different working conditions and fluid properties require appropriate instruments to achieve optimal measurement results. Choosing the right flow meter requires a thorough understanding of both the characteristics of the instrument and the production process.