The papermaking process is complex and diverse, involving multiple stages such as raw material preparation, pulping, bleaching, and papermaking. At each stage, the flow of water, slurry, and chemical additives must be precisely monitored. Flow measurement instruments provide real-time flow data. For example, during pulp blending, precise control of the flow rates of different components using magflo meter ensures stable pulp quality and helps maintain key paper properties—such as strength and brightness—within production requirements.
Various types of flow measurement instruments, including magflo meter, ultrasonic flow meters, and vortex flow meters, are widely used throughout papermaking operations. Among them, electromagnetic flow meters have become the most commonly used type in paper mills due to their strong adaptability, high measurement accuracy, and ease of installation and maintenance. The application rate of electromagnetic flow meters in pulping, bleaching, and papermaking processes has exceeded 70%, and they play a dominant role in wastewater treatment systems.
Problems in Flow Meter Applications in Paper Mills
The papermaking process involves a wide variety of liquid media, including pulp slurry, chemical additives, and water. These media have different physical and chemical properties—such as temperature, pressure, viscosity, and corrosiveness—which can all affect the measurement accuracy of flow meters. Especially in high-temperature or highly corrosive environments, conventional flow meters often cannot operate stably over long periods, resulting in measurement deviations.
In addition, pulp has a certain level of viscosity and contains suspended fibers, leading to complex flow conditions. This can easily cause clogging or wear inside the flow meter, further affecting measurement accuracy.
Measurement Challenges
(1) High Temperature and High Pressure
After mechanical refining, pulp temperatures can exceed 80 °C (176 °F). The extraction and circulation of black liquor also take place under high-temperature and high-pressure conditions.
(2) Liner Wear
High-consistency pulp, recycled fiber slurry, and digester blow lines can cause severe wear to the liner of magflo meter.
(3) Slurry Noise Interference
When high-consistency pulp and fibers pass through an electromagnetic flow meter, friction between the fibers and the electrodes can occur, generating spike noise interference that affects signal stability.
(4) Electrode Scaling
When measuring fuels, chemical agents, or liquids prone to crystallization, insulating deposits may form on the electrodes of the electromagnetic flow meter, which can interfere with accurate measurement.
Magflo Meter Selection for the Paper Industry
Based on the special characteristics of the papermaking process and the challenges involved, the application and selection of magflo meter in the paper industry can be analyzed as follows:
1. Liner Selection
The media measured in the papermaking process are characterized by high temperature and high pressure, and they contain large amounts of chemicals with corrosive properties. Therefore, magflo meter typically use high-temperature-resistant PTFE liners, and the meters are designed in a remote (separate) type configuration.
Although PTFE liners are resistant to high temperatures, they are not resistant to vacuum conditions. In certain special environments — such as at the outlet of medium-consistency pulp towers — the medium not only has high consistency and high temperature, but intermittent vacuum conditions may also occur. In such cases, a PFA liner with a stainless steel backing mesh should be selected to prevent PTFE liner deformation or bulging.
Based on many years of practical application, PTFE, PFA, or F46 (FEP) liners are commonly used in the paper industry. In addition, installing neck-type grounding rings during meter installation can significantly improve liner wear resistance.
2. Electrode Selection
The selection of electrodes for magflo meter in the paper industry mainly considers two factors:
- Corrosion resistance
- Anti-scaling performance
A large amount of chemicals is added during the papermaking process, such as NaOH, Na₂SiO₃, concentrated H₂SO₄, and H₂O₂. Different electrodes must be selected according to the specific chemicals involved. For example:
- Tantalum electrodes are required for strongly acidic media
- Titanium electrodes are generally used for alkaline media
- 316L stainless steel electrodes are sufficient for ordinary water measurement
Improper electrode selection can lead to electrode corrosion, which may result in moisture ingress into the electrodes and measurement failure.
In the wastewater treatment system of a paper mill, flow measurement instruments had long suffered from inaccurate readings, resulting in unstable treatment performance. The system originally used ultrasonic flow meters, but because the wastewater contained a large amount of suspended solids and air bubbles, the meters frequently showed fluctuating readings and could not accurately reflect the actual flow.
To address this, the plant adopted an ARTang insertion electromagnetic flow meter, specifically designed to measure wastewater with high levels of suspended solids and air bubbles. Before installation, the team thoroughly cleaned and calibrated the pipeline to ensure that the flow meter’s measuring section was free of deposits. An magflo meter with anti-bubble interference design was selected, and a bypass line was added during installation so that wastewater treatment could continue uninterrupted during meter maintenance.
