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Views: 2 Author: Site Editor Publish Time: 2025-02-11 Origin: Site
In pulp and paper production, most liquids used have a conductivity greater than 20 µS/cm, meeting the fundamental measurement requirements of electromagnetic flowmeters. Electromagnetic flowmeters do not have components that reduce the nominal diameter of the pipeline or that can be blocked by fibers, making them particularly advantageous for measuring pulp flow. As a result, the use of electromagnetic flowmeters for pulp flow measurement has become increasingly widespread in recent years.
High Temperature and High Pressure
The temperature of pulp after mechanical refining can exceed 80°C (176°F).
The extraction and circulation of black liquor also occur in high-temperature, high-pressure environments.
Liner Wear
High-concentration pulp, recycled paper liquid, and cooking blow lines can cause severe wear on the flowmeter’s liner.
Pulp Noise Interference
High-concentration pulp and fibers can create friction with the flowmeter’s electrodes, generating peak noise interference.
Electrode Scaling
When measuring fuel, chemicals, or easily crystallized liquids, insulating deposits can accumulate on the electrodes, affecting measurement accuracy.
The measured medium in the papermaking process is characterized by high temperature and high pressure, along with a significant presence of corrosive chemicals. Therefore, electromagnetic flowmeters typically use high-temperature-resistant PTFE linings and adopt a remote (split-type) design.
Although PTFE is resistant to high temperatures, it is not resistant to negative pressure. In certain special environments, such as the outlet of a medium-consistency vertical pipe, where the medium has high concentration, high temperature, and occasional vacuum conditions, a PFA lining with a stainless steel reinforcement mesh is required to prevent PTFE from bulging.
Through years of practice, PTFE, PFA, and F46 linings have been widely used in the paper industry. Additionally, installing flanged grounding rings during flowmeter installation can greatly enhance the lining’s wear resistance.
The selection of electrodes for electromagnetic flowmeters in the paper industry primarily considers two factors: corrosion resistance and anti-scaling properties.
A large number of chemicals, such as NaOH, Na₂SiO₃, concentrated H₂SO₄, and H₂O₂, are used in the papermaking process. Different chemicals require different electrode materials:
Tantalum electrodes for strongly acidic media.
Titanium electrodes for alkaline media.
316L stainless steel electrodes for general water measurement.
Incorrect electrode selection can lead to corrosion and water ingress, ultimately affecting the performance and lifespan of the flowmeter.
In the design of anti-fouling of electrodes, spherical electrodes can be selected for the medium mainly composed of fibrous substances for the general degree of fouling. The spherical electrode has a large contact area with the measured medium and is not easily covered by fibrous substances.
Select the correct pipe size to match the flow rate and avoid pressure drops.
Ensure proper grounding and installation to avoid measurement errors.
Ensure compatibility with control systems (e.g., 4-20 mA, pulse output, or digital protocols like Modbus, HART, or PROFIBUS).
No Moving Parts: Reduces wear and maintenance, especially in abrasive slurries.
High Accuracy: Typically ±0.5% of reading, ensuring precise control of processes.
Wide Range of Applications: Suitable for conductive liquids, including water, chemicals, and slurries.
Low Maintenance: Minimal downtime and long service life.
Bidirectional Flow Measurement: Useful for processes involving flow reversal.
Electromagnetic flowmeters dominate liquid measurement in the paper industry. When using them in practice, consider the following precautions:
Straight Pipe Requirements: Install the flowmeter with a minimum upstream straight pipe length of 5D and a downstream straight pipe length of 3D (D = nominal pipe diameter).
Full Pipe Condition: Ensure the flowmeter operates in a full-pipe condition and avoid installing it at the highest point of the pipeline, where air pockets may form.
Grounding Requirements: If installed on an insulated pipeline, the flowmeter must be equipped with grounding rings or grounding electrodes.
Measuring Different Conductivity Media: When measuring two media with different conductivities, install the flowmeter upstream of the mixing point or where the media are fully mixed.
Adhesive, Depositing, or Scaling Fluids: For fluids prone to adhesion, deposition, or scaling, the flow velocity should be at least 2 m/s, preferably 3–4 m/s or higher.
Abrasive Fluids: For highly abrasive fluids, the recommended flow velocity should be below 2–3 m/s to minimize wear.
Avoid Electromagnetic Interference: Do not install the flowmeter near variable frequency drives (VFDs), high-power motors, large transformers, or power cables to prevent signal interference.
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