Best Practices Neat Polymer Flow Sensing for Pump Protection

Many polymer makedown systems use progressive cavity pumps to transfer the neat polymer from the storage container to the mixing chamber. While these pumps are ideal for pumping polymer, they are easily damaged if the flow of polymer is interrupted due to the container being empty of an inlet valve being shut off. To protect these pumps, a polymer feed system should be equipped with a loss of polymer flow sensing technology. There are three main methods – thermal flow sensing, magnetic flowmeter measurement and optical flow sensing of the finished solution.

Here is a summary of how these three technologies perform in polymer service:

1. Thermal Flow Sensing

Thermal flow sensors (often called Thermal Dispersion sensors) operate on the principle of heat transfer. They typically use two sensors: one that measures the ambient temperature of the polymer and another that is heated.

• How it works: When the polymer is flowing, it carries heat away from the heated sensor. If the flow stops or slows down, the temperature difference between the two sensors changes.
• Application to Polymers: This is highly effective for detecting "no-flow" conditions because it doesn't require the fluid to be conductive.
• Pros: No moving parts; very sensitive to low flow rates.
• Cons: Polymer "bake-on" or fouling on the sensor probe can create an insulating layer, leading to false readings or delayed response times.

2. Magnetic Flow Sensing (Magmeters)

Magnetic flow meters rely on Faraday’s Law of Electromagnetic Induction. They function by applying a magnetic field to the pipe and measuring the voltage generated as a conductive fluid passes through.

• How it works: As a conductive liquid moves through a magnetic field, it generates a voltage signal proportional to its velocity.
• Application to Polymers: This technology is only applicable if the polymer solution is conductive (e.g., water-based polymer solutions or those with conductive additives).
• Pros: Completely non-obstructive (the sensor is flush with the pipe wall), meaning it doesn't cause a pressure drop or get clogged by thick polymers.
• Cons: Will not work with some pure synthetic polymers or oil-based solutions, as they are typically dielectric (insulators).

3. Optical Flow Sensing

Optical sensing in a finished solution usually involves Laser Doppler Calorimetry or Turbidity/Opacity monitoring.

• How it works: These sensors pass a beam of light (often infrared) through the solution in a clear section of pipe on the solution discharge. Flow is detected either by the shifting frequency of reflected light from particles within the polymer or by the way the moving fluid scatters the light.
• Application to Polymers: This is excellent for "finished solutions" where clarity or consistency is a key metric. If the pipe is clear, the sensor can be mounted externally (non-invasive).
• Pros: High precision; can detect bubbles or impurities that might indicate a pump failure upstream.
• Cons: Requires the polymer solution to have consistent optical properties. If the polymer is too opaque (black or very dark) or if the pipe walls become coated with residue, the signal will be lost.

Summary Comparison Table

What type of polymer is your system primarily pumping?