In the field of industrial circulating cooling water treatment, Polymaleic Acid (PMA) is widely recognized as a powerful solution for treating high-hardness water due to its excellent high-temperature resistance, high alkalinity resistance, and strong crystal lattice distortion capabilities. However, in actual B2B field applications, we have found that many companies experience persistently high chemical costs while still facing frequent scaling problems.
The problem often lies not with the PMA chemical itself, but with misconceptions in the dosing process. Today, based on our experience in frontline technical support, we will deeply analyze common errors in the use of PMA scale inhibitors and provide practical correction strategies.
Misconception 1: Blindly believing that “more is better”
Many field operators, upon seeing increased system concentration ratios or deteriorating water quality, immediately double the dosage.
Truth: PMA is a typical “threshold effect” chemical. Within a certain concentration range, the scale inhibition rate increases significantly with increasing concentration; however, once the saturation critical point is exceeded, the improvement in scale inhibition becomes extremely weak, and may even produce side effects.
Consequences: Overdosing not only leads to direct waste of chemical costs, but excessively high concentrations of organic polymers may combine with multivalent metal ions in the water (such as high iron and high aluminum) under specific conditions, forming difficult-to-clean “organic scale” or colloidal substances.
Correction Strategy: Conduct dynamic simulation experiments: The optimal economic dosage for the specific water quality must be determined through rotating coupon or heat exchange simulation experiments based on the actual makeup water quality and circulating water indicators.
Linkage with concentration ratio: Establish a linkage model between the dosage and the makeup water volume and blowdown volume, rather than simply dosing based on intuition.
Misconception 2: Ignoring the influence of pH on PMA’s “behavior”
Although PMA’s stability in high pH environments (pH 8.5-9.5) is superior to Polyacrylic Acid (PAA), this does not mean it is completely unaffected by acidity and alkalinity.
Truth: The functional group of PMA is the carboxylic acid group, and its ionization degree is closely related to pH. In extremely high pH environments, although the ability to inhibit calcium carbonate is strong, the presence of high levels of phosphate (from other blended chemicals) in the system may affect the inhibition effect on calcium phosphate.
Consequences: This leads to the formation of complex scale, which engineers often mistakenly attribute to PMA failure.
Correction Plan: Monitor operating pH: Ensure the system pH operates within a controlled range.
Optimize blending ratio: If the site water quality has extremely high alkalinity, it is recommended to blend PMA with organic phosphonic acids (such as HEDP, ATMP) or sulfonic acid copolymers, utilizing synergistic effects to compensate for the limitations of a single chemical.
Misconception 3: Unscientific dosing point setting, leading to “instantaneous dilution” or “localized deactivation” of the chemical.
The location of the dosing point directly determines the utilization rate of the chemical.
The truth: Some factories add PMA near the wastewater discharge point, or in stagnant areas lacking turbulence; even worse, some mix PMA with oxidizing biocides (such as high-concentration sodium hypochlorite) in the same small dosing tank.
Consequences: The former results in the chemical being discharged before it can take effect; the latter may lead to oxidative damage to the PMA molecular chain, significantly reducing the chemical’s performance.
Correction Plan: Optimal dosing point selection: The dosing port should be located at the inlet of the circulating pump, utilizing the pump’s impeller to quickly and evenly disperse the chemical throughout the entire water system.
Physical isolation: The dosing points for strong oxidizing biocides and PMA should be at least 5 meters apart, or staggered in time.
Misconception 4: Using “shock dosing” instead of “continuous maintenance”
To save trouble, some sites manually add the entire day’s dosage every 24 hours.
The truth: The circulating water system is a dynamic equilibrium process. Shock dosing leads to drastic fluctuations in the chemical concentration within the system, showing a pattern of “oversaturation – severe deficiency – oversaturation”.
Consequences: During the period of insufficient concentration, calcium and magnesium ions will rapidly form crystal nuclei on the heat exchanger surface. Once the crystal nuclei are formed, subsequent addition of PMA will be difficult to completely remove them. Correction Plan: Adopt an automatic dosing system: It is recommended to equip a metering pump for continuous and balanced dosing 24 hours a day.
Online Monitoring: Ideally, fluorescence tracer technology should be used to monitor the tracer concentration in real time and adjust the metering pump frequency accordingly, ensuring that the system’s chemical concentration remains within the effective range.
Misconception Five: Neglecting the challenge of water temperature on scale inhibition effectiveness
Although PMA is temperature-resistant, it doesn’t mean it can maintain its effectiveness at any temperature.
The Truth: On high-temperature heat exchange surfaces (such as crystallizers in steel plants or condensers in the power industry), the local water temperature may far exceed the bulk water temperature. High temperatures accelerate the crystallization rate and may also accelerate the degradation of some inferior PMA products.
Consequences: Reduced heat exchange efficiency, increased flue gas temperature or exhaust pressure.
Correction Plan: Verify product thermal stability: When making B2B purchases, do not only consider the price; require suppliers to provide thermal stability test reports for PMA.
Targeted Adjustment: During the high-temperature load period in summer, the flow rate of circulating water should be appropriately increased to reduce retention time, and the PMA dosing ratio should be fine-tuned.
