Dosage of scale inhibitor ATMP

The dosage of ATMP (Aminotris(methylenephosphonic acid)) as a scale inhibitor is not a single number but depends on a wide range of factors.

Always consult the specific technical data sheet (TDS) from your supplier and consider performing a compatibility test (jar test) with your actual system water for the most accurate dosage.

Here is a comprehensive guide to determining the correct dosage of ATMP.

Key Factors Influencing ATMP Dosage

1. Water Chemistry: The most critical factor. The levels of calcium, magnesium, barium, alkalinity, pH, and total dissolved solids (TDS) directly determine scaling potential.

2. System Type: Operating conditions (temperature, pressure, contact time) vary greatly between systems.

3. Target Scale: Is the primary concern calcium carbonate, calcium sulfate, barium sulfate, or a mix?

4. Concentration Factor (Cycles of Concentration): In cooling systems, as water evaporates, minerals become more concentrated. Higher cycles require higher inhibitor dosage.

5. Presence of other chemicals: ATMP is often used in formulations with other inhibitors (e.g., HEDP, PBTC) or polymers for synergistic effects.

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Typical Dosage Ranges by Application

ATMP is almost always fed continuously to the system to maintain a constant, low concentration.

1. Cooling Water Systems (Open Recirculating)

This is the most common application. Dosage is based on holding a specific residual level of ATMP in the water.

• Initial Dosage (for first fill or after cleanup): 20 – 100 mg/L

  • This provides a high initial dose to clean the system and establish a protective film.

• Maintenance (Continuous Feed) Dosage: 2 – 20 mg/L (as active product)

  • Low Hardness Water: 2-10 mg/L

  • High Hardness/High Scaling Water: 10-20+ mg/L

• Goal: Maintain a residual concentration of 1 – 5 mg/L of ATMP in the system water. This is often monitored using a phosphonate test kit (Hach, etc.).

2. Boiler Water Treatment

Used to control carbonate and sulfate scale, especially in low-pressure boilers.

• Dosage Range: 1 – 10 mg/L (as active product) into the feedwater.

• Note: For high-pressure boilers, other chemistries are often preferred due to potential thermal degradation of phosphonates, though ATMP is more stable than many older phosphonates.

3. Reverse Osmosis (RO) & Desalination Systems

Used as an antiscalant in the feedwater to prevent scale on membranes.

• Dosage Range: 2 – 10 mg/L (as active product)

• Critical: A pretreatment compatibility test is essential. Overdosing can lead to fouling from the precipitation of ATMP with calcium (calcium-ATMP salt).

4. Oilfield Water Treatment (Squeeze Application)

In oil and gas production, a concentrated “pill” of scale inhibitor is injected (“squeezed”) into the formation to prevent downhole scale.

• Dosage: This is a highly specialized operation. Concentrations are very high (5-20% active solutions), and the volume is calculated based on formation geology and water volume. This must be designed by a specialist.

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Important Calculation: Dilution and Feed Rate

ATMP is typically sold as a liquid concentrate (e.g., 50% active content). You need to dilute it and set a feed pump rate.

Formula:
Feed Rate (L/hr) = (System Flow Rate (m³/hr) * Desired Dose (mg/L) * 0.001) / (Product Concentration (%) * 10)

Example:
You have a cooling system with a recirculation flow rate of 1000 m³/hr. You want to maintain a 5 mg/L dose of active ATMP. Your product is a 50% solution.

1. Calculate the amount of active ATMP needed per hour:

   • 1000 m³/hr * 5 g/m³ (because 5 mg/L = 5 g/m³) = 5000 g/hr

2. Calculate the amount of commercial product (50%) needed:

   • 5000 g/hr / (0.50) = 10,000 g/hr = 10 kg/hr

3. If your product is diluted (e.g., you have a 10% solution):

   • 5000 g/hr / (0.10) = 50,000 g/hr = 50 kg/hr

This is why using a concentrated product is often more practical.

Critical Precautions & Best Practices

• Overdosing Risk: Excessive ATMP can itself form a calcium-ATMP precipitate, causing scale. More is not better.

• pH Sensitivity: ATMP is most effective in a neutral to alkaline pH range (pH 7-9.5). Its performance can decrease in highly acidic conditions.

• Chlorine Tolerance: ATMP is not highly stable under strong oxidizers like chlorine. If chlorination is used, a stabilizer or a more oxidizer-resistant inhibitor like PBTC might be needed.

• Compatibility: Ensure it is compatible with corrosion inhibitors (e.g., zinc salts can precipitate) and other chemicals in your program.

• Jar Testing: The gold standard. Simulate your system’s water chemistry and temperature in a lab to determine the minimum effective dosage before full-scale application.

In summary, start with a dosage in the range of 5-10 mg/L for a cooling system, but the final dosage MUST be determined by testing your specific water and monitoring the residual inhibitor level and scaling tendency.