The typical dosage of HPMA (Hydrolyzed Polymaleic Anhydride) varies significantly depending on the application, water quality, and system operating conditions.
HPMA is a low-toxicity, high-efficiency scale inhibitor, particularly effective against calcium phosphate and carbonate scales. It also acts as a dispersant for particulate matter like clay and iron oxide.
Here is a breakdown of its typical dosage concentrations in different applications:
1. Industrial Cooling Water Systems (Circulating Water)
This is the most common application for HPMA. The dosage is highly dependent on the cycles of concentration and the hardness of the makeup water.
-
Typical Dosage Range: 2 – 20 mg/L (ppm)
-
Initial/Shock Dosage: When starting a system or after a cleaning, a higher “shock” dose of 10 – 30 mg/L might be used to quickly establish a protective film.
-
Maintenance Dosage: The ongoing dose is calculated based on the bleed-off rate and makeup water quality. It’s often maintained at a residual concentration of 2 – 10 mg/L in the circulating water.
-
Key Factors:
-
Calcium Hardness: Higher calcium levels require a higher dosage.
-
pH: HPMA is effective in a wide pH range (7.0-9.5), but dosage may need adjustment at higher pH levels.
-
Cycles of Concentration: More cycles mean higher scaling potential, requiring a higher dosage.
-
2. Reverse Osmosis (RO) & Nanofiltration (NF) Systems
In membrane systems, HPMA is used to prevent scaling on the membrane surface, especially in the concentrate stream where scaling ions are most concentrated.
-
Typical Dosage Range: 2 – 10 mg/L (ppm)
-
Dosing Point: It is continuously injected into the feed water upstream of the cartridge filters.
-
Key Factors:
-
LSI (Langelier Saturation Index) or S&DSI (Stiff & Davis Index): The scaling potential of the feed water is the primary determinant. Systems with a positive scaling index require higher dosages.
-
Membrane Type: Always check with the membrane manufacturer’s guidelines for compatibility and maximum allowable dosage for phosphonate-based antiscalants.
-
Recovery Rate: Higher recovery rates increase scaling potential, necessitating a higher dose.
-
3. Boiler Water Treatment
In low to medium pressure boilers, HPMA is used for scale inhibition and sludge conditioning.
-
Typical Dosage Range: 1 – 10 mg/L (ppm)
-
Dosing: Fed continuously to the boiler feedwater.
-
Key Factors:
-
Boiler Pressure: For high-pressure boilers, volatile treatments (like amines) are often preferred over solid polymers like HPMA.
-
Feedwater Hardness: The dosage is directly proportional to the hardness of the feedwater.
-
4. Oil Field Applications
In oilfield water treatment, HPMA is used in squeeze treatments (to prevent scale in the formation) and in surface equipment.
-
Typical Dosage Range: Varies Widely (10 – 100+ mg/L)
-
Squeeze Treatment: In “scale squeeze” applications, a very high concentration slug (thousands of ppm) is injected into the formation, which then desorbs slowly over time to provide long-term protection.
-
Surface Equipment: For continuous injection into produced water to control scale in pipes and vessels, dosages are more typical, in the 10 – 50 mg/L range, depending on scaling tendency.
5. Dispersant Applications
HPMA is also used as a dispersant for oxides (e.g., iron oxide) and particulates in various industrial processes.
-
Typical Dosage Range: 5 – 50 mg/L (ppm)
-
Application: The dosage is highly dependent on the concentration and type of suspended solids it is meant to disperse.
Summary Table
| Application | Typical Dosage Range (mg/L or ppm) | Key Purpose |
|---|---|---|
| Cooling Water Systems | 2 – 20 | Inhibit Ca₃(PO₄)₂ and CaCO₃ scale |
| Reverse Osmosis (RO) | 2 – 10 | Prevent membrane scaling |
| Boiler Water | 1 – 10 | Scale inhibition & sludge conditioning |
| Oil Field (Continuous) | 10 – 50 | Prevent scale in downhole & surface equipment |
| Oil Field (Squeeze) | 1,000 – 10,000+ (as a slug) | Long-term formation protection |
| Dispersant | 5 – 50 | Disperse suspended solids and oxides |
Critical Considerations for Dosing
-
Water Chemistry is Key: These are general guidelines. The optimal dosage must be determined based on a detailed analysis of the specific water chemistry (calcium, alkalinity, pH, phosphate, iron, etc.).
-
Overdosing Risk: While low in toxicity, overdosing can lead to increased organic load in the system and potentially contribute to microbial growth (biofouling) or fouling of the polymer itself.
-
Blended Products: HPMA is often sold as part of a blended formulation that may contain other phosphonates (like HEDP, PBTCA), polymers, or corrosion inhibitors. The dosage of the final product will be specified by the chemical supplier.
-
Consult Suppliers: Always follow the dosing recommendations provided by your water treatment chemical supplier, as they are based on your specific system conditions.