Pipe-mounted static mixing elements for coagulant flash-mixing, pH correction blending, and low-intensity post-coagulation flocculation. No moving parts, low maintenance, continuous operation.
Static mixers use fixed helical or corrugated elements within a pipe section to split, rotate, and recombine the flow, achieving rapid radial mixing without any energy input beyond the existing line pressure drop. In water treatment, they are principally used at the coagulant injection point for flash mixing (G > 300 s−¹ in < 1 second) and at pH-adjustment dosing points for acid or alkali blending.
G-value for static mixers: G = √(u·ΔP / μ·L/v) where u = mean velocity (m/s), ΔP = pressure drop across element (Pa), L = mixer length (m), v = mean fluid velocity (m/s), μ = dynamic viscosity. Typical flash-mix G values are 300–1,000 s−¹ over a contact time of 0.5–2 seconds, giving GT ≈ 500–2,000 — well within the required rapid-mix window.
Zero mechanical wear, no seal maintenance, no drive or motor. Maintenance is limited to periodic inspection for element fouling or scale deposition — typically once per year in clean water duties.
Coagulant is uniformly distributed across the full pipe cross-section within 3–5 element diameters (typically < 300 mm mixer length). This prevents localised over-dosing and the formation of aluminium hydroxide precipitates before particle contact.
Optimised element pitch and open area limit the pressure drop to 0.3–1.5 m H2O at design flow. For larger installations, multi-element designs distribute the mixing work to keep total head loss below 0.5 m.
Available in DN50 to DN1200, flanged or wafer-mounted. Elements in SS316L, CPVC, PVDF, or HDPE for aggressive chemical streams. Carbon steel housings with internal epoxy lining for large-bore municipal duties.
| Application | Duty | Design G (s−¹) | Contact Time | Chemical Dosed |
|---|---|---|---|---|
| Raw water coagulation | Flash mix — coagulant dispersion | 500–1,000 | 0.5–1 s | Alum / PAC / ferric sulphate |
| pH correction | Acid or alkali blending | 300–600 | 1–2 s | NaOH, H&sub2;SO&sub4;, CO&sub2; |
| Flocculant aid addition | Polymer dispersion | 100–300 | 2–5 s | Anionic or cationic polymer |
| Chlorination / disinfection | Chlorine contact — initial mixing | 200–500 | 1–3 s | Sodium hypochlorite / Cl&sub2; |
| Antiscalant injection (RO) | Inline blending before membranes | 150–400 | 1–4 s | Antiscalant / acid |
Static mixers are installed at chemical injection points, typically immediately downstream of a dosing pump outlet. For coagulant addition, the injection nozzle is located 3–5 pipe diameters upstream of the first mixing element to allow the chemical jet to penetrate the pipe cross-section before entering the mixing zone.
Paired with chemical dosing pumps and flow-paced dosing controllers. The static mixer ensures the dosed chemical is fully dispersed before the coagulated water reaches the flocculation chamber.
Installed 1–5 m upstream of paddle or turbine flocculators. The static mixer handles coagulant dispersion (high G, short contact), leaving the downstream flocculator to grow flocs at lower G over longer residence times.
For flows below 200 m³/h, a correctly sized static mixer followed by a short plug-flow pipe contact section can replace a mechanical flocculator chamber entirely, reducing capital cost and eliminating moving parts from the treatment train.
Related equipment: Static mixers are commonly supplied with chemical dosing skids, metering pumps, and inline TOC analysers as a complete chemical conditioning package.
Slow-speed horizontal or vertical paddle wheels for gentle, sustained floc growth.
View PageAxial and radial turbine impellers for higher-intensity or multi-stage flocculation.
View PageChemical coagulant flash-mixing without moving parts using pipe-mounted static elements.
View PageCamp & Stein G-value calculations, GT product, tapered flocculation staging, and chamber sizing.
View PageDiagnose pin floc, carry-over, excessive breakup, and drive mechanical faults.
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