Inline Static Mixers

Inline Static Mixers provide rapid, efficient chemical mixing in pressurized pipelines by using fixed internal elements to create turbulence and blend flows. These motionless devices rely on flow energy to generate mixing through helical elements, baffles, or vanes that split, redirect, and recombine fluid streams within the pipe. Typical mixing efficiency exceeds 95% with residence times of 0.5-2 seconds at velocities of 3-8 ft/sec. While highly effective for coagulant, polymer, and disinfectant injection in municipal applications, they require sufficient head pressure to overcome 2-15 feet of additional head loss depending on element design and flow conditions.

• Chemical Feed Mixing (0.5-15 MGD plants): Static mixers installed 3-5 pipe diameters downstream of chemical injection points for coagulant, polymer, or disinfectant mixing. Selected for consistent mixing without moving parts or power requirements. Typically 6-24 inch diameter units handling 1-8 MGS flows. Connects between chemical feed manifolds and downstream flocculation or contact basins.

• Pre-aeration Mixing (2-25 MGD plants): Installed after air injection points in raw water lines to enhance oxygen transfer and strip hydrogen sulfide. 12-36 inch mixers handling 3-40 MGD flows provide 15-30 seconds contact time. Selected over mechanical mixers for lower maintenance and energy costs.

• Lime Slaking Applications (5-50 MGD plants): Used in lime feed systems for pH adjustment, mixing slaked lime with process water. 8-18 inch units handle 0.5-5 MGD lime slurry flows. Selected for ability to handle abrasive slurries without wear parts.

• Blend Tank Recirculation: Enhances mixing in chemical storage tanks through external recirculation loops with 4-12 inch static mixers.

Daily Operations: Operators monitor upstream and downstream pressure gauges to track pressure drop across mixing elements, indicating fouling or blockage. No adjustments required during normal operation. Flow rate verification through plant SCADA confirms proper mixing energy. Visual inspection of chemical feed rates ensures proper dosing ratios.

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Maintenance: Elements require inspection every 6-12 months depending on water quality and chemical applications. Confined space entry procedures and fall protection required for larger units. Maintenance staff need basic rigging skills for element removal. Cleaning typically involves high-pressure washing or chemical cleaning for biological growth. Gasket replacement during reassembly prevents leakage.

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Troubleshooting: Excessive pressure drop indicates fouling or debris accumulation, requiring element cleaning or replacement. Poor mixing performance downstream suggests damaged or missing elements. Service life ranges 10-20 years for elements in clean water service, 3-8 years in aggressive chemical applications. Corrosion or erosion damage requires material upgrade evaluation.

• Mixing Elements: Helical or tab-style internals creating flow division and radial mixing. Stainless steel 316L for potable water, Hastelloy C-276 for aggressive chemicals. Element count varies from 6-24 based on required mixing intensity. Typical pressure drops of 0.5-3.0 psi per element.

• Housing/Pipe Section: Carbon steel with epoxy lining or stainless steel construction. Flanged connections standard for 6+ inch sizes, threaded for smaller applications. Wall thickness per ANSI B31.3 for 150-300 psig ratings.

• Support Structure: Welded pipe supports rated for filled weight plus dynamic loads. Critical for larger units (24+ inches) handling high flows.

• Access Ports: Removable sections or flanged cleanout ports for element inspection/replacement. Required for applications with fouling potential.

• Flow Straighteners: Upstream perforated plates ensure uniform velocity profile entering mixer elements.

• Flow Velocity: 3-8 ft/sec through mixer elements for effective mixing; minimum 2 ft/sec to prevent settling

• Pipe Diameter: 4"-48" typical for municipal applications; larger sizes require custom fabrication

• Pressure Drop: 0.5-5 psi per mixer element; budget 2-3 psi for standard helical designs

• Reynolds Number: >2,000 for turbulent flow required; >10,000 preferred for chemical mixing applications

• Mixing Length: 6-12 pipe diameters downstream for 95% uniformity; polymer applications may require 15-20 diameters

• Chemical Dosing: 0.1-50 mg/L typical range; injection point 1-2 pipe diameters upstream of mixer

• Residence Time: 2-10 seconds contact time depending on chemistry; coagulation requires minimum 30 seconds total

• Material Selection: 316SS standard; Hastelloy C-276 for chlorine dioxide; PVC/CPVC for non-pressure applications

• Temperature Range: -20°F to 200°F for metallic units; verify gasket compatibility

• Coefficient of Variation: <5% achievable with proper sizing; <2% possible with multiple elements

• How many mixer elements are required for target uniformity? Single element achieves 90-95% mixing; dual elements reach 98%+. Consequence: Under-mixing leads to chemical waste and poor treatment performance. Need: Specific mixing requirements, allowable pressure drop budget, and downstream sampling capability.

• What injection method and location optimize chemical distribution? Single-point injection acceptable for <12" pipes; multi-point required for larger diameters. Poor injection causes dead zones and chemical stratification. Need: Pipe size, chemical properties, flow velocity profile, and available injection pressure.

• Should mixer be removable or permanent installation? Removable cartridge designs cost 20-30% more but enable maintenance access. Permanent welded units require pipeline modifications for cleaning. Need: Chemical fouling potential, maintenance philosophy, and pipeline accessibility.

• What pressure rating matches system requirements with safety margin? Standard 150# ANSI adequate for most municipal applications; 300# required for high-pressure zones. Under-rating causes catastrophic failure; over-rating increases costs unnecessarily. Need: Maximum operating pressure, surge conditions, and applicable safety factors per AWWA standards.

• Primary: Division 40-05-23 (Chemical Feed Mixing Equipment)

• Secondary: Division 40-05-13 (Chemical Solution Feed Equipment) - when integrated with chemical feed systems

• Alternative: Division 33-11-00 (Water Utility Transmission and Distribution) - for distribution system installations

• Material/Equipment Verification: Verify 316SS construction for chlorinated applications, Confirm ANSI flange ratings match piping system, Check element configuration matches hydraulic calculations

• Installation Requirements: Minimum 5D upstream, 3D downstream straight pipe required, Support piping independently - mixers add significant weight, Access ports needed for element inspection/cleaning

• Field Challenges: Welded elements difficult to clean if fouling occurs, Pressure drop higher than calculated when elements partially blocked

• Coordination Issues: 12-16 week lead times typical for custom configurations

• Sulzer - SMX and SMV series mixers dominate municipal chlorine contact and polymer mixing applications

• Komax - KMX and KMS series popular for lime slaking and alum mixing systems

• Chemineer (NOV) - Kenics KM and KME series widely specified for phosphorus removal and pH adjustment

• Ross Engineering - ISG series gaining traction in smaller municipal plants (0.5-5 MGD) for coagulant mixing applications

• Mechanical mixers cost 2-3x more initially but offer variable mixing intensity - preferred for batch processes or varying flow conditions

• Jet mixers using plant water provide excellent mixing at 50% lower capital cost but require higher operating pressure (30-40 psi minimum)

• Pipeline tees with baffles cost 80% less than static mixers but provide inconsistent mixing - acceptable only for non-critical applications like lime slaking

Specify removable elements for applications with potential fouling - saves thousands in cleaning costs versus welded designs. Komax and Sulzer field service teams provide valuable troubleshooting support but charge premium rates. Consider oversizing mixer slightly (10-15%) rather than operating at maximum capacity - provides operational flexibility and reduces pressure drop sensitivity to minor fouling. Standardize on one manufacturer across facility to simplify spare parts inventory.