Cyclone Degritter (Hydro Cyclone)

Cyclone degritters remove sand, grit, and heavy inorganic particles from wastewater using centrifugal force in a conical vessel. Raw wastewater enters tangentially at the top, creating a vortex that forces heavier particles (specific gravity >2.65) to the outer wall where they settle to the underflow, while treated water exits through the overflow. Typical removal efficiency ranges from 85-95% for particles larger than 75 microns in municipal plants processing 0.5-50 MGD. The primary limitation is reduced efficiency on lighter organic materials and fine particles, requiring upstream screening and potential downstream polishing for complete grit removal in sensitive applications.

• Primary Clarifier Underflow: Installed downstream of primary clarifiers to remove grit from settled sludge before thickening. Selected for 95% removal efficiency of 100+ mesh particles while maintaining 85-90% organic solids retention. Typical sizing: 6-12 inch diameter units for 2-10 MGD plants.

• Grit Chamber Overflow: Used after aerated grit chambers when conventional classifiers cannot achieve <5% organics in grit discharge. Handles 50-200 GPM flows with 15-25 psi feed pressure. Connects upstream to grit pumps, downstream to grit dewatering.

• Secondary Treatment Bypass: Emergency application during high-flow events to protect downstream processes from grit carryover. Installed on plant bypass lines with automated activation at 2.5x design flow.

• Digester Feed Pretreatment: Protects anaerobic digesters from grit accumulation in 5-20 MGD facilities processing high inorganic loads from combined sewer systems.

Daily Operations: Monitor inlet pressure (15-25 psi typical), underflow discharge consistency, and overflow clarity. Adjust apex orifice size based on grit loading - smaller orifices increase underflow concentration but reduce capacity. Check for proper spray pattern at underflow discharge indicating good cyclonic action.

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Maintenance: Weekly inspection of wear components, monthly apex orifice measurement, quarterly pressure testing. Requires confined space entry procedures for internal inspection. Standard PPE plus respiratory protection for grit dust exposure. Maintenance staff need basic hydraulics knowledge and torque wrench skills for proper reassembly.

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Troubleshooting: Reduced separation efficiency indicates worn apex or plugged vortex finder. Excessive pressure drop suggests inlet blockage. Rope discharge at underflow signals improper feed pressure or apex sizing. Typical service life: 2-3 years for apex components, 5-7 years for cyclone body in municipal service.

• Feed Inlet Assembly: Tangential entry design with 4-8 inch flanged connections. 316 SS construction standard for municipal service. Sizing based on 8-12 ft/sec inlet velocity to maintain proper cyclonic action.

• Cylindrical Body: 6-24 inch diameter depending on flow (50-500 GPM typical). Height-to-diameter ratio of 2.5:1 optimizes separation efficiency. Abrasion-resistant urethane or ceramic lining for grit-laden applications.

• Vortex Finder: Central overflow pipe extending 0.3-0.5 diameters into cyclone body. Controls split ratio between overflow (clean) and underflow (grit-laden) streams. Adjustable length affects cut point.

• Apex/Underflow Orifice: Variable diameter discharge (0.5-3 inches) controls underflow concentration. Replaceable wear components, typically polyurethane or tungsten carbide for extended service life.

• Pressure Monitoring: Differential pressure transmitters across inlet/overflow monitor performance and detect plugging conditions.

• Flow Rate Parameters: Unit capacity: 50-2,000 GPM per cyclone, Inlet velocity: 8-15 ft/sec (optimal 10-12 ft/sec), Overflow rate: 85-95% of inlet flow, Underflow rate: 5-15% of inlet flow

• Pressure Requirements: Operating pressure: 15-40 psi at inlet, Pressure drop: 8-25 psi across unit, Minimum head requirement: 20-35 feet

• Particle Separation: Cut size (d50): 75-150 microns for grit, Separation efficiency: 85-95% for particles >100 microns, Organic removal: <5% (maintains organic content in liquid stream)

• Physical Sizing: Diameter: 6-36 inches for municipal applications, Length-to-diameter ratio: 3:1 to 5:1, Cone angle: 10-20 degrees (typically 15°), Vortex finder diameter: 0.3-0.4 × cyclone diameter

• Loading Criteria: Hydraulic loading: 10-40 GPM/ft² of inlet area, Solids loading: 100-2,000 mg/L influent TSS, Grit loading: 0.5-5.0 cubic feet per MG treated

• What inlet pressure and flow variability must the system handle? Need minimum 20 psi with flow variations ±30%. Insufficient pressure (<15 psi) reduces separation efficiency below 70%. Requires influent pumping analysis, peak flow projections, and downstream hydraulic profile to determine if booster pumping needed.

• What particle size removal is required for downstream equipment protection? Target d50 of 75-100 microns for membrane protection, 100-150 microns for conventional treatment. Oversizing for finer particles increases organic removal (>10%) and reduces downstream biological performance. Requires influent characterization and downstream process sensitivity analysis.

• How will underflow be handled and what concentration is acceptable? Underflow typically 2-8% solids by weight, requiring grit washing or dewatering. Higher underflow rates (>15%) indicate poor separation. Need to evaluate grit handling capacity, washing requirements, and disposal methods.

• What redundancy and turndown capability is required? Multiple smaller units provide better turndown (minimum 30% of design flow per unit) versus single large cyclone. Wrong sizing limits operational flexibility during maintenance or low-flow periods. Requires evaluation of diurnal flow patterns and maintenance philosophy.

• Primary: Division 46 23 61 - Grit Removal Equipment

• Secondary: Division 40 32 00 - Grit Chambers (if integrated into channel system)

• Cyclone degritters fall under water treatment process equipment, specifically grit removal systems within water and wastewater treatment specifications

• Material/Equipment Verification: Verify polyurethane liner thickness and hardness rating, Confirm stainless steel housing material grade (316SS minimum), Check inlet/outlet connection sizes and flange ratings

• Installation Requirements: Requires 10-15 feet vertical clearance for underflow discharge, Foundation must handle dynamic loading from pulsating flow, Access platforms needed for liner inspection/replacement

• Field Challenges: Achieving proper inlet pressure (15-30 psi typical), Maintaining consistent feed concentration, Liner wear monitoring and replacement scheduling

• Coordination Issues: Coordinate with pump sizing for proper pressure delivery, Interface with downstream thickening equipment, 12-16 week lead times for custom municipal units

• Krebs Engineers - millTRAC 15" and 20" units for municipal applications

• WesTech Engineering - HydroFloat systems with integrated cyclones for water treatment

• Metso Outotec - Cavex hydrocyclones, typically 6"-15" diameter for grit removal

• Schlumberger (M-I SWACO) - VORTOIL series for oil/water separation in municipal applications

• Vortex Grit Chambers - Lower capital cost, simpler operation, but larger footprint and lower removal efficiency. Typically 30-40% less expensive.

• Horizontal Flow Grit Chambers - Proven technology, minimal maintenance, but requires more space and produces wetter grit. Cost similar to cyclones.

• Centrifugal Separators - Higher removal efficiency, better dewatering, but significantly higher capital and operating costs (2-3x cyclone cost).

Size conservatively - municipal grit loading varies significantly with weather events. Plan for 150% of calculated capacity. Establish spare liner inventory early; polyurethane liners typically last 6-18 months depending on abrasive content. Maintain strong relationship with manufacturer's field service team for startup and troubleshooting. Consider package deals combining cyclones with feed pumps for better performance guarantees and single-source responsibility.