Ammonia Gas Feed Systems

Ammonia Gas Feed Systems deliver anhydrous ammonia gas directly into water or wastewater streams for pH adjustment, chloramine formation, and nutrient supplementation in municipal treatment plants. The system vaporizes liquid anhydrous ammonia (stored at 250 psi) through pressure reduction and heat exchange, then injects the gas through diffusers or eductors into the process stream. Typical feed rates range from 5-500 pounds per day for plants serving 0.5-50 MGD capacity. The primary trade-off is safety risk versus chemical cost efficiency - anhydrous ammonia costs 40-60% less than aqua ammonia but requires extensive safety systems, emergency response protocols, and specialized operator training due to its toxicity and corrosive nature.

• Chloramine Formation for Secondary Disinfection: Ammonia gas is injected downstream of chlorine contact chambers to form monochloramine, maintaining 2-4 mg/L residual in distribution systems. Systems typically feed 0.2-0.8 lb NH3 per lb Cl2, with precise ratio control preventing free chlorine breakthrough. Flow-paced controllers adjust feed rates from 1-50 lbs/day based on treated water flow.
• Breakpoint Chlorination pH Control: During breakpoint chlorination at 5-15 MGD plants, ammonia addition reduces chlorine demand by 7.6 mg Cl2 per mg NH3-N, lowering chemical costs 15-25%. Post-breakpoint ammonia addition prevents pH depression below 6.5, eliminating need for caustic feed.
• Taste and Odor Control: Small plants (0.5-3 MGD) use ammonia to form chloramines, reducing chlorinous taste complaints by 60-80% compared to free chlorine systems. Particularly effective with high-TOC source waters where chlorine produces trihalomethanes.

Daily Operations: Operators check cylinder weights, manifold pressures (80-120 psig typical), and solution tank levels twice daily. Feed rate verification involves comparing controller setpoint to actual gas flow meters. Residual testing confirms proper Cl2:NH3 ratios, typically 3:1 to 5:1 by weight for monochloramine formation.

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Maintenance: Monthly tasks include calibrating gas detection sensors, inspecting cylinder connections for leaks using ammonia detection tubes, and cleaning eductor nozzles. Quarterly cylinder changeouts require proper PPE (SCBA, chemical suits) and two-person teams. Valve rebuilds needed every 2-3 years depending on feed rates and gas purity.

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Troubleshooting: Low feed rates often indicate plugged eductors or insufficient water pressure (<30 psig). Cylinder freeze-up occurs during high withdrawal rates (>40 lb/day from 150-lb cylinder). Gas detection alarms typically result from loose fittings or over-pressurized solution tanks. System components typically last 8-12 years with proper maintenance.

• Gas Cylinder Manifold System: 150-lb cylinders arranged in duty/standby configuration with automatic switchover valves. Manifolds sized for 7-14 day supply at maximum feed rates. Stainless steel piping with 316SS fittings handles corrosive ammonia vapors.
• Gas Feed Control Valve: Diaphragm-operated valve with 0.1-100 lb/day capacity range, controlled by 4-20mA signal from flow-paced controller. Teflon-lined components resist ammonia corrosion. Vacuum operation prevents gas leaks.
• Solution Tank and Eductor: 50-300 gallon polyethylene tanks with level switches create 10-20% ammonia solution. Water-powered eductors provide vacuum for gas dissolution and positive pressure for injection. Sized for 15-30 minute detention.
• Gas Detection System: Continuous ammonia monitors with 25-ppm alarm setpoints trigger ventilation and safety shutoffs. Electrochemical sensors require monthly calibration and 12-18 month replacement intervals.

• Feed Rate Capacity: 5-500 lbs/day (2.3-227 kg/day) for typical municipal applications, with turndown ratios of 20:1 to 50:1 for operational flexibility
• System Pressure: Anhydrous ammonia cylinders operate at 114-250 psig depending on temperature. Feed systems require pressure reduction to 5-15 psig for safe injection into water streams
• Dosing Accuracy: ±2% of set point for automated systems, ±5% for manual control systems. Critical for chloramine formation where NH₃:Cl₂ ratios must maintain 3:1 to 5:1 weight ratios
• Injection Point Pressure: Must overcome system backpressure plus 10-15 psi safety margin. Typical injection pressures range 15-60 psig for clearwell applications, 60-150 psig for distribution system injection
• Ambient Temperature Range: Systems must operate reliably from 32°F to 120°F. Cylinder heating may be required below 60°F to maintain adequate vapor pressure
• Turndown Requirements: Minimum 10:1 turndown for seasonal demand variations. Advanced systems achieve 50:1 turndown using multiple feed trains or variable orifice control
• Safety Detection: Ammonia leak detection systems required with alarm setpoints at 25 ppm (OSHA exposure limit)

• What maximum daily ammonia demand drives system sizing? Systems sized for peak day demand plus 25% safety factor. Undersized systems cannot maintain chloramine residuals during high-demand periods, risking regulatory violations. Requires historical chlorine usage data and population growth projections.
• Should the system use cylinder manifolds or bulk storage? Facilities using >150 lbs/day typically justify bulk storage tanks (150-2000 gallon capacity). Cylinder manifolds work for smaller facilities but require frequent changeouts and higher labor costs. Decision impacts building footprint, safety systems, and operating expenses.
• What level of automation and redundancy is required? Basic manual systems cost $15,000-25,000 but require constant operator attention. Automated systems with PLC control, flow pacing, and residual feedback cost $40,000-80,000 but ensure consistent dosing. Redundant feed trains add 40-60% to capital cost but prevent treatment interruptions.
• Where should ammonia injection occur for optimal mixing? Injection before rapid mix chambers allows 30-60 seconds contact time for chloramine formation. Post-filter injection requires static mixers and longer contact time. Poor mixing locations create localized high ammonia concentrations and nitrification potential.

• Division 40-48: Process Integration
• Primary: 40 23 43 - Chemical Feed Systems (Ammonia Gas)
• Secondary: 40 05 00 - Common Work Results for Process Equipment (safety systems, leak detection)

• Material/Equipment Verification: Verify 316SS wetted parts and Hastelloy C-276 for gas service, Confirm AWWA B300 compliance for ammonia handling equipment
• Installation Requirements: Dedicated ammonia building with emergency ventilation (12 air changes/hour minimum), Eyewash/shower stations within 25 feet of equipment, Leak detection systems with 25 ppm alarm setpoints
• Field Challenges: Coordination with electrical for intrinsically safe wiring, HVAC sequencing for emergency ventilation activation, Concrete pads must cure 28 days before equipment setting
• Coordination Issues: Early coordination with fire marshal for emergency response procedures, Lead times: 16-20 weeks for gas feed equipment, 12-16 weeks for bulk storage systems

• Evoqua Water Technologies - ChemFeed series gas chlorinators adapted for ammonia service, widely used in 1-50 MGD plants
• Hayward Gordon - Rotary gas feeders with municipal references across Canada
• Neptune Chemical Pump - Solution feed systems for smaller plants under 5 MGD
• Capital Controls/Evoqua - Series 2000 gas feeders, standard in many large municipal facilities

• Aqueous ammonia feed (19-29% solution) - Preferred for plants under 2 MGD due to simpler handling and lower capital costs, roughly 20% higher chemical costs
• Liquid ammonium sulfate - Gaining popularity for pH-sensitive applications, 40-50% higher chemical costs but eliminates gas handling concerns
• On-site ammonia generation - Emerging technology for large plants (>25 MGD), high capital cost but eliminates transportation/storage risks

Establish relationships with local ammonia suppliers early - delivery logistics often drive system sizing more than treatment requirements. Consider redundant vacuum regulators; single-point failures shut down entire chloramine systems. Specify manual backup capability for critical applications. Bulk storage systems (1-ton containers) typically cost 30-40% less per pound than cylinder systems but require higher capital investment and more complex permitting.