Chlorine Gas Feed Systems

Chlorine gas feed systems inject pressurized chlorine gas into water streams for disinfection and oxidation in municipal treatment plants. The system uses vacuum-operated ejectors or solution feed pumps to draw chlorine gas from pressurized cylinders through rotameters that control feed rates typically ranging from 5-500 pounds per day. These systems achieve 99.9% pathogen kill rates with contact times of 30-60 minutes at residual concentrations of 0.5-2.0 mg/L. The primary trade-off is the significant safety risk from chlorine gas leaks, requiring extensive ventilation systems, leak detection equipment, emergency scrubbers, and specialized operator training compared to safer liquid hypochlorite alternatives.

• Primary Disinfection (Post-Secondary Treatment): Chlorine gas feeds directly into clear wells or contact basins through vacuum-operated chlorinators, typically dosed at 2-8 mg/L depending on effluent quality. Selected for reliable pathogen kill and residual maintenance in distribution systems.

• Distribution System Boosting: Remote booster stations use smaller gas feeds (50-150 lb/day capacity) to maintain 0.2-2.0 mg/L free chlorine residuals. Preferred over liquid systems for consistent dosing and lower chemical costs at remote locations.

• Peak Flow Disinfection: Large plants (10+ MGD) utilize multiple chlorinator trains with 150 lb/hr cylinders for storm event treatment. Gas systems provide rapid dose adjustment capability during wet weather flows.

• Dechlorination Pre-Treatment: Smaller applications use controlled gas feeds for sulfur dioxide generation or direct ammonia chloramine formation, typically 1-4 mg/L dosing rates for biological treatment protection.

Daily Operations: Operators check cylinder scales, vacuum levels (-20" Hg typical), and gas flow rates every 4-8 hours. Residual monitoring requires grab samples or online analyzers with 0.1 mg/L precision. Feed rate adjustments respond to flow changes and residual targets, typically requiring 15-30 minutes for system response. Gas leak detectors require daily functional checks with calibration gas.

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Maintenance: Monthly tasks include diaphragm inspection, vacuum line cleaning, and injector nozzle replacement. Cylinder changeouts require confined space procedures, full-face respirators, and two-person teams. Annual calibration of scales, flow meters, and leak detection systems demands certified technicians. Scrubber solution testing and replacement occurs quarterly. Level 2-3 water treatment certification typically required with hazmat training.

• Chlorine Cylinders/Ton Containers: 150 lb cylinders for plants <5 MGD, one-ton containers for larger facilities. Steel construction with fusible plugs rated at 158°F-165°F. Selection based on daily usage rates - typically size for 7-14 day supply with automatic switchover capability.

• Vacuum Chlorinators: Wall-mounted units (Kapco, Wallace & Tiernan) rated 5-8,000 lb/day capacity. Diaphragm-operated with integral vacuum regulators maintaining -15" to -25" Hg. Sized at 150% peak hourly demand with redundant units for reliability.

• Gas Leak Detection Systems: Fixed-point detectors at 1 ppm alarm, 3 ppm evacuation levels. Photoionization or electrochemical sensors with battery backup. Required every 300 sq ft in chlorine rooms per OSHA standards.

• Scrubber Systems: Caustic solution (15% NaOH) neutralization for emergency gas releases. Sized for 150% maximum feed rate with 30-minute retention. Includes pH monitoring and automatic makeup systems.

• Injector Water Systems: Dedicated service water at 30-60 psi, 2-5 gpm flow rates for vacuum creation and chlorine solution transport. Requires backflow prevention and pressure regulation.

• Chlorine Demand and Capacity: Peak day demand: 1-15 mg/L for water treatment, 5-25 mg/L for wastewater; Feed rate capacity: 5-2,000 lb/day (0.5-50 MGD range); System turndown ratio: minimum 10:1, preferably 20:1 for operational flexibility

• Feed Accuracy and Control: Dosing accuracy: ±2% of setpoint for rotameter systems, ±1% for electronic mass flow; Response time: <30 seconds for 90% of setpoint change; Minimum controllable feed rate: 5-10% of maximum capacity

• Operating Pressures and Vacuum: Chlorinator operating vacuum: 5-15 inches Hg; Solution line pressure: 15-30 psi above injection point pressure; Chlorine cylinder pressure: 85-200 psi (temperature dependent)

• Physical Requirements: Ambient temperature range: 60-80°F for consistent gas withdrawal; Ventilation: minimum 6 air changes per hour, emergency scrubber activation; Scale accuracy: ±0.5 lb for cylinder monitoring; Injector water pressure: minimum 35 psi, flow 2-8 gpm per lb/day capacity

• What is the required feed rate range and accuracy for your disinfection requirements? Threshold: Systems <100 lb/day typically use rotameter control (±2%), while >100 lb/day benefit from electronic mass flow (±1%). Undersized systems cannot meet peak demands; oversized systems lose accuracy at low flows.

• Should you specify ton containers versus 150-lb cylinders for chlorine supply? Threshold: >300 lb/day consumption typically justifies ton containers for reduced handling. Wrong choice affects operating costs by $0.10-0.30/lb chlorine and labor requirements.

• What level of automation and remote monitoring is required? Threshold: Plants >5 MGD typically specify SCADA integration and automatic switchover capabilities. Manual systems save $15,000-25,000 initially but increase operator requirements and response times.

• How will you handle chlorine leak detection and emergency response? Threshold: >1,000 lb storage requires emergency scrubber systems per OSHA standards. Inadequate detection risks regulatory violations and safety incidents.

• Division 40-48: Process Integration

• 40 31 33 - Chemical Feed Equipment (Primary)

• 40 32 00 - Disinfection Equipment Systems

• Note: Chlorine gas systems span chemical feed and disinfection categories, with primary specification under chemical feed equipment covering feeders, scales, and control systems.

• Material/Equipment Verification: Verify Hastelloy C construction for gas-wetted components; Confirm vacuum regulator and ejector materials meet specifications; Check rotameter accuracy certification and range

• Installation Requirements: Chlorine room ventilation coordination critical - 1 CFM/sq ft minimum; Gas detector placement per OSHA requirements; Structural support for 150 lb cylinders or ton containers

• Field Challenges: Moisture infiltration during startup causes corrosion; Vacuum line routing conflicts with other utilities; Scale tank foundation often undersized

• Coordination Issues: HVAC contractor for emergency ventilation interlocks; Electrical for gas leak detection system; 12-16 week lead times typical for engineered systems

• Capital Controls (Evoqua) - Series 100 gas chlorinators dominate municipal market with proven reliability

• Wallace & Tiernan (ProMinent) - DULCOMETER gas feed systems popular for mid-size plants

• Hach (Xylem) - CL17 series chlorinators common in smaller municipalities

• De Nora - SEACHLOR systems gaining traction for larger installations

• Capital Controls maintains largest North American municipal installed base with extensive service network

• Sodium hypochlorite generation preferred for plants under 2 MGD due to safety concerns and operator skill requirements. Capital cost 20-30% higher but eliminates hazardous chemical handling.

• Liquid sodium hypochlorite suitable for smaller systems with good supplier access - lower capital cost but higher operating expense.

• UV disinfection with chloramination increasingly popular for plants over 10 MGD seeking to minimize DBP formation while maintaining residual.

Establish direct relationship with manufacturer's local service technician before startup - they know common installation mistakes and can prevent costly delays. Specify redundant rotameters on critical systems; they're inexpensive compared to emergency service calls. Order spare ejectors with initial equipment - they're prone to clogging and having spares prevents extended downtime. Many operators prefer Capital Controls for parts availability and service network, even at 10-15% premium over competitors.