Introduction to Marine Vapor Control Systems

Purpose:

Limit volatile organic hydrocarbon vapor emissions during cargo transfer to reduce air pollution and protect nearby personnel from toxic exposure.

Regulatory Background:

• Established based on the Clean Air Act of 1990.

• Governed by 46 CFR Part 39 for tank vessels and 33 CFR 154 for facilities.

• State regulations were published by the US Coast Guard in 1992 and revised in 2013 to enhance safety and environmental protection measures.

Principles of Vapor Control

Vapor Recovery Systems:

• Engineering Controls: Designed to minimize vapor emissions from barge cargo tanks, ensuring compliance with environmental regulations.

Methods of Vapor Control:

1. Combustion: The most common method; vapor is burned via:

   • Flares: High-temperature flames that ensure complete combustion of vapors.

   • Enclosed Chambers: Flares are arranged in controlled environments to optimize efficiency and minimize visible emissions.

2. Condensation: Cools vapor, returning it to liquid without atmospheric release by passing it through a heat exchanger.

3. Adsorption: Activated charcoal is used to capture and hold vapors, allowing for subsequent recovery and reuse.

4. Vapor Balancing: Ensures vapor that would normally be vented is recirculated back into the delivering vessel or facility, thus reducing emissions.

Components of Vapor Control Systems

Piping and Valves:

• Color-coded Vapor Piping: Indications for different types of gases to prevent operator errors.

• Vapor Header Flanges: Secure connections to maintain system integrity and prevent leaks.

• Vapor Tight Hatch Covers: Reduce vapor leakage during cargo operations.

• Closed Gauging Devices: Facilitate accurate measurement of liquid levels without exposure to vapors.

• Sight Glasses and Gauges: Allow quick visual inspections of system status.

Vapor Collection System:

• Must be permanently fixed to the barge, designed to prevent liquid condensation.

• Incorporates various safety features including:

  • Manually operated valves to control vapor flow.

  • Pressure vacuum gauges to monitor system performance.

Vapor Vent Stack:

• Equipped with flame screens that prevent ignition of vapors during venting.

• Regularly monitored for safety during operations; essential for managing vapor dispersion and preventing excessive concentration in the atmosphere.

Safety Precautions

Monitoring:

• Continuous monitoring of pressure and vacuum to prevent hazards from developing during cargo transfer. High-tech sensors provide real-time data.

Static Ignition Prevention:

• Careful procedures during loading, startup, and gauging to avoid static electricity discharges, which can ignite flammable vapors.

Tank Overfill Protection:

• Critical to monitor level gauges and alarms to prevent overfills, which can have catastrophic consequences.

Hazards Associated with Vapor Control Systems

1. Excessive Cargo Tank Pressure: Monitoring systems should warn operators of excessive pressures to prevent damage to barge structure and ensure operational integrity.

2. Static Ignition Risk: Flammable vapors can ignite due to static; strict adherence to procedures during operations is essential.

3. Vapor Release: Open hatches or a failure at connection points can lead to unexpected vapor emissions, creating immediate hazards.

4. Cargo Tank Overfills: Monitored to avoid catastrophic failures; vapor control systems must be effective in ensuring safe pressure management.

Operational Requirements

Cargo Vapor Management:

• Systems must be capable of destroying, processing, or recovering vapors using combustion, condensation, adsorption, or vapor balancing.

High Level Safety Systems:

• Must integrate with facility systems, creating safety alarms at 95% tank capacity and automatic shutdowns at 100% to mitigate overflow risks.

• High-level alarms are crucial for preventing spills and must connect with shore facilities for automated control, enhancing safety protocols.

Key Components and Functions

• Vapor Hose Specifications: Must endure significant pressures, be electrically continuous to prevent static discharge, resist abrasion, and allow for proper fittings that ensure tight seals. At least 25 psig burst pressure rating and 5 psig maximum allowable working pressure.

• Vapor Pressure Vacuum Valve: Regulates cargo vapor discharge, ensuring safety under maximum transfer rates and preventing backflow into the cargo tank.

• High-Level Alarms and Control Systems: Devices such as 3 meter magnetic gauge sticks and alarms signal safe operational limits, crucial for maintaining cargo levels without risk.

Conclusion

Effective vapor control systems are crucial in maritime transport, safeguarding both the environment and crew safety by adhering to stringent regulations and operational standards, thereby preventing environmental harm and ensuring compliance with legal requirements.