Vapor Control System (VCS)

The Vapor Control System (VCS) involves essential calculations concerning pressure drops during cargo transfers that must be executed for both maximum and minimum transfer rates. This is crucial as part of the barge transfer procedures ensuring safety and compliance with regulations. The calculated cargo transfer rates must respect limits derived from pressure drop calculations to prevent excessive pressure or vacuum in the cargo tanks.

Cargo Tank Pressure/Vacuum Limitations

• Safety Threshold: The cargo tank pressure or vacuum must not exceed 80% of the Pressure Vacuum (PV) valve setting to maintain safe operations. This is vital for preventing tank overpressure or vacuum situations which could lead to tank failures.

Cargo Tank Monitoring

• Continuous Monitoring: It's imperative to closely monitor the pressure and vacuum readings using the barge's pressure vacuum gauge. Additional data from the facility’s vapor control system is retrievable through the designated Person in Charge (PIC), allowing for comprehensive oversight.

• Capacity Limits: Cargo tanks must not exceed 98.5% of their capacity as this is the threshold at which an overfill alarm will activate, signalling the need to halt the transfer immediately.

High Level Alarm Testing

• tankerman PIC Responsibilities: Routine testing of high-level alarms is crucial, which can be done using the alarm test rod. Magnetic gauge sticks on each cargo tank function with high level alarms; as liquid levels rise, magnets on floats cause these sticks to rise, visibly indicating levels.

Alarm Activation

• Immediate Action Required: When the cargo liquid triggers the suspended alarm float, it activates a high-level alarm. Tankers are mandated to cease all liquid transfer operations immediately upon alarm activation, as established procedures dictate in pre-transfer conferences with the designated PIC.

Equipment Safety Measures

• Static Accumulating Cargo: To mitigate the risk of static discharge, all metallic sampling and gauging equipment must be bonded to the vessel throughout the operation. In scenarios where the cargo tank is not inerted, a critical waiting period of 30 minutes is required after halting cargo transfer before any equipment can be lowered into the tank.

Vapor Control Transfer Procedures

• Tank Opening Guidelines: Opening a cargo tank is permissible only under specific conditions: it must not be actively filling, or the pressure in the vapor space must be reduced to atmospheric levels, ensuring that both the cargo is not restricted and does not require closure.

Pressure Vacuum Valve Settings

• Transfer Rate Management: The maximum allowable transfer rate is critical to ensure that the pressure does not exceed 80% of the PV valve setting at the most remote area of the barge. PV valve settings are typically detailed on an attached plate on the valve housing for reference.

Pressure Drop Criteria

• Calculation Aids: Utilizing tabulated pressure drop data along with a calculation worksheet is key to evaluating the pressure drop criteria effectively. Additionally, cargo vapor density plays a significant role in shaping loading rates, connecting the physical properties of the cargo with the PV valve settings.

Loading Rate Situations

• No Specific Pressure Drop Requirement: In cases where there is no stringent pressure drop requirement, loading rates can be strategically determined to minimize pressure impacts from the vapor control systems.

• Specific Pressure Drop Requirement: Where scenarios require adherence to specific pressure drop limits, these are often dictated by the docking specifications for both the pressure and vacuum systems. Careful monitoring and compliance with these criteria are crucial for safe operations.

• Vacuum System without Dock Limits: These systems provide ease of monitoring yet necessitate strict compliance with the restriction of not exceeding 80% of the PV valve vacuum setting, ensuring safety in operations.

Adjusting for Safe Loading Rates

• Constant Monitoring: Operators should continually monitor the pressure vacuum gauge readings throughout the transfer process. Loading rates may need to be adjusted downwards to maintain adherence to safety limits already established.

• Pressure Drop Usage: If desired loading rates fall below the smallest listed rate in the pressure drop tables, operators must utilize the corresponding pressure drop rate from the lowest listed figure in order to ensure safe loading practices. For example, if the smallest rate indicated is 2500 barrels per hour and the desired rate is 1,500 barrels per hour, the pressure drop from the 2500 barrels per hour rate must be applied to maintain safety and compliance during loading operations.